Method for manufacturing high surface quality 980mpa grade steel sheet in a headless mode

Abstract

The application relates to a preparation method of a 980MPa-grade steel plate with high surface quality in a headless mode, and belongs to the technical field of steel preparation; the method comprises the following steps: heating and descaling a casting blank; rolling the casting blank after the heating and descaling, so as to obtain a strip steel, wherein the rolling comprises finish rolling, and the inlet temperature of the finish rolling is 1180-1220 DEG C; coiling the strip steel, so as to obtain a 980MPa-grade steel plate; by controlling the inlet temperature of the finish rolling, the generation of iron oxide scale can be reduced, the iron scale is prevented from being exploded, the final iron scale pressing-in defect is reduced, and the surface quality of the 980MPa-grade steel plate is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel production, in particular to a method for preparing 980MPa grade martensite steel with high surface quality in a no-head mode. BACKGROUND

[0002] The no-head rolling technology can avoid the problems of low rolling mill operation rate and difficult to guarantee the quality of the head and tail of the steel caused by frequent steel biting, steel throwing and rolling speed changing in the traditional block rolling mode, and the product quality and precision have also been greatly improved. However, in the no-head rolling mode of the continuous casting and rolling short process, the rolling mill is in a high temperature state for a long time due to the limitation of the casting speed, and the surface of the hot-rolled steel coil is prone to iron oxide scale indentation defects, especially the high strength grade steel is more prone to oxidation defects.

[0003] When producing 980MPa grade steel plate in a no-head mode, flaky or powdery iron oxide scale peeling and a large number of iron scale indentation defects are prone to occur, which affects the surface quality. SUMMARY

[0004] The present application provides a method for preparing 980MPa grade steel plate with high surface quality in a no-head mode to improve the surface quality of 980MPa grade steel plate.

[0005] The present application provides a method for preparing 980MPa grade steel plate with high surface quality in a no-head mode, which comprises:

[0006] heating and descaling the casting blank;

[0007] rolling the casting blank after heating and descaling to obtain a strip, the rolling comprising finish rolling, and the inlet temperature of the finish rolling being 1180-1220℃;

[0008] coiling the strip to obtain 980MPa grade steel plate.

[0009] As an optional implementation, the composition of the casting blank comprises, by mass fraction: C: 0.15%-0.20%, Mn: 1.0%-1.6%, Si: 0.3%-0.5%, Alt: 0.03%-0.05%, Cr: 0.03%-0.05%, Ti: 0.01%-0.03%, and the balance being Fe and unavoidable impurities.

[0010] As an optional implementation, the casting speed of the heated continuous casting blank is 4-5m / min.

[0011] As an optional implementation, the heating is performed by a roller tunnel furnace, and the heating temperature is 1160-1200℃.

[0012] As an optional implementation, the temperature of the heating is 1165-1175 ℃.

[0013] As an optional implementation, the rough rolling stand H2 of the rolling adopts rolling lubrication.

[0014] As an optional implementation, side water spraying is arranged between the finishing rolling stands F3 and F4.

[0015] As an optional implementation, the outlet temperature of the finishing rolling is not lower than 820 ℃.

[0016] As an optional implementation, the outlet temperature of the finishing rolling is 820-840 ℃.

[0017] As an optional implementation, the temperature of the coiling is 150-250 ℃.

[0018] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0019] The method provided by the embodiments of the present application can reduce the generation of iron scale, avoid the occurrence of scale burst defects, and reduce the final scale indentation defects, thereby achieving the effect of improving the surface quality of the 980MPa grade steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the present application.

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0022] Figure 1 The flowchart of the method provided by the embodiments of the present application;

[0023] Figure 2 The surface morphology diagram of the steel plate provided by the embodiment 1 of the present application;

[0024] Figure 3 The surface morphology diagram of the steel plate provided by the embodiment 2 of the present application;

[0025] Figure 4 The surface morphology diagram of the steel plate provided by the embodiment 3 of the present application;

[0026] Figure 5A surface morphology map of a steel plate provided for Comparative Example 1 of the present application;

[0027] Figure 6 A surface morphology map of a steel plate provided for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0029] Unless otherwise specifically indicated, all the various raw materials, reagents, instruments and equipment and the like used in the present application can be purchased from the market or can be prepared by existing methods.

