| 摘要 |
PROBLEM TO BE SOLVED: To provide a free-cutting steel for machine structural use having excellent machinability and high chip-breakability, and in which both are obtained in a good balance, and to provide a method of producing the steel. SOLUTION: A steel having a composition comprising, by weight, 0.05 to 0.8% C, 0.01 to 2.0% Si, 0.1 to 3.5% Mn, 0.01 to 0.2% S, 0.001 to 0.020% Al, 0.0005 to 0.02% Ca, 0.0005 to 0.01% O and 0.001 to 0.04% N, and the balance being Fe and inevitable impurities is melted. At this time, controlled deoxidization is conducted by operation meeting certain conditions so that a certain amount of "duplex inclusion" having a specific composition may be formed, and Ti and/or Zr is added to precipitate finely dispersed MnS inclusions with nuclei of Ti-oxide and/or Zr-oxide. The finely dispersed MnS inclusions must share a determined part of the total sulfide inclusions. COPYRIGHT: (C)2004,JPO
|
