Stainless SteelHigh Ni & Cr Content

Low (Controlled) Interstitials

Austenitic Nitrogen Strengthened Austenitic

Martensitic Ferritic

Precipitation Hardened Super Austenitic

Super Ferritic Duplex

Argon & Oxygen

AOD Furnace

Linnert, Welding MetallurgyAWS, 1994

Today, more than 1/2 of the high chromium steels are produced in the AOD Furnace

Castro & Cadenet, Welding Metallurgy of Stainless and Heat-resisting SteelsCambridge University Press, 1974

A=Martensitic AlloysB=Semi-FerriticC=Ferritic

We will look at these properties in next slide!AWS Welding Handbook

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Static Resistance Comparison

Workpieces

Electrode

Electrode

Resistance

Stainless Steel

Plain-carbon Steel

Higher Bulk ResistanceAlloy Effect

Higher Surface ResistanceChromium Oxide

Class 3 ElectrodeHigher Resistance

Higher Resistances = Lower Currents Required

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Weld Nugget

Base Metal

Base Metal

Only 40 - 50% Heat conduction in SSLess Heat Conducted Away

ThereforeLower Current Required

Less Time Required (in some cases less than 1/3)

Conduction in Plain Carbon

Conduction in SS

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Weld NuggetBase Metal

Base Metal

Melting Temp of Plain Carbon

Melting Temp of SS

Melting Temp of SS is lowerNugget Penetrates More

ThereforeLess Current and Shorter Time Required

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Ferritic, Martensitic, Ppt. = 6 - 11% greater expansionAustenitic = 15% greater expansion than Plain Carbon Steel

ThereforeWarpage occurs especially in Seam Welding

Hot Cracking can OccurDong et al, Finite Element Modeling of Electrode Wear Mechanisms,Auto Steel Partnership, April 10, 1995

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

High StrengthHigh Hot Strength

Force

• Need Higher Electrode Forces• Need Stronger Electrodes (Class 3, 10 & 14 Sometimes Used)

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Oxide from Hot Rolling

Oxide Protective Film

• Chromium Oxide from Hot Rolling must be removed by Pickle• Ordinary Oxide Protective Film is not a Problem

General Properties of Stainless Steels• Electrical Resistivity

– Surface & bulk resistance is higher than that for plain-carbon steels

• Thermal Conductivity– About 40 to 50 percent that

of plain-carbon steel

• Melting Temperature– Plain-carbon:1480-1540 °C

– Martensitic: 1400-1530 °C

– Ferritic: 1400-1530 °C

– Austenitic: 1370-1450 °C

• Coefficient of Thermal Expansion– Greater coefficient than plain-

carbon steels

• High Strength– Exhibit high strength at room

and elevated temperatures

• Surface Preparation– Surface films must be

removed prior to welding

• Spot Spacing– Less shunting is observed

than plain-carbon steels

Austenitic

Nitrogen Strengthened Austenitic

Martensitic

Ferritic

Precipitation Hardened

Super Ferritic

Duplex

Super Austenitic

Look at Each Grade & Its Weldability

Austenitic• Contain between 16 and 25 percent chromium, plus sufficient amount of nickel, manganese and/or nitrogen• Have a face-centered-cubic (fcc) structure• Nonmagnetic • Good toughness• Spot weldable• Strengthening can be accomplished by cold work or by solid-solution strengthening

Applications:Fire Extinguishers, pots & pans, etc.

AWS Welding Handbook

AWS Welding Handbook

AWS Welding Handbook

PseudobinaryPhase Diagram@ 70% Iron