1. The hot-rolled strip steel for the carriage plate is characterized by comprising the following chemical components in percentage by mass: c: 0.05 to 0.1 percent, Si: 0.03-0.15%, Mn: 1.5-2.0%, P < 0.02%, S < 0.005%, Al: 0.02% -0.05%, Nb: 0.03-0.05%, Ti: 0.08-0.12%, Cr: 0.25 to 0.5 percent, less than or equal to 40ppm of N and the balance of Fe and inevitable impurities.

2. The hot-rolled strip steel for the carriage plate as claimed in claim 1, wherein the metallographic structure of the hot-rolled strip steel for the carriage plate is as follows by volume percent: ferrite is more than or equal to 90 percent and pearlite is less than or equal to 10 percent.

3. The hot-rolled steel strip for a carriage plate as claimed in claim 2, wherein the ferrite has a grain size of 3 μm to 5 μm.

4. The hot-rolled strip steel for the carriage plate as claimed in claim 1, wherein the thickness of the hot-rolled strip steel for the carriage plate is 3-14 mm.

5. A method for preparing a hot-rolled strip steel for a carriage plate according to any one of claims 1 to 4, wherein the method for preparing the hot-rolled strip steel comprises the following steps:

smelting and continuously casting the chemical components of the hot-rolled strip steel for the carriage plate according to any one of claims 1 to 4 to obtain a plate blank;

heating, rough rolling and finish rolling the plate blank to obtain a hot rolled plate;

and cooling the hot rolled plate to 580-620 ℃ by laminar flow, coiling, and slowly cooling to obtain the hot rolled strip steel for the carriage plate.

6. The preparation method of the hot-rolled strip steel for the carriage plate as claimed in claim 5, wherein the heating temperature of the slab is controlled to be 1200-1260 ℃ during heating, and the heating time is controlled to be 170-300 min.

7. The method for preparing the hot-rolled strip steel for the carriage plate as claimed in claim 5, wherein the rough rolling termination temperature is 980-1080 ℃.

8. The preparation method of the hot-rolled strip steel for the carriage plate as claimed in claim 5, wherein the finish rolling temperature is 810-880 ℃, and the final rolling speed of the last pass is controlled to be more than or equal to 3.5 m/s.

9. The method for preparing the hot-rolled strip steel for the carriage plate as claimed in claim 5, wherein the laminar cooling adopts a front section upper 2 lower 2 mode, and the ratio of the water amount of an upper collecting pipe to the water amount of a lower collecting pipe of the laminar cooling is 1: 1.2.

10. the preparation method of the hot-rolled strip steel for the carriage plate as claimed in claim 5, wherein the slow cooling time is 45-50 h.

Background

The steel for the carriage plate of the dump truck is mainly used for loading ores, sand and soil and the like, has severe use environment and needs good strength and smashing resistance. With continuous progress of steel market technology, the dimensional accuracy and the temperature control accuracy of steel materials are remarkably improved, but the research on the surface quality is not broken through, the problem of the scale of high-strength steel, especially thick scale, is a difficult problem troubling various steel mills, and with continuous increase of environmental protection working strength, the paint for coating the dumper is forcibly changed into water paint by oil paint, and because the water paint is poor in adhesion, the sensitivity to the surface quality of a steel plate is increased, so that the defect of craters generated by the scale falling and pressing in the process of flattening the surface of the steel plate needs to be solved while the strength of the steel for the carriage plate is ensured. Therefore, the hot rolled strip steel for the carriage plate in the prior art has the problems of low strength, poor smashing resistance, surface iron sheet peeling, powder falling and the like.

Therefore, how to develop a hot-rolled strip steel for a carriage plate and a preparation method thereof to solve the technical problems becomes a technical problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a hot-rolled strip steel for a carriage plate and a preparation method thereof, and the hot-rolled strip steel has the advantages of high strength, high wear resistance, smooth surface, and excellent plate shape and cold bending performance.

