Spring steel and spring having superior corrosion fatigue strength
A high-strength spring steel and a spring are provided that have superior corrosion fatigue strength. The spring steel comprises, in mass percent, 0.35-0.55% C, 1.60-3.00% Si, 0.20-1.50% Mn, 0.10-1.50% Cr, and at least one of 0.40-3.00% Ni, 0.05-0.50% Mo and 0.05-0.50% V, the balance being substantially Fe and incidental elements and impurities.
1. A steel alloy comprising, in terms of percent by mass:
0.47 to 0.49% C;
2.10 to 2.40% Si;
0.40 to 0.50% Mn;
0.20 to 0.30% Cr;
0.40-0.60% Ni;
0.05-0.20% Mo and
0.05-0.20% V;
the balance being substantially Fe and incidental elements and impurities, and
wherein the following formulas (6)-(8) are satisfied:
0.730%≦C(%)+Mn(%)/6+Si(%)/24+Ni(%)/40+Cr(%)/5+Mo(%)/4+V(%)/14≦0.780% (6);
0.630%≦C(%)+Mn(%)/6+Si(%)/24≦0.670% (7); and
1.35%≦Si(%)−0.46C(%)−1.08Mn(%) (8).
2. The steel alloy according to claim 1 , wherein both of the following formulas (9) and (10) are also satisfied:
159C(%)−Si(%)+8Mn(%)+12Cr(%)≦82% (9) and
6.0C(%)−Si(%)−0.3Mn(%)+1.4Cr(%)≦1.0% (10).
3. The steel alloy according to claim 2 , wherein the lower limit value of formula (8) is 1.45%.
4. The steel alloy according to claim 3 , wherein the upper limit value of formula (9) is 0.81%.
5. The steel alloy according to claim 4 , wherein the lower limit value of formula (10) is 0.65%.
6. The steel alloy according to claim 5 , wherein the steel alloy further has 0.05% or less Cu.
7. A spring comprising the steel alloy of claim 6 .
8. The spring according to claim 7 , wherein the spring is a coil spring.
9. The steel alloy according to claim 2 , wherein the upper limit value of formula (9) is 0.81%.
10. The steel alloy according to claim 2 , wherein the lower limit value of formula (10) is 0.65%.
11. A spring comprising the steel alloy of claim 1 .
12. The spring according to claim 11 , wherein the spring is a coil spring.
13. The steel alloy according to claim 1 , wherein the lower limit value of formula (8) is 1.45%.
14. The steel alloy according to claim 1 , wherein after quenching and tempering, the steel alloy has the property that its number of corrosion endurance oscillating cycles is at least 45,000.
15. The steel alloy according to claim 1 , wherein after quenching and tempering, the steel alloy has the property that its Charpy impact value is at least 80 J/cm 2 .
16. The steel alloy according to claim 1 , wherein after quenching and tempering, the steel alloy has the property that its delayed fracture strength is at least 910 MPa.
17. The steel alloy according to claim 1 , wherein the spring steel has a Rockwell hardness of HRC 53 to 56.
18. The steel alloy according to claim 1 , wherein the steel alloy further has:
0.010% or less P,
0.010% or less S,
0.20% or less Cu,
0.005-0.030% Ti, and
0.0015-0.0025% B.
19. The steel alloy according to claim 1 , wherein the steel alloy further has 0.05% or less Cu.