CN116287991A

CN116287991A - 780 MPa-grade hot rolled high-reaming steel with excellent welding performance and manufacturing method thereof

Info

Publication number: CN116287991A
Application number: CN202310189232.5A
Authority: CN
Inventors: 谷海容; 卢茜倩; 马聪; 刘阳; 崔磊; 张军; 计遥遥
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2023-02-27
Filing date: 2023-02-27
Publication date: 2023-06-23

Abstract

The invention discloses 780 MPa-grade hot rolled high-reaming steel with excellent welding performance and a manufacturing method thereof, belonging to the technical field of hot rolled acid-washing steel. The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance comprises the following chemical components in percentage by weight: 0.05 to 0.1 percent of C, 0 to 0.4 percent of Si, 1.2 to 1.6 percent of Mn, 0.1 to 0.2 percent of Mo, 0.02 to 0.04 percent of Nb, 0.1 to 0.2 percent of Ti and 0.1 to 0.4 percent of Cr; 0.0005 to 0.015 percent of B, and the balance of Fe and unavoidable impurities. The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, an object of the present invention is to provide 780 MPa-grade hot rolled high-hole-enlarging steel with excellent welding performance and a manufacturing method thereof, wherein the structure is controlled and treated through effective combination of the process and alloy elements, so that the excellent strength, plasticity and hole-enlarging property are matched, and meanwhile, the welding problem of the hole-enlarging steel is solved through low carbon, cr, B and Nb+Ti microalloy addition design, so that the high-hole-enlarging steel with excellent welding performance is manufactured.

Description

780 MPa-grade hot rolled high-reaming steel with excellent welding performance and manufacturing method thereof

Technical Field

The invention belongs to the technical field of hot-rolled pickled steel, and particularly relates to 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance and a manufacturing method thereof.

Background

The contradiction between the rapid development of the automobile industry and the environmental pollution caused by the discharge of the automobile industry is increasingly prominent, and the continuous rising of the oil price makes the call of consumers for low oil consumption increasingly rise, so that the oil consumption index becomes an important reference basis for the vehicle purchaser. The main way of realizing the light weight of the automobile is as follows: firstly, high-strength steel is used for replacing common steel, and the thickness of a steel plate is reduced, so that the quality of parts is reduced; secondly, the structural design is optimized, and structural optimization is carried out on parts such as an automobile body, a chassis, an engine and the like. The high-reaming steel is an important steel grade of advanced high-strength steel, has higher strength, elongation, excellent formability and flanging performance, can meet the requirements of complex-shaped automobile parts with high forming performance requirements, and is widely applied to automobile chassis, rear axle suspension, swing arms and the like. Therefore, high-strength high-reaming steel with excellent reaming performance is still the focus of research in the automobile industry.

At present, research on high-expansion steel is still focused on how to improve the strong plasticity and the reaming performance of the high-expansion steel, and the design process lacks the consideration of application performances such as weldability and the like. Because the connection mode of the automobile parts is mainly welding at present, developing high-reaming steel with excellent weldability has very important significance for promoting the light weight process of the automobile and improving the safety of the automobile.

Through searching, related technologies of high-reaming steel are disclosed in related patent documents, such as China patent application number: 202010896459.X, the invention is named 780MPa grade high surface ultra-high reaming steel and a manufacturing method thereof, and the chemical components in percentage by weight are as follows: 0.03 to 0.08 percent of C, less than or equal to 0.2 percent of Si, 0.5 to 2.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.08 percent of Al, less than or equal to 0.004 percent of N, 0.05 to 0.20 percent of Ti, 0.1 to 0.5 percent of Mo, less than or equal to 0.005 percent of Mg, less than or equal to 0.0030 percent of O, and the balance of Fe and other unavoidable impurities. The steel plate/coil obtained by the method has good surface quality, avoids red iron scales on the surface of strip steel, and improves the surface quality of acid-washed high-strength steel; the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 780MPa, the elongation A50 is more than or equal to 17%, the hole expansion rate is more than or equal to 80%, the good matching of high surface quality, high strength, high plasticity and ultrahigh hole expansion rate is realized, and the high-strength and thin-reducing composite material can be applied to the parts of chassis parts of passenger vehicles, such as control arms, auxiliary frames and the like, which need high strength and thin thickness.

