Threaded coupling for pipe

Provided is a threaded coupling for a steel pipe having excellent galling resistance and seal performance as a radial-seal type connector. With this threaded coupling a plating having a Vickers hardness of not less than 310 is applied to the screw portion of the box and the inner surface of the box corresponding to the seal portion, and the seal interference amount ratio of the seal part in the pipe circumferential direction is not less than 0.002 as calculated with δ/D, where D is the seal diameter, defined by the pin outer diameter at the seal point, which is the region on the outer circumferential surface of the nose part on the pin-side that first makes contact with the inner circumferential surface of the nose part on the box-side when the threaded engagement is established, and δ is the amount of interference as defined by the amount by which the diameter of the seal point is reduced when the diameter of the seal point is reduced by the box, when the threaded engagement is established.