| High chromium cast irons (HCCIs) are considering the best wear resistance materials now and widely spread all trades and professions. Compare with the Hypoeutectic HCCIs, as the result of carbonization inside the Hypereutectic HCCIs highly increased, the hardness of Hypereutectic HCCIs obviously improved via more carbon and chromium content inside. However, the coarser and larger primary carbides will be precipitated during the solidification of the hypereutectic alloy, more primary carbides affect adversely on the improvement of the wear resistance of alloy.In this study, we designed a reasonable alloy composition and added into titanium to refine the microstructure of alloys. By means of the different mould to obtain different cooling rate and examine the influence of cooling rate over microstructure of the hypereutectic HCCIs. At the end, to find a better heat treatment process to improve the wear resistance of hypereutectic HCCIs.When cooling rate increased, the shape of primary M7C3type carbides altered from stripe shape into hexagonal block shape, The quantity of primary M7C3increased and distributed relative-uniformity. With this cooling range, the primary carbides was refined, also the hardness and wear resistance were improved.Under this solidification process, TiC was created from the reaction both Ti and C. TiC particles precipitated before the primary M7C3carbides, which improved the nucleation rate of primary carbides and acted as the heterogeneous substrate to inhibit the coarser and larger of primary M7C3carbides generated. As a result, when the volume of Ti increased, primary M7C3carbides gradually refined and uniform-distributed. Meanwhile, the hardness and wear resistance less altered.Based on the above mentioned, with the method of uniform design, a local heat treatment process was generated firstly, then, under a series of experiments to test the influence of different quenching and tempering from the process, finally the best heat treatment process was found. The result was, with the increase of quenching temperature, there were Mo2C and M3C carbides precipitated, the macro hardness of the alloy increased firstly and reduced secondly, when the temperature up to peak values at950℃(65HRC). Abrasion and weight loss of the alloy always in raising trend, only at900℃the least value could be obtained (0.1378g). The alloy was unsuited to temper on the base of quenching at900℃. The best wear resistance could be obtained by tempering at300℃on the base of quenching at950℃.Under the condition of best heat treatment process, to investigate the effect of heat treatment with different Ti content, and the results showed that both hardness and wear resistance improved, especially the contents of1.5%Ti alloy performed best in the process of heat treatment. |
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