A 125KSi grade high-strength corrosion-resistant seamless steel pipe and its production method

Abstract

The invention discloses a 125KSi grade high-strength corrosion-resistant seamless steel pipe and a production method thereof, belonging to the technical field of seamless steel pipes. The main chemical components and weight percentages of the 125KSi grade high-strength corrosion-resistant seamless steel pipe are as follows: C 0.20-0.25%, Si 0.17-0.37%, Mn 0.30-0.40%, Cr 2.00-4.00%, W 0.20-0.30%, V 0.10-0.20% , Nb0.010~0.030%, Mo050~0.70%, B0.0005~0.0015%, Al0.020~0.040%, Ti0.015~0.025%, Ca0.0010~0.0020%, Mg0.0003~0.0005%. The seamless steel pipe has excellent mechanical properties and good corrosion resistance, and is a 125KSi grade high-strength and corrosion-resistant seamless steel pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of seamless steel pipes, and specifically relates to a 125KSi grade high-strength corrosion-resistant seamless steel pipe and a production method thereof. Background Art

[0002] With the increasing consumption of international oil resources, oil and gas extraction is gradually developing towards harsh working conditions with higher hardness, higher humidity, and higher CO2 and H2S gas. When oil casing is used in this environment, it is prone to electrochemical corrosion, which leads to thinning of steel pipes, pitting and perforation, and may also cause various failure accidents caused by hydrogen damage.

[0003] Due to the problems of material composition design and heat treatment process design, there is a certain contradiction between the strength and corrosion resistance of steel pipes. At present, major steel pipe factories can only successfully produce ordinary steel pipes with a strength grade of 125KSi, such as Q125, and corrosion-resistant steel pipes with a strength grade of 110KSi, such as C110, and there is no news of producing corrosion-resistant steel pipes with a strength grade of 125KSi. In the enterprise specifications of API5CT and major oil manufacturers, the highest strength of corrosion-resistant steel pipes is 110KSi. The more representative ones are API standard C110 grade steel pipes, SM100S (S) and SM-C110 of Sumitomo Metal of Japan, NT-110S (S) of Nippon Steel, VM-110S (S) of V&M of Europe, TP-110S (S) of Tianjin Steel Pipe Group Co., Ltd. in China, and BG-110S (S) of Shanghai Baosteel.

[0004] The existing C110 alloy composition range is designed to be C: 0.20~0.30%, Mn: 0.30~0.50%, P≤0.010%, S≤0.003%, Cr: 0.50~1.20%, Mo: 0.70~1.10%, V: 0.05~0.10%, Ni≤0.20%, etc., [H]≤1.5ppm, [O]+[N]≤120ppm, five harmful elements≤200ppm. This chemical composition design has the following problems:

[0005] 1. Considering the adverse effects of Cr, Mn and other elements on high temperature temper brittleness, we dare not add more Cr elements in the composition design, resulting in the unsatisfactory strength of the steel pipe;

[0006] 2. In terms of corrosion resistance, on the one hand, due to the low Cr content, the ferrite electrode potential is low and the corrosion resistance is poor; on the other hand, the number of microalloy carbides in the steel is small, resulting in fewer hydrogen-induced traps and poor corrosion resistance. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a 125KSi grade high-strength corrosion-resistant seamless steel pipe and a production method thereof. The seamless steel pipe has excellent mechanical properties and good corrosion resistance, and is a 125KSi grade high-strength corrosion-resistant seamless steel pipe.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A 125KSi grade high-strength corrosion-resistant seamless steel pipe, the 125KSi grade high-strength corrosion-resistant seamless steel pipe comprises the following chemical components by mass percentage: C: 0.20-0.25%, Si: 0.17-0.37%, Mn: 0.30-0.40%, P≤0.010%, S≤0.003%, Cr: 2.00-4.00%, W0.20-0.30%, V: 0.10-0.20%, Nb: 0.010-0.03 0%, Mo: 050~0.70%, B: 0.0005~0.0015%, Al: 0.020~0.040%, Ti: 0.015~0.025%, Ca: 0.0010~0.0020%, Mg: 0.0003~0.0005%, [H]≤1.5ppm, [O]+[N]≤120ppm, Pb+Sn+As+Sb+Bi≤200ppm, the balance is Fe and unavoidable impurities.

