Process for the low-pressure carburisation of metal workpieces

Abstract

The invention relates to a process for the low-pressure carburisation of metal workpieces in an evacuable furnace, in which acetylene is added to the furnace atmosphere as the carburisation gas, wherein the partial pressure of the acetylene is varied intermittently and wherein the partial pressure of the acetylene in the furnace atmosphere is kept below 10 mbar. In order to specify a process for the low-pressure carburisation of metal workpieces that leads to an improvement, particularly with regard to the carburisation result, the invention proposes the use of a pot furnace as the furnace.

1 . A process for the low-pressure carburisation of metal workpieces, comprising the following steps:
 providing a pot furnace;   supplying acetylene to the pot furnace atmosphere as a carburisation gas; and   intermittently varying the partial pressure of the acetylene at a pressure below 10 mbar.   
     
     
         2 . The process according to  claim 1 , wherein the partial pressure is kept below 6 mbar. 
     
     
         3 . The process according to  claim 1 , wherein the carburisation temperature is set at 350° C. to 1,050° C., preferably 800° C. to  1 , 050  ° C., more preferably at 950° C. to  1,050° C.    
     
     
         4 . The process according to  claim 1 , wherein the flow rate of the acetylene is set at 150 l/m 2  to 500 l/m 2  h. 
     
     
         5 . The process according to  claim 1 , wherein the step of intermittently varying the partial pressure comprises providing a pulse duration in a range of 2 to 6 minutes. 
     
     
         6 . The process according to  claim 1 , further comprising a step of exposing removable carburisation samples to the furnace atmosphere during implementation of the process. 
     
     
         7 . The process according to  claim 1 , further comprising a step of providing a control mechanism, which uses a measuring device to measure the temperature in the furnace and gives off a signal according to the temperature measured, which uses a comparator circuit to compare the signal supplied by the measuring device with a presettable target value and, depending on the result of the comparison, triggers a tracking of the temperature, so that the temperature gradient within the furnace atmosphere is set at +5° C., preferably at +3° C. 
     
     
         8 . The process according to one of the preceding claims, further comprising a step of forming the furnace atmosphere within a retort provided by the pot furnace. 
     
     
         9 . The process according to  claim 8 , further comprising a step of producing a support vacuum in an annular space surrounding the retort. 
     
     
         10 . The process according to  claim 9 , further comprising a step of setting the support vacuum in the annular space at a pressure in the region of 15 mbar to 25 mbar. 
     
     
         11 . Use of a pot furnace to implement a process for the low-pressure carburisation of metal workpieces according to  claim 1 .