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ADVANCEDHIGH STRENGTH STEELS

FOR FORGING APPLICATIONS

MT PERROT- SIMONETTA, B RESIAK, M CONFENTEMittal Steel Europe R&D - FRANCE

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PRESENTATION

1. Design process for steel innovation

2. Example of development with partnership

A micro-alloyed medium carbon steel grade for heavy duty crankshafts

3. Examples of innovative developmentto prepare the future

A medium carbon steel grade with acicular ferrite microstructure

A low carbon bainitic steel grade with improved toughness

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TO PROPOSE THE BEST STEEL GRADE, TAKING INTO CONSIDERATION

THE TECHNICAL NEEDS

- to achieve the required properties of the finished part (improvement of the properties and/or weight saving of parts)

- to be compatible with the process of the steel producer- to be adapted to the constraints of the processes of the customers

THE ECONOMICAL CONSTRAINTS

- to obtain a finished part at a cost which satisfies all parties concerned- to save energy by removing heat treatment

THE ENVIRONMENTAL EXPECTATIONS

- to reduce the environmental impact of all the manufacturing chain

OBJECTIVES OF DESIGN PROCESS

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SHAPING THE FUTURE OF STEEL

Evaluate the feasibility of the project

BenchmarkingFunctional analysisProcessingEnvironmental constraints & regulations

COST/PROFITABILITY

DESIGN PROCESSCustomers needs

& expectationsOEM, tier 1, tier 2

Collect initial data Establish a partnershipWorkshop

Define the requirements of the partHeat treatments, machinability, fatigue

YS, TS Toughnesss, Jominy, microstructure,cleanness

Define the properties of the steel

Define the steel gradeData baseknow howcomputer modelling

Verification of the design by the workshop

Quality evaluationof the bars

Quality evaluation of the forged parts

Participation to the approval process

Commercial production

Industrial heat

Process development and trials

Laboratory investigations

Cast and forge lab ingots

Assistance to the customers

With new chemistries

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A micro alloyed medium carbon grade for heavy duty crankshafts

A successful partnership betweenTHYSSEN KRUPP AUTOMOTIVEand MITTAL STEEL

DEVELOPMENT WITH PARTNERSHIP

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INDUSTRIAL AIM

To develop a heavy duty crankshaft• with high torsional fatigue strength • as forged (without bulk heat treatment after forging)

The Project Team :The 1st tier supplier for automotive industry : ThyssenKrupp MavilorThe 2nd tier supplier or forging partner : ThyssenKrupp GerlachThe 3rd tier supplier or steel production company : Mittal Steel Ruhrort

Mittal Steel Europe R&D

With better mechanical properties than the actual crankshafts ( C38N2 or 38MnSiV6) (TS>1000MPa, fatigue bending, torsional fatigue)

With properties equivalent to a quenched and tempered grade (34CrNiMo6 )( machinability, deep drilling, induction hardening without cracks)

With a price of the finished crankshaft lower than with steel grade 34CrNiMo6

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LABORATORY INVESTIGATIONS

1. To characterise the forging process especially the cooling

2. To conceive the steel grade chemistry

3. To cast laboratory ingots with different steel chemistries

4. To study the phases transformation -- > Select chemistries

5. To test the aptitude of the new grade to be forged

6. To simulate the cooling of the crankshaft on bar samples

7. To carry out the induction hardening treatment

8. To characterise the machinability

9. To perform the mechanical tests and fatigue tests on samples

After that, parts are forged, machined and tested

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FORGING PROCESS SIMULATION

Temperature measurements on a heavy duty crankshaft

Thermocouple 3Thermocouple 1

Æ 58 mm L: 500 mm

Thermocouple 2Thermocouple 4

Temperature measurements on bars forged from Ingots

Cooling from 1100-1150°C

A cooling chamber was set up to reproduce the cooling rate of the crankshaft on bars

Cooling from 1100-1150°C

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COOLING SIMULATION

Laboratory simulation treatment

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Time (h:min:s)

Tem

pera

ture

°C

core of the bar

core of the crankshaft

subsurface of the crankshaft

subsurface of the bar

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LABORATORY INGOTS CASTING

Ingots : 30 to 40 kg , 120x120 (mm2)

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1,0

10,0

100,0

100 1000

Speed of rotation (tr/min)

Tool

dea

th d

iam

eter

(mm

)

350 tr/min

D350 = 19 mm

D350 = 30 mm

D 0,2 (mm)

MACHINABILITY TEST

STANDARD MATHON TEST

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RESULTS ON DIFFERENT GRADES

Grade HV30 TS YS El RA Microstructure D350MPa MPa % % mm

C38+N2 (ind) 250 800 470 17 55 Ferrite+Pearlite 3134CrNiMo6(ind) 320 1020 900 16 56 Tempered Martensite 13

HEAT A (lab) 345 1080 710 17 35 Bainite+Pearlite 30HEAT B (lab) 270 890 535 18 47 Pearlite+Ferrite 25HEAT C (lab) 340 1180 685 18 33 Bainite 9

HEAT A HEAT CHEAT B

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INDUSTRIAL HEAT

Best compromise mechanical properties/machinability-- > the laboratory heat A

An industrial heat was cast at MITTAL STEEL RUHRORT based on the same chemistry -- > CRIE A7

G ra d es T SM P a

YSM P a

E l%

R A% H v 30 S tru c tu re

M ath o nD 35 0m m

C R IE A7IN D U S TR IAL

H E AT1195 7 35 13 17 350 B + 10% P 9

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THE FORGED CRANKSHAFTS

The industrial grade CRIE A7 having promising mechanical properties, the project team decided to forge 2 kinds of heavy duty crankshafts.C1 and C2 were forged at ThyssenKrupp.

