CN116121508A - A kind of high-strength and high-corrosion-resistant economical oil well tubular steel and its preparation method - Google Patents

Abstract

The invention discloses high-strength high-corrosion-resistance economic oil well pipe steel and a preparation method thereof, belongs to the technical field of corrosion-resistance steel, and solves the problems that the oil well pipe steel in the prior art is high in cost, high in strength and high in corrosion resistance and is difficult to match. The preparation method of the oil well pipe steel comprises the following steps: step 1: smelting a metal raw material into molten steel; step 2: smelting molten steel into a continuous casting blank or an ingot; step 3: forging and cogging the continuous casting blank or the cast ingot to prepare a forging blank; hot rolling the forging stock into a hot rolled plate; step 4: and carrying out solution treatment on the hot rolled plate, and carrying out quantitative cold rolling on the hot rolled plate subjected to solution treatment with a deformation of 5% -25%, thereby finally preparing the oil well pipe steel with the ferrite-austenite-martensite three-phase mixed structure. The oil well pipe steel prepared by the preparation method disclosed by the invention has the advantages of high strength, good plastic toughness and excellent corrosion resistance.

Description

A kind of high-strength and high-corrosion-resistant economical oil well tubular steel and its preparation method

technical field

The invention relates to the technical field of corrosion-resistant steel, in particular to a high-strength, high-corrosion-resistant economical oil well tubular steel and a preparation method thereof.

Background technique

Oil well pipe is an important consumable in the process of oil and natural gas exploration and development. Due to the flow of corrosive liquid in the oil well pipe, various anti-corrosion products must be selected according to the corrosion situation. At present, 13Cr martensitic stainless steel is the main material for CO ₂ corrosion-resistant oil well pipes, but martensitic steel cannot be used in environments containing H ₂ S. Although the selection of 22Cr (or 25Cr, 27Cr, the higher the Cr content, the better the corrosion resistance) duplex stainless steel with a higher alloy content can meet the requirements for the use of oil well pipes, but the higher raw material costs are not suitable for mass production in oil and gas exploration scenarios. application. In view of the actual situation of China's oil and gas exploitation and the limitation of mineral resources, it is of great significance to develop an economical high-strength corrosion-resistant oil well tubular material with high strength and high corrosion resistance and controllable cost.

At present, there are many patents on the varieties of oil well tubular steel with good comprehensive performance and the corresponding technological process at home and abroad, but most of them have problems such as high cost or complicated process, which cannot meet the needs of large-scale production and practical application.

Contents of the invention

In view of the above, the present invention aims to provide a high-strength, high-corrosion, economical oil well tubular steel and its preparation method, which are used to solve the problems of high cost and difficulty in matching high strength and high corrosion resistance of existing oil well tubular steel.

The purpose of the present invention is mainly achieved through the following technical solutions:

On the one hand, the present invention provides a method for preparing high-strength, high-corrosion and economical oil well tubular steel, comprising:

Step 1: Smelting metal raw materials into molten steel;

Step 2: Smelting molten steel into continuous casting slabs or ingots;

Step 3: Forging the continuous casting billet or ingot to make a forging billet; hot rolling the forging billet into a hot-rolled plate;

Step 4: The hot-rolled sheet is subjected to solution treatment, and the hot-rolled sheet after solution treatment is subjected to quantitative cold rolling with a deformation of 5% to 25%, and finally a three-phase ferrite + austenite + martensite is obtained Oil well tubular steel with mixed structure.

In a possible design, in step 3, the forging blanking temperature is 1150-1250°C.

In a possible design, in step 3, water cooling to room temperature after hot rolling.

In a possible design, in step 4, the solid solution treatment process includes: holding at 1000-1150° C. for 1-3 hours and then water cooling.

On the other hand, the present invention also provides a high-strength, high-corrosion and economical oil well tubular steel, which is prepared by the above-mentioned preparation method.

In a possible design, the components of high-strength and high-corrosion-resistant economical oil well tubular steel include: C: ≤0.03%, Cr: 17.4%-18.4%, Mo: 0.5%-2.5%, Ni: 1.0%～2.8%, Mn: 1.0%～3.5%, Si: 0.1%～0.5%, N: 0.1%～0.25%, P: ≤0.03%, S: ≤0.01%, the balance is Fe and unavoidable Impurities.

