Research On The Heat Treatment And Properties Of High Chromium Cast Iron For Hammer

The effect of heat treatment on microstructure, mechanical properties, wear resistance and corrosion resistance for high chromium cast iron with and without Nb was studied in this paper. The wear mechanism of high chromium cast iron was analyzed and The interaction between corrosion and wear of high chromium cast iron was discussed.The optical microscope and XRD for the two groups of different compositions of high chromium cast iron with different destabilization-tempering treatments were studied. The results showed that the microstructure of as-cast high chromium cast iron mainly consists of M7C3-type carbides (Primary or eutectic carbides) and austenite, and a small amount of Nb existing in NbC-type had the effect of grain refinement. In the destabilization and tempering process, the matrix transformed to secondary carbides, martensite and residual austenite. NbC-type carbides gradually decomposed and melted into the matrix, and Nb made grain refined. With the increase of destabilization temperature and destabilization time, the amount of precipitation of secondary carbides increased first and then decreased.Considering the hardness, toughness, wear resistance and corrosion resistance of high chromium cast iron, the optimum heat treatment parameter of high chromium cast iron without Nb was destabilizating under 1000℃for 3h and then tempering under 250℃ for 6h after air-cooling, and that of sample with Nb was destabilizating under 1000℃ for 3h and then tempering under 250 ℃ for 4h after air-cooling. A small amount of Nb could significantly increase the hardness and wear resistance, though it had no significant effect on corrosion resistance.The cryogenic treatment promote decarbonization of pro-precipitate martensite, while new martensite and small carbides generated, which further increased the hardness and wear resistance of high chromium cast iron. Compared to cryogenic treatment after 30 days, the amount of martensite precipitation of the immediately cryogenic treatment of high chromium cast iron was higher, but the carbon content of martensite reduced. Tempering treatment reduced the content of residual austenite, resulting in the reduce of martensite which transformed from austenite in the subsequent cryogenic treatment.Dry sliding friction and wear tests showed that, a large number of dispersed small carbide and tempered martensite with better toughness precipitated during the destabilization-tempering process treatment, and the wear resistance of the sample improved. Asperity of the dual material embedded in the matrix during the sliding process, which caused to the producing of groove and the exfoliation of carbide of the sample and lead to the abrasive wear, which interacting with the adhesive wear caused by the deformation thermal during the localized contact.The corrosion resistance of high chromium cast iron in weakly acidic solution was lower than that in the 3.5% NaCl solution. The matrix was corroded while the carbide bulged, which reduced the contact area of matrix and dual material during the wear process and thus decreased the amount of wear. The sensitive of microcrack-tip of the carbide increased after the corrosion of abrasion surface, which caused more exfoliation in the subsequent wear process and the amount of wear increased.