| It was investigated, whether high speed steel part could be directly fabricated to near net shape by normal P/M process, ie. powder mixing, compacting and sintering procedure. Fe-, W-, Cr₃C₂and VC powders, whose composition is equivalent to the commercial T1 grade high speed steel, were thoroughly mixed in ball mill, and compacted into a disc-type specimens of 10㎜ diameter and about 5㎜ height at a hydraulic pressure of 5.5 ton/㎠. This compact was sintered in alumina tube furnace at temperature between 1220℃ and 1340℃, both in H₂ atmosphere and in vacuum for various sintering time. The fully densified structure could be obtained only by the sintering at the temperature above 1340℃, or by prolonging the sintering time at 1320℃. The heat treatment behavior of a directly sintered P/M HSS was similar to that of a wrought HSS, so far as the alloying components were fully homogenized during sintering process. The microstructure of the sintered, quenched or tempered high speed steel was also observed in order to elucidate the relationship between the structure and properties of the sintered high speed steel. It could be cautiously concluded that the directly sintered HSS. prepared by normal sintering process could be used supplementary for the production of near net shape HSS part, so far as the more finer Fe-powder would be used and the sintering might be carried out at the optimal temperature. |
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