In a possible design, among the components of high-strength and high-corrosion-resistant economical oil well tubular steel, Cr+3.3Mo+16N≥26.

In a possible design, among the components of high-strength and high-corrosion-resistant economical oil well tubular steel, 50Ni+17Mn-12Mo-800N≤0.

In a possible design, the components of the high-strength and high-corrosion-resistant economical oil well tubular steel include: C: 0.01% to 0.03%, Cr: 17.4% to 18.3%, Mo: 1.1% to 2.2%, Ni: 1.0% to 2.4%, Mn: 1.2% to 3.2%, Si: 0.1% to 0.5%, N: 0.1% to 0.2%, P: ≤0.03%, S: ≤0.01%, and the balance is Fe or not Avoid impurities.

In a possible design, among the components of high-strength and high-corrosion-resistant economical oil well tubular steel, 50Ni+17Mn-12Mo-800N≤-3.

Compared with the prior art, the beneficial effects of the present invention are as follows:

a) The high-strength and high-corrosion-resistant economical oil well tubular steel of the present invention precisely controls the mass percentages of Cr, Ni, Mn, Mo, and N elements in the steel, and combines the process of hot rolling + solid solution + cold rolling, and can Obtain a mixed structure of ferrite + austenite + martensite; further, through quantitative cold deformation, a part of the austenite that has not undergone quenching martensite transformation in the structure undergoes deformation-induced martensite transformation to obtain ferrite It is a mixed structure with martensite as the main part and a certain amount of austenite. Since the oil well tubular steel of the present invention has a martensite content close to 50%, the tensile strength of the oil well tubular steel can reach 110 and 125 steel grades, realize multi-phase structure synergy, and obtain a high strength equivalent to that of martensitic stainless steel. Stronger, but lower material cost oil well tubular steel. Compared with the martensitic stainless steel in the prior art, the multi-phase coexistence microstructure in the oil well tubular steel of the present invention has better intergranular corrosion resistance and H ₂ S stress corrosion resistance. In addition, the stainless steel of the present invention has a certain austenite content, and has better plasticity under the premise of similar strength to martensitic stainless steel.

b) The steel of the present invention not only ensures high strength and good ductility, but also has excellent corrosion resistance. The yield strength of the steel of the present invention is greater than 800MPa (such as 812-1020MPa), and the tensile strength is greater than 1000MPa (such as 1095-1300MPa). ), the elongation is greater than 10% (for example, 11% to 20%). (180°C) CO ₂ corrosion rate below 0.035g/m ² h (for example 0.0289～0.0324g/m ² h); (200°C) CO ₂ corrosion rate below 0.12g/m ² h (for example 0.104～0.112g/m ² h); the pitting corrosion rate is below 2.6g/m ² h (for example, 2.138～2.521g/m ² h); the crevice corrosion rate is below 6.1g/m ² h (for example, 5.421～6.023g/m ² h); H ₂ S stress corrosion test passed.

c) The steel of the present invention has good strength, toughness and excellent corrosion resistance, and has both the high strength of super martensitic stainless steel oil well tubular materials and the stress corrosion resistance, intergranular corrosion resistance and small amount of H ₂ S stress corrosion resistance of duplex stainless steel. Because the content of Cr and Ni in the steel of the invention is low, the cost of raw materials is equivalent to or even slightly lower than that of the super 13Cr martensitic stainless steel in the prior art, and at the same time, the hot workability is good, so the steel of the invention has low overall cost, economy and excellent performance.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Description of drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be considered as limitations of the invention, and like reference numerals refer to like parts throughout the drawings.

Fig. 1 is the microstructure figure of the steel of embodiment 1 of the present invention;

Fig. 2 is the EBSD two-phase distribution figure of the final structure of the steel of embodiment 1 of the present invention;

Fig. 3 is the microstructure figure of the steel of embodiment 2 of the present invention;

Fig. 4 is the microstructure figure of the steel of embodiment 3 of the present invention;

Fig. 5 is a graph showing the results of the H ₂ S stress corrosion test in Example 1 of the present invention.

Detailed ways

The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention.