[0010] The metallographic structure of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is tempered troostite; and the grain size grade is 8.5.

[0011] The 125KSi grade high-strength corrosion-resistant seamless steel pipe has a yield strength of 130-160 KSi, a tensile strength of 140-170 KSi, and an elongation A≥23%; and has excellent SSC resistance.

[0012] The present invention also provides a production method for the 125KSi grade high-strength corrosion-resistant seamless steel pipe, comprising the following steps: electric furnace steelmaking → LF refining → VD vacuum treatment → continuous casting → heating → rolling → finishing → flaw detection → tube blank heating → hot perforation → tube rolling → sizing → water cooling → heat treatment → finishing → flaw detection.

[0013] The heat treatment includes quenching and tempering steps;

[0014] The quenching method is: keeping the temperature at 500-680°C for 2.5-3.5h, during which dispersed carbonitride particles of 10-20nm are fully precipitated from the steel, and the particles can subsequently pin the grain boundaries to inhibit the coarsening of the grains when the steel pipe is heated at high temperature; then heating to 855-865°C and keeping the temperature for 2.5-3.5h, and finally water quenching;

[0015] The tempering method is to keep the temperature at 650-680° C. for 8-12 hours to ensure that the carbides in the steel are fully precipitated, and at the same time eliminate the high-density subgrain dislocations formed by quenching, thereby improving the corrosion resistance of the steel pipe.

[0016] Furthermore, the tube blank is heated at 1200-1260°C for 5-10 hours for hot perforation; and the surface temperature of the steel tube after tube rolling is controlled at 800-850°C.

[0017] The water cooling allows the surface temperature of the steel pipe to be cooled to below 500° C. at a cooling rate of 10-15° C. / s, ensuring that carbonitrides of the steel pipe do not precipitate in large sizes at high temperatures.

[0018] Furthermore, in the LF refining step, the top slag and final slag compositions are CaO 50%-60%, Al2O3 15%-25%, SiO24%-8%, CaF2 3%-10%, and MgO 5-8%.

[0019] In the VD vacuum treatment step, the VD high vacuum degree is ≤67Pa, the high vacuum holding time is ≥15min, the soft blowing time is ≥15min, the H in the molten steel is removed to within 1.2ppm, and aluminum wire, silicon calcium wire, magnesium wire and ferroboron are fed in sequence.

[0020] In the heating step, in order to ensure that the carbonitride is fully dissolved, the temperature of the preheating section is controlled to be less than 900°C, and the preheating of the steel billet can reduce the risk of cracking of the steel billet, and the time is greater than 1.05h; the temperature of the heating section I is 900-1100°C, and the time is ≥1.0h; the temperature of the heating section II is 1200-1260°C, and the time is ≥4h; the temperature of the soaking section is 1200-1260°C, and the time is ≥5h; the total heating time is ≥11.0h. Through two-stage heating and one-stage soaking, the temperature inside and outside the round billet is uniform, and the carbonitride-forming elements in the steel are fully dissolved.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The 125KSi grade high-strength corrosion-resistant seamless steel pipe provided by the present invention reduces the cost by reducing the Mo content and increases the Cr content on the basis of the chemical composition of the existing C110 grade corrosion-resistant oil well pipe, and solidifies the N content in the steel by adding the element Ti, increases the free B content in the steel, thereby improving the stability of the supercooled austenite, changing the shape of its continuous cooling curve, and improving the hardenability of the steel.

