TWI Industrial Member Report Summary 681/1999
S M I Birch
The use of laser welding for steel plates in excess of 10mm in thickness is attractive in offering high joint completion rates. Other advantages of laser welding include reduced distortion during welding, easier automation and mechanisation and low hydrogen level. In steels, however, welding speed is limited by weld metal solidification cracking which occurs as a result of the typically deep, narrow profile of laser welds.
It has been found, in earlier work at TWI, that the solidification cracking tendency strongly decreased in steels with carbon contents of 0.09-0.16%, as carbon content increased . It was suggested that this was related to the solidification temperature range which decreases with C content over the range studied. An implication of this is that as the carbon content increases above this range, and the solidification temperature range increases again, the cracking susceptibility will increase. It was also indicated in the previous work that increasing sulphur content increases the cracking tendency.
The aim of the present study was to examine the effects on cracking susceptibility of higher carbon contents and also of changes in the welding speed.
- To extend the compositional cracking index, developed in the previous work, by incorporating steels with higher carbon contents than previously considered.
- To quantify the effect of the welding speed on the risk of solidification cracking in fully penetrating weld beads.