Kinetic analysis of austenite transformation for B1500HS high-strength steel during continuous heating
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Kinetic analysis of austenite transformation for B1500HS high-strength steel during continuous heating Mu-yu Li 1,2), Dan Yao 1,2), Liu Yang 1,2), Hao-ran Wang 1,2), and Ying-ping Guan 1,2) 1) Key Laboratory of Advanced Forging & Stamping Technology and Science (Ministry of Education of China), Yanshan University, Qinhuangdao 066004, China 2) School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China (Received: 28 September 2019; revised: 22 December 2019; accepted: 26 December 2019)
Abstract: The dilatometric curves of B1500HS high-strength steel at different heating rates were measured by a Gleeble-3800 thermal simulator and analyzed to investigate the effect of heating rate on austenitization. Results show that the value of starting temperature and ending temperature of austenite transformation increase with the rise of heating rates, whereas the temperature interval of austenite formation decreases. The kinetic equation of austenite transformation was solved using the Johnson–Mehl–Avrami model, and the related parameters of the equation were analyzed by the Kissinger method. For those calculations, the activation energy of austenite transformation is 1.01 × 106 J/mol, and the values of kinetic parameters n and ln k0 are 0.63 and 103.03, respectively. The relationship between the volume fraction of austenite and the heating time at different heating rates could be predicted using the kinetic equation. The predicted and experimental results were compared to verify the accuracy of the kinetic equation. The microstructure etched by different corrosive solutions was analyzed, and the reliability of kinetic equation was further verified from the microscopic perspective. Keywords: B1500HS high-strength steel; dilatometric curve; austenite transformation; kinetic equation; Johnson–Mehl–Avuami model
1. Introduction With the development of the automotive industry and the aggravation of energy crisis, the requirements of energy saving and environmental protection in the automotive industry have increased. The reduction in fuel consumption and greenhouse gas emissions has become the main research direction of the automotive industry. In practical applications, vehicle lightweight is the most effective way of solving this problem. Hot stamping greatly improves the strength of steel. This process reduces the amount of reinforcing plates used in the car body and thus reduces the weight of automobile car and eventually exhausts emissions. In the automotive industry, the application of high-strength steel in hot stamping has been developed rapidly. Austenitization treatment plays an important role in hot stamping. It can affect the mechanical properties of highstrength steel. Incomplete austenitization reduces the content of martensite, which could decrease the strength of steel [1–3]. By contrast, excessive austenitization increases the grain size of austenite, which could lead to the formation of coarse lath martensite after quenchin
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