Effect of quenching process on microstructure and properties of a 500 MPa grade hot-rolled offshore engineering steel

doi:10.13251/j.issn.0254-6051.2025.01.017

Abstract

Abstract: In order to study the main factors affecting the microstructure and low temperature toughness of a 500 MPa grade offshore engineering steel, quenching and tempering process was carried out to explore the effect of quenching temperature on microstructure and mechanical properties of the as-hot-rolled tested steel, and to identify the propagation mechanism of cracks in different microstructure. The results show that the microstructure is dominated by ferrite and martensite after subcritical quenching at 800 ℃ and 850 ℃, and with the increase of quenching temperature, the volume fraction of ferrite decreases. After higher temperature quenching at 910-1010 ℃, the microstructure is completely composed of lath martensite, and the size of martensitic lath increases with the increase of quenching temperature, resulting in the increases of strength, and the decrease of low temperature toughness and uniform elongation. The best heat treatment process for the tested steel to obtain the best strength and toughness is quenching at 910-960 ℃ and tempering at 500 ℃. Most of the cracks in the tested steel originate at the interface of the soft and hard phases in the tempered microstructure, propagate in straight line along the interface between ferrite grains and martensitic laths, and end at the prior austenite grain boundary. The increase of the proportion of large angle grain boundary is helpful to improve the low temperature toughness of the tested steel.

Key words: offshore engineering steel, quenching, strength and toughness, crack

CLC Number:

TG156.4

Tuo Chende, Gao Qing, Zhang Yongwei, Shi Shuhua, Feng Zan. Effect of quenching process on microstructure and properties of a 500 MPa grade hot-rolled offshore engineering steel[J]. Heat Treatment of Metals, 2025, 50(1): 110-118.

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