CN1502425A - A kind of manufacturing method of high-performance seamless steel pipe - Google Patents

Abstract

The invention relates to a rolling process of a seamless steel pipe and the rolled steel type thereof, in particular to a manufacturing method of a high-performance seamless steel pipe used as a high-performance oil well pipe. It solves the defect that the existing seamless steel pipe rolling process requires cumbersome technology for quenching and tempering treatment after the pipe is rolled. The technical solution is: a manufacturing method of high-performance seamless steel pipe, including steel grade design and rolling process. The rolling process is to heat and perforate the tube billet at 1250-1300°C, continuous rolling at 950-1050°C, and then remove the rod. Heating to 950-980°C for austenitization treatment, tension reducing machine or stretching machine to roll the tube at 920-950°C, the feature is: after the tube is rolled, it is rapidly cooled to 400-600°C, and then air-cooled. The weight ratio of the constituent elements of rolled non-quenched and tempered steel is: C: 0.22-0.4%, Si: 0.1-0.5%, Mn: 1.0-2.0%, V: 0.05-0.25%, Al: 0.005-0.050%, N: 0.015 to 0.030%, the rest is iron and unavoidable impurities. It is mainly used for rolling high-performance seamless steel pipes such as N80 oil well pipes.

Description

A kind of manufacturing method of high-performance seamless steel pipe

Technical field: The present invention relates to a rolling process of a seamless steel pipe and the rolled steel grade thereof, in particular to a manufacturing method of a high-performance seamless steel pipe used as a high-performance oil well pipe.

Background technology: The main process of traditional production of high-performance oil well pipes is: heating and piercing of the tube blank at 1250-1300°C, continuous rolling at 950-1050°C, austenitizing treatment at 950-980°C after stripping, and tension reduction. Roll the pipe at 920～950℃ in the diameter mill, air cool to room temperature, and then quench and temper heat treatment. Due to the high continuous rolling temperature and coarse grains, the steel pipe enters the reheating furnace immediately after stripping, and the temperature of the steel pipe is still higher than the Acl point before entering the furnace, so that the coarse austenite grains after continuous rolling are retained until before tension reduction rolling. Due to the high temperature of the rolling tube in the stretching and reducing machine, in the austenite recrystallization zone, the grains are still coarse under the condition of air cooling after rolling. This microstructure is mainly adjusted by quenching and tempering heat treatment after rolling of quenched and tempered steel, and the required microstructure and properties can be obtained through quenching and tempering after rolling.

Due to the high cost of quenching and tempering heat treatment, in order to reduce production costs and improve competitiveness, steel pipe re-line normalization technology has emerged. Its essence is to reduce the temperature of the steel pipe after continuous rolling to below Acl, through the transformation of austenite to ferrite, so that the steel pipe undergoes a phase transformation before entering the reheating furnace, and the austenite is reheated in the reheating furnace After refining, the austenite grains are refined by recrystallization. In this way, the grains of the air-cooled steel pipe after stretching and reduction will be more refined than before, generally from 6-7 grades to 9-10 grades, and the toughness will also be improved.

Although this process can improve the toughness of the steel pipe, because the steel pipe is air-cooled after the tension is reduced, the cooling speed is relatively slow, and the strength is not greatly improved. In order to improve the strength, on the basis of online normalization, an online accelerated cooling process that increases the cooling rate after tension reduction has appeared.

Using this process, although the strength and toughness of the material can be improved, there are still two problems. First, due to the limitation of the original process layout, it is difficult to quickly cool the steel pipe after stripping to below the Acl temperature under the original production rhythm; second, the accelerated cooling speed of the steel pipe after final rolling is not fast enough, and only iron The body-based organization cannot produce oil well pipes of N80 and above grades. In addition to the traditional tube rolling process, 3 patents related to the present invention are also found through online search for accelerated cooling of steel tubes after rolling. They are U.S. Patent US5186769, British Patent GB2101014A, and British Patent GB2137539A. All three patents require that the steel pipe after continuous rolling and stripping be cooled to below the Acl temperature, and after a recrystallization from austenite to ferrite, it is re-entered. Furnace re-austenitization. There are also deficiencies in the recrystallization treatment mentioned above.

