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.

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   0.0001-0.0025% boron;   wherein the steel sucker rod is manufactured by a method including providing the steel composition and processing the steel composition, wherein the processing consists essentially of:
 hot rolling the steel composition at a forging ratio greater than about 15 to form a steel sucker rod; 
 austenitizing the hot rolled steel sucker rod at a heating rate greater than about 100° C./sec to a temperature between a critical temperature (Ac3) and a maximum temperature that satisfies a formula Tmax=1025° C.-210° C.*sqrt (wt. % C)+50° C.*wt. % Mo to form an austenitized steel sucker rod; 
 quenching the austenitized steel sucker rod below about 100° C. to produce a martensitic microstructure to form a quenched steel sucker rod; and 
 tempering the quenched steel sucker rod at a temperature between 565° C. and a lower critical temperature (Ac1) to form a tempered steel sucker rod comprising at least 90 volume % tempered martensite; 
   wherein a time between a maximum austenitizing and quenching is between 1 second and 10 seconds,   wherein an austenitic grain size prior to quenching is  5  microns or less; and   wherein the processing does not comprise additional austenitizing or quenching steps.   
     
     
         2 . The steel sucker rod of  claim 1 , wherein the steel composition further comprises, by weight:
 0 to 0.05 wt. % vanadium; and   0 to 0.2 wt. % nickel.   
     
     
         3 . The steel sucker rod of  claim 1 , wherein the steel composition comprises iron and, 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.   
     
     
         4 . The steel sucker rod of  claim 3 , wherein the steel composition comprises iron and, 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.   
     
     
         5 . The steel sucker rod of  claim 1 , wherein the austenitic grain size prior to quenching is between 2 and 5 microns. 
     
     
         6 . The steel sucker rod of  claim 1 , wherein quenching the austenitized steel sucker rod comprises a quenching rate of greater than about 50° C./sec. 
     
     
         7 . The steel sucker rod of  claim 1 , wherein the tempered steel sucker rod comprises a yield strength greater than 100 ksi. 
     
     
         8 . The steel sucker rod of  claim 1 , wherein the tempered steel sucker rod comprises an ultimate tensile strength between about 115 and about 140 ksi. 
     
     
         9 . The steel sucker rod of  claim 1 , wherein the tempered steel sucker rod comprises a minimum absorbed energy in a Charpy V-notch impact test of 100 Joules at room temperature. 
     
     
         10 . The steel sucker rod of  claim 1 , wherein the tempered steel sucker rod comprises:
 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 a Charpy V-notch impact test of 100 Joules at room temperature.   
     
     
         11 . The steel sucker rod of  claim 1 , wherein an average grain size of the final microstructure of the tempered steel sucker rod is 5 microns or less. 
     
     
         12 . The steel sucker rod of  claim 1 , wherein the heating rate is greater than the rate of quenching the austenitized steel sucker rod. 
     
     
         13 . 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   0.0001-0.0025% boron;   wherein the steel sucker rod is manufactured by a method including providing the steel composition and processing the steel composition, wherein the processing consists of:
 hot rolling the steel at a forging ratio greater than about 15 to form a steel sucker rod; 
 austenitizing the hot rolled steel sucker rod at a heating rate greater than about 100° C./sec to a temperature between a critical temperature (Ac3) and a maximum temperature that satisfies a formula Tmax=1025° C.-210° C.*sqrt (wt. % C)+50° C.*wt. % Mo to form an austenitized steel sucker rod; 
 quenching the austenitized steel sucker rod below about 100° C. at a rate to produce a martensitic microstructure to form a quenched steel sucker rod; and 
 tempering the quenched steel sucker rod at a temperature between 565° C. and a lower critical temperature (Ac1) to form a tempered steel sucker rod comprising at least 90 volume % 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. 
   
     
     
         14 . A steel sucker rod formed from a steel composition comprising iron and, by weight:
 0.2-0.3% carbon;   0.4-0.7% manganese;   0.8-1.2% chromium;   0.01-0.04% aluminum;   0.2-0.3% silicon;   0.3-0.8% molybdenum;   0.02-0.04% niobium;   0.005-0.02% titanium;   0.0001-0.002% boron;   at most 0.005% sulfur;   at most 0.015% phosphorus; and   at most 0.01% nitrogen;   wherein the steel sucker rod comprises a final microstructure comprising tempered martensite,   wherein an average grain size of the final microstructure is between about 2 and 3.7 micrometers,   wherein a final microstructure of the steel sucker rod comprises at least 90 volume % tempered martensite,   wherein the steel sucker rod comprises a minimum absorbed energy in Charpy V-notch impact test of 100 Joules at room temperature, and   wherein the steel sucker rod comprises a corrosion fatigue life of more than 10 5  cycles in a buffered solution saturated with H 2 S or CO 2  with a maximum and minimum applied stress of 47 Ksi and 12 Ksi, and a cycling frequency of 20 cycles/min.   
     
     
         15 . The steel sucker rod of  claim 14 , wherein the steel sucker rod comprises approximately twice the average life of conventional sucker rod materials in corrosion fatigue under CO2 or H2S environments. 
     
     
         16 . The steel sucker rod of  claim 14 , wherein the minimum absorbed energy in Charpy V-notch impact test of the steel sucker rod is 150 Joules at room temperature. 
     
     
         17 . The steel sucker rod of  claim 14 , wherein the steel composition satisfies the formula: (A1/27+Ti/48+V/51+Nb/93−N/14)*100 between about 0.08 and about 0.15% by weight. 
     
     
         18 . The steel sucker rod of  claim 14 , 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. 
     
     
         19 . The steel sucker rod of  claim 14 , wherein the steel sucker rod comprises a yield strength greater than about 100 ksi. 
     
     
         20 . The steel sucker rod of  claim 14 , wherein the steel sucker rod comprises an ultimate tensile strength between about 115 and about 140 ksi. 
     
     
         21 . The steel sucker rod of  claim 14 , wherein the steel sucker rod comprises a solid bar body, a first upset and threaded end and a second upset and threaded end.