C - Chemistry – Metallurgy – 23 – C
Patent
C - Chemistry, Metallurgy
23
C
148/42
C23C 8/22 (2006.01)
Patent
CA 1176547
12,872 Process for Carburizing Steel Abstract of the Disclosure In a process for carburizing steel parts in a furnace having one or more temperature zones at a carburizing temperature in the range of about 1500°F to about 2200°F in a carburizing atmosphere comprising Image said percent by volume being based on the total volume of the atmosphere, wherein it is desired to shut down the carburizing process for a predetermined period of time without removing the parts, which have not achieved 100 percent carburization, from the furnace, the improvement comprising the following steps: (a) introducing parts, which would not achieve 100 percent carburization prior to the shut down of the carburizing process, into the furnace; (b) determining the temperature (Tc,s) for each temperature zone at about which the parts introduced in step (a) are to be maintained in step (c) according to the following formula: Image wherein -1- 12,872 Image teq,susp being allocated to at least one temperature zone R = gas constant Q = activation energy for carbon diffusion in austenite ln = natural log tn = carburizing time ti = time at beginning of shutdown ta,c = time during cooling at which T = Ta ta,h = time during heating at which T = Ta tf = time at end of shutdown at which T = Tc,s Tn = carburizing temperature T = temperature during cooling and heating, a function of time, t Ta = austenitic transformation temperature, provided that Tc,s is no less than about 1400°F or the austenitic transformation temperature of the steel, whichever is the greater; (c) maintaining the parts in the carburizing atmosphere in at least one of the temperature zones for the period of time, which would be necessary to achieve about 1 to about 99 percent carburization at the carburizing temperature, each of said temperature zones being at the temperature determined in step (b) for that temperature zone; (d) reducing the amount of the hydrocarbon component of the atmosphere; (e) gradually lowering the temperature from the level of step (c) to a predetermined level, less than about 1400°F; (f) during step (e), but before the temperature reaches about 1400°F, changing the atmosphere to one comprising an inert atmosphere; -2- 12,872 (g) maintaining the parts in the atmosphere, which is the result of step (f), for the predetermined period of time; (h) after the predetermined period of time expires, heating the furnace to a temperature in the range of about 1400°F to about 1500°F; (i) changing the atmosphere to the carburizing atmosphere; (j) raising the temperature in each zone to about the temperature determined in step (b); (k) maintaining the parts at the temperature of step (j) for the period of time necessary to bring the carburization initiated in step (c) to about 100 percent carburization; and (l) removing the parts from the furnace. S P E C I F I C A T I O N -3-
383285
Roberge Raymond P.
Solomon Jack
Hopley William G.
Union Carbide Corporation
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