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

本研究以开发兼顾高强度、高韧性和耐腐蚀性的等温淬火球墨铸铁为目标，首先从金属表面腐蚀的预防和诊断的角度出发，设计了一套简便的评价系统。该系统采用数字图像处理技术，对金属表面腐蚀的分布、形态和发展程度进行分析。第二项研究通过电化学腐蚀试验评估了所开发材料的耐腐蚀性。采用自然电位法和阳极极化法，对Ni-Cu合金球墨铸铁进行了耐蚀性测试。另外，将球墨铸铁、高Si含量球墨铸铁、白色铸铁和碳钢用作比较材料。此外，还研究了Cu-Ni合金球墨铸铁对各种基体的影响，结果表明，Cu-Ni合金球墨铸铁通过Cu的保护膜阻止了腐蚀的进行。这种材料显示出最优异的耐腐蚀性。马氏体和奥氏体组织使微合金化后的不动维持电流密度变小，提高了耐蚀性。另一方面，利用分形维数分析的数字图像处理技术，对金属表面的腐蚀评价进行了分析。今后的研究是从防腐蚀的观点出发，利用数字图像处理进行诊断和评价，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.