Effect of isothermal bainite temperature on microstructure and properties of ship steel after intercritical rolling

doi:10.13251/j.issn.0254-6051.2024.11.025

Abstract

Abstract: Effect of isothermal bainite temperature on microstructure and mechanical properties of ship steel after intercritical rolling was investigated by means of scanning electron microscope (SEM), X-ray diffractometer (XRD) and mechanical properties tests. The results show that the microstructure is M/A island and a small amount of ferrite after hot rolling. When the isothermal temperature is 400 ℃ and 450 ℃ followed by air cooling, the microstructure is composed of the lath bainite, granular bainite and ferrite. When the isothermal temperature is 500 ℃, the microstructure is composed of granular bainite and ferrite. The yield strength of the tested steel ranges from 981 MPa to 1116 MPa, and the tensile strength ranges from 997 MPa to 1124 MPa after bainite isothermal treatment. Compared to the other two isothermal temperatures, the retained austenite volume fraction is the highest when isothermal treated at 500 ℃, resulting in the elongation and impact absorbed energy reaching the maximum values of 11.7% and 104.1 J, respectively. Through comprehensive comparison, the mechanical properties of the steel reaches the optimum when isothermal treated at 450 ℃, with the tensile strength of 1124 MPa, yield strength of 1116 MPa, elongation of 11.3%, and impact absorbed energy of 71.4 J.

Key words: ship steel, intercritical rolling, isothermal bainite treatment, microstructure, mechanical properties

CLC Number:

TG156.1

Tian Yaqiang, Yao Shuo, Zhang Mingshan, Li Hongbin, Hu Baojia, Chen Liansheng. Effect of isothermal bainite temperature on microstructure and properties of ship steel after intercritical rolling[J]. Heat Treatment of Metals, 2024, 49(11): 167-171.

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