[0023] At the same time, the V and Ti contents are increased, and the micro-alloying elements in the steel are fully dissolved by controlling the heating temperature, rolling deformation and cooling rate after rolling of the steel pipe. These alloying elements dissolved in the steel pipe, during the quenching heat treatment of the steel pipe, are heated in stages to fully precipitate the micro-alloying compounds of vanadium, pin the grain boundaries, reduce the coarsening of the grains, and thus improve the strength of the steel pipe.

[0024] By adding 0.20-0.30% W and 0.10-0.20% V, the impurity elements (such as Sb, Sn, P, etc.) are inhibited from segregating to the original austenite grain boundary, so that the impurity elements produce precipitation phases in the grains, which greatly improves the temper brittleness resistance of the steel. At the same time, W and V can also improve the tempering performance of the steel, which can ensure that the steel pipe can be tempered at a higher temperature, reduce the number of deformed grains and dislocation density, and improve the corrosion resistance of the steel pipe while improving the plasticity of the steel.

[0025] By adding 0.0010-0.0020% Ca and 0.0003-0.0005% Mg, through calcium-magnesium composite treatment, small-sized and dispersed MnS-CaS-MgO (-Al2O3-CaO) composite inclusions are generated. Compared with strip-shaped sulfide inclusions, these composite inclusions can improve the irreversible hydrogen traps of MnS inclusions, improve the hydrogen embrittlement sensitivity of steel, and improve the corrosion resistance of steel pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the metallographic structure diagram of the 125KSi grade high-strength corrosion-resistant seamless steel pipe in Example 1, which is a fine tempered troostite structure;

[0027] Figure 2 The substructure grain diagram of the 125KSi grade high strength corrosion resistant seamless steel pipe in Example 1;

[0028] Figure 3 This is a schematic diagram of the quenching process of the 125KSi grade high-strength corrosion-resistant seamless steel pipe in Example 1;

[0029] Figure 4 Schematic diagram of the quenching process of the 125KSi grade high-strength corrosion-resistant seamless steel pipe in Example 2;

[0030] Figure 5 This is a schematic diagram of the quenching process of the 125KSi grade high-strength corrosion-resistant seamless steel pipe in Example 3. DETAILED DESCRIPTION

[0031] The present invention provides a 125KSi grade high-strength corrosion-resistant seamless steel pipe, whose chemical composition and mass percentage are as follows: C: 0.20-0.25%, Si: 0.17-0.37%, Mn: 0.30-0.40%, P≤0.010%, S≤0.003%, Cr: 2.00-4.00%, W0.20-0.30%, V: 0.10-0.20%, Nb: 0.010-0.030%, Mo: 050~0.70%, B: 0.0005~0.0015%, Al: 0.020~0.040%, Ti: 0.015~0.025%, Ca: 0.0010~0.0020%, Mg: 0.0003~0.0005%, [H]≤1.5ppm, [O]+[N]≤120ppm, Pb+Sn+As+Sb+Bi≤200ppm, the balance is Fe and unavoidable impurities.

[0032] The production method of the 125KSi grade high-strength corrosion-resistant seamless steel pipe comprises the following steps: heating the tube blank→hot perforation→tube rolling→sizing→water cooling→heat treatment→finishing→defect detection; wherein the heat treatment comprises quenching and tempering steps; the quenching step comprises: keeping the temperature at 500-680°C for 2.5-3.5h, then heating to 855-865°C for 2.5-3.5h, and finally water quenching; the tempering step comprises: keeping the temperature at 650-680°C for 8-12h.

[0033] Furthermore, the tube blank is heated at 1200-1260°C for 5-10 hours for hot perforation; and the surface temperature of the steel tube after tube rolling is controlled at 800-850°C.

[0034] The water cooling allows the surface temperature of the steel pipe to be cooled to below 500° C. at a cooling rate of 10-15° C. / s, ensuring that carbonitrides of the steel pipe do not precipitate in large sizes at high temperatures.

