| 摘要 |
PROBLEM TO BE SOLVED: To provide a die for aluminum extrusion free from reduction in substrate hardness even if nitriding treatment is repeatedly executed. SOLUTION: The hardness of a hot tool steel as a die substrate is regulated to 50 to 53HRC, and this hot tool steel is subjected to nitriding treatment. As the nitriding treatment, gas nitriding of executing heating at 480 to 550 deg.C for 5 to 10hr in an NH3 -N2 atmosphere is exemplified. The NH3 -N2 atmosphere may be added with a gas having a carbon source. As for the die subjected to the nitriding treatment, the hot tool steel is used as the substrate, the hardness of the substrate after the nitriding treatment is regulated to 50 to 53HRC, the Vickers hardness of a surface nitriding layer is regulated to 1050 to 1150HV, the thickness of the surface nitriding layer is regulated to 0.025 to 0.15mm, and the thickness of a white layer is regulated to 4 to 8μm.
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