CN113549817A

CN113549817A - 770 MPa-level low-alloy high-strength high-toughness seamless steel pipe and manufacturing method thereof

Info

Publication number: CN113549817A
Application number: CN202110722491.0A
Authority: CN
Inventors: 吴红; 王善宝; 廖德勇; 袁琴; 赵波; 解德刚; 洪汛; 张尧; 李应雄; 纪烈霞
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2021-06-28
Filing date: 2021-06-28
Publication date: 2021-10-26

Abstract

770 MPa-level low-alloy high-strength high-toughness seamless steel pipe and a manufacturing method thereof, wherein the seamless steel pipe comprises the following chemical components in percentage by weight: 0.13 to 0.18 percent of C, 0.30 to 0.45 percent of C, 1.20 to 1.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.20 to 0.80 percent of Cr0.20, 0.20 to 0.50 percent of Mo0, 0.30 to 0.45 percent of Ni0, 0.03 to 0.06 percent of V, 0.015 to 0.045 percent of Al, 0.015 to 0.025 percent of Ti, and the balance of Fe and inevitable impurities, the invention reduces the steel cost by optimizing the added alloy elements and reducing the alloy content, and can also reduce the probability of cracks on the surface of the continuous casting billet; and by optimizing the heat treatment process, the development requirements of improving the product quality, reducing the production cost and saving the alloy resources are realized.

Description

770 MPa-level low-alloy high-strength high-toughness seamless steel pipe and manufacturing method thereof

Technical Field

The invention relates to the technical field of manufacturing of low-alloy high-strength seamless steel pipes, in particular to a low-alloy high-strength high-toughness economical seamless steel pipe with yield strength of more than or equal to 770MPa and a manufacturing method thereof. The seamless steel tube produced by the method can be widely applied to the main coil of the jib of the crawler crane and various high-strength structural members, and can also radiate to the fields of hydraulic oil cylinders, ocean platform structures and the like.

Background

With the rapid development of economy in recent years, the scale of national basic construction is getting larger, the quality, the volume and the lifting height of objects needing to be lifted in various engineering constructions are increased, the crawler crane shows the superiority more and more, the market capacity is rapidly increased, the attention of international famous manufacturers is attracted, and the development of the crawler crane is hot in the domestic crane industry.

The seamless steel pipe for the high-strength high-toughness structure has high low-temperature impact toughness requirement when operating in a severe low-temperature environment and bears huge pressure. Therefore, in order to ensure the safety of the structural pipe in the use process, the seamless steel pipe for the high-strength and high-toughness structure must have high steel purity, high strength, excellent toughness, high geometric precision, good surface quality and good welding performance, so the production difficulty is high.

The seamless steel pipe for the high-strength high-toughness structure in advanced industrial countries in the world is formed by adding a proper amount of alloy elements such as Cr, Ni, Mo, W, V, Nb, Ti and the like on the basis of low-carbon manganese steel, and the excellent performance is realized by utilizing the solid solution strengthening of the elements such as Mn, Cr, W, Ni, Mo and the like and the precipitation strengthening and fine grain strengthening of micro alloy elements such as Nb, V, Ti and the like.

At present, with the surplus of global steel productivity and the emergence of resource crisis, the steel industry faces unprecedented challenges, mainly reflecting the contradiction between the rise of alloy cost and the great decline of enterprise profit, thereby realizing a low-cost strategy and playing an important role in improving enterprise competitiveness. Therefore, the reduction of the addition of the alloy elements in the steel product needs to be considered during the component design so as to meet the development requirements of reducing the production cost and saving the alloy resources. Therefore, the development of an economical seamless steel tube production process with the yield strength of more than or equal to 770MPa is very necessary. The invention designs a low-cost manufacturing mode of a seamless steel pipe with the yield strength of more than or equal to 770MPa, wherein the composition design considers that alloy elements such as Cr, Ni, Mo, V, Ti and the like are added on the basis of C, Mn steel, thereby avoiding adding high-price alloy such as W and the like, and simultaneously, the addition of Nb is not considered, so that the probability of surface cracks of a continuous casting billet can be reduced. Under the composition, the strength and low-temperature toughness indexes of the seamless steel pipe meet the requirements through a quenching and tempering heat treatment process for the steel pipe.

