Hai-lian Wei

Bio: Hai-lian Wei is an academic researcher from Anhui University of Technology. The author has contributed to research in topics: Flow stress & Constitutive equation. The author has an hindex of 1, co-authored 2 publications receiving 3 citations.

Determination method of thermal-deformation microstructure evolution mechanisms and thermal machining performance of C-Mn-Al high-strength steel

Abstract: The invention belongs to the technical field of high-strength steel machining engineering, and particularly relates to a determination method of thermal-deformation microstructure evolution mechanismsand thermal machining performance of C-Mn-Al high-strength steel. According to the method, firstly, a high-temperature compression test is carried out on the novel C-Mn-Al high-strength steel, and true stress-true strain curve data of the steel are obtained; then a rheology stress prediction model of the steel is established, model selection is based on creep theory, a class of constitutive models which are of relationships of Young's modulus and a self-diffusion coefficient of austenite and temperature and have physics bases are considered, and the established constitutive model can accurately predict rheology stress of the steel; a thermal-deformation machining graph of the steel is established, and microstructures are combined to determine the microstructure evolution mechanisms of different regions in the machining graph. The constitutive model of thermal deformation and the machining graph are combined, the thermal-deformation rheology stress and thermal-deformation power dissipation efficiency under arbitrary deformation conditions are analyzed, thus the corresponding microstructure evolution mechanisms and thermal machining performance information are obtained, and resultshave great significance for thermal machining process control of the high-strength steel.

Physical and Apparent Arrhenius Constitutive models of a Nb–Ti Microalloyed C–Mn–Al High Strength Steel: A Comparative Study

Abstract: The flow stress curves of a Nb–Ti microalloyed C–Mn–Al high strength steel were obtained by hot compression experiment with Gleeble-1500 thermal simulator at the temperatures from 900 to 1100 °C and strain rates from 0.01 to 30 s−1. Firstly, strain-compensated physical constitutive models considering the temperature dependence of Young's modulus (E) and austenite self-diffusion coefficient (D) with creep stress exponent 5 and variable stress exponent $$n^{\prime}$$ were established, respectively. Secondly, the traditional apparent Arrhenius constitutive model was established to compare the accuracy of the models. The results show that the physical constitutive model with exponent $$n^{\prime}$$ has higher accuracy to predict the flow stress of the experimental steel (correlation coefficient R = 0.992, average absolute relative error δ = 3.83%) than the model with exponent 5 (correlation coefficient R = 0.990, average absolute relative error δ = 10.54%). This is because when the stress exponent in the physical constitutive model is 5, it means that the deformation mechanism considered is only slip and climb, and the constitutive model with variable stress exponent $$n^{\prime}$$ considers all the deformation mechanisms comprehensively, so the prediction accuracy is higher. The correlation coefficient R of the Arrhenius constitutive model is 0.991, and the average absolute relative error δ is 4.58%. Therefore, the physical constitutive model with exponent $$n^{\prime}$$ has the highest prediction accuracy in this study, thus can be an alternative way to predict the flow curves of steels.

A Comparative Study on Hot Deformation Behaviors of Niobium Microalloyed Low‐Carbon and Medium‐Carbon Steels by Physical Constitutive Analysis

Abstract: Hot compression tests are performed on low‐carbon (LC) and medium‐carbon (MC) niobium microalloyed steels at temperatures of 900–1100 °C and strain rates of 0.01–10 s−1. The constitutive equations are studied by a physical method based on creep theory considering the relationship between the self‐diffusion coefficient, Young's modulus, and temperature. It is found that carbon addition in niobium microalloyed steels shows an obvious softening effect. The physical constitutive analysis indicates that the deformation mechanism of MC steel is the slide and climb of dislocation; however, other deformation mechanisms may occur in LC steel. The accuracy of the physical constitutive equations is quantified by employing correlation coefficient (R) and average absolute relative error (AARE). For LC steel, the R value of the equation containing exponent 5 and exponent n is 0.98 and 0.99; the AARE value is 9.06% and 4.15%, respectively, and the accuracy of the latter equation is significantly higher. For MC steel, the R value of the two equations is the same and equal to 0.99, the AARE value is 5.96% and 4.91%, respectively, the accuracy of the equations is quite close to each other. The accuracy analysis is also in reasonable agreement with the speculation of the deformation mechanism.

