Claims
- 1. A spring made from a rolled steel bar and having the steel composition, the microstructure and the physical characteristics recited below:
- said steel composition consisting essentially of, in wt. %:
- ______________________________________carbon 0.40-0.50manganese 1.10-1.40phosphorous 0.025 max.sulfur 0.015 max.silicon 1.15-1.50chromium 0.45-0.75aluminum 0.04 max.vanadium 0.12-0.17columbium 0.015-0.030nitrogen 0.010-0.022iron essentially the balance______________________________________
- said microstructure comprising a microstructure consisting essentially of (i) a matrix of tempered martensite and (ii) particles of Fe.sub.3 C and of vandadium and columbian carbonitrides within said matrix;
- said physical characteristics comprising a Rockwell C hardness no less than 52, and a fracture toughness substantially greater than 27 MPa.m.sup.1/2.
- 2. A spring as recited in claim 1 wherein:
- said tempered martensitic microstructure reflects an austenitic grain size at least as fine as ASTM 10.
- 3. A spring as recited in claim 1 or 2 wherein:
- said particles of vanadium carbonitride are dispersed throughout said matrix and have a spacing no greater than 100 angstroms (100.times.10.sup.-10 meters).
- 4. A spring as recited in claim 1 or 2 wherein:
- said physical characteristics comprise a fracture toughness in the range 36.0-38.5 MPa.m.sup.1/2.
- 5. A spring as recited in claim 1 or 2 wherein said composition also includes 0.005-0.020 wt. % titanium.
- 6. A spring as recited in claim 1 or 2 wherein said composition comprises, in wt. %:
- carbons: 0.43-0.50
- manganese: 1.10-1.35.
- 7. A spring as recited in claim 1 or 2 wherein said composition comprises 0.015 wt. % max. phosphorous.
- 8. A spring as recited in claim 1 or 2 wherein said composition comprises 0.012 wt. % max. sulfur.
- 9. A spring as recited in claim 1 or 2 wherein said composition comprises, in wt. %:
- carbon: 0.43-0.50
- manganese: 10-1.35
- phosphorous: 0.015 max.
- sulfur: 0.012 max.
- 10. A spring as recited in claim 9 wherein:
- said particles of vanadium carbonitride are dispersed throughout said matrix and have a spacing no greater than 100 angstroms (100.times.10.sup.-10 meters);
- and said physical characteristics comprise a fracture toughness in the range 36.0-38.5 MPa.m.sup.1/2.
- 11. A method for producing a spring from a rolled steel bar, said method comprising the steps of:
- employing a hot rolled steel bar having a steel composition consisting essentially of, in wt. %:
- carbon: 0.40-0.50
- manganese: 1.10-1.40
- phosphorous: 0.025 max.
- sulfur: 0.015 max.
- silicon: 1.15-1.50
- chromium: 0.45-0.75
- aluminum: 0.04 max.
- vanadium: 0.12-0.17
- columbium: 0.015-0.030
- nitrogen: 0.010-0.022.
- iron: essentially the balance
- heating said rolled steel bar to an austenitizing temperature, for a time sufficient to produce a steel microstructure consisting essentially of fine grained austenire;
- forming said rolled steel bar into the shape of a spring, while said steel bar is at said austenitizing temperature and has said steel microstructure;
- quenching said spring shape, from said austenitizing temperature, at a cooling rate sufficient to provide a microstructure consisting essentially of untempered martensite, at ambient temperature;
- tempering said quenched spring shape at a temperature of about 625.degree.-675.degree. F. (329.degree.-357.degree. C.) for about 3/4-2 hours to provide a tempered, martensitic microstructure consisting essentially of (i) a matrix consisting essentially of tempered martensite and (ii) particles of Fe.sub.3 C and of vanadium and columbium carbonitrides dispersed within said matrix;
- and then setting said spring shape to produce the final spring.
- 12. A method as recited in claim 11 wherein:
- said fine grained austenire has an austenitic grain size at least as fine as ASTM 10.
- 13. A method as recited in claim 11 or 12 wherein:
- said particles of vanadium carbonitride are dispersed throughout said matrix and have a spacing no greater than 100 angstroms (100.times.10.sup.-10 meters).
- 14. A method as recited in claim 11 or 12 wherein said method produces a steel coil spring having the following physical properties:
- a Rockwell C hardness no less than 52 and a fracture toughness substantially greater than 27 MPa/m.sup.1/2.
- 15. A method as recited in claim 14 wherein:
- said particles of vanadium carbonitride are dispersed throughout said matrix and have a spacing no greater than 100 angstroms (100.times.10.sup.-10 meters);
- and said physical characteristics comprise a fracture toughness in the range 36.0-38.5 MPa/m.sup.1/2.
- 16. A method as recited in claim 11 or 12 wherein said composition also includes 0.005-0.020 wt. % titanium.
- 17. A method as recited in claim 11 or 12 wherein said composition comprises, in wt. %:
- carbon: 0.43-0.50
- manganese: 1.10-1.35.
- 18. A method as recited in claim 11 or 12 wherein said composition comprises 0.015 wt. % max. phosphorous.
- 19. A method as recited in claim 11 or 12 wherein said composition comprises 0.012 wt. % max. sulfur.
- 20. A method as recited in claim 11 or 12 wherein said composition comprises, in wt. %:
- carbon: 0.43-0.50
- manganese: 1.10-1.35
- phosphorous: 0.015 max.
- sulfur; 0.012 max.
- 21. A method as recited in claim 11 wherein:
- said austenitizing temperature is in the range 1650.degree.-1750.degree. F. (899.degree.-954.degree. C.).
- 22. A method as recited in claim 11 or 21 wherein said cooling rate is sufficient to produce a microstructure containing greater than 90% martensite.
- 23. A method as recited in claim 11 wherein said hot rolled steel bar is produced by a hot rolling procedure comprising:
- finishing hot rolling at an austenitic finishing temperature less than 1650.degree. F. (899.degree. C.) and so as to provide a fine austenitic grain size at said finishing temperature at least as fine as ASTM 9;
- cooling the resulting hot rolled steel bar from said finishing temperature, initially at a rate which substantially avoids coarsening of said fine austenitic grain size, and then at a rate through the time, temperature, transformation zone which provides a microstructure, at room temperature, consisting essentially of ferrite, pearlite and bainite and a hardness less than 32 Rockwell C.
- 24. A method as recited in claim 11 and comprising:
- shot peening said quenched, spring shape after said tempering step;
- and coating said final spring to improve its corrosion resistance.
- 25. A steel spring having a hardness no less than 52 Rockwell C and a fracture toughness substantially greater than 27 MPa/m.sup.1/2.
- 26. A steel spring as recited in claim 25 wherein said fracture toughness is in the range 36.0-38.5 MPa/m.sup.1/2.
- 27. A steel spring as recited in claim 25 or 26 wherein said spring has a yield strength of at least 250 ksi (1,724 MPa), a tensile strength of at least 270 ksi (1,861 MPa) and a total elongation of at least 7%.
Parent Case Info
This is a division of application Ser. No. 07/821,974, filed Jan. 16, 1992, now U.S. Pat. No. 5,282,906.
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Divisions (1)
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Number |
Date |
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Parent |
821974 |
Jan 1992 |
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