For example, the Chinese patent application number is: 2018800448194A super-high strength hot rolled steel sheet with a tensile strength of 800MPa grade and a method for manufacturing the same, which have excellent surface quality, workability and weldability by using a headless rolling mode in a continuous casting-rolling direct-connecting process, and simultaneously remarkably reduce the material deviation in the width and length directions of the steel sheet.

Disclosure of Invention

1. Problems to be solved

The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, an object of the present invention is to provide 780 MPa-grade hot rolled high-hole-enlarging steel with excellent welding performance and a manufacturing method thereof, wherein the structure is controlled and treated through effective combination of the process and alloy elements, so that the excellent strength, plasticity and hole-enlarging property are matched, and meanwhile, the welding problem of the hole-enlarging steel is solved through low carbon, cr, B and Nb+Ti microalloy addition design, so that the high-hole-enlarging steel with excellent welding performance is manufactured.

2. Technical proposal

In order to solve the problems, the invention adopts the following technical scheme.

The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance comprises the following chemical components in percentage by weight: 0.05 to 0.1 percent of C, 0 to 0.4 percent of Si, 1.2 to 1.6 percent of Mn, 0.1 to 0.2 percent of Mo, 0.02 to 0.04 percent of Nb, 0.1 to 0.2 percent of Ti and 0.1 to 0.4 percent of Cr; 0.0005 to 0.015 percent of B, and the balance of Fe and unavoidable impurities.

Carbon is the most cost effective strengthening element in steel. Carbon plays a very important role in improving the strength of steel as a interstitial atom in steel, and has the greatest influence on the yield strength and tensile strength of steel. Therefore, the carbon content in the steel is at least 0.05% or more, otherwise the strength is difficult to reach 780 MPa. Meanwhile, the content of carbon cannot be too high, the content of carbon needs to be controlled to be less than or equal to 0.1%, otherwise, pearlite type tissues are easy to form, the strength of the material is influenced, and meanwhile, the welding performance of the material is also seriously influenced. Therefore, the invention controls the content of C within the range of 0.05-0.1%.

Si: silicon is the basic element in the steel of the invention, but not a critical element, which plays a part in partial deoxidation during the steelmaking process. Si content is too high, which is unfavorable for the welding performance of the steel plate, so the Si content in the steel is controlled to be 0-0.4%.

Mn: manganese is the most basic element in the steel of the invention. Manganese is an important element for expanding the austenite phase region, and can stabilize austenite, refine grains and delay the transformation from austenite to pearlite. In the invention, the manganese content is controlled to be 1.2% -1.6%.

Mo, molybdenum is one of the important elements in the steel of the present invention. Molybdenum can retard ferrite and pearlite transformation. Molybdenum also has a strong weld softening resistance. Since the main purpose of the invention is to ensure strength by precipitating enhanced bainite, which is easily softened after welding, the addition of a certain amount of molybdenum can effectively reduce the degree of welding softening. The addition of Mo element can improve the strength of the weld joint, and the weld joint is matched with Ti to be used with both high strength and high toughness, so that the welding performance of steel can be improved while good comprehensive mechanical properties are maintained. Therefore, the content of molybdenum should be controlled between 0.1% and 0.2%.

