Research On The Solidification Micro Structures Of Low Superheat Hypereutectic High Chromium Cast Iron Melt Under Electric Current Pulse Treatment

Hypereutectic high chromium cast iron (HHCCI) has the high hardness and good abrasion resistance. Under the harsh environment, the alloy shows good performance and economic benefit, so it is better than other wear-resistant materials on applications. Many primary carbides exist in the microstructure, which as the hard phase make the material shows good abrasion resistance. These primary carbides reduce the toughness and service life of HHCCI, because of their larger size. So if these primary carbides is refined, to improve its morphology and the continuity of matrix, thus improve the toughness of HHCCI is great significance for it’s engineering applications.The electric current pulse (ECP) treatment methods are mainly used in this article. The solidification microstructure of low superheat HHCCI can be refined by changing the parameters and processing mode of ECP. The temperature of HHCCI sample is heated to 1360 ℃ (the liquidus line is 1337 ℃) by using the tube furnace, overheating 23 ℃, and cooling to the room temperature with furnace cooling after heat preservation 3 min. The ECP treatment is used when the HHCCI sample is cooling, and the techniques of OM, XRD and SEM have revealed a slight difference in parameter with analysis between size and morphology of primary carbides. The rules of refinement on the solidification microstructure of HHCCI under ECP treatment are investigated.The results shown that, the effect of ECP on the solidification microstructure of HHCCI in the low superheat above liquidus line (1360 ℃-1337 ℃), above liquidus line to the solid phase line temperature range (1360 ℃-1276 ℃) and liquid-solid temperature range (1337 ℃-1276 ℃) is decline in turn. The end temperature of ECP treatment is more close to the solid phase line, the effects of mixing and impact on the melt make the eutectic carbides refined obviously. With the increase of processing time, the sizes of the primary carbides decreased from 95.56 m to 62.32 μm, after increases to78.32 μm, and eutectic organization density increased. Voltage of 1000 V, its effect of mixing and impact on the melt is high intensity, so processing within liquid-solid temperature range can accomplish refinement. When the voltage is 500 V, the effect of mixing and impact on the melt is small, so processing within the low superheat above liquidus line which refinement is better.After ECP treatment, concentration difference of matrix is The nucleation rate of carbides in HHCCI is improved, the growth way and morphology are changed, which make the microstructure refinement. And the content of Cr in the matrix is increased, the potential difference of matrix is decline, which result in the corrosion volume decreased 57.87% and corrosion rate decreased 62.47%, so the microhardness of sample is improved from 1398 HV-1420 HV to 1485 HV-1501 HV.