WO2024016419A1

WO2024016419A1 - Low-yield-ratio weather-resistant bridge steel and manufacturing method

Info

Publication number: WO2024016419A1
Application number: PCT/CN2022/114327
Authority: WO
Inventors: 王军; 谯明亮; 崔强; 陈林恒; 唐春霞; 孟令明; 秦玉荣; 刘涛; 李新亮
Original assignee: 南京钢铁股份有限公司
Priority date: 2022-07-22
Filing date: 2022-08-23
Publication date: 2024-01-25
Also published as: CN115341141A

Abstract

A low-yield-ratio weather-resistant bridge steel and a manufacturing method, relating to the technical field of steel production. The chemical components of the bridge steel are as follows, in percentage by mass: 0.06%-0.09% of C, 0.15%-0.30% of Si, 1.51%-1.65% of Mn, 0.009%-0.015% of P, ≤0.002% of S, 0.020%-0.050% of Nb, 0.010%-0.020% of Ti, 0.010%-0.030% of V, 0.30%-0.40% of Cu, 0.30%-0.45% of Ni, 0.45%-0.60% of Cr, 0.16%-0.25% of Mo, 0.02%-0.04% of Alt, and the balance being Fe and inevitable impurities. By means of scientific design on components and the matched manufacturing method of controlled rolling, controlled cooling and tempering, the weather-resistant bridge steel has the characteristics of low yield ratio, high low-temperature toughness and high ductility.

Description

A kind of low yield strength ratio weather-resistant bridge steel and its preparation method

Technical field

The invention relates to the technical field of steel production, and in particular to a low yield-strength ratio weather-resistant bridge steel and a preparation method.

Background technique

As large-scale steel structure bridges develop toward large-span, heavy-load, and fully welded structures, the safety and reliability requirements for bridge structures become increasingly stringent. This puts forward higher requirements for designers, and also puts forward higher standards for the quality of steel plates. That is, the steel plates are not only required to have high strength to meet the requirements of lightweight structures, but also have excellent plasticity, low-temperature toughness, and weldability. , corrosion resistance, etc., to meet the working conditions of bridges with larger spans and heavier loads. Therefore, the application of high-strength, high-toughness, high-plasticity and high-weather-resistant bridge steel can reduce the weight of the bridge structure, reduce the difficulty of bridge engineering design, manufacturing, and construction, and at the same time increase the service life.

However, as the strength of steel increases, the yield-to-strength ratio of steel generally increases, and can even reach more than 0.93. Due to the high yield ratio, once the component is overloaded, such as under earthquake and other conditions, it will quickly reach the ultimate strength of the steel type and cause an accident. Therefore, the high yield-strength ratio limits the application of high-strength structural steel in bridge engineering. The frequent occurrence of earthquakes and their catastrophic consequences have attracted great attention abroad to the seismic resistance of bridges, and relevant provisions have been made in some structural design specifications. Bridge steel with low yield-to-strength ratio, high strength, high toughness, high plasticity and high weather resistance is the development trend of bridge construction.

Patent No. CN108486466B "A high-toughness weathering steel plate with a yield strength of 550MPa and its preparation method" discloses a preparation method of a high-toughness weathering steel plate with a yield strength of 550MPa. The product is hot-rolled and has a thin thickness and a high yield-strength ratio. High, unable to meet the steel requirements for modern bridge manufacturing with large spans and heavy loads.

Contents of the invention

The present invention aims at the above technical problems, overcomes the shortcomings of the existing technology, and provides a low yield ratio weather-resistant bridge steel. Its chemical composition and mass percentage are as follows: C: 0.06% ~ 0.09%, Si: 0.15% ~ 0.30%, Mn : 1.51%～1.65%, P: 0.009%～0.015%, S≤0.002%, Nb: 0.020%～0.050%, Ti: 0.010%～0.020%, V: 0.010%～0.030%, Cu: 0.30%～0.40 %, Ni: 0.30% to 0.45%, Cr: 0.45% to 0.60%, Mo: 0.16% to 0.25%, Alt: 0.02% to 0.04%, the balance is Fe and inevitable inclusions.