Nb: nb is the most effective element for inhibiting recrystallization and refining grains, and Nb dissolved in austenite can significantly improve hardenability of a steel sheet. Nb also combines with C, N in the steel to form fine precipitates, improving the strength of the steel. The Nb content is too low, the effect on grain refinement is not obvious, the free diffusion path of C atoms cannot be effectively reduced, and the C atoms cannot be fully diffused and distributed at a lower temperature; in addition, the Nb content is too low, the hardenability of the steel is reduced, and a melting zone and a heat affected zone are easy to soften during welding, so that the fatigue fracture phenomenon of parts is easy to occur at the welding position. The Nb content is too high, and the Nb is precipitated during continuous casting, so that the high-temperature plasticity of steel is obviously reduced, and a large number of cracks are easy to generate on the surface of a casting blank; in addition, too high Nb combines with C, thereby decreasing the stability of metastable austenite. Therefore, the Nb content is controlled within the range of 0.02-0.04%.

Ti is one of the important elements in the steel of the present invention. Ti is combined with N in steel to form TiN precipitate, so that austenite grains in a high temperature area are effectively prevented from growing; especially, during welding, the crystal grains in the heat affected zone and the melting zone can be effectively prevented from growing, the structure is thinned, the precipitate can also be pinned with dislocation to play a role in delaying the expansion of crack sources at the welding seam, and the toughness of the material is obviously improved, so that the welding performance is improved. The Ti content is too low, so that the structure of a heat affected zone and a melting zone cannot be effectively refined, and the mechanical property of a welding line zone is deteriorated; the Ti content is too high, and the excessive Ti is combined with C to form TiC particles, so that the stability of metastable austenite is reduced. Therefore, the Ti content is controlled within the range of 0.1-0.2%.

Cr is one of the important elements in the steel of the present invention. The addition of a small amount of chromium element is not used for improving the hardenability of steel, but is combined with B, so that the acicular ferrite structure is formed in a welding heat affected zone after welding, and the low-temperature toughness of the welding heat affected zone can be greatly improved. Because the final application part related to the invention is a chassis product of a passenger car, the low-temperature toughness of a welding heat affected zone is an important index. In addition to ensuring that the strength of the weld heat affected zone does not decrease too much, the low temperature toughness of the weld heat affected zone also meets certain requirements. Therefore, the content of chromium element is controlled within the range of 0.1-0.4%.

B is one of the important elements in the steel of the present invention. Boron in steel mainly gathers at the original austenite grain boundary, and inhibits the formation of proeutectoid ferrite; boron and chromium are combined to improve the structure of a welding heat affected zone, and a needle-shaped ferrite structure with good toughness is obtained. The boron element in the steel is controlled between 0.0005% and 0.015%.

As a further improvement of the invention, the yield strength of the high-reaming steel is more than or equal to 660MPa, the tensile strength is more than or equal to 780MPa, the elongation is more than or equal to 15 percent, and the reaming rate is more than or equal to 35 percent.

The invention relates to a manufacturing method of 780 MPa-grade hot rolled high-reaming steel with excellent welding performance, which comprises the following process flows: smelting, casting, hot rolling, cooling, coiling, pickling and straightening, wherein in the hot rolling process step, the initial rolling temperature is 1080-1200 ℃, the final rolling temperature is 850-950 ℃, and the steel plate is water-cooled to 450-580 ℃ after the final rolling is finished, and the water cooling speed is more than or equal to 30 ℃/s.

As a further improvement of the invention, rough rolling is carried out for 3-5 passes at the temperature of more than 1000 ℃ in the hot rolling process step, and the accumulated deformation of the rough rolling is more than or equal to 50%.

As a further improvement of the invention, the temperature of the intermediate billet after rough rolling is reduced to 900-950 ℃, and then 3-5 passes of finish rolling are carried out, and the accumulated deformation of the finish rolling is more than or equal to 70%.

As a further improvement of the invention, the running speed of the strip steel in the pickling process step is 30 m/min-100 m/min, and the pickling temperature is controlled within the range of 75-85 ℃.

As a further improvement of the invention, the withdrawal and straightening rate is controlled to be less than or equal to 2 percent, the strip steel is rinsed in the temperature range of 35-50 ℃, and the surface of the strip steel is dried and oiled, wherein the drying temperature is 120-140 ℃.

As a further improvement of the invention, the heating temperature of the casting blank or the cast ingot in the casting process step is more than or equal to 1230 ℃, and the heating time is 1-2 h.

