阅读说明：本技术 一种低成本高性能x80级热煨弯管钢及制备方法和应用 (Low-cost high-performance X80-grade hot-bending elbow steel and preparation method and application thereof ) 是由 徐锋 徐进桥 尹云洋 崔雷 李利巍 邹航 魏兵 王立新 于 2021-06-24 设计创作，主要内容包括：本发明特别涉及一种低成本高性能X80级热煨弯管钢及制备方法和应用,属于低合金高强钢制造技术领域,通过对贵重合金元素采用低Mo,去Ni,同时弥补强度韧性损失则创造性的通过添加Cr、Cu、及Mg等元素提高成品弯管强度及低温冲击韧性,有效降低合金成本。(The invention particularly relates to low-cost high-performance X80-grade hot-bending bend steel, a preparation method and application, and belongs to the technical field of low-alloy high-strength steel manufacturing.)

1. The low-cost high-performance X80-grade hot-bent pipe steel is characterized by comprising the following chemical components in parts by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

2. The low-cost high-performance X80 grade hot-bent pipe steel according to claim 1, wherein the chemical composition of the steel comprises in mass fraction: c: 0.065-0.075%, Si 0.20-0.25%, Mn 1.65-1.80%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.025-0.035%, Nb: 0.060-0.070%, V: 0.04-0.05%, Ti: 0.013-0.017%, Cr: 0.25-0.35%, Mo: 0.10-0.13%, Cu 0.35-0.40%, Mg: 0.0012-0.0017%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0012-0.0017 percent, and the balance of Fe and inevitable impurities.

3. The low cost high performance X80 grade hot-bent pipe steel according to claim 1, wherein the metallographic structure of the steel comprises: lath bainite and acicular ferrite, the grain size of the steel being of grade 12-13.

4. A method of making a low cost high performance X80 grade hot-bend steel according to any one of claims 1 to 3, comprising:

heating a casting blank, and then carrying out rough rolling to obtain an intermediate blank;

and (2) finish rolling the intermediate blank, and then carrying out forced cooling to obtain an X80-grade hot-bending bent steel plate, wherein the steel comprises the following chemical components in percentage by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

5. The method for preparing the low-cost high-performance X80-grade hot-bent pipe steel according to claim 4, wherein the heating temperature is 1150-1200 ℃, and the heating time is 200-240 min.

6. The method for preparing the low-cost high-performance X80-grade hot-bent pipe steel according to claim 4, wherein the finish rolling temperature of the rough rolling is 1020-1080 ℃, and the thickness of the intermediate billet is 3-4 times of the thickness of a target finished product.

7. The method for preparing the low-cost high-performance X80-grade hot-bent pipe steel according to claim 4, wherein the cooling rate of the forced cooling is 20-30 ℃/s, and the final cooling temperature of the forced cooling is less than or equal to 350 ℃.

8. Use of the low cost high performance X80 grade hot bend steel of any one of claims 1 to 3, comprising applying the low cost high performance X80 grade hot bend steel to make a hot bend, the step of making a hot bend comprising:

finishing and straightening an X80-grade hot-bending elbow steel plate, and then carrying out JCOE welding to obtain a main pipe;

carrying out induction heating on the mother pipe, and then bending to obtain an initial product;

and cooling the primary product, and then tempering to obtain the hot-bending elbow.

9. The use of a low cost high performance X80 grade hot-bent pipe steel according to claim 8, wherein the JCOE weld has a weld line energy of 15KJ/cm to 30 KJ/cm; the JCOE welding adopts Y-shaped groove welding, and the number of welding passes of the JCOE welding is 8-10;

the heating temperature of the induction heating is 980-1020 ℃; the bending speed of the bending is 15mm/min-25 mm/min;

the cooling is carried out by adopting 10% of ice brine by mass fraction; the tempering temperature is 550-650 ℃, and the tempering heat preservation time is 90-120 min.