In order to achieve the above object, the present invention provides a hot-rolled steel strip for a car body panel, the hot-rolled steel strip for a car body panel comprising the following chemical components by mass: c: 0.05 to 0.1 percent, Si: 0.03-0.15%, Mn: 1.5-2.0%, P < 0.02%, S < 0.005%, Al: 0.02% -0.05%, Nb: 0.03-0.05%, Ti: 0.08-0.12%, Cr: 0.25% -0.5%, N: less than or equal to 40ppm, and the balance of Fe and inevitable impurities.

Further, the metallographic structure of the hot-rolled strip steel for the carriage plate comprises the following components in percentage by volume: ferrite is more than or equal to 90 percent and pearlite is less than or equal to 10 percent.

Further, the grain size of the ferrite is 3 to 5 μm.

Furthermore, the thickness of the hot-rolled strip steel for the carriage plate is 3-14 mm.

The invention also provides a preparation method of the hot-rolled strip steel for the carriage plate, which comprises the following steps:

smelting and continuously casting the chemical components of the hot-rolled strip steel for the carriage plate to obtain a plate blank;

heating, rough rolling and finish rolling the plate blank to obtain a hot rolled plate;

and cooling the hot rolled plate laminar flow to 580-620 ℃ and coiling to obtain the hot rolled strip steel for the carriage plate.

Further, in the heating process of the plate blank, the heating temperature is controlled to be 1200-1260 ℃, and the heating time is 170-300 min.

Further, the rough rolling termination temperature is 980-1080 ℃.

Furthermore, the finish rolling temperature is 810-880 ℃, and the final rolling speed of the last pass is controlled to be more than or equal to 3.5 m/s.

Further, the cooling adopts a front section upper 2 lower 2 mode, the ratio of the water amount of the laminar cooling upper collecting pipe to the water amount of the laminar cooling lower collecting pipe is 1: 1.2.

further, the slow cooling time is 45-50 h.

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

the invention provides a hot-rolled strip steel for carriage plates and a preparation method thereof, which adopts Nb-Ti-Cr element design, is matched with a rolling process, adopts Nb element reinforcement, and mainly aims to refine austenite grains and refine the structure of a finished product, wherein Ti element is a strong carbide forming element and can be combined with C to form TiC which is dispersed and distributed on a matrix, and the content of N element is controlled to increase the effective Ti content in the steel and reduce the content of large-particle TiN; the addition of the Cr element can improve the strength, hardness and wear resistance of the steel, has high oxidation resistance, can form stable fine carbide with the C element and is uniformly distributed in a steel matrix, so that the diffusion of the C element is slowed down, a layer of compact and firm oxidation film is formed on the surface layer, the further oxidation of the surface of a steel billet is prevented, the strength is improved, and the thickness of a thin iron skin is reduced. The carriage plate has the characteristics of high strength, high wear resistance, smooth surface, plate shape and excellent cold bending performance.

Drawings

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

FIG. 1 is a flow chart of a method for preparing a hot-rolled strip steel for a carriage plate according to an embodiment of the present invention;

fig. 2 is a curved surface profile of a hot-rolled strip steel for a car body panel according to embodiment 1 of the present invention;

fig. 3 is a metallographic structure diagram of a hot-rolled strip steel for a car body panel according to embodiment 1 of the present invention.

FIG. 4 is a metallographic structure drawing of a hot-rolled strip steel for a car body panel according to comparative example 3 of the present invention.

Detailed Description

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

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

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

The technical scheme provided by the embodiment of the invention aims to provide the hot-rolled strip steel for the carriage plate, and the general idea is as follows:

according to a typical embodiment of the invention, the hot-rolled strip steel for the carriage plate comprises the following chemical components in percentage by mass: c: 0.05 to 0.1 percent, Si: 0.03-0.15%, Mn: 1.5-2.0%, P < 0.02%, S < 0.005%, Al: 0.02% -0.05%, Nb: 0.03-0.05%, Ti: 0.08-0.12%, Cr: 0.25% -0.5%, N: less than or equal to 40ppm, and the balance of Fe and inevitable impurities.

