Abstract: This case hardened steel has a composition including, in mass %: C: 0.05 to 0.45%; Si: 0.01 to 1.0%; Mn: over 0 to 2.0%; Al: 0.001 to 0.06%, N: 0.002 to 0.03%, S: over 0 to 0.1%, P: over 0 to 0.05%; and balance: Fe and inevitable impurities. Equation (1) described below and Equation (2) described below are satisfied in equiaxed zone, or Equation (3) described below is satisfied in columnar zone. Re=(Ae/Ao)×100?30%??Equation (1) (Cmin, 1/Co)?0.95??Equation (2) (Cmin, 2/Co)?0.

Abstract: This case hardened steel has a composition including, in mass %: C: 0.05 to 0.45%; Si: 0.01 to 1.0%; Mn: over 0 to 2.0%; Al: 0.001 to 0.06%, N: 0.002 to 0.03%, S: over 0 to 0.1%, P: over 0 to 0.05%; and balance: Fe and inevitable impurities. Equation (1) described below and Equation (2) described below are satisfied in equiaxed zone, or Equation (3) described below is satisfied in columnar zone. Re=(Ae/Ao)×100?30%??Equation (1) (Cmin,1/Co)?0.95??Equation (2) (Cmin,2/Co)?0.

Abstract: The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 ?m in a microstructure of the steel being not more than 5%.

Abstract: The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 ?m in a microstructure of the steel being not more than 5%.

Abstract: The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 ?m in a microstructure of the steel being not more than 5%.

Abstract: An object of the invention is to provide a steel having good fatigue life characteristics and acoustic characteristics by eliminating the harmful effects of oxide based inclusions. The object is attained by the following steel. A steel having at least a part comprising: REM of which amount meets formula (1); and REM-containing inclusions of which number meets formula (2); wherein the concentration of Al203 in the REM-containing inclusions is 30 mass % or less (including 0%); Formula (1); ?30<REM(ppm)?(T.O(ppm)×280/48)<50, Formula (2); number of REM-containing inclusions/total number of inclusions >0.8, wherein the inclusions of Formula (2) having an equivalent diameter of 1 ?m or more.

Abstract: The present invention provides steel superior in machinability comprised of, by wt %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.2 to 3.0%, P: 0.001 to 0.2%, S: 0.03 to 1.0%, T.N: 0.002 to 0.02%, T.O: 0.0005 to 0.035%, and the balance of Fe and unavoidable impurities, said steel satisfying one or both of Mn/S in the steel being 1.2 to 2.8 or an area ratio of pearlite over a grain size of 1 ?m in a microstructure of the steel being not more than 5%.

Abstract: The present invention is a steel, excellent in machinability, wherein forging workability is improved by suppressing the deterioration of mechanical properties in the direction in which the mechanical properties are the lowest, and more specifically, is a steel excellent in forgeability and machinability, characterized in that: the steel contains, in mass, C: 0.1 to 0.85%, Si: 0.01 to 1.5%, Mn: 0.05 to 2.0%, P: 0.003 to 0.2%, S: 0.003 to 0.5%, and Zr: 0.0003 to 0.01%; the following steel components are controlled in the following ranges respectively, in mass, Al: 0.01% or less, total O: 0.02% or less, and total N: 0.02% or less; the average aspect ratio of MnS grains is 10 or less and the maximum aspect ratio of those is 30 or less; and the balance of the steel components consists of Fe and unavoidable impurities.