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Up Topic Welding Industry / Technical Discussions / ss 316L welding
- - By metalcoat (*) Date 05-28-2007 18:29
I have prepared butt weld joint from SS 316L 40mm plates. Though the test coupons have qualified macro, tensile, radiography, Ultra sound and impact test, joints have failed in micro analysis. Grain boundry carbide precipitation is observed in HAZ as well as in weld. We have conducted IGC practice A, results have been satisfactory. Can somebody suggest me my test coupon still qualify the welding procedure? I have maintained  interpass temp. 175° degree C throughout the process. Working temerature of my equipment is 150 degree centigrade.
Parent - By js55 (*****) Date 05-29-2007 14:09
If you look close enough there will always be some carbide precipitation, even with L's. What you have to do is engineer your application and determine if that level of precipitation is acceptable. In almost all cases it will be through the use of the L grades.
Also, since any visual carbide precipitation criteria is arbitrary, or drvien by service requirements, you may want to do a re-evaluation of your rejection criteria and determine if indeed it is more restrictive than what your application rerquires. That would be my guess.
If you determine that the resulting precipitation is too excessive for your service, if your service requires the complete absence of any carbides (essentially impossible), I would suggest going to a higher alloy. Perhaps a nickel base alloy.
Parent - By rafael Angarita (*) Date 05-29-2007 15:03
316L in an austenistic SS, so Waht is your consumible?
Parent - By chuck meadows (***) Date 05-29-2007 17:38
While it is not uncommon to experience grain growth in the weld and HAZ, especially HAZ, is is uncommon to see chromium carbide precipitation in those areas. This is known as sensitization, which is a function of time, temperature, and carbon content. Exceeding these will  lead to IGA, or sensitization. It is not the carides that lower the corrosion resistance, but the areas adjacent to the carbides that are detrimental to corrosion protection. If you have done a corrosion test and it passed, then evidentally it is so insignificant that it is acceptable. Also, the recommended interpass temperature for 316L SS welding is 150C, or 300F. Even a "L" grade SS can experience sensitization, but it needs to be at temperature longer than an "H" grade. Sometimes, during procedural qualification it is harder to maintain these temperatures due to the size of the test coupon. The longer it stays in the 800-1500F range, the greater possibility of IGA. Test coupons are not always indicitive of production welding, so a test coupon needs to have special precautions.   
Up Topic Welding Industry / Technical Discussions / ss 316L welding

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