Solidification Cracking in Low Alloy Steel Weld Metals

Abstract

A study has been made of the effects of material composition and welding variables, particularly speed, on weld metal solidification cracking. This has involved low alloy steels to specifications En24, SAE4130, ASTM A387B, and several aircraft steels. Existing relationships between composition and cracking have been critically examined, and an improved expression, based on regression analysis, has been developed using data relating to some 80 Steels. Practical cracking tests were carried out using the Huxley test, and a comparison of these results with the predictions of the regression analysis confirmed the crack-promoting influences of sulphur, phosphorus and carbon, and isolated the important crack inhibiting effect of oxygen. The influence of welding speed was found to be complex and varied with the composition of the steel. In general an increase in speed is detrimental at low speeds, but becomes beneficial when the speed is raised. This phenomenon is explained by a model in which changes of speed are shown to cause opposing effects, which interact to give the characteristic relationship. The morphology of inclusions was also examined, and crack susceptibility was found to be associated with sulphide films. The practical significance of the work is also discussed. Apart from exposing important new effects, the results facilitate the assessment of chemical effects on cracking; and demonstrate the importance of selecting welding variables appropriate to the particular materials being used. Two different tests have been used in the work for specific purposes. The results demonstrate the overwhelming importance of selecting a test suitable for the situation under examination.