High strength steel wire for spring
View Patent ↗High strength steel wire for spring containing, by mass %, C: 0.67% to less than 0.75%, Si: 2.0 to 2.5%, Mn: 0.5 to 1.2%, Cr: 0.8 to 1.3%, V: 0.03 to 0.20%, Mo: 0.05 to 0.25%, W: 0.05 to 0.30%, and N: 0.003 to 0.007%, having a total of contents of Mn and V of 0.70%≦Mn+V≦1.27% and a total of contents of Mo and W of 0.13%≦Mo+W≦0.35%, limiting P: 0.025% or less, S: 0.025% or less, and Al: 0.003% or less, and having a balance of iron and unavoidable impurities, having a microstructure comprised of, by volume percent, over 6% to 15% of retained austenite and tempered martensite, having a prior-austenite grain size number of 10 or more, having a density of presence of spheroidal carbides with a circle equivalent diameter of 0.2 to 0.5 μm of 0.06 particles/μm 2 or less, having a density of presence of spheroidal carbides with a circle equivalent diameter of over 0.5 μm of 0.01 particles/μm 2 or less, and having a tensile strength of 2100 to 2350 MPa.
1. High strength steel wire for spring containing, by mass %,
C: more than 0.70 and less than 0.75%,
Si: 2.0 to 2.5%,
Mn: 0.5 to 1.2%,
Cr: 0.8 to 1.3%,
V: 0.03 to 0.10%,
Mo: 0.05 to 0.25%,
W: 0.05 to 0.30%, and
N: 0.003 to 0.007%,
having a total of contents of Mn and V of 0.70%≦Mn+V≦1.27% and a total of contents of Mo and W of 0.13%≦Mo+W≦0.35%,
limiting
P: 0.025% or less,
S: 0.025% or less, and
Al: 0.003% or less, and having a balance of iron and unavoidable impurities, having a microstructure comprised of, by volume percent, over 6% to 15% of retained austenite and tempered martensite, having a prior-austenite grain size number of 10 or more, having a density of presence of spheroidal carbides with a circle equivalent diameter of 0.2to 0.5 μm of 0.06 particles/μm 2 or less, having a density of presence of spheroidal carbides with a circle equivalent diameter of over 0.5 μm of 0.01 particles/μm 2 or less, and having a tensile strength of 2100 to 2350 MPa.
2. High strength steel wire for spring as set forth in claim 1 , wherein the yield strength is 1470 to 1980 MPa.
3. High strength steel wire for spring as set forth in claim 1 or 2 , wherein a Vicker's hardness after heat treatment holding the wire at 500° C. for 1 hour is 570 or more.