High-Mn steel and method of producing same

A high-Mn steel comprising:

• a chemical composition consisting of, in mass %,
• C:
• 0.100% or more and 0.700% or less,
• Si:
• 0.05% or more and 1.00% or less,
• Mn:
• 20.0% or more and 35.0% or less,
• P:
• 0.030% or less,
• S:
• 0.0070% or less,
• Al:
• 0.010% or more and 0.070% or less,
• Cr:
• 0.50% or more and 5.00% or less,
• N:
• 0.0050% or more and 0.0500% or less,
• O:
• 0.0050% or less,
• Ti:
• 0.005% or less,
• Nb:
• 0.005% or less, and
• optionally at least one group selected from the following (A) to (B);
• (A) one or more selected from
• Cu:
• 0.01% or more and 0.50% or less,
• Mo:
• 2.00% or less,
• V:
• 2.00% or less, and
• W:
• 2.00% or less;
• (B) one or more selected from
• Ca:
• 0.0005% or more and 0.0050% or less,
• Mg:
• 0.0005% or more and 0.0050% or less, and
• REM:
• 0.0010% or more and 0.0200% or less,
• with a balance consisting of Fe and inevitable impurities;
• and
• a microstructure having austenite as a matrix,
• wherein in the microstructure, a Mn concentration of a Mn-concentrated portion is 38.0% or less, and an average of Kernel Average Misorientation value is 0.3 or more,
• yield stress is 400 MPa or more,
• absorbed energy vE−196 in a Charpy impact test at −196° C. is 100 J or more, and
• percent brittle fracture is less than 10%, and
• wherein the high Mn steel has a surface roughness Ra of 200 μm or less.