Corrosion-resistant and high toughness oil casing and method for manufacturing same

Abstract

A corrosion-resistant and high toughness oil casing includes a chemical composition. The chemical composition includes, by mass %, C: 0.01% to 0.04%, Si: 0.1% to 0.8%, Mn: 0.05% to 0.25%, Cr: 11.0% to 14.0%, Mo: 1.5% to 2.8%, Cu: 0.5% to 1.8%, Ni: 3.7% to 5.0%, N: 0.03% to 0.05%, Al: 0.001% to 0.05%, B: 0.001% to 0.005%, Ti: 0.03% to 0.08%, La: 0.07% to 0.35%, Ce: 0.12% to 0.40%, P: 0.013% or less, S: 0.001% or less, and the balance being Fe and inevitable impurities. The mass % of the chemical composition satisfies the following relationships: [Ni]/[Cu]≥3.0, and 4360≤([Ni]+[Cr]+[Mo])/[B]≤16200. The microstructure of the oil casing includes, in terms of volume fraction, 10% to 20% of a ferrite phase, 5% to 20% of a retained austenite phase and the balance of a tempered martensite phase.

1 . An oil casing, comprising a chemical composition, wherein the chemical composition comprises, by mass %, C: 0.01% to 0.04%, Si: 0.1% to 0.8%, Mn: 0.05% to 0.25%, Cr: 11.0% to 14.0%, Mo: 1.5% to 2.8%, Cu: 0.5% to 1.8%, Ni: 3.7% to 5.0%, N: 0.03% to 0.05%, Al: 0.001% to 0.05%, B: 0.001% to 0.005%, Ti: 0.03% to 0.08%, La: 0.07% to 0.35%, Ce: 0.12% to 0.40%, P: 0.013% or less, S: 0.001% or less, and a balance being Fe and inevitable impurities;
 wherein the mass % of the chemical composition satisfies the following relationships: [Ni]/[Cu]≥3.0, and 4360]≤([Ni]+[Cr]+[Mo])/[B]≤16200, wherein [Ni] represents the mass % of the Ni element, [Cu] represents the mass % of the Cu element, [Cr] represents the mass % of the Cr element, [Mo] represents the mass % of the Mo element, and [B] represents the mass % of the B element; and   a microstructure of the oil casing comprises, in terms of volume fraction, 10% to 20% of a ferrite phase, 5% to 20% of a retained austenite phase and the balance of a tempered martensite phase.   
     
     
         2 . The oil casing of  claim 1 , wherein the chemical composition further comprises, by mass %, W: 0.01% to 1.3% and V: 0.06% to 0.1%. 
     
     
         3 . The oil casing of  claim 1 , wherein the chemical composition further comprises, by mass %, one or two elements selected from Ca: 0.0001% to 0.005% and Mg: 0.0001% to 0.005%. 
     
     
         4 . A method for manufacturing an oil casing comprising a chemical composition, wherein the chemical composition comprises, by mass %, C: 0.01% to 0.04%, Si: 0.1% to 0.8%, Mn: 0.05% to 0.25%, Cr: 11.0% to 14.0%, Mo: 1.5% to 2.8%, Cu: 0.5% to 1.8%, Ni: 3.7% to 5.0%, N: 0.03% to 0.05%, Al: 0.001% to 0.05%, B: 0.001% to 0.005%, Ti: 0.03% to 0.08%, La: 0.07% to 0.35%, Ce: 0.12% to 0.40%, P: 0.013% or less, S: 0.001% or less, and a balance being Fe and inevitable impurities;
 the mass % of the chemical composition satisfies the following relationships: [Ni]/[Cu]≥3.0, and 4360]≤([Ni]+[Cr]+[Mo])/[B]≤16200, in which, wherein [Ni] represents the mass % of the Ni element, [Cu] represents the mass % of the Cu element, [Cr] represents the mass % of the Cr element, [Mo] represents the mass % of the Mo element, and [B] represents the mass % of the B element; and   a microstructure of the oil casing comprises, in terms of volume fraction, 10% to 20% of a ferrite phase, 5% to 20% of a retained austenite phase and the balance of a tempered martensite phase;   wherein the method comprises the following processes:   a smelting and casting process: preparing raw materials according to the mass % of the chemical composition, and performing a smelting in an electric furnace, a ladle refining, a vacuum degassing and a curved continuous casting on the raw materials in sequence to obtain a billet;   a steel pipe making process: heating the billet to obtain a hot billet; piercing the hot billet to obtain a hollow shell having an outer diameter of 300 millimeters (mm) to 302 mm; rolling the hollow shell in a Premium Quality Finishing mill to form a shell having an outer diameter of 264 mm to 266 mm; and performing a slight stretch reducing and a cooling in a walking beam cooler on the shell to obtain an as-rolled steel pipe; and   a heat treatment process: heating the as-rolled steel pipe to 980° C. to 1030° C. for 15 minutes (min) to 25 min, air-cooling or water-cooling the heated steel pipe to 80° C. to 100° C. for quenching; then, heating the quenched steel pipe to 650° C. to 700° C. for 20 min to 40 min, air-cooling the heated quenched steel pipe for tempering.   
     
     
         5 . The method of  claim 4 , wherein the process of rolling the hollow shell in the Premium Quality Finishing mill comprises: spraying borax into the hollow shell, then spraying nitrogen, a pressure of the spraying nitrogen being 3 bar to 8 bar, and a time of spraying borax being 5 seconds(s) to 12 s. 
     
     
         6 . The method of  claim 5 , wherein in the quenching process, a rate of air-cooling is 5° C./min to 20° C./min; or a rate of water-cooling is 10° C./s to 65° C./s. 
     
     
         7 . The method of  claim 4 , wherein the process of ladle refining comprises: adding lime, fluorite and calcium carbide into the ladle for slagging, then refining in a gradual temperature rising mode, a time of the refining being 60 min to 70 min. 
     
     
         8 . The method of  claim 4 , wherein in the process of curved continuous casting, a speed of casting is 2.8 m/min to 3.2 m/min, a vibration frequency of a mold is 163 min −1  to 178 min −1 , an amplitude of the mold is 10.0 mm to 10.3 mm, and a negative slip rate is 30% to 32%. 
     
     
         9 . The method of  claim 4 , wherein the steel pipe making process comprises: heating the billet to 1220° C. to 1260° C. and holding the temperature for 90 min to 110 min to obtain the hot billet; and a temperature of piercing the hot billet is 1150° C. or more. 
     
     
         10 . The method of  claim 4 , wherein in the process of rolling the hollow shell in the Premium Quality Finishing mill, an amount of hollow shell feeding is 62 mm to 113 mm, a roll speed is 20 revolutions per minute (rpm) to 40 rpm, and a wind pressure is 5.2 bar to 6.3 bar. 
     
     
         11 . The oil casing of  claim 2 , wherein the chemical composition further comprises, by mass %, one or two elements selected from Ca: 0.0001% to 0.005% and Mg: 0.0001% to 0.005%.