stainless steel high ni & cr content low (controlled) interstitials austenitic nitrogen...
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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
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