Ultra-high-strength and ultra-high-toughness oil casing and manufacturing method thereof

Abstract

There is disclosed an ultrahigh strength and ultrahigh toughness oil casing pipe, comprising the following chemical elements in mass percentages: C: 0.12-0.18%; Si: 0.1-0.4%; Mn: 1.1-1.6%; Cr: 0.1-0.4%; Mo: 0.2-0.5%; Nb: 0.02-0.04%; Ti: 0.02-0.05%; B: 0.0015-0.005%; Al: 0.01-0.05%; Ca: 0.0005-0.005%; N≦0.008%; with the proviso of 0<(Ti—3.4N)≦0.02%, Ti/B≧10; and the balance of Fe and other unavoidable impurities. The strength of the oil casing pipe can be equal to or higher than 150 ksi steel grade, and the zero degree lateral Charpy impact work is not less than 10% of the yield strength of the 150 ksi steel grade.

1 . An ultrahigh strength and ultrahigh toughness oil casing pipe, comprising the following chemical elements in mass percentages:
 C: 0.12-0.18%; Si: 0.1-0.4%; Mn: 1.1-1.6%; Cr: 0.1-0.4%; Mo: 0.2-0.5%; Nb: 0.02-0.04%; Ti: 0.02-0.05%; B: 0.0015-0.005%; Al: 0.01-0.05%; Ca: 0.0005-0.005%;   N≦0.008%; with the proviso of 0<(Ti—3.4N)≦0.02%, Ti/B≧10; and the balance of Fe and other unavoidable impurities.   
     
     
         2 . The ultrahigh strength and ultrahigh toughness oil casing pipe of  claim 1 , further comprising V: 0<V≦0.1 wt %. 
     
     
         3 . The ultrahigh strength and ultrahigh toughness oil casing pipe of  claim 1 , wherein the oil casing pipe has a microstructure of tempered sorbite. 
     
     
         4 . The ultrahigh strength and ultrahigh toughness oil casing pipe of  claim 1 , wherein the oil casing pipe has a yield strength of 1034-1241 MPa, a tensile strength ≧1103 MPa, an elongation of 20%-30%, a zero degree lateral Charpy impact work not less than 10% of the yield strength, and a ductile-brittle transition temperature ≦−70° C. 
     
     
         5 . The ultrahigh strength and ultrahigh toughness oil casing pipe of  claim 1 , wherein the oil casing pipe has a yield strength of 1069-1276 MPa, a tensile strength ≧1138 MPa, an elongation of 20%-25%, a zero degree lateral Charpy impact work not less than 10% of the yield strength, and a ductile-brittle transition temperature ≦−60° C. 
     
     
         6 . A method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe of  claim 1 , comprising the following steps: smelting; continuous casting; perforating; rolling; sizing; and heat treatment. 
     
     
         7 . The method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe according to  claim 6 , wherein, in the continuous casting step, a molten steel superheat is controlled to be less than 30° C., and a continuous casting speed is controlled in the range of 1.8-2.2 m/min. 
     
     
         8 . The method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe according to  claim 6 , wherein, in the piercing step, a round blank from the continuous casting step is heated homogeneously in a furnace at 1200-1240° C., and a piercing temperature is 1180-1240° C. 
     
     
         9 . The method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe according to  claim 6 , wherein, in the rolling step, an end rolling temperature is controlled in the range of 900-950° C. 
     
     
         10 . The method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe according to  claim 6 , wherein, in the sizing step, a sizing temperature is 850-900° C. 
     
     
         11 . The method of manufacturing the ultrahigh strength and ultrahigh toughness oil casing pipe according to  claim 6 , wherein, in the heat treatment step, an austenitizing temperature is controlled in the range of 900-930° C., and the austenitizing temperature is held for 30-60 min, followed by hardening; subsequently, tempering is conducted at a temperature in the range of 450-550° C., and this temperature is held for 50-80 min; finally, hot sizing is conducted at a temperature in the range of 400-550° C.