CN114411053B

CN114411053B - High-efficiency low-cost large-deformation-resistant X70M pipeline steel plate and manufacturing method thereof

Info

Publication number: CN114411053B
Application number: CN202111625989.1A
Authority: CN
Inventors: 曲之国; 张友健; 刘振华; 范明达; 王东明; 杨海峰; 白学飞
Original assignee: Rizhao Steel Yingkou Medium Plate Co Ltd
Current assignee: Rizhao Steel Yingkou Medium Plate Co Ltd
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-12-20
Anticipated expiration: 2041-12-29
Also published as: CN114411053A

Abstract

The invention discloses a large deformation resistant X70M pipeline steel plate produced in an efficient and low-cost mode and a manufacturing method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: 0.04-0.06%; si:0.15 to 0.25 percent; mn:1.30 to 1.40 percent; p is less than or equal to 0.015 percent; s is less than or equal to 0.003 percent; nb:0.028-0.035%; cr:0.12 to 0.25 percent; ti:0.008 to 0.020 percent; ni:0 to 0.30 percent; mo: less than or equal to 0.06 percent; ca is less than or equal to 0.005 percent; and Als:0.015-0.045%; b is less than or equal to 0.0005 percent; the balance of Fe and inevitable impurities. The steel plate produced by the method has the advantages of simple and efficient production process and lower cost, and has good application prospect in the field of pipeline steel production.

Description

High-efficiency low-cost large-deformation-resistant X70M pipeline steel plate and manufacturing method thereof

Technical Field

The invention belongs to the technical field of pipeline steel plate production, and particularly relates to an efficient low-cost large-deformation-resistant X70M pipeline steel plate and a manufacturing method thereof.

Background

With the increasing demand of economic development on oil and gas resources, the construction of oil and gas pipelines gradually develops from economically developed areas to remote areas, and long distance, high strength, large caliber and high pressure become the development direction of pipeline construction. Meanwhile, the inevitable earthquake zones, landslide disaster areas, frozen soil melting areas and the like in the pipeline construction all provide new challenges for pipeline construction, construction and operation. For this reason, pipeline designers propose concepts based on strain design. The pipeline steel is required to have large deformation resistance, namely, the pipeline steel has the performances of lower yield ratio (less than or equal to 0.85), higher uniform elongation (more than or equal to 10%) and the like on the premise of meeting the requirements of high strength and high toughness.

According to the existing data, the large deformation resistance X70M and X80M is realized in batch application, but the problems of complex alloy design, high cost, complex process and the like generally exist, so that the actual production cost is high, the efficiency is reduced, and the pipeline construction cost is increased indirectly. For example, the publication No. CN103343300A proposes engineering steel with a thickness of more than 26mm and a longitudinal yield strength of more than or equal to 500MPa and a production method thereof, the produced steel plate is added with elements such as Cr, ni, cu, mo and the like, and an alloy system is complex and has higher cost; the publication No. CN102828125A, a strain design-based steel X70 for pipeline and a manufacturing method thereof, the produced steel plate has high C content and adopts a relaxation process, and the comprehensive performance and the production efficiency of the steel plate are not high; the publication No. CN102534377A, X70 grade large deformation resistant pipeline steel with excellent toughness and a preparation method thereof adopt three-stage controlled rolling and two-stage water cooling, which seriously influences the improvement of rolling efficiency; the publication number CN101914723A, a hot-rolled large deformation resistant pipeline steel and a preparation method thereof, although the cost is lower, two rolling ideas are designed, one is common air cooling relaxation, and the other is two-phase zone low temperature final rolling, although superior large deformation resistance can be obtained, the rolling production efficiency is negatively affected; the publication No. CN109957709A, a V-containing large deformation X70M pipeline steel plate and a manufacturing method thereof, adopts V microalloying to improve the strength, also adopts a two-phase zone final rolling mode, controls the low temperature open cooling mode after rolling, has extremely high requirements on the load of a rolling mill, and can generate adverse effects on the shape of the steel plate by the low temperature final rolling at 720-754 ℃. Aiming at the problems, the production process adopted by the steel plate is simple and efficient, the cost is low, various performances meet the requirement of large deformation resistance X70M pipeline steel, and the steel plate has a good application prospect.

Disclosure of Invention

The invention aims to provide an efficient low-cost large-deformation-resistant X70M pipeline steel plate and a manufacturing method thereof, and aims to achieve the effects of efficient low-cost production by simple component design and production by adopting a conventional TMCP (thermal mechanical control processing) process.

