| Microstructure and mechanical properties of 10Cr-MoVNbN steels with increasing nitrogen contents were investigated. The nitrogen contents of the steels were 0.025 wt%(N02) and 0.045 wt%(N05), respectively. After tempering, the microstructure of the steels consisted of the tempered martensite matrix and various precipitates(M_(23)C_6, Nb(C, N), Cr₂N, V(C, N)). V-rich fine precipitates(5-20 ㎚) observed in the N05 steel hindered the movement of dislocation and consequently delayed formation of subgrain during tempering. It is clarified by transmission electron microscopy that Cr₂N nitride starts to precipitate at a lower tempering temperature and to decompose at a higher tempering temperature in the N05 steel than in the N02 steel. With increasing nitrogen content, hardness, tensile strength, high temperature creep strength and creep rupture elongation increased, but impact property and minimum creep rate decreased. |
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