Quenching is a heat treatment process that involves heating the steel to a temperature above the critical temperature Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel), holding it for a period of time to fully or partially austenitize the steel, and then Rapidly cool it to a temperature lower than Ms at the critical cooling rate for martensitic (or bainite) transformation (or isothermal near Ms). Sometimes, quenching also requires solid solution treatment of materials such as aluminum alloys, copper alloys, titanium alloys, and tempered glass; or heat treatment involving rapid cooling processes.