The technical solution further limited by the present invention is:

The aforementioned low yield ratio weather-resistant bridge steel has the following chemical composition and mass percentage: C: 0.06% ~ 0.07%, Si: 0.20% ~ 0.30%, Mn: 1.56% ~ 1.65%, P: 0.011% ~0.015%, S≤0.002%, Nb: 0.020%~0.040%, Ti: 0.010%~0.020%, V: 0.010%~0.030%, Cu: 0.32%~0.36%, Ni: 0.35%~0.45%, Cr : 0.45% ~ 0.60%, Mo: 0.16% ~ 0.20%, Alt: 0.02% ~ 0.04%, the balance is Fe and inevitable inclusions.

The aforementioned low yield ratio weather-resistant bridge steel has the following chemical composition and mass percentage: C: 0.07% ~ 0.09%, Si: 0.17% ~ 0.20%, Mn: 1.54% ~ 1.59%, P: 0.009% ~0.015%, S≤0.002%, Nb: 0.030%~0.040%, Ti: 0.010%~0.020%, V: 0.015%~0.025%, Cu: 0.30%~0.35%, Ni: 0.30%~0.40%, Cr : 0.45% ~ 0.55%, Mo: 0.20% ~ 0.25%, Alt: 0.02% ~ 0.04%, the balance is Fe and inevitable inclusions.

Another object of the present invention is to provide a method for preparing low yield ratio weather-resistant bridge steel, which includes smelting, continuous casting, soaking, rolling, relaxation, cooling and off-line tempering:

The thickness of the continuous casting billet used is 150~320mm, and the continuous casting billet in the continuous casting process is heap-cooled for more than 24 hours; the continuous casting billet is heated to a center temperature of 1130~1230°C in the soaking process, and the temperature uniformity is less than 20°C. The heating time ≥Thickness of continuous casting slab×1min/mm;

The rolling process involves rolling the descaled continuous casting billet in the recrystallization zone and the non-recrystallization zone. The cumulative deformation of the recrystallization zone rolling is more than 50% of the thickness of the continuous casting billet;

The intermediate billet is heated to 780-990°C, and the thickness is 2.0-4.0 times the thickness of the finished product. After reaching the temperature, the non-recrystallized area is rolled, and the final rolling temperature is controlled at 770-830°C;

In the relaxation process, the relaxation to initial cooling temperature is 730℃~760℃;

The cooling process is laminar flow cooling from the initial cooling temperature, the red return temperature is controlled at 400-600°C, and then air-cooled to room temperature;

In the offline tempering process, the tempering temperature is between 500 and 600°C, and it is kept at this temperature for 20 to 40 minutes. The holding time is proportional to the thickness of the finished product, and then it is naturally cooled to room temperature.

In the aforementioned method for preparing low-yield-ratio weather-resistant bridge steel, the thickness of the continuous casting billet increases, and the stack cooling time increases accordingly. For a 320mm continuous cast billet, the stack cooling time is more than 48 hours.

The aforementioned method for preparing low-yield-strength-ratio weather-resistant bridge steel, the thickness of the steel plate is 8 to 80 mm.

The aforementioned method for preparing low-yield-ratio weather-resistant bridge steel, the yield strength of the steel plate is above 578MPa, the tensile strength is above 698MPa, the yield-strength ratio is ≤0.85, the Akv at -40°C is above 188J, and the elongation is ≥20%; it is resistant to the atmosphere. Corrosion index I≥6.5, I=I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni) -9.10(%Ni)(%P)-33.39(%Cu) ² .

In the aforementioned method for preparing low-yield-ratio weather-resistant bridge steel, the metallographic structure of the steel plate is tempered bainite.

