| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot tool steel which has improved machinability while maintaining characteristics relating to a die life such as toughness and heat check resistance. SOLUTION: The free cutting hot tool steel comprises, by mass, 80 to 96% Fe, 0.3 to 0.6% C, 0.02 to 2% Si, 0.1 to 3% Mn, 0.005 to 0.05% S, 3.5 to 6.5% Cr, 0.3 to 5% Mo+1/2W, 0.05 to 2.5% V, 0.001 to 0.02% Al, 0.0005 to 0.01% Ca, 0.001 to 0.01% Mg and 0.0005 to 0.01% O. Also, the number of inclusions with double structure consisting of an oxide nuclear part and a Ca-containing sulfide phase part formed therearound is≥5 pieces per field area of 3.5 mm<SP>2</SP>. Also, the content of Ca in the sulfide phase part composing the inclusions with double structure is 1 to 10%. COPYRIGHT: (C)2004,JPO&NCIPI
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