A Study On Influencing Mechanism Of Double Quenching On Die-casting Die Service Life

Since the beginning of the 21 th century, die-casting technology has been dramatically developed based on the characters of its products, such as complex, high precision, light weight, energy saving, etc. In addition, as domestic auto industry is blooming, our die-casting industry is developing at a topspeedit never had before.As one of three major elements of die-casting industry, die-casting die costs 1/3 of the total production cost. Thus, the service life of die-castingdie is a crucial problem that concerns die-casting enterprise.In this paper, the influencing mechanism of double quenching process on the service life of die-casting die were studied by optical microscope(op), X-ray diffraction(XRD), energy dispersive X-ray(EDS) and mechanical performance testing. The conclusions are as follows:①The mechanical property testing results indicate that double quenching process improved toughness of H13 and 1.2344 steel, and had no influence on strength, ductility and hardness. And those effects could decrease the risk of cracking failure caused by mechanical stress and thermal stress.②Moreover, testing results show that double quenching process improved the thermal stability of these two materials which could improve the resist of thermal crack. During the tempering process, down trends of hardness of 4 group materials in the first 5 hours were similar. Then the down trends of double quenching samples retarded obviously compared to single quenching process.③Double quenching process could lead to grain refinement in comparison with single quenching process and grain boundary effect which would separate the matrix of materials. And it was found that fine grains gathered in areas. The distribution of fine gains and orientation of martensite indicate the grain refinement mechanism of double quenching process conform to the law of heating process of non-equilibrium microstructure. The heating progress accords with medium-speed heating transformation which is widely used today. And structuralheredity effect would keep oversized gain left over from first high temperature quenching if the heating speed was reduced. This is the suppression factor of grain refinement effect of double quenching.④According to results of EDS, double quenching process minished element segregation by promoting the dissolution of alloy carbide. That’s the reason why double quenching process could improve the thermal stability of materials. Besides, this effect could decrease martensite content which could improve mechanical properties of materials.⑤The martensite does not exist as a homogeneous type but as a mix of lath martensite and acicular martensite in single quenching process samples, the only difference between these two materials is the content of lath martensite. These two materials can be sorted as H13, 1.2344, according to the content of lath martensite(from less to more). After double quenching treatment, almost all of the martensite is lath martensite and its orientation indicates that it was still in the oversized austenite grain but refined. This kind of microstructure could promote the resist of thermal crack growth and thus prolong the service life of die-casting die.