[0030] Under the endless rolling mode of the continuous casting and rolling short process, due to the limitation of the casting speed, the roll is in a high temperature state for a long time, and the surface of the hot-rolled steel coil is prone to appear iron oxide scale indentation defects, especially the high-strength grade steel is more prone to oxidation defects. When producing 980MPa grade steel plate under the endless mode, it is easy to appear surface iron oxide scale flaky or powdery peeling and a large number of scale indentation defects, which affect the surface quality.

[0031] The applicant intends to improve the surface quality of 980MPa grade martensitic steel under the endless mode. After micro-mechanism analysis and process adjustment of the 980MPa grade martensitic steel, a method for solving the iron oxide scale indentation and peeling defects is provided, and the process route is: molten steel-continuous casting-roller tunnel furnace-high pressure descaling HSB-large reduction rough rolling H0-H1-H2-induction heating device IH-high pressure descaling FSB-precision rolling F1-F2-F3-F4-F5-laminar cooling-coiler; The specific process is as follows:

[0032] As shown in Figure 1 The embodiments of the present application provide a preparation method of 980MPa grade steel plate with high surface quality under endless mode, which comprises:

[0033] S1. Heating and descaling the casting blank;

[0034] In some embodiments, the composition of the casting blank includes, in mass fraction: C: 0.15% to 0.20%, Mn: 1.0% to 1.6%, Si: 0.3% to 0.5%, Alt: 0.03% to 0.05%, Cr: 0.03% to 0.05%, Ti: 0.01% to 0.03%, and the balance of Fe and unavoidable impurities.

[0035] Due to the high-temperature rolling process of the billet, the C element is oxidized into a gaseous state and diffuses to the surface of the steel matrix, causing the blistering of the iron scale to increase the stress of the scale, resulting in the explosion of the scale defect into the matrix. Therefore, the C element in the steel should be controlled at the lower limit of the composition design during smelting. Because the steel also contains a certain amount of Si and Mn elements, on the one hand, the increase of the Si element makes it difficult to remove the oxidized iron scale, resulting in the scale defect being pressed in, and on the other hand, the high Si and Mn cause the surface grains of the steel to produce grain boundary oxidation. After the grain boundary is oxidized, the C element is more likely to diffuse from the matrix to the oxidized iron scale, increasing the explosion of the scale defect. Therefore, under the existing low-cost composition system, the present scheme avoids the surface scale pressing in and the explosion of the scale defect caused by excessive C element, Si and Mn element through fine control of the content of C, Si and Mn elements.

[0036] In some embodiments, the casting speed of the heated continuous casting billet is 4-5 m / min. The heating is carried out by a roller tunnel furnace, and the heating temperature is 1160-1200℃. Further, the heating temperature is 1165-1175℃.

[0037] By increasing the casting speed of the billet, reducing the high-temperature oxidation time of the tunnel furnace, and at the same time, reducing the temperature of the billet tunnel furnace, the degree of high-temperature oxidation is reduced, thereby reducing the thickness of the oxidized scale and the possibility of subsequent defects caused by pressing in.

[0038] S2. The heated and descaled billet is rolled to obtain a strip, and the rolling includes finish rolling, and the inlet temperature of the finish rolling is 1180-1220℃.

[0039] A suitable finish rolling temperature can reduce the phenomenon of surface scale pressing in and scale explosion of the final hot-rolled steel coil, especially for steel with relatively high C content, which is more sensitive to the finish rolling inlet temperature. When the finish rolling temperature exceeds 1230℃, the oxidized scale splashes, causing the scale to be pressed in. When the finish rolling inlet temperature is lower than 1180℃, it is difficult to ensure the finish rolling outlet temperature, and therefore it is difficult to prevent the increase of the scale pressing in defect. Therefore, the finish rolling inlet temperature is 1180-1220℃.

