Abstract: Microstructure evolution and change of properties of the 60Si2Mn hot rolled spring steel annealed at the temperature slightly lower than the initial austenite transformation temperature Ac₁ were studied by means of metallographic, EDS analysis and mechanical property tests. The results show that the strength and hardness of the tested steel first decrease and then increase with the increase of annealing time. While the plasticity and toughness first increase and then decrease. The results of metallographic analysis show that during annealing, the cementite lamellae in the pearlite are firstly thickened and the spacing increases, and then the cementite lamellae are fractured and spheroidized, and the spheroidization rate increases with the increase of annealing time. When the annealing time exceeds 10 h, the “island structure” appears in the specimen, with its volume fraction increasing with the increase of annealing time, and reaching 20% when annealed for 30 h. Further analysis demonstrates that the “island structure” is the martensite, in which the Si content is significantly lower than that in the matrix, while the Mn content is significantly higher than that in the matrix.

Key words: 60Si2Mn steel, annealing, cementite, spheroidization, martensite