METHOD FOR MANUFACTURING STEEL FOR PLASTIC MOLDING DIE

摘要

PROBLEM TO BE SOLVED: To improve specularity of a die while keeping the dimensional accuracy of the die after heat treatment.

SOLUTION: A method for manufacturing a prehardened steel for a plastic molding die includes: a first hardening step of keeping a steel material composed of a prescribed alloy composition at a hardening temperature being an austenite transformation point or higher and cooling it from the hardening temperature to 500°C at a cooling speed of 1-5°C/min; a second hardening step of cooling it from 500°C to 200°C at a cooling speed of 2.5-10°C/min; and a tempering step of tempering the steel material at 420-520°C. The cooling speed in the second hardening step is higher than the cooling speed in the first hardening step.

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