The patent document CN201110419213.4 discloses a high-strength seamless steel tube with excellent low-temperature toughness and a manufacturing method thereof, the yield strength of the product is required to be more than or equal to 125ksi (863MPa), and the impact energy at-60 ℃ is more than 40J. The steel comprises the following components: c: 0.15% -0.20%, Si: 0.20-0.30%, Mn: 0.20-0.50%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Cr: 0.60% -0.80%, Mo: 0.40-0.70%, Ni: 1.0% -1.4%, Nb: 0.010% -0.035%, Als: 0.01 to 0.05 percent of iron and the balance of iron. The defects of the invention are as follows: 1. the components of the invention are added with high content of Ni alloy (1.0-1.4%) and Mo alloy (0.40-0.70%), thereby greatly increasing the steel cost; 2. the P is required to be less than or equal to 0.010 percent and the S is required to be less than or equal to 0.003 percent, so that the smelting difficulty is increased and the production cost is increased; the invention is not in the economic category.

In patent document CN201810112600.5, the steel tube for crane arm support and the manufacturing method thereof, the yield strength of the product of the invention is required to reach 960MPa, and the steel comprises the following components: c: 0.10% -0.20%, Si: 0.10-0.90%, Al: 0.008% -0.070%, Cr: 0.80% -3.60%, Mo: 0.40% -0.80%, V: 0.03% -0.16%, Nb: 0.03% -0.35%, W: 0.10% -1.50%, N: 0 to 0.005 percent and the balance of iron. The defects of the invention are as follows: 1. in order to meet the requirement of yield strength of 960MPa, the components of the invention are added with higher Mo alloy (0.40-0.70%) and W alloy (0.10-1.50%), thereby greatly increasing the cost of steel; 2. the invention adds 0.03-0.35% Nb alloy, which increases the probability of cracks on the surface of continuous casting billet.

The invention discloses a crane jib tube and a manufacturing method thereof with application number of CN200710192494.8, which requires that the yield strength of the product reaches 770MPa and the impact energy at-20 ℃ is more than 55J, and the steel comprises the following components: c: 0.14% -0.18%, Si: 0.20-0.50%, Mn: 1.20-1.70%, P is less than or equal to 0.025%, S is less than or equal to 0.015%, W: 0.10% -0.70%, V: 0.05-0.12%, Al: 0.01-0.06%, Cr: less than or equal to 0.80 percent, Mo: 0.20-0.40%, Ni: less than or equal to 0.40 percent, and the balance of (20 ℃ impact) iron and residual elements; the defects of the invention are as follows: 1. the W alloy (0.10-0.70%) is added into the components of the invention, and the addition amount of the V alloy (0.05-0.12%) is higher, thereby greatly increasing the cost of steel and having no economy. 2. The low-temperature impact of the steel pipe required by the invention is that the impact energy at-20 ℃ is more than 55J, but the impact energy at-40 ℃ is not required to be more than 45J.

In the patent document CN200610032437.9, the steel type of the pipe for crane chord member and the manufacturing method thereof comprises the following components: c: 0.26-0.31%, Si: 0.17% -0.35%, Mn: 1.30% -1.50%, Ti: 0.01% -0.04%, B: 0.0005 to 0.002 percent of the total weight of the alloy, and the balance of iron. The invention requires that the yield strength of the product reaches 800MPa and the tensile strength reaches 980MPa, and the steel pipe is quenched and tempered at 470 ℃ to obtain a tempered martensite structure. The defects of the invention are as follows: 1. in the invention, alloy elements such as Cr, Mo, V, Ni and the like are not added, and the strength requirement is ensured by adopting higher C (0.26-0.31%) and adding B, which can bring poor low-temperature impact toughness index. 2. The steel pipe produced by the process of the invention obtains a tempered martensite structure instead of a tempered sorbite structure, and has no characteristics of high strength, high low temperature toughness.

Patent document CN201010121651.8, the patent components of the microalloy high toughness non-quenched and tempered crane jib tube and the production method thereof are: c: 0.16% -0.22%, Si: 0.10-0.50%, Mn: 1.30-1.50%, P is less than or equal to 0.030%, S is less than or equal to 0.020%, V: 0.08-0.18%, Al: 0.01 to 0.06 percent, and the balance being iron. The defects of the invention are as follows: 1. the invention adopts non-quenching and tempering technology to ensure the performance of the steel pipe, and the yield strength is only required to reach the level of more than or equal to 550 MPa. Practice proves that the low-temperature impact value of the steel pipe produced by adopting the non-tempering process cannot reach the low-temperature impact value level produced by adopting the tempering process, and the process is only suitable for producing the steel pipe with thinner wall thickness. 2. The non-tempering process of the invention needs to cool the steel pipe to a certain temperature before the steel pipe is subjected to the stretching or sizing, and then the steel pipe is reheated by a reheating furnace, and the process has limitations.

