CN111041165A

CN111041165A - A kind of medium manganese oil well pipe steel and preparation method thereof

Info

Publication number: CN111041165A
Application number: CN201911365613.4A
Authority: CN
Inventors: 童帅; 黄涛; 李拔
Original assignee: Zhonglian Advanced Steel Technology Co ltd; China Iron and Steel Research Institute Group
Current assignee: Zhonglian Advanced Steel Technology Co ltd; China Iron and Steel Research Institute Group
Priority date: 2019-12-26
Filing date: 2019-12-26
Publication date: 2020-04-21
Anticipated expiration: 2039-12-26
Also published as: CN111041165B

Abstract

The invention relates to a medium manganese oil well pipe steel and a preparation method thereof, belongs to the field of medium manganese steel preparation, and solves the problems of insufficient strength and toughness and high production cost of the oil well pipe steel in the prior art. A medium manganese oil well pipe steel, the mass percentages of chemical constituent elements are: C: 0.08-0.12wt%, Si: 0.1-0.2wt%, Mn: 3.0-4.0wt%, P:≤0.025wt%, S:≤ 0.005wt%, V: 0.02-0.04wt%, Cu: 0-0.4wt%, Al: ≤0.06wt%, the balance is Fe and inevitable inclusions. The invention realizes the matching of high strength and high toughness of medium manganese oil well pipe steel.

Description

Medium manganese oil well pipe steel and preparation method thereof

Technical Field

The invention relates to the technical field of metal materials, in particular to medium manganese oil well pipe steel and a preparation method thereof.

Background

With the development of the petroleum industry, the demand of oil well pipes is gradually increased. At present, the total quantity of oil well pipes in the world is 1370 ten thousand tons, the total capacity of the oil well pipes in the world is more than 1700 ten thousand tons, and the situation of supply and demand is achieved. However, even if the supply is larger than the demand, the supply is limited to a part of the region, and countries and regions other than european countries and china are still in a state of supply shortage. With the continuous development of economy, the global oil well pipe demand is continuously increased, and the demand is mostly in the united states, and then in russia, china, the middle east and the northern part of africa, which accounts for 85% of the total oil well pipe consumption. In addition to the major oil well pipe importing countries in the world, there are also a lot of countries and regions with great market demands.

In the domestic market, the most used products in various domestic oil fields are J55, N80 and P110. For high steel grade oil well pipes, the common problem is that the toughness is unstable or low. Since high strength steel has brittleness at low temperature and it is difficult to achieve a balance between impact toughness and strength, it is a major means to improve strength and toughness of materials by changing the composition of steel and heat treatment process.

In the existing production technology of oil well pipes, noble metal elements such as Nb, Ti, Cr, Mo and the like are mostly added to improve the strength and toughness of oil well pipe steel. But the prices of Nb, Ti, Cr and Mo are relatively high, and the production cost of steel is increased.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a medium manganese steel for oil well pipes and a preparation method thereof, so as to solve the problems of mismatched toughness and high production cost of the existing steel for oil well pipes.

The invention is realized by the following technical scheme:

the medium manganese oil well pipe steel comprises the following chemical components in percentage by mass: c: 0.08 to 0.12 wt%, Si: 0.1-0.2 wt%, Mn: 3.0-4.0 wt%, P: less than or equal to 0.025 wt%, S: less than or equal to 0.005 wt%, V: 0.02 to 0.04 wt%, Cu: 0-0.4 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

Further, the medium manganese oil well pipe steel comprises the following chemical components in percentage by mass: c: 0.09-0.11 wt%, Si: 0.12-0.18 wt%, Mn: 3.2-3.8 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.0045 wt%, V: 0.025 to 0.038 wt%, Cu: 0-0.35 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

Further, the microstructure of the medium manganese oil well pipe steel comprises tempered martensite, bainite and nanometer VC precipitates attached to the tempered martensite and bainite structures.

The preparation method of the medium manganese oil well pipe steel is characterized by comprising the following steps:

step 1: smelting and external refining the steel ingot or the rough steel blank to obtain a steel billet, and heating the steel billet;

step 2: directly carrying out hot rolling after discharging the steel billet;

and step 3: carrying out quenching and tempering heat treatment on the hot rolled steel billet;

and 4, step 4: and cooling the quenched and tempered steel billet to obtain the medium manganese oil well pipe steel.

