Failure Analysis And Surface Strengthening Of H13 Gear Dies For Precision Forging

During the process of forging and working, H13 gear dies for precision forging continuously bear heat-cold alternate thermal load and impulsive load. Because of these above reasons, the dies easily form failures of heat fatigue flaw, wear and dehiscence, resulting in the dies life falling consumedly. Thus it is significant to carry out failure analysis and strengthening measure for prolonging H13 gear dies life.The thesis consists of the following sectors. Based on practical conditions of certain factory, the synthetical failure analysis of H13 gear dies for precision forging was carried out in view of structural design, machining process, service conditions and maintenance. TiN and TiYN coatings were obtained on H13 steel using the techniques of magnetron sputtering and ion plating. Surface topography of coatings was analyzed by use of metallographic microscope and SEM. The composition and phase structure of coatings was investigated utilizing SEM and XRD. Microhardness, coating-substrate binding strength, high-temperature wear and friction performance and high-temperature oxidation performance was analyzed. The strengthening effect of two depositing method on H13 steel surface and influence of RE element Y for TiN film performance and high spot review strengthening mechanics were studied.Analysis results indicate that three main failure forms of H13 gear dies for precision forging are surface abrasion, addendum collapse and body fracture. Temper mollification reduces the surface hardness of die and interior strength is very low, so corner angles of impression are abrased when high temperature frictional wear occurs. * The hardness of addendum is too low and the high-temperature strength of the die is not high enough, which leads to the addendum collapse. In the working environment of high-temperature, low speed and heavy-duties, the interior small expansion of cracks on gear dies leads to body fracture.Research on the plating test shows that high-grade TiN and TiYN coatings can be deposited on H13 steel using rational test scheme and processing parameters. TiN and TiYN coatings largely improve the wear and friction performance and high-temperature antioxidation performance of H13 steel. In the comparable conditions of depositing process, the coatings gained by the ion plating experiment have better wear-resisting effect and high-temperature antioxidation performance. The difference between friction coefficients of the samples gained by magnetron sputtering test and ion plating test is not apparent.In addition, the tightness, coating-substrate bond strength, wear-resistance performance, antifriction performance and high-temperature oxidation performance of TiN films are apparently increased after adding REY, except that the microhardness decreased a little. In comparison, the effect of adding RE element Y in ion plating expetiment is apparent.