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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