2011, Volume 13, Issue 1
Strategic Study of CAE >> 2011, Volume 13, Issue 1
Comprehensive strengthening mechanism of steel based on nano scale cementite precipitates
1. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China;
3. Beijing General Research Institute of Mining and Metallurgy, Beijing 100044, China;
4. Guangzhou Zhujiang Steel Co., Ltd., Xiji Industrial Zone, Economic and Technical Development Zone, Guangzhou 510730, China
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Abstract
This paper summarized the status of comprehensive strengthening mechanism of steel. By using chemical phase analysis, X-ray small-angle scattering, RTO and high-resolution TEM observation, the properties of nano-scale cementite precipitates in Ti micro-alloyed high strength weathering steels produced by thin slab continuous casting and rolling process were analyzed. Except nano-scale TiC, cementites precipitates less than 36 nm and high volume fraction were also found in Ti micro-alloyed high strength weathering steels.The volume fraction of cementite less than 36 nm is 4.4 times as much as that of TiC in the same size. Cementite with high volume fraction has stronger precipitation strengthening effect than that of nano-scale TiC, which can not be ignored.The precipitation strengthening contributions of nano-scale precipitates of different types and sizes should be calculated respectively according to the mechanisms of dislocation intersection and dislocation bypass, and then be added up with the contributions of solid solution strengthening and grain refinement strengthening.A formula for calculate the yield strength of low carbon steel is proposed, and the calculated yield strength considering the precipitation strengthening contributions of nano-scale precipitates and the comprehensive strengthening mechanism of steels matches the experimental results well. The calculated σs=630~676 MPa, while the examined σs=630~680 MPa. The reason for grain refinement strengthening can not directly plus dislocation strengthening and the performance form of phase transformation's influence on steel strength were debated.The applications for comprehensive strengthening theory were summarized, and several scientific questions for further study were put forward.
Keywords
yield strength ; nano-scale cementite ; nano-scale titanium carbide ; precipitation strengthening ; comprehensive strengthening of steel
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