| 摘要 |
PROBLEM TO BE SOLVED: To improve resistance to seawater pitting corrosion and crevice corrosion by specifying the composition of elements and applying specific heat treatment. SOLUTION: A casting is used for a suction 1, an impeller 2, and a bearing 4, and its material has a chemical composition consisting of, by weight, <=0.03% C, <=1.50% So, <=1.50% Mn, <=0.04% P, <=0.03&% S, 4.50-8.50% Ni, 21.00-26.00% Cr, 2.50-4.00% Mo, 0.08-0.03% N, and the balance Fe, and further, heat treatment is applied at 950-1250 deg.C for 1hr and the amount of ferrite at that time is requlated to <=70% by area ratio. A rolled steel is used for a main shaft 3, and its material has a composition almost identical with that of the above members and similar heat treatment is applied. By this heat treatment, the pitting corrosion potential of the material can be increased and corrosion resistance can be improved, and the frequency of maintenance and administration against pitting corrosion and crevice corrosion can be reduced.
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