Research on Application of High Strength and High Toughness Austempered Spheroidal Graphite Cast Iron to Environmental Material

本研究以开发高强度、高韧性、耐腐蚀的等温淬火球墨铸铁为目标，首先从预防和诊断金属表面腐蚀的角度出发，构筑了一套简便的评价体系。该系统利用数字图像处理技术，对金属表面的腐蚀分布、腐蚀形态和腐蚀程度进行了分析。研究二通过电化学腐蚀试验评价了所研制材料的耐腐蚀性。采用自然电位法和阳极极化法相结合的方法，制备了镍铜合金球墨铸铁，以期提高其耐蚀性。此外，还用球墨铸铁、高硅球墨铸铁、白口铸铁和碳钢作为对比材料。此外，还考察了铜镍合金球墨铸铁对耐蚀性能优良的铸铁各种基体的影响。铜镍合金球墨铸铁通过形成铜保护膜阻碍了腐蚀的进行。该材料表现出最优异的耐腐蚀性。马氏体相和奥氏体相的组织使细小的无运动保持电流密度变小，提高了耐蚀性。另一方面，利用分维分析的数字图像处理技术，可以对金属表面的腐蚀评价进行分析。今后的研究方向是利用数字图像处理技术，从防腐、诊断和评价的角度制定客观的评价判断标准。

This research is in the aim of the development of the austempered spheroidal graphite cast iron which considers high strength, a high toughness, and corrosion resistance.The first research planned the construction of a handy evaluation system from the viewpoint of prevention and the diagnosis of corrosion in the metallic surface. The system analyzes the corrosion distribution, the form, and the progress degree of the metallic surface by using a digital image processing. The second research evaluated the corrosion resistance of the developed material by the electrochemical corrosion test. It was a natural potential measurement and an anodic polarization measurement.The test material prepared the Ni-Cu alloy spheroidal graphite cast iron to expect the corrosion resistance improvement. In addition, the spheroidal graphite cast iron, the high Si content spheroidal graphite cast iron, the white cast iron, and the carbon steel were used as the comparison material. In addition, the effect on various matrixes of the cast iron which showed an excellent property in corrosion resistance was examined in the experiment.The Cu-Ni alloy spheroidal graphite cast iron obstructed the progress of corrosion by the protection film formation of Cu. This material showed the most excellent corrosion resistance. The martensite and the ausferite structure made minute become small no movement maintenance current density, and have improved corrosion resistance.On the other hand, the corrosion evaluation of the metallic surface was able to be analyzed by a digital image processing which used the fractal dimension analysis. The research in the future is to make the objective evaluation judgment standard from the viewpoint of the corrosion prevention and the diagnosis and the evaluation by using a digital image processing.