10. The use of the low cost high performance X80 grade hot bend steel according to claim 8, wherein the metallographic structure of the parent matrix of the hot bend comprises: bainite, the grain size of the parent metal matrix of the hot-bending bend is 8-9 grades, and the metallographic structure at the welding seam of the hot-bending bend comprises: quasi-polygonal ferrite, pearlite and granular bainite, wherein the grain size of the weld joint of the hot-bending elbow is 10-11 grades; the metallographic structure of the heat affected zone of the hot bend comprises: granular bainite and quasi-polygonal ferrite, wherein the grain size of a heat affected zone of the hot-bending pipe is 10-11 grades.

Technical Field

The invention belongs to the technical field of low-alloy high-strength steel manufacturing, and particularly relates to low-cost high-performance X80-grade hot-bending bend steel, and a preparation method and application thereof.

Background

Along with the promotion of the urbanization process of China, the demand of the market on oil and gas resources is rapidly expanded. The established backbone networks of the west gas transmission of one, two and three lines in east China, the middle and Russian east line, the Shaanjing four line and the like are long-distance transmission trunk lines crossing the cities of a plurality of provinces, and the pipelines need to be turned for a plurality of times in the construction to meet the actual engineering requirements. The hot bending elbow is used as a main steering component, and a main pipe made of a steel plate is bent into a certain angle under the heating of an induction coil to realize the change of the pipeline trend.

The manufacturing process of the hot-bending bend is different from that of a main net pipe, and the original strengthening and toughening shape after hot-mechanical rolling is destroyed after high-temperature heating, so that the cost is higher due to the fact that a large amount of noble alloy elements such as Ni and Mo are added in the manufacturing process of the hot-bending bend to ensure the strengthening and toughening of a finished bent pipe, and carbon equivalent (C) is caused due to the fact that a large amount of alloy elements are added_IIW) High, poor toughness of welding seams and HAZ areas after welding, and threatens the safety of the service of the whole pipeline. Meanwhile, in recent years, in order to further improve the conveying efficiency, high-pressure conveying is a development trend of pipeline conveying, which requires further increase of steel grade, wall thickness and toughness, and the pipeline steel production enterprises which are mainstream at home at presentIt is common to ensure the strength after hot bending by adding higher carbon content and alloy content, but less attention is paid to the toughness. The applicant finds in the course of the invention that: because the hot-bending elbow is produced by a hot-bending manufacturer after raw materials are provided by a steel enterprise and welded into a main pipe by a pipe-making enterprise, the process is long and complex, the matching of the steel plate raw material production and the whole process of welding and hot-bending manufacturing in the current published reports is very little, which is the key point of high cost and poor quality of the final hot-bending elbow finished product.

At present, the Chinese patent application CN 103981460A discloses a hot-rolled flat steel for a high-toughness X80 elbow and a production method thereof, wherein C: 0.060-0.085%, not only are microalloy elements Nb, V and Ti added, but also the composite addition of Cu, Cr, Ni and Mo is required, the content of Ni and Mo is required to be more than or equal to 0.15%, and the carbon equivalent CEIIW is required to be controlled: 0.43-0.50%, and the high cost caused by the simultaneous addition of a large amount of Ni and Mo.

In addition, the chinese patent application CN 102286705 a discloses a production process of a high-strength X80 steel plate for a bent pipe, the scope of Cu, Cr, Ni and Mo in the claims is wide, but in the examples, Mo and Ni reach 0.5%, and meanwhile, the production process of the main pipe and the hot-bending process are not disclosed, the production cost is high according to the components and the process, and the toughness of the hot-bent product is poor, which cannot meet the application requirements.

The Chinese patent application CN 102268612A discloses an X80 steel low temperature resistant elbow and a manufacturing process thereof, wherein the contents of alloy elements Cr, Ni and Mo in a component system are high, particularly the content of Ni is as high as 1.0%, the hot bending process is provided, but the production of a hot rolled steel plate is not controlled, so that the performance is good, but the alloy cost is high.

Disclosure of Invention

The application aims to provide low-cost high-performance X80-grade hot-bending bend steel, a preparation method and application, so that the problem of high cost in manufacturing high-steel-grade hot-bending bend alloy is solved, and meanwhile, a weld joint and HAZ of a finished bend have excellent low-temperature impact toughness.

