Microstructures of Fe-C System Hard Alloys Produced from Mechanically Alloyed Powders

摘要

Fe-C system hard alloys were produced from mechanically alloyed powders and their properties were examined by means of hardness testing and microstructural examinations. Mixtures of iron and graphite powders(Fe-2-6mass percent C) were mechanically alloyed with vibration-ball-mi]] in Ar atmosphere. MA powders obtained were packed in stainless steel tubes and then sealed in vacuum after degassing at 873K. The stainless steel tubes were hot-rolled in the temperature range of 923K-1273K to consolidate MA powders. Bulk materials were subjected to isothermal annealing at 1273K, followed by water quenching. After the ball-milling of 360ks, extremely large deformation energy was stored within powder particles. This leads to the formation of ultra-fine a-Fe grain and very fine dispersion of graphite. On heating to a consolidation temperature, the reaction forming Fe_3C takes place at around 600K. MA powders were completely densified to full density by hot-rolling at 1123K where the structure is of (Fe_3C+#gamma# Fe) two-phase, and this consolidation process does not accompany significiant coarsening of the microstructure. In a case of an Fe-6mass percent C MA bulk material the structure at room temperature is composed of 80vol percent Fe_3C and 20vol percent #alpha#-Fe , so that hardness of a bulk material reaches to Hv900. But, Fe_3C is not so stable at elavated temperatures that it easily decomposes to Fe and graphite after long annealing.