Method for Thermally Treating a Component Consisting of a Fully Hardenable, Heat-Resistant Steel and a Component Consisting of Said Steel

Abstract

The aim of the method is to achieve a higher penetration depth of the diffusion element coupled with a greater depth of case hardening and a higher case hardening degree, whilst preventing an excessive enrichment of the case, thus obtaining an increased fatigue limit for the component. To achieve this, the full hardening of the component and the plasma-ion hardening of the case of the component are carried out in a common working step. The component is heated to a common hardening and diffusion temperature T H+D lying above the upper transformation temperature A C3 , the component being held at the common hardening and diffusion temperature T H+D until the carbon in the component has fully austenitized and dissolved and until the case has been enriched to the desired degree by the diffusion element. The component is then quenched.

1 . A method for thermally treating a component of a fully hardenable heat-resistant steel, the thermal treatment comprising a full hardening, a case hardening and an annealing of the component, the full hardening involving a heating of the component to a hardening temperature above the upper transformation temperature A C3 , a holding of the component at the hardening temperature and a quenching of the component, in which the case hardening takes place under the action of a diffusion element, involves a heating of the component to a diffusion temperature, a holding of the component at the diffusion temperature and a cooling of the component and is carried out as plasma ion hardening, and in which the annealing involves a once-only or multiple heating of the component to an annealing temperature below the lower transformation temperature A C1 , a holding of the component at the annealing temperature and a cooling of the component, wherein the full hardening of the component and the plasma ion hardening of the case of the component are carried out in a joint work step, in that the component is heated to a joint hardening and diffusion temperature T H+D  above the upper transformation temperature A C3 , in that the component is held at the joint hardening and diffusion temperature T H+D  up to the complete austenitizing and dissolving of the carbon contained and up to the desired enrichment of the case with the diffusion element, and in that the component is subsequently quenched and internal compressive stresses are thereby formed in the outer case.  
   
   
       2 . The method as claimed in  claim 1 , wherein the height of the joint hardening and diffusion temperature T H+D  is adapted essentially to the required hardening temperature T H  of the steel grade of the component.  
   
   
       3 . The method as claimed in  claim 2 , wherein the joint hardening and diffusion temperature T H+D  is set in a temperature range of between 1070° and 1150° C.  
   
   
       4 . The method as claimed in  claim 2 , wherein the duration of holding Δt H+D  at the joint hardening and diffusion temperature T H+D  is adapted to the longer of the two required holding durations, the required hardening holding duration Δt H  or the required diffusion holding duration Δt D .  
   
   
       5 . The method as claimed in  claim 4 , wherein, in the event of a longer required diffusion holding duration Δt D , the joint hardening and diffusion temperature T H+D  is lowered in order to avoid a coarsening of the core structure of the component.  
   
   
       6 . The method as claimed in  claim 5 , wherein the lowering of the joint hardening and diffusion temperature T H+D  takes place by about 20° to 40° C.  
   
   
       7 . The method as claimed in  claim 1 , wherein carbon (C) and/or nitrogen (N) is used as diffusion element for the plasma ion hardening of the case of the component, and in that, for this purpose, during the plasma ion hardening the component is subjected to an ionizable gas emitting carbon (C) and/or nitrogen (N).  
   
   
       8 . The method as claimed in  claim 7 , wherein during a subsequent annealing of the component, the annealing temperature T A  is adapted to the fractions of the diffusion element which are dissolved in the steel, in such a way that, after cooling, the greatest hardness is established in the case of the component.  
   
   
       9 . The method as claimed in  claim 8 , wherein the annealing temperature T A  is set at a value in the range of 500° to 600° C.  
   
   
       10 . The method as claimed in  claim 1  wherein a heat-resistant steel is used as the source material of the component.  
   
   
       11 . A component consisting of a fully hardenable heat-resistant steel which has undergone thermal treatment which comprises a full hardening of the component, a case hardening of the component and an annealing of the component, wherein the thermal treatment has taken place as claimed in  claim 1 .  
   
   
       12 . The component as claimed in  claim 11 , wherein the component forms a bearing component of a rolling bearing.  
   
   
       13 . The component as claimed in  claim 12 , wherein the rolling bearing is designed for mounting a mechanically and thermally highly loaded shaft of a thermal engine.