AWS Welding Handbook Pseudobinary Phase Diagram @ 70% Iron

6d Stainless Steels 2

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Page 1: 6d Stainless Steels 2

AWS Welding Handbook

PseudobinaryPhase Diagram@ 70% Iron

Page 2: 6d Stainless Steels 2



AWS Welding Handbook

Prediction of WeldMetal SolidificationMorphology

Page 3: 6d Stainless Steels 2

A few % Ferrite Reduces Cracks

But P&S Increase Cracks

AWS Welding Handbook

Hot Cracking

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Some Solidification Porosity Can Occur:• As a result of this tendency to Hot Crack when Proper

Percent Ferrite is not Obtained• Because of higher Contraction on Cooling

Suggestions:• Maintain Electrode Force until Cooled• Limit Nugget Diameter to <4 X Thickness of thinner piece• More small diameter spots preferred to fewer Large Spots

Spot Welding Austenitic Stainless Steel

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Spot Welding Austenitic Stainless Steel

Some Discoloration May Occur Around Spot Weld

Solutions•Maintain Electrode Force until weld cooled below oxidizing

Temperature• Post weld clean with 10% Nitric, 2% Hydrofluoric Acid

(Hydrochloric acid should be avoided due to chloride ion stress-corrosion cracking and pitting)

Oxide Formation in HAZ


Page 6: 6d Stainless Steels 2

Knifeline Corrosion Attack in Austenitic Stainless Steel Seam Welds

Seam Welding Austenitic Stainless Steel

Somewhat more Distortion Noted Because of Higher Thermal

ContractionSolution• Abundant water cooling to remove heat

Solution• See Next Slide for more description

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Chromium Carbide Precipitation Kinetics Diagram






1500 °F

1200 °F

800 °F

1500 F

800 F

Chromium OxideChromium Oxide






Page 8: 6d Stainless Steels 2

Preventative Measures

Short weld times Low heat input Lower carbon content in the base material

304L, 316L Stabilization of the material with titanium additions

321 (5xC) Stabilization with columbium or tantalum additions

347, 348 (10xC) Lower nitrogen content (N acts like C)

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Projection Welding Austenitic Stainless Steel

Because of the Greater Thermal Expansion and Contraction, Head Follow-up is critical

Solution• Press Type machines with low inertia heads• Air operated for faster action

In Welding Tubes to tube sheets with Ring projections for leak tight application, electrode set-up is critical

Solution• Test electrode alignment

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Cross Wire Welding Austenitic Stainless Steel

Often used for grates, shelves, baskets, etc.

• Use flat faced electrodes, or• V-grooved electrodes to hold wires in a fixture• As many as 40 welds made at one time

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Flash Welding Austenitic Stainless Steel

• Current about 15% less than for plain carbon• Higher upset pressure• The higher upset requires 40-50% higher clamp force• Larger upset to extrude oxides out

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Super AusteniticAlloys with composition between standard 300 Austenitic SS and Ni-base Alloys• High Ni, High Mo• Ni & Mo- Improved chloride induced Stress Corrosion Cracking

Used in• Sea water application where regular austenitics suffer pitting, crevice and SCC

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AWS Welding Handbook

Page 14: 6d Stainless Steels 2

The Super Austenitic Stainless Steels are susceptible to copper contamination cracking. RESISTANCE WELDING NOT NORMALLY PERFORMED

Copper and Copper Alloy Electrodes can cause cracking:• Flame spray coated electrodes• Low heat

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Nitrogen-Strengthened Austenitic•High nitrogen levels, combined with higher manganese content, help to increase the strength level of the material

•Consider a postweld heat treatment for an optimum corrosion resistance

Little Weld Data Available

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Martensitic• Contain from 12 to 18 percent chromium and 0.12 to 1.20 percent carbon with low nickel content• Combined carbon and chromium content gives these steels high hardenability• Magnetic• Tempering of the low-carbon martensitic stainless steels should avoid the 440 to 540 °C temperature range because of a sharp reduction in notch-impact resistance

Applications:Some Aircraft & Rocket ApplicationsCutlery

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Martensitic SS Wrought Alloys are divided into two groups• 12% Cr, low-carbon engineering grades (top group)• High Cr, High C Cutlery grades (middle group)

AWS Welding Handbook

Page 18: 6d Stainless Steels 2

From a Metallurgical Standpoint, Martensitic SS is similar to Plain Carbon

AWS Welding Handbook

(12% Chromium)

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Spot Welding• HAZ Structural Changes

