Impact Strength of Austenitic Stainless-Steel Welds at −320 F—Effects of Composition, Ferrite Content, and Heat-Treatment

Abstract

A statistical evaluation has been made of the effect of weld rod composition, ferrite content, and heat-treatment upon the impact strength of certain austenitic stainless-steel welds in 304 stainless-steel plate at −320 F. The data indicate that suitable and approximately equivalent properties are obtained with 310 stainless-steel rod in the as-welded condition, type 308 stainless-steel rod in the as-welded condition (ferrite less than 6 percent), and 308L stainless-steel rod either as-welded or stress-relieved at 1750 F (ferrite less than 9 percent). The impact resistance of 310 stainless steel is adversely affected by stress relief, apparently due to carbide precipitation in this alloy. The 308 and 308L stainless-steel rods are both adversely affected by a stress relief at 1550 F, indicative of sigma formation. The carbon content in 308 stainless-steel rods apparently is not a major factor, as indicated by the lack of adverse effects with a 1750 F stress relief, from which the rate of cooling through the sensitizing range of 800 to 1500 F is identical with that in the 1500 F stress relief. The basic practical conclusion to be drawn from these data is that regular carbon 304 stainless steel welded with 308L stainless-steel rod can be used in cryogenic applications, and that the decision as to whether to stress relieve or not may be left to the mechanical engineer, subject only to the stipulation of a minimum stress-relieving temperature of 1750 F.