Fracture Toughness of Double Austenitized AISI M2 High Speed Tool Steel

Abstract

Fracture toughness of double austenitized AISI M2 high speed steel has been studied using both fracture toughness testing and electron metallography. Double austenitization leads to a fine precipitation of M6C carbides with sizes in the range 0.10±0.05 µm and the volume fraction in the 1–6% range. At equal hardness levels double austenitized M2 yields lower KIC values compared with the one singly austenitized at 1220oC. As the austenitization temperature decreases the difference between these KIC values increases. The inferior fracture toughness of the double austenitized M2 is explained on the basis of the fine M6C precipitation in the martensitic matrix. It is shown that the critical parameter in determining the KIC is not the size of the carbides but their distribution and particularly their interparticle spacing.