TOOLING SOLUTIONS FOR ADVANCED HIGH STRENGTH STEELS

TOOLING SOLUTIONS FOR AHSS 1

TOOLING SOLUTIONS FOR

ADVANCEDHIGH STRENGTH

STEELS

TOOLING SOLUTIONS FOR AHSS2

This information is based on our present state of knowledge and is intended toprovide general notes on our products and their uses. It should not therefore beconstrued as a warranty of specific properties of the products described or awarranty for fitness for a particular purpose.

Classified according to EU Directive 1999/45/ECFor further information see our “Material Safety Data Sheets”.

Edition: 2, 10.2016

© UDDEHOLMS ABNo part of this publication may be reproduced or transmitted for commercial purposeswithout permission of the copyright holder.


CONTENTS

Introduction 5

Uddeholm’s offer to the automotive industry 5

Sheet steels and tool steels 6 – Advanced high strength steels 6 – Tool steels 7

Tool steel selection guidelines 9 – Overview 9 – Forming tool operations 11 – Cutting tool operations 16 – Application examples 30

Lubrication 31 – Forming tool operations – Cutting tool operations

Tooling economy 32

Technical support 33 – Experts to help you – Advanced resource for analysis – Courses and seminars – Technical information

Selecting a tool steel supplier is a key decision for all parties, including the tool

maker, the tool user and the end user. Thanks to superior material properties,

Uddeholm’s customers get reliable tools and components. Our products are

always state-of-the-art. Consequently, we have built a reputation as the most

innovative tool steel producer in the world.

Uddeholm produce and deliver high quality Swedish tool steel to more than

100,000 customers in over 100 countries.

Wherever you are in the manufacturing chain, trust Uddeholm to be your number

one partner and tool steel provider for optimal tooling and production economy.


B-Pillar to a car.


INTRODUCTIONUsing advanced high strength steels (AHSS) canprovide organizations with many advantages.However, with the increasing use of advancedhigh strength steel in new product designs, higherdemands are also placed on tool steels used informing and blanking/punching operations. Thepurpose of this publication is to provide selectionguidelines that enable design engineers andmaterial experts to find the best tooling solutionfor forming and blanking/punching advanced highstrength steels with the following steel types:• micro alloyed steels

• bainitic steels

• dual phase steels

• complex phase steels

• roll forming steels

• martensitic steels

From an environmental standpoint, advancedhigh strength steels can significantly reduceweight in producing a detail, allow for smalleramounts of raw material to be used and consumeless energy. At the same time, less energy isneeded to transport the steel and the steel itself isalso totally renewable.

There are also applications where advancedhigh strength steel makes it possible to excludetempering furnaces from the manufacturingprocess, and consequently the environmentalhazards involved.

In the automotive industry, lower emissionlevels can be achieved by reducing vehicleweight. On the other hand, the ever increasingdemand for safety in cars necessitates higherstrength materials to be used in critical safetyelements in the car body. There are also manyindustrial products where reduced weight andincrease product durability can be achieved byutilizing advanced high strength steel in theirdesigns.

The use of advanced high strength steel mayrequire higher force to cut and form the sheetsteel. Therefore, the need for higher hardness andductility in the tool steel becomes obvious. Thepresent situation and future development inadvanced high strength steel forces the desiredtool steel properties to develop even further tomatch the requirements.

The guidelines presented here reflect the latestresults and best working practices developed byUddeholm at the time of release of this publica-tion. The information is based on comprehensiveresearch and testing performed over a longperiod, and in close cooperation with many of ourmost advanced customers.

The main goal for Uddeholm is to provide solidinformation to enable customers to select thebest combination of advanced high strength steeland tool steel for any given product design.

UDDEHOLM’S OFFERTO THE AUTOMOTIVEINDUSTRYThe world’s automotive industry is one of Udde-holm’s most important customer groups.

Uddeholm’s package for the automotiveindustry is created to meet the need of theautomotive OEM’s for shorter delivery times. Thepackage focuses on optimal total economy, lessdowntime in production and shorter lead times,within the following areas.• In cold work, a new generation of presswork

tool steels has been developed.

• Within the hot work segment Uddeholmespecially focus on long run die casting produc-tion, hot forging and hot stamping.

• In plastic moulding, as the leading developer ofhigh quality plastic mould steels, the tool lifeand performance can be maximized and greatsavings in productivity and total tooling costcan be achieved.

Uddeholm is a global company. In our global offerto OEM’s we focus on products and services on aworldwide basis. Our message for the OEM’s isthat we have the best products and we cansupport them both technically and commerciallywherever they decide to build their tools orproduce their products.

This means that we don’t sell just a piece ofsteel, we sell a full package including services likeheat treatment, machining and welding.


SHEET STEELS ANDTOOL STEELSADVANCED HIGHSTRENGTH STEELSAdvanced high strength steels can be obtained ashot rolled, cold reduced, hot-dip galvanized andelectro galvanized products. For example,Advanced High Strength Steels are used in:

• safety components in cars

• trailers

• tippers

• seat components

• containers

• cranes

• trains

• various tube applications such as furniture,bicycles and baby carriages

There are several parameters that decide which ofthe Advanced High Strength Steel types to beused. The most important parameters arederived from the geometrical form of the com-ponent and the selection of forming and blankingmethod.

MICRO ALLOYED STEELSThe micro alloyed cold-forming steels derive theirhigh strength from the addition of very smallquantities of micro-alloying elements such asniobium and titanium. These steel grades aredesignated according to the lowest guaranteedyield strength. The difference between their yieldstrength and tensile strength is small. These steel

DUAL PHASE STEELSDual Phase, cold-forming steel has a micro-structure that consists of two phases, ferrite andmartensite. Ferrite is soft and contributes to goodformability. Martensite is hard and contri-butes tothe strength of the material. The strength in-creases with increasing proportion of the hardmartensite phase. Depending on the application,dual phase steels in different yield ratio (YS /TS)can be achieved. The figures in the steel designa-tion specify the minimum tensile strength. Dualphase steels are easy to cut and form and can bewelded with conventional welding methods.

COMPLEX PHASE STEELSThe microstructure of complex phase steelscontains small amounts of martensite, retainedaustenite and pearlite within the ferrite/bainitematrix. CP steels are characterized by a high yieldstrength, moderate strain hardening and goodability for bending and flanging. The figures in thesteel designation specify the minimum tensilestrength. The complex phase steels are availableas hot-dip galvanized steel grades.

grades have excellent bendability, pressformingand flanging properties in relation to their yieldstrength. The weldability is also good.

BAINITIC STEELSThe bainitic steels are available as hot rolledmaterial. These types of steels are thermo-mechanical rolled. The figures in the steel desig-nation specify the minimum yield strength.

ROLLING TYPE MECHANICAL PROPERTIES STEEL TYPE COATING TYPE

CR = Cold rolled xxxY xxxT MC = Small grain size EG = Electrogalvanized zincHR = Hot rolled xxx = Rp0.2 min. xxx = Rm, min. low alloyed coating

LA = Low or micro ZN = Electrogalvanized zinc- alloyed nickel coating

FB = Ferritic bainitic GI = Hot dip zinc coating

DP = Dual phase GA = Hot dip zinc-iron coating

CP = Complex phase AS = Hot dip aluminium-silicon

MS = Martensitic coating

Table 1. These designations are used in the following text to characterize the high strength work materials.

Examples: CR780Y-CP = cold rolled steel with minimum yield strength of 780 MPa of complex phase type HR1180T-MS = hot rolled steel with minimum tensile strength of 1180 MPa of martensitic type

NOMENCLATURE OF ADVANCED HIGH STRENGTH STEELS


ROLL FORMING STEELSThe roll forming steels are available as coldreduced and hot-dip galvanised products. Thisgroup of steel is primarily designed for applica-tions where roll forming is used as a formingmethod. The roll forming steels are characterizedby high yield ratio (YS /TS), high internal cleanli-ness and a microstructure with homogeneoushardness distribution. These characteristicsminimize the risk for twisting and bending of theprofile, and make it possible to roll form intonarrow radii.

MARTENSITIC STEELSMartensitic steels contain 100% martensite.Martensitic steels characterize a material in veryhigh yield and tensile strength. For hot rolledmaterial, the figures in the steel designationspecify the minimum yield strength, and for coldrolled material, the minimum tensile strength.

