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Effect of Tempering Temperature on Microstructure Evolution and Hardness of 9Cr1. 5Mo1CoB(FB2) Steel
Author(s) -
Zhang Yongqiang,
Li Chuanwei,
Shen Gang,
Han Lizhan,
Gu Jianfeng
Publication year - 2021
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.202000519
Subject(s) - tempering , materials science , microstructure , martensite , carbide , metallurgy , volume fraction , high speed steel , analytical chemistry (journal) , composite material , chemistry , chromatography
The microstructure evolution and hardness variation of FB2 steel influenced by tempering are investigated. The results show that water‐cooling from 1100 °C produces lathy martensite microstructure. After tempering at 500 °C, the steel exhibits a martensite structure with 4.2% needle‐like Fe 3 C particles. The (Cr, Mo) 2 C and Cr‐rich M 7 C 3 particles are detected in the sample tempered at 570 °CAs the tempering temperature enhances from 620 to 700 °C the (Cr, Mo) 2 C and Cr‐rich M 7 C 3 in the matrix are replaced by Cr‐rich M 23 C 6 . Besides, the (V, Nb)C particles are identified in samples tempered above 620 °C. Thus, the evolution of carbides in FB2 steel during tempering can be summarized as: Fe 3 C→(Cr, Mo) 2 C + Cr‐rich M 7 C 3 →(Cr, Mo) 2 C + Cr‐rich M 7 C 3 + Cr‐rich M 23 C 6 →Cr‐rich M 23 C 6 . Furthermore, the results suggest that M 3 C, M 2 C + M 7 C 3 , M 23 C 6 , and MX have high reaction rates at 500, 570, 620, and 700 °C respectively. In addition, the dislocation density reduces from 6.8 × 10 14 m −2 to 2.1 × 10 14 m −2 , and the volume fraction of carbides increases from 4.2% to 12.6% with increasing temperatures from 500 to 700 °C leading to hardness decrease from 485 to 284 Hv. Finally, the quantitative relationship between the hardness and microstructure evolution during tempering is discussed.