High-strength and high-ductility steel for spring, method for producing same, and spring
AssigneeNHK Spring Co., Ltd.
InventorsTakeshi Suzuki, Yoshiki Ono
Life of this patent
Estimating the term…
Abstract
A steel for spring includes C: 0.5 to 0.6%, Si: 1.0 to 1.8%, Mn: 0.1 to 1.0%, Cr: 0.1 to 1.0%, P: 0.035% or less, S: 0.035% or less, by mass %, and residue consisting of iron and inevitable impurities, as the overall composition, wherein an area ratio of an internal structure on an optional cross section comprises bainite: 65% or more, retained austenite: 6 to 13%, and martensite: residue (including 0%), and average C content in the retained austenite is 0.65 to 1.7%. The steel for spring can have high strength in which tensile strength is 1800 MPa or more and have high ductility.
Claims6
A steel for spring comprising C:
- 0.5 to 0.6%, Si:
- 1.0 to 1.8%, Mn:
- 0.1 to 1.0%, Cr:
- 0.1 to 1.0%, P:
- 0.035% or less, S:
- 0.035% or less, by mass %, and residue consisting of iron and inevitable impurities, as the overall composition,
- wherein an area ratio of an internal structure on an optional cross section comprises bainite:
- 65% or more, retained austenite:
- 6 to 13%, and martensite:
- residue (including 0%), and average C content in the retained austenite is 0.65 to 1.7%.
A method for producing steel for spring comprising:
- austenitizing a steel comprising C:
- 0.5 to 0.6%, Si:
- 1.0 to 1.8%, Mn:
- 0.1 to 1.0%, Cr:
- 0.1 to 1.0%, P:
- 0.035% or less, S:
- 0.035% or less, by mass %, and residue consisting of iron and inevitable impurities, as the overall composition, at temperature of more than Ac3 point and (Ac3 point+250° C.) or less,
- cooling at a cooling rate 20° C./s or more,
- holding at a temperature of more than Ms point and (Ms point+70° C.) or less for 400 to 10800 seconds, and
- cooling to room temperature at a cooling rate of 20° C./s or more.
Dependencies are inferred from the claim text.