ASME STP-PT-058

Abstract

<strong>INTRODUCTION</strong> <br>Post-weld heat treatment (PWHT) is applied to steel assemblies in order to reduce the likelihood of brittle fracture; this is achieved through the combined effect of a reduction in residual stresses and the tempering of hard, brittle microstructures. <br>For fabrications where the need for a welded repair has been identified, but for which a post-weld heat treatment would be impractical or expensive, it is possible to affect a repair by using a procedure which is intended to give rise to significant refinement and tempering of the heat-affected zone (HAZ) microstructure. Furthermore, for materials operating within the creep regime, and particularly for a repair with near-matching weld metal, whilst the imposition of a PWHT would substantially reduce the level of residual stress, it is likely to shorten creep life by inducing precipitate growth and substructure recovery in the HAZ. <br>Several slightly different approaches have been developed for repair without PWHT, from conventional buttering to a half-bead technique, and later a two-layer approach. A schematic diagram of a weldment, together with the relevant regions of the Fe-C phase diagram is shown in Figure 1 [1]. The principle of the various controlled deposition repair strategies is that weld beads in the first layer are overlapped such that at least part of the coarse-grained region produced by the previous bead is replaced with fine-grained HAZ. A second layer, with appropriate penetration, can achieve further refinement, and further layers may be added to achieve tempering.