Stainless Steel
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Transcript of Stainless Steel
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Stainless SteelHigh Ni & Cr Content
Low (Controlled) Interstitials
Austenitic Nitrogen Strengthened Austenitic
Martensitic Ferritic
Precipitation Hardened Super Austenitic
Super Ferritic Duplex
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Argon & Oxygen
AOD Furnace
Linnert, Welding MetallurgyAWS, 1994
Today, more than 1/2 of the high chromium steels are produced in the AOD Furnace
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Castro & Cadenet, Welding Metallurgy of Stainless and Heat-resisting SteelsCambridge University Press, 1974
A=Martensitic AlloysB=Semi-FerriticC=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 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
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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
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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
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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
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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
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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
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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
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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
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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
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High StrengthHigh 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 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
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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 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
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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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AWS Welding Handbook
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AWS Welding Handbook
PseudobinaryPhase Diagram@ 70% Iron