초록 ▼

The present invention provides a carburizing method that involves heating a steel component quickly to a relatively high carburizing temperature (e.g. 1900 degrees F. and above), contacting the component at the relatively high carburizing temperature with a methane-containing carburization atmospher

The present invention provides a carburizing method that involves heating a steel component quickly to a relatively high carburizing temperature (e.g. 1900 degrees F. and above), contacting the component at the relatively high carburizing temperature with a methane-containing carburization atmosphere for time to form a carbon-enriched surface case on the component, and cooling the component at a relatively slow rate effective to provide a relatively soft martensite-free surface case on the component. The component then is subjected to a hardening treatment wherein the carburized component is heated to a hardening temperature in the austenitic range followed by quenching and tempering to form a tempered martensitic surface case on an underlying non-martenistic core.

대표청구항 ▼

We claim: 1. A method of carburizing a steel component, comprising: heating said component to a carburizing temperature of about 1900 degrees F. and greater; contacting said component at said carburizing temperature with a methane-containing endothermic carburizing atmosphere that comprises methane

We claim: 1. A method of carburizing a steel component, comprising: heating said component to a carburizing temperature of about 1900 degrees F. and greater; contacting said component at said carburizing temperature with a methane-containing endothermic carburizing atmosphere that comprises methane, carbon monoxide, hydrogen, and nitrogen for a carburization time; monitoring concentration of methane in said carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to said carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere to further control carburizing of a carbon-enriched surface case on an underlying non-carburized core of said component; and cooling said component at a relatively slow rate effective to provide said surface case free of martensite on said component. 2. The method of claim 1 wherein said component is heated to said carburizing temperature of about 1900 degrees F. to about 2000 degrees F. 3. The method of claim 1 wherein said component is relatively slowly cooled to a lower temperature to produce said surface case comprising substantially pearlite on an underlying core of said component, said core comprising pearlite and ferrite. 4. The method of claim 1 including heating said component at the hardening temperature for a controlled time in the presence of ammonia to form a shallow depth of retained austenite on an outermost region of said surface case. 5. The method of claim 1 wherein said component is heated to said carburizing temperature of about 1900 degrees F. and greater in said carburizing atmosphere comprising about 1 to about 2 volume % methane, 18 to 22 volume % carbon monoxide, 38 to 42 volume % hydrogen, less than 0.1 volume % carbon dioxide, and balance nitrogen. 6. The method of claim 5 wherein said component is heated to said carburizing temperature in about 30 minutes or less. 7. A method of carburizing a steel component, comprising transporting said component through a heating zone of a furnace to heat said component to a carburizing temperature of about 1900 degrees F. and greater; transporting said component through a carburizing zone of said furnace to carburize said component at said carburizing temperature in a methane-containing endothermic carburizing atmosphere that comprises methane, carbon monoxide, hydrogen, and nitrogen for a carburization time; monitoring concentration of methane in said carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere by feedback control of said monitored concentration of methane according to said carburization time and said carburizing temperature, wherein said level of methane enrichment is selectively modified in a substantially continuous manner to further control carburizing of a carbon enriched surface case on an underlying non-carburized core of said component; and transporting said component through a cooling zone of said furnace to cool said component at a relatively slow rate effective to provide said surface case free of martensite on said component. 8. The method of claim 7 wherein said component is transported on a belt through said furnace. 9. The method of claim 7 wherein said component is heated to said carburizing temperature in about 30 minutes or less. 10. The method of claim 7 wherein said component is relatively slowly cooled to a lower temperature to produce said surface case comprising substantially pearlite on an underlying core of said component, said core comprising pearlite and ferrite. 11. The method of claim 7 including heating said component at the hardening temperature for a controlled time in the presence of ammonia to form a hallow depth of retained austenite on an outermost region of said surface case. 12. The method of claim 7 wherein said component is heated to said carburizing temperature of about 1900 degrees F. and greater. 13. The method of claim 12 wherein said component is heated to said carburizing temperature of about 1900 degrees F. to about 2000 degrees F. 14. A method of making a steel component, comprising heating said component to a carburizing temperature, contacting said component at said carburizing temperature of about 1900 degrees F. and greater with a methane-containing endothermic carburizing atmosphere that comprises methane, carbon monoxide, hydrogen, and nitrogen for a time using methane concentration monitoring and feedback control of said carburizing atmosphere, wherein said methane concentration is selectively modified in a substantially continuous manner to control carburizing of a carbon-enriched surface case on an underlying non-carburized core of said component, cooling said component at a relatively slow rate effective to provide a surface case free of martensite on said component, heating said component having said surface case free of martensite to a hardening temperature, quenching said component, and tempering said component to form a surface case comprising tempered martensite. 15. The method of claim 14 wherein said component is relatively slowly cooled to a lower temperature to produce a surface case comprising substantially pearlite on an underlying core of said component, said core comprising pearlite and ferrite. 16. The method of claim 14 including heating said component at the hardening temperature for a controlled time in the presence of ammonia to form a shallow depth of retained austenite on an outermost region of said surface case. 17. The method of claim 14 wherein said component is heated to said carburizing temperature of about 1900 degrees F. and greater. 18. The method of claim 17 wherein said component is heated to said carburizing temperature of about 1900 degrees F. to about 2000 degrees F. 19. The method of claim 14 wherein said component is heated to said carburizing temperature in about 30 minutes or less. 20. The method of claim 19 wherein said component is quenched and tempered to form a tempered martensitic surface case on an underlying core of said component, said core comprising a mixture of ferrite and pearlite or banite. 