TWI Industrial Member Report Summary 12/1976
By P H M Hart
The Implant cracking test has many obvious potential advantages over weld cracking tests, such as the controlled thermal severity (CTS) test, both for the comparative behaviour of steels with respect to hydrogen cracking and for predicting safe weld procedures.
Because of the possibility of an effect of steel composition on the developed residual stress and strain in real welds, suggested by recent work, it was considered important to establish the extent to which any correlation between the CTS and Implant cracking test existed and allowed a more quantitative use of the latter test than has previously been possible.
CTS and Implant cracking tests carried out on three C-Mn steels (of 0.38, 0.43 and 0.54CE) have confirmed the dependence of critical hardness in fillet welds, on composition (CE) and are consistent with the hypothesis that residual stress in a weld can be affected by the steel transformation characteristics.
It was found that the Implant cracking test could not be reliably used to accurately predict welding procedures or the relative risk of cracking in the CTS test. It is believed this is a direct result of a lack of a precise knowledge of the actual acting stress and strain in a weld and the probability that the acting stress and strain may be dependent on the transformation behaviour of a steel. It is recommended that the evaluation of hydrogen cracking resistance of a steel should be made using self-restraining weld cracking tests.