Yan Fuyao, Zhu Lei, Chen Hongtao, Yang Ying, Li Yuyang, Xuan Huanhuan, Zhang Jun, Cai Yougang, Duan Pirong, Li Guo, Zhou Maohua, Luo Dingxiang, Zhang Yanxiang, Yan Mufu. Annealing process and stacking method for reducing hardness of as rolled/forged high quality special steel[J]. IRON STEEL VANADIUM TITANIUM, 2021, 42(2): 152-160. doi: 10.7513/j.issn.1004-7638.2021.02.025
Citation:
Yan Fuyao, Zhu Lei, Chen Hongtao, Yang Ying, Li Yuyang, Xuan Huanhuan, Zhang Jun, Cai Yougang, Duan Pirong, Li Guo, Zhou Maohua, Luo Dingxiang, Zhang Yanxiang, Yan Mufu. Annealing process and stacking method for reducing hardness of as rolled/forged high quality special steel[J]. IRON STEEL VANADIUM TITANIUM, 2021, 42(2): 152-160. doi: 10.7513/j.issn.1004-7638.2021.02.025
Yan Fuyao, Zhu Lei, Chen Hongtao, Yang Ying, Li Yuyang, Xuan Huanhuan, Zhang Jun, Cai Yougang, Duan Pirong, Li Guo, Zhou Maohua, Luo Dingxiang, Zhang Yanxiang, Yan Mufu. Annealing process and stacking method for reducing hardness of as rolled/forged high quality special steel[J]. IRON STEEL VANADIUM TITANIUM, 2021, 42(2): 152-160. doi: 10.7513/j.issn.1004-7638.2021.02.025
Citation:
Yan Fuyao, Zhu Lei, Chen Hongtao, Yang Ying, Li Yuyang, Xuan Huanhuan, Zhang Jun, Cai Yougang, Duan Pirong, Li Guo, Zhou Maohua, Luo Dingxiang, Zhang Yanxiang, Yan Mufu. Annealing process and stacking method for reducing hardness of as rolled/forged high quality special steel[J]. IRON STEEL VANADIUM TITANIUM, 2021, 42(2): 152-160. doi: 10.7513/j.issn.1004-7638.2021.02.025
The technical issues such as machinability, hardness uniformity and longer annealing time present for a wrought and hot-rolled special steels (e.g. CTHQ25, 1Cr11Ni2W2MoV, 30CrNi4Mo) manufactured by Pangang Jiangyou Changcheng Special Steel Co., Ltd. In order to address those issues, a a hot-rolled CTHQ25 drill steel had been used, a single-step heat-treating route was designed to soften the steel to less than HB 260 based on thermodynamic calculations of phase stability and experimental study on kinetics of phase evolution. To accelerate the annealing process, a double-step annealing, where the first step annealed at a lower temperature to promote the decomposition of retained austenite and the second step annealed at a higher temperature to accelerate microstructure coarsening, was designed and carried out to achieve a hardness of HB 240. In the meantime, special consideration was given to workpiece layout in the furnace to ensure hardness uniformity. With the coupled numerical simulation of temperature-fluid field of the furnace, the workpiece layout in the furnace was optimized with fixture topologically re-designed to achieve the maximum fuel efficiency and temperature uniformity in contrast to originally random stacks of workpieces.
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Figure 1. The microstructure characterization of as-rolled CTHQ25 steel
Figure 2. The OM microstructure of as hot rolled CTHQ25 steel
Figure 3. EPMA Backscatter image of as-rolled CTHQ25 steel
Figure 4. Equilibrium phase diagram of CTHQ25 steel
Figure 5. Microstructure and hardness of as-rolled CTHQ25 steel after different austenitizing processes
Figure 6. Schematic diagram of austenitizing and single-step annealing process
Figure 7. Hardness of different initial microstructures annealed at 680 ℃ and 700℃ for 48 h
Figure 8. Microstructure of as-rolled CTHQ25 steel austenitized at 680 ℃ for 1 h with air cooling and then single-step annealed at 680 ℃ for 48 h
Figure 9. Schematic diagram of austenitizing and double-step annealing
Figure 10. Microstructure of as-rolled CTHQ25 steel treated under 680 ℃/1 h/AC and 500 ℃/1～7 h/ AC conditions
Figure 11. Microstructure of as-rolled CTHQ25 steel treated under 680 ℃/1 h/AC and 500 ℃/5 h-680 ℃/24～30 h/AC conditions
Figure 12. Hardness of sample annealed for same annealing time and at different annealing temperatures
Figure 13. Car-type fuel furnace and optimal design of steel configuration
Figure 14. Temperature field of furnace with steel bar and heating curve of characteristic points (the illustration shows cross section’s the temperature field distribution from furnace door direction)
Figure 15. Block for flat configuration of steel bar
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