The hot-rolled strip steel for the carriage plate with the chemical components is formed by optimizing the composition elements, and is based on the following principle:

c: 0.05-0.1 percent, C is the main element determining the room temperature structure and the mechanical property of the carbon steel, the tensile strength is increased along with the increase of the C content in the hypoeutectoid range, and the proper increase of the C content is beneficial to obtaining the pearlite structure. Too small content of C is not favorable for strength control, and too much is not favorable for welding performance.

Si: 0.03% -0.15%, the increase of Si content can improve the strength of ferrite matrix and promote the formation of ferrite structure, generally, the Si content is within 0.3%, which is beneficial to improving the strength of strip steel, the Si content is too much, which is easy to form red scale, and is not beneficial to surface quality control, and meanwhile, when the Si content is more than 1%, the material becomes brittle, and the plasticity, impact toughness and weldability of the material are reduced.

Mn: 1.5 to 2.0 percent, and more than 1.5 percent of Mn is added to improve the matrix strength, and the interlayer spacing of the pearlite sheet is refined, and the rust resistance and the weldability of the material are influenced by over high content.

P: less than or equal to 0.02 percent, S: less than or equal to 0.005 percent, P and S are easy to segregate in the continuous casting process, the material performance is adversely affected, and the content of P and S in the steel is strictly controlled as much as possible.

Ti: 0.08 to 0.12 percent of Ti element which is a strong carbide forming element can be combined with C to form TiC which is dispersed and distributed on a matrix and can refine grains. When the Ti content is too small, Ti preferentially combines with N, S element of steel grade to form large size TiN and Ti₄C₂S₂The strength is not improved, the cost is wasted due to excessive increase, and the toughness is not controlled easily.

Al: 0.02% -0.05%; aluminum is a commonly used deoxidizer in steel. A small amount of aluminum is added into the steel, so that crystal grains can be refined, and the impact toughness is improved; too much is detrimental to the welding performance.

Nb: 0.03-0.05%; adopting Nb element to strengthen, mainly aiming at refining austenite grains to refine the structure of a finished product; too high Nb content can generate delta ferrite or other brittle phases, reducing the toughness and processability of the material.

Cr: 0.25 to 0.5 percent of steel, and proper amount of Cr element is added to play a role of solid solution strengthening to promote the formation of pearlite structure, the addition of the Cr element can improve the strength, hardness and wear resistance of the steel, has high oxidation resistance, and can form stable fine carbide with the C element and be uniformly distributed in a steel matrix, so that the diffusion of the C element is slowed down, a layer of compact and fastened oxidation film is formed on the surface layer, the further oxidation of the surface of a billet is prevented, the strength is improved, and the thickness of a thin iron skin is reduced. Too much Cr is detrimental to plasticity and toughness.

N is less than or equal to 40ppm, N and Ti of the steel grade are preferentially combined to form high-melting-point large-size TiN particles, the content of N element is controlled to increase the effective Ti content in the steel and reduce the content of large-particle TiN, so that the precipitation amount of small-size TiC is increased to improve the strength;

finally, the embodiment of the invention adopts the Nb-Ti-Cr element design and is matched with the rolling process, so that the carriage plate has the characteristics of high strength, high wear resistance, smooth surface, excellent plate shape and excellent cold bending performance.

As an alternative embodiment, the metallographic structure of the hot-rolled strip steel for the carriage plate is as follows in percentage by volume: ferrite is more than or equal to 90 percent and pearlite is less than or equal to 10 percent.

As an alternative embodiment, the grain size of the ferrite is 3 μm to 5 μm. The grain size is refined, and the strength of the heat-producing rolled plate is ensured.

As an optional implementation mode, the thickness of the hot-rolled strip steel for the carriage plate is 3-14 mm.