The embodiment of the invention provides low-cost high-performance X80-grade hot-bending elbow steel, which comprises the following chemical components in parts by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

Optionally, the chemical composition of the steel comprises, in mass fraction: c: 0.065-0.075%, Si 0.20-0.25%, Mn 1.65-1.80%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.025-0.035%, Nb: 0.060-0.070%, V: 0.04-0.05%, Ti: 0.013-0.017%, Cr: 0.25-0.35%, Mo: 0.10-0.13%, Cu 0.35-0.40%, Mg: 0.0012-0.0017%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0012-0.0017 percent, and the balance of Fe and inevitable impurities.

Optionally, the metallographic structure of the steel comprises: lath bainite and acicular ferrite, the grain size of the steel being of grade 12-13.

Based on the same inventive concept, the embodiment of the invention also provides a preparation method of the low-cost high-performance X80-grade hot-bending elbow steel, which comprises the following steps:

heating a casting blank, and then carrying out rough rolling to obtain an intermediate blank;

and (2) finish rolling the intermediate blank, and then carrying out forced cooling to obtain an X80-grade hot-bending bent steel plate, wherein the steel comprises the following chemical components in percentage by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

Optionally, the heating temperature is 1150-1200 ℃, and the heating time is 200-240 min.

Optionally, the finish rolling temperature of the rough rolling is 1020-1080 ℃, and the thickness of the intermediate billet is 3-4 times of the thickness of the target finished product.

Optionally, the cooling speed of the forced cooling is 20 ℃/s-30 ℃/s, and the final cooling temperature of the forced cooling is less than or equal to 350 ℃.

Based on the same inventive concept, the embodiment of the present invention further provides an application of the low-cost high-performance X80-grade hot-bent pipe steel, wherein the application includes applying the low-cost high-performance X80-grade hot-bent pipe steel to a hot-bent pipe preparation, and the hot-bent pipe preparation includes:

finishing and straightening an X80-grade hot-bending elbow steel plate, and then carrying out JCOE welding to obtain a main pipe;

carrying out induction heating on the mother pipe, and then bending to obtain an initial product;

and cooling the primary product, and then tempering to obtain the hot-bending elbow.

Optionally, the energy of the welding line for the JCOE welding is 15KJ/cm-30 KJ/cm; the JCOE welding adopts Y-shaped groove welding, and the number of welding passes of the JCOE welding is 8-10;

the heating temperature of the induction heating is 980-1020 ℃; the bending speed of the bending is 15mm/min-25 mm/min;

the cooling is carried out by adopting 10% of ice brine by mass fraction; the tempering temperature is 550-650 ℃, and the tempering heat preservation time is 90-120 min.

Optionally, the metallographic structure of the base metal matrix of the hot-bending bend includes: bainite, the grain size of the parent metal matrix of the hot-bending bend is 8-9 grades, and the metallographic structure at the welding seam of the hot-bending bend comprises: quasi-polygonal ferrite, pearlite and granular bainite, wherein the grain size of the weld joint of the hot-bending elbow is 10-11 grades; the metallographic structure of the heat affected zone of the hot bend comprises: granular bainite and quasi-polygonal ferrite, wherein the grain size of a heat affected zone of the hot-bending pipe is 10-11 grades.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

the low-cost high-performance X80-grade hot-bending elbow steel provided by the embodiment of the invention comprises the following chemical components in parts by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities; the alloy has the beneficial effects that the precious alloy elements are low in Mo and free of Ni, the loss of strength and toughness is compensated, the strength and the low-temperature impact toughness of the finished bent pipe are creatively improved by adding elements such as Cr, Cu and Mg, and the alloy cost is effectively reduced.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a flow chart of a method of an embodiment of the present invention;

FIG. 2 is a metallographic structure diagram of a base material of a pipe provided by an embodiment of the invention;

FIG. 3 is a metallographic structure of a weld provided by an embodiment of the invention;

