Microstructure Characteristics of 16MnDR Steel Welded Joint and Its Corrosion Behavior in Hydrofluoric Acid Environment
The welding joint of 16MnDR steel medium thickness plate nuclear lean material storage tank is made by pulse argon tungsten arc welding(P-TIG)for priming and submerged arc welding(SAW)for filling and covering.The bottom layer of P-TIG welding is acicular ferrite+sorbite,but the bottom layer filled by SAW is transformed into polygonal ferrite+vorm-like troostite.Through the welding joint in the 0.1 M hydrofluoric acid immersion corrosion test,the corrosion resistance of root pass after SAW filling degraded seriously was found,the reason is that microgalvanic corrosion occurs between the very fine lamellar structure of worm-like troostite in the corrosion solution,so that the troostite near the surface is equivalent to a massive cementite.Then the formation of corrosion galvanic of big cathode and small anode between worm-like troostite and periphery polygon ferrite accelerated the corrosion dissolution of ferrite,and then troostite loses support,loosens and falls off and finally forms corrosion pits on the macro.This discovery lays a theoretical foundation for the safe service of nuclear lean material storage tank and points out the direction for the optimization design of the subsequent process.
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