The beneficial effects of the present invention are:

(1) Through scientific component design and matching manufacturing methods of controlled rolling, controlled cooling + tempering, the present invention enables the weather-resistant bridge steel to have the characteristics of low yield-strength ratio, high and low temperature toughness and high ductility;

(2) The structure type mainly composed of tempered bainite in the present invention achieves low yield ratio, high and low temperature toughness and high elongation. The description of each component and content is as follows:

C is an indispensable element in steel that improves the strength and hardness of steel. It has a significant impact on the steel structure. C dissolves into the matrix to form an interstitial solid solution, which plays the role of solid solution strengthening and significantly increases the strength of the matrix. As the carbon content increases, The tensile strength and yield limit of steel will increase while the elongation and notched impact toughness will decrease; when the C content in the steel is high, it is easy to intensify and produce cold cracks. Therefore, the present invention adopts an ultra-low carbon design, and a small amount of C in the steel Microalloying element carbides are formed in the medium, which plays the role of strengthening the second phase and refining the grains. The C percentage in the present invention is set to 0.06% to 0.09%;

Mn is a main element in steel. Manganese element can improve the strength of the material. Although increasing the C content or Cr can also improve the strength, too much carbon element affects the formability and welding line. The Cr element is too expensive and has limited reserves, so it is not suitable for It is beneficial to reduce costs. The Mn element is still the main element in preventing thermal brittleness in steel. Considering the role of Mn comprehensively, the Mn percentage content in the present invention is set to 1.51% to 1.65%;

Si element in steel mainly improves the strength of steel in the form of strong solid solution strengthening. It is also a necessary element for deoxidation in steelmaking. It can improve the resistance to atmospheric corrosion, but it significantly reduces the plasticity and toughness of steel and significantly reduces the surface coating of steel. Performance, therefore, taking into account strength, toughness, plasticity and other factors, the Si percentage in the present invention is set to 0.15% to 0.30%;

P promotes the amorphous transformation of the rust layer. Generally speaking, Cu and P composites have the best weather resistance effect and are relatively economical corrosion-resistant elements. Considering that P causes low-temperature brittleness and crack sensitivity, weather-resistant steel is used in important welded structures. , the content of P is generally limited, and the narrow range of P percentage control in the present invention is 0.009% to 0.015%;

The Cu element mainly plays a solid solution strengthening role in steel. An appropriate amount of copper can increase the strength without reducing the toughness, and can also improve the corrosion resistance of the steel. The percentage content of Cu in the present invention is 0.30% to 0.40%;

Ni is the only element that can improve low-temperature impact toughness (NDT, CTOD, DWTT, etc.) and can also effectively prevent copper-induced surface cracking during continuous casting and hot rolling. The percentage of Ni in the present invention is 0.30% to 0.45%. ;

Cr is widely used in actual industrial production. It is second only to carbon in improving the yield strength of steel and is detrimental to reducing the yield-strength ratio. Moreover, my country has small reserves of chromium, so the content of chromium is reduced. Mn and Instead of Si element, the Cr content in the present invention is 0.45% to 0.60%;

Mo is a strong solid solution strengthening element, which strongly improves hardenability, significantly improves hot hardness, improves tempering stability, and significantly reduces temper brittleness. The Mo percentage in the present invention is 0.16% to 0.25%;

V is a moderate carbide-forming element that can form alloy carbide VC with a simple cubic crystal structure. It can enter cementite to improve cementite stability and tempering stability. The V percentage in the present invention is 0.010%~ 0.030%;

Ti can shift the C curve to the right. Titanium can significantly increase the strength, refine the grains, and also improve the toughness of steel. An appropriate amount of Ti can form the second mass point and improve the toughness of the metal. The percentage of Ti in the present invention It is 0.010%~0.020%.

Description of drawings

Figure 1 is a 500x optical metallographic structure diagram of the steel plate in Example 3.

Detailed ways

Example 1

The composition and mass percentage of the 550MPa grade low-yield weathering bridge steel in this embodiment are: C: 0.06%, Si: 0.27%, Mn: 1.65%, P: 0.014%, S: 0.0010%, Nb: 0.020 %, Ti: 0.015%, V: 0.010%, Ni: 0.30%, Cu: 0.35%, Cr: 0.45%, Mo: 0.18%, Alt: 0.02%, the balance is Fe and unavoidable impurities.

