Ultra-fine grained steels having corrosion-fatigue resistance

Abstract

Embodiments of an ultra-fine-grained, medium carbon steel are disclosed herein. In some embodiments, the ultra-fine grained steel can have high corrosion fatigue resistance, as well as high toughness and yield strength. The ultra-fine grained steels can be advantageous for use as sucker rods in oil wells having corrosive environments.

What is claimed is: 
     
         1 . A steel sucker rod formed from a steel composition comprising iron and, by weight:
 0.15-0.4% carbon;   0.1-1.0% manganese;   0.5-1.5% chromium;   0.01-0.1% aluminum;   0.2-0.35% silicon;   0.1-1.0% molybdenum;   0.01-0.05% niobium;   0.005-0.03% titanium; and   0.0001-0.005% boron;   wherein the steel has a final microstructure comprising tempered martensite; and   wherein an average grain size of the final microstructure is between about 2 and about 5 micrometers.   
     
     
         2 . The steel sucker rod of  claim 1 , wherein the rod has approximately twice the average life of conventional sucker rod materials in corrosion fatigue under CO 2  or H 2 S environments. 
     
     
         3 . The steel sucker rod of  claim 1 , wherein the steel composition comprises, by weight:
 0 to 0.05 wt. % vanadium; and   0 to 0.2 wt. % nickel.   
     
     
         4 . The steel sucker rod of  claim 1 , wherein the final microstructure comprises at least 90 volume % tempered martensite. 
     
     
         5 . The steel sucker rod of  claim 1 , comprising:
 a yield strength greater than about 100 ksi;   an ultimate tensile strength between about 115 and about 140 ksi; and   a minimum absorbed energy in Charpy V-notch impact test of 100 Joules at room temperature.   
     
     
         6 . The steel sucker rod of  claim 1 , wherein the steel composition comprises, by weight:
 less than 0.01% sulfur;   less than 0.015% nitrogen; and   less than 0.02% phosphorus.   
     
     
         7 . The steel sucker rod of  claim 1 , wherein the steel composition comprises, by weight:
 0.15-0.3% carbon;   0.3-0.7% manganese;   0.2-0.35% silicon;   0.01-0.05% niobium;   less than 0.008% sulfur;   less than 0.018% phosphorus;   less than 0.015% nitrogen;   0.5-1.2% chromium;   0.2-0.8% molybdenum;   0.01-0.03% titanium;   0.0010 to 0.0025% boron; and   0.01 to 0.05% aluminum.   
     
     
         8 . The steel sucker rod of  claim 7 , wherein the steel composition comprises, by weight:
 0.2-0.3% carbon;   0.4-0.7% manganese;   0.2-0.3% silicon;   0.02-0.04% niobium;   less than 0.005% sulfur;   less than 0.015% phosphorus;   less than 0.01 nitrogen;   0.8-1.2% chromium;   0.3-0.8% molybdenum;   0.01-0.02% titanium;   0.001 to 0.002% boron; and   0.01 to 0.04% aluminum.   
     
     
         9 . The steel sucker rod of  claim 1 , wherein the steel composition satisfies the formula: (Al/27+Ti/48+V/51+Nb/93-N/14)*100 between about 0.08 and about 0.15% by weight. 
     
     
         10 . The steel sucker rod of  claim 1 , wherein the steel composition satisfies the formulas: C+Mn/10 between about 0.1 and about 0.4% by weight, and Ni/10+Cr/12+Mo/8+Nb/2+20*B+V between about 0.1 and about 0.25% by weight. 
     
     
         11 . The steel sucker rod of  claim 10 , wherein the steel composition satisfies the formulas: C+Mn/10 between about 0.2 and about 0.3% by weight, and Ni/10+Cr/12+Mo/8+Nb/2+20*B+V between about 0.15 and about 0.25% by weight. 
     
     
         12 . A method of manufacturing a steel sucker rod, the method comprising:
 providing a steel composition comprising iron and:
 0.15-0.4 wt. % carbon; 
 0.1-1.0 wt. % manganese; 
 0.5-1.5 wt. % chromium; 
 0.2-0.35 wt. % silicon; 
 0.1-1.0 wt. % molybdenum; 
 0.01-0.05 wt. % niobium; 
 0.005-0.03 wt. % titanium; 
 0.0001 to 0.0025 wt. % boron; 
 0.01 to 0.1 wt. % aluminum; 
   hot rolling the steel composition at a forging ratio greater than about 15;   austenitizing the hot rolled steel composition at a temperature between the critical temperature (Ac3) and a maximum temperature that satisfies the formula Tmax=1025° C.−210° C.*sqrt(wt % C)+50° C.*wt % Mo;   quenching the steel composition below about 100° C. at a rate to produce a martensitic microstructure; and   tempering at a temperature between 565° C. and a lower critical temperature (Ac1) to form tempered martensite;   wherein a time between a maximum austenitizing and quenching is between 1 second and 10 seconds; and   wherein an austenitic grain size prior to quenching is 5 microns or less.   
     
     
         13 . The method of  claim 12 , wherein the austenitizing and tempering treatments are characterized by temperature equivalent parameters 
       
         
           
             
               
                 
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         where T is the absolute temperature in ° K, t is the time in seconds, R is the gas constant (J/mol ° K), Q is an activation energy (425,000 J/mol) and B is a constant (14,000° C.), P A  is below 800° C., P T  is above 700° C., and the difference between P A  and P T  is less than or equal to 200° C. 
       
     
     
         14 . The method of  claim 13 , wherein the steel composition comprises, by weight:
 0 to 0.05 wt. % vanadium; and   0 to 0.2 wt. % nickel.   
     
     
         15 . The method of  claim 13 , wherein the difference between P A  and P T  is less than 100° C. 
     
     
         16 . The method of  claim 12 , wherein the austenitic grain size prior to quenching is between 2 and 5 microns. 
     
     
         17 . The method of  claim 12 , wherein the steel is quenched at a rate greater than about 50° C./sec. 
     
     
         18 . The method of  claim 17 , wherein the steel composition comprises, by weight:
 0.15-0.3% carbon;   0.3-0.7% manganese;   0.2-0.35% silicon;   0.01-0.05% niobium;   less than 0.008% sulfur;   less than 0.018% phosphorus;   less than 0.015% nitrogen;   0.5-1.2% chromium;   0.2-0.8% molybdenum;   0.01-0.03% titanium;   0.0010 to 0.0025% boron; and   0.01 to 0.05% aluminum.   
     
     
         19 . The method of  claim 18 , wherein the steel composition comprises, by weight:
 0.2-0.3% carbon;   0.4-0.7% manganese;   0.2-0.3% silicon;   0.02-0.04% niobium;   less than 0.005% sulfur;   less than 0.015% phosphorus;   less than 0.01 nitrogen;   0.8-1.2% chromium;   0.3-0.8% molybdenum;   0.01-0.02% titanium;   0.001 to 0.002% boron; and   0.01 to 0.04% aluminum.   
     
     
         20 . A steel formed from a steel composition comprising iron and, by weight:
 0.15-0.4% carbon;   0.1-1.0% manganese;   0.5-1.5% chromium;   0.01-0.1% aluminum;   0.2-0.35% silicon;   0.1-1.0% molybdenum;   0.01-0.05% niobium;   0.005-0.03% titanium; and   0.0001-0.0025% boron;   wherein the steel has a final microstructure comprising tempered martensite; and   wherein an average grain size of the final microstructure is between about 2 and about 5 micrometers.