| Mold is important process equipment in manufacture industry. The manufacturing level of mold has become one of the important symbols of manufacturing level of products. Up to now, the mold has largely determined the quality and benefit of products. Mold materials and their advanced preparing technology are the most basic and critical core guarantee for obtaining mold products with high quality and life. At present, most of the frequently-used mold materials for stamping is alloying spheroidal graphite cast iron oversea. Because of technical backwardness in china, these mold materials can only rely on import. Undoubtedly this increases the cost of domestic mold companies. Therefore, it is imperative to develop an advanced ductile cast iron materials with excellent mechanical properties, heat resistance, anti-fatigue property and anti-oxidation property to replace the traditional mold steel.The goal is to develop a kind of heat-resistant spheroidal graphite cast iron material for manufacturing mold in this paper. The main research contents are as follows:First, the alloy composition of the ductile cast iron was optimized by orthogonal test. The microstructures of the ductile irons with different element contents were observated by an optical microscope. The hardness and tensile strength were characterized using HB-3000 Brinell hardness tester and CSS-44000 electronic universal test machine. The results show that when the composition is Si5.0 wt%, Mn0.6 wt.%, and Cr0.8 wt.%, the microstructure of the nodular cast iron was optimum. The role of Si element is to promote the graphitization, but the content of Si element can not too high. Mn and Cr can promote the pearlite transformation and enhance the toughness and hardness of the nodular cast iron.Second, that the effects of three kinds of alloying elements on oxidation resistance of materials are different was obtained through determining the oxidation resistance of the nodular cast iron under high temperature. SiO2 oxide film was generated after Si element was added. MnFe2O3 oxide film formed at high temperature after Mn element was added. Cr element can be oxidized to Cr2O3 oxide film. These oxide films can prevent oxidation of these materials. Third, the anti-fatigue property of materials was studied by fatigue test. Through observing the internal structure of cracks by SEM, we can summarize that the main reasons of the thermal fatigue crack initiation and growth include the plastic strain concentration, the high temperature oxidation and pitting of surface, the existence of the inclusions and oxides. Comparing the thermal fatigue resistances of heat-resistant nodular cast iron mold material and heat-resistant gray cast iron, we found that the former is better than the latter, and the main reason is the difference in graphite shapes.Fourth, the dry friction and wear properties of materials were investigated using MG-2000 type tribometer. The effects of the alloying element contents, the applied load, and the wearing time on the friction and wear properties of the material were analyzed comprehensively. The wear mechanism was discussed. The results show that with the increase of Mn and Cr element contents, the wear mass loss of the material reduced, and the friction coefficient decreased. When Si<5.5%, the wear resistance was improved. When Si≥5.5%, the number of pearlite in microstructure dropped, and the wear resistance reduced. The wear mass loss and friction coefficient increase with the increase of the applied load and the wearing time. Comparing the wear resistances of the heat-resistant nodule cast iron mold material and the heat-resistant gray cast iron, we found that the wear resistance of the former was better than that of the latter.Fifth, considering comprehensively the microstructure, mechanical properties, heat resistance, and wear resistance of the material, we think the optimum composition of the heat-resistant nodule cast iron mold material is Si5.5 wt.%, Mn0.6 wt.%, and Cr0.8 wt.%.
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