The Study On Corrosion Behavior Of CLAM Steel Welded Joints In Dynamic Lead-Bismuth Alloy At 550?

In order to propel the safe application of fusion energy, a great amount of research on fusion reactor design and fabrication has been accomplished by many research teams. It is generally believed that in the future fusion demonstration power plant and commercial fusion power plant, the liquid metal are considered as cladding modules breeder and a coolant material due to the good physical and chemical properties, and the low activation ferritic/martensitic steel(RAFM) is generally considered as the primary candidate structural material for blanket components. China Low Activation Martensitic(CLAM) steel, a type of RAFM steel with China's independent intellectual property rights, composition and performance optimization is considered to be a very promising candidate material for C hina future fusion reactor structural. Fusion welding is consid ered to be a key technology to obtain good quality of C ladding member, C LAM steel welded joints are usually accompanied by thick martensite lath and large residual stress, which may make t he corrosion behavior of welded joints different from the parent metal and more complicated. During the operation of fusion reactors, the cladding structure materials need to bear the high neutron flux and work with liquid phase LBE for a long time. Therefore, according to the working conditions of the CLAM steel structure, it is of great significance to improve the corrosion resistance of the weld zone in high temperature liquid LBE to improve the service life of the structure materials.In this paper, CLAM steel was welded by tungsten inert gas(TIG) welding, and the corrosion behavior of the welded joints in flowing liquid lead bismuth eutectic alloy was investigated at 550? for 1000 hour, and the corrosion testing device was developed independently by our research group. The main research contents were the effects of the relative flow rates and heat treatment process on corrosion resistance of CLAM steel welded joints, the flow rate was 1.70m/s, 2.31m/s, 2.98m/s respectively, and the heat treatment process was without post weld heat treatment, 710?/0.5h, 760?/0.5h, 810?/0.5h, 760?/1.5h, 760?/2.5h. The studies found:In the dynamic corrosion test, the surface of CLAM steel welded joints were corroded significantly, a protective double layer oxide film which consists of Fe3O4 outer layer and FeCr2O4 inner layer was formed on surface of all the samples. The Pb, Bi infiltrated into the outer oxide layer, generated a large amount of PbFe4O7. Corrosion resistance of the heat affected zone was superior to the weld zone. The main corrosion was oxidation corrosion and erosion corrosion, the oxidation corrosion was diffusion migration process of elements Fe, Cr, O, Pb, Bi. The rate of oxidation corrosion decreased with time, erosion corrosion was the main form of liquid metal corrosion. The increase of relative flow rates accelerated diffus ion element migration and new Bi-Fe-O generated on the surface at 2.98m/s. Meanwhile, with the relative flow rates increasing, especially reached 2.31m/s and above, the erosion corrosion was more serious to the outer oxide layer, and the tendency of cracks in the inner oxide layer was also growing. At 2.98m/s, with tempering temperature increasing, corrosion resistance of the samples firstly increased and then decreased, the corrosion properties of the specimen was best at 760?. At 2.31m/s, with the extension of the tempering time, the corrosion resistance of specimens didn't exhibit a uniform trend, considering the properties of mechanical and corrosion resistance, the best tempering time was about 1.5 hour.Corrosion studies have shown that the effect of relative velocity on the corrosion process is a complex process: when the rate is too low, can't reach the mass transfer and cooling effect; while the flow rate is too high, affecting the life of structural materials. The post weld heat treatment has significantly improved the corrosion resistance of C LAM steel welded joints, and 760oC/1.5h is the best. The decisive factor of the corrosion resistance is the Martensite morphology, evenly distributed and homogeneous fine martensite and carbide precipitated at grain boundary of martensite can significantly improve the corrosion resistance of welded joints, and extending the service life of CLAM steel in fusion reactors.