TOOL STEELS

CHARACTERISTICS FORFORMING AND CUTTING OPERATIONS

A typical req uest for tools used in cold workapplications is a high hardness. The reason is thatthe work materials to be formed are often hard.A high tool hardness is therefore necessary toprevent plastic deformation and/or heavy toolwear.

A negative consequence of high hardness levelis that the tool material becomes more brittle.

Tool steel for cold work applications need highwear resistance, sufficient compressible strengthand toughness/ductility or, more specifically:• high wear resistance to increase tool life and

to reduce the need for production stoppagesfor tool maintenance

• sufficient compressible strength to avoid plasticdeformation of the active tool surfaces

• sufficient toughness/ductility to avoid prema-ture tool breakage and chipping

High wear resistance is not just a question ofhardness. Typically, tool steel grades for coldwork applications also contain hard carbides,giving an extra contribution to the wear resist-ance. These carbides are chemical compounds of

carbon and carbide forming elements such aschromium, vanadium, molybdenum or tungsten.Generally, the more frequent, larger and harderthe carbides are, the better wear resistance isachieved in the tool. There are, however, conflict-ing consequences as high hardness makes thematerial sensitive to notches. This may lead tolarge carbides acting as crack initiators in afatigue process. The majority of broken tools faildue to fatigue cracking.

Fatigue cracking occurs when the material isexposed to alternating/pulsating loads and canbe divided in a crack initiation stage and a crackpropagation stage. Crack initiation normally takesplace at notches, which magnify the stress locallyby stress concentration. The higher the hardnessthe more efficient the stress concentrationbecomes. Typical for a high hardness is also thatas soon as a crack is initiated, the time to a totaltool breakage is very short.

The difficulty with cold work applications ingeneral, especially when blanking hard workmaterials, is that you must minimize crack initiat-ing defects. This must be done while maintainingwear resistance which demands high hardnessand hard particles in the steel matrix.

Crack initiating defects such as notches are notnecessarily due to carbides. Large slag inclu-sions, defects in the tool surface or sharp cornersin combination with high hardness may also actas sites for crack initiation at fatigue loading. Forthis reason, the cleanliness of the metallurgicalprocess and the surface finish of the tool or thetool design will strongly influence tool perform-ance. In Table 2 on page 8, the Uddeholmproduct range of tool steels suitable for advancedhigh strength steel is shown.


UDDEHOLM TYPE OF CHEMICAL COMPOSITION (WEIGHT %)STEEL GRADE METALLURGY AISI / W.-NR. C Si Mn Cr Mo W V

Sleipner Conventional – 0.90 0.9 0.5 7.8 2.5 – 0.5

Sverker 21 Conventional D2 / 1.2379 1.55 0.3 0.4 11.3 0.8 – 0.8

Calmax Conventional – /1.2358 0.60 0.35 0.8 4.5 0.5 – 0.2

Unimax Electro slag remelting – 0.50 0.2 0.5 5.0 2.3 – 0.5

Caldie Electro slag remelting – 0.70 0.2 0.5 5.0 2.3 – 0.5

Vanadis 4 Extra SuperClean Powder metallurgy – 1.40 0.4 0.4 4.7 3.5 – 3.7

Vanadis 8 SuperClean Powder metallurgy – 2.30 0.4 0.4 4.8 3.6 – 8.0

Vancron 40 SuperClean Powder metallurgy – 3.001) 0.5 0.4 4.5 3.2 3.7 8.5

UDDEHOLM PRODUCT RANGE OF TOOL STEELSSUITABLE FOR ADVANCED HIGH STRENGTH STEELS

1) % (C + N)

Table 2.

POWDER METALLURGYIn the powder metallurgy process nitrogen gas isused to atomize the melted steel into smalldroplets, or grains. Each of these small grainssolidifies quickly and there is little time forcarbides to grow. These powder grains are thencompacted to an ingot in a hot isostatic press athigh temperature and pressure. The ingot is thenrolled or forged to steel bars by conventional

Figure 1. Electro slag remelting (ESR) process.

CONVENTIONAL METALLURGYWhen manufacturing conventional high alloyedtool steels, the use of large ingots means that thesteel melt will solidify slowly. This results incoarse carbide networks being developed. Thesecarbide networks will cause coarse carbidestreaks in the tool material after rolling or forging.These carbide streaks are positive for the wearresistance but have a negative influence on themechanical strength of the tool material, espe-cially at fatigue loading.

To reduce the negative influence of carbidenetworks the chemical composition has to bebalanced to reduce or even avoid coarse carbidenetworks, while compensating for the loss ofwear resistance by the increased matrix hard-ness.

An alternative way is to develop a metallurgicalprocess which gives small and well distributedcarbides that have less negative impact onfatigue strength but still protect the tool fromwear.

Uddeholm has two metallurgical processes thatimprove the situation compared with conventionalmetallurgy. These are:

• Electro Slag Remelting (ESR), Figure 1

• Powder Metallurgy (PM), Figure 2

ELECTRO SLAG REMELTINGMETALLURGYElectro slag remelting is a well-known metallurgyprocess in which a conventionally produced ingotis successively remelted in a pro-with a small

steel melt. This smaller steel melt solidifies muchfaster than a larger steel melt, giving less time forcarbide growth after solidifying. The remeltingprocess gives steel with improved homogeneityand less overall carbide sizes. The process alsoincludes a slag filter, which improves the steelcleanliness.


methods. The resulting structure is completelyhomogeneous steel with evenly distributed smallcarbides, harmless as sites for crack initiation butstill protecting the tool from wear.

Large slag inclusions can take the role as sitesfor crack initiation instead. Therefore, the powder

Figure 2. Powder metallurgy (PM) process.

TOOL STEEL SELECTION GUIDELINES

Figure 3. Process steps from tooldesign to tool maintenanceOVERVIEW

In forming and cutting operations of sheet metalparts, as in all industrial manufacturing opera-tions, it is important that the production runswithout trouble. The chain from tool design to toolmaintenance includes many different steps asshown in Figure 3.

metallurgical process has been further developedin stages to improve the cleanliness of the steel.Powder steel from Uddeholm today is of the thirdgeneration. They are considered the cleanestpowder metallurgy tool steels on the market.

HEAT TREATMENTTOOL MATERIAL

PRODUCTION CONDITIONS

TOOL DESIGN

TOOL MAINTENANCE

WORK MATERIAL

TOOL PRODUCTION


To achieve good productivity and toolingeconomy it is essential that the right tool steel isselected and that all steps in the chain are carriedout correctly.

To select the right tool steel for the applicationin question it is essential to identify the mecha-nisms which can lead to premature tool failures.In forming and cutting operations there are fiveprincipal failure mechanisms.

• Wear, abrasive or adhesive, related to theoperation, the work material and the frictionforces due to sliding contact between the tooland the work material.

• Plastic deformation, which appears when theoperating stress level exceeds the compressiveyield strength (hardness) of the tool material.

• Chipping, which is a result of high workingstresses compared to the fatigue strength ofthe tool material.

• Total cracking, which is a result of high workingstresses compared to the fracture toughness ofthe tool material.

• Galling (pick-up), which is a result of heavyfriction forces due to the sliding contact andthe adhesive nature of the work material. Thegalling mechanism is closely related to adhesivewear.

Wear, abrasive or adhesive

Chipping

Galling

Plastic deformation, chipping and total crackingare spontaneous failures and result in severe andcostly production disturbances. They must beavoided if possible. Wear and galling are morepredictable and can, to a certain extent, behandled by tool maintenance schedules. A con-sequence of this is that it may be worthwhile toallow more tool wear rather than to run intosituations with chipping and cracking.

The yield strength of the steel sheet has to beexceeded during forming and the shear rupturestrength has to be exceeded during cutting. Thismeans that in forming and cutting operations inadvanced high strength steel sheets, the forcesneeded to perform the operation are higher thanfor softer sheets of the same thickness.

In the same way, the demands on wear resist-ance and mechanical strength of the tool materialincrease. The cutting operation is more sensitivesince it requires a combination of high wearresistance, high galling resistance, high compres-

sive strength, high chipping and total crackingresistance. On the other hand, the formingoperation is more concerned with high wear andgalling resistance and compressive strength.

Furthermore, the die clearance has to bechanged. Shock waves may appear in the tooland the burr formation is different when blanking/punching sheets with Rm 1200–1400 MPa. Seealso Figure 15, page 20. Forming of advancedhigh strength steels also means a reducedformability, increased spring back and increasedwrinkling tendencies.

