HOT ROLLED STEEL BAR OR WIRE FOR COLD FORGING, AND MANUFACTURING METHOD OF STEEL WIRE FOR COLD FORGING

• Main Authors: OFUJI YOSHIHIRO, SUENO HIDEKAZU
• Format: Patent
• Language: English
• Published: 22.11.2012
• Subjects: ALLOYS; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKINGWITHOUT ESSENTIALLY REMOVING MATERIAL; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; FORGE FURNACES; FORGING; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; HAMMERING; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES,OTHERWISE THAN BY ROLLING; MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVINGMATERIAL; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; PERFORMING OPERATIONS; PRESSING METAL; PUNCHING METAL; RIVETING; TRANSPORTING; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To provide a hot rolled steel bar or wire excellent in cold forgeability and a γ grain coarsening prevention property.SOLUTION: The hot rolled steel bar or wire includes by mass: 0.1-0.3% of C; 0.05-1.0% of Si; 0.4-2.0% of Mn; 0.003-0.05% of S; 0.5-3.0% of Cr; 0.010-0.025% of N; 0.02-0.05% of Al; and a remainder consisting of Fe and impurities, has a chemical composition in the impurities of P≤0.025%, Ti≤0.003%, and O≤0.002%, consists of a ferrite and bainitic structure or a ferrite, bainite, and pearlite structure, has a metal structure in which a bainite structural percentage>70%, and a ferrite average particle diameter≤40 μm, wherein the Al amount precipitated as AlN in a region from the surface of the steel bar or wire to 1/5 of the radius and a region from the center part to 1/5 of the radius is ≤0.010%, and the number density of AlN of the diameter≥100 nm is ≤5 piece/100 μm.