The technique of austenitizing steel by heating rapidly through the Ac1 to Ac3 range, limiting the maximum temperature to the minimum required for complete austenitization and quenching immediately is discussed. Rapid austenitizing refines the austenite grain size if the initial microstructure is a fine aggregate, such as martensite or tempered martensite. Additional grain refinement usually results from two or more cycles and most steels hardenable by heat treatment become ultrafine grained and hence exhibit increased strength and toughness. Rapid austenitizing can also be applied, particularly to high-carbon steels, to develop a unique microstructure comprised of a uniform dispersion of very small carbide particles in an ultrafine grained martensitic matrix.
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