The tooling environment becomes accordinglymore complex and demanding with these newadvanced high strength steel materials.

Forming and cutting operations in sheets ofhigher strength steel grades may lead to rapiddeterioration of the tool surface, or cracking ofthe tool if inadequate tool steels are selected.This means the selection of tool steel and coatingprocesses for forming and cutting operations in


Hardness/Resistanceto plastic

deformation

Wear resistance Abrasive wear Adhesive wear

Resistance to fatigue crack initiation

Ductility/Resistance to

chipping

Toughness/Resistance togross cracking

UDDEHOLMSTEEL GRADE

Calmax

Caldie

Sleipner

Sverker 21

Unimax

Vanadis 4 Extra*

Vanadis 8*

Vancron 40*

AISI

–

–

–

D2

–

–

–

–

* Uddeholm PM SuperClean tool steel

advanced high strength steel should not be basedon what was done in the past with softer mildsteel sheet materials. Instead, one should use thelatest technical innovations to optimize theproduction economy.

In the table below a relative comparison of theresistance to different types of tool failure mecha-nisms for the Uddeholm product range intendedfor advanced high strength steel applications isshown.

Table 3.

RELATIVE COMPARISON OF THE RESISTANCETO DIFFERENT TYPES OF FAILURE MECHANISMS

FORMING TOOL OPERATIONS

GENERALAdvanced high strength steels have good form-ability and can be formed in the traditional way,despite their high strength.

The somewhat poorer formability compared tomild steels can almost always be compensatedfor by modifying the design of the component orthe forming process. Larger radii in the tool thathelp the material flow in combination with opti-mized blank shape are factors that can make theforming of advanced high strength steels easier.A good example when these design issues havebeen taken into account is shown in Figure 4.Here it was possible to stamp a quite complexpart in CR1200T-MS even tough in general termsthe formability of advanced high strength steel islower compared with mild steel, se Figure 5.

Figure 4. A battery holder for aSUV-car, stamped in CR1200T-MS.

Figure 5. Maximum- cup height and dome height fordeep drawing and stretch forming, respectively.Sheet steel grades (from left to right): CR4, CR600T-DP, CR800T- DP, CR1000T- DP, CR1200T- MS andCR1400T- MS.


The spring back effect is larger for high strengthsteel than for milder materials. Several methodsto reduce spring back are possible, for example:

• over-bending

• increasing blank holder force

• using calibration step

• using draw beads

• adding stiffeners to flat areas and bends ofthe part

• using the correct blank shape

In the following sections of forming operationssuch as bending, roll forming, stamping and holeflanging, as well as some aspects regarding toolloads and galling using the Finite Element Method(FEM), are discussed. Recommendations forsurface treatment and tool steel selection are alsogiven.

BENDINGWhen bending a soft material, the resulting innerradius is determined mainly by the die width andnot by the bending knife radius. A high strengthmaterial, on the contrary, follows the bendingknife radius and the resulting inner radius is lessdependent on the die width. Therefore, a largerdie width can be used with high strength steelswithout compromising the required inner radius.This has a large influence on the bending forceand also on the tool wear, which are both reducedwhen the die width is increased.

When transferring from softer to high strengthsheet steel, the sheet thickness is generallyreduced. The bending force may therefore remainunchanged, since the reduced thickness oftencompensates for the higher strength.

ROLL FORMINGRoll forming is extremely suited for advanced highstrength steel. Experiments show that signifi-cantly sharper radii can be obtained using rollforming compared to conventional bending.

STAMPINGPress forces increase with increasing workmaterial strength. Generally, a high strengthmaterial also requires higher blank holder force toprevent wrinkling. High surface pressure locally inthe tool puts high demands on the tooling

material and on the tool surface properties (referalso to section Overview page 9).

HOLE FLANGINGThe hole flanging ability for high strength sheetsteel is poorer than for softer materials. Becauseof this, it is more important to optimize theprocess as far as possible, for example byblanking the hole in opposite direction to theflanging direction. The burr is then located on theinside of the hole where it is least subjected totension. Pre-forming before hole punching isanother method to achieve higher flangingheights.

FEM – ANALYSIS OF TOOL LOADSAND GALLINGNumerical simulation using the Finite ElementMethod (FEM) can give valuable assistance in theselection of tool steel. One important question intool steel selection is whether a sheet metalforming application can be performed without theoccurrence of galling, which is often the dominat-ing damage mechanism in sheet forming. Themain reason for galling is too high contactpressure between the die and the sheet. The FEmethod can be used to calculate the contactpressure for a given combination of tool andsheet material. An example of a simulation of asuccessful application is shown in Figure 7. Theapplication involves U-bending of 2 mm CR 800T-DP. The result indicates that the pressure limit forgalling is 1200 MPa for this combination of sheetand tool material.

Choosing the right tool steel and surfacetreatment can increase the pressure limit forgalling, allowing the forming of higher strength

Figure 6. Complex stamping tool.


Figure 7.Computed die pressure distribution(MPa) from FE simulation of a U-bendingapplication with CR 800T- DP.

sheet material and/or more demanding ge-ometries. The high nitrogen alloyed PM tool steelUddeholm Vancron 40 SuperClean has a higherresistance to galling than conventional tool steel.The contact pressure limit when forming HR700Y- MC and CR 800T-DP is approximately 1600MPa when using Vancron 40 SuperClean materialin the tool. As a rule of thumb, it can be assumedthat the limiting pressure for galling is about2.6 times the yield strength when using Vancron40 SuperClean as tool steel material, but only1.2 times the yield strength when using conven-tional tool steel materials such as AISI D2. This isvalid for forming of sheet with strength up toCR 800T-DP, since above this strength, thetemperature will increase and the lubricating filmmay no longer be able to carry the pressure.With the present knowledge the limits for recom-mended use of Uddeholm Vancron 40 Super-Clean can be stated as shown in Figure 8.

Other important factors which will influence thegalling limit are; choice of lubrication, surfaceroughness of the tool and sliding speed. Onereason for the effect of the factors mentionedhere is that they all influence temperature, whichshould be kept as low as possible to avoidgalling.

The pressure limit can be combined with a FEMsimulation to predict whether an application (witha given geometry) will produce low enoughcontact pressure to be successful with a conven-tional tool steel, or if you have to use a moreadvanced tool steel like Vancron 40 SuperClean.However, a simulation that predicts low enoughpressure is not a guarantee for success if the diesurface preparation is poor. On the other hand, ifthe predicted contact pressure is just above thelimit, improved lubrication, further reduction of thesurface roughness or reduced forming speed canbe sufficient to prevent galling.

Figure 8.Limits to guide the use of uncoated

Uddeholm Vancron 40 SuperClean to form carbonsteel. Recommendations are based on application

tests and FEM simulation. For comparison theapproximate level of the galling limit of uncoated

AISI D2 tool steel is included.

CPRESS

12411103

965827689551414276138

0

CPRESS

Maximum die pressure, MPa

2000

1800

1600

1400

1200

1000

800

600

400

200

Yield strength of sheet, MPa

Galling limit ofUddeholm Vancron 40 SuperClean

Not recommendedRecommended

Cf. AISI D2:

PCrit =2.6 Rp0.2

PCrit =1.2 Rp0.2

PCrit =1600 MPa

200 400 600 800 1000


TOOL STEEL SELECTIONAND SURFACE TREATMENT INFORMING APPLICATIONSIn forming applications, galling, adhesive wearand plastic deformation are the most commonfailure mechanisms encountered. Forming ofadvanced high strength steel sheet (or thickerhigh strength sheet) means that higher pressforces are needed due to the higher yieldstrength.

Forming tools with better galling resistancewill be needed in the future as the trend istowards an increased use of higher strength sheetmaterials, higher press speeds, the use ofprogressive dies with fewer steps and the use ofmore environmentally friendly (but normally lesseffective) lubricants. Surface treatment such asPVD, CVD and TD coating on the forming tool isan effective way to prevent galling. Selection ofthe tool steel and the coating process used forforming advanced high strength sheet steelsdepend mainly on:

• the strength of the sheet steel

• the thickness of the sheet steel

• whether the sheet steel is coated or not

• the complexity of the forming operation

• the number of parts to be produced

At present, there is only limited experience withforming of advanced high strength steels. How-ever, some preliminary tests with 2 mm CR600 –1000T- DP(GA) have indicated the following.

