Post-Weld Heat Treatment Stress Relaxation in Zircaloy 4 Plasma Welds

Abstract

We have studied the effect of a post-weld heat treatment on plasma arc welds on Zircaloy 4 plates. The samples consist of two 100 mm long, 50 mm wide, and 6.25 mm thick plates, welded along the rolling (longitudinal) direction. The heat-treatment consisted of a steady increase in temperature from room temperature to 450oC over a period of 4.5 hours; followed by cooling with an equivalent cooling rate. Residual strains and stresses along the longitudinal, transverse and normal directions on an as-welded and a heat-treated specimen were measured by neutron diffraction on the ENGIN-X beamline at the Isis Facility, Rutherford Laboratory, UK. Peak tensile stresses of (105±25) MPa were found in the as-welded specimen, which were reduced to (70±20) MPa after the heat-treatment. Thermal compressive stresses of (-80±20) MPa were found along the normal direction, which were not affected by the heat treatment. The use of a full-pattern Rietveld refinement for the determination of bulk strains in Zircaloy specimens is also discussed.

Forensic engineering: applying materials and mechanics principles to the investigation of product failures

“…They are typically induced into materials by forming operations, where different degrees of plastic deformation in different regions leads to a locked-in stress field. In particular, very high residual stresses, approaching the yield stress of the material, can be induced by welding processes; although components are often post weld heat-treated to try to minimize the level of residual stress [16]. Residual stresses in a component can add to in-service stresses to cause failure.…”