Si含有4340鋼の微細組織と機械的性質に及ぼす改良オーステンパーの影響

概要

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The effects of the modified austemper(designated MA)on the microstructure and mechanical properties of silicon-modified 4340 steel have been studied with the aim of developing a MA steel for ultrahigh strength applications. The microstructure of the MA steel consisted of triple phases of carbide-free upper bainite, light-tempered martensite and retained austenite. This microstructure was produced by a partial transformation at either 593 or 623K for a required time, followed by oil quenching and subsequent tempering at 473K after austenitization at 1173K(designated 593K-MA, 623-MA, respectively). Compared to the quenched and tempered steel, the 593K-MA treatment improved the fracture toughness(K_<IC>)at high strength level of 2000 MPa, owing to an increase in total elongation and also improved the Charpy impact energy. According 623K-MA treatment, its K_<IC> was dramatically developed at strength level of 1700 MPa, owing to a remarkable increase in total elongation and Charpy impact energy, as compared to the QT steel. Compared to the corresponding conventional austemper treatment, its K_<IC> becomes significantly increased with a remarkable increase in strength.
社団法人日本材料学会の論文
1995-04-15