• Tool hardness levelsTool hardness should be more than 58–59 HRC tocounteract wear, galling and plastic deformation.

• Tool surface finishActive tool surfaces should be polished to a lowsurface roughness (Ra ≤ 0.2 µm).

• Conventional uncoated tool steelsThese steels do not fulfil the requirements forpress tools for uncoated sheet material. However,they might be suitable for simpler forming opera-tions with thinner advanced high strength sheetmaterial at the lower end of the strength range.

• Plasma nitrided conventional tool steelsSuch tool steels do not show sufficient gallingresistance for long production runs due todelaminating of the nitride layer. However, theymight be suitable for simpler forming operations

with thinner advanced high strength sheetmaterial at the lower end of the strength range.

• PVD coated toolsPVD coatings in combination with a substratesteel having sufficiently high hardness (>58 HRC)is one solution to avoid galling.

• CVD or TD coated toolsProperly prepared CVD or TD coated tools alsoavoid galling.

• Uddeholm Vancron 40 SuperCleanforming toolsUddeholm Vancron 40 SuperClean, which is anitrogen alloyed, high performance PM steel, hasshown very good industrial application results.Forming tooling (with a surface finish ofRa ≤0.2 µm) made from Uddeholm Vancron 40SuperClean usually performs much better thancoated tooling.

A summary of suitable tool steels for forming ofadvanced high strength steels is given in Table 4.Table data is based on experience to date buttesting will be continued and table data will beregularly updated. The mentioned tool steelgrades can be used as mono block dies or incombinations of base die material with inserts,depending on the size of the tool and the severityof the forming operation.


As stated earlier there is a need for surfacetreatment or surface coating to achieve properperformance of the tools. This means that thecoatings are taking care of the wear (except forUddeholm Vancron 40 SuperClean). The tool steelacts as a substrate for the coatings. The maindemand on the substrate material is to supportthe very brittle coating, i.e. the substrate materialmust have enough compressive strength andhardness when the tool is put into service.Furthermore, the dimensional changes after thecoating process must be negligible, or predictableto fulfil desired tolerances of the tool. Finally, thesubstrate material has to withstand many cyclic

loads at high stress levels, i.e. a high fatigue limitis needed.

To give some guidance for tool steel selectionat different demands on serial length, a relativeranking of actual tool steel grades without andwith coating is given in Table 5. In case of ionnitriding one of the factors, that has to be con-sidererd, is that the ductility is heavily deterio-rated. A comparison of the ductility after nitridingto a case depth of 50 µm is made for the actualgrades. As Uddeholm Vancron 40 SuperClean isused without any surface treatments it shows avery much superior rating than all other grades.

SHEET STRENGTH STEEL GRADE SURFACE TREATMENT / COATING TOTAL HARDNESS

Rm (MPa) Uddeholm /AISI/ W.-Nr. Type Serial length HRC

Calmax /–/ 1.2358 Nitriding/PVD Medium runsUnimax PVD/CVD Medium runsSverker 21 /D2/ 1.2379 PVD/CVD Medium runs

350–570 Caldie PVD/CVD Medium-long runs > 56Sleipner PVD/CVD Medium-long runsVanadis 4 Extra SuperClean PVD/CVD Long runsVanadis 8 SuperClean PVD/CVD Long runsVancron 40 SuperClean No coating needed All

Calmax /–/ 1.2358 Duplex (Nitriding + PVD) AllUnimax PVD/CVD AllSverker 21 /D2/ 1.2379 PVD/CVD All

>570–800 Caldie PVD/CVD All ≥ 58Sleipner PVD/CVD AllVanadis 4 Extra SuperClean PVD/CVD AllVanadis 8 SuperClean PVD/CVD AllVancron 40 SuperClean No coating needed All

Caldie PVD/CVD AllSleipner PVD/CVD All

>800–1400 Vanadis 4 Extra SuperClean PVD/CVD All ≥ 60Vanadis 8 SuperClean PVD/CVD AllVancron 40 SuperClean No coating needed All

Table 4. Suitable tool steels for forming of advanced high strength steels.

WITHOUT COATING WITH COATING WITH ION NITRIDING

UDDEHOLM Wear resistance Resistance to Substrate material properties

STEEL GRADE Abra- Adhe- Gall- Chipping/ Plastic Fatigue Dim. stability Ductility after nitridingsive sive ing cracking deformation limit after re-hardening to 50 µm depth

Calmax 1 3 1 8 1 4 4 6Unimax 1 4 1 10 1 5 7 7Sverker 21 6 2 1 1 5 1 1 1Caldie 2 5 2 8 5 9 7 5Sleipner 5 4 2 3 8 2 4 3Vanadis 4 Extra* 8 8 3 8 10 10 9 5Vanadis 8* 10 8 5 6 10 9 9 4Vancron 40* 6 10 10 6 10 9** 10** 10**

Table 5. The table shows a relative performance ranking for the grades, both without and with surface coating.Relative scale = 1–10, where 10 is best.

*Uddeholm SuperClean tool steel **Without any surface treatment.


CUTTING TOOL OPERATIONSGENERALIt is very difficult to give conclusive adviceregarding tool steel selection for a specificproduction situation because production con-ditions in different plants will never be the same,even if the same part is being produced at eachplant. The best way is to base the selection of thetool steel on the experience gained from earlierproduction runs using the same or similar produc-tion equipment.

Regarding advanced high strength steel, thereis little previous experience to date to go on. Asmentioned earlier, it is important not to base thetool steel selection on what was done for softerproduction materials using older grades such asAISI A2 or D2. Remember that there is a newgeneration of tool steels which are much moresuitable for tooling when blanking and punchingthe advanced high strength steels.

In blanking and punching the main failuremechanisms usually are wear, chipping andgalling. These failure mechanisms are influencedby:

• the strength of the production material

• the thickness of the production material

• the design features such as sharp radii

• the geometry of the part to be produced

• the number of parts to be produced

The tool must have sufficient hardness to preventplastic deformation of the cutting edge. In addi-tion, special attention must be given to thesurface quality of the tool to prevent prematurefailure by chipping or cracking and also to preventgalling. In the following sections, cutting opera-tions such as blanking, punching, cutting andshearing are discussed. Recommendations forsurface treatment and tool steel selection are alsogiven.

BLANKING AND PUNCHING

Appearance of a cut edge

Commonly used blanking and punching methodsgenerate a cut edge consisting of a rollover, aburnish, a fracture zone and a burr. The burnish issmaller for high strength steel than for mild steel.The burr height is reduced with increasing tensilestrength. An important factor to achieve a goodedge is the die clearance.

Die clearance

The die clearance is the radial distance betweenthe punch and the die, see Figure 10.

The edge is often characterized by the foursections illustrated in Figure 9. Compared toblanking/punching in mild steel, the choice of dieclearance has a greater influence on the tool life.However, the burr formation is smaller and notsignificantly affected by changing the die clear-ance. The rollover and fracture zone will increasewith increasing die clearance, but less than formild steel. In Figure 11 the recommended dieclearance for blanking and punching is shown.

In Figure 12, an edge can be seen after punch-ing in CR 1400T-MS with 6% and 14% dieclearance. In general, it is better to use a largerdie clearance when blanking/punching highstrength sheet steel. However, for the higheststrength sheet steels a very large die clearancecan be a disadvantage. This will be explainedlater.

When blanking/punching steels up to 1000 MPatensile strength, a small die clearance gives ahigh amount of galling on the tool. A too largeclearance gives less tool wear, but generatesmore bending or rollover in the work objectresulting in lower edge quality. This is why thedesired edge quality of the work object affects thechoice of die clearance. The relation between toolwear and die clearance is shown in Figure 13.

When blanking/punching in the highest strengthmaterial, too small a die clearance also givessome galling on the tool, but the main wearmechanism is abrasive wear. Because of thematerial strength, there is a limit on how large thedie clearance can be. Too large a die clearancegenerates high bending stresses on the punchedge, which increases the risk of chipping, seeFigure 14. This is especially important in sheetmaterials with a small difference between yieldand tensile strength as in the martensitic CR MSand MS-EG sheets.


Rollover

Burnish

Fracture zone

Burr

Figure 9. Appearance of a cut edge.

Die clearance Punch

Work material

Die

Figure 10. Die clearance definition.

