Development of High Performance Sintered Alloy Steels by Metal Injection Molding

Research Project

Project/Area Number	04805068
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	金属加工(含鋳造)
Research Institution	Kumamoto University
Principal Investigator	MIURA Hideshi Kumamoto Univ., Eng., Asso.Prof., 工学部, 助教授 (30117254)
Co-Investigator(Kenkyū-buntansha)	ANDO Shinji Kumamoto Univ., Eng., Assistant, 工学部, 助手 (40222781) HONDA Tadatoshi Kumamoto Univ., Eng., Prof., 工学部, 教授 (80040393)
Project Period (FY)	1992 – 1993
Project Status	Completed (Fiscal Year 1993)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1993: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1992: ¥1,300,000 (Direct Cost: ¥1,300,000)
Keywords	Metal Injection molding / Sintered Alloy Steel / Carbon Control / Solvent Debinding / Mechanical Property / High Performance
Research Abstract	The purpose of the work is to test the feasibility of using the mental injection molding (MIM) approach to attain the high performance through a new fabrication route. However, there still remains the issue of controlling the carbon content and structure in the final product by the difference of powder type. In this study, MIM process for the 4600 steels has been studied at first by using prealloyed fine powder (particle size : 12mum) contained 0.71wt.% carbon. For the debinding approach, solvent debinding followed by final thermal debinding produced the homogeneous structure and stiff compact enough for handling. The residual carbon content was mainly controlled by changing the fraction of H_2 in gas mixture of H_2 and N_2 during the final thermal debinding. Mechanical properties of the sintered and the heat treated MIM compacts with prealloyed fine powders were inferior to those of the same treated MIM compacts with mixed elemental powders, especially in the ductility. This is due to the insufficient densification of prealloyed fine powder (relative sintered density : 93-94%) and the difference of microstructures. Subsequently, the same experiment has been performed for the Ni-Mo and Cr-Mo steels. For the nearly carbon-free prealloyed Cr-Mo powder, carburization could take place in the debinding by using a carburizing atmosphere such as CO gas and carbon could be restored to the desired level by adjusting the CO concentration in gas mixture of H_2 and CO.The mixed elemental powder was used for the Ni-Mo steels, resulted in the heterogeneous structure by segregation of Ni. However, this tempered steel showed a excellent strength compared to that of the prealloyed powder steel. This seems to be due to the structure consisted of martensite surrounded by a network of tempered martensite. The obtained results indicate the attainability of high performance ferrous materials by the MIM techniques.