[특허]Low temperature carburization under soft vacuum

Swagelok Company

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Low temperature carburization under soft vacuum

특허상세정보
국가/구분	United States(US) Patent 등록
국제특허분류(IPC7판)	C23C-008/22 C23C-008/20
출원번호	US-0850925 (2010-08-05)
등록번호	US-9212416 (2015-12-15)
발명자 / 주소	Williams, Peter C. Collins, Sunniva R. Marx, Steven V.
출원인 / 주소	Swagelok Company
대리인 / 주소	Calfee, Halter & Griswold LLP
인용정보	피인용 횟수 : 1 인용 특허 : 53

초록

Low temperature carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. As a result, formation of soot and the undesirable thermal oxide film that normally occurs during low temperature carburization is eliminated virtually completely.

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1. A process for surface hardening a workpiece made from stainless steel by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising hydrogen, natural gas, propane, another C1-C6 alkane or another saturated hydrocarbon, and(5) the partial pressure of the companion gas in the carburizing gas is at least twice the partial pressure of the carburizing specie. 2. The process of claim 1, wherein the carburizing gas comprises acetylene and hydrogen. 3. The process of claim 1, wherein the carburizing gas is essentially free of an inert gas. 4. The process of claim 1, wherein the total pressure of the carburizing gas is about 5-25 torr (˜666 to ˜3,333 Pa). 5. The process of claim 4, wherein the total pressure of the carburization gas is about 6-9 torr (800-1,200 Pa) and the concentration of carburization specie in the carburization gas is about 10-33 vol. %. 6. The process of claim 1, wherein the carburization potential of the carburizing gas is changed over the course of the carburization reaction. 7. The process of claim 6, wherein carburization is carried out in a carburization reactor, and further wherein the carburization potential is changed by pulsing the flowrate of carburizing specie to the carburization reactor. 8. The process of claim 6, wherein the carburization potential of the carburizing gas is changed by at least one of (3) interrupting the flow of carburizing specie to the carburization reactor, and (4) interrupting the flow of carburizing specie the carburization reactor and, in addition, contacting the workpiece with a halogen containing gas during this interruption. 9. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon, and(5) wherein the carburization potential of the carburizing gas is changed over the course of the carburization reaction by at least one of (1) reducing the reaction temperature from a higher reaction temperature during an earlier stage of carburization to a lower reaction temperature during a later stage of carburization, and (2) reducing the concentration of carburization specie in the carburization gas from a higher concentration during an earlier stage of carburization to a lower concentration during a later stage of carburization. 10. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising hydrogen, natural gas, propane, another C1-C6 alkane or another saturated hydrocarbon, and(5) the workpiece is activated by contact with an activating gas, with activation and carburization being done in the same reactor without removing the workpiece from the reactor or otherwise exposing the workpiece to the atmosphere between activation and carburization steps. 11. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon, and(5) wherein the workpiece is activated by contact with an activating gas, activation and carburization being done in the same reactor without removing the workpiece from the reactor or otherwise exposing the workpiece to the atmosphere between activation and carburization steps, wherein the workpiece is activated at an activation pressure and an elevated activation temperature by contact with an activating gas mixture comprising a mixture of said activating gas and said companion gas, wherein the activation and carburization temperatures differ by no more than 100° C., and further wherein the activation and carburization pressures differ by no more than 20 torr. 12. The process of claim 11, wherein the activation and carburization temperatures differ by no more than 50° C., and further wherein the activation and carburization pressures differ by no more than 10 torr. 13. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon, and(5) wherein the workpiece is activated by contact with an activating gas, activation and carburization being done in the same reactor without removing the workpiece from the reactor or otherwise exposing the workpiece to the atmosphere between activation and carburization steps, wherein the absolute pressure of the activating gas in the reactor during activation, and the absolute pressure of the carburizing gas in the reactor during carburization differ by no more than ±10%. 14. A process for surface hardening a stainless steel workpiece by gas carburization inside a carburization reactor in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon, and(5) wherein the workpiece is activated inside the carburization reactor by causing an activating gas comprising a mixture of 0.1 vol. % to 20 vol. % hydrogen chloride in hydrogen gas to flow into the reactor and contact the workpiece at 350° C. to 510° C. and 3.5 to 100 torr pressure for ¼ to 4 hours, after which the workpiece is carburized in a main carburization step without removing the workpiece from the carburizing reactor. 15. The process of claim 14, wherein an activating gas comprising a mixture of 0.5 vol. % to 10 vol. % hydrogen chloride in hydrogen gas is caused to flow into the reactor and contact the workpiece at 350° C. to 450° C. and 5 to 25 torr pressure, after which the workpiece is carburized in a main carburization step without removing the workpiece from the carburizing reactor by causing a carburization gas comprising 7% to 40% acetylene and the balance hydrogen to flow into the reactor and thereby contact the workpiece at a temperature of 350° C. to 450 C and a pressure of 5 to 25 torr. 16. The process of claim 15, wherein an activating gas comprising a mixture of 1 vol. % to 5 vol. % hydrogen chloride in hydrogen gas is caused to flow into the reactor and contact the workpiece at a pressure of 6 torr to 9 torr, after which the workpiece is carburized in a main carburization step without removing the workpiece from the carburizing reactor by causing a carburization gas comprising 10% to 35% acetylene and the balance hydrogen to flow into the reactor and thereby contact the workpiece at a pressure of 6 to 9 torr. 17. The process of claim 14, wherein the flow of activating gas to the reactor is interrupted, during this interruption the workpiece is subjected to a preliminary carburization step in which the workpiece is contacted with a carburizing gas comprising 10% to 35% acetylene and the balance hydrogen at a temperature of 350° C. to 450 C and a pressure of 6 to 9 torr for ¼ to 1 hour, after which activation of the workpiece is resumed. 