PURPOSE: To manufacture a link chain having superior characteristics, by heating engaged part and parallel part to different temps. by induction heating under a specified condition while passing the link chain in cylindrical body, then passing in carburizing and nitriding gases to carburize and nitride only joint part of the chain.

CONSTITUTION: The link chain W is moved in an arrow direction in a cylindrical vessel 1 made of quartz. Inert gas is introduced from a lower inlet 4 of the vessel 1 and air therein is exhausted. Successively, carburizing gas such as propane and nitriding gas such as NH3 are blown from a lower part inlet 3, parallel part and joint part of the chain W are heated by an induction heating coil 2 to 900°C and further temp. higher than by 100W150°C respectively under condition of 8W400kHz frequency, 50W150kW out put, 20W60sec according to material quality of the chain W, only high temp. joint part is carburized and nitrided by passing in carburizing and nitriding gases, then it is rapidly cooled and quenched by a cooling fluid jetting jacket 6. Link chain superior in elongation and toughness at parallel part and strength and wear resistance at joint part is obtd.