Further, the heating temperature for heating the steel billet in the step 1 is 1180-1220 ℃.

Further, the hot rolling process in the step 2 comprises rough rolling and finish rolling; the rough rolling is divided into 2 passes, the deformation of the first pass is 8-10%, and the deformation of the second pass is 9-11%; the finish rolling is divided into 4 passes, the deformation of the first pass is 13-15%, the deformation of the second pass is 20-22%, the deformation of the third pass is 31-33%, and the deformation of the fourth pass is 47-49%.

Further, in the step 2, the finishing temperature of hot rolling is controlled to be 820-880 ℃.

Further, the quenching and tempering in the step 3 adopts a heat treatment process of quenching first and then high-temperature tempering.

Further, in the step 3, the quenching process is water quenching after heat preservation is carried out for 30-90 min at the temperature of 900-920 ℃; the high-temperature tempering temperature is controlled to be 640-660 ℃, and the temperature is kept for 2-3 hours.

Further, in step 4, directly carrying out natural air cooling on the steel billet subjected to high-temperature tempering in the step 3 to obtain the medium manganese oil well pipe steel.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

1. compared with the prior art, the medium manganese oil well pipe steel provided by the application has the advantages that the addition amount of Mn is increased, the hardenability and the strength of the steel are obviously improved, tempered martensite and bainite are obtained, the yield strength of the steel reaches 900MPa, and the room temperature impact energy is more than 200J.

2. According to the method, the microstructure of the steel, including tempered martensite, bainite and vanadium carbide precipitates, is obtained by adjusting the alloy content in the steel and matching with rolling and a post-rolling quenching and tempering heat treatment process. The tempered martensite structure ensures that the medium manganese oil well pipe steel has good yield strength and tensile strength, the bainite structure has toughness, the medium manganese oil well pipe steel also has good toughness besides excellent strength performance, and the nano vanadium carbide precipitate is attached to the tempered martensite and the bainite structure, so that the fine grain strengthening effect and the precipitation strengthening effect can be achieved. Tempered martensite, bainite and vanadium carbide precipitates attached to the tempered martensite and the bainite, and the crystal structure can effectively increase the dislocation energy of steel and enhance the strength and toughness of medium manganese oil well pipe steel.

3. According to the medium manganese oil well pipe steel and the preparation method thereof, only three elements of Mn, V and Cu are added into metal elements, Mn is a metal cheaper than Fe, V and Cu belong to metal elements with higher prices, but the addition amounts of the two metal elements are small; in addition to the above-mentioned metal elements mentioned in this application, Cr, Ni, Ti, Mo and other rare metal elements may be added to the existing production of medium manganese oil well pipe steel, and Cr, Ni, Ti and rare metals belong to noble metal elements. Therefore, the medium manganese oil well pipe steel and the preparation method thereof have the advantages that the types of the added noble metal elements are few, the production cost is effectively reduced, and meanwhile, the yield strength of the medium manganese oil well pipe steel can reach 800-900 MPa, which is superior to that of the existing medium manganese oil well pipe steel in 600-800 MPa.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a graph of the structure of tempered martensite and bainite in the steel for an oil well pipe of example 1;

FIG. 2 shows the morphology of the tempered martensite and bainite structures in the steel for the oil well pipe of example 2.

Detailed Description

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.

Example 1

The invention provides a chemical composition of medium manganese oil well pipe steel, which comprises the following elements in percentage by mass: c: 0.08 to 0.12 wt%, Si: 0.1-0.2 wt%, Mn: 3.0-4.0 wt%, P: less than or equal to 0.025 wt%, S: less than or equal to 0.005 wt%, V: 0.02 to 0.04 wt%, Cu: 0-0.4 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

In one possible design, the medium manganese oil well pipe steel comprises the following chemical components in percentage by mass: c: 0.09-0.11 wt%, Si: 0.12-0.18 wt%, Mn: 3.2-3.8 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.0045 wt%, V: 0.025 to 0.038 wt%, Cu: 0-0.35 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

The elements of the present invention are explained in detail below, and the contents refer to the mass percentages of the respective elements in the steel.

