Method and device for quenching steel in pressurized air

Abstract

The method for quenching a steel charge after carburizing or carbonitriding is carried out at atmospheric pressure and comprises the following steps: the charge is extracted from a treatment furnace (1) at a temperature ranging from 750 ° C. to 1100 ° C.; b) the charge is transferred to a quenching cell (3); c) a quenching fluid is introduced at a pressure which is higher than atmospheric pressure; d) the charge is cooled to a temperature of less than 400 ° C. According to the invention, the fluid is primarily composed of air, and the part is brought to a temperature of at least 400 ° C., whereby an oxide layer preventing decarburization is formed in the time period starting from the moment when the charge exits ( 1 ) from the furnace.

1 . Method of quenching of a steel charge after a treatment of carburization or carbonitriding, carried out at atmospheric pressure, comprising the following steps: 
 a. the charge is removed from the treatment furnace ( 1 ) at a temperature between 750° C. and 1100° C.,    b. the charge is transferred to a quenching cell ( 3 ),    c. a quenching fluid is introduced under a pressure greater than atmospheric pressure and it is put into circulation inside the cell,    d. the charge is cooled to a temperature below 400° C., characterized by the fact that the fluid is composed mostly of air, and that the piece is brought to a temperature of at most 400° C. within a time from removal from the furnace ( 1 ) during which an oxide layer is formed which prevents decarburization of the steel.    
     
     
         2 . Method according to  claim 1 , characterized by the fact that the transfer is carried out with open air, and the temperature of the charge is lowered to 600° C. in less than forty seconds, preferably in less than twenty seconds.  
     
     
         3 . Method according to  claim 1  or  2 , characterized by the fact that the thickness of the oxide layer formed is less than 12 μm, preferably less than 5 μm.  
     
     
         4 . Method according to  claim 1 , characterized by the fact that the transfer is carried out under a protecting atmosphere.  
     
     
         5 . Method according to one of  claims 1  to  4 , characterized by the fact that the fluid is a mixture of air and of a gas, which modifies its density and/or its thermal conductivity.  
     
     
         6 . Method according to one of  claims 1  to  4 , characterized by the fact that the fluid is a two-phase mixture of air/atomized liquid.  
     
     
         7 . Method according to one of the preceding claims, in which the quenching fluid inside the cell is at a pressure between 3 and 40 bars, preferably between 5 and 20 bars.  
     
     
         8 . Device for carrying out the method according to one of the preceding claims, characterized by the fact that it comprises a transfer handler and a quenching cell capable of holding the charge between the furnace and the cell at a surface temperature of 600° C. in less than forty seconds.  
     
     
         9 . Device according to the preceding claim, characterized by the fact that the handler permits transfer in less than thirty seconds.  
     
     
         10 . Device according to  claim 8  or  9 , characterized by the fact that the quenching cell comprises a turbine which allows lowering of the temperature of the surface of the pieces of the charge to 400° C. in less than 10 seconds.  
     
     
         11 . Device according to one of  claims 8  to  10 , characterized by the fact that it is associated with a continuous furnace, a batch furnace, a bell furnace, a pit furnace operating at atmospheric pressure.