Process for manufacturing a cold rolled trip steel product

Abstract

The present invention is related to a process comprising a cold rolling step, for the production of uncoated, electro-galvanised or hot dip galvanised TRIP steel products, hot rolling a slab of a specific composition, wherein the finishing rolling temperature is higher than the Ar3 temperature, to form a hot-rolled substrate, cooling said substrate to a coiling temperature (CT) between 500° C. and 680° C., coiling said substrate at said coiling temperature, pickling said substrate to remove the oxides, cold rolling said substrate to obtain a reduction of thickness, with a minimum reduction of 40%.

1 . A process for manufacturing a cold rolled TRIP steel product, comprising the steps of:
 preparing a steel slab having the following composition:
 C: between 1300 ppm and 2600 ppm, 
 Mn: between 10000 ppm and 22000 ppm, 
 Al: between 8000 ppm and 15000 ppm, 
 Si: between 2000 ppm and 6000 ppm, 
 P: between 400 and 1000 ppm, 
 S: maximum 120 ppm, 
 N: maximum 200 ppm, 
 Ti: maximum 1000 ppm, 
 Nb: maximum 1000 ppm, 
 V: maximum 1000 ppm, 
 B: maximum 10 ppm. 
 the remainder being substantially iron and incidental impurities, 
   hot rolling said slab, wherein the finishing rolling temperature is higher than the Ar3 temperature, to form a hot-rolled substrate,   cooling said substrate to a coiling temperature (CT) between 500° C. and 680° C.,   coiling said substrate at said coiling temperature,   pickling said substrate to remove the oxides,   cold rolling said substrate to obtain a reduction of thickness, with a minimum reduction of 40%.   
     
     
         2 . The process according to  claim 1 , further comprising the steps of:
 soaking said substrate at a temperature between 760° C. and 850° C.,   cooling said substrate with a cooling rate higher than 2° C./s to a temperature in the range 360° C. to 450° C.,   holding said substrate in said temperature range for a time less than 700 s,   cooling said substrate to room temperature at a cooling rate higher than 1° C./s.   subjecting said substrate to a skinpass reduction of maximum 1.5%.   
     
     
         3 . The process according to  claim 2 , further comprising an electrolytic zinc coating step. 
     
     
         4 . The process according to  claim 1 , further comprising the following processing steps:
 soaking said substrate at a temperature between 760° C. and 850° C.,   cooling said substrate with a cooling rate higher than 2° C./s to the temperature of a Zn-bath,   holding said substrate in the temperature range between 490° C. and 460° C. for less than 200 seconds,   hot dip galvanising said substrate in said Zn-bath,   cooling said substrate to room temperature at a cooling rate higher than 2° C./s.   
     
     
         5 . The process according to  claim 4 , further comprising the step of subjecting said substrate to a skinpass reduction of maximum 1.5%. 
     
     
         6 . The process according to  claim 1 , wherein the carbon content of said composition is between 1300 ppm and 1900 ppm. 
     
     
         7 . The process according to  claim 1 , wherein the carbon content of said composition is between 1350 ppm and 1900 ppm. 
     
     
         8 . The process according to  claim 1 , wherein the carbon content of said composition is between 1400 ppm and 1900 ppm. 
     
     
         9 . The process according to  claim 1 , wherein the carbon content of said composition is between 1700 ppm and 2300 ppm. 
     
     
         10 . The process according to  claim 1 , wherein the carbon content of said composition is between 2000 ppm and 2600 ppm. 
     
     
         11 . The process according to  claim 6 , wherein said composition comprises:
 Mn: between 13000 ppm and 22000 ppm,   Al: between 8000 ppm and 14000 ppm,   Si: between 2500 ppm and 4500 ppm,   P: between 600 and 1000 ppm,   S: maximum 120 ppm,   N: maximum 150 ppm,   Ti: maximum 200 ppm,   Nb: maximum 100 ppm,   V: maximum 100 ppm,   B: maximum 5 ppm.   
     
     
         12 . The process according to  claim 11 , wherein the aluminium content of said composition is between 9000 ppm and 13000 ppm.