The purpose of the invention is realized by the following technical scheme: the utility model provides an anti big deformation X70M pipeline steel sheet of high-efficient low-cost which characterized in that: the paint comprises the following components in percentage by mass: c:0.04-0.06%; si:0.15 to 0.25 percent; mn:1.30-1.45%; p is less than or equal to 0.016 percent; s is less than or equal to 0.003 percent; nb:0.028-0.035%; cr:0.12 to 0.25 percent; ti:0.008 to 0.020 percent; ni:0 to 0.30 percent; mo: less than or equal to 0.06 percent; ca is less than or equal to 0.005 percent; and (3) Als:0.015-0.045%; b is less than or equal to 0.0005 percent; the balance of Fe and inevitable impurities; wherein C + Mn/6+ Cr/5 is more than or equal to 0.27 percent and less than or equal to 0.31 percent, and C + (Mn + Mo)/3.87 is more than or equal to 0.42 percent.

Further: the paint comprises the following components in percentage by mass: c:0.042-0.055%; si:0.16-0.20%; mn:1.30-1.40%; p is less than or equal to 0.015 percent; s is less than or equal to 0.002%; cr:0.12 to 0.18 percent; mo: less than or equal to 0.05 percent; the balance of Fe and inevitable impurities; wherein C + Mn/6+ Cr/5 is more than or equal to 0.27 percent and less than or equal to 0.31 percent, and C + (Mn + Mo)/3.87 is more than or equal to 0.42 percent.

The manufacturing method of the X70M pipeline steel plate with high efficiency, low cost and large deformation resistance comprises the steps of molten iron pretreatment, smelting, continuous casting, rolling and water cooling, and is characterized in that:

in the rolling step, two-stage controlled rolling is adopted, wherein the heating temperature of a steel billet is 1200-1220 ℃, the thickness of an intermediate billet is more than or equal to 4.0t, and the reduction rate of a single pass of the last two times of rough rolling is more than or equal to 20%; the final rolling temperature of the second stage is controlled to be T' +30 +/-10 ℃, even pass rolling is adopted, the reduction rate of each pass is more than or equal to 15%, direct water cooling is carried out after the last pass deformation, the cooling speed is 10-15 ℃/s, and the final cooling temperature is 300 +/-20 ℃; where T is the finished product thickness, T' = 925-288 (C + (Mn + Mo)/3.87 + Cr/20+ Ni/6) -0.45T.

And further: in the rolling step, the thickness of the steel billet is more than or equal to 11t, and the single-pass reduction rate of the last two times of rough rolling is more than or equal to 20 percent; wherein t is the finished product thickness.

Further: and in the second stage of finish rolling, the even pass rolling is adopted, the water cooling is directly carried out after the last pass deformation, the water inlet temperature is more than or equal to T', the cooling speed is controlled to be 10-15 ℃/s, the final cooling temperature is 300 +/-20 ℃, and the steel plate is straightened and then is subjected to off-line stacking or direct cutting.

Further: the thickness of the steel plate is 25.4-28.6mm.

The invention has the advantages that: compared with other large deformation resistant pipeline steel, the steel has the advantages of simple component system and low alloy cost, and precious alloys such as Mo, cu, nb and V are not added or are less added to the steel plate, so that smelting components can be greatly reduced; on the other hand, by matching the component design with the TMCP process, the structure type of fine ferrite, bainitic ferrite and MA is obtained on the basis of not adopting a two-phase region rolling, post-rolling relaxation or heat treatment process, the X70M grade pipeline steel with excellent large deformation resistance can be obtained, and through the rolling process, the number of rolled blocks of the same specification steel plate per hour is increased by at least 2, and the steel rolling production efficiency is improved. The yield strength of the developed steel plate is 440-520Mpa, the tensile strength is 570-735Mpa, the yield ratio is less than or equal to 0.75, the uniform deformation elongation is more than or equal to 10 percent, the impact energy at minus 40 ℃ is more than or equal to 200J, and the DWTT at minus 10 ℃ is more than or equal to 85 percent. The steel plate produced by the method has the advantages of simple and efficient production process and lower cost, and has good application prospect in the field of pipeline steel production.

Drawings

FIG. 1 shows the structure (200X) of the steel sheet of the present invention;

FIG. 2 shows the structure (200X) of the steel sheet of comparative example 2.