Figure 11. Recommended die clearance for blanking/punching advanced high strength steel.

Die clearance, %

15

14

13

12

11

10

9

8

7 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Sheet thickness, mm

Galling / Adhesive wear area

Chipping area

Tool wear

Tool wear

Figure 13. Relation between tool wear and dieclearance when blanking in CR 800T-DP, sheetthickness = 1 mm.

6 8 10 12 14

Die clearance, % of sheet thickness

Figure 14. Relation between tool wear and dieclearance when blanking in CR 1400T-MS, sheetthickness 1 mm.

6 8 10 12 14 Die clearance, % of sheet thickness

Figure 12. Edge cut with varying die clearance.

Punch Punch

Die Die

Sheetthick-ness


A-pillar reinforcement

Roof rail

Front side member

Crash box

Bumper reinforcement

The tool steels Uddeholm Caldie, Uddeholm Sleipner,Uddeholm Vanadis 4 Extra SuperClean, Uddeholm Vanadis 8SuperClean and Uddeholm Vancron 40 SuperClean aretypical grades used for manufacturing these car parts.Other grades can be used depending on factors likedesign, sheet steel type and thickness.

Tube for dashboard

Suspension head


Roof bow

C-pillar reinforcement

B-pillar reinforcement

Waist reinforcement

Cross member

Recliner

Door beams

Seat frame

Seat track

Sill reinforcement


Blanking and punching force

The blanking/punching force required is propor-tional to the sheet steel strength, the sheetthickness and the length of the blanked/ punchedline. In Figure 15 the varying punching force isshown when punching a Ø 5 mm hole in 1 mmthick sheet, with a 10% die clearance in ad-vanced high strength steel. The blanking/punch-ing force can be quite high when blanking/punching the hardest advanced high strengthsteel grades. However, the reduction of sheetthickness will normally compensate for theincreased blanking/ punching forces.

When blanking/punching in the fully martensiticCR MS and CR MS-EG sheets, the force is higherand the work material ductility is low. This meansthat a shock wave or recoil force may be gener-ated. This is noticed as a fast negative forceamplitude as shown in Figure 15. The shock wavegenerates stress on the tool, which may lead tofatigue cracking after a relatively short time. Thisis shown in Figure 16. To avoid productiondisturbances, the effects of the high blanking/punching forces on the fittings and sharp radiishould be considered, as well as the surfacefinish of the tool.

When blanking/punching in advanced highstrength steel with lower strength, the workmaterial ductility is higher which reduces theeffects of fatigue and cracking in the tool. For thisreason, focus should be on the forces generatedwhen blanking/punching advanced high strengthsteel with the highest strength and also how theforces can be reduced. Experiments have shownthat the die clearance has a marginal effect on theblanking/punching force. However, the force issomewhat reduced with increased die clearance.Typically a 3 to 5% reduction of the force ispossible to reach with an increased die clearance.

Reducing blanking/punching force

It is important to use the correct blanking/punching parameters. How to select the dieclearance when blanking/punching is explained insection Die clearance, page 16. To avoid simul-taneous blanking/punching when making severalholes in one operation, the punches can be ofdifferent length. This reduces the required blan-king/punching force which otherwise can beconsiderable. To coat the punching tool is not aneffective way to reduce the force. On the contrary,the force can increase as shown in Figure 19.

A coated punch produces a higher blanking/punching force due to a lower friction betweenthe end surface of the punch and the sheetsurface. The lower friction makes the crackinginitiation more difficult in the sheet, which in-creases the blanking/punching force. The increas-ing force facilitates fatigue cracking in the tool.When cracking starts the coating rapidly comeslose. The most effective way to reduce the forceis to chamfer the tool.

Preferably this is made symmetrically to avoidinclined loads on the tool. Chamfering can alsobe a way to reduce noise. Different ways tochamfer the tool is shown in Figure 17 and Figure18. How much the blanking/punching force canbe reduced using symmetrically chamferedpunches is shown in Figure 19.

Figure 15. Blanking force and shock waves whenpunching advanced high strength steel grades.

Figure 16. Cracking developed as a result of fatigue.

15000

13000

11000

9000

7000

5000

3000

1000

-1000

-3000

CR 1400T-MSCR 800T-DPCR 500Y-LACR 280Y-LA

Blanking/punching force, N

Punch displacementShock waves


The blanking/punching force can be reduced by30% for CR 1400T-MS with a chamfer of0.7 times the sheet thickness. The size of theeffect of a chamfered punch depends on the workmaterial as shown in Figure 20.

To obtain a larger reduction effect when blank-ing/punching mild steel the chamfering mustincrease to approx. 1–1.5 times the sheet thick-ness. The chamfer should not be unnecessarily

large when blanking/punching in advanced highstrength steels, just large enough to start the cutbefore the whole punch end surface area is incontact with the sheet surface. Using an unnec-essarily large chamfer will increase the risk ofplastic deformation of the punch tip.

Another way to reduce the risk of plasticdeformation is to use a chamfered punch with aflat centre section as shown in Figure 21.

Figure 19.Effect of chamferingon blanking/punchingforce and shockwaves when punchinga Ø 5 mm hole in1 mm thick CR 1400T-MS with 10% dieclearance.

Figure 20. Reduction in % of the blanking/punchingforce for different types of chamfering of the punch(height of chamfer 0.7 times the sheet thickness). Figure 21.

A chamfered punch witha flat centre section.

Figure 17. Chamfered tools for blanking andpunching.

a)

F1F1

(F1)

F2

F2

Punch displacement

Punch displacement

Figure 18. Blanking/punching force as a functionof punch displacement for a) flat punch orb) chamfered punch.

CR280Y-LA CR500Y-LA CR800T-DP CR1400T-MS

Note: Using a chamfered punch does not neces-sarily mean that the tool wear will be less. Themain advantages are force and noise reductions.

Force, N

15000

12000

9000

3000

1000

0

-3000Punch displacement

Coated punch

Uncoated punch

Inverted chamfered punch

Chamfered punch

b)a)

b)

-4% -13% -25% -30%

-8% -13% -15% -10%


SHEARING

Cutting clearance and shearing angle

In shearing the cutting clearance is the horizontaldistance between the upper and lower shear, andthe shearing angle is the angle between the upperand lower shear, see Figure 22. The shearingangle is normally applied on the upper shear.

In general, similar cutting clearance can beused as for softer sheet steel. The cutting clear-ance can be somewhat larger when using ashearing angle compared with parallel knives.Cutting clearances are usually smaller comparedwith blanking and punching. Recommendedcutting clearances for advanced high strengthsheet can be seen in Figure 23.

The selection of shearing angle can be seen inFigure 24 for different strength levels and sheetthicknesses.

Figure 22. Cutting clearance and shearing anglerespectively.

Figure 23. Recommended cutting clearance whenshearing

Figure 24. Recommended shearing angles depend-ing on sheet thickness.

Appearance of cut edge of a sheet

The appearance of the cut edge of a sheet issimilar as when blanking and punching, seesection Blanking and punching on page 16.Typical sheet edge appearances for three sheetsteel grades can be seen in Figure 25.

When changing the cutting parameters in shear-ing the sheet edge appearance changes as well.A larger cutting clearance with parallel knivesgives a larger burnish. On the other hand, a largercutting clearance when using a shearing anglewill give a smaller burnish. When using a highshearing angle in combination with a large cuttingclearance, splitting or tearing marks can some-times be seen in the fracture zone, see the leftphoto in Figure 26.

Figure 25. Sheet edge appearance for HR 700Y-MC,CR 800T-DP and CR 1400T-MS respectively inthickness 2 mm with 7% cutting clearance and 1°shearing angle.

Figure 26. Sheet edge appearance for HR 700Y-MC,t =2 mm with different cutting conditions. The leftimage indicates that cutting clearance and/orshearing angle is too large. The right image indicatesthat the cutting conditions are OK.

Shearing angle, degrees2.0

1.6

1.2

0.8

0.4

200 400 600 800 1000 1200 1400

Yield strength, MPa

t = 12 mmt = 8 mmt = ≤ 5 mm

Cutting clearance in % of sheet thickness12

10

8

6

4

2 1 1.5 2 2.5 3 3.5 4 4.5 5

Sheet thickness, mm


angle. There is no benefit to use shearing angles>1.5° The reduction in total shearing force is lowbut the tool edge load will be higher and willincrease the risk of edge chipping.

