The effect of heat treatment on hardness of a chromium-cobalt alloy

Abstract

The fabrication of Ticonium alloy casting was carried out with simultaneous temperature determinations. Subsequent use of the Kentron Micro-Hardness Tester for Knoop hardness determinations of the heat treated castings has been described. On the basis of the hardness data reported, it appeared that heat soaking is unnecessary and that the standard burnout time may be safely shortened by 45 minutes. In addition, the internal temperatures of the Ticonium castings had reached a temperature of approximately 500 ° C. after bench cooling for 30 minutes. This temperature is considerably lower than the temperature at which significant hardness changes occur. Therefore, it appears unnecessary to extend the bench coolling interval beyond 30 minutes. There are no statistically significant Knoop hardness variations between the as-cast specimens on the same Stellite casting. The optimum heat treatment temperature for the Ticonium alloy was found to be 700 °C. and the lowest Knoop hardness values were recorded when the heat treatment temperature approached the Ticonium alloy's solidus temperature. Maximum Knoop hardness values were attained after one-half hour of heat treatment of the Ticonium alloy at 700 °C.; the hardness remained essentially constant for specimens heat treated at that temperature for four hours. While the Knoop hardness was sufficiently increased by heat treatment to be statistically significant, the increase is not considered to be of clinical significance per se. Additional work is needed to ascertain the possible effect of heat treatment upon ductility.