The invention provides a method for preparing high-strength, high-corrosion and economical oil well tubular steel, comprising:

Step 1: Smelting metal raw materials into molten steel;

Step 2: Smelting the molten steel into continuous casting slabs or ingots by means of continuous casting or die casting;

Step 3: Heat the continuous casting billet or ingot at 1150-1250°C and keep it warm, then forge and open the billet to make a forging billet; rolling plate;

Step 4: The hot-rolled sheet is subjected to solution treatment, and the hot-rolled sheet after solution treatment is subjected to quantitative cold rolling with a deformation amount of 5% to 25%, and an economical oil well pipe with high strength and high corrosion resistance is finally obtained steel. Among them, the structure of economical oil well tubular steel with high strength and high corrosion resistance is: ferrite + austenite + martensite three-phase mixed structure, and the content of the three-phase mixed structure is: ferrite volume percentage content 30 % to 50%, the content of martensite is 25% to 50%, and the content of austenite is 10% to 30%.

Specifically, in the above step 1 and step 2, smelting in a converter or an electric furnace, LF refining, and casting into a slab are used.

Specifically, in the above step 3, the forging blanking temperature is 1150-1250°C. This is because the material of the present invention is a two-phase ferrite + austenite when it is higher than 800°C, and the ratio of the two phases changes with the heating temperature. The higher the temperature, the more ferrite content, and the corresponding decrease of austenite content. Selecting this temperature range for heating ensures sufficient re-dissolution of harmful precipitated phases, and also makes the ferrite phase content in the material greater than 70%, so that the steel can be forged and opened in the single-phase region with better thermoplasticity, avoiding due to ferrite and The difference in the hot deformation ability of the two phases of austenite leads to the uncoordinated deformation of the two phases in the forging process and causes forging cracking.

Specifically, in the above step 3, water cooling to room temperature after hot rolling is performed to avoid the precipitation of harmful phases.

Specifically, in the above step 4, before cold rolling, in order to eliminate the difference in structure caused by the rolling temperature (high rolling temperature at the head end and low rolling temperature at the tail end) in different regions of the plate during the hot rolling process, it is necessary to carry out solid solution deal with. The process of solid solution treatment includes: keeping warm at 1000-1150°C for 1-3 hours and then water-cooling.

Specifically, in the above step 4, since the austenite in the structure of the present invention is prone to martensitic transformation during cold deformation, it is necessary to control the amount of cold deformation in a smaller interval, for example, control the amount of cold deformation 5% to 25% (for example, 10% to 20%).

Specifically, the components of the above-mentioned high-strength and high-corrosion-resistant economical oil well tubular steel include: C: ≤0.03%, Cr: 17.4%-18.4%, Mo: 0.5%-2.5%, Ni: 1.0%-2.8% %, Mn: 1.0% to 3.5%, Si: 0.1% to 0.5%, N: 0.1% to 0.25%, P: ≤0.03%, S: ≤0.01%, and the balance is Fe and unavoidable impurities.

Specifically, among the components of the above-mentioned high-strength and high-corrosion-resistant economical oil well tubular steel, Cr+3.3Mo+16N (ie PREN)≥26, and 50Ni+17Mn-12Mo-800N≤0. Wherein, Cr, Mo, N, Ni, and Mn refer to the mass percentage of these elements×100. For example, if the mass percentage of Cr element is 18.4%, the Cr here is 18.4.

The effect and consumption selection of contained component in the present invention are described in detail below:

C: Although the addition of carbon can significantly improve the hardness and strength of steel, due to the high diffusion capacity of carbon, it is easy to combine with Cr to form M ₂₃ C ₆ carbides. This type of carbides is mainly in the temperature range of 700-900 ° C. Rapid precipitation (≤0.5 hours), or precipitation at 550-700 ° C for a long time. The precipitation of carbides results in local Cr deficiency, which increases the intergranular corrosion sensitivity of the material and deteriorates the corrosion resistance. Therefore, in the present invention, the comprehensive effect of strength and corrosion resistance is considered, and its content is controlled to be ≤0.03%.

Cr: The main element to ensure the corrosion resistance of stainless steel is also a ferrite-forming element. Improper control of Cr content will increase the ferrite content in the structure and reduce the strength. Comprehensive consideration should be given to controlling its content at 17.4% to 18.4%.

