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Stainless SteelHigh Ni & Cr Content

Low (Controlled) Interstitials

Austenitic Nitrogen StrengthenedAustenitic

Martensitic Ferritic

Precipitation Hardened Super Austenitic

Super Ferritic Duplex

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Resistance Welding

Lesson Objectives

When you finish this lesson

you will understand:

Learning Activities

1. View Slides;2. Read Notes,

3. Listen to lecture

4. Do on-line workbook

Keywords

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Argon & Oxygen

AOD Furnace

Linnert, Welding Metallurgy

AWS, 1994

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

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Castro & Cadenet, Welding Metallurgy ofStainless and Heat-resisting Steels

Cambridge University Press, 1974

A=Martensitic Alloys

B=Semi-Ferritic

C=Ferritic

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

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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Static Resistance Comparison

Workpieces

Electrode

Electrode

Resistance

Stainless Steel

Plain-carbon Steel

Higher Bulk Resistance

Alloy Effect

Higher Surface Resistance

Chromium Oxide

Class 3 Electrode

Higher Resistance

Higher Resistances = Lower Currents Required

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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Weld Nugget

Base Metal

Base Metal

Only 40 - 50% Heat conduction in SS

Less Heat Conducted Away

Therefore

Lower Current Required

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

Conduction in Plain Carbon

Conduction in SS

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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Weld Nugget

Base Metal

Base Metal

Melting Temp of Plain Carbon

Melting Temp of SS

Melting Temp of SS is lower

Nugget Penetrates More

Therefore

Less Current and Shorter Time Required

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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Ferritic, Martensitic, Ppt. = 6 - 11% greater expansion

Austenitic = 15% greater expansion than Plain Carbon Steel

Therefore

Warpage occurs especially in Seam WeldingHot Cracking can OccurDong et al, Finite Element Modeling ofElectrode Wear Mechanisms,

Auto Steel Partnership, April 10, 1995

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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High Strength

High Hot Strength

Force

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

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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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

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General Properties of Stainless Steels

Electrical Resistivity

Surface & bulk resistance ishigher 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 roomand elevated temperatures

Surface Preparation

Surface films must be

removed prior to welding

Spot Spacing

Less shunting is observed than

plain-carbon steels

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Austenitic

Nitrogen Strengthened Austenitic

Martensitic

Ferritic

Precipitation Hardened

Super Ferritic

Duplex

Super Austenitic

Look at Each Grade & Its Weldability

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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.

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AWS Welding Handbook

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PseudobinaryPhase Diagram

@ 70% Iron