Lesson 5 - Welding Filler Metals for Stainless Steels

Lesson 1
The Basics of Arc Welding

Lesson 2
Common Electric
Arc Welding Processes

Lesson 3
Covered Electrodes for Welding
Mild Steels

Lesson 4
Covered Electrodes for Welding Low Alloy Steels

Lesson 5
Welding Filler Metals for Stainless Steels

Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW

Lesson 7
Flux Cored Arc Electrodes Carbon Low Alloy Steels

Lesson 8
Hardsurfacing Electrodes

Lesson 9
Estimating & Comparing Weld Metal Costs

Lesson 10
Reliability of Welding Filler Metals

5.4.1.2 If the weldment is to be used in corrosive service, the carbide precipitation and resultant intergranular corrosion must be eliminated. Three dependable methods of controlling this problem are defined below: a. Carbide precipitation is a function of the carbon content. Keeping the carbon content as low as possible in the steel (0.04% maximum) and welding it with low carbon elec- trodes is one solution. b. If the carbon of the steel and weld metal are tied up by an element that has a stronger affinity for carbon than does chromium, carbide precipitation cannot occur. Columbium and titanium are alloys that have a stronger affinity for carbon. Steels with columbium or titanium, and covered electrodes with columbium present, are made for this purpose. c. Another method, although not as practical, is to heat the finished weldment to at least 1850°F allowing all of the precipitated carbides to go back into solution. The weldment is then rapidly cooled and quenched so that it passes through the critical temperature (1200°F) very quickly, allowing little or no carbides to reform. However, stainless steel weldments heated to such high temperatures would be subject to warping, sagging and other loss of dimension as well as being covered with heavy scale. 5.4.2 Ferrite in Austenitic Stainless Steel - Stainless weld metal that is fully austenitic is non-magnetic and has a relatively large grain structure. This results in the weld being crack- sensitive. By controlling the balance of the alloying elements in the electrode, small amounts of another phase, ferrite, can be introduced in the weld metal. The ferrite phase causes the austenitic grains to be much finer and the weld becomes more crack-resistant. 5.4.2.1 Certain alloying elements used in stainless steels and weld metals behave as austenite stabilizers and others as ferrite stabilizers. Among the austenite stabilizers are nickel, carbon, manganese and nitrogen. The ferrite stabilizers are chromium, silicon, molyb- denum and columbium. It is the balance between the two types of alloying elements that controls the quantity of ferrite in the weld metal. INSIDE OF TANK HEAT AFFECTED ZONES WELD METAL INTERGRANULAR CORROSION FIGURE 8

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