SHEET FROM STRUCTURAL CRYOGENIC HIGH-STRENGTH STEEL AND METHOD OF ITS PRODUCTION Russian patent published in 2025 - IPC C22C38/50 C22C38/48 C22C38/44 C22C38/42 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to production of sheets from structural cryogenic high-strength steel used for production of equipment intended for transportation and storage of liquefied natural gas. Continuously cast steel slab is produced containing the following components, wt.%: carbon 0.05-0.10, silicon 0.15-0.35, manganese 0.30-1.00, aluminium 0.02-0.05, chrome not more than 0.20, nickel 5.50-7.00, titanium from more than 0.025 to 0.035, sulphur not more than 0.003, phosphorus not more than 0.015, nitrogen not more than 0.012, arsenic not more than 0.08, copper from more than 0.40 to 1.00, molybdenum 0.10-0.20, niobium 0.02-0.06, the rest is iron and unavoidable impurities. Slab is heated and hot rolled to produce sheets and cooled to ambient temperature. Normalization of sheets by heating to temperature of 900-960 °C with subsequent holding for at least 1-2 min/mm and further cooling in air to ambient temperature. Sheets are quenched by heating to temperature of 700-750 °C with holding for at least 1-2 min/mm and subsequent cooling with water to ambient temperature and tempering at temperature of 600-720 °C with holding 1.0-5.5 min/mm and subsequent cooling in air to ambient temperature to obtain a structure which is a rack-type martensite of a dislocation type with finely dispersed cuprous precipitates and containing at least 5% of residual austenite along the boundaries of martensite crystals.

EFFECT: providing high strength properties and compliance with requirements for values of impact strength at cryogenic temperatures.

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