PURPOSE: To heat uniformly a steel slab with good thermal efficiency without uneven temp. by using heat resistant alloy rails having a specific construction on water cooling pipes for the hearth rails of a walking beam type heating furnace for the steel slab.

CONSTITUTION: A hearth rail 3 for a slab in a walking beam furnace for heating a steel slab is made of a heat resistant Fe-Ni-Cr alloy and is attached onto a water cooling skid pipe 2 by fitting loosely holding pieces 9, 9 into the hollow grooves 10, 10 provided to the rail 3. The area in the top part of the rail 3 is decreased and a hollow groove 5 is provided to said part to decrease the contact area with a slab 4. The rail is made into the sectional shape consisting of an upper vertical face X, the inclined face Y below the same and a lower vertical face Z. A recess 6 is provided therein and alumina 8 or the like which is a heat insulating material is packed therein. The slab 4 has the smaller contact area with the rail 3 and the temp. difference between the slab 4 and the rail 3 is eliminated by the heat insulating material 8. The slab is thus uniformly and quickly heated to the prescribed temp.