| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot tool steel having a low thermal expansion coefficient, free from anisotropy in the thermal expansion coefficient, and excellent resistance to heat cracks even in a die with a complicated shape in which radius at the corner parts is reduced. SOLUTION: The hot tool steel has a composition comprising, by mass, 0.30 to 0.45% C, 0.05 to 0.25% Si, 0.50 to 0.70% Mn, 5.30 to 5.75% Cr, 3.00 to 3.50% Mo, 0.65 to 0.95% V, 0.45 to 0.75% Ni, 0.45 to 0.75% Co,≤0.005% S,≤0.0010% P and≤0.0050% W, and the balance Fe with inevitable impurities. The cleanliness of nonmetallic inclusions is controlled to≤0.005% in dA60×400, and to≤0.005% in dB60×400, the total area ratio of carbides and nonmetallic inclusions in an annealed material is controlled to≤0.004% in the particle diameter of >1μm, and to≥15.0% in≤1μm, and the aspect ratio is controlled to 1.0 to 1.3. COPYRIGHT: (C)2005,JPO&NCIPI
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