The martensite steel manufacturing method

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Provided is a method for producing martensitic steel which imparts ductility thereto while maintaining the excellent strength properties thereof, or in other words, which balances ductility and strength. This method for producing martensitic steel involves preparing an annealing material having a composition which : contains, in mass%, C in the amount of 0.18-0.30%, Al in the amount of 1-2%, V in an amount greater than 0 and not greater than 0.3%, Cr in the amount of 2-5%, Ni in the amount of 10.5-15%, with Ni≥7+3.5Al, Co in the amount of 5-7%, and Mo alone or Mo+W/2 in the amount of 1-4%; and contains selected elements consisting of B, Si, Mn, Ca, rare earth elements, Cu, and Nb, wherein B represents 0-50ppm, Si represents 0-0.4%, Mn represents 0-0.4%, Ca represents 0-500ppm, rare earth elements represent 0-500ppm, Cu represents 0-1%, and Nb represents 0-0.1%, with Fe and impurities constituting the remainder. This method for producing martensitic steel also includes a step for annealing, performing a solution treatment, performing a sub-zero treatment, and performing an age-hardening treatment. Therein, the sub-zero treatment is performed for 0.5 to 5 hours at a temperature range of higher than -50°C and not higher than 0°C.