Article ID: ISIJINT-2019-293
A composition-modulated Co–Ni laminated plating has been developed to prolong the lifetime of molds to be employed in continuous steel casting. We have investigated the relationship between the laminated structure and the mechanical properties of the plating films. The tensile strength of as-plated film was enhanced by the thinned thickness of the constituent layers, while the elongation received no effect of the thickness change of the constituent layer and remained almost stable in the range from 3 to 5%. Heat treatment at 400°C have brought about the improvement both in the tensile strength and the elongation. The improvement in the elongation was as remarkable as reached 13% in the film composed of layers with a thickness of 0.8 µm. The layer with low Ni content had an hcp structure, and that with high Ni content produced two phases of the hcp and fcc structures in the as-plated state. By the heat treatment, the high Ni-content layer turned into the single fcc phase, while the low Ni-content layer kept the hcp phase, and accordingly, the film structure changed into the one where the lamination of the hcp and fcc layers was distinct. The fact that the fcc layers, which was easily deformed, were formed continuously in the lateral direction, was seemed to contribute to the significant improvement in the elongation after heat treatment.