COMPUTER-AIDED-DESIGN OF SINTERABLE TOOL STEELS - TOWARDS IMPROVED SINTERABILITY AND IMPROVED MECHANICAL-PROPERTIES STARTING FROM WATER-ATOMIZED POWDERS

Background/aims: In a European Union supported project, the idea that the sintering window for a tool steel, i.e., temperature region where full density is reached with no distortion and a sound microstructure, corresponding to a 3-phase region, austenite + carbide + liquid, of t he multicomponent phase diagram, has been validated and exploited. An additional objective was to achieve sintering to full density as close as possible to 1150 degrees C, the current limit for continuous sinte ring furnaces. Methods: Using thermodynamic calculations, novel alloys have been designated, based on tungsten or molybdenum bearing iron-ba se quaternaries. Alloys have been processed following the more economi cal route of water atomisation/cold pressing/vacuum sintering/heat tre ating. Property assessment, include bend testing, tribological testing and cutting tests. The sintering windows were extended up to 40 degre es C and densification was achieved in some alloys at 1170 degrees C. Results and conclusions: The grades that come closest to the objective s of the study include a carbon-enriched T1 and novel compositions: a quaternary Fe- 1.3 C- 3.5 Cr- 14.1 Mo and a quinary Fe- 1.4 C- 4.0 Cr- 14.0 Mo- 8 Co. In correctly processed materials, grain size is typica lly 10/15 mu m and carbide size does not exceed 15 mu m, slightly more than in conventional wrought high-speed steels. Hardness ranges from 810 to 960 Hv. Friction wear resistance (pin on disc testing) was gene rally somewhat inferior to that of conventional grades, but vanadium-b earing grades behave better as the MC carbides are harder than the M(6 )C. Initial single point turning trials show characteristics comparaba le to or better than those of standard butt welded T1 and M2 tools at speeds up to 45 m/min.