Microstructure and properties of a grade 10.9 bolt steel with wide tempering time window

doi:10.13251/j.issn.0254-6051.2023.09.039

Abstract

Abstract: Microstructure and mechanical properties of a vanadium microalloyed Si-Mn-Cr bolt steel after quenching at 870 ℃+tempering at 550 ℃ for different time were studied by means of optical microscope, scanning electron microscope, transmission electron microscope, and Rockwell hardness test. The results show that the microstructure of the tested steel after quenching at 870 ℃ is lath martensite, and the microstructure after tempering at 550 ℃ for 40, 60 and 80 min, respectively, is clear martensie with accompaning by fine dispersed carbide precipitates. When the tempering time is 40-80 min, the tensile strength of the tested steel is 1081-1120 MPa, the yield strength is 993-1013 MPa, and the percentage reduction of area is 56.0%-56.3%, all of which are relatively stable, and the tensile fracture of the tested steel has obvious neck contraction phenomenon. The fracture source areas are all ductile fractures with small dimples and tearing edges, and the comprehensive mechanical properties are good. Therefore, the tempering time window of the 10.9 grade bolt steel is broad, and the comprehensive mechanical properties are stable, which is conducive to expanding the range of use of bolt steel.

Key words: grade 10.9 bolt steel, tempering time, microstructure, mechanical properties, wide heat treatment window

CLC Number:

TG142.1

Wang Jiaojiao, Liu Hongchun, Liu Yong, Chen Hongwei, Tian Zhiqiang, Zhang Hongqi. Microstructure and properties of a grade 10.9 bolt steel with wide tempering time window[J]. Heat Treatment of Metals, 2023, 48(9): 233-237.

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