Detailed Description

The invention discloses an efficient low-cost large-deformation-resistant X70M pipeline steel plate which comprises the following components in percentage by mass: c:0.04 to 0.06 percent; si:0.15 to 0.25 percent; mn:1.30-1.45%; p is less than or equal to 0.016 percent; s is less than or equal to 0.003 percent; nb:0.028-0.035%; cr:0.12 to 0.25 percent; ti:0.008 to 0.020 percent; ni:0 to 0.30 percent; mo: less than or equal to 0.06 percent; ca is less than or equal to 0.005 percent; and Als:0.015-0.045%; b is less than or equal to 0.0005 percent; the balance of Fe and inevitable impurities; wherein C + Mn/6+ Cr/5 is more than or equal to 0.27 percent and less than or equal to 0.31 percent, and C + (Mn + Mo)/3.87 is more than or equal to 0.42 percent.

Preferably: the paint comprises the following components in percentage by mass: c:0.042-0.055%; si:0.16-0.20%; mn:1.30-1.40%; p is less than or equal to 0.015 percent; s is less than or equal to 0.002%; cr:0.12 to 0.18 percent; mo: less than or equal to 0.05 percent; the balance of Fe and inevitable impurities; wherein C + Mn/6+ Cr/5 is more than or equal to 0.27 percent and less than or equal to 0.31 percent, and C + (Mn + Mo)/3.87 is more than or equal to 0.42 percent.

The invention adopts the above components and is mainly based on the following considerations:

c: carbon mainly plays a role in solid solution strengthening in steel, but the increase of the carbon content seriously affects the welding performance and the low-temperature toughness, and if the carbon content is too low, ferrite phase transformation is easily caused to quickly generate to cause insufficient strength, so the invention sets C:0.04-0.06%, preferably C:0.045-0.055%.

Mn: manganese has the functions of reducing the phase transition temperature and refining the structure, can make up for the problem of insufficient strength caused by low carbon, but if the manganese is too high, the stability of austenite is increased, and the low yield ratio is not favorable under the rolling process. Thus, the present invention sets Mn:1.30 to 1.45%, preferably Mn:1.30-1.40%. In the invention, the limitation of C, mn, C + Mn/6+ Cr/5 and C + (Mn + Mo)/3.87 is one of the obvious characteristics, and through the design, on one hand, the austenite-ferrite phase transformation is promoted, and a foundation is laid for obtaining a low yield ratio; on the other hand, the strength of the matrix is also considered, and the problem that the overall strength cannot reach the requirement of X70 level is avoided.

Si: in the present invention, silicon mainly plays a role of solid solution strengthening, but too high content also affects toughness of steel, so the present invention sets Si:0.15-0.25%, preferably 0.16-0.20%.

Niobium and titanium have the effects of refining structures and precipitation strengthening in steel, particularly, the Nb element can effectively enlarge a non-recrystallization region, but the content is too high, the yield strength is easily improved, the yield ratio is not favorably controlled, and the components are high, the Nb:0.028-0.035%; ti:0.008-0.018%.

Mo: mo has a strong effect of delaying austenite-ferrite phase transformation, under the condition of a non-relaxation process, the steel contains more Mo, the needle-shaped ferrite group type is easily formed, the control of low yield ratio is not facilitated, and the Mo belongs to noble metals, so that the Mo is set to be less than or equal to 0.06%.

Cr and Ni: the addition of Cr and Ni mainly plays a role in improving the strength of the steel plate, and the addition of Ni also has a role in improving the low-temperature toughness, and the ratio of Cr:0.12-0.25%, preferably 0.12-0.18%; ni:0 to 0.14 percent.

P, S, ca: p and S are elements harmful to low-temperature toughness and need to be respectively controlled to be less than or equal to 0.016 percent; the S is less than or equal to 0.003 percent, and the better low-temperature toughness can be obtained. Meanwhile, the Ca content of the molten steel is preferably selected by carrying out Ca treatment on the molten steel: 0.0005 to 0.0018 percent of the total weight of the additive, can meet the spheroidizing effect of sulfides, and easily causes the increase of calcium-containing inclusions and increases the wire feeding cost at the same time when the total weight of the additive is too high.

