Papers by Author: Jian Sheng Liu

Abstract: The hot compression tests of 06Cr19Ni9NbN steel were conducted at strains rate of 0.005-5s^-1 and temperature of 900-1200 °C on Gleeble1500 thermal mechanical simulation tester. Based on stress-strain data, processing maps of the steel were established. According to the results of processing maps, the optimal process parameters of hot compression were obtained, which lies in the temperature range of 1000-1200°C and strain rate of 0.005-0.1s^-1. And then, the process of plane strain compression of 06Cr19Ni9NbN steel was investigated and carried out at the temperature of 1000-1200 °C and reduction ratio of 10%-50%. After the hot compression tests, the room temperature tensile tests were carried out. The results indicated that the grain size and the mechanical properties gradually become stable when the reduction ratio increases to 30%, 34% and 40% at 1200 °C, 1100 °C and 1000 °C, respectively. Finally, a new model was presented to describe critical forging penetration efficiency, which is significant to optimize the steel forging process. Furthermore, the calculated results based on this new model were consistent with experimental results, indicating that the model is suitable to predict the critical FPE for the steel.

Abstract: In order to obtain the high temperature flow behavior of as-cast SA508-3 low alloy steel, the stress-strain curves of steel are obtained by Gleeble thermal simulation compression test at deformation temperature 800°C-1200°C and strain rate 0.001s^-1-1s^-1. Based on Laasraoui two-stage flow stress model, a high temperature flow stress model is established by multiple linear regression method. The results show that the peak stress characteristics are not obvious at low temperature and high strain rate, which is a typical dynamic recovery characteristic. Meanwhile, the peak stress characteristics are obvious at high temperature and low strain rate, which is a typical dynamic recrystallization characteristic. By means of the comparisons between experiments and calculations, the Laasraoui two-stage flow stress model can truly reflect flow behavior of steel at high temperature, which provides theoretical guidance for the hot deformation of the steel.

Abstract: Head forging is an indispensable part of major technical equipment, which is required to produce high quality products because of its large volume and complex structure and long service under high temperature and high pressure. By means of DEFORM-3D numerical simulation and scaling experiment, the dynamic recrystallization dynamics model of SA508-3CL steel is established. Meanwhile, the head forming scheme is designed. The effects of different blank height-diameter ratio size, punch shape size and upper and lower die matching relationship on forging forming are emphatically analyzed. Finally, the reasonable head forming scheme is determined, and the 1:8 head forming scale test is carried out. The results show that the size of the head forging basically coincides with the design size and meets the load of the hydraulic press, which proves the rationality of the forming process of the head. The study provides a theoretical basis for the manufacture of the same type of large variable wall thickness head forgings.

Abstract: Hot Deformation behaviors and microstructural evolution of Al-Zn-Mg-Cu alloy with as-homogenized, as-forged and as-over-aged starting structures were studied at temperatures in the range of 300-420°C, strain rates in the range of 0.01-1s-1, and reductions in the range of 20%-80% by high-temperature compression tests. The flow stresses increase with increasing strain rate or decreasing temperature, which can be described by a hyperbolic-sine equation with the deformation activation energies of 246.35KJ/mol, 188.87KJ/mol and 178.25KJ/mol for the homogenized, the forged and the over-aged samples respectively. At the same deformation condition, the flow stress of the homogenized samples is greater than that of the forged and over-aged samples. For the homogenized samples, dendritic coarse grains elongated along the deformation direction, and interdendritic boundaries within coarse grains disappeared gradually due to diffusion at higher temperatures. When deformation is heavy, microstructures became into homogenous and geometric recrystallization occurs and new small grains appear within the severe elongated grains. For the forged samples, higher temperatures promote dynamic recrystallization. Recrystallized new small grains were developed along prior grain boundaries at large strains. For the over-aged samples, prior grains elongated along the deformation direction, and there is not much more dynamic recrystallized grains observed.

Abstract: The effect of various deformation degree and temperature on static recrystallization of 304 stainless steel during two-passes hot compression deformation with the strain rate of 0.1s-1 was investigated by use of Gleeble-1500D thermo-mechanical simulation. It is indicated that deformation degree is the most obvious factor to static recrystallization. Besides, the grain sizes after deformation were also measured by metallographic method. The results show that the grain sizes decreased dramatically with the conditions of deformation temperature (1050°C), holding time (30s) and total deformation degree (0.35). The result has provides the corresponding scientific basis for the quality forecast of 304 stainless steel during hot thermoplastic deformation.

