Effect of tempering temperature on microstructure and precipitation of a 1100 MPa high strength marine engineering steel

doi:10.13251/j.issn.0254-6051.2023.10.021

Abstract

Abstract: Microstructure and mechanical properties of an ultra-high strength Cu-bearing marine engineering steel quenched at 850 ℃ and tempered at different temperatures were studied by means of OM, EBSD and TEM. The results show that when the tested steel is tempered at 425 ℃, a hardness peak of 435 HV5 appears, which is the synergistic strengthening effect of finely dispersed 5 nm Cu particles and a small amount of carbide particles in the matrix. In the overtempering state of 525 ℃, the Cu particles in the tested steel matrix are coarsened (6.5 nm), the strength of the tested steel decreases, and factors such as that the brittle phase M₃C cementite in the tested steel is completely dissolved and transforms into more stable M₂C precipitates, and the increase of the density of high-angle grain boundaries, as well as the content of film-like reverse-transformed austenite make the KV₂ at -40 ℃ increase from 6 J tempered at 475 ℃ to 180 J tempered at 525 ℃, thus the low temperature toughness is significantly improved. As the tempering temperature increases again, the softening of the martensite matrix is more obvious, and the Cu particles and M₂C carbides are further coarsened, and the strength of the tested steel is significantly reduced. It is concluded that the properties of the tested steel tempered at 525 ℃ achieves a good match of strength and toughness, the tensile strength and yield strength are 1188 MPa and 1119 MPa, respectively, and the impact absorbed energy KV₂ at -40 ℃ is 180 J.

Key words: marine engineering steel, tempering temperature, temper brittleness, Cu precipitation strengthening

CLC Number:

TG142.1

Zhao Song, Ya Bin, Luo Xiaobing, Zhang Xingguo. Effect of tempering temperature on microstructure and precipitation of a 1100 MPa high strength marine engineering steel[J]. Heat Treatment of Metals, 2023, 48(10): 143-150.

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