C: c is an austenitizing stabilizing element, and can improve the hardenability of the steel and the strength obviously. However, the C content is not preferably too high, and too high C causes coarse carbide precipitation in the steel, which affects the toughness and weldability of the steel, so the C content is preferably 0.08 to 0.12 wt%.

Si: si can increase the yield strength of steel and inhibit the formation of cementite. However, too much Si lowers the plasticity and toughness of the steel and causes deterioration of weldability of the steel, so that the Si content should be controlled to 0.1 to 0.2 wt%.

Mn: mn is an austenite forming element and also an important toughening element. The toughness and plasticity of the steel can be improved by improving the thermodynamic stability of austenite, obviously improving the hardenability of the steel, obtaining more retained austenite and reversing transformed austenite. However, if the Mn content is too high, hardenability of the steel is increased, and weldability and toughness are affected, and if the Mn content is too low, stable reverse transformed austenite cannot be obtained at room temperature. The Mn element has obvious action effect, namely, in order to obtain excellent hardenability of the material and improve the toughness of the material by forming reverse transformation austenite, the content of Mn is controlled to be 3.0-4.0%.

P: p can increase the strength of the ferritic steel to some extent, but too much P is segregated at grain boundaries, embrittling the grain boundaries, and deteriorating toughness. In addition, the steel with excessively high P content generates cold brittleness in a low-temperature service environment.

S: s is easy to form MnS in steel to reduce the toughness of the steel, and the S content in medium manganese oil well pipe steel needs to be strictly controlled.

V: v can be combined with C to form a VC pinning crystal boundary, the grain size is reduced, V can also be dissolved in a matrix in a solid mode, the yield strength of the matrix is obviously improved, and the toughness is improved. However, since V is too expensive, it is not preferable to add too much V, and thus V is controlled to 0.02 to 0.04 wt%.

Cu: cu is an austenite forming element and one of the most effective elements for improving corrosion resistance, and is mainly present as a solid solution, but too high copper content in steel causes cracking of a cast slab. The hardenability of the steel can be improved by improving the thermodynamic stability of austenite, and more retained austenite and reversed austenite can be obtained. The invention controls the copper content to be below 0.4 wt% from the comprehensive consideration of the precipitation strengthening of Cu and the matching of improving the corrosion resistance.

Example 2

On the other hand, the invention also provides a preparation method of the medium manganese oil well pipe steel, which comprises the following steps:

step 2: directly carrying out hot rolling after discharging the steel billet;

Specifically, the temperature for heating the steel billet in the step 1 is controlled to be 1180-1220 ℃. The step 2 of hot rolling comprises two processes of rough rolling and finish rolling. Wherein the rough rolling is divided into 2 passes, the deformation of the first pass is 8-10%, and the deformation of the second pass is 9-11%; the finish rolling is divided into 4 passes, the deformation of the first pass is 13-15%, the deformation of the second pass is 20-22%, the deformation of the third pass is 31-33%, and the deformation of the fourth pass is 47-49%. In a specific embodiment, the rough rolling is divided into two passes, wherein the deformation of the first pass is 8.33%, and the deformation of the second pass is 9.09%; the finish rolling is divided into 4 passes, the deformation of the first pass is 14.0%, the deformation of the second pass is 20.93%, the deformation of the third pass is 32.35%, and the deformation of the fourth pass is 47.83%. After the final rolling, the thickness of the steel was 12 mm.

It is worth noting that in the hot rolling process, the finishing rolling temperature is only controlled to be 820-880 ℃, and no requirement is made on the opening rolling temperature. The finish rolling temperature has great influence on the structure of steel, when the finish rolling temperature is low to the rolling in a two-phase region, a banded structure is generated, and the performance is deteriorated due to uneven mixed crystal structure; if the finishing rolling temperature is too high, the austenite structure after rolling is fully recrystallized and the crystal grains grow up, and the performance of the steel is reduced. Therefore, the required structure can be obtained by controlling the proper initial rolling temperature and the proper final rolling temperature, and the performance of the steel can be ensured. The purpose of rough rolling and finish rolling is to obtain fine grain structure, refine grains, and improve the strength and impact toughness of the steel.