[0040] In some embodiments, the rough rolling mill H2 of the rolling and the finish rolling mills F1 and F2 of the rolling use rolling lubrication.

[0041] After the billet enters the three large reduction mills H0, H1 and H2 for continuous reduction, an intermediate billet is obtained. When the billet passes through the H2 rolling mill, rolling force fluctuation is prone to occur, the rolling mill is prone to wear, and scale pressing in defects occur on the surface of the strip. The same rule also applies when the billet is rolled in the finish rolling mills F1 and F2. Therefore, rolling lubrication is used in the rough rolling mill H2 and the finish rolling mills F1-F2 to avoid excessive wear of the rolling mill.

[0042] In some embodiments, side water spraying is provided between the finishing rolling stands F3 and F4.

[0043] It is found through the high temperature oxidation characteristics of the steel grade that the tendency of rapid growth of the scale is most likely to occur between the F3 and F4 stands. Therefore, side water spraying is used between F3-F4 to prevent the strip from being exposed to air oxidation between the stands.

[0044] In some embodiments, the finishing rolling exit temperature is not lower than 820°C. Further, the finishing rolling exit temperature is 820-840°C.

[0045] The finishing rolling exit temperature is controlled to be not lower than 820°C, which can ensure the austenite rolling in the finishing rolling zone, and the austenite is more uniform when controlled to be 820-840°C.

[0046] S3. The strip is coiled after the laminar cooling to obtain a 980MPa grade steel plate.

[0047] In some embodiments, the laminar cooling is performed by post-cooling, and the coiling temperature is 150-250°C.

[0048] The appropriate coiling temperature can reduce the defects of scale indentation and scale explosion on the surface of the final hot-rolled steel coil. In particular, the steel with relatively high C content is more sensitive to the finishing rolling entry temperature, and the coiling temperature affects the structure of the oxide scale. The higher the FeO content in the scale structure, the more likely the scale is to be pulverized, which is not conducive to the surface quality. It is found in actual production that the higher the coiling temperature, the lower the FeO content, and the better the scale adhesion. However, when the coiling temperature is higher than 250°C, the mechanical properties do not meet the requirements. When the coiling temperature is too low, lower than 150°C, the FeO content in the scale increases sharply, and the defects of scale pulverization and scale explosion increase significantly. Therefore, the coiling temperature is set to be 150-250°C.

[0049] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods in the following examples are not specified, and the methods are generally determined according to the national standards. If there is no corresponding national standard, the methods are determined according to the general international standards, conventional conditions, or the conditions recommended by the manufacturers.

[0050] Example 1

[0051] A method for preparing a 980MPa grade steel plate with high surface quality in a continuous rolling mode, the method comprising:

[0052] S1. Heating and descaling the cast slab;

[0053] S2. Rolling the cast slab after the heating and descaling to obtain a strip;

[0054] S3. coiling the strip to obtain a 980MPa grade steel plate.

[0055] The composition of the cast slab is as follows: C: 0.19%, Mn: 1.4%, Si: 0.3%, Alt: 0.035%, Cr: 0.045%, Ti: 0.02%, the balance being Fe and inevitable impurities. The casting speed of the cast slab is 4.5 m / min in the endless mode, the tunnel furnace heating temperature is 1170℃, no rolling lubrication is used in rough rolling H2 and finish rolling F1-F2; side water spraying is used in F3-F4. The finish rolling inlet temperature is 1200℃, and the finish rolling outlet temperature is controlled at 830℃. The interpass cooling uses the post-stage cooling, and the coiling temperature is controlled at 200℃.

