PURPOSE: To obtain a tool for hot extrusion having a scale layer excellent in denseness characteristic, having long service life, and also having high strength with superior warkability, by subjecting a tool for hot extrusion made of low-alloy steel to heating and holding in an inert mixed-gas atmosphere of prescribed composition, to slow cooling down to a temp. right above the A2 transformation point, and then the quenching hardening.

CONSTITUTION: A tool for hot extrusion made of 3Cr-1Ni or 1Cr-3Ni low-alloy steel is heated and held at ≤1,000°C, e.g., 950°C in an inert-gas atmosphere which contains ≥5.0vol.% steam and 0.5W5.0vol.% O2 and in which he volume ratio of O2 to steam is regulated to ≤1/3. Subsequently, the above tool for extrusion heated and held as mentioned above is cooled slowly (e.g., furnace cooling, about 50°C/h cooling rate) down to a temp. right above the A2 transformation point (e.g., 795°C) in order to prevent cracking and then subjected to quenching hardening. As a result, the tool for hot extrusion having a dense scale having high resistance to wear, erosion, seizure, etc., and excellent in adhesive strength on the surface, also having high strength, and remarkably improved in service life can be obtained surely and stably with superior workability.