The invention also provides a preparation method of the hot-rolled strip steel for the carriage plate, which comprises the following steps:

s1, smelting and continuously casting the chemical components of the hot-rolled strip steel for the carriage plate to obtain a plate blank;

s2, heating, rough rolling and finish rolling the plate blank to obtain a hot rolled plate;

in the step S2, in the step S,

heating the plate blank by using a heating furnace, wherein the discharging temperature is 1200-1260 ℃, and the in-furnace time is 170-300 min; the temperature range is favorable for remelting Nb/Ti composite strengthening elements, the tapping temperature is too low to be favorable for remelting alloy elements, and the tapping temperature is too high to be favorable for burning loss, surface quality and tissue control.

Controlling the rough rolling termination temperature RT2 to be 980-1080 ℃; the surface quality and the structure are adversely affected when the temperature is too high, and the rolling stability is not favorably affected when the temperature is too low;

controlling the finish rolling temperature FDT to be 810-880 ℃, and controlling the final frame rolling speed to be more than or equal to 3.5 m/s; when the finishing temperature is too high, a coarse ferrite structure can be formed, and when the finishing temperature is too low, the rolling force can be increased, and meanwhile, strip steel is rolled in a two-phase region, which is not beneficial to the control of the uniformity of the structure; when the rolling speed of the frame is less than 3.5m/s, the in-layer cooling rate is low, the structure is not easy to refine, and the iron sheet control is not easy to realize; different rolling temperatures are adopted for different thickness specifications, a lower finish rolling temperature (such as 830 ℃) within the range is adopted for the thickness of more than 7mm, so that the generation amount of the three-time iron sheet is reduced, sparse cooling is matched, the number of cold layer boiling water groups is increased, isolation between the cold layer and air is realized in the cold layer process, and the generation of the iron sheet is reduced;

s3, cooling the hot rolled plate laminar flow to 580-620 ℃ and coiling to obtain the hot rolled strip steel for the carriage plate.

In the step S3, in the step S,

the coiling temperature is 580-620 ℃, so that the effective precipitation amount of TiC can be improved, the TiC precipitation is increased, the residual stress of a steel plate is eliminated, the plate shape is improved, meanwhile, the contact between the strip steel and the atmosphere in the cold process of the isolation layer can be effectively realized, and the generation of three times of iron sheets is reduced; the thickness of the steel sheet of the strip steel is too thick due to overhigh coiling temperature, and meanwhile, the size of the precipitate is relatively large, and the precipitation of TiC is not facilitated due to overlow coiling temperature, so that the performance of the finished product is influenced;

laminar cooling adopts 2 modes under 2 on the anterior segment, and laminar cooling upper header water yield and lower header water yield ratio are 1: 1.2; the cooling rate is reduced through sparse cooling, and the eutectoid reaction of FeO is promoted to generate Fe₃O₄To increase Fe₃O₄The scale improves the adhesiveness and the ductility of the iron sheet, so that the iron sheet is thinner and the capability of coordinating deformation with the matrix is improved, thereby reducing the stripping degree. The water quantity of the upper collecting pipe and the water quantity of the lower collecting pipe in laminar cooling adopt 1: 1.2, the temperature uniformity of the plate coil is controlled, so that a uniform tissue in the thickness direction and a better plate shape are obtained;

and after the steel coil is off-line, the steel coil enters a slow cooling pit, and the slow cooling time is 45-50 h. The reason for the arrangement is that the slow cooling is beneficial to eliminating the internal stress of the plate coil and enhancing the precipitation of TiC, if the slow cooling time is too long, the inventory turnover and order delivery are affected, and if the slow cooling time is too short, the slow cooling effect cannot be achieved, and the internal stress of the plate coil cannot be well released;

in conclusion, the high-surface high-strength steel for automobile structures, which has the advantages of yield strength of more than 700MPa, tensile strength of more than 800MPa, total elongation after fracture of more than 20%, excellent plasticity and cold bending performance and good wear resistance, can be obtained by adopting an Nb-Ti-Cr component system, adopting niobium-titanium-chromium microalloying, taking precipitation strengthening and fine grain strengthening as main strengthening means and matching with the adjustment of hot continuous rolling temperature control and a cooling mode.

Hereinafter, a hot rolled steel strip for a car body panel and a method for manufacturing the same according to the present invention will be described in detail with reference to examples, comparative examples, and experimental data.

