Heat treatment method and assembly method for fitted component

An assembly method for a fitted component comprising:

• a heating step of heating a second steel component to a first temperature equal to or higher than a tempering temperature of the second steel component, the first temperature being higher than a temperature of a first steel component by a temperature difference for achieving shrink fitting, the first steel component being formed with a coating thereon, the second steel component subjected to a quenching treatment being formed with a first hole;
• and
• a shrink-fitting step of, in the first hole in a state of maintaining the temperature difference for achieving shrink fitting between the first steel component and the second steel component, inserting the first steel component into the first hole so that the coating passes through the first hole, inserting the first steel component into a second hole of a third component so that the coating is in sliding contact with the second hole, and shrink-fitting a part of the first steel component other than a part where the coating is formed in the first hole.