Ni: It is an element that strongly forms and stabilizes austenite and expands the austenite phase zone. Ni is an element that improves the toughness and corrosion resistance of stainless steel in reducing media. Ni also improves the austenite phase resistance to transcrystalline stress in various media. An important element for corrosion. At the same time, compared with Mn, Ni can reduce the cold work hardening tendency of austenite phase. In consideration of cost control, the present invention controls its content at 1.0% to 2.8%.

Mn: It can increase the solubility of N in steel and inhibit the precipitation of harmful phase chromium nitride, but Mn reduces the toughness of stainless steel. Compared with Ni, Mn is an economical austenite-forming element. The hardening effect of the bulk phase and the overall material is different, so the present invention controls its content at 1.0% to 3.5%.

Mo: In addition to improving the corrosion resistance of stainless steel in oxidizing media, it has a good effect on improving the corrosion resistance of stainless steel in reducing media. At the same time, in order to ensure pitting corrosion resistance, Cr, Mo and other alloying elements that increase the PREN value should not be too low At the same time, it is also necessary to take into account the cost control and phase balance of the alloy, and comprehensively consider its content to be controlled at 0.5% to 2.5%.

Si: Added as a deoxidizer in the smelting process, it can achieve the effect of deoxidation. If it is added too high, it will deteriorate the intergranular corrosion resistance of the material. The present invention controls its content at 0.1% to 0.5%.

N: Like Ni, it is an element that strongly forms and stabilizes austenite and expands the austenite phase zone. N can also significantly improve the pitting corrosion resistance of the austenite phase in stainless steel, thereby improving the overall pitting corrosion resistance of stainless steel. In some media, N has a good effect on the stress resistance of stainless steel, and there is an optimal value, further increasing the N content, and its stress corrosion resistance will decrease. N is also a relatively economical alloying element, but N reduces the hot workability of stainless steel, so the present invention controls its content at 0.1%-0.25%.

S: It will significantly reduce the hot workability of steel, and it is easy to react with Mn to form MnS inclusions, which will reduce the pitting corrosion resistance and crevice corrosion resistance of the material. Therefore, its content is controlled to be less than or equal to 0.01%.

P: It is a harmful impurity element, which will not only deteriorate the plasticity of the material, but also reduce the corrosion resistance of the material, so its content is controlled to be ≤0.03%.

Specifically, this application comprehensively considers the guarantee of corrosion resistance, the cost of raw materials caused by the matching of alloying elements, the precipitation of harmful phases caused by the matching of alloying elements, and the cost change caused by the yield of thermal processing. In addition to the control of the content of individual elements of alloying elements Cr, Ni, Mn, N, in order to ensure corrosion resistance, control Cr+3.3Mo+16N≥26, in order to make the maximum precipitation temperature of harmful phases lower than 750°C, and ensure that the material has good corrosion resistance. Thermal processing performance, while considering that the three-phase ratio can be controlled during thermal processing between 900 and 1180 °C, it is necessary to control the content of Ni, Mn, Mo, and N elements to meet: 50Ni+17Mn-12Mo-800N≤0.

In order to further improve the overall performance of the above-mentioned high-strength, high-corrosion, and economical oil well tubular steel, the composition of the above-mentioned high-strength, high-corrosion, and economical oil well tubular steel may be: C: 0.01% to 0.03%, Cr: 17.4% to 18.3% %, Mo: 1.1% to 2.2%, Ni: 1.0% to 2.4%, Mn: 1.2% to 3.2%, Si: 0.1% to 0.5%, N: 0.1% to 0.2%, P: ≤0.03%, S: ≤0.01%, the balance is Fe and unavoidable impurities.

Specifically, 50Ni+17Mn-12Mo-800N≤-3.

Specifically, the microstructure of the above-mentioned high-strength and high-corrosion-resistant economical oil well tubular steel after solid solution treatment is a mixed structure of ferrite + austenite + martensite, wherein the volume percentage of austenite is 10%~ 30%. Austenite is in a metastable state in this structure, and can further transform into martensite in plastic deformation, especially the quenched martensite that already exists in the structure of the present invention has a promoting effect on the phase transformation behavior in the above-mentioned deformation process (for The phase transformation provides nucleation sites and increases the stress state of austenite). Utilizing the characteristics that austenite in the structure after solution treatment is prone to martensitic transformation, a part of the austenite phase is deformed by quantitative cold rolling to induce martensitic transformation, and a small deformation (5% ～25%) can obtain ultra-fine martensite volume percentage of 25%～50%, ferrite content of 30%～50% and austenite volume percentage content of 10%～30%. Corrosion-resistant economical oil well tubular steel.