The invention discloses a low-alloy seamless steel tube for supporting a crane cantilever, which is applied to a patent document CN201210035362.5, wherein the invention requires that the yield strength of the product reaches 890MPa and the impact energy at-40 ℃ is more than 45J, and the steel comprises the following components: c: 0.10% -0.20%, Si: 0.20-0.80%, Mn: 0.60% -1.50%, Cr: 0.30% -0.80%, Mo: 0.20-0.60%, Ti: 0.001-0.050%, Al: 0.02% -0.06%, Ni: 0.2% -0.8%, V: 0.01 to 0.10 percent, Nb: 0.01 to 0.08 percent of iron and the balance of iron. The invention has the following disadvantages: the Nb alloy of 0.01-0.08% is added, so that the probability of cracks on the surface of a continuous casting billet is increased, and the cost of the billet is increased.

In the patent document CN200710094177.2, the steel plate with 800MPa grade yield strength and low welding crack sensitivity and the manufacturing method thereof, the steel comprises the following components: c: 0.03% -0.08%, Si: 0.05-0.70%, Mn: 1.30% -2.20%, Mo: 0.10% -0.30%, Nb: 0.03% -0.10%, V: 0.03-0.45%, Ti: 0.002% -0.040%, Al: 0.02% -0.04%, B: 0.0010 to 0.0020 percent, and the balance of iron. And (3) rolling and cooling control is carried out when the steel plate is rolled, and the finishing temperature is 780-840 ℃. The invention has the following disadvantages: the invention aims at the production of plates, and the rolling mode is controlled rolling and cooling, so that the method is not suitable for the production of seamless steel tubes.

The patent document CN201210214597.0 discloses a seamless steel tube for high-strength and high-toughness structure and a manufacturing method thereof, the invention requires that the yield strength of the product reaches 890MPa, and the impact energy at-40 ℃ is more than 45J, and the steel comprises the following components: c: 0.14% -0.18%, Si: 0.20-0.50%, Mn: 0.90-1.30%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, Cr: 0.20% -1.00%, Mo: 0.20-0.80%, Ni: 0.90% -1.50%, V: 0.02-0.10%, Nb is less than or equal to 0.05%, Al: 0.015-0.050%, Cu not more than 0.35%, N not more than 0.020%, Ti not more than 0.050%, and the balance of iron. The invention has the following disadvantages: 1. the Nb alloy of 0.02-0.05% is added, so that the probability of cracks on the surface of the continuous casting billet is increased, and the cost of the billet is increased. 2. The invention adds high content Ni (0.90-1.50%), which increases the cost of steel greatly and has no economy.

Disclosure of Invention

The invention aims to provide a 770 MPa-grade low-alloy high-strength high-toughness seamless steel tube and a manufacturing method thereof, which reduce the steel cost by optimizing the added alloy elements and reducing the alloy content, and can reduce the probability of cracks on the surface of a continuous casting billet so as to improve the flaw detection qualification rate of the steel tube; and by optimizing the heat treatment process, the product performance is ensured to be qualified, and finally the development requirements of improving the product quality, reducing the production cost and saving the alloy resources are realized. The high-strength high-toughness seamless steel pipe with the yield strength of more than or equal to 770MPa produced by the method has outstanding production benefit and application value, and production practice proves that the product has good performance and is popularized and used.

In order to achieve the purpose, the invention adopts the following technical scheme:

the 770 MPa-level low-alloy high-strength high-toughness seamless steel pipe comprises the following chemical components in percentage by weight: 0.13 to 0.18 percent of C, 0.30 to 0.45 percent of Si, 1.20 to 1.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.20 to 0.80 percent of Cr, 0.20 to 0.50 percent of Mo, 0.30 to 0.45 percent of Ni, 0.03 to 0.06 percent of V, 0.015 to 0.045 percent of Al, 0.015 to 0.025 percent of Ti, and the balance of Fe and inevitable impurities.

The invention has the following design reasons:

in the production practice, the probability of cracks on the surface of the continuous casting billet is higher when the Nb alloy is adopted for microalloying treatment, and in order to avoid and reduce the surface crack defects of the continuous casting billet, the Nb alloy added with refined grains is not considered in the invention, but only Ti + Al + V is considered to be added for microalloying treatment, so that the effect of refining the grains is achieved. Meanwhile, the problem caused by the fact that no Nb alloy is contained is solved by controlling the quenching temperature in the subsequent process, and the performance requirement is met.

