발간논문

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Vol.38, No.3, 466 ~ 474, 2000
Title
Pesearch Paper / Mechanical Behavior : Effect of Intercritical Heat Treatment and Tempering Conditions on Toughness and Strength in Mn-Mo-Ni Low Alloy Steel
안연상Yeon Sang Ahn,오용준Yong Jun Oh,김홍덕Hong Deok Kim,김길무Gil Moo Kim,홍준화Jun Hwa Hong
Abstract
The effect of intercritical heat treatment (IHT) and tempering conditions on impact toughness and strength in a Mn-Mo-Ni low alloy pressure vessel steel (SA508 Gr.3 steel) has been investigated. The optimum condition of the IHT for toughness improvement was developed. The application of IHT resulted in the increase of ductility and upper shelf energy and in the decrease of strength and ductile-to-brittle transition temperature (DBTT). The modification of tempering conditions reduced the loss of strength resulting from the IHT and maximized toughness improvement. The beneficial effects from the IHT were consistently maintained in spite of the changes of heating and cooling rates. Additionally, the cause of the increase in toughness was investigated in relation to the microstructural change. The IHT produces a composite structure of hard martensite and soft tempered bainite. Tempering following IHT results in spheroidization of carbides and finer effective grain size, which enhance resistance to the brittle fracture.
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