Steel sheet for liquefied hydrogen storage tank, method for producing same, and liquefied hydrogen storage tank

Abstract

Provided is a steel sheet for a liquefied hydrogen storage tank, said steel sheet having a chemical composition that satisfies C: 0.010-0.070 mass%, Si: 0.01-0.30 mass%, Mn: not more than 0.70 mass%, P: not more than 0.0050 mass%, S: not more than 0.0030 mass%, Al: 0.005-0.055 mass%, Ni: 8.0-9.5 mass%, and N: not more than 0.0050 mass%, with the balance being Fe and inevitable impurities, wherein the sum of the proportions of a martensite structure and a bainite structure in the entire structure is not less than 80 area%, retained austenite is contained, and the parameter X represented by prescribed formula (1) is not less than 0.29.

Claims

1. A steel sheet for liquefied hydrogen storage tanks having a chemical composition that satisfies the following: C: 0.010% by mass or more and 0.070% by mass or less, Si: 0.01% by mass or more and 0.30% by mass or less, Mn: 0.70% by mass or less, P: 0.0050% by mass or less, S: 0.0030% by mass or less, Al: 0.005% by mass or more and 0.055% by mass or less, Ni: 8.0% by mass or more and 9.5% by mass or less, and N: 0.0050% by mass or less, with the remainder being Fe and unavoidable impurities, the total proportion of martensitic and bainite structures in the overall structure being 80% by area or more, containing retained austenite, and having a parameter X represented by the following formula (1) of 0.29 or more. Here, a: amount of retained austenite (volume %) b: amount of solid-solution carbon in retained austenite (mass %) c: grain size (10) of crystal grains surrounded by large-angle grain boundaries with an orientation difference of 25° or more, as determined by EBSD －６ m) d: Represents the Mn content (mass %) in the steel.

2. The steel plate for a liquefied hydrogen storage tank according to claim 1, wherein parameter X is 0.31 or greater.

3. A liquefied hydrogen storage tank formed from a steel plate for liquefied hydrogen storage tanks according to claim 1 or 2.

4. A method for manufacturing a steel sheet for a liquefied hydrogen storage tank according to claim 1 or 2, comprising: using a steel material whose chemical composition satisfies C: 0.010% by mass or more and 0.070% by mass or less, Si: 0.01% by mass or more and 0.30% by mass or less, Mn: 0.70% by mass or less, P: 0.0050% by mass or less, S: 0.0030% by mass or less, Al: 0.005% by mass or more and 0.055% by mass or less, Ni: 8.0% by mass or more and 9.5% by mass or less, and N: 0.0050% by mass or less, with the remainder being Fe and unavoidable impurities; obtaining a rolled material by hot rolling with a total reduction ratio of 80% or more; and performing heat treatment on the rolled material by sequentially applying (a) to (c) below. (a) The rolled material is quenched by holding it at a temperature of 720°C to 820°C for 0.5 minutes to 40 minutes, and then water-cooled. (b) After the quenching, two-phase quenching is performed by holding it at a temperature of 610°C to 690°C for 5 minutes to 60 minutes, and then water-cooled. (c) After the two-phase quenching, tempering is performed by holding it at a temperature of 510°C to 600°C for 5 minutes to 60 minutes, and then water-cooled or air-cooled.

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