Bingxing Wang

Improving the High-Cycle Fatigue Lives of Fe-30Mn-0.9C Twinning-Induced Plasticity Steel Through Pre-straining

The tensile properties, high-cycle fatigue properties, and microstructure evolutions during fatigue process of as-received and pre-strained Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel were investigated. It is found that the fatigue lives of the TWIP steel can be effectively improved through pre-straining, since the deformation twins induced by pre-straining could effectively lead to the improved yield strength and the homogenized deformation. This study may provide possible ways for improving the high-cycle fatigue properties of TWIP steels.

Calculation Method of Optimal Speed Profile for Hot Plate During Controlled Cooling Process

The healthy and rapid development of the controlled cooling technology was hampered by the uneven cooling phenomenon. During the process of hot plate production, the homogeneous cooling along the length direction of plate was constrained by lots of factors. And because the speed was a flexible control parameter, the calculation method of optimal speed profile was developed based on the measured start cooling temperature and its matrix equation was solved by the Cholesky decomposition method. The optimal speed profile was used in online control system. As a result, the temperature distribution along the plate length direction was relatively uniform, and 95% of measured final cooling temperature difference from the target temperature; 700 °C was controlled within +20 °C.

Cooling Efficiency of Laminar Cooling System for Plate Mill

Heat transfer was researched from a perspective of the industry application. On the basis of the first law of thermodynamics, the cooling efficiency was deduced from the change of enthalpy inside hot plate. The relationship between the cooling efficiency and its influencing parameters was regressed from plenty of data collected from the worksite and discussed in detail. The temperature profiles resulting from the online model and the model modified by regressed formulas were presented and compared. The results indicated that the control accuracy of the modified model was increased obviously.

An On-line Finite Element Temperature Field Model for Plate Ultra Fast Cooling Process

Taking the element specific-heat interpolation function into account, a one-dimensional (1-D) finite element temperature field model for the on-line control of the ultra fast cooling process was developed based on the heat transfer theory. This 1-D model was successfully implemented in one 4300 mm plate production line. To improve the calculation accuracy of this model, the temperature-dependent material properties inside an element were considered during the modeling process. Furthermore, in order to satisfy the real-time requirements of the on-line model, the variable bandwidth storage method and the Cholesky decomposition method were used in the programming to storage the data and carry out the numerical solution. The on-line application of the proposed model indicated that the deviation between the calculated cooling stop temperature and the measured one was less than ±15 °C.

A Kind of Plate Laminar Cooling Strategy With High Response and Steady Precision

After Smith Predictor being used to laminar cooling system, the control law for integral regulators is introduced. New notion of plate sample length is given for evading the delay time varying with the roll table speed. It is found that the integral algorithm is more controllable for system regulating process and has better steady state precision. Compared with the traditional control strategies, the new control law has faster response speed and higher steady state precision. The controller can be regulated in shorter time and the response is faster than that of routine controller and it can effectively eliminate the oscillatory instability. Owing to its easy realization and high stability, it has been applied to a plate mill. The accuracy of finish cooling temperature can be controlled within ±10 °C.

Correlation of microstructures and low temperature toughness in low carbon Mn–Mo–Nb pipeline steel

Abstract By adjusting thermomechanical controlled processing parameters, different microstructures were obtained in a low carbon Mn–Mo–Nb pipeline steel. The microstructural characteristic and its effect on low temperature toughness were investigated. The results show that under higher reduction in austenite non-recrystallisation region and faster cooling rate during accelerated cooling, the microstructure is dominated by acicular ferrite (AF) accompanied by a small amount of fine martensite/austenite (M/A) islands. In contrast, lower reduction and slower cooling rate lead to a predominantly quasi-polygonal ferrite microstructure with coarse M/A islands. The fine effective grain size (EGS) and the high fraction of high angle grain boundaries (HAGBs) make the cleavage crack propagation direction deflect frequently. The coarse M/A islands can lead to cleavage microcracks at the M–A/ferrite matrix interfaces. Compared with the microstructure mainly consisting of quasi-polygonal ferrite, the microstructure dominated by AF exhibits excellent low temperature toughness because of fine EGS, high fraction of HAGBs and fine M/A islands.

Dynamic recrystallisation behaviour and microstructural evolution in a Mn–Cr gear steel

Abstract Using a Gleeble 1500 hot simulator, the dynamic recrystallisation (DRX) behaviour and changes of DRX grain size of a Mn–Cr type gear steel have been investigated at deformation temperatures of 900–1150°C, strain rates of 0·1–1 s-1, and initial austenite grain sizes of 70–150μm. The experimental results show that the Mn–Cr gear steel exhibits a typical DRX behaviour under higher deformation temperatures, lower strain rates and smaller initial austenite grain sizes. The DRX takes place under conditions such that the Zener–Hollomon parameter Z is less than a critical value Z c . By regression analysis, activation energy and stress exponent were determined to be 378 kJ mol-1 and 5·8 respectively. The DRX grain size is a power law function of Z with an exponent of -0·25. The reason why the Z parameter determines uniquely the DRX grain size was analyzed.

Microstructure and mechanical properties of Nb-B bearing low carbon steel plate: Ultrafast cooling versus accelerated cooling

The microstructure and mechanical properties of low carbon bainite high strength steel plate were studied via different cooling paths at the pilot scale. There was a significant increase in mechanical properties, and notably, the yield strength, tensile strength, and toughness at -40 °C for the tested steel processed by ultra-fast cooling were 126 MPa, 98 MPa and 69 J, respectively, in relation to steel processed by accelerated cooling. The ultra-fast cooling rate not only refined the microstructure, precipitates, and martensiteaustenite (M/A) islands, but also contributed to the refinement of microstructure in thick plates. The large size M/A constituents formed at lower cooling rate experienced stress concentration and were potential sites for crack initiation, which led to deterioration of low-temperature impact toughness. In contrast, the acicular ferrite and lath bainite with high fraction of high-angle grain boundaries were formed in steel processed by ultra-fast cooling, which retarded cleavage crack propagation.