| Quench and tempering heat treatment was evaluated for alleviating the brittle characteristics of the weld zone of flash butt welded Ni-Cr-Mo steel. From the study of the effects of transformed microstructure on the impact properties and fracture toughness of the weld zone, it was concluded that the microstrueture of quenched and tempered weld zone and that of the base metal were similar, and the fine ferrite and cementite structure produced by high temperature tempering improved charry V-notched impact strength and fracture toughness The finer prior austenite grain produced by low temperature austenitizing was found to contribute to superiority of these properties. However, as followed by low temperature tempering at which retained austenite existed, the coarser prior austenite existed, the coarser prior austenite grain produced by high temperature austenitizing was found to contribute superior fracture toughness compared to the finer one. A high temperature austenitizing followed by 350℃ tempering was found to show tempered martensite embrittlement in both K_IC and charpy V-notched impact strength. |
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