Development and Practical Use of Toughened Austempered Ductile Iron

本研究分为以下三个步骤。(1)一种新型等温淬火球墨铸铁的研制与评价通过拉伸试验、示波冲击试验和断裂韧性试验，阐明了新研制的增韧等温淬火球墨铸铁（TADI）比常规等温淬火球墨铸铁（ADI）具有更高的强度和韧性。此外，已澄清的是，在ADI中的塑性损失是由于形成的chi-carbide和二次石墨的析出。(2)TADI的疲劳性能、耐久性和噪声评价首先进行了疲劳扩展试验。结果表明，该合金的疲劳裂纹萌生抗力和疲劳裂纹扩展抗力均高于普通奥贝球铁。其原因可能是残余奥氏体相的TRIP效应提高了裂纹形核能。其次，对由TADI制造的齿轮进行了耐久性试验和噪声试验。实践证明，TADI能延长齿轮的使用寿命，降低齿轮的噪声。(3)TADI大齿轮的试验将TADI大齿轮装入减速器组合电机中，进行了耐久性试验。已经发现，TADI齿轮与SCM材料制成的齿轮具有几乎相同的耐久性。从这些结果中我们可以确信，TADI可以实际用作齿轮材料。

This research is consisting of three steps as follows.(1) Development and evaluation of a new austempered ductile cast ironfrom the results of various tests such as tensile test, instrumented Charpy impact test and fracture toughness test, it has been clarified that the newly developed toughened austempered ductile cast iron (TADI) has greater strength and toughness than the conventional austempered ductile cast iron (ADI). Moreover, it has been clarified that the loss of ductility in the ADI is due to the formation of chi-carbides and the precipitation of the secondary graphites.(2) Evaluation of fatigue properties, durabilty and noise of TADIat first, the fatigue propagation test has been conducted. It has been confirmed that both of the fatigue crack initiation resistance and fatigue crack propagation one are higher than the conventional ADI. Its cause can be considered due to the increasing of the crack nucleation energy by the TRIP effect in the retained austenite phase. Next, the durability test and the noise one have been conducted for the gear wheel made from the TADI. It has been confirmed that TADI can prolong the life time and lower the noise of the gear wheel.(3) Trial test of the TADI gear wheelThe TADI gear wheel has been put into the reduction gear combined motor and the durability test has been conducted. It has been found that the TADI gear wheel has almost the same durability with the one made from SCM material. We can have the confidence from these results that the TADI can be used practically as the gear wheel material.