INFLUENCE OF MICROSTRUCTURES IN HEAT-AFFE CTED ZONE OF STEELS ON THE MECHANICAL-PROPERTIES DURING POST-WELD HEAT-TREATMENT

Influence of post-weld heat treatment (PWHT) on the mechanical propert ies of high strength steel for welded structure (TMCP steel), especial ly the relation between the microstructures of Heat-affected zone (HAZ ), the stress relaxation behavior and high temperature deformability w as investigated. The synthetic-weld heat treatment were carried out by Weld-heat cycle simulator and a maximum temperature of 1623K. PWHT co nditions were done at heating rate 55.6K/ks. The mechanical properties during PWHT process were evaluated by means of high temperature tensi le test, constant-strain rate test on heating and constant-load test o n heating. Influence of PWHT on the stress relaxation behavior and the reducing ductility was discussed by each microstructures of HAZ (Bain itic or Lath-martensitic structure). The results are summarized as fol lows. 1) As a result of high temperature tensile test, the value of el ongation and the reduction of area of Bainitic structure specimens wer e lower than that of Lath-martensitic and Bainitic-ferritic structure specimens. 2) The stress relaxation behavior of Bainitic structure spe cimens 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 t emperature deformability of Bainitic structure specimens were a remark able reducing tendency of ductility at 850-900K. The difference of the se tendency of the microstructures of HAZ could be explained by the sh ape and site of precipitated carbides during PWHT process.