Effect of annealing soften on microstructure and hardness of high strength steel 300M

doi:10.13251/j.issn.0254-6051.2021.03.020

Abstract

Abstract: In order to improve the subsequent machinability of 300M steel and widen the application field, the effect of annealing process on microstructure and hardness of 300M steel was studied. The results show that annealing at 730 ℃ below Ac₁, the microstructure of 300M steel is transformed from martensite to tempered sorbite with spherical or granular carbides. The microstructure is consisting of ferrite, lamellar pearlite with partial spheroid carbides when annealing at 780 ℃ in intercritical phase region. Annealing at 860 ℃ above Ac₃, The microstructure is ferrite and lamellar pearlite with long thin sheet carbide. The cooling rate has a significant effect on the hardness of 300M steel, the slow cooling rate results in the spheroidization of carbides and the decrease of hardness. The softening effect of 300M steel is more obvious annealing at intercritical phase region with low cooling rate, and the hardness can be less than 240 HBW.

Key words: 300M steel, annealing, microstructure, hardness

CLC Number:

TG156.2

Wang Hongli, Wu Chengchuan, Du Simin, Li Yuan, Luo Xianghua, Ye Wenbing. Effect of annealing soften on microstructure and hardness of high strength steel 300M[J]. Heat Treatment of Metals, 2021, 46(3): 100-103.

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