The Effect of Microstructure on Unidirectional Chilled Solidification of High Chromium White Cast Iron

Abstract

This study mainly investigates the characteristics of carbide and the matrix structure of ASTM A532–87 CLASS Ⅲ high-chromium white cast iron under directional solidification. The two components of high-chromium white cast iron were put in a 3-level Furan sand model, which is placed in a cold-water circulation copper model, producing unidirectional chilled solidification. A K-type thermocouple is employed to measure data for solidification temperature with time. The move velocities of the liquidus phase and solidus phase is calculated. The matrix and the growth characteristics of M7C3 carbide are explored. As determined from the experiment, the liquidus temperature gradient GL is 0.45~ 0.9oC/mm, and the solidus temperature gradient Gs is 4.3~6.2oC/mm. Around 300 nm of the primary carbide is formed from the added elemental nickel being less than 0.3 mm from the chilled end and from the nickel-free alloy being less than 5 mm from the chilled end. As the distance from the chilled end increases, the primary carbide gradually becomes coarser, and the distance between eutectic carbide groups is increased. This study employs EPMA to analyze the changes of primary carbide, eutectic carbide and matrix components with distance from the chilled end, as well as changes in the distributions of chemical elements.