Summary of the invention: The technical problem to be solved in the present invention is to ensure that mixed crystals and coarse grains do not appear during high-temperature rolling, so that the steel pipe after stripping does not need to be cooled below the Acl temperature for recrystallization treatment, but can be directly reheated furnace, and can omit the quenching and tempering process after rolling, and directly obtain high-performance seamless steel pipes. In order to solve the above-mentioned technical problems, the following technical solutions are adopted: a high-performance seamless steel pipe manufacturing method, first of all, designing a non-quenched and tempered steel grade that does not appear mixed crystals and coarse grains during high-temperature rolling; In terms of pipe rolling process, the conventional tube billet is heated in an annular heating furnace at 1250-1300°C, pierced by a piercer, and rolled at 950-1050°C. After stripping, the steel pipe directly enters the reheating furnace above the Acl temperature. After heat preservation at 980°C, enter the tension reducing machine or stretching machine and roll it into a finished pipe at 920-950°C, add a rapid cooling process after rolling, and add water or water within 10 seconds after the steel pipe comes out of the stretching and reducing machine or stretching machine. The gas is rapidly cooled to 400-600°C at a cooling rate of 20-200°C/S, and then air-cooled.

Invented non-quenched and tempered steel, its constituent elements include: Fe, C, Si, Mn, V, Al, N, characterized in that: the weight ratio of each constituent element is (wt%):

C: 0.22 to 0.4%

Si: 0.1-0.5%

Mn: 1.0-2.0%

V: 0.05～0.25%

Al: 0.005～0.050%

N: 0.015～0.030%

The rest is iron and unavoidable impurities

Or add on top of the ingredients above:

One or two or three of Mo: 0.10-0.40%, Nb: 0.01-0.05%, Ti: 0.005-0.05%, after the tube is rolled according to the above-mentioned requirements, no heat treatment is required, and it is directly made to meet the requirements. API 5CT standard N80 oil casing is used.

The beneficial effects of the present invention are: adopting the steel type of the present invention, the rolling tube condition of about 1000°C is in a state of complete dynamic recrystallization, thereby ensuring that no mixed crystal phenomenon occurs; the elements such as C, V, Ti, N contained in the material , can ensure that a large amount of vanadium and titanium carbonitrides are precipitated under high temperature rolling conditions, which can pin the grain boundaries and refine the grains. Therefore, after the continuous rolling of the steel pipe, it is not necessary to cool to below the Acl temperature for a recrystallization transformation, thereby saving the recrystallization treatment after the stripping, but can enter the reheating furnace above the Acl temperature. It is beneficial to realize the process on the original production line.

With the steel grade of the present invention, under the final rolling condition of about 850°C, within 10 seconds after rolling, dynamic and static recrystallization will not occur, and only rolling deformation of crystal grains will occur. At this time, the steel pipe is rapidly cooled to a temperature range of 400-600°C, and a fine bainite structure can be formed to produce high-performance oil casing.

The following describes the role of each alloying element:

C: 0.22 to 0.4 (wt%, the following elements are the same), C is a carbide forming element that can increase the strength of steel, if it is too low, the effect is not obvious, and if it is too high, the toughness of steel will be greatly reduced.

Mn: 1.0～2.0, Mn is an austenite forming element, which can improve the hardenability of steel. When the content is less than 1.0, the effect is not obvious. When the content is greater than 2.0, the amount of retained austenite in the steel will be greatly increased, which will affect the hot-rolled structure. uniformity.

N: 0.015～0.030, N is a carbide forming element, which can improve the strength of steel, especially when the cooling rate is accelerated, the effect is more obvious. When the N content is too low, the effect is not obvious, and when the N content is too high, large nitride inclusions will be formed and the performance of the steel will be reduced. The combination of N and C can increase the strength while effectively reducing the carbon equivalent.

V: 0.05-0.25, can refine grains, form carbides, and improve the strength and toughness of steel. But when the content reaches a certain amount, the increase in its effect will not be obvious. At the same time, because the price is high, the usage amount should be limited.

Ti: 0.005-0.05, can refine grains, form carbides, and improve the strength and toughness of steel. But when the content reaches a certain amount, the increase in its effect will not be obvious. At the same time, because the price is high, the usage amount should be limited.

Mo: 0.1～0.4: It is mainly to increase the strength of steel through carbide and solid solution strengthening. If the content is too high, the toughness of steel will be reduced.

The difference and improvement from the existing technology: At present, the pipe rolling process commonly used by continuous pipe rolling mills in various countries in the world is: heating and piercing the tube billet at 1250-1300 °C, continuous rolling at 950-1050 °C, and reheating the steel pipe to 950 °C after the mandrel is removed. ～980℃ austenitization treatment, the steel pipe coming out of the reheating furnace is rolled at 920～950℃ through a tension reducer, and air-cooled to room temperature after rolling.

