The Preparation And Properties Research Of Bulk Alloyed Cementite

As one of the most important phases in carbon steel, the performances study of cementite has attracted great concerns owing to its distinctive mechanical properties and optical, electrical, magnetic, thermal feature.But it is very difficult to prepare single phase bulk cementite due to its metastability, which seriously impedes the understanding of its properities in depth. Therefore, in the present work, we explored a new effective method to prepare single phase cementite, and the effects of Mn, Cr and Si on its properties had also been studied.Through mechanical alloying(MA) and vacuum heat treatment, we have prepared single phase cementite powder.The approximately single phase cementite was obtained by milling for 90h with sterric acid as dispersant followed by vacuum heat treatment at 873K for 3h. It was found that the cementite formed at about 478℃ and decomposed at about 762℃. The addition of Mn and Cr had promoted the stability of cementite while Si suppressed the formation of cementite strongly. The magnetism test results showed that the saturation magnetization (Ms) of cementite powder was 103 emu/g and the coercivity (He) was 374.553G. Both the Ms and He of alloyed cementite were lower.The bulk cementite with high relative density had obtained by MA combined hot-press sintering or spark plasma sintering (SPS). And the relative density of bulk cementite had reached 99.3% under 50MPa at 1000℃. The decomposition temperature of bulk cementite had increased to 930℃.The magnetism test results showed that the Ms of bulk cementite was 141.56emu/g and the He was 221.62G, both the Ms and He of alloying cementite were lower.The mechanical test results showed that the micro-hardness of bulk cementite obtained by the present method had exceed 1100HV and compression strength was 3GPa. The thermal conductivity of bulk cementite obtained by MA and SPS was 7.719±0.034 W/mK and the specific heat capacity was 0.598±0.002 W/m-K, the values for micro-alloyed cementite were slightly higher. The DSC results and thermal conductivity test results showed that Mn and Cr increased the decomposition temperature of cementite. And cementite revealed negative abnormal character between 0～300℃.