A steel ring includes a locking component. The locking component is provided on an inner surface of a ring body in a protruding manner. The locking component includes locking teeth, and the locking tooth is sheet-like and includes a fixed part and a contact part. Multiple locking teeth constitute a first locking tooth group, and with regard to the locking teeth in the first locking tooth group, the distance between the fixed parts is smaller than the distance between the contact parts. Multiple locking teeth constitute a second locking tooth group, and with regard to the locking teeth in the second locking tooth group, the distance between the fixed parts is greater than the distance between the contact parts. The ring body has a first state and a second state. When the ring body is in the first state, the ring body is in an unclosed annular shape, and when the ring body is in the second state, the ring body is in a closed annular shape.