Heat treatment of cobalt-chromium alloy wire.

This study shows that the ability of cobalt-chromium wire to resist permanent deformation is definitely affected by the temperature of heat treatment. For each temperature of heat treatment up to 1200 degrees F there is progressively greater resistance to permanent deformation; at temperatures of heat treatment above 1200 degrees F, however, there is a rapid decline in resistance to permanent deformation due to partial annealing. The maximum resistance to permanent deformation occurs from heat treatment in the temperature range of 1100 degrees to 1200 degrees F. A clinician desiring maximum resistance to permanent deformation from a .016 inches x .022 inches cobalt-chromium archwire should heat-treat the wire at 1100 degrees to 1200 degrees F for 5 minutes in a dental furnace. If the wire was in a highly work-hardened condition as were the wire specimens of this study, he could expect an increase in resistance to permanent deformation of approximately 174 percent. Heat treatment at lower temperatures could be used in situations requiring less than maximum resistance to permanent deformation. Heat treatment at 900 degrees F would give approximately a 95 percent increase in resistance to permanent deformation. Of course, heat treatment would not be indicated when the desired level of resistance to permanent deformation was not greater than the amount exhibited in the untreated wires of this study. When an electrical resistance heat-treatment unit and 950 degrees F temper-indicating paste were used, the clinician would expect increased resistance to permanent deformation similar to that seen in the wires heat-treated with a dental furnace at 800 degrees and 900 degrees F, i.e., about half of that obtained by the 1200 degrees F treatment. This study has determined the effects that various temperatures of heat treatment have on the resistance to permanent deformation of cobalt-chromium wire specimens which were formed into a specific pattern of loops. The following conclusions can be drawn from the results of this investigation: 1. Heat treatment at 1200 degrees F gives the maximum resistance to permanent deformation to .016 inches x .022 inches cobalt-chromium wire. 2. Increases in resistance to permanent deformation of approximately 95 percent and 174 percent may be expected from heat treatment of .016 inches x .022 inches cobalt-chrome wire at 900 degrees and 1200 degrees, respectively. 3. Wires, heat-treated with an electrical resistance unit using 950 degrees F temper-indicating paste, exhibit increases in resistance to permanent deformation similar to wires heat-treated in a dental furnace at 800 degrees and 900 degrees F.