[0035] The preparation method of the tube blank comprises the following steps: electric furnace steelmaking → LF refining → VD vacuum treatment → continuous casting → heating → rolling → finishing → flaw detection. The requirements of each step are as follows:

[0036] (1) Electric furnace smelting requirements

[0037] ① The end point of steelmaking in the electric furnace is C ≥ 0.10%, which prevents the molten steel from being over-oxidized, is conducive to the removal of inclusions, and reduces the primary Al2O3 inclusions.

[0038] ② The target P of electric furnace steel tapping is ≤0.006%, and the target temperature is ≥1640℃; control the appropriate steel tapping temperature and effectively control the return of molten steel to P.

[0039] ③ Add 1000kg lime, 200kg fluorite, and produce 110-130kg aluminum per furnace.

[0040] LF refining requirements

[0041] ① Through lime and fluorite, a high basicity top slag is formed to ensure the S removal ability of the top slag. The top slag final slag composition is CaO: 50%-60%, Al2O3: 15%-25%, SiO2: 4%-8%, CaF2: 3%-10%, MgO: 5-8%.

[0042] ② Ensure that the white slag time is ≥25min and the smelting time is ≥40min;

[0043] ③ The oxygen content in the molten steel can be fully removed through sufficient white slag time, and the appropriate smelting cycle can ensure the precise control of the alloy composition and the full floating and removal of inclusions.

[0044] VD vacuum processing requirements:

[0045] ①VD high vacuum degree ≤67Pa, high vacuum holding time ≥15min, soft blowing time ≥15min, and H in molten steel is removed within 1.2ppm;

[0046] ②Wire feeding sequence: Wire feeding sequence: aluminum wire - calcium silicon wire - magnesium wire - ferroboron wire.

[0047] ③ 200m of calcium silicon wire and 100m of magnesium wire can denature and spheroidize the inclusions and improve the final corrosion resistance of the steel.

[0048] (4) Casting requirements

[0049] The continuous casting process is: first cooling water 4000L / min, first cooling water rapid cooling to increase the proportion of columnar crystals, better billet density. Second cooling water 800L / min; crystallizer electromagnetic stirring 250A / 2Hz, casting strand stirring 200A / 8Hz, final stirring 1200A / 8Hz. The electromagnetic stirring technology is beneficial to the shrinkage of molten steel and improves the center defects of continuous casting billets; the pulling speed is 0.19m / min; and finally a billet of φ800mm is obtained.

[0050] (5) Heating and rolling process requirements

[0051] ① In order to prevent the microalloyed carbonitrides from growing and causing surface defects when they are directly hot-rolled at high temperatures for a long time, hot-rolling is prohibited for this steel grade.

[0052] ② To ensure that carbonitrides are fully dissolved, the heating temperature and heating time of this steel grade are as follows: preheating stage temperature <900℃, target 860℃, billet preheating reduces the risk of billet cracking, time >1.05h, heating stage I temperature 900-1100℃, target temperature 1000℃, time ≥1.0h, heating stage II temperature 1200-1260℃, target temperature 1230℃, time ≥4h, soaking stage temperature 1200-1260℃, target temperature 1240℃, time ≥5h, total heating time ≥11.0h. Through two-stage heating and one-stage soaking, the temperature inside and outside of the round billet is uniform, and the carbonitride-forming elements of this microalloyed steel are fully dissolved.

[0053] ③Rolling to obtain a tube billet with a specification of φ200mm.

[0054] The present invention is described in detail below with reference to the embodiments. Example 1

[0055] A 125KSi grade high-strength corrosion-resistant seamless steel pipe, whose chemical composition and weight percentage are as follows: C 0.20%, Si 0.17%, Mn 0.30%, P 0.006%, S 0.0015%, Cr 2.00%, W 0.20%, V 0.10%, Nb 0.010%, Mo 050%, B 0.0005%, Al 0.020%, Ti 0.015%, Ca 0.0015%, Mg 0.0003%, [H] 0.7ppm, [O]+[N] =50ppm, Pb+Sn+As+Sb+Bi= 100ppm, and the balance is Fe and unavoidable impurities.

