Phase and structure chances during the sintering of compacts of high-speedsteels obtained from powders with various rates of solidification

An investigation was made of the phase and structure transformations in com pacts of high-speed steel R6M5F3 powder fractions -630+50 mu m at the tempe rature of solid-phase (1160-1220 degrees C) and liquid-phase (1240 degrees C) sintering. The structure of the compacts was crystalline or quasicrystal line, depending on the degree of superheating and cooling rate of the melt during powder spraying. This was related to the presence of a cellular stru cture in particles of a critical size in the powder. Compacts of powder wit h the cellular structure experienced higher shrinkage during solid-phase si ntering as a result of structure relaxation and recrystallization. The driv ing force of these processes is the change in chemical potential arising fr om the decomposition of highly supersaturated metastable solid solutions, a nd the excess grain-boundary energy of the quasicrystalline matrix structur e.