Abstract: Forging temperature is usually around 1000°C in free forging scene. Manual measurement leads to large measurement errors. Adopting the non-contact 3D scanning technology, make the laser beam sweep across the forging surface to get three-dimensional coordinates of the points on the forging surface in space. Neighboring scan points separate by less than 0.25mm. The measurement error is less than 6mm. The coordinate^,s data are sent to the LabVIEW procedure. The procedure analyzes the coordinates to calculate the size of the large-size forging to realize automatic measurement of the forgings. The procedure can also reconstruct the image of the large-size forging. These make us detect the real-time changes of the forging far from the free forging scene.

Abstract: The hot hole flanging process of a connection tube in a thick-wall head was researched by finite element analysis and experiment in this paper. The deforming mechanism, main influencing factor and defects in hole flanging were analyzed. According to the stress state and the flow mode of deforming metal, the hole flanging process can be divided into two stages, that is, blending and hole flanging. Processing parameters, such as diameter of pre-holes, space ratio of die cavity, punch shape and size and their effect on forming were researched. The 1:3 scaled experiment was done in 30MN hydraulic press using A508-Ⅲ steel. The formed connection tube had a good quality and its end face was smooth without any crack. The measuring result showed that the error between simulation data and test data was less than 5%, which verified the feasibility of hot hole flanging process and provided an important reference for virtual production. Keywords: Connection Tube Thermal Hole Flanging Thick-wall Head Pro-hole Diameter Space Ratio Scaled Experiment

Abstract: As-cast 30Cr2Ni4MoV steel was researched quantificationally to obtain the distribution and pattern of the microcosmic defect. By means of finite element simulation and experiment research, porosity consolidating and relative density evolution of as-cast 30Cr2Ni4MoV steel were investigated for a FM stretching process at a constant strain rate 0.001s-1. The studied parameters included three temperatures (800°C, 1000°C, 1250°C) and three deforming passes(1,2,3) and three friction factors(0.3,0.5,0.7), which bracketed the parameters that were used during most primary break-down processes. Temperature had an obvious effect on the porosity consolidating, but friction factor had no effect on the ultimate soundness nearly. When beginning temperature was 1250°C and heat exchanged considered, initial porosity can be eliminated after the accumulated effective strain reached 1.0 at least. The residual defect of the wrought material at different strain lever was compared to the initial defect of as-cast material and found to be somewhat reduced. The impact toughness of the wrought material at different strain lever was also compared to the as-cast material and found to be obvious improved. The difference in these behaviors between as-cast and wrought material could be attributed to the healing of the porosity defect and the enhancement of the soundness at a certain extent.

Abstract: This paper dealt with the outstanding problems which were forging cracks existing in the process of forging.The forming reasons of forging cracks were analyzed. From the perspective of damage mechanics, the conventional mesoscopic models and fracture criteria of ductile metal material damage were introduced. The problems in recent research of forging cracks were pointed out. Some corresponding suggestions for the future research of forging carcks were put forward based on the existing problems. The existed ductile fracture criteria have only predicted the damage of specific process yet ,while the diversities of metal forming processes require ductile fracture criterion to have wide scope of application,so,for reason given above,the emphasis is placed on the necessity of establishing new ductile fracture criteria and fracture parameter library with the method of combination of theory and experiment and numerical simulation.

Abstract: Hot compression experiments of 304 austenite stainless steel were carried out with Gleeble-1500D simulator under the strain rates of 0.05 s-1~0.5 s-1 at 950°C~1200°C. The effects of temperatures and strain rates on flow stresses during hot compression deformation of 304 austenite stainless steel were investigated. The regression analysis of experiment data was used to evaluated the stress exponent and deformation activation energy, and fit the constitutive equation of the flow stress during hot compression of 304 austenite stainless steel. In addition, the kinetic model and the grain size model of dynamic recrystallization of the steel were obtained by use of the metallographic analysis of the microstructure. The results can provide theoretical basis for design of hot deformation parameters and prediction of microstructure of 304 austenite stainless steel.