具有性能梯度特性的贝-马-奥球墨铸铁磨球的制备工艺

Preparation technology of property gradient bainite-martensite-austenite ductile cast iron grinding ball

采用10 kg真空中频感应炉熔炼铁液,经炉前一次球化及两次孕育处理,真空浇注得到球墨铸铁球。使用电热炉加热磨球到不同的奥氏体化温度,并在不同温度的硝酸盐和亚硝酸盐混合介质中进行连续冷却淬火,后经低温回火得到球墨铸铁磨球。其中,性能最佳的为贝-马-奥球墨铸铁磨球,其显微组织为:球状石墨(体积分数12%左右)+下贝氏体+高碳针状马氏体+残留奥氏体(质量分数16.6%~18.1%)。石墨球化率达到92%、球化级别为2级,球墨尺寸级别为9.2级;磨球表面硬度为55~58 HRC,表面与心部硬度差【5 HRC;磨球表层的常温冲击韧性为20.5 J/cm2,心部冲击韧性为25.3 J/cm2,表现出表层高硬度,耐磨损;心部高韧性,抗破碎的性能梯度特性。进一步研究表明:下贝氏体和残留奥氏体组织对提高磨球的性能有着显著的作用,而上贝氏体组织则不利于磨球的综合性能。

Cast iron was melted in a vacuum mid-frequency induction furnace with 50 Hz in frequency and 10 kilogram in capacity. After the processing of nodularization-inoculation,cast iron grinding balls were obtained by vacuum pouring. The bainite ductile cast iron grinding balls were prepared by quenching the grinding balls from different austenizing temperatures in cooling medium with different temperatures,and then tempering at low temperature. Microstructure analysis shows that the spheroidization rate of graphite is 92% and graphite size reaches up to grade 9. 2. The microstructure consists of 12%( volume fraction) spheroidal graphites,a mass of lower bainite,a little amount of high carbon acicular martensite and 16. 6%- 18. 1%( mass fraction) retained austenite. Further tests show that the hardness of the ball surface layer is 55- 58 HRC,and the impact toughness at room temperature is 20. 5 J / cm2. Meanwhile,the hardness of the ball center is not lower than 50 HRC,with the impact toughness of 25. 3 J / cm2. Therefore,the grinding balls with high hardness on the surface and high toughness inside have been obtained,which presents property gradient characteristics. The further research shows that the performance of the grinding ball is improved obviously by lower bainite and retained austenite,while upper bainite is not conducive to the comprehensive performance of grinding ball.