Coated hot- and cold-rolled steel sheet comprising a very high resistance after thermal treatment

Abstract

Hot-rolled steel sheet which then can be cold-rolled, coated, the steel in the sheet having the following composition by weight: 0.15%<carbon<0.5% 0.5%<manganese<3% 0.1%<silicon<0.5% 0.01%<chromium<1% titanium<0.2% aluminum<0.1% phosphorus<0.1% sulfur<0.05% 0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, the shoot ensuring a very high mechanical resistance after thermal treatment and the aluminum-based coating ensuring a high resistance to corrosion.

What is claimed is: 
     
       1. A hot-rolled coated steel sheet comprising a hot-rolled steel sheet coated with an aluminum or aluminum alloy coating, wherein the steel in the sheet comprises the following composition by weight:
 0.15%<carbon<0.5%   0.5%<manganese<3%   0.1%<silicon<0.5%   0.01% <chromium<1%   titanium<0.2%   aluminum<0.1%   phosphorus<0.1%   sulfur<0.05%   0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, and the steel sheet has a very high mechanical resistance after thermal treatment and the aluminum or aluminum alloy coating provides a high resistance to corrosion of the steel sheet.   
     
     
       2. The coated steel sheet according to  claim 1 , wherein the composition by weight of the sheet further comprises the following:
 0.20%<carbon<0.5%   0.8%<manganese<1.5%   0.1%<silicon<0.35%   0.01%<chromium<1%   titanium<0.1%   aluminum<0.1%   phosphorus<0.05%   sulfur 0.03%   0.0005%<boron<0.01%, the remainder being iron and impurities inherent in processing.   
     
     
       3. A heat treated coated steel sheet prepared by subjecting the coated steel sheet according to  claim 2 , to an increase in temperature at a speed in excess of 600° C./second. 
     
     
       4. A process for producing a casting comprising
 shaping the coated steel sheet of  claim 2 ,   subjecting the shaped coated steel sheet to an increase in temperature at a speed in excess of 5° C./sec.   
     
     
       5. The coated steel sheet according to  claim 1 , wherein the ratio of titanium to nitrogen in the steel sheet in weight % is in excess of 3.42. 
     
     
       6. A process for producing a casting comprising
 shaping the coated steel sheet of  claim 5 ,   subjecting the shaped coated steel sheet to an increase in temperature at a speed in excess of 5° C./sec.   
     
     
       7. The coated steel sheet according to  claim 1 , wherein the aluminum or aluminum alloy coating comprises from 9% to 10% silicon by weight, from 2% to 3.5% iron by weight, the remainder being aluminum. 
     
     
       8. A process for producing a casting comprising
 shaping the coated steel sheet of  claim 7 ,   subjecting the shaped coated steel sheet to an increase in temperature at a speed in excess of 5° C./sec.   
     
     
       9. The coated steel sheet according to  claim 1 , wherein the coating comprises from 2% to 4% iron by weight, the remainder being aluminum. 
     
     
       10. A process for producing a casting comprising
 shaping the coated steel sheet of  claim 9 ,   subjecting the shaped coated steel sheet to an increase in temperature at a speed in excess of 5° C./sec.   
     
     
       11. A process for producing a casting comprising
 shaping the coated steel sheet of  claim 1 ,   subjecting the shaped coated steel sheet to an increase in temperature at a speed in excess of 5° C./second.   
     
     
       12. The process according to  claim 11 , wherein the casting is heated to a temperature in excess of 750° C. 
     
     
       13. A heat treated coated steel sheet prepared by subjecting the coated steel sheet according to  claim 1  to an increase in temperature at a speed in excess of 600° C./second. 
     
     
       14. A land motor vehicle comprising the heat treated coated steel of  claim 13 . 
     
     
       15. A land motor vehicle comprising the coated steel sheet of  claim 1 . 
     
     
       16. A heat treated coated steel sheet prepared by subjecting the coated steel sheet according to  claim 1  to a temperature in excess of 750° C. 
     
     
       17. A hot-rolled coated steel sheet comprising a hot-rolled steel sheet coated with an aluminum or aluminum alloy coating, wherein said coated steel sheet is in the form of a delivery coil and the steel in the sheet comprises the following composition by weight:
 0.15%<carbon<0.5%   0.5%<manganese<3%   0.1%<silicon<0.5%   0.01%<chromium<1%   titanium<0.2%   aluminum<0.1%   phosphorus<0.1%   sulfur<0.05%   0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, and the steel sheet has a very high mechanical resistance in excess of 1500 MPa after thermal treatment and the aluminum or aluminum alloy coating provides a high resistance to corrosion of the steel sheet.    
     
     
       18. The coated steel sheet of claim 17 that is manufactured by a process comprising providing said hot rolled sheet; and coating said hot rolled sheet with an aluminum coating or aluminum alloy coating.  
     
     
       19. The coated steel sheet of claim 18 wherein said aluminum or aluminum alloy coating is obtained by hot-dipping and comprises, before said thermal treatment, a first alloy layer in contact with the surface of the steel, and a second alloy layer on top of the first alloy layer.  
     
     
       20. The coated steel sheet of claim 19 wherein the first coating layer comprises iron.  
     
     
       21. The coated steel sheet of claim 19 wherein the second coating layer comprises iron.  
     
     
       22. The coated steel sheet of claim 17 wherein the aluminum coating or aluminum alloy coating has a thickness of about 20 micrometers.  
     
     
       23. The coated steel sheet of claim 17 wherein the steel in the sheet is treated with calcium.  
     
     
       24. A coated steel sheet according to claim 17, manufactured by a process comprising a step of cold-rolling before said aluminum or aluminum alloy coating.  
     
     
       25. The coated steel sheet of claim 24 that is composed predominately of martensite.  
     
     
       26. The coated steel sheet of claim 24 wherein said subsequent thermal treatment includes hot-shaping the coated steel sheet, and cooling the hot-shaped sheet at a rate that produces martensitic structures, ferrite-martensitic structures , or ferrite-bainitic structures.  
     
     
       27. A hot-rolled coated steel sheet comprising a hot-rolled steel sheet coated with an aluminum or aluminum alloy coating, wherein the steel in the sheet comprises the following composition by weight:
 0.15%<carbon<0.5%   0.5%<manganese<3%   0.1%<silicon<0.5%   0.01%<chromium<1%   titanium<0.2%   aluminum<0.1%   phosphorus<0.1%   sulfur<0.05%   0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, and the steel sheet has a very high mechanical resistance in excess of 1500 MPa after a subsequent thermal treatment, and the aluminum or aluminum alloy coating provides a high resistance to corrosion and prevents decarburization during said subsequent thermal treatment of the steel sheet.    
     
     
       28. The coated steel sheet of claim 27 that is composed predominately of martensite.  
     
     
       29. The coated steel sheet of claim 27 wherein said subsequent thermal treatment includes hot-shaping the coated steel sheet, and cooling the hot-shaped sheet at a rate that produces martensitic structures, ferrite-martensitic structures, or ferrite-bainitic structures.