Experimental Study On Steam Oxidation Of Domestic Nuclear Grade 2.25Cr1Mo Steel And Its Welding Consumables

The steam generator is one of the most important components of sodium cooled fast reactor.Its heat exchange tube is mostly made of 2.25Cr1Mo steel in the established sodium cooled fast reactor at abroad.However,the lack of production experience of nuclear grade 2.25Cr1Mo steel and its welding consumables limits the development of sodium cooled fast reactor in China.To solve this problem,localization of those materials is in active progress.Oxidation of steam generator components in high temperature steam environment is an important factor affecting its safe operation.It is of great significance to carry out the research on steam oxidation resistance of those materials for promoting the localization of steam generator materials in fast reactor and accelerating the development of large-scale fast reactor in China.In this paper,long-term steam oxidation experiments were carried out on the domestic nuclear grade 2.25Cr1Mo steel and its welding consumables.Those samples were analyzed by various methods,including oxidation kinetics analysis,surface and cross-section oxide morphology observation,element and phase analysis.The oxidation kinetics of domestic nuclear grade 2.25Cr1Mo material approximately conformed to the parabolic law under the condition of high temperature steam(500?/17MPa)with dissolved oxygen content less than 20ppb.The outer oxide scale was composed of Fe3O4 and the inner oxide was a mixture of Fe3O4 and Fe3-xCrxO4.Small changes of chromium content would have a certain impact on the oxidation weight gain of domestic nuclear grade 2.25Cr1Mo material and the surface roughness would have an impact on the uniformity of the inner oxide film thickness of the material while the effect of growth stress caused by shape factors on the oxidation of the material was not observed.The oxidation resistance of the two kinds of welding wires increased with the increase of chromium content and the oxidation resistance of welding materials with different welding parameters increased with the increase of welding energy under the condition of high temperature steam(500?/0.1 MPa)with dissolved oxygen content of 8000ppb.The oxidation kinetics is approximately confirmd to the cubic law for all materials.The oxide film has a typical double-layer structure,and there are many flake like Fe2O3 oxides in the outer oxide film,while there are chromium rich Fe3-xCrxO4 oxides in the inner oxide film.