| In this paper, on the basis of investigating and analyzing the development bainitic steels all over the world, tempering procedure was studied in order to improve the mechanical properties of bainitic steels. The influence of tempering process on the microstructures and mechanical behavior were extensively investigated with optical microscope, mechanical tests,SEM,TEM and X-ray analyzer.The bainitic steels in our experiments were supplied by Anshan Iron& Steel Corporation. Six tempering systems were designed to carry out all-around lab research. The results of tensile test and Charpy U notch (CLN) impact test showed that, when the bainitic steel was tempered at 350℃ for 4h and above, its yield strength, ultimate tensile strength, elongation, reduction of area and Charpy U notch (CUN) impact energy were 1,000MPa,1,200MPa, 15%, 45% and 150J, respectively. The steels appear obviously temper embrittlement when tempered at 450℃ to 550℃. TEM and optical observations showed that the microstructure of bainitic steels was mainly consisted of granular bainite. The measurement of retained austenite in the bainitic steel under different tempering procedures and 3% tensile deformation showed that, the mechanical stability of retained austenite was excellent when tempered at 350℃.The strength and toughness of bainitic steels with different tempering procedure has a close relation to mechanical stability of retained austenite.
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