C1

C2

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RESULTS

Grades TSMPa

YSMPa El % RA% Hardness

Hv30 Structure Mathon D350

CRIE A7Crankshaft

C11206 829 13 18 300 - 345 B + P

( variable %) 13 - 20

CRIE A7Crankshaft

C21188 720 17 21 340-375 B + P

( variable %) 9

34CrNiMo6 1020 900 16 56 320 TemperedMartensite 13

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DEEP DRILLING CHARACTERISATION

The CRIEA7 structure can meet the machinabilityrequirements on condition of using the suitable parameters for machining

4550

5560

6570

750,025

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Vc (m/min)

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Drilled length (m)

34CrNiMo6 CRIEA7-BAINITE

(45; 0.025)(45; 0.030)

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WOHLER CURVES

COMPARAISON TENUE EN FATIGUE SUR NUANCES FORGEES

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1 100

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Nombre de cycles

Cont

rain

tes

(MPa

)

34CrNiMo6-vilebrequin

CRIA7 - vilebrequin

38MnSiV5 - galette forgée

585

σd

520420

Tests are performed on standard samples taken from forged parts

34CrNiMo6 crankshaft

CRIEA7 crankshaft

38MnSiV6 forged part

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FATIGUE RESULTS

STANDARD SAMPLES FROM CRANKSHAFTS

The rotative bending fatigue tests performed show good fatigue properties of the steel grade CRIE A7

TESTS ON CRANKSHAFTS

Bending fatigue tests are satisfying.

The torsional fatigue tests are in progress atThyssenKrupp MAVILOR : the first results are good

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YS (MPa)

TS (MPa)

F+P 38MnSi V 5/6

=C38 mod*

A LARGE STEP TOWARDS HIGH STRENGTH

Q+T Ma34CrNiMo6*

F+P38MnSi6+N2

=C38N2*

B+P or BCRIEA7=MCBS*

* Properties measured on finished parts

Spec area

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CONCLUSION

Thanks to this successful partnership between a steel producer (Mittal Steel) and steel transformers (ThyssenKrupp Automotive companies) …

A new micro alloyed grade CRIE A7has been developed for heavy duty crankshafts

It’s a medium carbon bainitic steel (MCBS).It has a mixed Bainite+ Pearlite microstructure and a TS superior to 1100 MPawhich gives it a good fatigue behaviour.

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YS (MPa)

TS (MPa)

F+P

38MnSiV5-6

TS -- > Toughness

INNOVATIVE DEVELOPMENTS

Usually

Aim : High Strength without losing toughness

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ACICULAR FERRITE

Innovative development with University collaborationNancy School of Mines

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Irregular AutocatalyticFine

AF MORPHOLOGY

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AF GERMINATION MECHANISM

DIAGRAM SEM PHOTOGRAPH

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AF MECHANICHAL PROPERTIES

PROPERTIES FA1 FA2 FA3 FA4 38MnSiV6STRUCTURE F+P(30%FA) >90% >90% >80% F+PTS Mpa 980 1008 1023 1106 860YS Mpa 696 665 678 682 595El % 17 21 21 20 17RA % 53 35 37 35 40

Toughness 20°C (KU358) (J/cm²) 45 45 39 50 36HARDNESS HV1 or HV30 288 290 295 300 258

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Objectives : High strength, high toughness

Given by : Bainitic microstructure with Nb additions , low carbon

Originally the low carbon Bainitic grades (named Freeform) were developed by MITTAL STEEL USA for cold heading applications

without any heat treatment

(PATENT filed in 1996)

New Grades developed with similar microstructures

For hot forging applications -> Freeform ™ DQ (Direct Quenched)

A LOW CARBON BAINITIC GRADE

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FREEFORM™ DQ FOR HOT FORGING

PartsQuenchingStandard grades

Blank heat AustenitisationNaturalcooling

Forging Tempering

Freeform Blank heat Forging PartsQuenching

Target : To obtain parts by hot forging and direct quenching without tempering

10°C/s 5°C/s 1°C/s 0,5°C/s

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FREEFORM™ DQ - FORGING TRIALS

UPSETTINGEXTRUSION

AXLE SHAPE

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FREEFORM™ DQ/QUENCHABILITY

Freeform™ DQ 50mm Water quenchedSURFACE CENTER12 mm depth

MECHANICALPROPERTIES

TS MPa

HARDNESS

YS MPa El % RA %

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MECHANICAL PROPERTIES

Freeform™ DQ is well adapted to the manufacture, by hot forging and direct quenching, of components demanding a combination of

high strength, ductility and toughness

TS MPaYS MPa El % RA %KU

J/cm2 20°C

40mm 1200 980 14 73 9550mm 1200 975 16 72 10040mm 1050 925 14 76 14050mm 1040 915 16 74 110

1200 1100 14 55 55

GRADES & HEAT TREATMENT

QUENCHED & TEMPERED

FREEFORM DQ

42CrMo4

WATERQUENCHED

OILQUENCHED

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YS (MPa)

TS (MPa)

FPS38MnSiV6

AFS

HIGH STRENGTH STEELS FOR FORGING MARKET

MCBS

1000

LCBS42CrMo4

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Forging ahead, TOGETHER,

we are shaping the future

of steel products