To solve the problem that when magnesium material is die-cast or injected, in the traditional steel for heat mold, the molten metal reacts to the mold in an early stage and hence the life of the mold is shortened.

Special steel containing chromium by 10-20 wt.%, with the hardness of HRC30 to HRC55 is used to form the mold, subsequently chromium nitride with thickness not more than 100 μm obtained by nitrification treatment is dissolved in the special steel surface to form a solid solution and a nitration hardened layer with surface hardness from Hv800 to Hv1300. The obtained mold has a sufficient structural rigidity as a mold as well as excellent in corrosion resistance and seizure-resistance of the magnesium against the molten metal.