For 770MPa grade high-strength seamless steel pipes, the situation is known at present, and the requirements of high strength and high toughness are realized by adding main alloy elements such as W, Mo, Cr and the like from the import of foreign V & M companies and the components adopted by domestic steel enterprises. In order to ensure that the material has better low-temperature toughness, realize the purpose of economy and facilitate the production organization, the invention adopts Ni to replace W and designs and adds main alloys of Ni, Mo, Cr and the like. As can be seen from the beneficial effects of the W alloy, on one hand, the W is partially dissolved in the iron to form a solid solution in the steel except for forming carbide, and the effect of the W is similar to that of Mo, so that the tempering stability can be increased, and the hardenability and hardness can be improved; on the other hand, W is frequently used in alloy tool steel because it forms hard-soluble carbide in steel, remarkably improves wear resistance and machinability, and ensures high-temperature strength. The 770-level high-strength seamless steel pipe requires high strength and good-40 ℃ low-temperature impact toughness, and does not need good high-temperature strength and wear resistance. The beneficial effects of the Ni alloy can strongly improve the strength of the steel on one hand, and the important effect of the Ni alloy is to ensure the low-temperature toughness of the material to be at a very high level all the time on the other hand. Therefore, the performance requirements of the material can be better met by adopting the combination of Ni, Mo and Cr alloys, and the cost of the material can be reduced.

C: 0.13-0.18%, wherein C is an important element for ensuring the strength of the seamless steel pipe, and C is an important element for ensuring the strength of the steel pipe, and the main function of C is solid solution strengthening. In order to improve hardenability and meet the requirement that the yield strength is more than 770MPa, C must be more than 0.12%. If C is greater than 0.18%, the plasticity and toughness of the steel may be reduced, and the welding properties of the steel may be deteriorated due to a high C content. Therefore, the preferable range of C is 0.13% to 0.18%, and the more preferable range of C content is 0.14% to 0.16%.

Mn: 1.20-1.50%, and the influence of Mn on the mechanical property of the quality-treated steel is mainly achieved by improving the hardenability of the steel. The Mn content is less than 1.00%, the expected strengthening effect cannot be obtained, the Mn content is more than 1.50%, the plasticity and toughness of the steel can be reduced, and meanwhile, the welding performance of the steel can be deteriorated due to the high Mn content. Therefore, the Mn content is designed to be controlled to be 1.20-1.50%, and the more preferable content range is 1.25-1.40%.

Cr: 0.20% to 0.80%, Cr can improve the hardenability of steel and increase the strength of steel, but it also tends to increase the temper brittleness of steel, so it should be used in combination with Mo or other elements. The effect is clearly exhibited when the content is 0.20% or more, but if the content is excessively added, the plasticity and toughness of the steel are reduced, and the weldability of the steel is deteriorated due to a high Cr content, so that the preferable range of Cr is 0.20% to 0.80%, and the more preferable range of Cr is 0.40% to 0.60%.

Mo: 0.20-0.50%, Mo can improve the hardenability of steel, improve the heat strength, prevent temper brittleness and the like. The effect is obvious when the Mo content is more than 0.20 percent, but the welding performance of the steel is poor due to higher Mo content, and the Mo belongs to precious metals, so the Mo content is added as little as possible under the condition of meeting the performance. Therefore, the preferable range of Mo is 0.20% to 0.50%, and the more preferable range of Mo is 0.25% to 0.40%.

Ni: 0.30 to 0.45 percent of Ni is a main alloy element for forming and stabilizing austenite, can improve the low-temperature toughness of steel and can realize the high-strength toughness matching of the steel. Considering that the yield strength of the product designed by the invention is only 770MPa and does not reach 890MPa, the preferable range of Ni is 0.30-0.45%.

V: 0.03% -0.06%, V mainly plays roles of precipitation strengthening and fine grain strengthening in low alloy steel, can increase the strength of steel and inhibit the time effect thereof, and the V content is more than 0.02% and has an effect, but the V content exceeds 0.10%, the toughness of the steel is reduced, so the preferable range of V is 0.03% -0.06%, and the more preferable range of V is 0.03% -0.05%.

Al: 0.015-0.05%, Al is the main deoxidation element in the steel, and is a cheap refined crystal grain element at the same time, the main purpose of adding Al in the invention is to refine crystal grains and fix N in the steel, thereby obviously improving the impact toughness of the steel. The Al content should be more than 0.015%, for example, more than 0.05% to cause an increase in non-metallic inclusions in the steel or deterioration in toughness, so that the upper limit is set to 0.050% or less. The preferable range is 0.020% to 0.040%.

