溶融硝酸塩中における鋼材の腐食疲労挙動

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Corrosion fatigue behaviour of plant materials such as 21/4Cr-1Mo, SUH309 and S20C was investigated in a molten salt environment of (NaNO_2 40%, NaNO_3 7%, KNO_3 53%) at 723 K. The rotating bending fatigue strength at 4×10^7 cycles of 21/4Cr-1Mo steel in the molten salt environmen was 8 percent lower than the fatigue limit in air.The fatigue strength at 4×10^7 cycles of SUH309 in the moten salt environment was deteriorated by 27 percent. Corrosion fatigue cracks were initiated from corosion pits and propagated accompanying striation predominantly in the molten solt environment. The morphology of the corrosion products on the specimen surface was examined by X ray-diffractions. The major corrosion product of these steels was Fe_3O_4. It may be cncluded that the formation of corrosion pits at h initiation of fracture surface is the major cause of fatigue stregth decrease of these steels in a molten salt environment containing Cl^-. The corrosion fatigue strength of S20C steel was higher than the fatigue limit in air. This may be caused by the retardation of crack initiation from the hardened surface layer due to nitriding in a molten salt environment. Neither the initiation nor the propagation of stress corrosion cracking of these steels was observed in the molten salt environment during the initiation test up to 2880 hrs and the propagation test up to 2160 hrs in the stress intensity factor range K_<IO> of 248 and 372 MPa√<m>, respectively.
社団法人日本材料学会の論文
1989-12-15

溶融硝酸塩中における鋼材の腐食疲労挙動

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