Specifically, in the cold-rolled structure of the above-mentioned high-strength, high-corrosion economical oil well tubular steel, martensite is dispersed in austenite in the form of ultra-fine sheets, alternately stacked with austenite, and separated from each other, so that austenite The body has a smaller grain size (for example, the austenite grain size <3 μm), and the thickness of the martensite plate is less than 100 nm.

Compared with the prior art, the structure of the high-strength, high-corrosion-resistant economical oil well tubular steel of the present invention is a three-phase structure consisting mainly of ferrite and martensite and containing a certain amount of austenite. The steel of the present invention has low Cr, The low content of alloying elements has the characteristics of higher strength, which can simultaneously have the characteristics of high strength, resistance to intergranular corrosion, stress corrosion, high toughness and good welding performance, and has excellent comprehensive performance. At the same time, the high martensite content in the structure of the steel of the present invention enables the steel to have high-strength mechanical properties superior to the traditional ~22Cr duplex stainless steel, which can reach 110 and 125 steel grades. Its multi-phase composite microstructure is superior to the corrosion resistance of single-phase martensitic stainless steel in H ₂ S stress corrosion resistance and intergranular corrosion resistance.

Compared with the existing technology, the high-strength and high-corrosion-resistant economical oil well tubular steel of the present invention precisely controls the mass percentages of Cr, Ni, Mn, Mo, and N elements in the steel, and combines the processes of hot rolling + solid solution + cold rolling, After solid solution, a mixed structure of ferrite + austenite + martensite can be obtained; further quantitative cold deformation is used to deform the austenite part of the structure that has not undergone quenching martensite transformation to induce martensite transformation A mixed structure consisting mainly of ferrite and martensite with a small amount of austenite is obtained. Because the steel of the present invention has a martensite content close to 50%, the tensile strength of the material is much higher than that of duplex stainless steel, and can reach 110 and 125 steel grades, and achieve a multiphase structure equivalent to that of martensitic stainless steel. high strength. Compared with the martensitic stainless steel in the prior art, the multi-phase coexistence microstructure in the stainless steel of the present invention has better intergranular corrosion resistance and H ₂ S stress corrosion resistance. In addition, the steel of the present invention has a certain austenite content, and has better plasticity under the premise of strength similar to that of martensitic stainless steel.

The steel of the present invention not only ensures high strength, good ductility and excellent corrosion resistance, but also ensures that the yield strength of the steel of the present invention is greater than 800MPa (such as 812-1020MPa), and the tensile strength is greater than 1000MPa (such as 1095-1300MPa), The elongation is greater than 10% (for example, 11% to 20%). (180°C) CO ₂ corrosion rate below 0.035g/m ² h (for example 0.0289～0.0324g/m ² h); (200°C) CO ₂ corrosion rate below 0.12g/m ² h (for example 0.104～0.112g/m ² h); the pitting corrosion rate is below 2.6g/m ² h (for example, 2.138～2.521g/m ² h); the crevice corrosion rate is below 6.1g/m ² h (for example, 5.421～6.023g/m ² h); H ₂ S stress corrosion test passed.

The steel of the invention has good strength, toughness and excellent corrosion resistance, and has both the high strength of the super martensitic stainless steel oil well pipe material and the stress corrosion resistance, intergranular corrosion resistance and small amount of H ₂ S stress corrosion resistance of duplex stainless steel. Because the content of Cr and Ni in the steel of the invention is low, the cost of raw materials is equivalent to or even slightly lower than that of the super 13Cr martensitic stainless steel in the prior art, and at the same time, the hot workability is good, so the steel of the invention has low overall cost, economy and excellent performance.

Example 1-4

The advantages of precise control of the composition and process parameters of the steel of the present invention will be demonstrated by specific examples and comparative examples below. Select 13Cr as the comparison object of corrosion performance.

Examples 1-4 of the present invention provide a highly corrosion-resistant economical oil well tubular steel and a preparation method thereof. The chemical composition of the steels in Examples 1-4 is shown in Table 1.

