Advanced Materials Research Vols. 97-101

Abstract: Closed upsetting is the first step of steel pipe vertical extrusion technology. In this paper, the closed upsetting process was investigated by upper bound method, slip-line field and thermo-mechanical coupled FEM based on Deform 2D. The flow behavior, effective strain, temperature field and upsetting load were examined. The influence of billet temperature and die velocity on filling factor and upsetting load was discussed. The error percentage of upsetting load computed by upper bound method and FEM was less than ±1%. Simulation results showed that the closed upsetting process of P91 was more sensitive to temperature, while the impact of velocity was not as significant as temperature.

Abstract: The influences of different hot working conditions on the microstructures and mechanical properties at weld zone of the Ti3Al/TC4 dual alloy have been investigated. The experimental results show that forging and heat treatment has significant influence on room temperature tensile strength (RTTS for short) of the weld zone. The influence of forging strain and temperature on its elongation at temperature 500°C is also conspicuous. The results of intuitional and variance analysis show that affecting factors of its RTTS are heat treatment, forging strain, forge temperature and condition of billet in sequence. The affecting factors of its room temperature (RT for short) ductility and the tensile strength (TS for short) at temperature 500 °C are forging strain, forge temperature, heat treatment and condition of billet. Good comprehensive properties are obtained under optimal conditions: forging at 1020°C, annealing at 700°C for 12 hours, air cooled, about 40% strain and as-rolled billet. The microstructures of the weld zone worked according as those conditions are uniform and the grain size is also fine.

Abstract: In the process of blanking, the work hardening capability of material possesses very important significance. It not only affects the internal stress value of distorting material, the distribution of stress and the value of blanking force, but also blanking deforming limit and quality of blanked work piece. This paper carries through pure shearing fine-blanking processing experiment with negative clearance for the ASTM-Gr.D and ASTM-1022 steel as well as the micro hardness of the sheared surface for the blanked work pieces in breadthways and lengthways direction measured by Vickers-micro hardness instrument (MH-6). Mechanism of work hardening for fine-blanking with negative clearance is discussed. Meanwhile, the work hardening capability of blanked work piece is analyzed. The work hardening degree of the materials possessing different hardening index is compared. It could be concluded that the work hardening degree of the blanking work pieces was strengthened evidently by the fine-blanking with negative clearance. The hardening layer of blanking fracture could enhance structure intensity and wear resistance of blanking work piece evidently. Therefore, it could improve fatigue strength and the working life of work piece greatly.

Abstract: The Fine-blanking with negative clearance processing is very complicated process because the blanking clearance is negative clearance, for this reason, the state of stress and strain in sheet inside are also more complicated than conventional blanking. In the process of fine-blanking with negative, plastic deformation of the material is fiercer than conventional blanking, and the change of material inner structure and hardness is more intense because of plastic deformation. The deformation principle of fine-blanking deformation with negative clearance is analyzed by means of streamline and metallographic photograph and micro hardness. The impact of fine-blanking with negative clearance on the materials microstructure and hardness is discussed. The research result indicates that the hardening value is 1.8 times than original material itself and the maximum harden depth is 2.2mm for AISI-1045 steel in the process of blanking with negative clearance. Therefore, it could enhance fatigue strength and the working life of workpiece greatly because of the improvement of the material inner structure.

Abstract: The microstructures and room temperature and 600°C tensile properties of Ti-5.8Al-4.0Sn-4.0Zr-0.7Nb -0.4Si-1.5Ta alloy after isothermal forging have been studied. The forging temperature range was from 850°C to 1075°C, and the constant strain rate of 8×10-3/S-1 was adopted. With the increase of forging temperature, the volume fraction of primary α phase decreased and the lamellar α phase became thicker when the temperatures were in range of 850°C -1040°C; The grain size became uneven and the α phase had different forms when the forging temperature was 1040°C and 1075°C respectively; The tensile strength was not sensitive to the temperature and the most difference was within 20MPa. Tensile strength and yield strength attained to the maximum when temperature was 1020°C; the ductility decreased with the increase of forging temperature, and this trend became more obvious if forging temperature was above the β-transus temperature.

Abstract: Incremental sheet forming (ISF), based on the ‘layered manufacturing’ principle of rapid prototype manufacturing technology, is an innovative and highly flexible technology for forming complex shaped parts without the need for costly dies. This paper presents a numerical investigation on the influence of forming process parameters by modeling the forming process. ANSYS/LS-DYNA has been used for the simulation. The results of study show that small vertical step size can improve the accuracy of the forming. Moreover, large forming angle can increase plastic strain and the four screwdown point optimization paths is an effective method to increase the accuracy of the formed sheet.

Abstract: The strip wound die, which is characterized by significant improvement in strength and stiffness over the conventional compound die with several layers of stress rings, is prestressed by the thin high-strength steel strips. The performance of the strip wound die is determined mainly by the winding tension during manufacture process. In this paper, the stress analysis of die body is conducted based on Lamé’s equation. Two kinds of die materials are analyzed based on strength theory in order to establish the required contact pressure in working condition which keeps the die material within the safety range. The number of winding layers can be determined by considering the strength of strip in working condition. The analytical method and the equations to determine the winding tension have been presented by following yield criterion, Euler’s equation and iso-strength principle.

Abstract: The numerical simulation of tube hydropiercing process on a typical tubular component was conducted by employing the FEM code MARC in order to investigate the deformation mechanism of tube hydropiercing. The 3D FEM models have been established in both inward and outward punching operations. Based on the calculation results of the distributions and their changes of stress and deformation, a plastic bending deformation zone in the vicinity of the hole’s edge has been discovered, which differs greatly from that in the conventional sheet metal punching process. Influence of inner pressure on the quality of hydropierced hole was also investigated.

Abstract: Fine-blanking process has been paid more and more attention for its shearing surface having low tearing-ratio, low roughness, low cost and high dimensional precision characteristics. It is not suitable for fine-blanking process if the carbon content of non-alloy steel is higher than 0.15% in the traditional view. Only the spheroidization is over 95%, the ideal shearing surface could obtain [1]. Methods of SEM and optical microscopy are used to research the tearing and metallographic characteristics in the region of the tearing of the shearing surface. With the help of the numerical simulation and micro-hardness testing, the tearing on the shearing surface and the shearing surface of fine-blanking is investigated. The conclusion is that without the spheroidizing annealing, 3mm thick cold-rolled 45 steel sheet having a clear flowing fiber of metallographic characteristic can get ideal shearing surface having such fine characteristics as small tear ratio, higher surface hardness and high surface finish by fine-blanking, with the help of optimized parameters from ANOVA and regression method, which considering the interaction between the height of the vee-ring indenter and the distance between vee-ring indenter and blanking contour. The present findings is great significant for expanding the scope of application of fine-blanking technology.

Abstract: In order to investigate microstructure evolution of Mn18Cr18N retaining ring during the multi-fire forging, a series of constitutive equations for dynamic recrystallization, static recrystallization, meta-dynamic recrystallization and grain growth were developed and implemented into a Deform FE simulator. The single-axial hot upsetting test has been performed to investigate the process of microstructure evolution and to show validity and effectiveness of the developed program. Then based on the modified boundary condition, hot forging process for 300MW retaining ring was put into effect. The results have displayed that the microstructure prediction tool was validated by comparing the simulated grain structure with that of the experiment and it could provide a reference to optimize forging processes in the production of retaining ring.