We are working with a heat treated torsion bar of .5'' diameter and 36'' long (HRC 43). We have been welding it to standard A36 we had plasma cut on both ends. One for a tab, and one for a mounting point. So far even with 140 ksi of subjected stress the weld has held with no heat treatment (preheat heat or PWHT) despite repeated cycles. In fact normally the tab or bar itself fails first. After reading about the risk of cracking with 4140 welds, especially PHT 4140, I was curious if fatigue life could be improved by adding in a preheat to 400 degrees F and slow cooling via an insulated blanket without risk of compromising the tensile strength of the heat treated bar. Does anyone have experience with this?
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