FIG. 4 is a metallographic structure diagram of a Heat Affected Zone (HAZ) provided by an embodiment of the invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the general idea of the embodiment of the application is as follows:

according to an exemplary embodiment of the invention, a low-cost high-performance X80 grade hot-bend steel is provided, the steel comprises the following chemical components in percentage by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

C: 0.055-0.080%, carbon is the most economically important strengthening element in steel, the strength of the steel can be greatly improved, for a hot-bending bend, the structure phase change strengthening and precipitation strengthening are weakened due to the need of a high-temperature bending process, so the solid solution strengthening is more important, the carbon content of the hot-bending bend needs to be correspondingly improved by a little compared with that of an X80 grade backbone network pipeline in a controlled rolling and controlled cooling state, but the low-temperature toughness is seriously deteriorated by too high carbon, so the carbon content range is required to be 0.055-0.080%, the strength is insufficient when the carbon content is too low, and the toughness is insufficient when the carbon content is too high.

Si:0.15 to 0.30%, the element has solid solution strengthening and deoxidizing effects, and the content of the element is less than 0.15% and cannot play a strengthening effect, but if the content is more than 0.30%, the plasticity and toughness of the pipeline steel are deteriorated, and particularly the impact on a welding heat affected zone is remarkably reduced.

Mn: 1.60-1.85%, and a higher economic alloying element manganese is added, so that the strength loss caused by alloy reduction can be compensated, and meanwhile, the manganese can refine grains to a certain extent, so that the impact toughness of steel is improved, but excessive manganese easily forms central segregation, so that the components and the structure of the steel are uneven, and the low-temperature drop hammer toughness is deteriorated.

P: less than or equal to 0.012 percent, S: less than or equal to 0.0020%: p, S is the most harmful element in steel, P is easy to be deviated in the center of casting blank, which causes the plasticity and impact toughness to be reduced obviously, especially at low temperature, it makes the steel become brittle obviously. S is easy to combine with Mn to form MnS to reduce the low-temperature toughness of the steel, so the P, S content is strictly controlled in the scheme.

And (3) Alt: 0.015-0.045%, wherein aluminum is a main deoxidizing element in the steel, so that the oxygen content in the steel can be remarkably reduced, and meanwhile, AlN is formed by the combination of the aluminum and nitrogen, so that grains can be effectively refined. However, when the content of aluminum in the steel exceeds a certain amount, the oxide inclusion of aluminum is easily increased obviously, the cleanliness of the steel is reduced, and the low-temperature toughness of the steel is unfavorable.

0.050-0.080% of Nb, wherein the Nb can remarkably improve the austenite recrystallization temperature of the steel, enlarge the range of a non-recrystallization region, facilitate the realization of high-temperature controlled rolling and reduce the load of a rolling mill, can inhibit the growth of austenite grains, has remarkable double effects of fine grain strengthening and precipitation strengthening, and can compensate the strength reduction caused by the reduction of carbon, remarkably refine the grains and improve the low-temperature toughness. If the content is less than 0.05%, the effect is insufficient, and if it is more than 0.080%, the cost is high.

0.010-0.020% of Ti, similar functions of titanium and niobium in steel, stronger fine grain strengthening and precipitation strengthening functions, and trace titanium can be combined with carbon and oxygen at high temperature to form precipitates which are refractory at high temperature, so that austenite grains in a welding heat affected zone can be inhibited from growing greatly, and the toughness of the welding heat affected zone is obviously improved. Excessive Ti can be combined with N to form large-particle TiN particles, and the low-temperature toughness of the steel is obviously reduced. Therefore, the Ti content in the scheme is designed to be 0.010-0.020% of micro-titanium treatment.

Cr: 0.20-0.40%, strong solid solution strengthening effect of chromium and improvement of hardenability, and Cr is a strong medium-temperature transformation structure forming element, is low in price, can effectively replace precious alloy elements such as Mo and Ni, and reduces production cost. In order to compensate for the reduction of Mo and Ni elements, the content of Cr is 0.2-0.4%, the effect is not obvious when the content is less than 0.2%, and the impact toughness is damaged when the content is more than 0.4%.

