EFFECT OF QUENCHING TEMPERATURE ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 550 MPa GRADE THICK STEEL PLATE
WAN Decheng, YU Wei, LI Xiaolin, ZHANG Jie, WU Huibin, CAI Qingwu
Metallurgical Engineering Research Institute, University of Science and Technology Beijing, Beijing 100083
Cite this article:
WAN Decheng, YU Wei, LI Xiaolin, ZHANG Jie, WU Huibin, CAI Qingwu. EFFECT OF QUENCHING TEMPERATURE ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 550 MPa GRADE THICK STEEL PLATE. Acta Metall Sin, 2012, 48(4): 455-460.
Abstract The heat treatments of 730-910 ℃ quenching and 600 ℃ tempering were applied to enhance the low temperature toughness of 550 MPa grade thick steel plate. Moreover, the effect of quenching temperature on the microstructure and mechanical properties was studied. The results showed that strength and toughness of the specimen decreased at first and then increased as quenching temperature increased within intercritical region. When the quenching temperature was raised up to austenite region, the strength increased further, but the toughness decreased. Mechanical properties of the steel subjected to intercritical quenching at 760 ℃ and tempering were the worst of all of the specimen, due to coarsened polygonal ferrite and the lath, acicular M/A constituent along grain boundaries and inside the grains, which deteriorated the toughness seriously. On the other hand, the steel treated by intercritical quenching at 850 ℃ and tempering showed the optimum combination of strength and toughness compared with the steel treated by quenching after austenization and tempering. This is attributed to microstructure refinement, higher fraction of high angle grain boundaries caused by the formation of ferrite, abundant homogeneous dislocation cell substructure and stable thin film retained austenite.