At what temperature and duration is heat hardening typically performed?

Show Answers

Gradually heating to 750°C and then slowly cooling down to 0°CRapidly heating to 450°C followed by immediate quenchingHeating up to 250°C and maintaining for 15 to 30 minutesHeating at 750°C and then rapidly cooling to ambient temperature

Explanation

Heat hardening involves heating the material to approximately 250°C and holding it there for 15 to 30 minutes to improve hardness. Other options describe different heat treatment methods such as slow cooling or quenching at higher temperatures, which are not characteristic of heat hardening.