[0056] Example 2

[0057] A method for preparing a 980MPa grade steel plate with high surface quality in the endless mode, the method comprising:

[0058] S1. heating and descaling the cast slab;

[0059] S2. rolling the cast slab after the heating and descaling to obtain a strip;

[0060] S3. coiling the strip to obtain a 980MPa grade steel plate.

[0061] The composition of the cast slab is as follows: C: 0.18%, Mn: 1.5%, Si: 0.45%, Alt: 0.05%, Cr: 0.04%, Ti: 0.023%, the balance being Fe and inevitable impurities. The casting speed of the cast slab is 4.6 m / min in the endless mode, the tunnel furnace heating temperature is 1180℃, rolling lubrication is used in rough rolling H2 and finish rolling F1-F2; side water spraying is used in F3-F4. The finish rolling inlet temperature is 1200℃, and the finish rolling outlet temperature is controlled at 825℃. The interpass cooling uses the post-stage cooling, and the coiling temperature is controlled at 180℃.

[0062] Example 3

[0063] A method for preparing a 980MPa grade steel plate with high surface quality in the endless mode, the method comprising:

[0064] S1. heating and descaling the cast slab;

[0065] S2. rolling the cast slab after the heating and descaling to obtain a strip;

[0066] S3. coiling the strip to obtain a 980MPa grade steel plate.

[0067] The composition of the casting blank is: C: 0.12%, Mn: 1.7%, Si: 0.03%, Alt: 0.034%, Cr: 0.045%, Ti: 0.028%, the balance being Fe and inevitable impurities in terms of mass percentage. The casting blank speed is 5 m / min in the endless mode, the tunnel furnace heating temperature is 1163℃, the rough rolling H2 and the finish rolling F1-F2 adopt rolling lubrication; F3-F4 adopts side water spraying. The finish rolling inlet temperature is 1184℃, and the finish rolling outlet temperature is controlled at 822℃. The layer cooling adopts the rear section cooling, and the coiling temperature is controlled at 248℃.

[0068] Comparative Example 1

[0069] A method for preparing a 980MPa grade steel plate with high surface quality in an endless mode, the method comprising:

[0070] S1. heating and descaling the casting blank;

[0071] S2. rolling the casting blank after the heating and descaling to obtain a strip;

[0072] S3. coiling the strip to obtain a 980MPa grade steel plate.

[0073] The composition of the casting blank is: C: 0.21%, Mn: 1.8%, Si: 0.5%, Alt: 0.045%, Cr: 0.025%, Ti: 0.015%, the balance being Fe and inevitable impurities in terms of mass percentage. The casting blank speed is 3.9 m / min in the endless mode, the tunnel furnace heating temperature is 1200℃, the rough rolling H2 and the finish rolling F1-F2 do not adopt rolling lubrication; F3-F4 adopts side water spraying. The finish rolling inlet temperature is 1210℃, and the finish rolling outlet temperature is controlled at 840℃. The layer cooling adopts the rear section cooling, and the coiling temperature is controlled at 300℃.

[0074] Comparative Example 2

[0075] A method for preparing a 980MPa grade steel plate with high surface quality in an endless mode, the method comprising:

[0076] S1. heating and descaling the casting blank;

[0077] S2. rolling the casting blank after the heating and descaling to obtain a strip;

[0078] S3. coiling the strip to obtain a 980MPa grade steel plate.

[0079] The composition of the casting blank is: C: 0.14%, Mn: 1.8%, Si: 0.7%, Alt: 0.042%, Cr: 0.020%, Ti: 0.018%, the balance being Fe and inevitable impurities, in terms of mass percentage. The casting blank speed in the endless mode is 4.1 m / min, the tunnel furnace heating temperature is 1200℃, the rough rolling H2 and the finish rolling F1-F2 do not use rolling lubrication; F3-F4 do not use side water spraying. The finish rolling inlet temperature is 1220℃, and the finish rolling outlet temperature is controlled at 815℃. The layer cooling uses the rear section cooling, and the coiling temperature is controlled at 107℃.