[0056] The production method of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is as follows: tube blank heating→hot perforation→tube rolling→sizing→water cooling→heat treatment→finishing→defect detection; wherein, the production of the tube blank is carried out according to the above process.

[0057] The process parameters for tube heating, water cooling and heat treatment are shown in Example 1 in Table 1. Example 2

[0058] A 125KSi grade high-strength corrosion-resistant seamless steel pipe, whose chemical composition and weight percentage are as follows: C: 0.23%, Si: 0.27%, Mn: 0.35%, P 0.006%, S 0.0015%, Cr: 3.00%, W 0.25%, V: 0.15%, Nb: 0.020%, Mo: 0.60%, B: 0.0010%, Al: 0.025%, Ti: 0.015%, Ca: 0.0018%, Mg 0.0003%, [H] 0.7ppm, [O] + [N] = 60ppm, Pb + Sn + As + Sb + Bi = 110ppm, and the balance is Fe and unavoidable impurities.

[0059] The production method of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is as follows: tube blank heating→hot perforation→tube rolling→sizing→water cooling→heat treatment→finishing→defect detection; wherein, the production of the tube blank is carried out according to the above process.

[0060] The process parameters for tube heating, water cooling and heat treatment are shown in Example 2 in Table 1. Example 3

[0061] A 125KSi grade high-strength corrosion-resistant seamless steel pipe, whose chemical composition and weight percentage are as follows: C: 0.25%, Si: 0.30%, Mn: 0.40%, P 0.005%, S 0.0012%, Cr: 4.00%, W 0.30%, V: 0.20%, Nb: 0.030%, Mo: 0.70%, B: 0.0015%, Al: 0.025%, Ti: 0.020%, Ca: 0.0020%, Mg 0.0003%, [H] 0.7ppm, [O] + [N] = 65ppm, Pb + Sn + As + Sb + Bi = 112ppm, and the balance is Fe and unavoidable impurities.

[0062] The production method of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is as follows: tube blank heating→hot perforation→tube rolling→sizing→water cooling→heat treatment→finishing→defect detection; wherein, the production of the tube blank is carried out according to the above process.

[0063] The process parameters for tube heating, water cooling and heat treatment are shown in Example 3 in Table 1.

[0064] Comparative Example 1

[0065] The rest is the same as Example 1, except that the chemical composition and weight percentage of the seamless steel pipe are as follows: C: 0.28%, Si: 0.25%, Mn: 0.38%, P 0.006%, S 0.0015%, Cr 1.20%, V: 0.12%, Nb: 0.028%, Mo: 0.95%, Al: 0.027%, Ti: 0.018%, [H] 0.5ppm, [O] + [N] = 70ppm, Pb + Sn + As + Sb + Bi = 121ppm, and the balance is Fe and unavoidable impurities.

[0066] Comparative Example 2

[0067] The other conditions are the same as those in Example 2, except that the quenching condition is to directly heat to 860°C and keep it for 3 hours without keeping it at 600°C, and finally to water quench it; the tempering condition is to keep it at 680°C for 8 hours.

[0068] Table 1

[0069]

[0070] The non-metallic inclusion grades of the seamless steel pipes produced in the above-mentioned embodiments and comparative examples are shown in Table 2, and the mechanical properties are shown in Table 3.

