Casting waste heat normalizing is a process method of normalizing with the help of residual temperature after casting solidification. The realization method is to control the time of unpacking, so that the casting can be unpacked and cooled within the eutectoid transformation temperature range, so as to obtain more pearlescent volume, and the casting can meet the requirements of mechanical properties in the as cast state. In addition, in order to ensure a certain amount of pearlite, some pearlite stabilized alloy elements are usually added, such as Cu, Sn, Sb, etc.
Many kinds of ductile iron castings in China have been produced as cast, and their fatigue properties and brittle fracture resistance fully meet the practical requirements of engineering. According to the literature (normalizing after casting waste heat of nodular cast iron), the body sampling of as cast S195 crankshaft has stable and good mechanical properties, AB: 70-84kgf / m2, 8:2.0 ~ 3.5%, Hb: 240-270, AK: 2 ~ 3kgf · M / cm2. The fracture toughness (K / C) and fatigue properties are good. Moreover, the process reduces the cost, shortens the production cycle and saves labor. According to statistics, the cost per ton of molten iron increases by about 2.27 Yuan due to the addition of trace alloy. However, due to the omission of normalizing + tempering process, the cost per ton of S195 crankshaft can be reduced by 50 yuan, which can shorten the production cycle by one week. According to the monthly production of 3000 S195 crankshafts, 6 workers can be saved. At present, the grades of as cast pearlitic ductile iron which is widely used in production in China are qt600.2, qt700.2, etc. As cast pearlite ductile iron has not yet met the higher requirements of mechanical parts and components for material properties, so it is necessary to develop as cast pearlite ductile iron with higher performance.
In the early stage of practical application of nodular cast iron, certain heat treatment methods are adopted to control the matrix structure of nodular cast iron, so as to achieve the required mechanical properties. In the 1960s, due to the improvement of production technology and the deepening of alloying research, the required matrix microstructure and mechanical properties can be obtained as cast. As cast ductile iron has the advantages of remarkable energy-saving effect, good casting performance, saving equipment investment, shortening production cycle and low waste rate. It can also avoid high-temperature oxidation and deformation during heat treatment. As cast ductile iron has become a new development trend in the application of ductile iron materials.