Nitrogen Sintering of High Speed Steel Processed by Starch Consolidation

Abstract

Two different high-speed steel (HSS) powders, M2 and T15 compositions, were evaluated in water-based processing by starch consolidation (SC) and sintering in a nitrogen atmosphere using different sintering temperatures. Materials were produced based on slurry compositions with different solids loading, 60.7 vol% for T15 and 61.5 vol% for M2. Shaped specimens were then sintered to near full density. T15 bodies were under-sintered at 1225°C whereas at 1240-1260°C a clear over-sintering by the presence of large grains and an extensive network of big carbides was found. M2 specimens reached optimum sintering temperature at 1275°C whereas an under-sintering at 1270°C and an over-sintering at 1280°C were achieved. Different alloy compositions and a varied degree of oxidation of the material during the water processing were considered as factors causing the different sintering performance for the both steels. These factors together with carbide to carbonitride transformation were also concluded to be responsible to the altering of the sintering temperatures compared to theoretically predicted by using Thermo-Calc©.