3. Advantageous effects

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

(1) The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance has relatively low C content, so that excellent welding performance can be ensured when a user uses the steel; and adding a small amount of silicon to inhibit and reduce cementite formation, reducing the unrecrystallized temperature, obtaining fine and uniform original austenite grains, and finally obtaining bainite with uniform tissues. The addition of a certain amount of manganese is mainly used for stabilizing austenite, while molybdenum greatly delays ferrite and pearlite transformation and promotes bainite transformation. The Nb+Ti microalloy has the advantages of refining the austenite grain size, improving the strong plasticity of the material and improving the low-temperature toughness of a welding heat affected zone. The comprehensive performance of the precipitation strengthening bainite structure is between ferrite and martensite, and the precipitation strengthening bainite structure has better strength, plasticity and hole expansibility matching. And a small amount of anti-welding softening elements such as Mo, cr, B and the like are added, and the combination of Cr and B is beneficial to forming acicular ferrite structures in a welding heat affected zone after welding, so that the low-temperature toughness of the welding heat affected zone can be greatly improved.

(2) The method for manufacturing 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance has the advantages that the manufactured high-strength high-reaming steel has excellent strength, plasticity and toughness matching, and simultaneously has excellent reaming performance and welding performance, can be applied to parts such as automobile chassis, girders and wheels which need high strength thinning and complex forming, and has good application prospect.

(3) According to the method for manufacturing 780 MPa-grade hot rolled high-reaming steel with excellent welding performance, provided by the invention, after finishing rolling, the high water cooling speed is adopted, and the water is quickly cooled to the coiling temperature. If the cooling speed is slower after rolling, the austenite deformed inside the steel plate can finish the recrystallization process in a short time, and the austenite grains grow. When bainite transformation occurs in the subsequent cooling process, coarse bainitic ferrite grains are formed, which is disadvantageous to the strength of the steel sheet.

(4) The invention relates to a method for manufacturing 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance, which aims to obtain 780 MPa-grade hot-rolled acid-washed high-reaming steel with best matching strength, plasticity and reaming performance. The coiling temperature needs to be strictly controlled, when the coiling temperature is more than or equal to 580 ℃, the precipitation strengthening of the bainite structure is enhanced, so that the difference between ferrite and bainite strength is overlarge, and the hole expansion rate is reduced. When the coiling temperature is less than or equal to 450 ℃, the structure is converted into martensite, so that the strength is too high, and the elongation and the hole expansion rate are reduced.

Drawings

FIG. 1 is a photograph of a typical scanning structure of hot rolled pickled high-hole-enlarging steel according to example 1 of the present invention;

FIG. 2 is a photograph of a typical scanning structure of hot rolled pickled high-hole-enlarging steel according to example 2 of the present invention;

FIG. 3 is a photograph of a typical scanning structure of hot rolled pickled high-hole-enlarging steel according to example 4 of the present invention.

Detailed Description

For a further understanding of the present invention, the present invention will be described in detail with reference to the drawings.

In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

The following describes the embodiments of the present invention in further detail by way of examples of implementation.

Example 1

The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance comprises the following chemical components in percentage by weight: 0.05 to 0.1 percent of C, 0 to 0.4 percent of Si, 1.2 to 1.6 percent of Mn, 0.1 to 0.2 percent of Mo, 0.02 to 0.04 percent of Nb, 0.1 to 0.2 percent of Ti and 0.1 to 0.4 percent of Cr; 0.0005 to 0.015 percent of B, and the balance of Fe and unavoidable impurities. Specifically, the high-reaming steel in the embodiment comprises the following chemical components in percentage by weight: 0.063% of C, 0.35% of Si, 1.5% of Mn, 0.15% of Mo, 0.035% of Nb, 0.15% of Ti and 0.4% of Cr; 0.0008% of B, and the balance of Fe and unavoidable impurities.

