ULTRA-FINE GRAINED STEELS HAVING CORROSION-FATIGUE RESISTANCE

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

P

A

/

T



(

T

,

t

)

=

-

B

/

ln



[

∫

0

t



exp



(

-

Q

R

·

T

)

·



t

]

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.