austenite to reform, but not so slow as to create intermetallic phases, nor too fast as to create excess ferrite in the heat-affected zone. Follow the manufacturer’s recommended procedures for the weld process and filler metal selected. Why do I keep adjusting the parameters when welding stainless steel? For fabricators who constantly adjust parameters (voltage, amperage, arc length, inductance, pulse width, etc.) when welding stainless steel, the typical culprit is inconsistent filler metal composition. Given the importance of alloying elements, lot-to-lot variations in chemical composition can have a noticeable affect on weld performance, such as poor wet out or difficult slag release. Variations in electrode diameter, surface cleanliness, cast, and helix also affect performance in GMAW and FCAW applications. How do I control carbide precipitation in austenitic stainless steel? At temperatures in the range of 800°–1600°F, carbon content in excess of 0.02% migrates to the grain boundaries of the austenitic structure, where it reacts with chromium to form chromium carbide. If the chromium is tied up with the carbon, it is not available for corrosion resistance. When exposed to a corrosive environment, intergranular corrosion results, allowing the grain boundaries to be eaten away — Fig. 6. To control carbide precipitation, keep the carbon content as low as possible (0.04% maximum) by welding with low-carbon electrodes. Carbon can also be tied up by niobium (formerly columbium) and titanium, which have a stronger affinity for carbon than does chromium. Type 347 electrodes are made for this purpose. How should I prepare for a discussion on filler metal selection? At a minimum, gather information on the end use of the welded part, including service environment (especially operating temperatures, exposure to corrosive elements, and degree of expected corrosion resistance) and desired service life. Information on required mechanical properties at operating conditions helps greatly, including strength, toughness, ductility, and fatigue. Most of the leading electrode manufacturers provide guidebooks for filler metal selection, and the authors cannot overemphasize this point: consult a filler metal applications guide or contact their technical experts. They are there to help with selecting the correct stainless steel electrode. JAY COUBROUGH (JCoubrough@esab.com) is global product manager, Stainless Steel & Nickel Solid Wires, ESAB, Mississauga, ON, Canada, and KARIN IVARSSON (karin.ivarsson@esab.se) is global project manager, Filler Metals, ESAB, Gothenburg, Sweden. EDUCATION Register by y July 19 and save Also, don’t forget e $ t to sign up to exhibit and ta ake s will earn 18 PDH continuin 36 WELDING JOURNAL / JULY 2016 CAT TION, FICAT O TION NCE cturing continues pic. LDI ING EDUC LS & CERTIF CO ONFEREN pending g skills gap in manufac to be a hot-button top now w we need to do a better j we also job of recruiting and training o need to learn how to s for re eal-life job situations s ® American Welding Society aws.org WEL SKILL Augu 0-12, 2016 / H ust 1 Houston, TX The imp While most of u us kn skilled welders s, w these candid ates During the AWS S We gain new elding w ins so they can be successful. Education, Skills & Ce ertification Conference you’ll sights, share best practices, better mentor and prepare exchange ideas, and **Attendees ultimately be part of the solution. 100 on Early Bird Registration!! ng ed Learn more at www. ducation credits by attending this conference. ws.org/events/conferences w.aw advantage of this targeted marketing opportunity! WJ
Welding Journal | July 2016
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