PURPOSE: To improve the surface hardness by laminating the slab or the steel plate containing the same amount or more of C as that in this slab on the face and the back surface of the slab, inserting the laminated slab in a heating furnace, heating it therein, and remove the slab or the steel plate on the face and the back surface after withdrawn from the heating furnace, and hot rolling the slab.

CONSTITUTION: Heating can be performed without exposing the slab surface to the decarburizing atmosphere by laminating a steel plate of a slab on the face and the back surface of the slab. Either the steel plate or the slab may be laminated on the face and the back surface of the slab, and different kind of the laminated one on the face and the back surface of the slab may cause no problems. What matters is the amount of C in the steel plate or the slab to be laminated. That means, C is diffused, and to prevent the decarburization due to the diffusion, the amount of C in the steel plate or the slab to be laminated is required to be the same as that in the slab to be laminated therebetween or more. The steel obtained in this manner can be used as the wear resistant steel, the steel of high strength for friction grip bolt, etc., where the surface hardness is required.