Strength-ductility Trade-off Design And Corrosion Behavior Research Of 9Cr ODS Steels

9Cr ODS steel is an important candidate material for key components of advanced nuclear energy systems due to its excellent radiation resistance and creep properties at high temperature.At present,its high DBTT and low impact toughness affect its long-term safe service in the reactors.Therefore,one of the key problem is to achieve the strength-ductility trade-off of 9Cr ODS steel.In addition,due to the low Cr content and poor corrosion resistance of 9Cr ODS steel,how to improve its corrosion resistance has become another key problem to be solved in its engineering application.In view of the above problems,adding A1 to improve the strength-ductility trade-off and corrosion resistance of 9Cr ODS steel are proposed in this study.In this paper,two kinds of 9Cr ODS steel were prepared by mechanical ball milling and hot isostatic pressing,namely 9CrTi ODS steels with 0.4Ti and 9CrAl ODS steels with different Al content.For 9CrTi ODS steel,the effects of different heat treatment conditions on its microstructure and mechanical properties were studied.The results show that the effect of heat treatment on strengthening and toughening is not obvious,because the oxide dispersion particles in ODS steel are very stable during the heat treatment.Therefore,in order to further optimize the strength and toughness of 9CrTi ODS steel,it was found that the homogeneity of oxide precipitates was significantly improved by doubling the ball-to-powder weight ratio,and the arrangement of fracture dimples was very uniform.The room temperature tensile strength of 9CrTi ODS steel reached about 1 GPa,and the elongation was 12.3%.For 9CrAl ODS steel,the influence of different A1 content(0.4?8.0 wt.%)on its microstructure and mechanical properties was studied.It was found that with the increase of A1 content,the characteristics of double grain size distribution are becoming more and more obvious.The strength-toughness trade-off of 9CrAl ODS steel could be achieved by the mechanism of back stress strengthening.At the same time,a two-step ball milling process for Al-ODS-containing steel was put forward according to the in-depth study of high aluminum content(8.0 wt.%)ball milling powder.The room temperature Chapy impact test showed that the impact energy of Al-added ODS steel prepared by two-step method is 59.23 J(55×10×5 mm3,V-notch),and the preparation of 0.5 mm cold-rolled plate can be realized by continuous cold rolling.The ultimate tensile strength and total elongation of the cold-rolled plate sample at room temperature can still reach 1.1 GPa and 10.4%even after annealing at 700? for 5 h.In addition,the supercritical water corrosion properties of 9Cr4.5Al ODS steel and 9Cr4.5A10.6Zr ODS steel were studied.Firstly,it was found that pre-oxidation treatment(850 ?/50h,air atmosphere)could make the sample produce 200 nm Al2O3 film,which could improve the initial corrosion resistance of the material.However,there were many coarse M23C6 clusters in 9Cr4.5Al ODS steel,which seriously deteriorated its corrosion resistance,while the carbon in 9Cr4.5AI0.6Zr ODS steel combined with Zr formed ZrC compound,which improved the corrosion resistance significantly.