A Fundamental Study of Tool Steels Processed from Rapidly Solidified Powders.
Annual rept. Oct 80-Sep 81,
DREXEL UNIV PHILADELPHIA PA DEPT OF MATERIALS ENGINEERING
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Powders of T15 and Rex 25 have been gas atomized and screened to specific particle size fractions to provide a spectrum of solidification rates, including the rapid solidification regime. Powders were then consolidated to full density by hot isostatic pressing. Atomized, annealed and consolidated powders of T15 have been characterized by means of optical and electron microscopy, x-ray diffraction and hardness. To date, a limited characterization of T15 after consolidation and heat-treatment has been accomplished. Similar studies have been initiated on the cobalt-free Rex 25 tool steel. Cubic and hexagonal MC carbides in the form of interconnected networks are present in each size fraction of atomized powder. Carbide size decreases and particle hardness increases with decreasing particle size. The dependence of particle hardness on particle size is understood in terms of cooling rate, solid solution strengthening, the constituents and scale of the matrix and carbides, and the partitioning of alloying elements between matrix and carbides. After hot isostatic pressing, carbides are in the form of individual particles three carbides have been identified namely cubic MC, cubic M6C and cubic M23C6 in a matrix of alpha-ferrite. Carbide size increases as the isostatic pressing temperature increases and this results in a decrease in the hardness of the tool steel. For a given consolidation temperature, hardness is relatively independent of prior particle size fraction. Properties and performance will be assessed in terms of bend strength, C-notch impact, wear, grindability, life and dimensional control during heat-treatment.
- Physical Chemistry
- Properties of Metals and Alloys