The preparation method of embodiment 1 comprises:

Step 1: smelting metal raw materials into molten steel; smelting molten steel into steel ingots by die casting;

Step 2: Heat the steel ingot to 1200°C for 2 hours, then forge and open the billet to make a forged billet, heat the forged billet at 1200°C for 2 hours, and hot-roll it into a hot-rolled plate in multiple passes;

Step 3: Heat the hot-rolled sheet at 1100° C. for 1 hour and water-cool it, and cold-roll it while controlling the cold-rolling deformation to 10%, so as to obtain an economical oil well tubular steel with high strength and high corrosion resistance. In this step, the volume fraction of austenite to martensite is adjusted by controlling the cold rolling deformation to 10%, and the final microstructure contains 40% ferrite, 45% martensite and 15% austenite.

The preparation method of embodiment 2 comprises:

Step 1: smelting metal raw materials into molten steel; smelting molten steel into steel ingots by die casting;

Step 2: Heat the steel ingot to 1180°C for 2 hours, then forge and open the billet to make a forged billet, heat the forged billet at 1210°C for 2 hours, and hot-roll it into a hot-rolled plate in multiple passes;

Step 3: Heat the hot-rolled sheet at 1050° C. for 1.5 hours and water-cool it, and conduct cold-rolling while controlling the cold-rolling deformation to 20%, so as to obtain an economical oil well tubular steel with high strength and high corrosion resistance. In this step, the volume fraction of austenite to martensite transformation is adjusted by controlling the cold rolling deformation to 20%. The final microstructure contains 35% ferrite, 49% martensite and 16% austenite.

The preparation method of embodiment 3 comprises:

Step 1: smelting metal raw materials into molten steel; smelting molten steel into steel ingots by die casting;

Step 2: Heat the steel ingot to 1210°C for 1 hour, then forge and open the blank to make a forged billet, heat the forged billet at 1190°C for 2 hours, and hot-roll it into a hot-rolled plate in multiple passes;

Step 3: Heat the hot-rolled sheet at 1140° C. for 1 hour and water-cool it, and cold-roll it while controlling the cold-rolling deformation to 10%, so as to obtain an economical oil well tubular steel with high strength and high corrosion resistance. In this step, the volume fraction of austenite to martensite is adjusted by controlling the cold rolling deformation to 10%. The final microstructure contains 42% ferrite, 42% martensite and 16% austenite.

The preparation method of embodiment 4 comprises:

Step 1: smelting metal raw materials into molten steel; smelting molten steel into ingots by die casting;

Step 2: Heat the ingot to 1200°C for 1 hour, then forge and open the blank to make a forged billet, heat the forged billet at 1200°C for 2 hours, and hot-roll it into a hot-rolled plate in multiple passes;

Step 3: Heat the hot-rolled sheet at 1150° C. for 1 hour and water-cool, control the cold-rolled deformation to 15% for cold-rolling, and obtain an economical oil well tubular steel with high strength and high corrosion resistance. In this step, the volume fraction of austenite to martensite is adjusted by controlling the cold rolling deformation to 15%. The final microstructure contains 42% ferrite, 47% martensite and 11% austenite.

The controlled cold rolling parameters of Examples 1-4 are shown in Table 1, and the mechanical properties of Examples 1-4 are shown in Table 2. FIG. 1 is a microstructure diagram of the steel of Example 1 of the present invention. The white arrow points to ferrite, and the gray phase at the black arrow is a mixed structure of martensite and austenite. Fig. 2 is the EBSD two-phase distribution diagram of the final structure of the steel of Example 1 of the present invention, the blue phase is austenite without martensitic transformation, and its content is 15%.

Figures 3-4 are microstructure diagrams of the steels of Examples 2-4 of the present invention; the microstructures of Examples 1-4 are shown in Table 3 below. The microstructure of the economical oil well tubular steel of the present invention is a mixed structure of ferrite + austenite + martensite, wherein the volume percentage of austenite is 10% to 30% (such as 11% to 16% ), the volume percentage of martensite is 25% to 50% (for example, 42% to 49%), and the content of ferrite is 30% to 50% (for example, 35% to 45%).