0.08-0.15% of Mo, and the element strongly promotes medium-temperature structure transformation and effectively generates phase transformation strengthening. Meanwhile, Mo has the effects of improving hardenability and homogenizing wall thickness structure for thick plates. The content of Mo designed in the invention is 0.08-0.15%. Below 0.08% this does not work and above 0.15% the alloy is expensive.

Cu: 0.25-0.50%, one of Cu strengthening elements has two functions of solid solution strengthening and precipitation strengthening, but the cost is much lower than that of Mo and Ni, the solid solubility of Cu in alpha-Fe is lower than that of Ni, and epsilon-Cu dispersed precipitates can be formed for matrix strengthening when the Cu content is higher.

Mg: 0.0010-0.0020%, Ca: the forming elements of strong oxygen and sulfide with the content less than or equal to 0.006 percent can be combined with oxygen and sulfur of steel grades to form dispersed Mg, Ca (O, S) and Mg-Ti composite inclusions to form acicular ferrite core particles, the crystal grains are refined, and excessive inclusions such as large-grain MgO/Ca2O3 and the like are formed to destroy the continuity of a matrix.

N is less than or equal to 0.006 percent, nitrogen is one of the main elements of the micro-alloy element precipitates, and the strength of the steel is obviously improved. However, since large-sized TiN is easily formed due to a high nitrogen content, the plasticity of the steel matrix is particularly poor, and therefore, N must be controlled to 60ppm or less in this embodiment.

O: 0.0010-0.0020%, steel inclusions form main elements, and excessive steel inclusions deteriorate the steel quality, 10-20 PPM is beneficial to production control, and meanwhile, oxides of Mg, Ca, Ti and the like are formed by combining an oxide metallurgy technology, grains are refined, and welding toughness is improved.

As an alternative embodiment, the chemical composition of the steel comprises, in mass fractions: c: 0.065-0.075%, Si 0.20-0.25%, Mn 1.65-1.80%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.025-0.035%, Nb: 0.060-0.070%, V: 0.04-0.05%, Ti: 0.013-0.017%, Cr: 0.25-0.35%, Mo: 0.10-0.13%, Cu 0.35-0.40%, Mg: 0.0012-0.0017%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0012-0.0017 percent, and the balance of Fe and inevitable impurities.

As an alternative embodiment, the metallographic structure of the steel comprises: lath bainite and acicular ferrite, the grain size of the steel being of grade 12-13.

According to another exemplary embodiment of the present invention, there is provided a method for preparing a low-cost high-performance X80-grade hot-bent pipe steel as described above, the method including:

s1, heating a casting blank, and then carrying out rough rolling to obtain an intermediate blank;

specifically, after smelting and casting into a continuous casting billet, the continuous casting billet is heated in a heating furnace to 1150-1200 ℃, the furnace time is 200-240 min, then rough rolling is carried out, a wide and thick plate rolling mill is adopted for rolling, the rough rolling finishing temperature is controlled to be 1020-1080 ℃, and the thickness of an intermediate billet is 3-4 times that of a finished product.

S2, finish rolling the intermediate blank, and then carrying out strong cooling to obtain an X80-grade hot-bending bent pipe steel plate, wherein the steel comprises the following chemical components in parts by mass: c: 0.055-0.085%, Si 0.15-0.30%, Mn 1.60-1.85%, P: less than or equal to 0.012%, S: less than or equal to 0.0020 percent and Alt: 0.015 to 0.045%, Nb: 0.050-0.080%, V: 0.03 to 0.06%, Ti: 0.010-0.020%, Cr: 0.20-0.40%, Mo: 0.08-0.15%, Cu 0.25-0.50%, Mg: 0.0010-0.0020%, N: less than or equal to 0.006 percent, Ca: less than or equal to 0.006 percent, O: 0.0010-0.0020 percent, and the balance of Fe and inevitable impurities.

