Method of manufacturing high strength steel member with a low yield ratio
AssigneeSumitomo Metal Industries, Ltd.
InventorsYasutaka Okada, Yasuhide Fujioka
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Abstract
A high tensile strength, low yield ratio steel member has a steel composition consisting essentially of, by weight: C: 0.15-0.40%, Si: 0.10-0.70%, Mn: 1.0-2.7%, Cr: 1.0-3.5%, sol.Al: 0.01-0.05%, P: not larger than 0.025%, S: not larger than 0.015%, Mo: 0-1.0%, Ni: 0-2.5%, V: 0-0.10%, Ti: 0-0.10%, Nb: 0-0.10%, B: 0-0.0050%. Fe and incidental impurities: balance the below-described bainite index (%) of the steel composition being 0-50%, the steel being comprised of a single phase of martensite or a martensite and bainite duplex structure containing 50% or less of bainite. Bainite Index (%)=-209C+43Si-48Mn-58Cr-0.416R+317 wherein R is a cooling rate (.degree.C./min).
Claims7
A method of producing a high strength, low yield ratio steel member having a steel composition which consists essentially of, by weight:
- C:
- 0.15-0.40%, Si:
- 0.10-0.70%, Mn:
- 1.0-2.7%,
- Cr:
- 1.0-3.5%, sol. Al:
- 0.01-0.05%,
- P:
- not larger than 0.025%, S:
- not larger than 0.015%,
- Mo:
- 0-1.0%, Ni:
- 0-2.5%,
- V:
- 0-0.10%, Ti:
- 0-0.10%, Nb:
- 0-0.10%,
- B:
- 0-0.0050%,
- Fe and incidental impurities:
- balance, the steel being comprised of a single phase of martensite or a martensite and bainite duplex structure containing 50% or less of martensite and having a bainite index of 0-50% defined by:
- Bainite Index (%)=-209C+43Si-48Mn-58Cr-0.416R+317
- wherein R is a cooling rate (.degree.C./min), the method comprising final hot working the steel member with a finishing temperature of 800.degree.-1000.degree. C., reheating the resulting steel member at a temperature of 850.degree.-1050.degree. C. for 0.5 minute-2 hours, and cooling the steel member at a cooling rate R defined by the following equation:
- 642-502C+103Si-115Mn-139Cr.ltoreq.R.ltoreq.762-502C+103Si-115Mn-139Cr.
A method of producing a high strength, low yield ratio steel member having a steel composition which consists essentially of, by weight:
- C:
- 0.15-0.40%, Si:
- 0.10-0.70%, Mn:
- 1.0-2.7%,
- Cr:
- 1.0-3.5%, sol. Al:
- 0.01-0.05%,
- P:
- not larger than 0.025%, S:
- not larger than 0.015%,
- Mo:
- 0-1.0%, Ni:
- 0-2.5%,
- V:0-0.10%, Ti:
- 0-0.10%, Nb:
- 0-0.10%,
- B:
- 0-0.0050%,
- Fe and incidental impurities:
- balance, the steel being comprised of a single phase of martensite or a marten site and bainite duplex structure containing 50% or less of martensite and having a bainite index of 0-50% defined by:
- Bainite Index (%)=-209C+43Si-48Mn-58Cr-0.416R+317
- wherein R is a cooling rate (.degree.C./min), the method comprising hot working the steel member with a finishing temperature of 800.degree.-1000.degree. C., carrying out additional working, reheating the resulting steel member at a temperature of 850.degree.-1050.degree. C. for 0.5 minute-2 hours, and cooling the steel member at a cooling rate R defined by the following equation:
- 642-502C+103Si-115Mn-139Cr.ltoreq.R.ltoreq.762-502C+103Si-115Mn-139Cr.
Dependencies are inferred from the claim text.