Experimental study on fracture toughness of quenched and tempered and TMCP high strength steels

摘要

In this study, the fracture toughness of five kinds of high strength steel (HSS) with the nominal yield strength of 550 MPa, 690 MPa and 890 MPa were experimentally studied. Two steel delivery conditions, i.e., quenched and tempered HSS and thermo-mechanical control process HSS, were included and compared. The effect of heat input on the fracture toughness of HSS was investigated. A comparative study was organized for the fracture toughness of base material (BM), heat-affected zone (HAZ) and weld metal (WM). Results indict that the fracture toughness of the heat-affected zone of QT steels (QT550 and QT690) first increases and then decreases slightly with the increase of heat input. There is an optimal heat input for quenched and tempered HSS welding to achieve satisfactory fracture toughness. Either too small or large heat input is not beneficial to the resistance to crack propagation. With increase of steel strength, it seems the optimal heat input for quenched and tempered HSS becomes smaller. The effect of heat input on fracture toughness of TMCP HSS is different with quenched and tempered HSS: higher heat input would normally produce higher fracture toughness for HSS TMCP550. With the increase of yield strength, the fracture resistance increases for both quenched and tempered HSS and TMCP HSS.