21. A method of carburizing a steel component, comprising heating said component to a carburizing temperature, monitoring concentration of methane in a carburizing atmosphere, controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature; contacting said component at said carburizing temperature with a methane-containing carburizing atmosphere for said carburizing time to form a carbon-enriched surface case on an underlying core of said component, and cooling said component at a relatively slow rate to a lower temperature to produce said surface case that is free of martensite and that comprises substantially pearlite on said underlying core of said component, said core comprising pearlite and ferrite. 22. The method of claim 21 wherein said component is cooled below about 500 degrees F. 23. A method of carburizing a steel component, comprising heating said component to a carburizing temperature; monitoring concentration of methane in a carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere; contacting said component at said carburizing temperature with said methane-containing carburizing atmosphere for said carburization time to form a carbon-enriched surface case on said component, wherein a predetermined amount of carbon is introduced to said carbon-enriched surface case to a preselected depth through said substantially continuous controlling of said level of methane enrichment of said carburizing atmosphere; cooling said component at a relatively slow rate effective to provide said surface case free of martensite on an underlying core comprising pearlite and ferrite of said component; and heating said component at a hardening temperature for a controlled time in the presence of ammonia to form a shallow depth of retained austenite on an outermost region of said surface case. 24. A method of carburizing a steel component, comprising transporting said component through a heating zone of a furnace to heat said component to a carburizing temperature; transporting said component to a carburizing zone of said furnace to carburize said component at said carburizing temperature in a methane-containing carburizing atmosphere, monitoring concentration of methane in said carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere; maintaining said component in said carburizing zone for said carburization time to form a carbon-enriched surface case on an underlying core of said component; and transporting said component through a cooling zone of said furnace to cool said component at a relatively slow rate to a lower temperature to produce said surface case that is free of martensite and that comprises substantially pearlite on said underlying core of said component, said core comprising pearlite and ferrite. 25. The method of claim 24 wherein said component is cooled below about 500 degrees F. in a carry-over atmosphere from the carburizing zone. 26. A method of carburizing a steel component, comprising transporting said component through a heating zone of a furnace to heat said component to a carburizing temperature; transporting said component through a carburizing zone of said furnace to carburize said component at said carburizing temperature in a methane-containing carburizing atmosphere for a carburization time to form a carbon-enriched surface case on said component, monitoring concentration of methane in said carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to said carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere; transporting said component through a cooling zone of said furnace to cool said component at a relatively slow rate effective to provide said surface case free of martensite on an underlying core comprising pearlite and ferrite of said component; and heating said component at a hardening temperature for a controlled time in the presence of ammonia to form a shallow depth of retained austenite on an outermost region of said surface case. 27. A method of making a steel component, comprising heating said component to a carburizing temperature; monitoring concentration of methane in a carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere; contacting said component at said carburizing temperature with said methane-containing carburizing atmosphere for said carburization time to form a carbon-enriched surface case on an underlying core of said component, cooling said component at a relatively slow rate to a lower temperature to produce a surface case that is free of martensite on said core of said component and that comprises substantially pearlite, said core comprising pearlite and ferrite, heating said component having said surface case to a hardening temperature, quenching said component, and tempering said component to form a surface case comprising tempered martensite. 28. The method of claim 27 wherein said component is heated to a hardening temperature in an austenitic phase range. 29. A method of making a steel component, comprising heating said component to a carburizing temperature in about 30 minutes or less, monitoring concentration of methane in a carburizing atmosphere, controlling a level of methane enrichment of said carburizing atmosphere in a substantially continuous manner by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere, contacting said component at said carburizing temperature with said methane-containing carburizing atmosphere for said carburization time to form a carbon-enriched surface case on an underlying core of said component, cooling said component at a relatively slow rate effective to provide a surface case free of martensite on said underlying core comprising pearlite and ferrite of said component, heating said component having said surface case free of martensite to a hardening temperature, quenching said component, and tempering said component to form a surface case comprising tempered martensite on said core, said core comprising a mixture of ferrite and pearlite or banite. 30. A method of making a steel component, comprising heating said component to a carburizing temperature; monitoring concentration of methane in a carburizing atmosphere; controlling a level of methane enrichment of said carburizing atmosphere by feedback control of said monitored concentration of methane according to a defined carburization time and said carburizing temperature, said methane enrichment controlling said carburizing atmosphere; contacting said component at said carburizing temperature with said methane-containing carburizing atmosphere for said carburization time to form a carbon-enriched surface case on said component, wherein said level of methane enrichment is selectively modified in a substantially continuous manner to introduce a predetermined amount of carbon to said carbon-enriched surface case to a preselected depth; cooling said component at a relatively slow rate effective to provide a surface case free of martensite on an underlying core comprising pearlite and ferrite of said component, heating said component having said surface case free of martensite to a hardening temperature for a controlled time in the presence of ammonia to form a shallow depth of retained austenite on an outermost region of said surface case; quenching said component; and tempering said component to form a surface case comprising tempered martensite having said retained austenite on said outermost region of said surface case.