Development of high strength and toughness austemper ductile cast iron and application to its structural part materials

本研究针对高强度、高韧性、耐腐蚀环境和实际使用的耐候等温淬火球墨铸铁进行了试验研究。研究确定了铜镍合金铸铁等温淬火的最佳热处理工艺条件。通过示波冲击试验和拉伸试验评价了材料的强度和冲击特性，并对等温处理条件和机理进行了阐明。通过疲劳裂纹扩展抗力试验，对铸铁的破坏行为和疲劳强度进行了试验研究。通过在硫酸铁溶液中的耐蚀性评价和大气暴露试验，结果表明，镍铜合金铸铁经热处理后获得了显著的冲击特性。强度和韧性在623K等温淬火时达到了20J的吸收能，随着裂纹萌生能的增加，断裂载荷达到一个较高的值。裂纹扩展在达到最大载荷值后逐渐扩展。通过等温淬火处理，获得了性能优良的高塑性和高强度材料。等温淬火铸铁的应力强度因子(Delta K)增大了裂纹扩展阻力，表现为裂纹的稳定扩展。此外，等温处理的阈值应力强度因子(Delta KTH)也表现出较高的值。铜镍合金铸铁在室外暴露试验和硫酸铁溶液中的耐蚀性是非合金材料的两倍。

This research aims at the development of atmospheric resistance austemper ductile cast iron which consider use in high strength, toughness, and the corrosion environment and practical use.The following experiment was carried out. The research clarified the best heat treatment conditions by austemper treatment of the Cu-Ni alloyed cast iron. The austemper treatment conditions and the elucidation of the mechanism evaluated strength and the impact characteristic by the instrumented Charpy impact test and the tensile test. Furthermore, the destruction behavior and the fatigue strength evaluation of the cast iron were experimented with the fatigue flaw growth resistance test. The evaluation of corrosion resistance was executed by in the ferric sulfate solutions and the atmospheric exposure examination.As a result of this research, the Ni-Cu alloyed cast iron obtained a remarkable impact characteristic with heat treatment. Strength and toughness reached absorbed energy of 20J by the austempering of 623K.As the crack initiation energy increases, the fracture load reached a high value. Crack propagation advanced gradual after reaching the maximum load value. An excellent high ductility and a high strength material were obtained by austemper treatment. Stress intensity factor (DELTA K) of the austempered cast iron enlarged the crack propagation resistance and showed the growth of a steady crack. Also, threshold stress intensity factor (DELTA Kth) showed a high value with austemper treatment. However, DELTA Kth was not able to be improved with the alloy material.Corrosion resistance of the Cu-Ni alloy cast iron have increased to two times that of non-alloy material in outdoor exposure test and in the ferric sulfate solutions.