S1, examples 1-8 and comparative examples 1-3 adopt the chemical components shown in the table 1 respectively, the alloy components are proportioned according to the design in the table 1, smelting is carried out at the temperature of 1630 ℃, and then slabs are cast;

TABLE 1 Mass fractions of chemical components of examples and comparative examples

Group of	C	N	Si	Mn	P	S	Cr	As	Nb	Ti
											Example 1	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1
Example 2	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1
											Example 3	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1
Example 4	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1
											Example 5	0.0685	0.0035	0.0948	1.67	0.0095	0.0014	0.269	0.0015	0.0484	0.106
Example 6	0.0685	0.0035	0.0948	1.67	0.0095	0.0014	0.269	0.0015	0.0484	0.106
											Example 7	0.0685	0.0035	0.0948	1.67	0.0095	0.0014	0.269	0.0015	0.0484	0.106
Example 8	0.0685	0.0035	0.0948	1.67	0.0095	0.0014	0.269	0.0015	0.0484	0.106
											Comparative example 1	0.0691	0.0060	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1
Comparative example 2	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.6	0.0014	0.06	0.15
											Comparative example 3	0.0691	0.0028	0.0885	1.69	0.0082	0.0015	0.26	0.0014	0.0495	0.1

S2, heating the plate blank in the embodiment, heating the continuous casting plate blank at 1200-1250 ℃, keeping the furnace time for 170-300 min, rough rolling and finish rolling to obtain a hot rolled plate, wherein the finishing temperature of the rough rolling is 1000-1080 ℃, and the finishing temperature is 810-860 ℃;

s3, cooling the hot rolled plate laminar flow to 580-620 ℃ and coiling to obtain the hot rolled strip steel for the carriage plate.

The process parameters of each example and comparative example are specifically shown in table 2;

TABLE 2

Mechanical property tests were performed on each group of samples of the finished product, and the results are shown in table 3. The phase size and volume fraction data for the microstructures were obtained from observation measurements at one quarter of the plate thickness. The phase size and volume fraction data for the microstructures were obtained from observation measurements at one quarter of the plate thickness.

TABLE 3 mechanical Properties of examples and comparative examples before and after Heat treatment

From the data in table 3, it can be seen that:

in the comparative example 1, N is 60ppm and is larger than the range of the embodiment of the invention, and the rest of the examples are the same as the embodiment 1, because the content of the N element is higher, partial Ti is consumed, and the strength of the strip steel is influenced;

the content of Nb-Ti-Cr element in comparative example 2 is out of the range of the examples of the present invention, and the rest of examples 1, although the content of Nb-Ti-Cr is increased, the contribution to the strength as a whole is not linear, thus causing a waste of alloy cost.

In comparative example 3, the process of the example of the present invention was not used, and the winding temperature was too high as in example 1, which resulted in a relatively thick sheet iron and a significant decrease in strength.

The hot rolled strip steel for the carriage plate finally prepared in the embodiments 1-8 of the invention has the yield strength of more than 700MPa, the tensile strength of more than 800MPa, the total elongation after fracture of more than 20 percent, excellent plasticity and cold bending performance and good wear resistance.

Description of the attached figures 3-4:

FIG. 3 shows the microstructure of a quarter of the thickness of a plate in example 4 of the present invention, wherein the microstructure of the plate is: ferrite (93% by volume, 5 μm in average grain size) + lamellar pearlite structure (7% by volume);

FIG. 4 is a schematic view of the microstructure of comparative example 3 of the present invention at a quarter of the thickness of the plate. The microstructure of the plate is as follows: ferrite (96% by volume, 5 μm in average grain size) + lamellar pearlite structure (4% by volume);

as can be seen from fig. 3 to 4, compared with the comparative example, the hot-rolled strip steel for a car body panel provided in the example of the present invention has more uniform structure at each portion of the plate thickness after heat treatment, has no micro-strip structure, and has more excellent impact toughness and fatigue performance.

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

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

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