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Microstructural control and mechanisms of strength-ductility enhancement for 1.0 GPa grade I&QP steel |
HOU Xiao-ying, SUN Wei-hua, WANG Ye-qin, JIN Guang-yu, CAO Guang-ming, REN Dong |
Shandong Iron and Steel Group Rizhao Co., Ltd., Rizhao 276805, Shandong, China |
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Abstract In order to investigate the microscopic morphological characteristics and the mechanisms of strength-ductility enhancement of I&QP steel,the characteristics for microstructures and mechanical properties and the effect on strength and plasticity were analyzed by using different annealing processes. The results indicated that the final mixed microstructure was controlled which was composed of "lath-shaped clusters" bainites with different orientations,a small amount of ferrite whose grain size was less than 2.5 μm,as well as lamellar retained austenites,when the needle-like bainite was controlled for the initial hot-rolled microstructure,whose volume percent was more than 85% and fine grain size was in the range of 3-5 μm. The volume pecent of "lath-shaped clusters" bainites was more than 70%,and the volume percent of lamellar retained austenites was more than 14.5%. When the intercritical heating temperature was decreased to 850 ℃ properly,the grain size of I&QP steel could be refined obviously,and the ratio of large misorientation angle was increased to 60.2%. Under the combined action for the mechanisms of strength-ductility enhancement which including the phase transformation,grain refinement,phase precipitation and dislocations,the tensile strength was more than 1.0 GPa,the product of tensile strength and ductility was reached to 30.2 GPa·%,and the expanding rate was up to 62%.
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Received: 12 May 2020
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