The core idea of the above component design is that the anti-large deformation X70M pipeline steel has a pro-eutectoid ferrite + bainite dual-phase structure characteristic, and the low-temperature austenite stability is reduced and the formation of pro-eutectoid ferrite is promoted by the optimized combination of C, mn, mo and Nb. But the invention is different from the defects that the pro-eutectoid ferrite obtained by the traditional two-phase zone rolling and relaxation process is generally larger in grain size and is easy to form a ferrite strip-shaped structure along an austenite grain boundary or a rolling deformation zone, and the like.

The method for manufacturing the steel plate comprises the following steps:

in the smelting link, the cleanliness of molten steel is improved by means of molten iron pretreatment, LF refining, RH vacuum treatment, argon soft blowing and other measures, and a foundation is laid for realizing excellent low-temperature toughness of the steel plate. In the continuous casting link, the thickness of the steel billet is preferably more than or equal to 11t (t is the thickness of the finished product, mm) according to the thickness of the finished product of the steel plate, so that the total compression ratio is ensured, and the excellent DWTT performance can be obtained at a relatively high finish rolling temperature.

The heating temperature design of the steel billet is an important link of the invention. Because the invention gives consideration to the cost and the efficiency, and the strengthening elements such as C, mn, mo, nb and the like are greatly reduced, in order to ensure the basic strength of the steel plate, a proper high-temperature heating mode is adopted for the heating temperature; in consideration of ensuring DWTT performance of thick pipeline steel, under the condition of low C and Nb contents, austenite grains grow rapidly by high-temperature heating, and DWTT performance of the steel plate is deteriorated. Therefore, the strength and DWTT performance are comprehensively considered, and aiming at the alloy components, the heating temperature of the steel billet is set to be 1200-1220 ℃, and the performance of the steel plate can not be achieved by too high or too low temperature.

The rolling process adopts two-stage rolling, wherein the first stage rolling is mainly used for obtaining fine recrystallized austenite, and tissue preparation is provided for obtaining more and more uniform nucleation points after the second stage rolling. The thickness of the intermediate billet rolled in the first stage is required to be more than or equal to 4.0t (t is the thickness of a finished product), and the reduction rate of the last two single passes is more than or equal to 20 percent, preferably more than or equal to 22 percent. If the value is less than this, coarse proeutectoid ferrite is easily obtained after the transformation, and the DWTT performance is poor.

The control of the finish rolling stage is another core of the process control of the invention, namely the time of separating out the ferrite is controlled by deformation and temperature, and the separation out of the ferrite before entering water is reduced or avoided. The rolling temperature is required not to be too high, otherwise the pipeline steel toughness requirement, especially DWTT requirement, cannot be met, but too low temperature easily causes deformation induced ferrite precipitation or ferrite precipitation before water entering, the ferrite is relatively coarse and is in strip distribution, and the rolled steel plate has dual-phase structure characteristics, but the yield strength is easy to be insufficient, and the DWTT performance is poor. Therefore, the finish rolling temperature in the second stage of finish rolling is controlled according to T '+30 ℃ (± 10 ℃), and T' = 925-288 (+ (Mn + Mo)/3.87 + Cr/20+ Ni/6) -0.45 + T. In addition, compared with the traditional X70M pipeline steel, the temperature of the finish rolling stage of the steel plate is relatively high, so that the reduction rate of each pass is required to be controlled to be more than or equal to 15 percent so as to improve the accumulated effect of two-stage rolling, promote the precipitation of second phase particles in the rolling stage and provide more nucleation points for ferrite nucleation.

After the last deformation, different from the relaxation process, the invention adopts a direct water cooling mode, and the water inlet temperature is required to be more than or equal to T', so the aim of avoiding excessive precipitation of ferrite before water cooling is also achieved.

The control of the cooling path of the steel plate is another core element of the present invention. On the premise of controlling the water inlet temperature, the cooling speed of the steel plate is controlled to be 10-15 ℃/s, so that on one hand, the formation of coarse precipitated ferrite is inhibited, a certain phase change driving force is provided through a certain cooling speed, the distribution of the precipitated ferrite at a high temperature stage is more uneven and fine, and meanwhile, the problem of too low yield strength is avoided; in the other invention, the cooling speed cannot be too high, because the amount of the pre-precipitated ferrite formed by phase change before entering water is very small, if the cooling speed is too high, the super-cooled austenite avoids the ferrite phase region to generate medium-low temperature transformation, and thus the ideal two-phase structure type of the large deformation resistant pipeline steel cannot be obtained. Through the control of the cooling path of the steel plate, the steel plate obtains uniform and fine ferrite tissues in a certain proportion under the condition of proper cooling speed, and meanwhile, the final cooling temperature of the steel plate is controlled to be 300 +/-20 ℃, so that the residual untransformed austenite can be converted into a mixed structure of bainitic ferrite and fine MA, and the matrix strength is further improved. The final cooling temperature is too low to be beneficial to the control of the plate shape, and simultaneously, higher requirements are put on the capacity of the hot straightener, and the risk of straightening failure exists; if the temperature is too high, the formed bainitic ferrite lath substructure is coarsened, MA is thick and is distributed in a strip shape, and the stability of the DWTT performance of the pipeline steel is not facilitated.