In power shearing of advanced high strengthsteels, the first thing asked is often:

– Will I manage a transition from mild sheetsteel to advanced high strength sheet steel withthe production equipment I have?

An expression for the shearing force is neededto answer that question. For this purpose, thefollowing equation can be used:

where:

F = shearing force

Ksk = shearing strength = Rm • e-factor

α = shearing angle

t = sheet thickness

A large shearing angle when working in CR-MSsheets can sometimes result in a wavy pattern inthe fracture zone, see Figure 27.

Figure 27. Sheet edge appearance for CR 1400T-MS, t =2 mm with different cutting conditions. Theleft image indicates that cutting clearance and/orshearing angle is too large. The right imageindicates that the cutting conditions are OK.

Shearing force

The shearing force required is proportional to thesheet steel strength, the sheet thickness and thelength of the cut. The shearing force can be quitehigh when shearing the hardest advanced highstrength steel grades. To avoid high shearingforces a shearing angle should be applied. Assoon as a shearing angle is used the differencebetween advanced high strength sheet steel andmild steel is much smaller, see Figure 28. Thecutting clearance has very little influence on thetotal shearing force. The largest force reduction iswhen going from a parallel shear to 1° shearing

The shearing strength is calculated as the tensilestrength times the e-factor. The e-factor varieswith the tensile strength of the material. For mildsteels, corresponding to CR1, the e-factor equals0.8, but for higher strength steels the e-factordecreases to 0.55 with a parallel shear. With ashearing angle it can decrease down to 0.3 forthe highest strength sheet material grades.

CR 1400T-MS 5% clearance



HR 700Y-MC 5% clearance



CR3 5% clearance

CR3 10% clearance

CR3 15% clearance

Figure 28. Shear force as a function of shearing angle for different cutting clearances. t =2 mm.

Shearing angle, degrees

Max. shear force, kN

100

90

80

70

60

50

40

30

20

10

0 ° 1° 2° 3°

Ksk • t2

2tanα = F


Example 1:Mild sheet steel with a sheet thickness of 8 mm.Work material: HR 220Y (Rm = 350 MPa)Shearing force: 0.8 x 350 x 64/2tan 0.9 = 570 kN

Example 2:Extra high strength sheet steel with the samesheet thickness = 8 mmWork material: HR 700Y-MC (Rm = 800 MPa)Shearing force: 0.47 x 800 x 64/2tan 1.5 =459 kN

Example 3:Extra high strength sheet steel with the sheetthickness reduced by 10% to = 7.2 mmWork material: HR 700Y-MC (Rm = 800 MPa)Shearing force: 0.47 x 800 x 51.84/2tan 1.5 =372 kN

The examples show that the shearing force in factdecreases if you transfer from mild to extra highstrength sheet steel (using a shearing angle in thesame sheet thickness.) If you reduce the sheetthickness for the extra high strength sheet steel(with a moderate reduction of only 10% inexample 3), the shearing force is reduced by~35% from the original level.

In Figure 29 the e-factor is shown as a function ofthe work material tensile strength with bothparallel shear and with a shearing angle. The e-factor is reduced significantly for advanced highstrength steel when using a shearing angle.

TOOL STEEL SELECTION ANDSURFACE TREATMENT IN CUTTINGAPPLICATIONS

Surface treatment

Whether to apply a coating on a tool or not is aquestion that often arises in tool making. Butbefore a coating is applied, it is important tocharacterise the wear type. For advanced highstrength steel, the type of wear differs dependingon the microstructure and strength level. For dualphase steels, such as CR 800T-DP, the adhesivewear is dominating and a coating will certainlyreduce the galling properties effectively, as shownin Figure 30. In hot dipped HR-MC sheets, thewear type is mixed with both adhesive andabrasive wear. If a HR sheet is to be blanked inunpickled condition the tool wear rate will beconsiderably higher and more abrasive. In anycase, a coating will significantly reduce the toolwear when blanking in HR sheets.

Figure 30. A blanking edge coated with a) PVD-coating (TiAlN) without galling and b) uncoated withgalling after 200 000 parts produced in CR 800T-DP.

100 µm

100 µm

a)

b)

e-factor

0.8

0.7

0.6

0.5

0.4

0.3

0.2

Tensile strength, MPa

Figure 29. e-factor as a function of the work materialtensile strength.

e-factor with shearing anglee-factor with parallel shear

300 500 700 900 1100 1300 1500


For the fully martensitic CR-MS grades, gallingwill not be the dominating wear mechanism. Thewear type will be mainly abrasive and sometimesfatigue cracks can be present in the worn area,as shown in Figure 31.

Figure 31. Typical tool wear of an uncoated blankingedge after 100 000 parts produced in CR 1400T-MS.

As long as fatigue cracks are generated, thecoatings will not stay on the tool particularly long.If the preparation before applying a coating isoptimized and the most suitable type of coating isapplied, the result can be improved so that mostof the coating is still present after 100 000 partsproduced, as shown in Figure 32. However, forfully martensitic steels, such as CR-MS sheets, acoating will not give a significant benefit and isnot recommended. In any case, nitriding of punchedges should be avoided due to a high risk ofcracking the punch edges.

Figure 32. Appearance of a tool edge after100 000 parts produced in CR 1400T-MS. a) shows aCVD TiCN coating, that has almost completely flakedoff, b) shows a multi-layer TiAlN coating with some-what better performance.

Tool steel selection

For tool steel selection purposes it is convenientto group the advanced high strength sheet steelmaterials as follows:

• HR-MC sheets

• CR-DP/DL and LA sheets

• CR-DP/CP + GI/GA sheets

• CR-MS and MS + EG/ZN sheets

This is because preliminary blanking/punchingtests have revealed that each of the steel groupsbehave differently during blanking/punching, i.e.each group puts different demands on the toolmaterial. To simplify access to needed informa-tion and reduce the risk of misunderstanding, theinformation relevant for a specific group ispresented independently of the information validfor the other groups, although the same informa-tion to some extent will be repeated severaltimes. The property profiles for these tool steelsare given in table 3 page 11.

a)

b)


Appropriate grades as a guideline to tool steelselection are given in table 6.

UDDEHOLM TOOLHR SHEETS STEEL GRADE HARDNESS

HR 460Y-MC CalmaxHR 500Y-MC UnimaxHR 550Y-MC Caldie

Sleipner > 56 HRC*Sverker 21Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

HR 600Y-MC CalmaxHR 650Y-MC CaldieHR 700Y-MC Sleipner ≥ 58 HRC*

Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

HR 900Y-MC CaldieHR 960Y-MC Sleipner

Vanadis 4 Extra SuperCleanVanadis 8 SuperClean ≥ 60 HRC*

* Tool hardness has to be selected carefully and adjusted both with thickness and complexity taken into account.

Table 6. Recommended tool steel grades for blankingHR sheets.

Below are some general aspects to consider forthe recommended tool steel grades for the HRMC sheet steel grades.

• Uddeholm Calmax, Uddeholm Unimax andUddeholm Caldie should be used when severechipping is expected.

• Uddeholm Sleipner or Uddeholm Sverker 21can be used for short to medium productionruns with thinner sheet material when wear isthe main concern.

• Uddeholm Vanadis 8 SuperClean can be usedfor long production runs when high wearresistance is the most important requirement.

• Uddeholm Vanadis 4 Extra SuperClean shouldbe used when a strong combination of wearresistance and chipping resistance is needed,i.e. for long production runs with thicker andgeometrically more complex parts.

• Uncoated Uddeholm Vancron 40 SuperCleanshould be used for long production runs tocounteract galling when blanking/punchingthinner, pickled sheet.

• Overlay coatings such as CVD or PVD can beused to counteract wear and galling. All of theabove mentioned tool steel grades can becoated, but Uddeholm Vancron 40 SuperCleanis normally used uncoated.

• Uddeholm Calmax can be CVD coated, butonly PVD coated below 250°C (480°F).

• Nitriding is not recommended as this can easilycause tool edge chipping due to surfaceembrittlement.

• The hardness level used depends on the sheetthickness and the part geometry. It will nor-mally be in the range 56–64 HRC.

HR MC sheets

These sheet steel grades are hot rolled, microalloyed steels with relatively high carbon content.They are available in pickled and non-pickledcondition, with a thickness range from 2–12 mm.

