Abstract
Kovar alloy now being used for glass sealing consists of a single γ phase at room temperature. But according to the phase diagram, two phases of α and γ may exist in the equiliburium state. Therefore when its Ms point is not so low under room temperature, the transformation from γ to α phase may take place during cold-working and may cause a decrease of workability by abnormal hardening. In this experiment the characteristics of work-hardening in unstable Kovar were examined by measuring the change of hardness with rolling and the stress-strain curve in tensile tests. An abnormal hardening was observed after about 40∼50% reduction in specimens with low nickel content. The hardening degree of such specimens was about 100%, while it was about a half in specimens with high nickel content, after about 80% reduction. The former specimens also showed about 40% increase of hardness by a low temperature annealing and a slight softening by a cold treatment. A nickel content over 29∼29.5% was necessary to prevent Kovar from hardening by transformation during cold-working.
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