Fluidized bed cryogenic apparatus and continuous cooling method for quenching of steel parts

Abstract

Apparatus and method for cryogenically heat treating steel work-pieces to cause the super-strengthening (higher strength, ductility, better fatigue properties, etc.) of same is disclosed. The apparatus includes a retort having a cavity containing a fluidized bed of particles. A cryogenic liquid cools the fluidized bed of particles and a fluidizing gas activates the fluidized bed. Steel work-pieces placed within the fluidized bed are rapidly and continuously cooled from their austenite phase through their martensitic phase transformation causing the work-pieces to have a finer martensitic structure, with higher dislocation density, than that which occurs in work-pieces that are hardened by other heat treating apparatus and/or methods, and which exhbit better physical properties (e.g., higher strength, ductility, better fatigue properties, etc.).

1 . Apparatus for quenching a steel work-piece comprising a retort having a cavity therein, a fluidized bed of particles within said cavity, means for maintaining said fluidized bed of particles in a substantially fluidic state, a cooling medium, and means for directing said cooling medium toward said cavity within said retort to cool same so as to provide a pre-determined quench cooling rate resulting in the substantially continuous cooling of the work-piece from its austenite phase through its martinsitic phase transformation.  
   
   
       2 . The apparatus as defined in  claim 1  wherein said cooling medium is cryogenic in nature.  
   
   
       3 . The apparatus as defined in  claim 1  wherein said fluidized bed of particles cools the work-piece placed within said fluidized bed from its austenite phase through its martensitic phase transformation.  
   
   
       4 . The apparatus as defined in  claim 3  wherein the resulting structure of the work-piece after being cooled by said fluidized bed of particles from its austenite phase through its martensitic phase transformation has a finer martensitic structure than that produced by other heat treating apparatus causing the super-strengthening of the work-piece.  
   
   
       5 . The apparatus as defined in  claim 3  wherein the resulting structure of the work-piece after being cooled by said fluidized bed of particles from its austenite phase through its martensitic phase transformation has a martensitic structure with higher dislocation density than that produced by other heat treating apparatus causing the super-strengthening of the work-piece.  
   
   
       6 . The apparatus as defined in  claim 3  wherein said cooling of the work-piece from its austenite phase through its martensitic phase transformation is at a rate sufficient to cause the super-strengthening of the work-piece.  
   
   
       7 . The apparatus as defined in  claim 1  wherein said fluidized bed maintaining means comprises a fluidizing gas.  
   
   
       8 . The apparatus as defined in  claim 7  wherein said fluidizing gas includes gas that has been evaporated from said cooling medium.  
   
   
       9 . The apparatus as defined in  claim 7  wherein said fluidizing gas includes gas with a high thermal conductivity to improve the heat transfer rate in the work-piece.  
   
   
       10 . The apparatus as defined in  claim 1  further including means for agitating said fluidized particles to improve the heat transfer rate in the work-piece.  
   
   
       11 . The apparatus as defined in  claim 1  further including means to permit the release of said fluidizing gas from said retort.  
   
   
       12 . The apparatus as defined in  claim 1  further including means to permit the release of vapors that have been evaporated from said cooling medium from said retort.  
   
   
       13 . A method for heat treating a steel work-piece comprising the steps of: 
 a) applying a cooling medium to a fluidized bed of particles to cool said fluidized bed;    b) applying a fluidizing gas to said fluidized bed to activate same;    c) placing the work-piece into said fluidized bed;    d) cooling the work-piece so as to transform the work-piece from its austensite phase to its martensite phase at a sufficiently high rate to cause the super-strengthening of the work-piece; and    e) removing the work-piece from the fluidized bed.    
   
   
       14 . The method as defined in  claim 13  further including in step b, combining at least a portion of the vapors from said cooling medium with said fluidizing gas to activate said fluidized bed.  
   
   
       15 . The method as defined in  claim 13  further including, before step c, the step of heat treating the work-piece utilizing the intensive quenching process.