Study on the Stress Relief Cracking in Welded Low Alloy Steels (Report 2)

The conditions under which Stress Relief Cracking (SR cracking) may occur and characteristics of SR cracking have been investigated with welded high tensile strength steels of tensile strength 80 kg/mm2 and low alloy steels, lCr-0.5Mo-V, Nb, or Ti steels using the bend restraint SR cracking test specimens and y groove restraint SR cracking test specimens.The following results were obtained from. this investigation.(1) SR cracking is an intercrystalline cracking which occurs in the coarsened grains region in H.A.Z. during stressrelieving heat treatment and does not occur in deposited metal and unaffected parent metal.(2) The residual stress and local stress raisers are necessary to initiate this cracking.(3) The aging in H.A.Z. during stressrelieving heat treatment, especially precipitation hardening by the secondary hardening elements, Nb, Ti, V, etc., promotes the initiation of SR cracking. Therefore, the initiation of SR cracking is suppressed when micro structures of the upper bainite, ferrite and perlite are produced in coarnsened grain region by the increase of heat input and pre-heating during welding process, and secondary hardenings are limited during stressrelieving heat treatment.