Abstract
The preventive of the cracking occurring in the partially penetrated corner-weld joint of HT-80 steels has become an interesting object for the last years, since the joint has both elements of the butt weld joint and the fillet one.
In order to make clear the influences of welding procedure, strength of weld metals and the diffusible hydrogen in weld metals on the cracking, both the restraint corner-weld cracking test and the no-restraint weld cracking test have been performed in this investigation.
It is shown that the combination of the highly basic agglomerated flux which generates plenty of CO2 gas in welding and the wire which contains an adequate amount of alloying element can make the crack-free corner-weld metal.
The main results obtained are as follows;
1) In 60 Kg/mm2 corner-weld metal the main cause of the root cracks is plastic deformation at the weld root region which is derived from the constriction of weld mead, and the effect of hydrogen on the crack is supplementary.
2) In 60Kg/mm2 corner-weld metal, the root crack propagates in the unmixed zone without relation to the grain boundaries of weld mead.
3) In the case of the submerged arc welding by using the fused flux, the hydrogen induced root crack and transverse crack occur in 80Kg/mm2 weld metal, and these cracks propagate along the austenite grain boundaries of weld metal.
4) The transverse crack observed in the corner-weld metal may occur by the same mechanism as those observed in the butt weld metal and in the fillet one.
5) Such defects are apt to occur in MIG -arc corner-weld joint with a root gap of greater than 2.8mm as a lack of fusion, hot cracking and burn through.
6) As far as partially penetrated corner-weld joint of HT-80 setels, the weld metal should have such characters as low hydrogen content, small thermal constriction and strength higher than that of the base plate and it should be deposited as much as possible per one pass.
