BAR OR WIRE PRODUCT FOR USE IN COLD FORGING AND METHOD FOR PRODUCING THE SAME

摘要

A bar or wire product for use in cold forging, characterized in that it comprises a steel having the chemical composition, in mass %: C: 0.1 to 0.65 %, Si: 0.01 to 0.5 %, Mn: 0.2 to 1.7 %, S: 0.001 to 0.15 %, Al: 0.015 to 0.1 %, B: 0.0005 to 0.007%, P: 0.035 % or less, N: 0.01 % or less, O: 0.003 % or less and balance: Fe and inevitable impurities, and it has, in the region from the surface thereof to the depth of the radius thereof x 0.15, a structure wherein ferrite accounts for 10 area % or less and the balance is substantially one or more of martensite, bainite and pearlite, and the average hardness in the region from the depth of the radius thereof x 0.5 to the center thereof is less than that of the surface layer thereof by 20 or more of HV; and a method for producing the bar or wire product. The bar or wire product is excellent in the ductility after spheroidizing and thus allows the prevention of occurrence of cracks in a steel product during cold forging, which has conventionally been a problem in manufacturing structural parts for a machine by cold forging.