Effect of Nb on microstructure and hardness of high Ti weathering steel after continuous cooling

doi:10.13251/j.issn.0254-6051.2022.08.007

Abstract

Abstract: Effect of Nb on continuous cooling transformation behavior of the high Ti weathering steel was studied by Gleeble thermal simulation testing machine. Microstructure and hardness of the tested steel without Nb addition and that added 0.050% Nb after continuous cooling transformation were observed and analyzed by optical microscope (OM), transmission electron microscope (TEM) and hardness test. The results show that Nb can inhibit ferrite transformation and promote bainite transformation. When the cooling rate increases from 5 ℃/s to 10 ℃/s, the grain refinement effect of the two tested steels is the most significant, and the hardness of the steels without and with Nb addition increases by 22 HV0.2 and 25 HV0.2, respectively. When the cooling rate is 40 ℃/s, the precipitate in the steel without Nb is mainly 6-13 nm spherical Ti(C,N), while the precipitates in the 0.050% Nb-microalloyed steel are mainly 5-12 nm spherical (Ti,Nb) (C,N) and 10-15 nm square (Ti,Nb) (C,N). The amount of precipitates in 0.050% Nb-microalloyed steel is more, so the precipitation strengthening effect is more significant. The effect of Nb on grain refinement is not significant in the high Ti weathering steel. The hardness of 0.050%Nb-microalloyed steel is only slightly higher than that of the steel without Nb at the same cooling rate, the maximum difference is only 11 HV0.2.

Key words: Nb, weathering steel, continuous cooling, microstructure, hardness

CLC Number:

TG142.1

He Bo, Peng Tianen, Hu Xuewen, Jiang Bo, Guo Rui, Shi Jian, Wang Fei, Wang Haibo. Effect of Nb on microstructure and hardness of high Ti weathering steel after continuous cooling[J]. Heat Treatment of Metals, 2022, 47(8): 46-51.

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