Abstract
Influence of post-weld heat treatment (PWHT) on the mechanical properties of high strength steel for welded structure (TMCP steel), especially the relation between the microstructures of Heat-affected zone (HAZ), the stress relaxation behavior and high temperature deformability was investigated. The synthetic-weld heat treatment were carried out by Weld-heat cycle simulator and a maximum temperature of 1623K. PWHT conditions were done at heating rate 55.6K/ks. The mechanical properties during PWHT process were evaluated by means of high temperature tensile test, constant-strain rate test on heating and constant-load test on heating. Influence of PWHT on the stress relaxation behavior and the reducing ductility was discussed by each microstructures of HAZ (Bainitic or Lath-martensitic structure). The results are summarized as follows.
1) As a result of high temperature tensile test, the value of elongation and the reduction of area of Bainitic structure specimens were lower than that of Lath-martensitic and Bainitic-ferritic structure specimens.
2) The stress relaxation behavior of Bainitic structure specimens during PWHT process were delayed clearly over 500K than that of another structure specimens. Bainitic structure specimens appeared to the resistance of softening tendency of matrix during PWHT.
3) High temperature deformability of Bainitic structure specimens were a remarkable reducing tendency of ductility at 850900K. The difference of these tendency of the microstructures of HAZ could be explained by the shape and site of precipitated carbides during PWHT process.
