射出成形機スクリュー用Mo<SUB>2</SUB>FeB<SUB>2</SUB>ベース硬質合金の諸特性

Abstract

Wear and corrosion problems become an everyday concern in the extrusion and injection molding process. In this investigation the effect of Ni content on the mechanical properties and structure of the ferrous binder was studied using model alloys whose composition was similar to that of the Mo2FeB2 complex boride base hard alloy applied to the injection molding machine parts. Compacts of the 5B-43Mo-8Cr-xNi-0.1C-bal. Fe model alloys were prepared from mixed and ball-milled powders of Fe-15.1B alloy, pure Mo, pure Cr, carbonyl nickel, carbonyl iron and graphite. The compacts were sintered in vacuum for 1.2 ks at 1523 K. Transverse rupture strength and hardness were measured. The microstructure was investigated by means of SEM, TEM and XRD. Wear and corrosive behaviors of the new hard alloys were also studied. The results are as follows:The ferrous binder of the model alloys changes from ferritic to martensitic and further to austenitic with increasing Ni content. About 2 mass%Ni content is considered to be the optimal content to obtain the best combination of TRS and hardness associated with the martensitic binder. Abrasive and sliding wear resistances increase with increasing hardness of the tested alloys. The Mo2FeB2 complex boride base new hard alloy, particularly the alloy with the martensitic binder, has better wear resistance than powder metallurgy (PM) high speed steel and an alloy steel SKD11, and is comparable to cemented carbide. The new hard alloys, especially high in Cr and Ni, show excellent corrosive resistance in hydrofluoric acid solution. These results indicate that the Mo2FeB2 complex boride base hard alloys are very suitable material for the injection molding machine parts.