Mechanical properties on high Cr-Mo steels at blevated temperature.; Tensile properties of high Cr-Mo steel forgings (250280mmt).

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This study was performed to examine the tensile properties of 9Cr-Mo steel forgings, which are promising as the candidate materials for steam generator of large scale fast breeder reactor the influence of thermal aging and sampling location/direction. These results are to be reflected on fundation of materials strength standard. Test materials are three kinds of 9Cr-Mo steel forgings (thichiness:250280mmt) such as Mod.9Cr-1Mo (F4,F8 heats), 9Cr-1Mo-Nb-V(G3 hrats), 9Cr-2Mo (H6 heats) steels. The heat treatment on the thermal aging were carried out at 500, 550C for 3000hours. Results obtained are summarized as follows. (1)Tensile properties were much about the same between Mod.9Cr-1Mo and 9Cr-1Mo-Nb-V Steel forgings. (2)Tensile strength of four materials at direction Z was slightly lower than that of direction L or C and there are no significant diffrence on the sampling location/direction. (3)Tensile strength of Mod.9Cr-1Mo steel and 9Cr-1Mo-Nb-V steel forgings after thermal aging for 3000hours was same as that of as-received ones. However, the strength of 9Cr-2Mo steel forging at high temperature dicreased because of aging effect. (4)The 0.2 percent yield stress and tensile strength of forged steels satisfied the PNC preliminary design standard values of Sy and Su, but inferior to plating and tubing steels. However, tensile strengh of Mod.9Cr-1Mo steel forging (F8 heat) at the lower temperature than 400C and 9Cr-2Mo steel forging after thermal aging were lower than that of preliminary values. These results were reflected to advance the specification of Mod.9Cr-1Mo steel thick forgings.