[0071] Table 2 Grade of non-metallic inclusions in steel pipes

[0072]

[0073] Table 3 Mechanical properties of steel pipe

[0074]

[0075] According to the requirements of "NACETM0177-2005 Laboratory Test Method for Resistance of Metals to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environment", the tensile specimen was immersed in a solution A (5% NaCl + 0.5% CH3COOH) with a pH value of 2.5~2.5 at 25℃±3℃, and H2S gas was introduced into the solution at a flow rate of 100~300mL / min to saturate the solution. A universal electronic tensile testing machine with an extensometer was used to apply a load of 731MPa for room temperature tensile testing. The steel pipes in Examples 1, 2, and 3 all passed the test without premature fracture; however, the steel pipes in Comparative Examples 1, 2, and 3 did not pass the test and premature fracture occurred.

[0076] From the above content, it can be seen that according to the technical solution provided by the present invention, a 125KSi grade high-strength corrosion-resistant seamless steel pipe can be produced, the yield strength of which is 130~160 KSi, the tensile strength is 140~170 KSi, and the elongation A≥23%; the anti-SSC performance is excellent.

[0077] The detailed description of a 125KSi grade high-strength corrosion-resistant seamless steel pipe and its production method with reference to the above-mentioned embodiment is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A 125KSi grade high-strength corrosion-resistant seamless steel pipe, characterized in that: The 125KSi grade high strength corrosion resistant seamless steel pipe comprises the following chemical components in mass percentage: C: 0.20-0.25%, Si: 0.17-0.37%, Mn: 0.30-0.40%, P≤0.010%, S≤0.003%, Cr: 2.00-4.00%, W0.20-0.30%, V: 0.10-0.20%, Nb: 0.010-0.030%, Mo: 050-0.70%, B: 0.0005-0.00015%, Al: 0.020-0.0 40%, Ti: 0.015-0.025%, Ca: 0.0010-0.0020%, Mg: 0.0003-0.0005%, [H]≤1.5ppm, [O]+[N]≤120ppm, Pb+Sn+As+Sb+Bi≤200ppm, the remainder is Fe and unavoidable impurities; the metallographic structure of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is tempered troostite; the grain size grade is 8.5; the yield strength of the 125KSi grade high-strength corrosion-resistant seamless steel pipe is 130-160 KSi, the tensile strength is 140-170 KSi, the elongation A≥23%; and the anti-SSC performance is excellent.

2. The method for producing a 125KSi grade high-strength corrosion-resistant seamless steel pipe according to claim 1, characterized in that: The production method comprises the following steps: electric furnace steelmaking→LF refining→VD vacuum treatment→continuous casting→heating→rolling→finishing→flaw detection→tube blank heating→hot perforation→tube rolling→sizing→water cooling→heat treatment→finishing→flaw detection.

3. The production method according to claim 2, characterized in that: The heat treatment includes quenching and tempering steps; The quenching method is: keeping the temperature at 500-680°C for 2.5-3.5h, then heating to 855-865°C for 2.5-3.5h, and finally water quenching; The tempering method is to keep the temperature at 650-680° C. for 8-12 hours.

4. The production method according to claim 2, characterized in that: The tube blank is heated at 1200-1260℃ for 5-10h for hot piercing; the surface temperature of the steel tube after rolling is controlled at 800-850℃.

5. The production method according to claim 2, characterized in that: The water cooling allows the surface temperature of the steel pipe to be cooled to below 500°C at a cooling rate of 10-15°C / s.

6. The production method according to claim 2, characterized in that: In the LF refining step, the top slag and final slag compositions are CaO 50%-60%, Al2O3 15%-25%, SiO2 4%-8%, CaF2 3%-10%, and MgO 5-8%.

7. The production method according to claim 2, characterized in that: In the VD vacuum treatment step, the VD high vacuum degree is ≤67Pa, the high vacuum holding time is ≥15min, the soft blowing time is ≥15min, the H in the molten steel is removed to within 1.2ppm, and aluminum wire, silicon calcium wire, magnesium wire and ferroboron are fed in sequence.

8. The production method according to claim 2, characterized in that: In the heating step, the temperature of the preheating section is less than 900°C, and the temperature of the soaking section is 1200-1260°C.

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