Discontinuous Grain Growth Phenomena and Grain RefiningTreatments in High Speed Tool Steel
1977 Volume 63 Issue 1 Pages 80-89
Details
1977 Volume 63 Issue 1 Pages 80-89
A discontinuous austenite grain coarsing phenomenon of double hardened high speed tool steel and the procedure to control the grain gtowth on the second hardening have been studied under various heat treatment conditions. It is found that the discontinuous austenite grain growth is caused by disolusion of metastable carbides which have precipitated as a fine dispersion during the early stage of second hardening and that the grain coarsing on the double hardening can be controlled by intermediate heat treatment, i. e., rapid colling from α zone just under Ac1 or γ zone just above Ac3.
A heat treatment that the high speed tool steel of 6-5-4-2 type is quenched from γ zone just above Ac3 followed by heating at α zone just under Ac1, is effective for preventing the discontinuous austenite grain growth and for refining austenite grain on subsequent austenitization.