The raw materials are smelted, refined, alloyed, and calcium treated to obtain molten steel. The molten steel is continuously cast into slabs. The slab thickness is 150 mm, and the atmospheric corrosion resistance index I is 6.56. The cast billet is piled and cooled for more than 24 hours. The billet is soaked at 1230°C with a temperature uniformity of less than 20°C. It is heated for 150 minutes and then descaled, followed by two-stage rolling. The rolling temperature in the recrystallization zone is 1080°C, the total deformation is 79%, and the thickness of the intermediate billet is controlled to be 4 times the thickness of the finished product. The rolling opening temperature in the non-recrystallized area is 990°C, reaching a final product thickness of 8mm, and the final rolling temperature is 830°C.

After final rolling, relax to the initial cooling temperature of 730°C. The steel plate at the initial cooling temperature is laminarly cooled. The red return temperature is 600°C, and then air-cooled to room temperature. Then the steel plate is tempered. The tempering temperature is 600°C. ℃, and keep it at this temperature for 20 minutes.

Observation of the metallographic structure of the sample after controlled rolling and controlled cooling + tempering found that the microstructure type is "tempered bainite" structure, the yield strength of the material is 592MPa, the tensile strength is 698MPa, and the yield strength of the finished steel The ratio is 0.85, the Akv at -40°C is 188J, and the elongation A is 20%.

Example 2

The composition and mass percentage of the 550MPa grade low-yield weathering bridge steel in this embodiment are: C: 0.08%, Si: 0.30%, Mn: 1.60%, P: 0.009%, S: 0.0012%, Nb: 0.035 %, Ti: 0.020%, V: 0.017%, Ni: 0.34%, Cu: 0.30%, Cr: 0.60%, Mo: 0.16%, Alt: 0.04%, the balance is Fe and unavoidable impurities. The raw materials are smelted, refined, alloyed, and calcium treated to obtain molten steel. The slab is cast continuously on the molten steel. The slab thickness is 320 mm, and the atmospheric corrosion resistance index I is 6.67. The slab is cooled for more than 48 hours, and the slab is heated at 1150°C with a temperature uniformity of less than 20°C. It is heated for 336 minutes and then descaled, followed by two-stage rolling. The rolling temperature in the recrystallization zone is 1060°C, the total deformation is 53%, and the thickness of the intermediate billet is controlled to be 2.5 times the finished product thickness. The rolling opening temperature in the non-recrystallized area is 840°C, reaching a final product thickness of 60mm, and the final rolling temperature is 800°C.

After the final rolling, relaxation treatment is performed to the initial cooling temperature of 750°C. The steel plate at the initial cooling temperature is laminarly cooled to a red temperature of 450°C, and then air-cooled to room temperature, and then the steel plate is tempered. The tempering temperature is between 550℃, and keep it at this temperature for 35min.

Observation of the metallographic structure of the sample after controlled rolling and controlled cooling + tempering found that the microstructure type is "tempered bainite" structure, the yield strength of the material is 583MPa, the tensile strength is 703MPa, and the yield strength of the finished steel The ratio is 0.83, the Akv at -40°C is 215J, and the elongation A is 21%.

Example 3

The composition and mass percentage of the 550MPa grade low-yield weathering bridge steel in this embodiment are: C: 0.09%, Si: 0.15%, Mn: 1.55%, P: 0.011%, S: 0.0020%, Nb: 0.040 %, Ti: 0.017%, V: 0.030%, Ni: 0.45%, Cu: 0.34%, Cr: 0.50%, Mo: 0.25%, Alt: 0.02%, the balance is Fe and unavoidable impurities. The raw materials are smelted, refined, alloyed, and calcium treated to obtain molten steel, which is then continuously cast into slabs. The slab thickness is 320 mm, and the atmospheric corrosion resistance index I is 6.58. The cast slab is pile-cooled for more than 48 hours. The slab is uniformly heated at 1130°C with a temperature uniformity of less than 20°C. It is heated for 320 minutes and then descaled, followed by two-stage rolling. The rolling temperature in the recrystallization zone is 1040°C, the total deformation of rough rolling is 50%, and the thickness of the intermediate billet is controlled to be 2.0 times the thickness of the finished product. The rolling opening temperature in the non-recrystallized area is 780°C, reaching a final product thickness of 80mm, and the final rolling temperature is 770°C.