18. The process of claim 17, wherein after activation of the workpiece is completed, the workpiece is carburized in a main carburization step in which the workpiece is contacted with a carburization gas whose acetylene content decreases from an initial value of about 20 vol. % to 35 vol. % to a final value of about 10 vol. %. 19. The process of claim 14, wherein the flowrate of at least one of (a) the hydrogen chloride content of the activation gas to the carburization reactor and (b) the acetylene content the carburizing gas to the carburization reactor is pulsed. 20. The process of claim 19, wherein the acetylene content of the carburizing gas to fed to the carburization reactor during the main carburization step is pulsed, and further wherein the carburization potential of the carburizing gas is decreased over the course of the main carburization step by decreasing the frequency of these pulses,decreasing the duration of these pulses,decreasing the concentration of the carburization specie in the carburization gas fed to the reactor during these pulses, orcombinations thereof. 21. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon, and(5) wherein the workpiece is activated by contact with an activating gas, activation and carburization being done in the same reactor without removing the workpiece from the reactor or otherwise exposing the workpiece to the atmosphere between activation and carburization steps, wherein the flow of activating gas to the reactor during the activating step is pulsed. 22. The process of claim 21, wherein the intensity of the activation treatment is reduced over the course of the activation treatment by decreasing the frequency of these pulses,decreasing the duration of these pulses,decreasing the concentration of the activating gas in the activating gas mixture fed to the reactor during these pulses, orcombinations thereof. 23. A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,(2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa),(4) the carburizing gas also contains a companion gas, the companion gas comprising hydrogen, natural gas, propane, another C1-C6 alkane or another saturated hydrocarbon, and(5) the carburization potential of the carburizing gas is changed over the course of the carburization reaction by at least one of (1) lowering the carburization temperature, (2) lowering the concentration of carburizing specie in the carburizing gas, (3) interrupting the carburization process while maintaining the workpiece at elevated temperature, and (4) interrupting the carburization process while maintaining the workpiece at elevated temperature and, in addition, reactivating the workpiece during this interruption by contact with a halogen containing gas. 24. The process of claim 23, wherein carburization is carried out in a carburization reactor, and further wherein the carburization potential is additionally changed by pulsing the flowrate of the carburizing specie fed to the carburization reactor. 25. A process for producing a surface-hardened, corrosion-resistant stainless steel workpiece exhibiting a shiny metallic appearance without requiring removal of byproduct soot or thermal oxide from the workpiece surfaces, the process comprising contacting the workpiece surfaces with a carburizing gas in a carburizing reactor under conditions of time and temperature which are sufficient to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein (1) the carburizing gas fed to the reactor comprises acetylene and hydrogen,(2) the partial pressure of acetylene in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa), and(3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa). 26. The process of claim 25, wherein the carburization potential of the carburizing gas is changed over the course of the carburization reaction by at least one of (1) lowering the carburization temperature, (2) lowering the concentration of carburizing specie in the carburizing gas, (3) interrupting the carburization process while maintaining the workpiece at elevated temperature, and (4) interrupting the carburization process while maintaining the workpiece at elevated temperature and, in addition, reactivating the workpiece during this interruption by contact with a halogen containing gas. 27. The process of claim 25, wherein the molar ratio of hydrogen to acetylene in the carburizing gas is at least 2:1. 28. The process of claim 27, wherein prior to contact of the workpiece with the carburizing gas, the workpiece is contacted with an activating gas comprising a mixture of hydrogen and a halogen containing gas. 29. The process of claim 28, wherein the workpiece is contacted with the activating gas and the carburizing gas in the same carburization reactor without exposing the workpiece to contact with the atmosphere between contact with the activating gas and the carburizing gas. 30. The process of claim 29, wherein the flowrate to the carburization reactor of at least one of (a) the activating gas and (b) the acetylene in the carburizing gas is pulsed. 31. The process of claim 30, wherein the acetylene content of the carburizing gas to the carburization reactor is pulsed. 32. The process of claim 31, wherein at least one of the duration of the pulse and the frequency of the pulse is shortened from an higher value at in early stages of carburization to a relatively lower value in later stages of carburization so that the carburization potential of the carburization gas decreases over the course of the carburization reaction.

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이 특허를 인용한 특허 피인용횟수: 1

Williams, Peter C.; Collins, Sunniva R.; Marx, Steven V.. Low temperature carburization under soft vacuum. USP20181210156006.

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Low temperature carburization under soft vacuum

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