| Lead-bismuth eutectic alloy(LBE)is an important candidate material for the accelerator driven sub critical system(ADS)and lead cooled fast reactor,and it is also the candidate material for spallation target of ADS system.Many parts of the ADS system,such as the nuclear main pump impeller,pipe bend and pipe joints at the junction of the flow,are manufactured and assembled by means of melt welding.These parts will produce serious cavitation corrosion when the liquid lead bismuth alloy flows in the pipeline at high speed.China low activation martensitic(CLAM)steel is a kind of low activation Ferritic / martensitic steel(RAFM steel),which is widely regarded as the preferred structural steel material for the ADS system and the future fusion reactor.The microstructure of CALM steel weld bead is coarse and uneven lath martensite structure,which would be the weak area of cavitation corrosion resistance in the whole cooling reflux pipeline of ADS.Therefore,it is necessary to study the cavitation corrosion of CLAM steel welded joint in liquid lead bismuth alloy in order to provide more theoretical basis for the application of ADS system in the future.In this paper,the first batch of CLAM steel base material is used as filler material,and the manual TIG plate butt welding of 5mm thick CLAM steel plate is carried out.Using the selfdesigned liquid metal cavitation erosion device,the cavitation erosion of CLAM steel weld bead and base metal in liquid LBE at 550? was then studied.By measuring the specimen surface morphology,roughness and depth of corrosion pit after different cavitation erosion time,and combining these with the microstructure and mechanical properties of weld bead and base metal,we studied the cavitation erosion process,corrosion mechanism and difference of corrosion resistance of weld bead and base metal in liquid LBE.The results showed that the surface roughness and the average corrosion pit depth of CLAM steel weld and base metal have been accelerated with the increase of cavitation erosion time.The cavitation erosion process in liquid LBE was including the incubation period and rising period.The cavitation erosion resistance of base metal was much better than that of the weld bead in the cavitation corrosion process.Through observing the changes of elements in the cross section of the weld specimens after cavitation corrosion and static corrosion for the same time,we found that the dissolution and oxidation corrosion and the cavitation erosion in liquid LBE could promote each other's corrosion process,and the combining effect could cause great damage on the surface of the specimens.This is also the main reason for that the cavitation erosion process in liquid LBE was including the incubation period and the rising period.Post weld heat treatment is the most direct and effective method to improve the performance of weld bead,and the weld bead with different heat treatments would have different mechanical properties,so this paper established several different post weld heat treatment schemes and studied the effect to the cavitation erosion resistance of CLAM steel weld bead.The test results showed that: after quenching and tempering treatment,the weld bead of CLAM steel was fine and uniform tempered martensite structure without ? ferrite,and the comprehensive mechanical property of the steel was recovered to the base material level,so the cavitation erosion resistance after PWHT was the best.The cavitation erosion resistance of the weld bead was improved to different degrees after tempering at different temperatures.After 760? tempering,the impact toughness of weld bead improved,and the high surface hardness and tensile strength remained almost unchanged,which were better than that after 710? tempering and 810? tempering,so the cavitation erosion resistance of weld bead after 760? tempering is better than that after 710? tempering and 810? tempering. |
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