High-strength bainitic steel

Abstract

A high-strength steel alloy and automotive components produced therefrom, as well as a method for forming a steel alloy, are provided. The high-strength steel alloy includes iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur; about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum. The steel alloy may also include boron, molybdenum, titanium, niobium, and/or nitrogen. The method includes air quenching a steel alloy component after mold shakeout until the component reaches a temperature in the range of 420 to 530 degrees Celsius.

What is claimed is: 
     
         1 . A high-strength steel alloy comprising:
 iron;   about 0.24 to about 0.80 weight percent carbon;   about 0.40 to about 2.10 weight percent manganese;   about 0.20 to about 1.60 weight percent silicon;   about 0.05 to about 0.14 weight percent sulfur;   about 0.10 to about 12.0 weight percent chromium;   about 0.10 to about 2.50 weight percent nickel; and   about 0.02 to about 0.07 weight percent aluminum.   
     
     
         2 . The high-strength steel alloy of  claim 1 , further comprising boron in an amount not exceeding 0.005 weight percent. 
     
     
         3 . The high-strength steel alloy of  claim 2 , wherein the iron is provided in an amount between about 75.0 and about 98.88 weight percent. 
     
     
         4 . The high-strength steel alloy of  claim 3 , further comprising molybdenum in an amount not exceeding 0.60 weight percent. 
     
     
         5 . The high-strength steel alloy of  claim 4 , further comprising vanadium in an amount not exceeding 0.20 weight percent. 
     
     
         6 . The high-strength steel alloy of  claim 5 , further comprising titanium in an amount not exceeding 0.20 weight percent. 
     
     
         7 . The high-strength steel alloy of  claim 6 , further comprising niobium in an amount not exceeding 0.20 weight percent. 
     
     
         8 . The high-strength steel alloy of  claim 7 , further comprising about 0.01 to about 0.04 weight percent nitrogen. 
     
     
         9 . The high-strength steel alloy of  claim 2 , wherein the high-strength steel alloy comprises:
 about 0.24 to about 0.40 weight percent carbon;   about 1.50 to about 2.00 weight percent manganese;   about 0.40 to about 0.80 weight percent silicon;   about 0.05 to about 0.12 weight percent sulfur;   about 0.10 to about 0.60 weight percent chromium;   about 0.60 to about 0.90 weight percent nickel;   about 0.20 to about 0.40 weight percent molybdenum;   about 0.02 to about 0.04 weight percent aluminum; and   about 0.001 to about 0.005 weight percent boron.   
     
     
         10 . The high-strength steel alloy of  claim 2 , wherein the high-strength steel alloy comprises:
 about 0.25 to about 0.50 weight percent carbon;   about 1.50 to about 2.00 weight percent manganese;   about 0.30 to about 0.60 weight percent silicon;   about 0.05 to about 0.12 weight percent sulfur;   about 0.20 to about 0.60 weight percent chromium;   about 0.50 to about 0.90 weight percent nickel;   about 0.15 to about 0.40 weight percent molybdenum;   about 0.02 to about 0.04 weight percent aluminum; and   about 0.001 to about 0.005 weight percent boron.   
     
     
         11 . A crankshaft for an automotive propulsion system, created from a high-strength steel alloy according to  claim 10 . 
     
     
         12 . A crankshaft for an automotive propulsion system, created from a high-strength steel alloy according to  claim 1 . 
     
     
         13 . The high-strength steel alloy of  claim 2 , having an ultimate tensile strength in the range of 750 to 1100 MPa. 
     
     
         14 . The high-strength steel alloy of  claim 13 , having an ASTM grain size number in the range of 5 to 8. 
     
     
         15 . A high-strength steel alloy consisting essentially of:
 about 0.35 weight percent carbon;   about 1.65 weight percent manganese;   about 0.45 weight percent silicon;   about 0.4 weight percent chromium;   about 0.7 weight percent nickel;   about 0.25 weight percent molybdenum; and   the balance iron.   
     
     
         16 . A method of forming a steel alloy component, the method comprising:
 creating a steel alloy comprising iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur, about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum;   casting in a mold the steel alloy to form the component;   shaking out the mold; and   air quenching the component until the component has a temperature in the range of 420 to 530 degrees Celsius.   
     
     
         17 . The method of  claim 16 , further comprising:
 holding the component at an isothermal temperature in the range of 420 to 530 Celsius starting immediately after the step of air quenching and continuing for a time period in the range of 1.5 to 3.5 hours.   
     
     
         18 . The method of  claim 17 , wherein the step of holding the component at the isothermal temperature is performed immediately after the step of air quenching without cooling the component to a temperature below 420 degrees Celsius between the step of air quenching and the step of holding the component at the isothermal temperature. 
     
     
         19 . The method of  claim 18 , wherein the step of creating the steel alloy further comprises creating the steel alloy comprising boron in an amount not exceeding 0.005 weight percent.