The relatively low C content adopted in the embodiment can ensure that a user has excellent weldability during use; and adding a small amount of silicon to inhibit and reduce cementite formation, reducing the unrecrystallized temperature, obtaining fine and uniform original austenite grains, and finally obtaining bainite with uniform tissues. The addition of a certain amount of manganese is mainly used for stabilizing austenite, while molybdenum greatly delays ferrite and pearlite transformation and promotes bainite transformation. The Nb+Ti microalloy has the advantages of refining the austenite grain size, improving the strong plasticity of the material and improving the low-temperature toughness of a welding heat affected zone. The comprehensive performance of the precipitation strengthening bainite structure is between ferrite and martensite, and the strength, plasticity and hole expansibility are well balanced. And a small amount of anti-welding softening elements such as Mo, cr, B and the like are added, and the combination of Cr and B is beneficial to forming acicular ferrite structures in a welding heat affected zone after welding, so that the low-temperature toughness of the welding heat affected zone can be greatly improved.

The yield strength of the high-reaming steel is more than or equal to 660MPa, the tensile strength is more than or equal to 780MPa, the elongation is more than or equal to 15%, and the reaming rate is more than or equal to 35%. Specifically, the yield strength of the high-hole-expansion steel in the embodiment is 720MPa, the tensile strength is 825MPa, the elongation is 19%, and the hole expansion rate is 36%.

The manufacturing method of 780 MPa-grade hot rolled high-reaming steel with excellent welding performance comprises the following process flows: smelting, casting, hot rolling, cooling, coiling, pickling and straightening, and smelting, refining and casting into casting blanks or cast ingots according to the chemical components, wherein the heating temperature of the casting blanks or cast ingots is more than or equal to 1230 ℃, and the heating time is 1-2 h. In the hot rolling process step of the embodiment, the initial rolling temperature is 1080-1200 ℃, the final rolling temperature is 850-950 ℃, and the steel plate is water-cooled to 450-580 ℃ after the final rolling is finished, and the water cooling speed is more than or equal to 30 ℃/s. After finishing the finish rolling, the rolling mill should be rapidly cooled to the coiling temperature at a high water cooling speed. If the cooling speed is slower after rolling, the austenite deformed inside the steel plate can finish the recrystallization process in a short time, and the austenite grains grow. When bainite transformation occurs in the subsequent cooling process, coarse bainitic ferrite grains are formed, which is disadvantageous to the strength of the steel sheet.

In order to obtain 780 MPa-grade hot-rolled and pickled high-reaming steel with best matching strength, plasticity and reaming performance. The coiling temperature needs to be strictly controlled, when the coiling temperature is more than or equal to 580 ℃, the precipitation strengthening of the bainite structure is enhanced, so that the difference between ferrite and bainite strength is overlarge, and the hole expansion rate is reduced. When the coiling temperature is less than or equal to 450 ℃, the structure is converted into martensite, so that the strength is too high, and the elongation and the hole expansion rate are reduced. For the above reasons, the coiling temperature needs to be controlled between 450 ℃ and 580 ℃. Based on the innovative components and technological design thought, the invention can obtain hot-rolled and pickled 780 MPa-grade bainite precipitation strengthening type high-reaming steel with excellent strength, plasticity and reaming performance.

In the hot rolling process step of the embodiment, rough rolling is carried out for 3-5 passes at the temperature of more than 1000 ℃, and the accumulated deformation of the rough rolling is more than or equal to 50%. And (3) reducing the temperature of the rough rolled intermediate blank to 900-950 ℃, and performing finish rolling for 3-5 passes, wherein the accumulated deformation of the finish rolling is more than or equal to 70%.

The running speed of the strip steel in the pickling process step is 30-100 m/min, and the pickling temperature is controlled within the range of 75-85 ℃. The withdrawal straightening rate is controlled to be less than or equal to 2 percent, the strip steel is rinsed in the temperature range of 35-50 ℃, and the surface of the strip steel is dried and oiled, wherein the drying temperature is 120-140 ℃.

