Study of welding characteristics of 0.3C–CrMoV(ESR) ultrahigh strength steel

摘要

A new ultrahigh strength low alloy steel 0.3C–CrMoV(ESR), having an ultimate tensile strength and 0.2% proof strength of above 1,700 and 1,500 MPa, respectively, in quenched and tempered condition, was developed primarily as a cost effective material for space launch vehicle applications. Welding is a major step in the fabrication of most of the pressure vessels, structures and equipments. Steels with carbon equivalent in excess of 0.40 wt% show a tendency to form martensite on welding, and therefore are considered difficult to weld. 0.3C–CrMoV(ESR) steel has a carbon equivalent value of nearly 1.0 that classifies it as a ‘very difficult to weld’ steel. In addition it has a niobium content of about 0.10% and a vanadium content of 0.25%. It is known that niobium content of more than 0.02 wt% has a deleterious effect on the toughness properties of low carbon welds. It has also been reported that the effect of niobium on weld metal toughness is more deleterious in the presence of vanadium. Hence, in the present study, the properties of the weldment of this new steel under different heat treatment conditions (HT-1 and HT-2) have been studied. In HT-1 condition, the plates were welded in hardened and tempered condition and no further heat treatment was given after welding, while in HT-2 condition, the annealed plates were subjected to welding followed by hardening and tempering heat treatments. For HT-1 condition, only tensile properties were evaluated. The welded plates under HT-2 condition were evaluated for tensile properties, fracture toughness, residual strength and microstructure features.