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Li H.-Y.,Central South University | Su X.-J.,Central South University | Chen G.,Central South University | Gong M.-T.,Hengyang Valin Steel Tube Co.
Cailiao Kexue yu Gongyi/Material Science and Technology | Year: 2013

65Mn spring steels were heat treated by medium-temperature tempering and high-temperature tempering. Its tensile properties were tested, and the fatigue crack propagation behavior as well as fatigue fracture mechanism were investigated. Results show that the crack growth rate m is different but the C-value is less difference after two kinds of tempering scheme, which reflects that the fatigue crack propagation is not sensitive to the microstructure in the region of stable crack propagation and the crack propagation rate decreases due to plastic deformation consume energy of crack propagation. With the tempering temperature increases, the characteristic of fatigue fracture transforms from brittle to ductile gradually, high-temperature tempering treatment improves the fatigue crack propagation threshold and reduces the fatigue crack growth rate. After high temperature tempered, the steel has better comprehensive mechanical property and fatigue property. Source


Li H.-Y.,Central South University | Wang X.-F.,Central South University | Wei D.-D.,Central South University | Hu J.-D.,Central South University | And 2 more authors.
Materials Science and Engineering A | Year: 2012

The true stress-strain data from isothermal hot compression tests on Gleeble-3500 thermo mechanical simulator, in a wide range of temperatures (1323-1473K) and strain rates (0.01-10s -1), were employed to establish the constitutive equations based on modified Zerilli-Armstrong and strain-compensated Arrhenius-type models respectively, and develop the artificial neural network model to predict the high-temperature flow stress of T24 steel. Furthermore, a comparative study has been made on the capability of the three models to represent the elevated temperature flow behavior of this steel. Suitability of the three models were evaluated by comparing the accuracy of prediction of deformation behavior, correlation coefficient and average absolute relative error of prediction, the number of material constants, and the time needed to evaluate these constants. The results showed that the predicted values by the modified Zerilli-Armstrong model could agree well with the experimental values except under the strain rate of 0.01s -1. The predicted flow stress of the other two models shows good agreement with the experimental data. However, the artificial neural network model could track the deformation behavior more accurately throughout the entire temperature and strain rate range though it is strongly dependent on extensive high quality data and characteristic variables and offers no physical insight. © 2012 Elsevier B.V. Source


Li H.-Y.,Central South University | Wei D.-D.,Central South University | Li Y.-H.,Central South University | Li Y.-H.,Hengyang Valin Steel Tube Co. | Wang X.-F.,Central South University
Materials and Design | Year: 2012

Isothermal hot compression of 28CrMnMoV steel was conducted on a Gleeble-3500 thermo-mechanical simulator in the temperature range of 1173-1473K with the strain rate of 0.01-10s-1 and the height reduction of 60%. Based on the experimental results, constitutive equations and an artificial neural network (ANN) model with a back-propagation learning algorithm were developed for the description and prediction of the hot compressive behavior of 28CrMnMoV steel. Then a comparative evaluation of the constitutive equations and the trained ANN model was carried out. It was obtained that the relative errors based on the ANN model varied from -3.66% to 3.46% and those were in the range from -13.60% to 10.89% by the constitutive equations, and the average absolute relative errors were 0.99% and 4.09% corresponding to the ANN model and the constitutive equations, respectively. Furthermore, the average root mean square errors of the ANN model and the constitutive equations were obtained as 1.43MPa and 5.60MPa respectively. These results indicated that the trained ANN model was more efficient and accurate in predicting the hot compressive behavior of 28CrMnMoV steel than the constitutive equations. © 2011 Elsevier Ltd. Source


Li H.-Y.,Central South University | Hu J.-D.,Central South University | Wei D.-D.,Central South University | Wang X.-F.,Central South University | And 2 more authors.
Materials and Design | Year: 2012

Hot compression tests of modified 2.25Cr-1Mo steel were conducted on a Gleeble-3500 thermo-mechanical simulator at the temperatures ranging from 1173 to 1473K with the strain rate of 0.01-10s-1 and the height reduction of 60%. Based on the experimental results, an artificial neural network (ANN) model and constitutive equations were developed to predict the hot deformation behavior of modified 2.25Cr-1Mo steel. A comparative evaluation of the constitutive equations and the ANN model was carried out. It was found that the relative errors based on the ANN model varied from -4.63% to 2.23% and those were in the range from -20.48% to 12.11% by using the constitutive equations, and the average root mean square errors were 0.62MPa and 7.66MPa corresponding to the ANN model and constitutive equations, respectively. These results showed that the well-trained ANN model was more accurate and efficient in predicting the hot deformation behavior of modified 2.25Cr-1Mo steel than the constitutive equations. © 2012 Elsevier Ltd. Source


Ren Z.-L.,Hunan Institute of Engineering | Tang M.-H.,Hunan Institute of Engineering | Hu S.-K.,Hengyang Valin Steel Tube Co. | Kuang J.-X.,Hunan Institute of Engineering
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2012

Hot rolled 25MnV steel was quenched by different quenching process. The influence of quenching cooling methods including direct quenching by water cooling to room temperature and water-air alternative quenching on microstructure and mechanical properties of the steel was studied by microstructure observation and mechanical property tests. The results show that under the condition of water-air-water alternative quenching, the quenching internal stress of the experimental steel can be effectively reduced, and the duplex micro structure of martensite and lower bainite decreases the tendency of cracking for the oill casing. After tempering at 590°C for 65 min, tensile strength, yield strength and impact energy of the steel reach 932 MPa, 870 MPa and 55 J, respectively, much higher than that of the commercial oil casing steel. It is suggested that the improvement of mechanical properties is attributed to the duplex microstructure of lath martensite, lower bainite small amount of residual austenite in the steel by water-air-water alternative quenching. Source

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