Influence of heat-affected-zone refinement on high-temperature crack growth in thick-section O·5Cr–O·5Mo–O·25V steel weldments

Abstract

Crack-growth tests have been made at 565°C on thick-section butt welds produced to assess the effect of manual metal arc process parameters on heat-affected-zone (HAZ) refinement in O·5Cr–0·5Mo–0·25 V steel. It was confirmed that the increased degree of HAZ refinement achieved by weld-procedure control resulted in improved resistance to crack propagation. It was also possible to relate instantaneous rates of crack growth to the local microstructures in the HAZ at the tip of the crack by potential-drop measurements andpost-test metallography. The behaviour of a weld subject to post-weld renormalizing and tempering, as an alternative means of achieving microstructural refinement, was also examined. In this case it wasfound that crack initiation was delayed and the overall growth rate reduced relative to the welded and tempered structures. However, crack growth was accompanied by low displacements, similar to those for an as-welded untempered specimen. These were attributed to the concentration of strain ahead of the crack tip within a narrow, fine-grained decarburized zone adjacent to the fusion boundary.