| 摘要 |
Disclosed is a free-cutting steel for machine structural use which always exhibits desired machinability, particularly, machinability by cutting with cemented carbide tools. This free-cutting steel is produced by preparing a molten alloy of the composition consisting essentially of, by weight %, C: 0.05-0.8%, Si: 0.01-2.5%, Mn: 0.1-3.5% and O: 0.0005-0.01%, the balance being Fe and inevitable, and adjusting the addition amounts of Al and Ca in such a manner as to satisfy the above ranges, S: 0.01-0.2%, Al: 0.001-0.020% and Ca: 0.0005-0.02%, and the conditions of ÄSÜ/ÄOÜ: 8-40 ÄCaÜxÄSÜ: 1x10<-5> - 1x10<-3> ÄCaÜ/ÄSÜ: 0.01-20 and ÄAlÜ: 0.001-0.020% to obtain a steel characterized in that the area in microscopic field occupied by the sulfide inclusions containing Ca of 1.0 % or more neighboring to oxide inclusions containing CaO of 8-62% is 2.0x10<-4>mm<2> or more per 3.5mm<2>. |
