Effect of Soaking Temperature on Carbide Precipitation, Hardness, and Wear Resistance of High-Chromium Cast Iron

Different variants of high-chromium cast iron are commonly used for wear-resistant applications in mining and steel industries. These alloys are often used in the as-cast condition that limits the optimization of wear properties through microstructural engineering. This paper aims at improving the wear resistance of 20Cr–2C cast iron through an inexpensive single-step heat treatment. In the present study, samples were soaked at temperatures between 700 and 1200 °C at an interval of 100 °C and were air-cooled for destabilization of primary carbide networks. Detailed microstructural analysis was carried out using a scanning electron microscope coupled with electron probe micro-analysis. Image analysis technique was used to determine the effect of soaking temperature on fraction of primary and secondary carbides. Hardness and dry sliding wear tests were conducted to determine the effect of microstructure on mechanical and wear properties. It was observed that the network of primary carbide began to break only at soaking temperature of 1000 °C and above. Up to 800 °C, there was coarsening of primary carbides that led to lowering of hardness and deterioration of wear resistance. At 900 and 1000  °C, precipitation of secondary carbides was observed. At 1100 °C, maximum hardness and wear resistance were achieved. This was attributed to disintegration of primary carbides and the highest fraction of finely dispersed secondary carbides. At 1200 °C, most of the secondary carbides dissolved in the matrix which resulted in sharp fall in hardness and wear resistance. Micro-mechanism of wear was studied using an optical laser scanning microscope. Post-wear hardness measurement confirmed that the extent of work hardening depends on destabilizing treatments. This study is expected to help the practicing engineers to improve life cycle of high-chromium cast iron components prone to wear.