[0080] The steel plates provided by Examples 1 to 3 and Comparative Examples 1 to 2 are observed in morphology, and the results are shown in FIGS. 1 to 4. Figures 2 to 6 As can be seen from the figures, the surface oxide scales of Examples 1 and 2 are relatively dense, and the scale indentation and scale burst phenomena are not obvious. Example 1 has slight scale indentation because lubrication rolling is not used. Example 2 has slightly severe scale burst because the finish rolling inlet temperature is at the upper limit (i.e. 1220℃), and the coiling temperature is at the lower limit (i.e. 150℃). Comparative Example 1 has severe scale indentation because the casting blank speed is lower than 4 m / min, the Si content is more than 0.5%, and lubrication rolling is not used. Comparative Example 2 has severe scale burst because the casting blank speed is lower than 4 m / min, the finish rolling inlet temperature is higher than 1220℃, and the coiling temperature is lower than 150℃, and the surface oxide scale is easy to be pulverized. The surface oxide scale of Example 3 is the densest, and the surface quality is the best.

[0081] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the described range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0082] In the present application, the orientation words such as "upper" and "lower" are specifically the directions of the drawing surface in the drawings, unless otherwise stated. In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but are not limited to".

[0083] In this document, relational terms such as "first" and "second", and the like can be used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. In this document, the term "and / or" is used to associate one or more items together, e.g., A and / or B can mean A alone, A and B together, or B alone. In this document, the term "at least one of" is used to associate one or more items together, e.g., at least one of A and B can mean A alone, B alone, or A and B together. In this document, the term "one or more of" is used to associate one or more items together, e.g., one or more of A and B can mean A alone, B alone, or A and B together. In this document, the term "at least one of", "one or more of", or the like, can be used to associate one or more items together, including any combination of single items or multiple items, e.g., at least one of a, b, or c, or at least one of a, b, and c, can mean a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c.

[0084] The foregoing is merely illustrative of the principles of this application and various modifications can be made by those skilled in the art without departing from the scope and spirit of the application. The above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the application should, therefore, be determined not with reference to the above description, but instead with reference to the appended claims, along with their full scope of equivalents.

Claims

1. A method of manufacturing a 980 MPa grade martensitic steel sheet with high surface quality in a headless mode, characterized in that, The method comprises: heating and descaling the cast slab; rolling the heated and descaled cast slab to obtain a strip, the rolling comprising finishing rolling, and the inlet temperature of the finishing rolling being 1180-1220 DEG C; coiling the strip to obtain a 980MPa grade steel plate; the composition of the cast slab comprises, by mass fraction: C: 0.15-0.20%, Mn: 1.0-1.6%, Si: 0.3-0.5%, Alt: 0.03-0.05%, Cr: 0.03-0.05%, Ti: 0.01-0.03%, and the balance being Fe and inevitable impurities; the casting speed of the heated continuous cast slab is 4-5 m / min; the rolling is continuous casting and rolling without head; the rough rolling stand H2 and the finishing rolling stands F1 and F2 of the rolling adopt rolling lubrication; side water spraying is arranged between the finishing rolling stands F3 and F4 of the rolling; the coiling temperature is 150-250 DEG C.

2. The method of producing a 980 MPa grade martensitic steel plate with high surface quality in a headless mode according to claim 1, characterized in that, the heating is performed by using a roller tunnel furnace, and the heating temperature is 1160-1200 DEG C.

3. The method of manufacturing a 980 MPa grade martensitic steel sheet with high surface quality in a headless mode according to claim 2, characterized in that, the heating temperature is 1165-1175 DEG C.

4. The method of producing a 980 MPa grade martensitic steel plate with high surface quality in a headless mode according to claim 1, characterized in that, the outlet temperature of the finishing rolling is not lower than 820 DEG C.

5. The method of manufacturing a 980 MPa grade martensitic steel sheet with high surface quality in a headless mode according to claim 4, characterized in that, the outlet temperature of the finishing rolling is 820-840 DEG C.

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