The scheme of the invention is explained in detail by the following specific examples.

According to the component design and production method, the casting blanks with the sections of 300 × 2000mm and 350 × 2000mm are adopted, the smelting process is subjected to LF + RH treatment, and the actual smelting components of the invention steel and the comparison steel are shown in Table 1:

the rolling is carried out by adopting a double-stand wide and thick plate rolling mill, the rolling specifications are respectively 25.4 mm and 28.6mm, wherein examples 1-4 and comparative example 1 are carried out according to the rolling process of the invention, comparative example 2 is carried out according to the relaxation process, and the specific process and the actual performance of a steel plate are shown in tables 2-4:

as can be seen from a structural electron microscope image, the embodiment 1 of the scheme is of a fine ferrite + bainitic ferrite + MA structure type, and is good in uniformity; comparative example 2 is a typical ferrite + bainite dual phase structure, and the uniformity of the structure is poor.

In conclusion, the 25.4-28.6mm X70M steel plate produced by the method has excellent large deformation resistance and toughness matching. The comparative example 1 adopts a conventional X70M component system, rolling is carried out according to the rolling process of the method, and because uniform precipitation of the pro-precipitation ferrite cannot be controlled, the strength of the rolled steel plate is high, the large deformation resistance cannot meet the requirement, and the low-temperature drop hammer performance is poor; compared with the invention, the steel cost is greatly increased, and the number of steel rolling blocks in hour is at least reduced by 2 according to the relaxation of 45 seconds according to the rhythm of rolling one steel in finish rolling every 3.5min, so that the production efficiency is obviously reduced.

Claims

1. A manufacturing method of an X70M pipeline steel plate with high efficiency, low cost and large deformation resistance comprises a molten iron pretreatment step, a smelting step, a continuous casting step, a rolling step and a water cooling step, and is characterized in that:

the high-efficiency low-cost large-deformation-resistant X70M pipeline steel plate comprises the following components in percentage by mass: c:0.042-0.055%; si:0.16-0.20%; mn:1.30-1.40%; p is less than or equal to 0.015 percent; s is less than or equal to 0.002%; nb:0.028 to 0.035 percent; cr:0.12 to 0.18 percent; ti:0.008-0.020%; ni:0 to 0.30 percent; mo: less than or equal to 0.05 percent; ca is less than or equal to 0.005 percent; and Als:0.015-0.045%; b is less than or equal to 0.0005 percent; the balance of Fe and inevitable impurities; wherein C + Mn/6+ Cr/5 is more than or equal to 0.27% and less than or equal to 0.31%, and C + (Mn + Mo)/3.87 is more than or equal to 0.42%;

the manufacturing method comprises the following steps:

2. The method for manufacturing the X70M pipeline steel plate with high efficiency, low cost and large deformation resistance according to claim 1, is characterized in that: in the rolling step, the thickness of the steel billet is more than or equal to 11t, and the single-pass reduction rate of the last two rough rolling passes is more than or equal to 20 percent; wherein t is the finished product thickness.

3. The method for manufacturing the X70M pipeline steel plate with high efficiency, low cost and large deformation resistance according to claim 1, is characterized in that: and in the second stage of finish rolling, the even pass rolling is adopted, the water cooling is directly carried out after the last pass deformation, the water inlet temperature is more than or equal to T', the cooling speed is controlled to be 10-15 ℃/s, the final cooling temperature is 300 +/-20 ℃, and the steel plate is straightened and then is subjected to off-line stacking or direct cutting.

4. The method for manufacturing the X70M pipeline steel plate with high efficiency, low cost and large deformation resistance according to claim 1, is characterized in that: the thickness of the steel plate is 25.4-28.6mm.