In the cold-rolled structure of the high-strength, high-corrosion-resistant economical oil well tubular steel of Examples 1-4, martensite is dispersed in austenite in the form of ultrafine sheets, alternately stacked with austenite, and separated from each other, so that Austenite has a smaller grain size (eg, austenite grain size < 3 μm), and the thickness of the martensite sheets is less than 100 nm.

The chemical composition wt% of table 1 embodiment 1-4

The mechanical property of table 2 embodiment 1-4

The microstructure of the steel of table 3 embodiment 1-4

In order to illustrate the corrosion resistance of the steel of the present invention, the steel of embodiment 1-4 is measured by 5 kinds of different conditions to corrosion resistance, and compare with 13Cr under the same test condition, evaluate the corrosion resistance of the present invention by this experiment Corrosion resistance of steel in different corrosive environments. The results of the corrosion resistance test are shown in Table 4, and the corresponding test conditions are as follows:

(180°C or 200°C) The corrosion conditions for the _CO2 corrosion rate are as follows:

1. Medium (formation water) mg/L: CO ₃ ^2- /0, HCO ₃ ^- /189, OH ^- /0, Cl ^- /128000, SO ₄ ^2- /430, Ca ²⁺ /8310, Mg ²⁺ /561,K ⁺ /6620,Na ⁺ /76500);

2. Partial pressure of _CO2 : 4.48MPa, total test pressure: 10MPa;

3. The test temperature is 180°C or 200°C;

4. The test time is 720 hours.

The corrosion conditions for the pitting corrosion rate are as follows:

1. Test temperature: 22±2℃;

2. Medium: 100g reagent grade ferric trichloride FeCl ₃ 6H ₂ O dissolved in 900mL type IV reagent grade water (mass ratio about 6%);

3. Test time: 72 hours;

4. Sample size: 50×25×3mm and grind to 2000# sandpaper.

The corrosion conditions for the crevice corrosion rate are as follows:

1. The test temperature is 22±2℃;

2. Dissolve 100g of reagent-grade ferric trichloride FeCl ₃ 6H ₂ O in 900mL of type IV reagent-grade water (mass ratio is about 6%);

3. Test time: 72 hours;

4. Sample size: 50×25×3mm and grind to 2000# sandpaper.

The corrosion conditions of the H ₂ S stress corrosion test are as follows:

1. The test temperature is 22±2℃;

2. 50g NaCl, 25g [23.8mL] CH ₃ COOH, 4.1g CH ₃ COONa were dissolved in 921mL type IV reagent grade water (mass ratio of about 5wt% sodium chloride, 2.5wt% glacial acetic acid and 0.41wt% acetic acid sodium);

3. Test time: 720 hours;

4. Sample size: 50×5×2mm, polished to 2000# sandpaper;

5. Four-point bending test, the loading force is 80% of the yield stress.

It can be seen from Table 4 that the (180°C) _CO2 corrosion rate of the high corrosion-resistant economical oil well tubular steel of Examples 1-4 is below 0.035g/m ² h (for example, 0.0289～0.0324g/m ² h); (200°C ) CO ₂ corrosion rate below 0.12g/m ² h (for example 0.104～0.112g/m ² h); pitting corrosion rate below 2.6g/m ² h (for example 2.138～2.521g/m ² h); crevice corrosion rate 6.1 g/m ² h or less (for example, 5.421~6.023g/m ² h); H ₂ S stress corrosion test all passed. The corrosion resistance of Examples 1-4 of the present invention is better than that of 13Cr, especially the _CO2 corrosion resistance at 200 ° C. The present invention is far superior to super 13Cr, and can be used in harsher environments, that is, applicable to larger well depths environment use. FIG. 5 is a graph showing the results of the H ₂ S stress corrosion test in Example 1.

Table 4 corrosion test data

The inventor has carried out a lot of in-depth research in the research. In order to further highlight the advantages of the present invention in terms of performance and composition, the super 13Cr martensitic stainless steel is now listed as a comparative example as follows:

Comparative example 1

This comparative example provides a corrosion-resistant oil well tubular steel and its preparation method. The corrosion-resistant oil well tubular steel in this comparative example is 13Cr, which is prepared by the current mature 13Cr process. The composition of the corrosion-resistant oil well tubular steel in this comparative example is C: 0.03%, Cr: 13%, Ni: 5%, Mo: 2%, Mn: 0.5%, Si: 0.5%, and the preparation method: heating and forging at 1150°C Finally, water cooling, then reheat to 860 ° C for 2 hours, quenching, and tempering at 620 ° C for 1 hour.