Compared with the above-mentioned process, the present invention is different in that after the steel pipe is finished rolling, it is rapidly cooled to 400-600° C. at a speed of 20-200° C./S, and then air-cooled to room temperature. Adopting the tube rolling process of accelerated cooling after rolling, high-performance oil well pipes can be produced in hot-rolled state by using non-quenched and tempered steel without quenching and tempering heat treatment, which can greatly reduce production costs.

In addition to the traditional tube rolling process, 3 patents related to the present invention are also found through online search for accelerated cooling of steel tubes after rolling. The pipe rolling process proposed by these 3 patents is compared with the present invention, as shown in Table 1.

Table 1 Comparison of tube rolling process heating furnace punching machine Continuous rolling mill recrystallization reheat Tension reduction machine cooling after rolling United States: 5186769 1200℃～1300℃ ~1200℃ ~1000℃ lower than Acl 900℃～950℃ 700℃～800℃ Cool to 600°C at 3~5°C/S United Kingdom: 2101014A 1200℃～1300℃ ~1200℃ ~1000℃ lower than Acl 850℃～980℃ 850℃～900℃ Rapid cooling to 100°C below Acl United Kingdom: 2137539A 1150℃～1220℃ ~1100℃ ~1000℃ lower than Acl 700℃～850℃ 700℃～800℃ Cool to 450～600℃ at ≥6℃/S this invention 1220℃～1320℃ ~1200℃ ~1000℃ no recrystallization 950℃～980℃ 850℃～900℃ Cool at 20～200℃/S to 400～650℃

The three patents all require that the steel pipe after continuous rolling and stripping be cooled to below the Acl temperature, and after a recrystallization from austenite to ferrite, it is then re-austenitized in a reheating furnace. The present invention is different from its process route. It does not need to be cooled below the Acl temperature after continuous rolling and can be recrystallized and refined, and can directly enter the reheating furnace, which simplifies the tube rolling process.

At the same time, in terms of accelerated cooling after hot rolling, it is required to cool at a high speed immediately after rolling. Due to the fast cooling speed and short cooling time, it is beneficial to the arrangement of accelerated cooling devices. For example, the steel pipe advances at a speed of 2M/S and is cooled from 850°C to 550°C. If the cooling rate is 100°C/S, it only takes 3 seconds to cool to 300°C. For a 6M long cooling device, if the cooling rate is 10°C/S , then it takes 30 seconds to cool down to 300°C, and a 60M long device is set up.

Quenched and tempered steel is generally used in the production of N80 oil well pipes in the world at present. Since the quenched and tempered steel is obtained by quenching and tempering to obtain the required structure and properties, the content of N in the steel is controlled to be low; while the non-quenched and tempered steel of the present invention is mainly The performance is improved through carbide precipitation strengthening, so the higher N is used to combine with carbide precipitation elements V, Ti, and Nb to improve the strength of the material.

In addition to quenched and tempered steels, the non-quenched and tempered steels used in the early production of N80 oil well pipes, such as 42MnMo7, 42MnCr52, etc., are also essentially different from the steels of the present invention. The above steel types are only suitable for the production of N80 oil well pipes under the condition of air cooling after rolling. Due to the slow cooling rate of air cooling after rolling, only the structure of ferrite and pearlite can be obtained, and the strength must be increased by increasing the C content. With the increase of C content, the toughness is greatly reduced, which can no longer meet people's requirements for high-performance oil well pipes. The steel grade of the invention reduces the C content, which is beneficial to improving the toughness of the material, and at the same time increases the strength by increasing the N content and adding more carbide forming elements, combined with accelerated cooling.

In recent years, some people in the world have begun to study the accelerated cooling process of steel pipes after rolling, and correspondingly published some articles and patents on steel types in conjunction with the research on the process.

Among them, U.S. Patent: US5019180 and British Patent: GB2137539A propose low-C microalloyed steels that do not contain N, and the C content is below 0.18%. They are strengthened by precipitation of V, Ti, and Nb, and are obtained under accelerated cooling conditions. The fine ferrite structure is mainly used to produce X series line pipes. However, the steel grade of the present invention mainly adds N, which can improve the strength more effectively.

