Transcript Document

Stainless Steel
High Ni & Cr Content
Low (Controlled) Interstitials
Austenitic
Nitrogen Strengthened
Austenitic
Martensitic
Precipitation Hardened
Super Ferritic
Ferritic
Super Austenitic
Duplex
AOD Furnace
Argon & Oxygen
Today, more than 1/2 of the high chromium steels
are produced in the AOD Furnace
Linnert, Welding Metallurgy
AWS, 1994
A=Martensitic Alloys
B=Semi-Ferritic
C=Ferritic
Castro & Cadenet, Welding Metallurgy of
Stainless and Heat-resisting Steels
Cambridge University Press, 1974
We will look at these properties in next slide!
AWS Welding Handbook
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
Electrode
Plain-carbon Steel
Stainless Steel
Higher Bulk Resistance
Alloy Effect
Workpieces
Higher Surface Resistance
Chromium Oxide
Electrode
Class 3 Electrode
Higher Resistance
Resistance
Higher Resistances = Lower Currents Required
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
Conduction in Plain Carbon
Conduction in SS
Base Metal
Weld Nugget
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)
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
Melting Temp of Plain Carbon
Base Metal
Weld Nugget
Base Metal
Melting Temp of SS
Melting Temp of SS is lower
Nugget Penetrates More
Therefore
Less Current and Shorter Time Required
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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 expansion
Austenitic = 15% greater expansion than Plain Carbon Steel
Therefore
Warpage occurs especially in Seam Welding Dong et al, Finite Element Modeling of
Electrode Wear Mechanisms,
Hot Cracking can Occur
Auto Steel Partnership, April 10, 1995
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
Force
High Strength
High Hot Strength
• Need Higher Electrode Forces
• Need Stronger Electrodes (Class 3, 10 & 14 Sometimes Used)
General Properties of Stainless Steels
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
• Coefficient of Thermal
Expansion
– Surface & bulk resistance is
• Electrical Resistivity
higher than that for plaincarbon 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
– Greater coefficient than plaincarbon 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
Look at Each Grade & Its Weldability
Austenitic
Super Austenitic
Nitrogen Strengthened Austenitic
Martensitic
Ferritic
Super Ferritic
Precipitation Hardened
Duplex
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
Pseudobinary
Phase Diagram
@ 70% Iron
AWS Welding Handbook