ASTM A240 and A249 have a nitrogen range of .18/.25 for grade UNS S31254. This specification has a range for the same grade of .18/.22. The benefits of nitrogen in 6 Moly grades is well understood. Higher nitrogen is beneficial to corrosion resistance and increases strength levels. Further, in this particular grade, the higher nitrogen range allows a melt code to be designed so that it solidifies in the totally austenitic mode. Solidifying in the totally austenitic mode eliminates formation of delta ferrite during casting and solidification. Delta ferrite can later transform into deleterious phases like sigma that are detrimental to corrosion resistance and impact strength. Allowing higher nitrogen levels is beneficial to the material. Hence, we propose to raise the nitrogen limit in this specification to .25 to match ASTM A240 and A249.
Keywordsalloy steel bars; alloy steel bolting; fasteners; hardness; heat treatment ; stainless steel bolting;
Ballot Item Approved as A193/A193M-2014 and Pending Publication