Demands on the tool steel are:• high wear resistance due to higher carbon

content, strength and thickness. High wearresistance is particularly necessary for non-pickled material as the mill scale on its surfaceis very abrasive

• high chipping resistance, partly due to rela-tively high strength, but mainly due to thethickness range

• good galling resistance due to relatively highstrength and thickness range

The HR MC sheets are the group that puts thehighest demands on the tool material because thethickness range for these grades is by far thewidest. For example with increased thicknessand/or complexity of the part the hardness mighthave to be reduced to improve cracking resist-ance.


UDDEHOLM TOOLCR SHEETS STEEL GRADE HARDNESS

CR 500Y-LA CalmaxCR 500T-DP Unimax

CaldieSleipner > 56 HRCSverker 21Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

CR 600T-DP CalmaxCaldieSleipner ≥ 58 HRCSverker 21Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

CR 800T-DP CaldieCR 1000T-DP SleipnerCR 1000T-DP Vanadis 4 Extra SuperClean ≥ 60 HRC+EG/ZN Vanadis 8 SuperClean

Vancron 40 SuperClean

Table 7. Recommended tool steel grades for blankingCR sheets.

CR- DP and LA sheets

The CR-DP sheet steel grades are cold-rolleddual phase steel with low carbon content. TheLA grade is a microalloyed steel.

Demands on the tool steel are:• high wear resistance due to the high sheet

strength level

• high chipping resistance due to the high sheetstrength level

• good galling resistance due to the high sheetstrength level and the presence of ferrite in thesheet

Appropriate grades and recommended hardnesslevels for the different sheet strength levels aregiven in Table 7.

Below are some general aspects to consider forthe recommended tool steel grades.

• Overlay coatings such as CVD or PVD can beused for all sheet materials to counteract wearand galling. All of the mentioned tool steelgrades in table 7 can be coated, but UddeholmVancron 40 SuperClean is normally used un-coated.


• Nitriding is not recommended as this can easilycause chipping.

• The hardness level used depends on the sheetthickness and the part geometry. It will nor-mally be in the range 56–64 HRC.

For the 500 LA/DP and 600 DP sheet steelgrades.

• Uddeholm Calmax, Uddeholm Unimax andUddeholm Caldie should be used when severechipping is expected.

• Uddeholm Sleipner and Uddeholm Sverker 21can be used for short to medium produc-tion runs when wear is the main concern.



• Uncoated Vancron 40 SuperClean should beused for long production runs to counteractgalling.

For the 800 DP and 1000 DP/DP+EG/ZNsheet steel grades.

• Uddeholm Caldie should be used to counter-act chipping.

• Uddeholm Sleipner can be used for short tomedium production runs with thinner sheetmaterial when wear is the main concern.



• Uncoated Vancron 40 SuperClean should beused for long production runs to counteractgalling.


Below are some general aspects to consider forthe recommended tooling steel grades.

• Overlay coatings such as CVD or PVD can beused for all sheet materials, to counteract wearand galling. All of the mentioned tool steelgrades in table 8 can be coated, but UddeholmVancron 40 SuperClean is normally useduncoated.



For the CR 460Y LA GI, CR 500Y LA/DP GI,CR600T DP/CP GI and CR780T CP GI sheetsteel grades.

• Uddeholm Calmax, Uddeholm Unimax andUddeholm Caldie should be used to counter-act chipping.

• Uddeholm Sleipner or Uddeholm Sverker 21can be used for short to medium productionruns with thinner sheet material when wear isthe main concern.



• Uncoated Uddeholm Vancron 40 SuperCleanshould be used for long production runs tocounteract galling.

For the CR 800T DP GI and CR 1000T DPGIsheet steel grades.

• Uddeholm Caldie should be used to counter-act chipping.



CR- DP/CP + GI/GA/AS sheets

The CR- DP/CP + GI/GA/AS sheet steel gradesare cold-rolled dual phase steel with low carboncontent and are hot-dip galvanized. Demands onthe tool steel are:

• high wear resistance is needed for longproduction runs but the wear is much less thanwith the non-galvanized grades, as the zinccoating acts as a lubricant

• high chipping resistance due to high sheetstrength level

• good galling resistance due to high sheetstrength level and presence of ferrite in thesheet

The soft, sticky zinc coating tends to adhere tothe tool surface and should be cleaned offperiodically.

Appropriate grades and recommended hard-ness levels for the different sheet strength levelsare given in Table 8.

HOT DIP UDDEHOLM TOOLSHEETS STEEL GRADE HARDNESS

CR 460Y-LA GI CalmaxCR 500Y-LA GI UnimaxCR 500T-DP GI Caldie

Sleipner > 56 HRCSverker 21Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

CR 600T-DP GI CalmaxCR 600T-CP GI CaldieCR 780T-CP GI Sleipner ≥ 58 HRC

Sverker 21Vanadis 4 Extra SuperCleanVanadis 8 SuperCleanVancron 40 SuperClean

CR 800T-DP GI CaldieCR 1000T-DP GI Sleipner

Vanadis 4 Extra SuperClean ≥ 60 HRCVanadis 8 SuperCleanVancron 40 SuperClean

Table 8. Recommended tool steel grades for blankingHot-dip galvanized sheets.



• Uncoated Uddeholm Vancron 40 SuperCleanshould be used for long production runs tocounteract galling.

CR MS and EG sheets

The MS and EG sheets are cold-rolled martensiticsteel with low carbon contents. The EG gradeshave an electrodeposited zinc coating. Thesesheet steel grades are available in thickness from0.5 to 2.1 mm.

Appropriate tool steel grades and recom-mended hardness levels for the different sheetstrength levels are given in Table 9.

CR MS/EG UDDEHOLM TOOLSHEETS STEEL GRADE HARDNESS

1200T-MS1400T-MS Caldie1500T-MS Sleipner1200T-MS EG Vanadis 4 Extra SuperClean ≥ 60 HRC1400T-MS EG Vanadis 8 SuperClean

Table 9. Recommended tool steel grades for blankingCR MS EG sheets.

Below are some general aspects to consider forthe recommended tooling steel grades.

• Uddeholm Caldie should be used to counter-act chipping and cracking.


• Uddeholm Vanadis 4 Extra SuperClean shouldbe used when a strong combination of wearresistance and chipping resistance is neededfor long production runs.

• Uddeholm Vanadis 8 SuperClean can be usedfor long production runs when high wearresistance is the most important requirement.Mainly for simple part geometries beingblanked/punched from thinner sheet material.

• Coatings are not recommended for the CR MSand EG grades as present experience hasshown that these flake off at a relatively earlystage due to the formation of fatigue cracks inthe tool surface.



APPLICATION EXAMPLES

B-pillar reinforcement.Courtesy of Finnveden MetalStructures, Olofström, Sweden.

COLD WORK OPERATIONS BLANKING AND BENDING

Work material CR 800T-DP

Work material thickness 2.0 mm

Number of parts produced per year 82 000

Tool material in left blanking punch Uddeholm Sleipner

Tool material in right blanking punch Uddeholm Sverker 21

Tool material in left blanking die Uddeholm Sleipner

Tool material in right blanking die Uddeholm Sverker 21

Hardness of left and right blanking tool HRC 62

Hardness of hole punch HRC 60

Tool material in left forming tool Uddeholm Vancron 40 SuperClean

Tool material in right forming tool Uddeholm Sleipner + CVD, TiC + TiN

Hardness of left forming die HRC 62

Hardness of right forming die HRC 62

Surface roughness of forming tools Ra 0.1 µm

Lubrication 8% oil emulsion


Work material CR 1000T-DP



Tool material in blanking tool Uddeholm Vanadis 4 Extra SuperClean

Hardness of blanking tool HRC 60

Tool material in forming tool Uddeholm Vancron 40 SuperClean

Tool material in right forming tool Uddeholm Vanadis 4 Extra SuperClean +CVD, TiCN

Hardness of forming tool HRC 60

Surface roughness of forming tools –

Lubrication –

TOOLING FOR BUMPERTO PASSENGER CAR

Bumper for passenger car.Courtesy of Essa Palau,Barcelona, Spain.

TOOLING FOR TOWHOOK BRACKET

Tow hook bracket. Courtesyof Finnveden Metal Structures,Olofström, Sweden.


