TWI Industrial Member Report Summary 290/1985
By I S Matharu and P H M Hart
The HAZ hydrogen cracking behaviour has been investigated for five modern low C-low CE (CEIIW 0.30-0.40) steels of 30mm thickness. The manual metal arc process was used, and testing was based on both CTS tests without preheat and JIS y-groove tests with preheat. The risk of cracking decreased with lowering CEIIW but the behaviour was unsatisfactorily described by the TWI nomograms. The critical hardness for cracking was not independent of CE, as assumed in the nomogram system, but was found to decrease with lowering CE value and this was the principal cause of the unsatisfactory description of the cracking behaviour. As an interim measure for low CE steels, a safe but very conservative approach to determining procedures to prevent cracking is to assume CEIIW = 0.40 for actual values of CEIIW < 0.40.
The recently proposed WE40 parameter provided no improvement over CEIIW for predicting the cracking behaviour of the steels, although Pcm and CEN were found to discriminate and rank the steels' behaviour more accurately than CEIIW. In contrast to the CTS test, the y-groove test produced no HAZ cracking and no relative ranking of the steels behaviour. The maximum HAZ hardness was conservatively predicted by the TWI system but not by either the Lorenz-Düren or Suzuki methods.