Modified low temperature case hardening processes
DCFirst Claim
1. A process for case hardening a workpiece 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 case of predetermined thickness without formation of carbide precipitates, wherein the instantaneous rate of carburization is reduced during carburization so as to foster rapid carburization during an earlier stage of carburization while avoiding formation of carbide precipitates at a later stage of carburization.
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Abstract
An iron-containing workpiece is case hardened by low temperature carburization during which one or more process steps—including adjusting the carburization temperature, adjusting the concentration of carburization specie in the carburization gas and reactivating the surfaces to be carburized—is carried out to enhance the overall rate and uniformity of carburization with minimized soot generation, whereby carburization can be completed faster than possible in the past.
70 Citations
60 Claims
- 1. A process for case hardening a workpiece 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 case of predetermined thickness without formation of carbide precipitates, wherein the instantaneous rate of carburization is reduced during carburization so as to foster rapid carburization during an earlier stage of carburization while avoiding formation of carbide precipitates at a later stage of carburization.
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6. A process for low temperature gas carburizing a workpiece containing iron, nickel or both comprising contacting the workpiece with a carburizing gas at an elevated carburizing temperature sufficient to promote diffusion of carbon into the surfaces of the article but insufficient to promote substantial formation of carbide precipitates in the article surfaces,
wherein the carburizing temperature is lowered from an initial carburizing temperature to a final carburizing temperature so as to achieve faster carburization than possible for carburization carried out at the final carburizing temperature only.
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24. A process for low temperature gas carburizing a workpiece containing iron, nickel or both comprising contacting the workpiece with a carburizing gas at an elevated carburizing temperature sufficient to promote diffusion of carbon into the surfaces of the article but insufficient to promote substantial formation of carbide precipitates in the article surfaces,
wherein the concentration of the carburizing specie in the carburizing gas is lowered from an initial concentration to a final concentration during carburization so as to achieve a harder case than possible for carburization carried out at the final concentration only and less soot generation than possible for carburization carried out at the initial concentration only.
- 43. A process for case hardening a workpiece 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 case of predetermined thickness without formation of carbide precipitates, wherein after carburization has started but before carburization is completed carburization is interrupted and the workpiece is treated to enhance diffusion of carbon into the workpiece surfaces.
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46. A process for low temperature gas carburizing a stainless steel workpiece comprising activating the surfaces of the workpiece to be carburized to make these surfaces previous to carbon atoms and then contacting the workpiece with a carburizing gas at an elevated carburizing temperature sufficient to promote diffusion of carbon into the surfaces of the article but insufficient to promote substantial formation of carbide precipitates in the article surfaces,
wherein after carburization is at least 10% complete as measured by the amount of carbon taken up by the workpiece surfaces but before carburization is 80% complete, carburization is interrupted and the workpiece is reactivated to enhance diffusion of carbon atoms into the workpiece surfaces.
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55. A process for case hardening a workpiece by gas carburization in which a workpiece electroplated with iron is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened case of predetermined thickness, wherein after carburization has started but before carburization is completed carburization is interrupted and the workpiece is contacted with a purging gas consisting essentially of an inert gas at a purging temperature below 600°
- F. so that the case formed at the end of carburization is harder than the case that would have been formed without contact with the purging gas.
- View Dependent Claims (56, 57)
- 58. A process for case hardening a workpiece 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 case of predetermined thickness without formation of carbide precipitates, wherein the instaneous rate of carburization is maintained at a higher level during earlier stages of carburization to thereby foster rapid carburization during these early states and then reduced to a lower level during later stags of carburization to allow formation of the hardened case to be completed without formation of carbide precipitates.
Specification