The microstructure of the steel of this comparative example is martensite (93%)+austenite (7%). The mechanical properties are shown in Table 3 above, and the results of corrosion resistance are shown in Table 4 above.

Comparing the examples and comparative examples, it can be seen that the high-strength and high-corrosion-resistant economical oil well tubular steel of the present invention precisely controls the mass percentages of Cr, Ni, Mn, Mo, and N elements in the steel, and cooperates with certain hot rolling + solid solution + cold rolling The process makes the austenite part undergo martensitic transformation, thereby obtaining a mixed structure of ferrite and martensite mainly containing a small amount of austenite, which greatly improves the corrosion resistance and toughness of oil well tubular steel. Realized that the strength of the steel of the present invention is equivalent to the super 13Cr martensitic stainless steel of the prior art and the cost of raw materials is lower, the corrosion resistance of the steel of the present invention is better than that of the super 13Cr martensitic stainless steel, so the comprehensive cost of the steel of the present invention Low cost, economical and practical.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention.

Claims (10)

1. A preparation method of high-strength and high-corrosion-resistant economical oil well tubular steel, characterized in that, comprising: Step 1: Smelting metal raw materials into molten steel; Step 2: Smelting molten steel into continuous casting slabs or ingots; Step 3: Forging the continuous casting billet or ingot to make a forging billet; hot rolling the forging billet into a hot-rolled plate; Step 4: The hot-rolled sheet is subjected to solution treatment, and the hot-rolled sheet after solution treatment is subjected to quantitative cold rolling with a deformation of 5% to 25%, and finally a three-phase ferrite + austenite + martensite is obtained Oil well tubular steel with mixed structure. 2. The preparation method according to claim 1, characterized in that, in the step 3, the forging blanking temperature is 1150-1250°C. 3. The preparation method according to claim 1, characterized in that, in said step 3, water cooling to room temperature after hot rolling. 4. The preparation method according to any one of claims 1-3, characterized in that, in the step 4, the process of solution treatment comprises: water cooling after heat preservation at 1000-1150° C. for 1-3 hours. 5. An economical oil well tubular steel with high strength and high corrosion resistance, characterized in that it is prepared by the preparation method described in any one of claims 1-4. 6. The high-strength, high-corrosion, and economical oil well tubular steel according to claim 5, characterized in that, the components of the high-strength, high-corrosion, and economical oil well tubular steel include: C: ≤0.03%, Cr : 17.4% to 18.4%, Mo: 0.5% to 2.5%, Ni: 1.0% to 2.8%, Mn: 1.0% to 3.5%, Si: 0.1% to 0.5%, N: 0.1% to 0.25%, P: ≤ 0.03%, S: ≤0.01%, the balance is Fe and unavoidable impurities. 7. The high-strength, high-corrosion, and economical oil well tubular steel according to claim 6, characterized in that, among the components of the high-strength, high-corrosion, and economical oil well tubular steel, Cr+3.3Mo+16N≥26. 8. The high-strength, high-corrosion, and economical oil well tubular steel according to claim 6, characterized in that, among the components of the high-strength, high-corrosion, and economical oil well tubular steel, 50Ni+17Mn-12Mo-800N≤0. 9. The high-strength, high-corrosion, and economical oil well tubular steel according to claim 6, characterized in that, the components of the high-strength, high-corrosion, and economical oil well tubular steel include: C: 0.01% to 0.03% in mass percentage , Cr: 17.4% to 18.3%, Mo: 1.1% to 2.2%, Ni: 1.0% to 2.4%, Mn: 1.2% to 3.2%, Si: 0.1% to 0.5%, N: 0.1% to 0.2%, P : ≤0.03%, S: ≤0.01%, and the balance is Fe and unavoidable impurities. 10. The high-strength, high-corrosion-resistant economical oil well tubular steel according to any one of claims 5-9, characterized in that, among the components of the high-strength, high-corrosion-resistant economical oil well tubular steel, 50Ni+17Mn-12Mo- 800N≤-3.

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