Effect of isothermal temperature on microstructure and hardness of ultra-low carbon bainitic steel

doi:10.13251/j.issn.0254-6051.2023.08.015

Abstract

Abstract: Effect of isothermal temperature on microstructure transformation and hardness of ultra-low carbon bainitic steel was studied by means of L78 quenching dilatometer, hardness tester, scanning electron microscope(SEM), optical microscope(OM). The results show that TTT curves of the steel includes ferrite transformation zone, bainite transformation zone, pearlite transformation zone. At isothermal temperature of 725-650 ℃, the microstructure is equiaxed ferrite with a small amount of pearlite and alloy carbides. The microstructure transforms into quasi polygonal ferrite from 625 ℃. When isothermal treated at 600-575 ℃, the ferrite appears as block and a small amount of needle-like. Under 575 ℃, the microstructure is all ultra-low carbon bainite structure. As the isothermal temperature decreases, the microstructure of the tested steel becomes finer and the hardness increases, but the hardness change is not significant. In the isothermal temperature range of 725-700 ℃, the pearlite content gradually decreases, and in the isothermal temperature range of 675-600 ℃, the bainite content shows an upward trend.

Key words: ultra-low carbon bainitic steel, isothermal temperature, microstructure transformation, hardness

CLC Number:

TG151.2

Sun Tingting, Chen Weili, Jia Zilong. Effect of isothermal temperature on microstructure and hardness of ultra-low carbon bainitic steel[J]. Heat Treatment of Metals, 2023, 48(8): 94-98.

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