PURPOSE: To obtain the steel sheet which is used for the devices used under a high vacuum and requiring the prevention of magnetic field disturbance and is easy of surface polishing by specifying the composition of a high Mn steel and a method for pickling this steel, respectively.

CONSTITUTION: A steel having a composition consisting of, by weight, 0.01-0.60% C, 0.5-12.0% Cr, 15.0-34.0% Mn. 0.05-1.0% Si, 0.02-0.5% V, 0.005-0.2% N, and the balance Fe is used, by which magnetic permeability can be maintained at a low value. This steel is subjected, by the ordinary methods, to casting, hot rolling, and annealing and then cold-rolled. The resulting cold-rolled steel sheet is heat-treated at 900-1200°C, immersed in a salt mixture of caustic soda and sodium nitrate of 380-460°C for ≥40sec or longer, and then immersed in a 10-25% solution of sulfuric acid of 60-85°C. By this procedure, the oxide scale formed at the time of annealing can be removed without increasing surface roughness. By this method, the desired high Mn non-magnetic cold-rolled steel sheet having 0.015 or a lower magnetic permeability and 0.10μ or smaller surface roughness Ra can be obtained.