In particular, in order to prevent the cracking phenomenon of the steel surface in the subsequent heat treatment process, the steel billet is subjected to brine cooling after the finish rolling is completed. After the medium manganese oil well pipe steel is subjected to rough rolling and finish rolling, the steel is completely austenitized, the completely austenitized steel pipe is rapidly changed into quenched martensite in water, and the surface of the steel can crack. Therefore, the step of adding brine cooling after hot rolling is firstly that the cooling speed of brine quenching is slow, so that the surface of the steel can be effectively prevented from cracking; secondly, a part of bainite structure can be obtained at a slow cooling speed of brine quenching, the toughness of the bainite structure is superior to that of quenched martensite, and the cracking of the surface of the steel can be prevented.

In order to enable the steel to obtain more martensite structures and improve the strength and toughness of the steel, the steel plate after finish rolling is subjected to quenching and tempering heat treatment process, and the quenching and tempering adopt a heat treatment process of quenching firstly and then high-temperature tempering. Quenching at 900-920 ℃, keeping the temperature for 30-90 min, and then performing water quenching; and controlling the high-temperature tempering temperature to be 640-660 ℃, and directly air-cooling the steel after heat preservation for 2-3 hours to obtain the steel plate. The higher the quenching temperature is, the larger the volume of austenite obtained in the steel is, and the higher the strength of the steel is; however, if the quenching temperature is too high, the volume of tempered martensite is reduced, and the impact toughness of the steel material is greatly reduced. The high-temperature tempering is adopted in the invention, so that the residual austenite in the matrix is reduced to a limited extent, and the strength of the steel is effectively improved.

The invention provides medium manganese oil well pipe steel and a preparation method thereof, wherein a low-carbon system is adopted to add alloy elements, and then the medium manganese oil well pipe steel with a microstructure comprising tempered martensite, bainite and nanometer VC precipitates attached to the tempered martensite and bainite structures is obtained through the adjustment of a heat treatment process. Mn element is an important strengthening and toughening element in the steel, the content of the Mn element is increased, the strength of the steel is enhanced, and the strength of the steel is further increased by tempered martensite in the steel and second-phase precipitates uniformly attached to the tempered martensite.

Regarding the toughness of steel materials, the hardenability of steel is improved by adding Cu and V elements, and the high toughness of the steel materials is ensured; on the other hand, in the quenching and tempering process, partial bainite is generated in the steel, and compared with tempered martensite, the bainite has good impact toughness and effectively improves the toughness of the medium manganese oil well pipe steel. As can be seen from FIGS. 1 and 2, the matrix structure of the medium manganese steel for oil well pipes prepared in the present invention is mainly composed of tempered martensite and has a small amount of bainite structure.

Meanwhile, the crystal grains are refined by the precipitate of VC, so that the crystal grain size of the steel is reduced, the precipitation strengthening effect and the fine-grain strengthening effect are achieved, and the strength of the steel is improved. The vanadium carbide precipitate crystal grains are nano-scale particles, and the average particle size of the vanadium carbide precipitate crystal grains is 10-60 nm. The nanometer precipitate pinning crystal boundary in the application reduces the crystal boundary energy, and is used as a primary phase nucleation core in molten steel solidification, so that steel crystal grains are refined, and the tissue matrix crystal grains grow up and are refined in the hot rolling and quenching and tempering processes. The second phase precipitates interact with dislocations through fine and dispersed second phases in the steel, so that the dislocation movement is obstructed, the dislocation energy of the steel is increased, and the strength of the steel is improved. Through detection, the nanometer VC precipitate refines the crystal grains in the medium manganese oil well pipe steel from 30 mu m to about 20 mu m, and improves the strength, the plasticity and the impact toughness of the medium manganese oil well pipe steel.

Example 3

Example 3 is the chemical composition and preparation method of 5 specific medium manganese oil well pipe steels. Through detection, the oil well pipe steel obtained through alloy component design and heat treatment process has the tensile strength of 860-900 MPa, the yield strength of 590-630 MPa, and the Charpy impact energy at normal temperature of more than 220J. Table 1 shows the chemical composition of the manganese steel for oil well pipes in examples 1 to 5, Table 2 shows the process parameters for preparing the manganese steel for oil well pipes in examples 1 to 5, and Table 3 shows the mechanical properties of the manganese steel for oil well pipes in examples 1 to 5.