• Tempering of hard martensite at BM side• Quench to hard martensite at WM side

• Likelihood of cracking in HAZ increases with Carbon• Pre-heat, post-heat, tempering helps

Flash Weld• Hard HAZ

• Temper in machine• High Cr Steels get oxide entrapment at interface

• Precise control of flashing & upset• N or Inert gas shielding

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Effect of Tempered Martensite on Hardness

FusionZone HAZ





Hardened MartensiteTempered Martensite

Loss of Hardness and Strength

SS with carbon content above 0.15% Carbon (431, 440) are susceptible to cracking and need Post Weld Heat Treatment

As Quenched

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Ferritic• Contain from 11.5 to 27 percent chromium, with additions of manganese and silicon, and occasionally nickel, aluminum, molybdenum or titanium• Ferritic at all temperatures, no phase change, large grain sizes• Non-hardenable by heat treatment• Magnetic (generally)

Applications: Water Tanks in EuropeStorage Tanks

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AWS Welding Handbook

Page 23: 6d Stainless Steels 2


Because No Phase Change, Get Grain Growth

Spot & Seam Welding

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HAZ Base




885 Embrittlement (Decomposition of Iron-Chrome Ferrite)

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Flash Weld

• Lower Cr can be welded with standard flash weld techniques• loss of toughness, however

• Higher Cr get oxidation• Inert gas shield recommended• long flash time & high upset to expel oxides

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Super Ferritic

AWS Welding Handbook

• Lower than ordinary interstitial (C&N)• Higher Cr & Mo• Better corrosion (Cr) & Higher Hot Strength (Mo)

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HAZ Base




885 Embrittlement

• 825F Sigma Phase (FeCr) precipitation embrittlement•885F Embrittlement (decomposition of iron-chromium ferrite)• 1560F Chi Phase (Fe36Cr12Mo10) precipitation embrittlement

Increased Cr & Mo promotes Embrittlement

Because of the Embrittlement,Resistance Welding is Usually Not Done on These Steels

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Precipitation-Hardened• Can produce a matrix structure of either austenite or martensite• Heat treated to form CbC, TiC, AlN, Ni3Al• Possess very high strength levels• Can serve at higher temperature than the martensitic grades

Applications:High Strength Components in Jet & Rocket EnginesBombs

Page 29: 6d Stainless Steels 2

AWS Welding Handbook

Page 30: 6d Stainless Steels 2

Martensitic• Solution heat treat above 1900F• Cool to form martensite• Precipitation strengthen• Fabricated

Semiaustenitic• Solution heat treat (still contain 5-20% delta ferrite)• Quench but remain austenitic (Ms below RT)• Fabricate• Harden (austenitize, low temp quench, age)

Austenitic• Remain austinite• Harden treatment

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AWS Welding Handbook

AC=Air cooledWQ=Water Quenched

RC=Rapid Cool to RT SZC= Rapid cool to -100F

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Effect on Aging on the Nugget Hardness in Precipitation-Hardened Stainless Steels








When Welded in the Aged Condition• Higher Electrode Forces• Post Weld Treatment

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Spot Welding• 17-7PH, A-286, PH15-7Mo, AM350 & AM355 have been welded• Generally welded in aged condition, higher forces needed• Time as short as possible

Seam Welding• 17-7PH has been welded • Increased electrode force

Flash Welding• Higher upset pressure• Post weld heat treatment

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Duplex• Low Carbon• Mixture: {bcc} Ferrite (over 50%) + {fcc} Austenite

• Better SCC and Pitting Resistance than Austenitics• Yield Strengths twice the 300 Series

Early grades had 75-80% Ferrite (poor weld toughness due to ferrite)

Later grades have 50-50

Page 35: 6d Stainless Steels 2

AWS Welding Handbook

Page 36: 6d Stainless Steels 2

Due to the Ferrite:• Sensitive to 885F embrittlement• Sigma Phase embrittlement above 1000F• High ductile to brittle transition temperatures (low toughness)• Solidifies as ferrite, subsequent ppt of nitrides, carbides which

reduces corrosion resistance• Rapid cooling promotes additional ferrite• Not Hot Crack Sensitive

Resistance Welds generally not recommended because low toughness and low corrosion resistanceUnless post weld solution anneal and quench.

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Some Applications

Page 38: 6d Stainless Steels 2

Larson, J & Bonesteel, D “Method of Making an Ultra Light Engine Valve” US Patent 5,619,796 Apr 15, 1997

Method of Making an Ultra Light Engine Valve

Deep Drawing of Plain Carbon Steel or Stainless Steel

Resistance Weld

Stainless Steel Cap

Page 39: 6d Stainless Steels 2