Welding Stainless Steel
Stainless steels are frequently welded. Austenitic grades are the most frequently welded, duplex grades are welded for service in critical environments, and the ferritic and martensitic grades are welded least. This defines the weldability of each different group of stainless steel, austenitic being the easiest to weld and martensitic the most problematical. All the arc welding processes, MMA, TIG, MIG, FCAW, MCAW, and submerged arc are suitable for all grades. Power beam processes are also being used increasingly. Gas welding requires use of aggressive fluxes and so is used less now than in the past. Consumables for austenitic grades are selected to closely match the parent metal composition, particularly in terms of carbon, chromium, and nickel contents. Problems such as weld decay, sigma embrittlement, and stress corrosion may occur in service. Consumables for duplex and super duplex tend to overmatch the parent in nickel content. If phase balance in weld metal and HAZ is not maintained, corrosion may result. Welding ferritic and martensitic grades is not straightforward. Matching consumables may be used but often an austenitic grade consumable will be chosen to make welding easier. Cracking and grain growth causing weakness are common problems. When required shielding gases may be inert, argon or helium rich mixtures (TIG), for MIG and MCAW oxygen or carbon dioxide may be added, and carbon dioxide or argon-carbon dioxide mixtures are used for FCAW. With MMA coatings may be basic, rutile, or acid-rutile. Submerged arc fluxes tend to be basic in nature and may be enriched in chromium. The main safety issues depend on the process but may include electrical, radiation, fume containing chromium or nickel, and inert compressed gases.
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