An invention closer to the present invention is a 1993 US patent: US5186769. Its main components are C 0.10-0.18%, Mn 0.1-2.0%, V 0.1-0.16%, Ti 0.008-0.012%, N0.015-0.022%. The design concept of this steel type is similar to that of the present invention, both of which use carbonitride precipitation of V and Ti as the main means of material strengthening. However, this steel type is suitable for finishing rolling at a relatively low temperature of 700-800°C, resulting in large strain deformation, and high strength can be obtained at a low C content. The present invention is suitable for finishing rolling at a temperature above 850°C, and the rolling mill with small deformation of the finishing rolling group. At this time, due to insufficient deformation, the content of alloys such as C and Mo must be increased to ensure higher strength.

Specific embodiments: 5 experimental steel grades are listed below, and their chemical compositions are shown in Table 2. They use two different processes to roll the tube: one is to roll the tube according to the original conventional process, the tube blank is heated at 1250-1300°C for piercing, 950-1050°C for continuous rolling, and then heated to 950-980°C for austenite Chemical treatment, tension reducing machine at 920 ~ 950 ℃ rolling tube, air cooling after rolling; another rolling process of the present invention is adopted, the tube billet is heated in an annular heating furnace at 1250-1300 ℃, pierced by a piercing machine, and rolled at 950 ~ The tube is rolled at 1050°C. After stripping, it directly enters the reheating furnace above the Acl temperature. After heat preservation at 950-980°C, it enters the tension reducing machine or stretching machine and rolls it into a finished tube at 920-950°C. After the steel pipe comes out of the stretching and reducing machine or the stretching machine, within 10 seconds, water or water is added with gas at a cooling rate of 20-200 °C/S, rapidly cooled to 400-600 °C, and then air-cooled. The results of the mechanical properties of the two processes are shown in Table 3. It can be seen from Table 3 that with the steel grade and process of the present invention, such as B2, B3, B4, and B5 components, the yield strength of the rolled steel pipe is greater than 600Mpa, which can meet the performance requirements of N80 oil casing.

Table 2 Chemical composition of test steel serial number C Si mn V Ti N Al Mo Nb B1 0.14 0.26 1.73 0.14 0.012 0.016 0.017 0.29 / B2 0.20 0.27 1.47 0.16 0.013 0.017 0.023 0.14 / B3 0.26 0.25 1.47 0.060 0.010 0.014 0.016 / / B4 0.26 0.29 1.49 0.059 0.010 0.018 0.018 0.14 / B5 0.25 0.31 1.42 0.064 0.009 0.016 0.019 / 0.026 B6 0.25 0.35 1.42 0.062 0.010 0.0083 0.018 0.15 0.030

Table 3 Mechanical properties serial number original craft this invention σ0.5 σb σ0.5 σb B1 485 734 548 755 B2 539 705 600 739 B3 483 655 653 749 B4 511 657 615 747 B5 462 621 623 745 B6 487 648 573 764

Claims (5)

1, a kind of manufacture method of performance seamless steel pipe, comprise steel grade design and rolling mill practice, its rolling mill practice is that 1250～1300 ℃ of pipes add hot piercing, 950～1050 ℃ of tandem rollings, take off and enter reheating furnace behind the rod and be heated to 950～980 ℃ of austenitizing processing, stretch-reducing mill or elongators again in 920～950 ℃ of tube rollings, it is characterized in that: be cooled fast to 400～600 ℃ after tube rolling is finished, then air cooling.

2, the manufacture method of a kind of performance seamless steel pipe according to claim 1 is characterized in that; Take off rod back steel pipe and more than the Acl temperature, directly enter reheating furnace.

3, the manufacture method of a kind of performance seamless steel pipe according to claim 1, it is characterized in that: steel pipe after stretch-reducing mill or elongator come out within 10 seconds water or water aerating with the cooling velocity of 20～200 ℃/S, be cooled fast between 400～600 ℃, then air cooling.

4, a kind of non-hardened and tempered steel kind that is used for the performance seamless manufacture of steel pipe, its component comprises: Fe, C, Si, Mn, V, Al, N is characterized in that: each component weight proportion is (wt%):

C：0.22～0.4％

Si：0.1～0.5％

Mn：1.0～2.0％

V：0.05～0.25％

Al：0.005～0.050％

N：0.015～0.030％

All the other are iron and unavoidable impurities.

5, non-hardened and tempered steel kind according to claim 4 is characterized in that: can also add elements Mo in the component: 0.10～0.40%, one or both in Nb:0.01～0.05%, Ti:0.005～0.05% or three kinds.