Superhigh Strengthening and Net Shaping for Sintered Low Alloy Steels by Utilizing the Partial Constituent Gradient Microstructure in MIM Process

金属注射成形(MIM)技术是一种先进的粉末加工技术，具有净成形、形状复杂、加工能量低、材料利用率高等优点。本研究旨在阐明和优化MIM超高强度烧结低合金钢(Fe-Ni系)的力学性能与显微组织之间的关系。质量分数为6%的镍基MIM钢具有2000 Mpa的抗拉强度、5%的伸长率和500 Mpa的疲劳强度。当团聚镍粉的尺寸小于18μm时，富镍相仅为马氏体组织，而当团聚镍粉的尺寸大于18μm时，富镍相的中心形成残余奥氏体相，因此，如果颗粒尺寸约为20μm的镍粉均匀地弥散在基体中，即使是相同成分的Fe-6Ni-0.5Mo-0.2Mn钢也可以获得良好的力学性能。此外，由于镍对人体有有害的影响，例如镍过敏，人们研究了铁锰低合金钢，以取代Fe-Ni，以获得高性能的性能。

Metal Injection molding (MIM) process is an advanced powder processing technique because of net shaping with shape complexity at low processing energy and 100% material utilization. This study has been performed to clarify and to optimize the relationship between the mechanical properties and the microstructures for the superhigh strengthening sintered low alloy steels (Fe-Ni system) by using MIM process. A 6%mass%Ni MIM steel showed excellent properties of 2000MPa tensile strength, 5% elongation, and 500MPa fatigue strength. The Ni rich phase consists of only the martensitic structure if the size of agglomerated Ni powders is below 18μm, whereas the retained austenite is formed in the center of Ni rich phases if the size of agglomerated Ni powders is above 18μm. If the Ni powders of approximately 20μm particle size is dispersed uniformly in the matrix, therefore, superior mechanical properties may be obtained by even the same composition of Fe-6Ni-0.5Mo-0.2Mn steels. Instead of Fe-Ni, moreover, the Fe-Mn low alloy steel was investigated to obtain high performance properties, because Ni has harmful influence upon the human body, for example, a Ni allergy.