Papers by Author: Jian Ping Shi

Abstract: Surface treatment was carried out on the butt joint weldment of P355NL1 steel by using the HJ-II-type ultrasonic impact machine. The ultrasonic impact current is 1.5A, the impact amplitude is 20 microns and ultrasonic impacting time is 5min. Tensile test was carried out for both treated specimen and un-treated specimen. The fracture observed with the scanning electron microscope of 6360LA type. The experimental results show that although the compressive residual stress can be obtained in the surface of weld toe area, and the grain size in the welded joint can be refined, but the mechanical property of the butt joint of P355NL1 steel can not be improved through the ultrasonic impact treatment. The main reason is that the ultrasonic impact layer is only 120um, it is to thin to compared to the thickness of the specimen.

Abstract: Surface treatment was carried out on the welded cruciform joint of P355NL1 steel by using the HJ-II-type ultrasonic impact machine. The ultrasonic impact current is 1.5A, the impact amplitude is 20 microns and ultrasonic impacting time is 5min. Tensile test was carried out for both treated specimen and un-treated specimen. The fracture observed with the scanning electron microscope of 6360LA type. The experimental results show that although the compressive residual stress can be obtained in the surface of weld toe area, and the grain size in the surface of welded cruciform joint can be refined, but the mechanical property of the welded cruciform joint of P355NL1 steel can not be improved through the ultrasonic impact treatment. The main reason is that the ultrasonic impact layer is only 70um, it is to thin to compared to the thickness of the specimen.

Abstract: It’s simple technology to manufacture big trimming die by hardfacing on the die insert of steel. In this paper, a kind of surface hardfacing technology which deposited by using D322 on 42CrMo steel were studied instead of traditional manufacturing process. The effect of hardfacing parameters on microstructure, hardness and wear resistance are tested and analyzed. The key points of manufacturing trimming die by using hardfacing method was given out. There are no defects in the hardfacing layer. The average hardfacing layer is higher than 57.5HRC. The hardfacing surface has good figurations and hardfacing layer has good wear resistance. The hardfacing for real product of trimming die is completed successfully and their properties reach or exceed those of dies made with traditional technology. This technology is also an effective approach of repairing other cold working dies. The experimental results indicate that the hardfacing technology has much more advantages, cheaper than that of traditional process. The wear resistant test of hardfacing layers were carried out by using different welding current. The best welding current for hadfacing 42CrMo steel is 110 Ampere. The wear mechanism of hardfacing layer is belongs to abrasive wear model.

Abstract: The wear resistance, corrosion resistance and hardness can be greatly increased by using low temperature QPQ salt-bath nitriding treatment. And it is a new strengthening method without distortion in the treating process. In this paper, 3Cr2W8V steel is dealt with QPQ salt-bath nitriding at 520°C, 540°C, 560°C and 2h, 4h, 6h, respectively. The treated surface microstructure was analyzed by using SEM. The depth of nitriding layer, scratch hardness and wear-resistance were tested for both QPQ salt-bath treated and untreated specimen. The corrosion resistance was tested in the 5%NaCl water by using spraying method. The experimental results indicate that a certain depth of white layer and diffusion layer of the steel can be obtained by using low temperature QPQ salt-bath nitriding treatment. The nitriding compound layer with high hardness, superior wear-resistance and stable microstructure can also be obtained on the surface of the parts. With increasing the temperature and the nitriding time, the depth of nitriding layer, scratch hardness and wear-resistance of 3Cr2W8V steel were greatly increased. Comparing with the untreated specimen, its hardness enhances 95.0%, wear resistance enhances 212.3%, anti-corrosion enhances 1288.9%. The experimental results show that the low temperature QPQ salt-bath nitriding treatment has many advantages, such as fast nitriding speed, uniform heating, short process time, low treating temperature, small distortion, high production rate, low cost, stable nitriding quality without pollution and so on.

Abstract: Porous cermets composites were prepared from mixed powders (Ni, Al, Ti and C) by SHS (Self-propagating High-temperature Synthesis) method. When Ni-Al intermetallics bonded TiC porous cermets substitute for TiC ceramic as perform in the process of manufacturing Ni-Al/TiC composites by pressureless melt infiltration, the wetting of the ceramic material and Ni-Al intermetallics can be improved. In this study, the microstructure and mechanical properties (density and compressive resistance strength) were reported. It is learnt from the study that the relation between the open porosity and the pore size does not exist, the former depends on the green density, and the latter depends on the particle size of the nickel powder. The porous cermets with porosity ranging from 40% to 50%, pore size from 1μm to 300μm, and the compressive resistance strength about 15 MPa can be prepared by SHS. SEM observations of fracture surface suggest the fracture mode is brittleness fracture, and the microstructures of the porous cermets are very homogenous.