Specifically, fine rolling is carried out, wherein the start rolling temperature of the fine rolling is 900-950 ℃, the finish rolling temperature is 800-850 ℃, and the thickness of a fine rolling outlet is 25-35 mm; after finishing the finish rolling, immediately carrying out strong cooling by adopting an online strong cooling system, wherein the cooling speed is controlled to be 20-30 ℃/s, and the final cooling temperature is less than or equal to 350 ℃; and (3) after finishing and straightening the steel plate, performing JCOE welding in a pipe manufacturing factory to form a mother pipe, wherein the welding line energy is 15-30 KJ/cm, a Y-shaped groove is adopted, and the welding passes are 8-10 times.

By adopting the design, two-stage rolling is carried out, and uniform and fine flattened austenite structures before phase transformation are obtained through rough and finish rolling temperature control; after rolling, strong cooling (cooling speed of 20-30 ℃/s) and low-temperature final cooling (less than or equal to 350 ℃) are adopted, medium-temperature transformation bainite and acicular ferrite tissues are obtained, and excellent toughness of the steel plate is obtained.

According to another exemplary embodiment of the present invention, there is provided a use of the low-cost high-performance X80 grade hot-bend steel as described above, the use comprising applying the low-cost high-performance X80 grade hot-bend steel to a hot-bend manufacturing process, the hot-bend manufacturing process comprising:

s1, finishing and straightening an X80-grade hot-bending bent steel plate, and then carrying out JCOE welding to obtain a main pipe;

specifically, a steel plate is subjected to finishing straightening and then is subjected to JCOE welding in a pipe manufacturing factory to form a mother pipe, the welding line energy is 15-30 KJ/cm, a Y-shaped groove is adopted, and the welding passes are 8-10 times.

The JCOE is adopted to weld a mother pipe, the welding line energy is 15-30 KJ/cm, a Y-shaped groove is adopted, the welding passes are 8-10 times, the process promotes the structure refinement of a welding line and a Heat Affected Zone (HAZ), and the low-temperature impact toughness is guaranteed.

S2, carrying out induction heating on the main pipe, and then bending to obtain an initial product;

specifically, the main pipe is subjected to medium-frequency (namely 1-10KHz) induction heating, the heating temperature is 980-1020 ℃, and the bending speed is 15-25 mm/min.

The intermediate frequency induction coil is adopted to carry out heat treatment on the main pipe, the heating temperature is 980-1020 ℃, the bending speed is 15-25 mm/min, and the guarantee is provided for obtaining the austenite structure with uniform wall thickness and keeping the austenite structure in a fine state

And S3, cooling the primary product, and then tempering to obtain the hot-bending bend.

Specifically, the main pipe is immediately cooled to room temperature by using 10% brine ice after being discharged from the induction coil, and then the cooled bent pipe is integrally tempered at the tempering temperature of 550-650 ℃ for 90-120 min.

After induction heating, quenching is carried out immediately by using 10% ice brine, so that the cooling speed after heating is improved, and the full-wall thickness structure transformation under the condition of low Mo is ensured. And the whole tube tempering at 550-650 ℃ is adopted, so that the residual stress after quenching is reduced, the strength and the toughness of the tube body are improved, and the low-temperature impact toughness of a welding line and a heat affected zone is improved.

The metallographic structure of different parts of the steel pipe is as follows: the matrix of the base material is a Granular Bainite (GB) structure, and the grain size is 8-9 grade; the weld joint is quasi-Polygonal Ferrite (PF), pearlite (P) and a small amount of Granular Bainite (GB), and the grain size is about 10-11 grades; the heat affected zone structure consists of Granular Bainite (GB) and a small amount of quasi-Polygonal Ferrite (PF), and the grain size is about 10-11 grades

The low-cost high-performance X80 grade hot-bent pipe steel and the preparation method and application thereof are described in detail in the following by combining the examples, the comparative examples and the experimental data.

Examples and comparative examples

The main component values of the low-cost high-performance X80-grade hot-bending bend steel in each embodiment and comparative example are shown in the following table:

in the table, "/" indicates that the component is not added or the amount of the component is not limited in the comparative example. The preparation method comprises the following steps:

s1, heating a casting blank, and then carrying out rough rolling to obtain an intermediate blank;

and S3, performing finish rolling on the intermediate blank, and then performing strong cooling to obtain an X80-grade hot-bending bent pipe steel plate.

