Journal
ISIJ INTERNATIONAL
Volume 61, Issue 1, Pages 361-371Publisher
IRON STEEL INST JAPAN KEIDANREN KAIKAN
DOI: 10.2355/isijinternational.ISIJINT-2020-293
Keywords
microstructure; tempering; precipitation; kinetics; cold ring rolling; M50 steel
Categories
Funding
- National Natural Science Foundation of China [51875426]
- 111 Project [B17034]
- Innovative Research Team Development Program of Ministry of Education of China [IRT_17R83]
- Important Science and Technology Innovation Program of HuBei Province [2019AAA001]
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The microstructure evolution and tempering transformation kinetics of M50 steel during cold ring rolling (CRR) were studied. The results showed that CRR weakened the brass texture and increased the low angle boundaries, leading to changes in activation energy and carbon content during tempering. Additionally, CRR affected the segregation of carbon atoms and precipitation of transition carbide, ultimately influencing the mechanical properties of the steel.
The microstructure evolution and tempering transformation kinetics of the M50 steel subjected to cold ring rolling (CRR) have been investigated. The results indicate that the brass R{110} < 110> texture is weakened with the enhancement of the < 111 > //ND texture during CRR. Due to the increased low angle boundaries by CRR, the Act temperature decreases while the carbon content and volume fraction of RA increase. During tempering, the activation energy of carbon atoms segregation and transition carbide precipitation decrease, while the activation energy of retained austenite (RA) decomposition increases after CRR. The kinetic analysis shows that the CRR is beneficial to the carbon atoms segregation during the beginning of tempering. Then, the CRR leads to the delay of the onset of transition carbide precipitation, but decreases the whole reaction time, which has been verified by the transmission electron microscopy (TEM) and hardness results. The lagging of transition carbide precipitation in the early stage is caused by the increased segregation trapping of carbon atoms, while the higher nucleation rate is responsible for the enhanced precipitation of transition carbide during the later stage. For the cementite formation, there are no significant changes in the predictive kinetics after the applied CRR. However, the kinetic transformation of RA decomposition is inhibited by the CRR, which is attributed to the higher carbon content and smaller grain size of RA. Additionally, the alloy carbides precipitation is also enhanced by the CRR process during secondary hardening.
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