Specifically, in this embodiment, the heating temperature of the cast slab or ingot is 1230 ℃, and the heating time is 1.3h. In the hot rolling process step of this example, the start rolling temperature is 1089 ℃, the finish rolling temperature is 865 ℃, the steel sheet is water-cooled to 450 ℃ to 580 ℃ after finish rolling, the water cooling speed is 35 ℃/s, and the coiling temperature is 487 ℃. The pickling speed of the strip steel is 95m/min, and the pickling temperature is 79 ℃.

TABLE 1 chemical Components (percent by mass) of examples 1-4 of the present invention

Examples	C	Si	Mn	Mo	Nb	Ti	Cr	B	P	S	Als
													1	0.063	0.35	1.5	0.15	0.035	0.15	0.40	0.008	0.011	0.0020	0.046
2	0.081	0.25	1.3	0.10	0.025	0.12	0.39	0.005	0.013	0.0019	0.038
												3	0.083	0.30	1.4	0.13	0.031	0.13	0.35	0.006	0.009	0.0016	0.035
4	0.092	0.25	1.6	0.13	0.025	0.11	0.29	0.005	0.009	0.0018	0.029

TABLE 2 Process parameters for examples 1-4 of the invention

TABLE 3 mechanical Properties of examples 1 to 4 of the invention

As can be seen from fig. 1 to 3, the microstructure of the steel sheet of the present invention is ferrite + fine bainite. As shown in Table 3, the invention can manufacture 780 MPa-grade hot-rolled and pickled high-strength high-reaming steel, the yield strength of the steel is more than or equal to 660MPa, the tensile strength is more than or equal to 780MPa, the elongation is more than or equal to 15%, the reaming ratio is more than or equal to 35%, the excellent strength, plasticity and reaming matching performance are shown, and the steel is particularly suitable for parts such as control arms and the like which need high-strength thinning and reaming flanging forming, and has wide application prospect.

Example 2

The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance basically keeps the same as the embodiment 1, and the difference is that the high-reaming steel in the embodiment comprises the following chemical components in percentage by weight: 0.081% of C, 0.25% of Si, 1.3% of Mn, 0.10% of Mo, 0.025% of Nb, 0.12% of Ti and 0.39% of Cr; b0.0005%, the balance being Fe and unavoidable impurities. Wherein the yield strength of the high-reaming steel is 668MPa, the tensile strength is 850MPa, the elongation is 18%, and the hole expansion rate is 53%.

In this example, the heating temperature of the cast slab or ingot was 1230℃and the heating time was 1.25 hours. In the hot rolling process step of this example, the initial rolling temperature is 1091 ℃, the final rolling temperature is 890 ℃, the steel plate is water-cooled to 450 ℃ to 580 ℃ after the final rolling is finished, the water cooling speed is 47 ℃/s, and the coiling temperature is 522 ℃. The pickling speed of the strip steel is 63m/min, and the pickling temperature is 76 ℃.

Example 3

The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance basically keeps the same as the embodiment 1, and the difference is that the high-reaming steel in the embodiment comprises the following chemical components in percentage by weight: 0.083% of C, 0.30% of Si, 1.4% of Mn, 0.13% of Mo, 0.031% of Nb, 0.13% of Ti and 0.35% of Cr; 0.0006% of B, and the balance of Fe and unavoidable impurities. Wherein the yield strength of the high-reaming steel is 811MPa, the tensile strength is 789MPa, the elongation is 21%, and the hole expansibility is 48%.

In this example, the heating temperature of the cast slab or ingot was 1230℃and the heating time was 1.92 hours. In the hot rolling process step of this example, the start rolling temperature is 1102 ℃, the finish rolling temperature is 892 ℃, the steel plate is water-cooled to 450 ℃ to 580 ℃ after finish rolling, the water cooling speed is 60 ℃/s, and the coiling temperature is 568 ℃. The pickling speed of the strip steel is 76m/min, and the pickling temperature is 85 ℃.

