Impact resistant high strength steel

Abstract

The present invention describes a novel steel sheet or plate formed of a martensitic steel alloy having iron, at least some of the iron having dislocations; less than 5% of any combination of nickel, manganese, and copper; from about 0.0001% to about 0.01% boron; from about 0.05% to about 6.5% titanium; more than 0.003% and less than 0.1% carbon; and less than 7% of all other elements. The steel has substantially no cementite, the titanium has clustered at the dislocations, and the steel sheet or plate has been formed by quenching off of a hot sheet or plate mill.

What is claimed is: 
     
         1 . A steel sheet or plate formed of a martensitic steel alloy comprising:
 a) iron, at least some of the iron having dislocations;   b) less than 5% of any combination of nickel, manganese, and copper;   c) from about 0.0001 to about 0.01% boron;   d) from about 0.05% to about 6.5% titanium;   e) more than 0.003% and less than 0.1% carbon; and   f) less than 7% of all other elements.   
     
     
         2 . The steel sheet or plate of  claim 1  wherein the alloy comprises more than 0.1% titanium. 
     
     
         3 . The steel sheet or plate of  claim 1  wherein the alloy comprises more than 0.12% titanium. 
     
     
         4 . The steel sheet or plate of  claim 1  wherein the alloy comprises more than 0.14% titanium. 
     
     
         5 . The steel sheet or plate of  claim 1  wherein the alloy comprises more than 0.2% titanium. 
     
     
         6 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.5% of any combination of nickel, manganese, and copper. 
     
     
         7 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 1% of any combination of nickel, manganese, and copper. 
     
     
         8 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 1.5% of any combination of nickel, manganese, and copper. 
     
     
         9 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 2% of any combination of nickel, manganese, and copper. 
     
     
         10 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 2.5% of any combination of nickel, manganese, and copper. 
     
     
         11 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 3% of any combination of nickel, manganese, and copper. 
     
     
         12 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.05% carbon. 
     
     
         13 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.04% carbon. 
     
     
         14 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.03% carbon. 
     
     
         15 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.02% carbon. 
     
     
         16 . The steel sheet or plate of  claim 1  wherein the alloy comprises less than 0.01% carbon. 
     
     
         17 . The steel sheet or plate of  claim 1 , wherein the alloy comprises at least 0.025% aluminum. 
     
     
         18 . The steel sheet or plate of  claim 1  that has been cold rolled. 
     
     
         19 . The steel sheet or plate of  claim 1 , after quenching, that has been reheated to a temperature of between 200 C and 750 C and maintained at that temperature for more than one minute. 
     
     
         20 . The steel sheet or plate of  claim 1 , wherein the alloy is substantially a martensitic structure with minor ferrite zones. 
     
     
         21 . The steel sheet or plate of  claim 18  that has been hot dip coated in zinc or an alloy containing zinc without substantially crystallizing the martensitic steel structure. 
     
     
         22 . The steel sheet or plate of  claim 1 , wherein the alloy comprises substantially no copper. 
     
     
         23 . The steel sheet or plate of  claim 1 , wherein the alloy has substantially no cementite. 
     
     
         24 . A steel sheet or plate formed of a martensitic steel alloy comprising:
 a) iron, at least some of the iron having dislocations;   b) less than 5% of any combination of nickel, manganese, and copper;   c) from about 0.0001 to about 0.01% boron;   d) from about 0.05% to about 6.5% titanium;   e) more than 0.003% and less than 0.1% carbon; and   f) less than 7% of all other elements;   
       wherein the sheet or plate has been formed by quenching off of a hot sheet or plate mill. 
     
     
         25 . The steel sheet or plate of  claim 1 , wherein the titanium has clustered at the dislocations. 
     
     
         26 . A method of making a steel sheet or plate formed of a martensitic steel alloy, the method comprising the steps of:
 a) heating the alloy steel defined in  claim 1  to a sufficiently high temperature that the steel transitions to an austenitic, face centered cubic lattice phase and the titanium removes substantially all of the carbon from the crystal lattice by forming a metal carbide other than iron carbide;   b) hot rolling the heated alloy steel of step (a); and   c) quenching the hot rolled steel of step (b) to a quench temperature with a quench faster than still air such that a body centered cubic lattice is formed by displacement.   
     
     
         27 . The method of  claim 26  comprising cold rolling the alloy steel to form the sheet or plate before the step of quenching. 
     
     
         28 . The method of  claim 26  wherein the quench temperature is from about 200 to about 750 degrees C. 
     
     
         29 . The method of  claim 26  wherein the step of heating comprises heating to a temperature greater than 1000 degree C. 
     
     
         30 . The method of  claim 26  wherein after quenching the hot rolled steel is maintained at a temperature of greater than 200 degree C. for a sufficient time to form order intermetallics. 
     
     
         31 . The method of  claim 26  wherein, after quenching, heating the rolled steel to a reheat temperature of between 200 C and 750 C and maintaining it at the reheat temperature for more than one minute. 
     
     
         32 . The method of  claim 26  comprising the additional step of hot dip coating the rolled steel in zinc or an alloy containing zinc without substantially crystallizing the martensitic steel structure. 
     
     
         33 . The steel sheet or plate of  claim 24  that has been hot dip coated in zinc or an alloy containing zinc without substantially crystallizing the martensitic steel structure.