IMPROVEMENT OF TOUGHNESS AND STRENGTH OF HIGH STRENGTH STEEL SUBMERGED ARC WELD METAL

Many investigations on HSLA steel weld metal have revealed that by increasing acicularferrite and decreasing proeutectoid ferrite the toughness of weld metal can be improved.But the majority of these invest igations covered only weld metal of about σS<550MPa.In this paper,the effects of Mn,Ni,etc.on the microstructure, toughness and strength of σ_s=550~800 MPa submerged arc weld metal were investigated systematically.It has been proved that the improvement of toughness and strength of the high strength weld metal can be best acquired refining the acicular ferrite.The selection of the kind and amount of alloying elements should be such that the benificial effect of refining acicular ferrite would overcome the harmful effect like solid solution hardening or embrittlement of M-A constituent,etc..In addition,this paper has made a preliminary investigation on the cause of SR embrittlement in high strength weld metal and pointed out the harmful effect of temper embrittlement.Based on the statistical analysis of the experimental data,proposals have been made for the proper selection of alloying elements for HQ70 and HQ80 steel submerged arc weld metal.