Effect of Annealing Process on Properties of Ferritic Ductile Iron for Subway

Abstract

In order to improve the comprehensive mechanical properties of the commonly used ductile iron QT400-18, the microstructure of the ductile iron in the cast state was improved by optimizing the heat treatment process, thereby improving its comprehensive mechanical properties. The mechanical properties of the heat-treated samples at different annealing rates were tested, and the microstructures of the samples were observed. Furthermore, the influence of different heat treatment processes on the mechanical properties was analyzed. The results indicated that the mechanical properties and tissue properties of ductile iron QT400-18 were significantly improved after heat treatment. With the increase of annealing rate, the spheroidization effect, low temperature impact toughness and elongation showed a tendency to increase first and then decrease, while the strength and hardness decrease. The microstructure and mechanical properties of ductile cast iron were optimal at annealing rate of 70 °C/h. According to the national standards and actual requirements of subway products, the annealing rate of 110 °C/h or 150 °C/h could also be chosen to improve production efficiency on the premise of meeting the performance requirements.