Stainless Steel High Ni & Cr Content Low (Controlled) Interstitials Austenitic Nitrogen Strengthened Austenitic Martensitic Ferritic Precipitation Hardened Super Austenitic Super Ferritic Duplex
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
Argon & Oxygen AOD Furnace Linnert, Welding Metallurgy AWS, 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 Steels Cambridge University Press, 1974 A=Martensitic Alloys B=Semi-Ferritic C=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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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 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
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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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 Only % 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
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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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 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
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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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. = % greater expansion Austenitic = 15% greater expansion than Plain Carbon Steel Therefore Warpage occurs especially in Seam Welding Hot Cracking can Occur Dong 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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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 Strength High 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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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: ° C –Martensitic: ° C –Ferritic: ° C –Austenitic: ° 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
Pseudobinary Phase 70% Iron