Wu Hongyan

MICROSTRUCTURE, MECHANICAL PROPERTIES AND STRENGTHENING MECHANISMS OF A Cu BEARING LOW-CARBON STEEL TREATED BY Q&P PROCESS

A low carbon steel containing Cu addition was treated by Q&P process using a CAS- 200 continuous annealing simulator. The microstructure of the steel was characterized by means of SEM, EBSD, XRD and TEM and its mechanical properties were investigated by tensile testing at room temperature. Cu-rich precipitates formed during the Q&P process were observed as spherical particles in martensitic laths and are 9 nm to 20 nm in diameter. According to the Orowan mechanism, those fine particles may have a contribution to the yield strength of the steel about 134 MPa. Also observed are three different morphologies of the retained austenite phase in the test steel, i.e. thin film-like, fine granular and blocky, formed at different locations. The test steel has a good comprehensive mechanical properties, of which the product of tensile strength and elongation, the tensile strength and the total elongation are as high as 21.2 GPa·%, 1326 MPa and 16%, respectively. The excellent combined properties can be attributed to the effect of transformation induced plasticity (TRIP) caused by the retained austenite.