Claims
- 1. A method for producing abrasive grit from steel particles comprising the steps of:
- (a) heating clean, dry steel particles in a non-oxidizing protective atmosphere at a temperature of about 1500.degree. F. to about 1800.degree. F.;
- (b) transporting the particles through a chute submerged below a quenching solution, the quenching solution forming an atmospheric seal;
- (c) bathing the heating steel particles in the quenching solution which comprises water to embrittle the particles, and
- (d) grinding the steel particles in a mill to form the grit.
- 2. The method of claim 1 wherein the mill is either a ball mill, a hammer mill, a dry vibratory mill, a rod mill, or a ring crusher.
- 3. The method of claim 1 further comprising the step of reheating the grit, after grinding, in a substantially inert atmosphere to temper the grit.
- 4. The method of claim 1 wherein the heating step comprises loading the particles into foraminous trays and sequentially pushing the trays through a furnace.
- 5. The method of claim 1 wherein the heating step comprises passing the particles through a rotating cylindrical retort furnace.
- 6. The method of claim 1 wherein the protective atmosphere comprises a gaseous carbon-containing compound which diffuses into the particles.
- 7. An abrasive grit which is a product of the method of claim 1 the grit having a size of form about 0.075 mm to about 2.0 mm.
- 8. The method of claim 1 wherein the particles are recycled steel scrap.
- 9. The method of claim 3 wherein the tempering is at a temperature of from about 315.degree. C. to about 650.degree. C.
- 10. A method of producing a steel powder which is suitable for use in sintering operations, comprising the steps of:
- (a) heating clean, dry steel particles, having a carbon content, in a non-oxidizing protective atmosphere at a temperature of about 1500.degree. F.;
- (b) adjusting the carbon content of the particles to a value in a range of about 0.3 weight percent to about 1.2 weight percent;
- (c) bathing the heated steel particles in a quenching solution which comprises water to embrittle the particles;
- (d) grinding the particles in a grinder in a first controlled atmosphere to produce a first product; and
- (e) annealing the first product in a second controlled atmosphere to adjust the hardness of the product, and,
- wherein the first controlled atmosphere is an oxidizing atmosphere which preoxidizes the powder and further wherein the second controlled atmosphere is substantially inert and the powder is heated to a temperature effective to cause the oxidized portion of the powder to react with the carbon content of the powder to substantially reduce said carbon content.
- 11. A method of decarburizing ferrous metal while substantially preventing the oxidation of the metal, said method comprising the steps of:
- (a) placing said metal in a first reducing atmosphere having a first dew point;
- (b) partially decarburizing said metal by heating said metal to a first temperature for a first predetermined period of time such that the rate of decarburization of said metal is substantially greater than the rate of oxidation of said metal;
- (c) placing said metal into a second atmosphere having a second and substantially lower dew point associated therewith;
- (d) partially decarburizing said metal by heating said metal to a second and higher temperature for a second predetermined period of time, said second temperature being slightly greater than the temperature at which said metal will reduce;
- (e) placing said metal into third atmosphere having a third dew point which is substantially lower than said second dew point; and
- (f) heating said metal to a third temperature which is substantially higher than said second temperature for a third predetermined period of time whereby oxides of said metal are reduced and then oxide reduction is effective to remove any residual carbon remaining within said metal.
- 12. The method of claim 11 wherein each of said first, second and third atmospheres comprises hydrogen and nitrogen.
- 13. The method of claim 11 wherein each of said first, second, and third atmospheres to contain approximately 75 percent, by weight, of hydrogen and 25 percent, by weight, of nitrogen.
- 14. The method of claim 11 wherein said metal comprises steel powder.
- 15. The method of claim 11 further comprising the step of defining said first predetermined time to be longer than said second predetermined time.
- 16. The method of claim 11 further comprising the step of defining said second predetermined time to be longer than said third predetermined time.
- 17. The method of claim 11 further comprising the step of defining said first temperature to be between about 1300.degree. F. and 1500.degree. F. (705.degree. to 815.degree. C.).
- 18. The method of claim 11 further comprising the step of defining said third temperature to be between 1875.degree. F. and 2000.degree. F. (1025.degree. to 1095.degree. C.).
- 19. A method of decarburizing ferrous metal having a certain amount of an oxidizable nonferrous metallic constituent therein while substantially preventing the oxidation of the metal, said method comprising the steps of:
- (a) placing said metal in a first atmosphere having a first dew point;
- (b) partially decarburizing said metal by heating said metal to a first temperature for a first predetermined period of time such that the rate of decarburization of said metal is substantially greater than the rate of oxidation of said metal;
- (c) placing said metal into a second atmosphere having a second and substantially lower dew point associated therewith;
- (d) partially decarburizing said metal by heating said metal to a second and higher temperature for a second predetermined period of time, said second temperature being slightly greater than the temperature at which said metal will reduce;
- (e) placing said metal into a third atmosphere having a third dew point substantially less than said second dew point; and
- (f) heating said metal to a third temperature which is substantially higher than said second temperature for a third predetermined period of time whereby oxides of said metal are reduced and this oxide reduction is effective to remove any residual carbon remaining within said metal.
- 20. The method of claim 19 further comprising the step of defining said third temperature to be between 1875.degree. F. and 2000.degree. F.
- 21. The method of claim 19 further comprising the step of defining said third dew point to be approximately -50.degree. F.
- 22. The method of claim 19 wherein the nonferrous metallic constituent is selected from the group consisting of manganese, silicon, chromium, vanadium, titanium, and mixtures thereof.
- 23. The method of producing a steel powder which is suitable for use in sintering operations, comprising the steps of:
- (a) heating clean, dry steel particles, having a carbon content, in a non-oxidizing protective atmosphere at a temperature of about 1500.degree. F. to about 1800.degree. F.;
- (b) adjusting the carbon content of the particles to a value in a range of about 0.3 weight percent to about 1.2 weight percent;
- (c) bathing the heated steel particles in a quenching solution which comprises water to embrittle the particles;
- (d) grinding the particles in a grinder in an oxidizing atmosphere to produce a partially oxidized powder;
- (e) preheating the first product in an oxidizing atmosphere at a temperature below a temperature for annealing, the preheating preoxidizing the first product;
- (f) annealing the powder in a substantially inert atmosphere to cause the oxidized portion of the powder to react with the carbon content whereby carbon content.
CROSS REFERENCED TO RELATED APPLICATIONS
The present application is a continuation-in-part of U.S. patent application Ser. No. 650,364 filed Feb. 1, 1991 now abandoned. The present application is also a continuation-in-part of U.S. patent application Ser. No. 650,365, filed Feb. 1, 1991 now U.S. Pat. No. 5,152,847. The present application is also a continuation-in-part of U.S. patent application Ser. No. 650,378, filed Feb. 1, 1991 now abandoned. The disclosures of each of the above-referenced U.S. patent applications are hereby incorporated by reference.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
102e Date |
371c Date |
PCT/US92/00807 |
1/31/1992 |
|
|
7/28/1993 |
7/28/1993 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO92/13664 |
8/20/1992 |
|
|
US Referenced Citations (17)
Non-Patent Literature Citations (2)
Entry |
Metals Handbook Ninth Edition, vol. 7. p. 361 discussing production sintering practices. |
"Production Sintering Atmospheres" by H. S. Nayar in Metals Handbook, Ninth Edition at pp. 339-350. |
Related Publications (2)
|
Number |
Date |
Country |
|
650365 |
Feb 1991 |
|
|
650378 |
Feb 1991 |
|
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
650364 |
Feb 1991 |
|