Microstructure and mechanical properties of high strength low alloy thick steel plates for offshore engineering

doi:10.13251/j.issn.0254-6051.2023.10.005

Abstract

Abstract: A 420 MPa grade high strength low alloy heavy plates with a thickness of 80 mm were produced by the process of TMCP plus tempering at 600 ℃. The microstructure and mechanical properties along the thickness direction were analyzed by using optical microscopy, scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction and mechanical tests. The results show that a fine-grained structure with an average grain size of 6-10 μm can be obtained by TMCP. After tempering, the microstructure near the surface of the plate is dominated by bainite, while the core is mainly characterized by aggregated carbides and ferrite. After tempering at 600 ℃, cementite precipitates on the ferrite grain boundary, and compound precipitation of carbides of Nb and Ti elements is found. Tensile tests show a decrease in yield strengths from 542 MPa on the surface to 384 MPa at the core. The fracture model of the plate is dominated by micro-hole coalescence fracture. Micro-holes are mostly formed between ferritic laths and near inclusions. The grain refinement strengthening and precipitation strengthening dominate the contribution of each strengthening mechanism to the yield strength.

Key words: high strength low alloy steel, heavy plate, microstructure and mechanical properties, offshore engineering, strengthening mechanism

CLC Number:

TG142.1

Cui Shugang, Shi Changxin, Gu Guochao, Xu Wenhua, Lü Yupeng. Microstructure and mechanical properties of high strength low alloy thick steel plates for offshore engineering[J]. Heat Treatment of Metals, 2023, 48(10): 37-44.

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