Effect of post rolling heat treatment on phase transformation microstructure and hardness of pearlitic steel rail

doi:10.13251/j.issn.0254-6051.2023.03.004

Abstract

Abstract: Microstructure and hardness of the tested steel under different heat treatment processes after rolling were studied by means of double-pass hot compression test on Gleeble-3500 thermal simulation tester. The effects of isothermal time, different cooling rates and isothermal temperatures after hot deformation on pearlite lamella and hardness and their mechanisms were analyzed. The results show that the pearlite + a small amount of ferrite are all obtained after 1 ℃/s continuous cooling, rapid cooling after quenching isothermal transformation at 1 ℃/s (1 ℃/s-580 ℃-30 s), rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) and rapid cooling after quenching isothermal transformation at 620 ℃ at 5 ℃/s (5 ℃/ s-620 ℃-60 s), respectively. However, martensite or bainite structure appears after 3 ℃/s continuous cooling and rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) due to insufficient isothermal time. Compared with continuous cooling at 1 ℃/s, rapid cooling after quenching isothermal transformation at 1 ℃/s plays a positive role in reducing the lamellar spacing of pearlite and increasing the hardness. The lamellar spacing of the tested steel obtained after rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) is the smallest, reaching 73.19 nm. The lamellar orientation is diverse, and some cementite flakes are broken. The small increase of hardness is related to the increase of pearlitic structure content. The pearlite lamellae of the tested steel after 1 ℃/s continuous cooling is the coarsest, and the hardness is the lowest due to the excessive growth of precipitated phase NbC and the spheroidization of fractured cementite. The relatively complete and fine pearlitic lamellae and the existence of residual dislocation make the higher hardness of the tested steel when rapid cooled after quenching isothermal transformation at 620 ℃ at 5 ℃/s (5 ℃/s-620 ℃-60 s), reaching 42.0 HRC.

Key words: pearlitic steel rail, post rolling heat treatment, isothermal time, isothermat temperature, low rate cooling, rapid cooling

CLC Number:

TG156.1

Jiang Hongli, Wang Dongmei, Wang Yeshuang, Zhang Heng, Chen Lin. Effect of post rolling heat treatment on phase transformation microstructure and hardness of pearlitic steel rail[J]. Heat Treatment of Metals, 2023, 48(3): 19-24.

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