Steel sheet for inner magnetic shield and method of producing the same, inner magnetic shield, and color cathode ray tube

A color cathode ray tube comprising an inner magnetic shield, wherein:

• the inner magnetic shield has a substantially truncated pyramidal body having a pair of short side members of a screen and a pair of long side members of a screen, and constructed such that said short side members are joined to said long side members at edge portions of the substantially truncated pyramidal magnetic shield;
• the inner magnetic shield is made of a steel sheet, a ratio of an anhysteretic magnetic permeability of the steel sheet in a rolling direction to an anhysteretic magnetic permeability of the steel sheet in a transversal direction being not higher than 0.7 or not lower than 1.4, and a higher value of the two anhysteretic magnetic permeability values in the rolling direction and in the transversal direction being not lower than 18000, or a ratio of an anhysteretic magnetic permeability of the steel sheet in the rolling direction to an anhysteretic magnetic permeability of the steel sheet in a transversal direction being not higher than 0.5 or not lower than 2.0, and a higher value of the two anhysteretic magnetic permeability values in the rolling direction and in the transversal direction being not lower than 18000;
• and
• the direction, in which the anhysteretic magnetic permeability of the steel sheet is said higher value, corresponds to the horizontal plane direction of said long side member and to the horizontal plane direction of said short side member.

An inner magnetic shield excellent in the shielding effect from geomagnetism used in a color cathode ray tube, the inner magnetic shield having a substantially truncated pyramidal body which has a pair of short side members of a screen and a pair of long side members of a screen, and constructed such that said short side members are joined to said long side members at edge portions of the substantially truncated pyramidal magnetic shield, wherein:

• the inner magnetic shield is made of a steel sheet, a ratio of an anhysteretic magnetic permeability of the steel sheet in a rolling direction to an anhysteretic magnetic permeability of the steel sheet in a transversal direction being not higher than 0.7 or not lower than 1.4, and a higher value of the two anhysteretic magnetic permeability values in the rolling direction and in the transversal direction being not lower than 18000, or a ratio of an anhysteretic magnetic permeability of the steel sheet in a rolling direction to an anhysteretic magnetic permeability of the steel sheet in a transversal direction being not higher than 0.5 or not lower than 2.0, and a higher value of the two anhysteretic magnetic permeability values in the rolling direction and in the transversal direction being not lower than 18000;
• and
• the direction, in which the anhysteretic magnetic permeability of the steel sheet is said higher value, corresponds to the horizontal plane direction of said short side member and to the horizontal plane direction of said long side member.

A method of manufacturing a steel sheet for inner magnetic shields excellent in a shielding effect from geomagnetism, comprising the steps of:

• hot rolling a steel slab consisting essentially of higher than 0.005% and not higher than 0.06% by weight of C, lower than 0.3% by weight of Si, not higher than 1.5% by weight of Mn, not higher than 0.05% by weight of P, not higher than 0.04% by weight of S, not higher than 0.1% by weight of Sol. Al, and the balance of Fe;
• cold rolling the resultant hot rolled steel band;
• continuously annealing the resultant cold rolled steel band at temperatures of 600° C. to 780° C. under a line tension not lower than 9.8 N/mm2;
• and
• tempering rolling the annealed steel sheet as required at an elongation rate not higher than 0.2%.