The production process parameters of the hot rolled steel sheets of the respective examples and comparative examples are shown in the following table:

it should be noted that "/" in the table indicates that the comparative example does not limit the process data.

The steel plate for the X80-grade hot-bending elbow is prepared into the X80-grade hot-bending elbow, and the preparation steps are as follows:

s1, finishing and straightening an X80-grade hot-bending bent steel plate, and then carrying out JCOE welding to obtain a main pipe;

s2, carrying out induction heating on the main pipe, and then bending to obtain an initial product;

and S3, cooling the primary product, and then tempering to obtain the hot-bending bend.

The parameters of the welding and hot bending process of the main pipe of each example and each comparative example are as follows:

it should be noted that "/" in the table indicates that the comparative example does not limit the process data.

Examples of the experiments

The hot bends obtained in examples 1 to 10 and comparative examples 1 to 2 were subjected to the performance test, and the test results are shown in the following table.

In the table, "/" indicates that no data was measured.

From the above table, the chemical components and the technical process in the invention are adopted to realize the production of the low-cost high-performance X80-grade hot-bending pipe, and the performances are excellent.

Detailed description of the drawings 2-4:

as shown in fig. 2, a metallographic structure diagram of a tube base material according to an embodiment of the present invention is obtained, and the metallographic structure diagram has a structure type of Granular Bainite (GB) and a grain size of 8 to 9 grades;

as shown in fig. 3, which is a metallographic structure diagram of a weld of a hot-bending bend according to an embodiment of the present invention, the metallographic structure diagram can be obtained from the diagram, wherein the structure type is quasi-Polygonal Ferrite (PF) + pearlite (P) + a small amount of Granular Bainite (GB), and the grain size is 10-11 grade;

as shown in FIG. 4, the metallographic structure of the Heat Affected Zone (HAZ) provided in the examples of the present invention is shown by the Granular Bainite (GB) + a small amount of quasi-Polygonal Ferrite (PF), and the grain size is 10 to 11 grades.

One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:

(1) the X80-grade hot-bending pipe steel provided by the embodiment of the invention adopts low Mo for precious alloy elements, removes Ni, compensates for the loss of strength and toughness, creatively improves the strength and low-temperature impact toughness of the finished bent pipe by adding Cr, Cu, Mg and other elements, and effectively reduces the alloy cost;

(2) the mechanical properties of the hot-bending elbow prepared by the steel provided by the embodiment of the invention reach: r_t0.5≥580MPa；R_m≥650MPa；YR≤0.92；A₅₀Not less than 21 percent; HV10 is less than or equal to 250; -20 ℃, tube body: KV₂More than or equal to 280J, welding seam: KV₂Not less than 120J; HAZ (heat affected zone): KV₂The mass is more than or equal to 230J. The product performance completely meets the requirements of technical conditions;

(3) the method provided by the embodiment of the invention carries out process innovation by integrating the rolling process, the main pipe making process and the hot bending process, and the cooperative matching relationship among the processes is as follows: obtaining a bainite and acicular ferrite steel plate with the grain size of 12-13 grades through component design and thermomechanical rolling; rolling a steel plate into a steel pipe by adopting JCOE (joint welding initiation) and then welding the steel pipe into a mother pipe, refining grains in a welding line and a heat affected zone by controlling the shape of a welding groove, the welding pass number and the like, and simultaneously adding oxides with stable high temperature in the welding process of Ti and Mg in the component design of a mother material to inhibit the coarsening of the grains in the heat affected zone so as to obtain the mother pipe with excellent impact toughness; finally, cooling by reasonable induction heating temperature and cooling process to obtain fine granular bainite structures, and finally carrying out whole-tube heat treatment to ensure that grain boundary carbides are redissolved and epsilon-Cu precipitation is strengthened to obtain a high-strength and high-toughness matched finished product X80-grade hot-bending bend; the method not only solves the problem of high cost of manufacturing high-grade steel hot-bending elbow alloy, but also ensures that the finished elbow welding seam and HAZ have excellent low-temperature impact toughness.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.