After the final rolling, relaxation treatment is performed to the initial cooling temperature of 760°C. The steel plate at the initial cooling temperature is laminarly cooled to a red temperature of 400°C, and then air-cooled to room temperature. Then the steel plate is tempered at a tempering temperature of 500℃, and keep it at this temperature for 40 minutes.

Observing the metallographic structure of the sample after controlled rolling and controlled cooling + tempering, it was found that the microstructure type under low magnification is "tempered bainite" structure, the uniformity of the structure is good, and the yield strength of the material is 578MPa, the tensile strength is 705MPa, the yield ratio of the finished steel is 0.82, the Akv at -40°C is 204J, and the elongation A is 22%.

Example 4

The composition and mass percentage of the 550MPa grade low-yield weathering bridge steel in this embodiment are: C: 0.07%, Si: 0.21%, Mn: 1.51%, P: 0.015%, S: 0.0015%, Nb: 0.050 %, Ti: 0.010%, V: 0.020%, Ni: 0.41%, Cu: 0.40%, Cr: 0.48%, Mo: 0.20%, Alt: 0.025%, the balance is Fe and unavoidable impurities. The raw materials are smelted, refined, alloyed, and calcium treated to obtain molten steel. The slab is continuously cast on the molten steel. The thickness of the cast slab is 260 mm, and the atmospheric corrosion resistance index I is 6.55. The cast billet is piled and cooled for more than 36 hours, and the billet is soaked at 1200°C with a temperature uniformity of less than 20°C. It is heated for 286 minutes and then descaled, followed by two-stage rolling. The finishing rolling temperature in the recrystallization zone is 1100°C, the total rough rolling deformation is 63%, and the thickness of the intermediate billet is controlled to be 3.0 times the finished product thickness. The rolling opening temperature in the non-recrystallized area is 870°C, reaching a final product thickness of 32mm, and the final rolling temperature is 820°C.

After the final rolling, relaxation treatment is performed to the initial cooling temperature of 740°C. The steel plate at the initial cooling temperature is laminarly cooled to a red temperature of 540°C, and then air-cooled to room temperature, and then the steel plate is tempered. The tempering temperature is between 530℃, and keep it at this temperature for 30 minutes.

Observation of the metallographic structure of the sample after controlled rolling and controlled cooling + tempering found that the microstructure type is "tempered bainite" structure, the yield strength of the material is 586MPa, the tensile strength is 724MPa, and the yield strength of the finished steel The ratio is 0.81, the Akv at -40°C is 333J, and the elongation A is 21%.

It can be seen from the above examples that the 550MPa low-yield-strength-ratio weather-resistant bridge steel produced by the medium-thick plate rolling mill can effectively reduce the manufacturing process of weather-resistant bridge steel through its composition design to assist controlled rolling, controlled cooling + offline tempering. The yield-to-strength ratio can ensure that the yield-to-strength ratio of the finished steel is ≤0.85.

In addition to the above embodiments, the present invention may also have other embodiments. Any technical solution formed by equivalent substitution or equivalent transformation falls within the protection scope of the present invention.

