Austenitic stainless sensitizes when it spends time between about 950 and 1450 °F, as in welding, stress relief or hot forming. Solution annealing dissolves the carbides and fast cooling stops them returning, which is why ASTM A193 Class 1A bolting is solution treated in the finished condition, for corrosion resistance. Low-carbon L grades resist sensitization during welding but not long exposure in that range; stabilized grades such as 321 and 347 tie up the carbon with titanium or niobium.
ASTM A193, A194, A320 and A962 have no intergranular corrosion requirement, so bolting buyers who need the test put it on the order and name the practice: ASTM A262 Practice E for stainless (Practice A may screen), or ASTM G28 Method A or B, with the acceptable corrosion rate, for nickel alloys.
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model dataPractices and solutions from ASTM A262 (Practices A, B, C, E and F) and ASTM G28 (Method A test times for alloys 625 and C-276); the sensitizing range of about 950–1450 °F from published stainless-industry guidance. The grain structure, its carbides, the chromium-depleted zone, the grooves and the etched structures on screen are schematic and greatly exaggerated. The Practice E exposure time and bend angle are set by the standard and are not shown; the strip, coupons and equipment are generic, and no weights or corrosion rates are shown.
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