Color CRT mask frame, a steel sheet used therefor and a manufacturing method for the steel sheet, and a color CRT equipped with the frame

A color CRT mask frame manufactured by a method including the following steps:

• a step of shaping a steel sheet to form a color CRT mask frame member, the steel sheet having a steel composition consisting essentially of, in mass %,
• C:
• 0.03-0.30%, Si:
• at most 0.30%, Mn:
• 0.05-1.5%,
• P:
• at most 0.05%, S:
• at most 0.02%, Mo:
• 0.02-0.50%,
• V:
• 0.02-0.20%, Al:
• at most 0.10%, N:
• 0.0040-0.0200%,
• cu:
• 0-1.0%, Ni:
• 0-1.0%, Cr:
• 0-2.0%,
• W:
• 0-1.0%, B:
• 0-0.003%, Ti:
• 0-0.030%,
• Nb:
• 0-0.030%,
• and a balance of iron and unavoidable impurities, with Al≦(7.0)N, and having a metal structure in which the ferrite grain size is at most 15 micrometers and the ferrite volume ratio is at most 90%,
• a step of joining four mask frame members, at least one of which are the above-described mask frame members, to form a color CRT mask frame, and
• a step of performing blackening treatment of the color CRT mask frame which was formed at a temperature in the range of 450-680° C. to form a black film on the frame surface.

A color CRT mask frame manufactured by a method including the following steps:

• a step of shaping a steel sheet to form a color CRT mask frame member, the steel sheet having a steel composition consisting essentially of, in mass %,
• C:
• 0.03-0.30%, Si:
• at most 0.30%, Mn:
• 0.05-1.5%,
• P:
• at most 0.05%, S:
• at most 0.02%, Mo:
• 0.02-0.50%,
• V:
• 0.02-0.20%, Al:
• at most 0.10%, N:
• 0.0040-0.0200%,
• cu:
• 0-1.0%, Ni:
• 0-1.0%, Cr:
• 0-2.0%,
• W:
• 0-1.0%, B:
• 0-0.003%, Ti:
• 0-0.030%,
• Nb:
• 0-0.030%,
• and a balance of iron and unavoidable impurities, with Al≦(7.0)N, and having a metal structure in which the ferrite grain size is at most 15 micrometers and the ferrite volume ratio is at most 90%,
• a step of joining four mask frame members, at least one of which are the above-described mask frame members, to form a color CRT mask frame, and
• a step of performing stress relief annealing of the color CRT mask frame which was formed at a temperature in the range of 400-680° C.