I&Q&P process of Nb microalloyed cold-rolled DP780 steel with high product of strength and elongation

doi:10.13251/j.issn.0254-6051.2022.10.032

Abstract

Abstract: Based on the theory of metastable austenite deformation induced phase transformation, the I&Q&P (intercritical annealing and quenching and partitioning) process of 800 MPa grade cold-rolled DP780 steel was investigated by using salt bath furnace in the laboratory. The microstructure and mechanical properties of the tested steel under different processes were studied by means of metallographic microscope, scanning electron microscope, tensile testing machine and XRD. The results indicate that the microstructure of the tested steel is composed of ferrite, martensite and retained austenite under the I&Q&P process. The ferrite grain size is mainly larger than 5 μm at annealing temperature of 830 ℃, however, the ferrite grain size is mainly smaller than 5 μm at annealing temperature of 860 ℃. The mechanical properties of the tested steel annealed at 830 ℃ fluctuate greatly with the change of quenching temperature, conversely, the mechanical properties of the tested steel annealed at 860 ℃ vary slightly. At annealing temperature of 860 ℃ and quenching temperature of 260 ℃, the optimum comprehensive mechanical properties are obtained with tensile strength of 802 MPa, elongation of 26.8%, and product of strength and elongation of 21.5 GPa·%, and the content of retained austenite in the steel is as high as 13.89%.

Key words: Nb microalloying, dual-phase steel DP780, I&Q&P process, microstructure, mechanical properties

CLC Number:

TG156

Yang Kang, Shi Na, Ding Jing, Yu Liang, Fang Qiang. I&Q&P process of Nb microalloyed cold-rolled DP780 steel with high product of strength and elongation[J]. Heat Treatment of Metals, 2022, 47(10): 191-197.

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