| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel for a plastic molding die, which balances machinability with weldability. SOLUTION: This steel for the plastic molding die is a pre-hardened steel superior in machinability and weldability for the plastic molding die, has a composition comprising 0.1-0.30 mass% C, 0.25 mass% or more but less than 0.5 mass% Si, 0.5-2.0 mass% Mn, 0.03 mass% or less P, 0.005-0.080 mass% S, 0.2-2.5 mass% Cr, 0.15 mass% or less Mo, 0.01-0.25 mass% V, 0.001-0.020 mass% Al and 0.01 mass% or less O, while satisfying 2.0-3.0 mass% Mn+ Cr+2×Mo, and the balance substantially Fe, has a ferrite structure and a pearlite structure, which occupy 80% or more of a total structure by area rate, has Brinell hardness (an HB value) of 156-217, and has a BH value of 550 or less, which is shown in the following expression: BH value=326+847.3×C +18.3×Si-8.6×Mn-12.5×Cr. COPYRIGHT: (C)2003,JPO
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