Masking device for a flat-screen color-display cathode-ray tube with a tensioned shadow mask made of Fe-Ni alloys

Masking device for a flat-screen color-display cathode-ray tube, comprising a support frame for a tensioned shadow mask and a tensioned shadow mask. The support frame is made of a hardened Fe-Ni alloy having a thermal expansion coefficient between 20° C. and 150° C. of less than 5x10Kand a yield stress Rp0.2 at 20° C. of greater than 700 MPa; the tensioned shadow mask is made of an Fe-Ni alloy having a thermal expansion coefficient between 20° C. and 150° C. of less than 3x10K; the Fe-Ni alloys are chosen so that: below a temperature T1, the mean expansion coefficient alpha20-T, between 20° C. and T, of the alloy of the support frame is greater than the mean expansion coefficient alpha20-T of the alloy of the shadow mask, and above T1 the coefficient alpha20-T of the alloy of the frame is less than the coefficient alpha20-T of the alloy of the shadow mask, where T1