The Crystallization Of Heat-resisting Nodular Malleable Cast Iron And Its Graphitizing

Heat-resisting nodular malleable cast iron is one kind of new heat-resisting cast iron. It's producing, normal and high temperature mechanical property, heat-resisting durability have been studied formerly. First crystallization, graphitizing annealing technology and cutability are developed in this article. This article use the way of liquid hardening to study its first crystallization, use quantitative image analysis to study the quantity of indigenous graphite, use X-ray defectoscopy to study the tendency of shrinkage cavity and porosity forming. The results showed that the graphite deposited during the period of primary and eutectic crystal helped to reduce the contract of liquid state and solidification, to improve the tendency of shrinkage cavity and porosity. The more the content of Si and wall of cast, the less the tendency of shrinkage cavity and porosity forming. In the condition of greensand mould, if the wall thickness of cast excess 20mm, the way of solidify is back to solidification of gruel form, the tendency of shrinkage cavity and porosity increase. With the aid of high temperature metallographic microscope and differential thermal analysis equipment, solid state graphitizing process and temperature during the process of temperature increasing investigated. The results indicated that carbide in heat-resisting nodular malleable cast iron start to decomposite at 900 . The speed of decomposition increased sharply when the temperature increased to 950 . It's revealed that the first stage of graphitizing annealing is more than 950 , but less than 1050 . Rockwell hardness indentation and longitudinal section of indention was investigated with scanning electron microscope. It demonstrated that the experiment of hardness is likely to upset in the experiment of compression. Hardness tester indenter make matrix metal plastic deformation and viscous flow happen. The hardness index of this cast iron can't reflect it's cutability. The carbide of heat-resisting nodular malleable cast iron is dispersing. When it was squeezing, it was pushing by the deformation and viscous flow of matrix metal, and it can't produce obvious resistance to cutability. The cutability of heat-resisting nodular malleable cast iron is corresponding to the cutability of matrix mental.