Effects of Preheating and Interpass Temperature on Stresses in S 1100 QL Multi-Pass Butt-Welds

Abstract

Most of the research on Hydrogen Assisted Cold Cracking (HACC) in high strength steel welds conducted over the last several decades has focused on single-pass welds, especially considering materials with yield strengths about 700 MPa. The guidelines for avoiding cracking that have been developed from such work are therefore useful only where a root pass is the critical event. The well-known guideline is using preheating temperature. Such guideline is very limited when applied to multi-pass welds. In order to support this need, this paper presents the influence of inhomogeneous Hydrogen Removal Heat Treatment (HRHT) procedures, i.e. sole preheating, controlled interpass temperature and combined preheating and controlled interpass temperature, on the residual stresses in multi-pass welds of S 1100 QL. Thereafter, these results are used to identify HACC problems in S 1100 QL and are not reported here. The results were achieved by decent thermal and structural finite element simulations of a five-layer welded 12 mm thick plate at a realistic restraint provided by respective Instrumented Restraint Cracking (IRC) test. The simulations show that the inhomogeneous heat treatment procedures significantly increase the residual stresses as compared to welding without any heat treatment. In contrast to more general anticipations, an increasing controlled interpass temperature does not necessarily lead to a stress reduction, but can even increase the stresses dependent on the location in the multi-pass welds. Maximum residual stresses generally appear in the upper third part of the weld and are not located beneath the top surface where is a typical location used to detect residual stresses in real welded components. If the restraint intensity given to the welded component is not proper, such heat treatment procedures with various temperatures seem to be useful to reduce residual stresses in multi-pass welds.