MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 1500 MPa GRADE ULTRA–HIGH STRENGTH LOW ALLOY STEEL
Received date: 2009-12-23
Revised date: 2010-03-19
Online published: 2010-06-11
Supported by
Supported by Project of Scientific and Technical Supporting Program of China during the 11th Five–Year Plan (No.2006BAE03A06)
A novel sort of 1500 MPa grade ultra–high strength low alloy structural steel with multi–element of Si–Mn–Cr–Ni–Mo was designed. Effects of four different processes of TMCP (thermo–mechanical controlled processing), controlled rolling+air–cooled, controlled rolling + direct quenching and controlled rolling+direct quenching+tempering at 250℃ on the microstructure and mechanical properties were investigated. The results indicate that the directly quenched steel has a maximum tensile strength of 1890 MPa, yield strength of 1280 MPa and elongation of 13%. After tempered at 250 ℃ for 30 min, the tensile strength of the steel decreased to 1820 MPa, while the yield strength increased to 1350 MPa, which is ascribed to the comprehensive effect of the softening mechanism due to the recoverof dislocation sub–structure and the strengthening mechanism due to the decomposition of retained austenite and "–carbide precipitation. Duplex phase microstructure involving lath bainite, martensite segmented by bainite, and retained austenite was obtained by the process of air–cooling and TMCP, so that it has excellent strength and plasticity. Carbon diffusion phenomenon exists in the quenching process of low–carbon steel. Both the decomposition of retained austenite and the carbon partitioning into austenite from martensite or bainite were found during tempering process. The paper demonstrates that the precipitation particles of cubic structure nucleated in austenite, growing up and coarsning uring the whole cooling process. Futhermore, the emergence of a lage number of second–phasprecipitation cores was not found in martensite or bainite after phase tansformation.
YU Li-Jun , WU Hui-Bin , SA Qiang-Wu , YU Wei , LEI Ai-Di . MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 1500 MPa GRADE ULTRA–HIGH STRENGTH LOW ALLOY STEEL[J]. Acta Metall Sin, 2010 , 46(6) : 687 -694 . DOI: 10.3724/SP.J.1037.2009.00855
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