Yielding behavior of low expansion invar alloy at elevated temperature

An invar alloy is used for a shadow mask in a color picture or display tube (CPT or CDT) for its low coefficient of thermal expansion, but in practice distortion or deformation of the shadow mask sometimes occurs after mold-pressing formation. This implies that the formation facilities and parameters do not conform with the mechanical response of the material, and that the mechanical performance of the material has not yet been clearly understood using strain gages, tensile tests were carried out at elevated temperatures to determine the yielding behavior of the invar alloy. The main results show that the yield stress decreases by 55% with increasing heating temperature from about 20 to 180°C and then remains stable at 120–130 MPa for 180–220°C for specimens pre-annealed at temperatures ranging from 790 to 850°C. The plastic elongation at the same time increases with the annealing and heating temperatures. Thus, the pressing force and deformation temperatures can be evaluated as important parameters controlling the formation of the shadow mask