渗铜对QT500-7组织及性能影响的研究

Effects of Copperizing on Microstructure and Properties of QT500-7

为提高QT500-7的表面力学性能,采用固体渗金属方法在其表面制备渗铜层,利用金相显微镜、扫描电镜、硬度计研究了铜在其中的扩散行为及其对组织和硬度的影响。根据计算结果可知,随着处理温度的升高,球铁基体相中的Cu固溶度随之提高,在1173 K温度下固溶度可达0.56%(质量分数),铜在球铁中的扩散距离随扩散温度的升高、扩散时间的延长而增大,在1173 K保温8 h的条件下其理论扩散深度为23μm。试验结果表明:Cu在QT500-7中的扩散抑制了珠光体转变阶段铁素体晶粒的长大,使珠光体的含量增多,铜向球铁中的扩散使得制备的渗铜层处石墨数量增加,缩小了与其心部石墨数量的差距。观察到的扩散层深度为40μm,较铜向铁的完整晶体的理论扩散距离有所增大。而球铁表面制备的渗铜层硬度较原始试样的略有提高。

In order to improve the surface mechanical properties of QT500-7,the copperizing layer was prepared on the surface of QT500-7 by solid diffusion metallizing method.The diffusion behavior of copper in QT500-7 and its influence on the microstructure and hardness were stud-ied by metallographic microscope,scanning electron microscope,hardness tester,respectively.According to the calculation results,the solid solubility of copper in ductile iron substrate enhanced with the increase of processing temperature,and the solid solubility was 0.56%(mass fraction)at temperature of 1173 K.The diffusion distance of copper in ductile cast iron rose with the increase of diffusion temperature and dif-fusion time.The theoretical diffusion distance was 23μm under the condition of 1173 K insulation for 8 h.The experimental results showed that the diffusion of Cu in QT500-7 inhibited the growth of ferrite grains in the pearlite transformation stage,causing that the content of pearlite increased.The diffusion of copper into the ductile iron increased the amount of graphite at the prepared copperizing layer,and narrowed the gap between the amount of graphite in the core and the copperizing layer.Besides,the observed diffusion layer depth was 40μm,larger than the theoretical diffusion distance of copper to the perfect crystal of iron.The hardness of the copperizing layer prepared on the surface of ductile cast iron was slightly higher than that of the original sample.