Effect of tempering temperature on microstructure and mechanical properties of 55NiCrMoV7 hot working die steel

doi:10.13251/j.issn.0254-6051.2023.01.023

Abstract

Abstract: The expansion curves of 55NiCrMoV7 steel during continuous coolingwith different speeds were measured by using Formastor-FII dilatometer, and the phase transformation temperature points were determined by expansion method and metallographic-hardness method, and then the CCT curves of the steel were drawn. Effect of tempering temperature on microstructure and mechanical properties of the 55NiCrMoV7 steel were studied by means of scanning electron microscope (SEM), optical microscope (OM), Rockwell hardness tester, tensile tester and impact tester. The results show that when the tempering temperature is in the range of 520-600 ℃, as tempering temperature increases, both the hardness and tensile strength of the 55NiCrMoV7 steel decrease, while the plasticity and toughness gradually increase. When the tempering temperature is 560-580 ℃, the hardening stress of the material is basically eliminated, martensite decomposing and retained austenite transformation is basically complete. The preferable mechanical properties of the 55NiCrMoV7 steel are obtained, with tensile strength, elongation and impact absorbed energy of 1300 MPa, 14.5% and more than 30 J, respectively.

Key words: 55NiCrMoV7 hot working die steel, tempering temperature, microstructure, mechanical properties, fracture morphology

CLC Number:

TG142.45

Yuan Yasha, Wang Yuchang, Wang Wenyan, Shi Ruxing, Yuan Sha, Zhang Yudong. Effect of tempering temperature on microstructure and mechanical properties of 55NiCrMoV7 hot working die steel[J]. Heat Treatment of Metals, 2023, 48(1): 133-138.

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