High hardness, high toughness iron-base alloys and methods for making same

Abstract

An aspect of the present disclosure is directed to low-alloy steels exhibiting high hardness and an advantageous level of multi-hit ballistic resistance with low or no crack propagation imparting a level of ballistic performance suitable for military armor applications. Various embodiments of the steels according to the present disclosure have hardness in excess of 550 BHN and demonstrate a high level of ballistic penetration resistance relative to conventional military specifications.

What is claimed is: 
     
         1 . An alloy comprising, in weight percentages based on total alloy weight:
 0.40 to 0.53 carbon;   0.15 to 1.00 manganese;   0.15 to 0.45 silicon;   0.95 to 1.70 chromium;   3.75 to 4.25 nickel;   0.0002 to 0.0050 boron;   0.001 to 0.015 cerium;   0.001 to 0.015 lanthanum;   no greater than 0.011 nitrogen;   iron; and   incidental impurities,   wherein the alloy has a hardness greater than 570 BHN and a microstructure comprising at least one of lath martensite phase and lower bainite phase.   
     
     
         2 . The alloy of  claim 1 , wherein the alloy has a hardness greater than 570 BHN and less than 675 BHN. 
     
     
         3 . The alloy of  claim 1 , wherein the alloy has a hardness greater than 600 BHN and less than 675 BHN. 
     
     
         4 . The alloy of  claim 1 , comprising at least 0.20 manganese. 
     
     
         5 . The alloy of  claim 1 , comprising no greater than 0.80 manganese. 
     
     
         6 . The alloy of  claim 1 , comprising at least 0.20 silicon. 
     
     
         7 . The alloy of  claim 1 , comprising no greater than 0.40 silicon. 
     
     
         8 . The alloy of  claim 1 , comprising at least 1.00 chromium. 
     
     
         9 . The alloy of  claim 1 , comprising no greater than 1.50 chromium. 
     
     
         10 . The alloy of  claim 1 , comprising at least 0.40 molybdenum. 
     
     
         11 . The alloy of  claim 1 , comprising no greater than 0.60 molybdenum. 
     
     
         12 . The alloy of  claim 1 , comprising 0.35 to 0.65 molybdenum. 
     
     
         13 . The alloy of  claim 1 , comprising at least 0.0015 boron. 
     
     
         14 . The alloy of  claim 1 , comprising no greater than 0.0025 boron. 
     
     
         15 . The alloy of  claim 1 , comprising:
 1.00 to 1.50 chromium; and   0.40 to 0.60 molybdenum.   
     
     
         16 . The alloy of  claim 1 , comprising:
 0.40 to 0.53 carbon;   0.20 to 1.00 manganese;   0.20 to 0.45 silicon;   1.00 to 1.50 chromium;   3.75 to 4.25 nickel;   0.0002 to 0.0050 boron;   0.001 to 0.015 cerium;   0.001 to 0.015 lanthanum;   no greater than 0.011 nitrogen;   iron; and   incidental impurities,   wherein the alloy has a hardness greater than 570 BHN and less than 675 BHN, and a microstructure comprising at least one of lath martensite phase and lower bainite phase.   
     
     
         17 . An article of manufacture comprising the alloy of  claim 1 . 
     
     
         18 . The article of manufacture of  claim 17 , wherein article of manufacture is a plate having a thickness of 0.188 to 0.300 inch. 
     
     
         19 . The article of manufacture of  claim 17 , wherein the article of manufacture is one of an armor plate and an armor sheet. 
     
     
         20 . The article of manufacture of  claim 19 , wherein the alloy has a hardness greater than 600 BHN and less than 675 BHN. 
     
     
         21 . The article of manufacture of  claim 17 , wherein the article of manufacture exhibits a V 50  ballistic limit value that exceeds the minimum V 50  ballistic limit value under specification MIL-DTL-32332 (Class 1) by at least 50 feet per second. 
     
     
         22 . The article of manufacture of  claim 17 , wherein the article of manufacture exhibits a V 50  ballistic limit value that is at least as great as a V 50  ballistic limit 100 feet per second less than the required V 50  ballistic limit under specification MIL-DTL-32332 (Class 2). 
     
     
         23 . The article of manufacture of  claim 17 , wherein the article of manufacture exhibits zero observable cracking when subjected to a .30 caliber M2, AP projectile strike. 
     
     
         24 . The article of manufacture of  claim 17 , wherein the alloy comprises:
 0.40 to 0.53 carbon;   0.20 to 1.00 manganese;   0.20 to 0.45 silicon;   1.00 to 1.50 chromium;   3.75 to 4.25 nickel;   0.0002 to 0.0050 boron;   0.001 to 0.015 cerium;   0.001 to 0.015 lanthanum;   no greater than 0.011 nitrogen;   iron; and   incidental impurities,   wherein the alloy has a hardness greater than 570 BHN and less than 675 BHN, and a microstructure comprising at least one of lath martensite phase and lower bainite phase.   
     
     
         25 . The article of manufacture of  claim 24 , wherein article of manufacture is a plate having a thickness of 0.188 to 0.300 inch. 
     
     
         26 . The article of manufacture of  claim 24 , wherein the article of manufacture is one of an armor plate and an armor sheet. 
     
     
         27 . The article of manufacture of  claim 26 , wherein the alloy has a hardness greater than 600 BHN and less than 675 BHN. 
     
     
         28 . The article of manufacture of  claim 26 , wherein the article of manufacture exhibits a V 50  ballistic limit value that exceeds the minimum V 50  ballistic limit value under specification MIL-DTL-32332 (Class 1) by at least 50 feet per second. 
     
     
         29 . The article of manufacture of  claim 26 , wherein the article of manufacture exhibits a V 50  ballistic limit value that is at least as great as a V 50  ballistic limit 100 feet per second less than the required V 50  ballistic limit under specification MIL-DTL-32332 (Class 2). 
     
     
         30 . The article of manufacture of  claim 26 , wherein the article of manufacture exhibits zero observable cracking when subjected to a .30 caliber M2, AP projectile strike.