THERMAL TREATMENT OF FORGINGS FROM HIGH-STRENGTH CORROSION-RESISTANT MARTENSITE STEEL Russian patent published in 2015 - IPC C21D6/02 

FIELD: metallurgy.

SUBSTANCE: to provide the required strength category of metal with yield strength at least 800 MPa and to increase corrosion resistance of the steel forging containing in wt %: carbon 0.08-0.10, chrome 15.0-16.0, nickel 4.0-4.5, manganese 0.2-0.5, silicon max. 0.6, niobium 0.2-0.4, molybdenum 0.20-0.30, nitrogen 0.10-0.15, sulphur max. 0.020, phosphorous max. 0.025, iron and admixtures - rest, is subjected to homogenization at 1150°C with holding for 1.5 minutes per 1 mm of cross-section depth, and cooling in air, tempering at 650°C with holding for 6 minutes per 1 mm of cross-section depth, and cooling in air, hardening in oil at 1050°C with holding for 2 minutes per 1 mm of cross-section depth, and cooling in oil, further tempering at 600°C with holding for 4 minutes per 1 mm of cross-section depth, and cooling in air.

EFFECT: chemical composition of martensite steel in combination with heat treatment creates optimal steel structure required to ensure high operability of the propeller shafts under long operation, in particular during manufacturing of forgings for the propeller shafts with diameter up to 250 mm and length 9,0 m.

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