Ti: 0.015% -0.025%, titanium and N, O, C have very strong affinity, add titanium iron to steel grade to carry on the little titanium treatment in the invention, utilize Ti and N in the steel to form TiN, TiN that is precipitated under the partial solidification state can prevent the growth of the crystalline grain in the heating process of the steel pipe, can improve the plastic toughness of the steel pipe, can also improve the weldability of the steel pipe at the same time. However, since too much Ti is added to easily form TiN inclusions and deteriorate the toughness of the steel pipe, the upper limit is set to 0.030% or less. The preferred range is 0.015% to 0.020%.

P: less than or equal to 0.020 percent, easy phosphorus segregation at grain boundaries, capability of increasing ductile-brittle transition temperature and reducing toughness of steel, and reduction of low-temperature impact toughness at minus 40 ℃ caused by too high content, so that the content is limited to less than 0.020 percent, and the more preferable range is controlled to less than 0.015 percent.

S: less than or equal to 0.010 percent, the sulfur and the manganese and the like are easy to form non-hard inclusions, the increase of the content of the non-hard inclusions can cause the increase of the number of the inclusions, the extension deformation is generated along the rolling direction in the processing process, the continuity of a material matrix is damaged, and the low-temperature impact toughness of the seamless steel pipe is reduced. Therefore, it is necessary to limit the content to 0.015% or less, and a more preferable range is 0.010% or less.

Si: 0.30% -0.45%, Si is an effective deoxidizing element, the deoxidizing effect is weakened when the content is too low, and the toughness of the steel is reduced when the content is too high, so 0.30% -0.45% is selected as the content range of Si.

The yield strength of the seamless steel tube is more than or equal to 770 MPa; the tensile strength is 820-1000 MPa; the elongation is more than or equal to 14 percent; -40 ℃ impact absorption energy KV₂Not less than 45J; the steel pipe structure is a tempered sorbite.

The outer diameter of the seamless steel pipe is phi 70 mm-phi 183mm, and the wall thickness is 4-20 mm.

The method for manufacturing the 770 MPa-level low-alloy high-strength high-toughness seamless steel pipe comprises the following steps:

molten iron pretreatment → converter smelting → external refining (LF + VD) → square billet continuous casting → continuous rolling round pipe blank → hot rolling steel pipe → quenching and tempering heat treatment → performance inspection → post-inspection such as flaw detection → packaging and warehousing.

1) Converter smelting, LF external refining + VD, and square billet continuous casting;

2) hot continuous rolling the continuous casting square billet to obtain a round pipe billet;

3) rolling the round pipe blank into a steel pipe by a steel pipe continuous rolling mill set, heating the round pipe blank to 1240-1280 ℃, and then perforating, rolling by a continuous rolling mill and sizing by a sizing mill;

4) the hot rolled steel pipe is heated by a stepping quenching furnace at 880-900 ℃, then is subjected to external spraying and internal water spraying quenching, and is then subjected to tempering heat treatment by a stepping tempering furnace at 640-660 ℃, wherein the cooling speed during water quenching of the steel pipe is above 40 ℃/s.

The specification of the continuous casting billet in the step 1) is 380mm by 280 mm.

The specification phi of the round tube blank in the step 2) is 210mm and 185 mm.

The reasons for the heat treatment for quenching and tempering according to the present invention are as follows:

1. quenching temperature is 880-910 ℃: the main purpose of quenching is to quench the austenitized steel tube entirely into martensite and bainite so that good texture and mechanical properties can be obtained after tempering at a suitable temperature. For low-alloy quenched and tempered steel containing Nb alloy, the quenching temperature is generally 910-940 ℃, in order to avoid crack defects on the surface of a continuous casting billet, the addition of a crack sensitive element Nb is not considered in the designed steel components, so that the quenching temperature is lower as much as possible in order to avoid grain growth during quenching and heating. The quenching temperature range is 880-910 ℃ according to the phase transformation temperature AC3 (860-870 ℃) measured for the steel grade of the invention, and the range is 880-900 ℃.

In order to ensure the high strength and high toughness of the steel pipe, enough cooling strength must be provided during water quenching, and the CCT curve made according to the steel grade of the invention designs the cooling speed of the steel pipe during water quenching to be more than 40 ℃/s, preferably more than 50 ℃/s.