Study on Hot Flow Behaviors and Deformation/Diffusion Mechanisms of V and V–Ti Microalloyed Steels by Physical Constitutive Modeling

Abstract: The hot compression tests of medium carbon V and V–Ti microalloyed steels are carried out at the temperature of 900–1100 °C and strain rate of 0.01–10 s−1. Three physical constitutive models based on creep theory are studied, the prediction accuracy is compared and analyzed by employing the correlation coefficient (R) and average absolute relative error (AARE), and the deformation/diffusion mechanisms are discussed. The results show that Ti has obvious hardening effect in V microalloyed steel and retards the onset of dynamic recrystallization. The physical constitutive model containing the theoretical value of creep exponent 5 can accurately describe the hot flow behavior of both steels, the prediction accuracy of which is comparable to that of the model containing exponent n, reflecting that the dominant deformation mechanism of both steels is dislocation climbing. Furthermore, a modified physical constitutive model combining diffusion mechanisms of lattice diffusion and grain boundary diffusion shows higher accuracy (R = 0.996, AARE = 3.81% of V steel and R = 0.994, AARE = 4.52% of V–Ti steel), indicating that the diffusion mechanism is controlled not only by lattice diffusion but also by grain boundary diffusion.

Determining method of bainite steel hot forming process window

Abstract: The invention relates to a determining method of a bainite steel hot forming process window. According to the technical scheme, true stress Sigma and true strain Epsilon data obtained through the heatsimulation experiment take as the basis, the dynamic recrystallization condition of bainite steel is determined, thermal machining graphs and activation energy graphs of the different kinds of straincan be drawn, the area, with the minimum activation energy Q change and fluctuation smaller than or equal to 1%, in the overlapping area of the safety area and the dynamic recrystallization area in the thermal machining graph is the thermal deforming process window of the corresponding strain; defects of rough grains, mixed grains, cracks and the like in the bainite steel can be effectively avoided, the relatively uniform dynamic recrystallization structure is obtained, and the product property quality is ensured.

Method for correcting rheological stress of zirconium alloy through temperature rise in rolling simulation process

Abstract: The invention aims to provide a method for correcting rheological stress of zirconium alloy through temperature rise in a rolling simulation process. The method comprises the following steps: 1) processing and preparing a Gleeble hot compression test sample, and carrying out a compression test; 2) performing calculating to obtain the temperature rise T of the sample at each temperature T0 and strain rate according to the deformation condition set by the experiment; 3) analyzing the relationship between the peak stress sigma p and the corresponding temperature Tp at different strain rates, andcalculating the relationship between the rheological stress sigma and the corresponding actual deformation temperature T in the deformation process through linear fitting; 4) calculating a stress change value sigma caused by the temperature rise T corresponding to each strain point at a set temperature by using a difference method; 5) correcting the rheological stress at the set temperature to obtain the true stress sigma' corresponding to each strain and the corrected true stress-strain curve, calculating and researching the relationship among the parameters in the thermal deformation processby utilizing the optimized data, and verifying the rheological stress correction condition.

Simulation method for thermal deformation of a sodium-cooled fast reactor single component

Abstract: The invention discloses a simulation method for predicting thermal deformation of a sodium-cooled fast reactor single component. The method comprises the steps of 1, determining three-dimensional temperature field data of an assembly, geometric parameters and physical parameters are obtained; 2, arranging three-dimensional temperature field data according to a two-dimensional array and carrying out reasonable difference; 3, performing discretization treatment on the cross section of the assembly; discretizing the data into 12 computing units; 4, solving the static moment of each discrete unit;5, solving the thermal strain of each discrete unit; 6, calculating the transverse thermal deformation displacement of each axial node; 7, calculating the thermal axial force of the axial node; 8, calculating the axial thermal deformation displacement of each axial node; and 9, obtaining the thermal deformation condition of the assembly in a three-dimensional space.