| The hot working die steel which is used for thermal processing has been widely reseached in many fields for its specific properties. Also because of the widely use of hot die steel, we could improve the quality of products, reduce the cost of producing and insurance the efficiency of working. At present,energy is indispensable in every field. Most of the resource used by us is non-renewable, which demands us to use it rationally. In this century,in order to achieve sustainable development we human must resolve these serious problems, such as high energy and resource consumption, environmental pollution and so on. As the long processing time and expensive producing cost, the consumption of hot die steel reachs up to sixty five billion every year. The hot working die steel is often used under high temperature conditions. With the extension of working hours, the microstruture probability will change and lead to failure. This requires us to repair it appropriately in order to avoid great waste.Welding technolody not only plays an important role in materials connection,but we could also use it to repair fatigue microcrack and iner defects of the hot working die to meet its performance. In this paper, the microstructure and properties of the weld joint are the main research objects.Different test methods, such as thermal treatment, thermal fatigue cycle and electropulsing technolody have been used to anaslyze the stimulation on its microstructure and properties. Also the theory that electropulsing treatment eliminate microcrack is discussed. These researches will be of great importance for the development of improving the properties of hot working die stee in the future. After TIG welding experiment, we need to examinate the weld joint microstructure. Both sides of the weld joint microstructure and properties have altered. The weld joint experiences many different times heat treatment which generate much carbide. Overall the microstructure distribution is not uniform in every zone of the weld joint. Especially there are much coarse grain in fusion zone which is the vulnerable area in the weld joint.Because of the effect of the heat treatment, the hot working die generate much coarse lath martensite which have poor plasticity and toughness. After the first tempering treatment, the microstructure of base metal is tempering martensite. There are some carbide near the grain boundary. The shape of martensite is similar with quench trait. The second time tempering is the continuance of the first time, also the microstructure are martensite and residual austenite. Although the martensite remains strip shape, the size decrease visible. The value of the hardness in every zone of the weld joint is constant after twice tempering treatment.The hot working die steel is treated with thermal fatigue cycle after TIG welding. First we use 500,1000,1500 times thermal fatigue cycle to affect on the sample, and then treat it with electropulsing. We could see that the region ahead of specimen notch which is not electropulsing generate small fatigue crack.The microcrack has narrow width and short length. After electropulsing treatment the size of microcrack decrease visibly. In the same experimental conditions, the thermal fatigue microcrack of specimen which is treated by trigger voltage of 5V and pulse current time for 380ms heals better than the others.Above all, heat treatment and electropulsing means differently, but they both could alter the microstruture and properties of material. We also predict the mechanics properties through analyzing it's morphology. Generally the material scientists pay close attention to the composition and technology. That is, they explain the material world of phenomena from the micro to the macro.
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