Example 4

The 780 MPa-grade hot rolled high-reaming steel with excellent welding performance basically keeps the same as the embodiment 1, and the difference is that the high-reaming steel in the embodiment comprises the following chemical components in percentage by weight: 0.092% of C, 0.25% of Si, 1.6% of Mn, 0.13% of Mo, 0.025% of Nb, 0.11% of Ti and 0.29% of Cr; b0.0005%, the balance being Fe and unavoidable impurities. Wherein the yield strength of the high-reaming steel is 786MPa, the tensile strength is 901MPa, the elongation is 22%, and the reaming ratio is 45%.

In this example, the heating temperature of the cast slab or ingot was 1230℃and the heating time was 1.63h. In the hot rolling process step of this example, the start rolling temperature is 1153 ℃, the finish rolling temperature is 926 ℃, the steel plate is water-cooled to 450 ℃ to 580 ℃ after finish rolling, the water cooling speed is 53 ℃/s, and the coiling temperature is 563 ℃. The pickling speed of the strip steel is 35m/min, and the pickling temperature is 81 ℃.

The examples of the present invention are merely for describing the preferred embodiments of the present invention, and are not intended to limit the spirit and scope of the present invention, and those skilled in the art should make various changes and modifications to the technical solution of the present invention without departing from the spirit of the present invention.

Claims

1. 780 MPa-grade hot rolled high-reaming steel with excellent welding performance is characterized by comprising the following chemical components in percentage by weight: 0.05 to 0.1 percent of C, 0 to 0.4 percent of Si, 1.2 to 1.6 percent of Mn, 0.1 to 0.2 percent of Mo, 0.02 to 0.04 percent of Nb, 0.1 to 0.2 percent of Ti and 0.1 to 0.4 percent of Cr; 0.0005 to 0.015 percent of B, and the balance of Fe and unavoidable impurities.

2. The 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance according to claim 1, wherein the yield strength of the high-reaming steel is more than or equal to 660MPa, the tensile strength is more than or equal to 780MPa, the elongation is more than or equal to 15%, and the reaming rate is more than or equal to 35%.

3. The method for manufacturing 780 MPa-grade hot rolled high-reaming steel with excellent welding performance according to claim 1 or 2, comprising the following process steps: smelting, casting, hot rolling, cooling, coiling, pickling and straightening, wherein in the hot rolling process step, the initial rolling temperature is 1080-1200 ℃, the final rolling temperature is 850-950 ℃, and the steel plate is water-cooled to 450-580 ℃ after the final rolling is finished, and the water cooling speed is more than or equal to 30 ℃/s.

4. The method for producing 780 MPa-grade hot-rolled high-reamed steel excellent in weldability according to claim 3, wherein the hot-rolling process step is performed with rough rolling of 3 to 5 passes at 1000 ℃ or higher and the cumulative deformation of the rough rolling is not less than 50%.

5. The method for producing 780MPa grade hot rolled high hole expansion steel with excellent welding performance according to claim 4, wherein the intermediate billet after rough rolling is cooled to 900-950 ℃ and then finish rolled for 3-5 passes, and the accumulated deformation of the finish rolling is not less than 70%.

6. The method for manufacturing 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance according to claim 3, wherein the running speed of the strip steel in the pickling process step is 30 m/min-100 m/min, and the pickling temperature is controlled within the range of 75 ℃ to 85 ℃.

7. The method for producing 780 MPa-grade hot-rolled high-reaming steel with excellent welding performance according to claim 3, wherein the withdrawal straightening rate is controlled to be less than or equal to 2%, the strip steel is rinsed in a temperature range of 35 ℃ to 50 ℃, and the surface of the strip steel is dried and oiled, wherein the drying temperature is 120 ℃ to 140 ℃.

8. The method for producing 780 MPa-grade hot-rolled high-reamed steel excellent in weldability according to any one of claims 3 to 7, wherein the heating temperature of the cast slab or ingot in the casting process step is not less than 1230 ℃, and the heating time is 1h to 2h.