2. The tempering temperature is 640-660 ℃: the main purpose of tempering the quenched and tempered steel is to eliminate the residual stress after the steel pipe is quenched and to increase the plasticity and toughness of the steel. Tempering temperatures below 640 ℃ result in tensile strengths that may exceed 1000MPa or elongation of less than 14%; and the tempering temperature is more than 660 ℃, the yield strength can be lower than 770 MPa. Therefore, the tempering temperature range is preferably 640 ℃ to 660 ℃.

Compared with the prior art, the invention has the beneficial effects that:

1) the performance of the low-alloy high-strength seamless steel pipe with the wall thickness of 4-20 mm manufactured by the process can meet the following requirements: the yield strength is more than or equal to 770MPa, the tensile strength is 820-1000 MPa, and impact absorption energy KV at-40 DEG C₂Not less than 45J. The invention has been successfully used on the key structure of the crawler crane arm support, and can provide seamless steel pipes for various projects such as engineering mechanical structural members, grid structures, ocean engineering, bridges and the like.

2) The invention carries out component design from the aspects of alloy reduction and casting blank surface crack reduction, and the product performance completely meets the standard requirement by matching with the designed heat treatment process, thereby realizing the development requirement of reducing the production cost and saving the alloy resource and leading the product to have more market competitiveness.

Drawings

FIG. 1 is a photograph x500 of metallographic structure of BJ770 steel tube of tempered sorbite.

Detailed Description

The present invention is described in more detail by way of examples, which are merely illustrative of the best mode of carrying out the invention and are not intended to limit the scope of the invention in any way.

In the invention, from the perspective of low cost and economy, firstly, the addition of high-price alloys such as W and the like is avoided in the component design, and the addition of proper amount of Cr, Mo and Ni alloys for solid solution strengthening is considered; v, Ti and Al are adopted for micro-alloying treatment to achieve the purpose of grain refinement, so that the addition of a crack sensitive element Nb is avoided, and the probability of cracks on the surface of the continuous casting billet is greatly reduced; meanwhile, the strength and low-temperature impact toughness indexes of the seamless steel pipe meet the requirements through adopting a low-temperature quenching process at 880-900 ℃ and a high-temperature tempering heat treatment process at 640-660 ℃.

The high-strength high-toughness low-alloy seamless steel pipe with the yield strength of more than or equal to 770MPa and the manufacturing method thereof can be realized as follows:

molten iron pretreatment → converter smelting → external refining (LF + VD) → square billet continuous casting → continuous rolling round pipe blank → hot rolling steel pipe → performance inspection → post-inspection.

The compositions of the inventive and comparative steels (comparative steels containing W or Nb) are shown in Table 1. The main performance indexes of the examples and the comparative examples in the quenched and tempered state are shown in table 2.

TABLE 1 composition (wt%) of inventive and comparative steels

TABLE 2 mechanical Properties of the products of the invention

Claims

The 1.770 MPa-level low-alloy high-strength high-toughness seamless steel pipe is characterized by comprising the following chemical components in percentage by weight: 0.13 to 0.18 percent of C, 0.30 to 0.45 percent of Si, 1.20 to 1.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.20 to 0.80 percent of Cr, 0.20 to 0.50 percent of Mo, 0.30 to 0.45 percent of Ni, 0.03 to 0.06 percent of V, 0.015 to 0.045 percent of Al, 0.015 to 0.025 percent of Ti, and the balance of Fe and inevitable impurities.
2. The 770MPa grade low alloy high strength high toughness seamless steel tube of claim 1, wherein the seamless steel tube yield strength is not less than 770 MPa; the tensile strength is 820-1000 MPa; the elongation is more than or equal to 14 percent; -40 ℃ impact absorption energy KV₂Not less than 45J; the steel pipe structure is a tempered sorbite.
3. The 770MPa grade low alloy high strength high toughness seamless steel pipe of claim 1, wherein the seamless steel pipe has an outer diameter of phi 70mm to phi 183mm and a wall thickness of 4 mm to 20 mm.
4. The method for manufacturing the 770 MPa-level low-alloy high-strength high-toughness seamless steel tube according to any one of claims 1 to 3, wherein the hot-rolled steel tube is heated by a step-type quenching furnace at 880 to 900 ℃, then is subjected to external shower and internal water spray quenching, and then is subjected to tempering heat treatment by a step-type tempering furnace at 640 to 660 ℃.
5. The method for manufacturing 770MPa grade low alloy, high strength and high toughness seamless steel tube according to claim 4, wherein the cooling rate of the steel tube during water quenching is 40 ℃/s or more.