Abstract: An air conditioning system comprising a duct structure, an evaporator unit positioned downstream of an air inlet end of the duct structure, an air heater unit positioned downstream of the evaporator unit, an air entrance chamber formed between the evaporator unit and the air heater unit, an air distribution chamber formed between the air heater unit and an air outlet end of the duct structure, an air-flow proportioning door positioned between the air entrance chamber and the air heater unit and movable between a position fully shutting of a flow of air from the air entrance chamber to the air heater unit and a position allowing the air heater unit to be fully open to the air entrance chamber, a bypass passageway bypassing the air heater unit, an air-flow guide vane positioned aside the bypass passageway and movable between a position withdrawn from the bypass passageway and a position in the bypass passageway, and a vane drive mechanism intervening between the air-flow proportioning door and the air-flow guid

Abstract: Titanium alloy or cast titanium alloy is heat-treated in vacuum or a neutral atmosphere to convert the abnormal structure of the alloy to normal .alpha. or .alpha. + .beta. structure. The titanium alloy or cast titanium alloy thus heat-treated can have sufficiently good material characteristics by the ordinary successive heat treatments.