Study On Process And Abrasive Resistance Of Plasma Beam Surface Alloying For Three-dimensional Surface Of Nodular Cast Iron Mould

Due to the demand for automobile lightweight, the high strength steel and ultra high strength steel are becoming more and more wildly used in automobile industry. The high strength steel and ultra high strength steel are usually formed by hot stamping technology. Compared with traditional stamping die, the material of hot stamping die not only need to have obdurability and abrasive resistance, but also have good thermal conductivity. Nod ular cast iron has excellent casting properties, good shock resistance, mechanical processing properties and low production cost, moreover its thermal conductivity is better than the alloy die steel's. Therefor nodular cast iron has been widely used in the field of automobile die manufacturing. It will reduce manufacturing costs and shorten manufacturing cycle to use nodular cast iron manufacture hot stamping die, in this way the more optimized cooling scheme could be obtained to improve the qualities of hot stamping products. However, the properties of nodular cast iron, specially the abrasion resistance, would obviously decrease at high temperature, which could reduce the service life of hot stamping die.The plasma beam hardening technology for three-dimensional mold surface has been applied to solve the problem above. This paper had investigated the process of preparing hardening layer dispersed with C u particles on nodular cast iron by surface alloying, then deeply studied the abrasive resistance of hardening layer. With the properties of soft texture and good thermal conductivity, Cu could not only improve the surface abrasive resistance of nodular cast iron, but also enhance the thermal conductivity of hardening layer.In the aspect of process, depending on the characteristics of surface alloying by plasma beam, this paper had researched the influences of basic process parameters(arc current and scanning speed) to surface alloying. Meanwhile, in order to accommodate the characteristics of three-dimensional plasma beam surface alloying technology, the influences of three-dimensional process parameters(nozzle height, deflection angle and scanning interval) had been detailed investigated. The results show that the arc current and the scanning speed has great influences on the dispersion of C u in hardening layer and the evolution of microstructures. The molten pool shape is affected by nozzle height, deflection angle and scanning interval: the depth and width of molten pool maximizes when the nozzle height is 4 mm, the molten pool offset varied linearly with the increase of deflection angle, the hardness and microstructures difference among different o verlapping areas. Therefore, the influence rules of these factors should be taken into consideration during three-dimensional plasma beam surface al oying, so that to control the al oying effects.In the aspect of abrasive resistance, surface alloying and surface remelting had been done on nodular cast iron. Through friction and wear properties test on alloying and remelting samples at different process parameters during room temperature and high temperature, this paper had studied the influencing mechanisms of C u particles on friction coefficient and friction properties, and analyze the influences of arc current and load on friction coefficient. The results show that the average friction coefficient of alloying samples is 0.04 less than the remelting samples' at room temperature, and it is 0.065 at high temperature. The C u particles have the function of antifriction, which reduce the roughness of friction surface and the phenomena of adhesive wear and plough wear. The friction coefficient of alloying layer increases with the arc current at room temperature, but decreases at high temperature. The friction coefficient of alloying layer decreases with the increase of load at room temperature, but there is no variation at high temperature.