Fe-Ni燒結硬化合金鋼中Ni之均質化及機械性質改善對策

Improvement on the Homogenization of Ni in Fe-Ni Sinter-Hardening Alloy Steels

蔡嘉正(Chia-Cheng Tsai)

指導教授 ： 黃坤祥

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.10044

摘要

金屬射出成形（Metal Injection Molding, MIM）適合製作形狀複雜的小零件，與傳統鋼鐵鑄鍛件加工產品相比，具有較大的競爭力。其中又以燒結硬化型合金鋼佔有較大的優勢，燒結硬化型合金鋼不需後續熱處理加工即可達到高硬度、高強度之機械性質。欲達到燒結硬化型合金鋼的效果，就必須添加可促進硬化能的合金元素（如錳、鉬、鉻、矽、銅、鎳等），使燒結後即可得到類似熱處理後的組織，進而達到具高強度的機械性質。合金元素在合金系統中的均勻程度也會影響到合金系統能否達到最高的機械性質，燒結硬化型合金鋼Fe-8Ni-0.8Mo-0.8Cr在前人的研究其抗拉強度已可達到約1900MPa，但鎳在鐵中的體擴散很慢，導致合金系統中鎳仍然不均勻，本研究以粒徑更細小的鎳粉取代原本在合金系統中的鎳粉，希望藉此使鎳在合金系統中擴散均勻，進而促進機械性質的提升。
結果顯示，當使用粉末粒徑較細的Ni-110取代Ni-123時，藉由EPMA的分析結果顯示燒結硬化型合金鋼Fe-8Ni-0.8Mo-0.8Cr中鎳擴散的非常均勻，且試片經超深冷處理與回火後，其抗拉強度超過2100MPa，硬度為52.2 HRC，密度為7.56 g/cm3，伸長量為3.9％。
除此之外，鉻在合金系統中也可促進鎳的均勻性，主要是因為鉻在合金系統中降低了鎳與碳的排斥，使鎳能更均勻的分散在組織中，進而提升機械性質。
研究結果也顯示，在合金系統中添加TiH2時，因為鈦的活性很大，在熱脫脂過程中TiH2脫氫後即與氧結合成二氧化鈦，並在組織中形成聚集，使得抗拉強度下降。
另外，經實驗結果發現，本合金系統在鎳含量為7wt％時，具有最高的抗拉強度值，而當使用預合金粉為基礎粉時雖鎳的分佈均勻，但因燒結後密度不高，使得抗拉強度無法提升。

關鍵字

金屬粉末射出成形 ； 燒結硬化型合金鋼 ； 超深冷處理 ； 粉末冶金 ； 燒結

並列摘要

Metal injection molding (MIM) process has many advantages in making small parts with complicated shapes over the press-and-sinter process and other manufacturing processes. The MIM parts usually must attain high sintered densities and good mechanical properties through high temperature sintering and heat treatment. However, the quenching process will cause problems in distortion and dimensional control. Thus, sinter-hardening process has become a focus of recent MIM industries. In this study, compositions and processing parameters of Fe-8Ni MIM 2700 alloys were adjusted in order to improve the mechanical properties of the sinter-hardened parts without the need of quenching.
The results show that fine Ni powders reduced the diffusion distance and improved the homogeneity of Ni and C in the matrix. The addition of Cr also had similar effect. It was found from the carburization test of Fe-Ni alloys that the presence of Cr helped reduce the repulsion effect between carbon and nickel. Thus, the homogeneity of C and Ni was improved and the mechanical properties were enhanced. The use of prealloyed powder showed no improvement due to the decrease of sintered density when the same sintering temperature was used despite that the Ni was uniformly distributed. The employment of cryogenic treatment after sintering caused transformation of the retain austenite to martensite and thus could increase the tensile strength and hardness.

並列關鍵字

Metal injection molding ； powder injection molding ； sinter-hardening,homogenization ； powder metallurgy.

參考文獻

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