Steel structure for hydrogen gas, mehtod for producing hydrogen storage tank, and method for producing hydrogen line pipe (as amended)

Abstract

Provided is a steel structure for hydrogen gas such as a hydrogen storage tank or a hydrogen line pipe which achieves a lower fatigue crack propagation rate in a high-pressure hydrogen atmosphere than steels used in the related art and has high hydrogen embrittlement resistance. The steel structure for hydrogen gas, which has high hydrogen embrittlement resistance in high-pressure hydrogen gas, has a steel microstructure including any one of 10% to 95% of bainite on an area-ratio basis, 10% to 95% of martensite on an area-ratio basis, and 10% to 95% of pearlite on an area-ratio basis, with the balance being substantially ferrite.

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         14 . A steel structure for hydrogen gas, the steel structure comprising a steel microstructure including any one of 10% to 95% of bainite on an area-ratio basis, 10% to 95% of martensite on an area-ratio basis, and 10% to 95% of pearlite on an area-ratio basis, with the balance being substantially ferrite. 
     
     
         15 . The steel structure for hydrogen gas according to  claim 14 , the steel structure having a steel composition containing, by mass, C: 0.05% to 0.20%, Si: 0.05% to 0.50%, Mn: 0.5% to 2.0%, Al: 0.01% to 0.10%, N: 0.0005% to 0.008%, P: 0.05% or less, S: 0.01% or less, and O: 0.01% or less, with the balance being Fe and inevitable impurities,
 wherein the steel microstructure includes 10% to 95% of bainite on an area-ratio basis with the balance being substantially ferrite.   
     
     
         16 . The steel structure for hydrogen gas according to  claim 14 , the steel structure having a steel composition containing, by mass, C: 0.05% to 0.35%, Si: 0.05% to 0.50%, Mn: 0.5% to 2.0%, Al: 0.01% to 0.10%, N: 0.0005% to 0.008%, P: 0.05% or less, S: 0.01% or less, and O: 0.01% or less, with the balance being Fe and inevitable impurities,
 wherein the steel microstructure includes 10% to 95% of martensite on an area-ratio basis with the balance being substantially ferrite.   
     
     
         17 . The steel structure for hydrogen gas according to  claim 14 , the steel structure having a steel composition containing, by mass, C: 0.05% to 0.10%, Si: 0.05% to 0.50%, Mn: 0.5% to 2.0%, Al: 0.01% to 0.10%, N: 0.0005% to 0.008%, P: 0.05% or less, S: 0.01% or less, and O: 0.01% or less, with the balance being Fe and inevitable impurities,
 wherein the steel microstructure includes 10% to 95% of pearlite on an area-ratio basis with the balance being substantially ferrite.   
     
     
         18 . The steel structure for hydrogen gas according to any one of  claims 15  to  17 , wherein the steel composition further contains at least one group selected from the groups A and B consisting of:
 Group A: one or more elements selected from Cu: 0.05% to 1.0%, Ni: 0.05% to 2.0%, Cr: 0.1% to 2.5%, Mo: 0.05% to 2.0%, Nb: 0.005% to 0.1%, V: 0.005% to 0.2%, Ti: 0.005% to 0.1%, W: 0.05% to 2.0%, and B: 0.0005% to 0.005% by mass 
 Group B: one or more elements selected from Nd: 0.005% to 1.0%, Ca: 0.0005% to 0.005%, Mg: 0.0005% to 0.005%, and REM: 0.0005% to 0.005% by mass. 
 
     
     
         19 . A method for producing the hydrogen line pipe, the method comprising heating a steel material having the steel composition according to any one of  claims 15  to  17  to an Ac 3  transformation temperature or more, followed by hot rolling; and subsequently performing cooling from an Ar 3  transformation temperature or more to 600° C. or less at a cooling rate of 1° C./sec. to 200° C./sec. 
     
     
         20 . A method for producing the hydrogen line pipe, the method comprising heating a steel material having the steel composition according to any one of  claims 15  to  17  to an Ac 3  transformation temperature or more, followed by hot rolling; performing quenching from an Ar 3  transformation temperature or more to 250° C. or less at a cooling rate of 1° C./sec. to 200° C./sec; and subsequently performing tempering at an Ac 1  transformation temperature or less. 
     
     
         21 . A method for producing the hydrogen storage tank, the method comprising forming a steel material having the steel composition according to any one of  claims 15  to  17  into a predetermined shape, followed by heating to an Ac 3  transformation temperature or more; performing quenching from an Ar 3  transformation temperature or more to 250° C. or less at a cooling rate of 0.5° C./sec to 100° C./sec; and subsequently performing tempering at an Ac 1  transformation temperature or less. 
     
     
         22 . A method for producing the hydrogen line pipe, the method comprising heating a steel material having the steel composition according to  claim 18  to an Ac 3  transformation temperature or more, followed by hot rolling; and subsequently performing cooling from an Ar 3  transformation temperature or more to 600° C. or less at a cooling rate of 1° C./sec. to 200° C./sec. 
     
     
         23 . A method for producing the hydrogen line pipe, the method comprising heating a steel material having the steel composition according to  claim 18  to an Ac 3  transformation temperature or more, followed by hot rolling; performing quenching from an Ar 3  transformation temperature or more to 250° C. or less at a cooling rate of 1° C./sec. to 200° C./sec; and subsequently performing tempering at an Ac 1  transformation temperature or less. 
     
     
         24 . A method for producing the hydrogen storage tank, the method comprising forming a steel material having the steel composition according to  claim 18  into a predetermined shape, followed by heating to an Ac 3  transformation temperature or more; performing quenching from an Ar 3  transformation temperature or more to 250° C. or less at a cooling rate of 0.5° C./sec to 100° C./sec; and subsequently performing tempering at an Ac 1  transformation temperature or less.