Table 1: chemical composition of manganese Steel for oil well pipes in examples 1 to 5 (% by mass)

Table 2: example 1-5 preparation Process parameters of Medium manganese oil well pipe Steel

Table 3: examples 1 to 5 Medium manganese oil well pipe Steel mechanical Properties

Comparative example

The existing medium manganese oil well pipe steel and the preparation method thereof comprise the following chemical components in percentage by mass: c: 0.15-0.2%; si: 0.5-0.55%; mn: 2.5-3.0%; al: 1.45-1.5 percent of iron and inevitable impurity elements in balance. The medium manganese oil well pipe steel produced by adopting the addition amount of the element is subjected to a series of smelting, continuous casting, hot rolling and quenching and tempering processes to obtain the medium manganese oil well pipe steel with an austenite matrix structure, the yield strength of the medium manganese oil well pipe steel is 500-600 MPa, and the elongation of the medium manganese oil well pipe steel is 30-40%.

Compared with a comparative example, the manganese content is increased, and simultaneously, a trace amount of V element is added, the medium manganese oil well pipe steel with matrix structure of tempered martensite, bainite and vanadium carbide precipitates is obtained through smelting, hot rolling and quenching and tempering processes, the yield strength is 850-900 MPa, the elongation after fracture is 35-40%, and the section elongation is 85-90%. This application has realized well manganese oil well pipe steel high strength and high tenacity phase-match.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims

1. The medium manganese oil well pipe steel is characterized by comprising the following chemical components in percentage by mass: c: 0.08 to 0.12 wt%, Si: 0.1-0.2 wt%, Mn: 3.0-4.0 wt%, P: less than or equal to 0.025 wt%, S: less than or equal to 0.005 wt%, V: 0.02 to 0.04 wt%, Cu: 0-0.4 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

2. The medium manganese oil well pipe steel according to claim 1, wherein the medium manganese oil well pipe steel comprises the following chemical composition elements in percentage by mass: c: 0.09-0.11 wt%, Si: 0.12-0.18 wt%, Mn: 3.2-3.8 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.0045 wt%, V: 0.025 to 0.038 wt%, Cu: 0-0.35 wt%, Al: less than or equal to 0.06wt percent, and the balance of Fe and inevitable impurities.

3. The medium manganese oil well pipe steel of claim 1, wherein the microstructure of the medium manganese oil well pipe steel comprises tempered martensite, bainite and nano VC precipitates attached to the tempered martensite and bainite structures.

4. A method for preparing medium manganese oil well pipe steel, which is used for preparing the medium manganese oil well pipe steel as claimed in claims 1-3, and is characterized by comprising the following steps:

step 2: directly carrying out hot rolling after discharging the steel billet;

and 4, step 4: and cooling the steel billet subjected to quenching and tempering heat treatment to obtain the medium manganese oil well pipe steel.

5. The method for preparing the medium manganese steel for the oil well pipe according to claim 4, wherein the heating temperature of the steel billet heated in the step 1 is 1180-1220 ℃.

6. The method for preparing medium manganese steel for oil well pipes according to claim 4, wherein the hot rolling process in the step 2 comprises rough rolling and finish rolling; the rough rolling is divided into 2 passes, the deformation of the first pass is 8-10%, and the deformation of the second pass is 9-11%; the finish rolling is divided into 4 passes, the deformation of the first pass is 13-15%, the deformation of the second pass is 20-22%, the deformation of the third pass is 31-33%, and the deformation of the fourth pass is 47-49%.

7. The method for preparing medium manganese steel for oil well pipes according to claim 4, wherein in the step 2, the finishing temperature of the hot rolling is controlled to be 820-880 ℃.

8. The method for preparing medium manganese steel for oil well pipes according to claim 7, wherein the quenching and tempering in the step 3 adopts a heat treatment process of quenching and high temperature tempering.

9. The method for preparing the medium manganese oil well pipe steel according to claim 8, wherein in the step 3, the quenching process is water quenching after heat preservation at 900-920 ℃ for 30-90 min; the high-temperature tempering temperature is controlled to be 640-660 ℃, and the temperature is kept for 2-3 hours.

10. The method for preparing medium manganese steel for oil well pipes according to claim 9, wherein in the step 4, the steel billet after the high temperature tempering in the step 3 is directly subjected to natural air cooling to obtain the medium manganese steel for oil well pipes.