Work material CR 1400T-MS



Tool material in blanking punch Uddeholm Sleipner

Tool material in blanking die Uddeholm Vanadis 4 Extra SuperClean

Hardness of blanking tool HRC 60

Tool material in forming punch Uddeholm Sleipner

Tool material in forming die Uddeholm Vanadis 4 Extra SuperClean

Hardness of forming punch HRC 58

Hardness of forming die HRC 60

Surface roughness of forming tools –

Lubrication No additional lubrication

B-PILLAR REINFORCEMENTB-pillar reinforcement toolwith two choices of tool steelmaterial. Both choices areproven to run smoothly.


LUBRICATION

FORMING TOOL OPERATIONSIn forming, the friction between two surfaces inrelative motion can be reduced by lubricating thesurfaces. The most common lubrication type instamping sheet steel is mixed lubrication, inwhich the lubricating film thickness allows forcontact between the peaks of the tool and thework material surface. The lubricant is locked upin the irregularities in the surface, and togetherwith the surface peaks, takes up the contactpressure in the forming process. This putsdemand on the work material surface roughness(for cold rolled material, EN 10130 – normalsurface is valid), and the lubricants ability toneutralise newly developed reactive surfaces.

The viscosity of the lubricant has a large impacton sheet forming process. Low viscosity lubri-cants (25–50 cSt) are used for simpler sheetforming operations, but for more demandingstamping operations, a higher viscosity lubricantshould be used.

CUTTING TOOL OPERATIONSThe importance of using additional lubricantsdepends on several factors when blanking/punching and cutting/shearing advanced highstrength steel. Steel grade, sheet thickness andsheet surface have a large influence as well as thetool geometry. In general, lubrication is moreimportant for lower sheet strengths, thickermaterial and more complex blanking/punching

shapes, for example, hole punching with sharpradii in a thick sheet material. Recommendedlubricants for blanking/punching in advanced highstrength steel are types that resist high contactpressure. The need for additional lubricantsdiffers depending on sheet grades as indicatedbelow.

HR MC SHEETSFor hot rolled sheets the use of additional lubri-cant will benefit the tool life. In particular thickersheets the lubricant can also reduce the cuttingforce as well as the retraction force due to lowerfriction.

CR DP AND LA SHEETSIt is good practice to use lubricants when blan-king/punching advanced high strength steel ofthis type. The ferrite content of these steelsintroduces a certain amount of sticking on thepunch tool, which can be reduced by usingadditional lubricants.

CR GI/GA SHEETSThe need for lubricants is less when blanking/punching hot-dip galvanized sheet materials. Thegalvanized surface offers a certain lubricatingeffect. The zinc coating tends to adhere to thetool surface after some production time andshould be cleaned off periodically.

CR MS (EG/ZN) SHEETSFor fully martensitic cold rolled sheet grades suchas CR MS, the need for additional lubricants issmall. The delivery oil gives adequate lubricationfor blanking/punching and cutting/shearing.These sheet grades do not have a tendency tostick onto the tool.

The need for lubricants is even less whenblanking/punching hot-dip galvanized sheetmaterials. The galvanized surface offers a certainlubricating effect. The zinc coating tends toadhere to the tool surface after some productiontime and should be cleaned off periodically.

The influence of lubricant viscosity on drawing.Maximum cup height using lubricant viscosity 500cSt (left cup) and 40 cSt (right cup).


Tool cost for production of 300 000 partsSteel 1: Ref. tool steel – Too low wear resistance 80 000Steel 2: Ref. tool steel -–Too low chipping resistance: 42 500Optimal tool steel for the application: 7000

PRODUCTION ANDMAINTENANCE COST

TOOLCOST

STEEL COST

welding

scrap

preheating

lost production

heat treatment

delivery delays

repairs

etc., etc...

adjustment

DIE MAKING COST

TOTALPRODUCT

COST

TOOLING ECONOMYIt is very important that a tool produces therequired number of parts with a minimum of downtime. Production stoppages due to tool breakageor frequent refurbishing cause costly productiondelays and lower productivity in general. Thereare several possible issues with the tooling.

The chain from tool design to tool maintenancemust remain intact – any weak link can lead todeficiencies. One very important link is the toolmaterial. The tool material has to have the rightproperties for the application and be of a consist-ent high quality in order to give reliable tooling.

Advanced tool steel manufacturing processessuch as powder metallurgy, ESR and high qualityconventional metallurgy mean that extra effortsare made during the production of the tool steelwhich result in steels that are more expensivethan standard grades. However, it should not beforgotten that the tool steel cost is only a smallfraction of the total cost of producing a tool – it isonly the tip of the iceberg!

Tool steel cost — only the tip of the iceberg.

Total tool cost considerations. Steps in lines indicates cost for refurbishment.

If the production costs, including costs forstoppages and maintenance for a certain batchsize are considered; the use of a higher qualitytool steel will lead to a small increase in the costof the tooling, but usually give a large return onthe investment. This is illustrated in the followinggraph.

Steel 1Steel 2Optimal steel

70 000

60 000

50 000

40 000

30 000

20 000

10 000

50 000 100 000 150 000 200 000 250 000 300 000

Serial length-number of parts

INITIAL COSTS

Tool steel price

Machining

Grinding

Treatments

RUNNING COSTS

Regrinds

Repairs

Corrections

Downtime

Tool cost C

CC

C


TECHNICAL SUPPORT

EXPERTS TO HELP YOUUddeholm can help you put the benefits ofadvanced high strength steels to full use.

Our experts have many years of experience inselecting the proper tool steel for use with ad-vanced high strength steel in cold work applica-tions.

When changing over to advanced high strengthsteel, it is important to integrate the materialselection, design and production processes rightfrom the beginning. It is then possible to optimizethe product and production process from both atechnical and economical viewpoint.

Our experts in the Technical Service Centre andother areas have a deep knowledge and experi-ence in tool steel selection, heat treatment of toolsteels and surface treatments. In the case of toolfailures, investigations can be made to explainand over-come actual tooling deficiencies.

The experts at the local sales offices canprovide advice and solve tooling issues throughdirect local visits.

ADVANCED RESOURCESFOR ANALYSISOur company has the very latest equipment toquickly assist customers to choose the right toolsteel with the right heat treatment solution.

THE FACILITIES INCLUDE

• Complete Laboratory

A complete laboratory for material investigationsand product development. The laboratory in-cludes a metallographic department with trans-mission and scanning electron microscopes, amechanical strength laboratory with both staticand fatigue test machines. It also includes amachining laboratory for evaluation and develop-ment of machining and grinding guidelines for ourtool steels.

• Finite Element Method

Finite Element Method simulations of tool loads.FEM is used for simulation of sheet formingmainly for computation of tool loads. Predictionsof galling is the main issue.

COURSES AND SEMINARSUddeholm regularly arrange courses and semi-nars on how the opportunities offered by ad-vanced high strength steel can be put to use.

• Tool steel course that offers fundamentalknowledge of tool steel production, tool steeltreatments, properties, applications and toolsteel selection.

• Seminars tailored for individual companies.

TECHNICAL INFORMATIONInformation about Uddeholm tool steel grades,their treatments and how to select a certain gradeare given in product brochures, treatmentbrochures and cutting data recommendations.Examples of Uddeholm treatment brochures are:

• Heat treatment of tool steel

• Welding of tool steel

• EDM of tool steel

• Grinding of tool steel

• Polishing of mould steel

Uddeholm has a large number of sales officesand agents all over the world. Product informationand questions can always be handled locally byour local experts.

Our technical information and guidelines canalso be found on www.uddeholm.com or in theUddeholm app available for iPhone and Androidsmartphones.



NETWORK OF EXCELLENCEUddeholm is present on every continent. This ensures you

high-quality Swedish tool steel and local support wherever

you are. Our goal is clear – to be your number one partner

and tool steel provider.


UD

DEH

OLM

10.2016 / 75

Uddeholm is the world’s leading supplier of tooling materials.

This is a position we have reached by improving our customers’

everyday business. Long tradition combined with research and

product development equips Uddeholm to solve any tooling

problem that may arise. It is a challenging process, but the goal is

clear – to be your number one partner and tool steel provider.

Our presence on every continent guarantees you the same high

quality wherever you are. We act worldwide. For us it is all a

matter of trust – in long-term partnerships as well as in developing

new products.

For more information, please visit www.uddeholm.com

Documents

TOOLING SOLUTIONS FOR ADVANCED HIGH STRENGTH STEELS