Method for cooling work pieces especially shape-rolled products from rail steel

Abstract

The invention relates to a method for producing especially shape-rolled products from rail steels that have a finely perlitic and/or ferritic/perlitic structure after cooling. The inventive method is characterized by guiding the workpiece through a cooling stretch that is composed of individual independent cooling modules ( 2 a - e ) having independently adjustable cooling parameters. Between said cooling modules ( 2 a - e ) intermediate zones ( 5 a - e ) are provided for relieving the stress of the structure comprising means for determining the actual temperature (T ACTUAL ) of the respective work piece in said intermediate zones ( 5 a - e ) Depending on the respective actual temperature values (T ACTUAL ) of the work piece in an intermediate zone ( 5 a - e ) the specific cooling parameters, especially the cooling intensity, of the respective subsequent cooling module ( 2 b - e ) are controlled in order to safeguard a defined temperature of the work piece during the entire passage through the cooling stretch ( 1 ), the defined temperature (T DESIRED ) of the work piece being above a critical temperature at which the bainitic portions of the structure are formed.

1 . A method of cooling workpieces, especially structural shape rolled products, of rail steels with a fine perlitic or ferritic or perlitic/ferritic structure, whereby the hot workpiece is guided through a cooling stretch ( 1 ) with an inlet region ( 12 ) and an outlet region and is subjected to a cooling process and whereby a transformation into a perlitic or ferritic/perlitic structure is effected, characterized in that the workpiece is passed through a cooling stretch which is comprised of individual independent cooling modules ( 2   a - e ) with independently adjustable cooling parameters, 
 whereby between the cooling modules ( 2   a - e ) intermediate zones ( 5   a - e ) for structure destressing or stress relief are provided with means for actual temperature measurement (T ACT ) of the respective workpieces in these intermediate zones ( 5   a - e ) and    whereby in dependence on the respective actual temperature value (T ACT ) of the workpiece in an intermediate zone ( 5   a - e ) the specific cooling parameters, especially the cooling intensity), of at least the respective subsequent cooling module ( 2   b - e ) are controlled to ensure a defined temperature of the workpiece during the complete passage through the cooling stretch ( 1 ), whereby the defined temperature (T SET ) of the workpiece respectively lies above a critical temperature at which bainitic structure components are formed.    
     
     
         2 . The method of cooling according to  claim 1  characterized in that the cooling process is carried out in dependence upon the cooling module traversed in individual cooling process steps and in dependence upon the intermediate zones traversed for structure stress relief in timed phases of reheating and/or timed phases of retention of heat and/or in timed phases of slow cooling in combination.  
     
     
         3 . A method of cooling according to  claim 1  characterized in that in dependence upon the respective measured actual temperature value (T ACT ) of one or any intermediate zone ( 5   a - e ) the specific cooling parameters of the respective subsequent cooling module ( 2   b - e ) and simultaneously the cool parameters of a preceding cooling module ( 2   a - d ) are controlled.  
     
     
         4 . A method of cooling according to  claim 1  characterized in that the surface temperature of the workpiece at the end of the intermediate zone ( 5   a - e ) is measured.  
     
     
         5 . A method of cooling according to  claim 1  characterized in that the actual temperature measurement (T ACT ) is carried out by means of an optical and contactless measurement.  
     
     
         6 . The method of cooling according to  claim 1  characterized in that the control of the cooling parameters, especially the cooling intensity is achieved by means of pressure control and/or temperature control of the cooling medium.  
     
     
         7 . A process for cooling according to  claim 1  characterized in that the cooling medium especially cooling water before impingement upon the workpiece surfaces is so preheated that an undershoot of the Leidenfrost temperature does not occur or occurs later than with nonpreheated cooling medium.  
     
     
         8 . A method of cooling according to  claim 1  characterized in that the temperature of the workpiece before entry or upon entry into the cooling stretch ( 1 ) is measured and this temperature value is used for presetting the cooling parameters of the individual cooling modules.