A method for joining a highly electroconductive core element (2) to a jacket element (1) made of refined steel. In said method, the electroconductive core element (2), such as a copper bar, and the joining agent element (3) are inserted in the jacket element (1), and at least the juncture area of the elements to be joined is thermally treated, so that there is created a metallurgical joint between the electroconductive core element (2) and the refined-steel jacket element (1).