Claims

A kind of low yield ratio weather-resistant bridge steel, characterized by: its chemical composition and mass percentage are as follows: C: 0.06% ~ 0.09%, Si: 0.15% ~ 0.30%, Mn: 1.51% ~ 1.65%, P: 0.009% ~0.015%, S≤0.002%, Nb: 0.020%~0.050%, Ti: 0.010%~0.020%, V: 0.010%~0.030%, Cu: 0.30%~0.40%, Ni: 0.30%~0.45%, Cr : 0.45% ~ 0.60%, Mo: 0.16% ~ 0.25%, Alt: 0.02% ~ 0.04%, the balance is Fe and inevitable inclusions.
A low yield ratio weather-resistant bridge steel according to claim 1, characterized in that its chemical composition and mass percentage are as follows: C: 0.06% ~ 0.07%, Si: 0.20% ~ 0.30%, Mn: 1.56% ~ 1.65%, P: 0.011%～0.015%, S≤0.002%, Nb: 0.020%～0.040%, Ti: 0.010%～0.020%, V: 0.010%～0.030%, Cu: 0.32%～0.36%, Ni: 0.35% to 0.45%, Cr: 0.45% to 0.60%, Mo: 0.16% to 0.20%, Alt: 0.02% to 0.04%, and the balance is Fe and inevitable inclusions.
A low yield ratio weather-resistant bridge steel according to claim 1, characterized in that its chemical composition and mass percentage are as follows: C: 0.07% ~ 0.09%, Si: 0.17% ~ 0.20%, Mn: 1.54% ~ 1.59%, P: 0.009%～0.015%, S≤0.002%, Nb: 0.030%～0.040%, Ti: 0.010%～0.020%, V: 0.015%～0.025%, Cu: 0.30%～0.35%, Ni: 0.30% to 0.40%, Cr: 0.45% to 0.55%, Mo: 0.20% to 0.25%, Alt: 0.02% to 0.04%, and the balance is Fe and inevitable inclusions.
A method for preparing low-yield-strength-ratio weather-resistant bridge steel, which is characterized in that: applied to any one of claims 1-3, including smelting, continuous casting, soaking, rolling, relaxation, cooling and off-line tempering:

The thickness of the continuous casting billet used is 150~320mm, and the continuous casting billet in the continuous casting process is heap-cooled for more than 24 hours; the continuous casting billet is heated to a center temperature of 1130~1230°C in the soaking process, and the temperature uniformity is less than 20°C. The heating time ≥Thickness of continuous casting slab×1min/mm;

The rolling process is to carry out rolling in the recrystallization zone and non-recrystallization zone of the descaled continuous casting billet. The cumulative deformation of the recrystallization zone rolling is more than 50% of the thickness of the continuous casting billet;

The intermediate billet is heated to 780-990°C, and the thickness is 2.0-4.0 times the thickness of the finished product. After reaching the temperature, the non-recrystallized area is rolled, and the final rolling temperature is controlled at 770-830°C;

In the relaxation process, the relaxation to initial cooling temperature is 730℃~760℃;

The cooling process is laminar flow cooling from the initial cooling temperature, the red return temperature is controlled at 400-600°C, and then air-cooled to room temperature;

In the offline tempering process, the tempering temperature is between 500 and 600°C, and it is kept at this temperature for 20 to 40 minutes. The holding time is proportional to the thickness of the finished product, and then it is naturally cooled to room temperature.
A method for preparing low-yield-ratio weather-resistant bridge steel according to claim 4, characterized in that: as the thickness of the continuous casting billet increases, the stack cooling time increases. For a 320mm continuous casting billet, the stack cooling time above 48h.
A method for preparing low-yield-ratio weather-resistant bridge steel according to claim 4, characterized in that: the thickness of the steel plate is 8 to 80 mm.
A method for preparing low-yield-ratio weather-resistant bridge steel according to claim 4, characterized in that: the steel plate yield strength is above 578MPa, the tensile strength is above 698MPa, the yield-strength ratio is ≤0.85, -40°C Akv is above 188J, and the extension Rate ≥ 20%; atmospheric corrosion resistance index I ≥ 6.5, I = I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 ( %Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu)2.
A method for preparing low-yield-ratio weather-resistant bridge steel according to claim 4, characterized in that: the metallographic structure of the steel plate is tempered bainite.