Effect of tempering time on mechanical properties and microstructure of high strength anti-seismic fire-resistant steel plate

doi:10.13251/j.issn.0254-6051.2022.01.026

Abstract

Abstract: Effect of tempering at 600 ℃ for different time on mechanical properties, microstructure and precipitation behavior of a 690 MPa grade high strength anti-seismic fire-resistant steel sheet was studied by means of OM, SEM, TEM, tensile test and impact test. The results show that different tempering time has an important influence on mechanical properties and microstructure of the fire-resistant steel plates. When tempered at 600 ℃, the strength of the fire-resistant steel plate decreases slightly, but the elongation increases and the yield ratio decreases, which improves its comprehensive mechanical properties, meanwhile, the low temperature impact absorbed energy decreases with the extension of tempering time. The optimum tempering time is 15 min, by which the yield strength, the hardness and the impact absorbed energy at -40 ℃ of the tested steel plate are 976 MPa, 396 HV and 164 J, respectively, and the microstructure is composed of bainite, ferrite and a small amount of martensite. There are dislocations and fine precipitates in both martensite and ferrite, the precipitated phase is Nb-rich Nb and Ti composite carbides, which plays a role of precipitation strengthening. When the tempering time extends to 60 min, a large number of fine composite carbides containing Nb, Ti and Mo are precipitated, but the precipitation strengthening is not capable of making up for the strength loss caused by ferrite. Therefore, in the process of tempering at the same temperature, the tensile strength and hardness decrease with the extension of tempering time.

Key words: 690 MPa fire-resistant steel plate, tempering time, mechanical properties, microstructure

CLC Number:

TG142

Lu Chunxiang, Lin Tianzi, Cao Jianchun, Gao Peng, Zhan Fang, Liu Xing. Effect of tempering time on mechanical properties and microstructure of high strength anti-seismic fire-resistant steel plate[J]. Heat Treatment of Metals, 2022, 47(1): 156-162.

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