| 摘要 |
<p>A heat-treated steel wire for a high strength spring, characterized in that it has a chemical composition, in mass %: C: 0.75 to 0.85 %, Si: 1.5 to 2.5 %, Mn: 0.5 to 1.0 %, Cr: 0.3 to 1.0 %, P: 0.015 % or less, S: 0.015 % or less, N: 0.001 to 0.007 %, W: 0.05 to 0.3 %, and balance: iron and inevitable impurities, and has a tensile strength of 2000 Mpa or more; and in that, with respect to spherical cementite carbide products in a microscopic examination area, products having a diameter of a corresponding circle of 0.2 νm or more account for 7 % or less of the area, products having a diameter of a corresponding circle of 0.2 to 3 νm are present in a density of 1 piece/νm2 or less, products having a diameter of a corresponding circle of more than 3 νm are present in a density of 0.001 pieces/νm2 or less; and in that the number of the grain diameter of an old austenite structure is 10 or more, a retained austenite structure accounts for 12 mass % or less, and the maximum diameters of a carbide product and an oxide product are both 15 νm or less. The steel wire for a spring has a high strength and also is excellent in coiling characteristics.</p> |
