Effects of transformation temperature and austenitization temperature on the transformation kinetics and microstructure of a Nb microalloyed high-carbon steel

Zhou Mingxing; Chi Yicheng; Liu Jingtao; Li Zhengqian; Liu Sihua; Zhang Daichen; Su Xue; Tian Junyu

doi:10.7513/j.issn.1004-7638.2024.04.020

Volume 45 Issue 4

Aug. 2024

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Article Navigation > IRON STEEL VANADIUM TITANIUM > 2024 > 45(4): 143-149

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Zhou Mingxing, Chi Yicheng, Liu Jingtao, Li Zhengqian, Liu Sihua, Zhang Daichen, Su Xue, Tian Junyu. Effects of transformation temperature and austenitization temperature on the transformation kinetics and microstructure of a Nb microalloyed high-carbon steel[J]. IRON STEEL VANADIUM TITANIUM, 2024, 45(4): 143-149. doi: 10.7513/j.issn.1004-7638.2024.04.020

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Effects of transformation temperature and austenitization temperature on the transformation kinetics and microstructure of a Nb microalloyed high-carbon steel

doi: 10.7513/j.issn.1004-7638.2024.04.020

The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China

Received Date: 2023-03-20
Publish Date: 2024-08-30

Abstract

Abstract

In order to optimize the heat treatment process of a Nb microalloyed high-carbon steel, the effects of reheating temperature and transformation temperature on pearlite transformation kinetics and microstructure and properties were studied by dilatometry, optical microscope, scanning electron microscope, electron backscattering diffraction and hardness tests. The results show that the pearlite transformation kinetics is reduced by increasing the reheating temperature. One reason is that the number of pearlite nucleation sites decreases with the increase of prior austenite grain size. On the other hand, the solubility of Nb increases with the reheating temperature, which decreases the carbon diffusion coefficient and thus decreases the pearlite growth rate. The pearlite transformation kinetics decreases as the transformation temperature decreases from 625 ℃ to 575 ℃. In addition, when the transformation temperature decreases from 625 ℃ to 575 ℃, the pearlite nucleation mechanism changes from nucleation mainly at the corners and edges of prior austenite to nucleation mainly at the surfaces and edges. Moreover, the decrease in transformation temperature can refine the pearlite lamellar spacing and improve the hardness of the pearlitic steel. The pearlite nodule size is also significantly refined with the decrease of transformation temperature and reheating temperature. Among the three studied processes, 900 ℃ reheating with 575 ℃ transformation technology provides the highest hardness and the smallest nodule size. Therefore, in order to obtain the best combination of strength and toughness, it is recommended to reduce the reheating temperature and transformation temperature.
- high-carbon steel,
- pearlite,
- Nb,
- reheat temperature,
- transformation kinetics,
- microstructure

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References

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