Impact resistant high strength steel

Abstract

The present invention describes a novel martensitic steel with iron, nickel, boron, a carbide former, manganese, and carbon. The steel has substantially no cementite, substantially no interstitial carbon and substantially no interstitial nitrogen. There are ordered intermetallics dispersed in the iron and ordered intermetallics clustered at the dislocations. The present invention also describes a method of making high strength steel by alloying steel comprising iron and carbon with a strong carbide former, boron, and titanium, followed by heating the alloy steel to a sufficiently high temperature that the steel transitions to an austenitic, face centered cubic lattice phase and the strong carbide former removes substantially all of the carbon from the crystal lattice by forming a metal carbide other than iron carbide. The alloy steel is then quenched to a quench temperature with a quench faster than still air such that a body centered cubic lattice is formed by displacement, which forms ordered intermetallics in the alloy steel.

What is claimed is: 
     
         1 . A martensitic steel comprising:
 a) iron, at least some of the iron having dislocations,   b) less than 10% nickel,   c) between 0.0001 and 0.01% boron,   d) more than 0.01% carbide former,   e) less than 10% manganese,   f) carbon, and   g) less than 7% of all other elements,   wherein the steel has substantially no cementite, substantially no interstitial carbon and substantially no interstitial nitrogen, and   wherein there are ordered intermetallics dispersed in the iron and ordered intermetallics clustered at the dislocations.   
     
     
         2 . The steel of  claim 1  wherein the carbide former comprises vanadium, titanium, niobium, zirconium, or a combination thereof. 
     
     
         3 . The steel of  claim 2  wherein the carbide former is titanium. 
     
     
         4 . The steel of  claim 1 , further comprising more than 0.025% titanium. 
     
     
         5 . The steel of  claim 1 , further comprising more than 0.05% titanium. 
     
     
         6 . The steel of  claim 1 , further comprising more than 0.075% titanium. 
     
     
         7 . The steel of  claim 1 , further comprising less than 6.5% titanium. 
     
     
         8 . The steel of  claim 1 , comprising at least 80% iron. 
     
     
         9 . The steel of  claim 1 , comprising less than 5% nickel. 
     
     
         10 . The steel of  claim 1 , comprising less than 5% manganese. 
     
     
         11 . The steel of  claim 1 , comprising at least 0.001% of carbon. 
     
     
         12 . The steel of  claim 1 , comprising at least 0.005% of carbon. 
     
     
         13 . The steel of  claim 1 , comprising between 0.005 to 0.2% carbon. 
     
     
         14 . The steel of  claim 1 , wherein the steel comprises at least 0.025% aluminum, and wherein the ordered intermetallics comprise ordered aluminum intermetallics. 
     
     
         15 . The steel of  claim 1 , wherein the steel comprises at least 0.01% titanium, and wherein the ordered intermetallics comprise ordered titanium intermetallics. 
     
     
         16 . A method of making a high strength steel comprising the steps of:
 a. alloying steel comprising iron and carbon with a strong carbide former, boron, and titanium   b. heating the alloy steel to a sufficiently high temperature that the steel transitions to an austenitic, face centered cubic lattice phase and the strong carbide former removes substantially all of the carbon from the crystal lattice by forming a metal carbide other than iron carbide;   c. quenching the alloy steel to a quench temperature with a quench faster than still air such that a body centered cubic lattice is formed by displacement; and   d. forming ordered intermetallics in the alloy steel.   
     
     
         17 . The method of  claim 16  wherein step (d) comprises maintaining the alloy steel at a temperature between 200° C. and 750° C. for more than one minute. 
     
     
         18 . The method of  claim 16  wherein step (d) comprises heating the alloy steel. 
     
     
         19 . The method of  claim 16  wherein step (d) comprises having the alloy steel at the quench temperature or higher for more than one minute. 
     
     
         20 . The method of  claim 16  wherein the carbide former comprises vanadium, titanium, niobium, zirconium, or a combination thereof. 
     
     
         21 . The method of  claim 16  comprising between steps (b) and (c) forming the steel by forging or hot rolling; 
     
     
         22 . The method of  claim 16 , wherein the steel is cold rolled after step c). 
     
     
         23 . The steel made by the method of  claim 16 . 
     
     
         24 . The steel of  claim 23  comprising at least 0.01% carbide former. 
     
     
         25 . The steel of  claim 23  wherein the ordered intermetallics comprise ordered titanium intermetallics.