Machine Structural Steel Excellent in Machinability and Strength Properties

Abstract

The invention provides a machine structural steel excellent in machinability and strength properties that has good machinability over a broad range of machining speeds and also has high impact properties and high yield ratio, which machine structural steel comprises, in mass %, C: 0.1 to 0.85%, Si: 0.01 to 1.5%, Mn: 0.05 to 2.0%, P: 0.005 to 0.2%, S: 0.001 to 0.15%, total Al: greater than 0.05% and not greater than 0.3%, Sb: less than 0.0150% (including 0%), and total N: 0.0035 to 0.020%, solute N being limited to 0.0020% or less, and a balance of Fe and unavoidable impurities.

1 . A machine structural steel excellent in machinability and strength properties comprising, in mass %:
 C, 0.1 to 0.85%,   Si: 0.01 to 1.5%,   Mn: 0.05 to 2.0%,   P: 0.005 to 0.2%,   S: 0.001 to 0.15%,   total Al: greater than 0.05% and not greater than 0.3%,   Sb: less than 0.0150% (including 0%), and total N, 0.0035 to 0.020%,   solute N being limited to 0.0020% or less, and a balance of Fe and unavoidable impurities.   
   
   
       2 . A machine structural steel excellent in machinability and strength properties according to  claim 1 , further comprising, in mass %, one or more of Ca: 0.0003 to 0.0015%, Ti: 0.001 to 0.1%, Nb: 0.005 to 0.2%, W: 0.01 to 1.0%, V: 0.01 to 1.0%, Mg: 0.0001 to 0.0040%, Zr: 0.0003 to 0.01%, REMs: 0.0001 to 0.015%, Sn: 0.005 to 2.0%, Zn: 0.0005 to 0.5%, B: 0.0005 to 0.015%, Te: 0.0003 to 0.2%, Bi: 0.005 to 0.5%, Pb: 0.005 to 0.5%, Cr: 0.01 to 2.0%, Mo: 0.01 to 1.0%, Ni: 0.05 to 2.0% and Cu: 0.01 to 2.0%.