Abstract
An investigation has been made of the effect of composition and welding variables on liquation cracking in the weld heat-affected zone of low-alloy steels to specifications SAE 4130, En 24, and ASTMA 387B. It involved examination of bead-on-plate cracking tests made using the metal-inert-gas arc welding process. It was shown that cracking occurred in a discrete zone adjacent to the fusion boundary in which liquation of inclusions had taken place. The severity of cracking proved to be a function of both composition and welding variables. Under fixed welding conditions, cracking severity was related quantitatively to composition (in wt-%) by a linear regression equation of the form crack index=5·47C +27·27S+75·29P+2·79Si-2·77 In addition to confirming that increasing carbon and sulphur increased cracking, it was shown that phosphorus was a cracking promoter in its own right. For a steel of constant composition, cracking increased with (a) increased heat input/length, (b) increased depth offinger penetration, and (c) application of external restraint.
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