Effect of Carbon Additions on Sintering to Full Density of BT1 Grade High Speed Steel

Abstract

The cold pressing and vacuum sintering characteristics of two batches of BTl high speed steel water atomized powder were investigated. The powder particle sizes, shapes, and microstructures before and after annealing were compared. Relationships were established between compacting pressure and green density, die fill, and linear shrinkage after sintering. Carbon was mixed with both batches before sirttering, 0·3% to batch 1 and 0'15%' to batch 2. The sintered densities of both batches with and without added carbon, are reported for a'range of sintering temperatures between 1230 and 1340°C together with typical sintered microstructures and grain and carbide size 'measurements. Carbon, oxygen, and nitrogen contents were estimated at major steps in the process. The differences found between the sintering characteristics of two batches of the same grade of high speed steel having only slight differences in alloy content were larger than expected. The addition of carbon, however, was found to promote sintering in several ways as well as bringing the final composition up to the specified value: the residual porosity in both batches was eliminated, the temperature range extended over which maximum density was achieved, and the microstructure at the optimum sintering temperature improved. PM/0328