Composite pressure vessel liner, composite pressure vessel, and method for producing composite pressure vessel liner

A composite pressure vessel liner that is made of a steel material including:

• a chemical composition containing, in mass %,
• C:
• 0.30% to 0.60%,
• Si:
• 0.01% to 2.0%,
• Mn:
• 0.5% to 3.0%,
• P:
• 0.0005% to 0.060%,
• S:
• 0.0001% to 0.010%,
• N:
• 0.0001% to 0.010%,
• Al:
• 0.01% to 0.08%,
• optionally one or more selected from the group consisting of Mo:
• 0.005% to 2.0%, Cr:
• 0.005% to 3.0%, and Ni:
• 0.005% to 3.0%, and
• optionally one or more selected from the group consisting of B:
• 0.0005% to 0.003%, Cu:
• 1.0% or less, and Ca:
• 0.005% or less,
• with the balance being Fe and inevitable impurities;
• and
• a metallic microstructure in which an area fraction of martensite at a position of ¼ of a wall thickness on an inner side is 30% or more, a total area fraction of martensite and bainite at the position of 1/4 of the wall thickness on the inner side is 95% or more, and a total area fraction of martensite and bainite in a wall thickness center part is 95% or more,
• wherein the composite pressure vessel liner has a wall thickness of 20 mm or more in a longitudinal center part, and a tensile strength of 850 MPa or more in the wall thickness center part.