Method for reducing edge cracks of 1300Mpa square pipe steel in cold rolling process

Abstract

The invention relates to a method for reducing edge cracks of steel for a 1300Mpa square tube in the cold rolling process, and belongs to the technical field of steelmaking processes. The method comprises the following steps: obtaining a plate blank with set chemical components; the plate blank is heated, and then high-pressure water descaling is conducted; rough rolling is conducted on the plate blank subjected to high-pressure water descaling, and an intermediate blank is obtained; the intermediate billet is subjected to finish rolling, and semi-finished strip steel is obtained; carrying out laminar cooling on the semi-finished strip steel, and then coiling; slowly cooling the coiled semi-finished strip steel; and carrying out cold rolling on the slowly cooled semi-finished strip steel to obtain finished strip steel. According to the method, on the basis of the characteristics of a steel grade component system of the steel for the 1300MPa square pipe, the edge cracking problem of the steel for the 1300MPa square pipe in the cold rolling process is effectively solved by accurately controlling all links such as a heating process, a descaling process, a rolling process and a cooling process, and the quality and the yield of the steel are improved.

Description

Technical Field

[0001] The present application relates to the technical field of steelmaking technology, and in particular to a method for reducing edge cracking during the cold rolling process of 1300Mpa square tube steel. Background Art

[0002] The use of lightweight materials in automobile lightweight technology is the current mainstream. On the premise of ensuring the safety performance of the bus, the use of high-strength square tubes to replace ordinary products can significantly reduce the weight of the entire bus, which is the development trend of high-end boutique buses in the future.

[0003] The hot rolling production process of high-strength square tube steel faces many challenges. The key issue affecting the product yield is the frequent occurrence of edge cracks during the cold rolling process of 1300Mpa square tube steel. The edge cracking rate is as high as 90%, and the head and tail are more serious than the middle part. The deepest edge crack can reach nearly 40mm. The occurrence of edge cracks can also easily induce strip breakage during the cold rolling process, damage the rollers, increase production costs, and extend the product promotion and certification cycle.

[0004] Shougang tackled the edge cracking problem of DP980 series steel and published a patent titled "A Method for Eliminating Cold-rolled Edge Cracks of Strip Steel". The focus is on controlling the amount of water sprayed on the side during the finishing process, so that the temperature difference between the middle and edge of the steel strip in the width direction is ≤50°C; the hot rolling process adopts a low-temperature coiling control idea to refine the MA island size; the hot-rolled strip is cold-rolled, and the cold rolling reduction rate is controlled to be ≤60%, which can achieve cold rolling edge crack control. However, field experimental tracking found that the above process adjustments have no obvious inhibitory effect on the cold rolling edge cracking problem of 1300Mpa square tube steel, and it is necessary to propose refined process means based on the characteristics of the steel composition system. Summary of the invention

[0005] The present application provides a method for reducing edge cracking during the cold rolling process of 1300Mpa square tube steel, so as to solve the following technical problem: how to reduce the edge cracking phenomenon occurring during the cold rolling process of 1300Mpa square tube steel.

[0006] The present application provides a method for reducing edge cracking during cold rolling of 1300Mpa square tube steel, the method comprising:

[0007] A slab with a set chemical composition is obtained;

[0008] The slab is heated and then descaled with high pressure water;

[0009] Rough rolling the slab after high-pressure water descaling to obtain an intermediate slab;

[0010] Finish rolling the intermediate billet to obtain a semi-finished steel strip;

[0011] laminar cooling the semi-finished steel strip and then coiling it;

[0012] Slowly cooling the semi-finished steel strip after coiling;

[0013] The semi-finished steel strip after slow cooling is cold rolled to obtain a finished steel strip.

[0014] Optionally, the set chemical composition of the slab includes, by mass fraction: C: 0.22% to 0.26%, Cr: 0.75% to 0.85%, Mn: 1.65% to 1.75%, Si: 0.35% to 0.45%, Nb+Ti: 0.05% to 0.07%, wherein Nb+Ti represents the sum of the contents of Nb and Ti.

[0015] Optionally, the total furnace time of the heating is 160 min to 200 min, and the heated furnace outlet temperature is 1230° C. to 1250° C.

[0016] Optionally, the water pressure of the high-pressure water descaling is ≥30Mpa.

[0017] Optionally, the rough rolling adopts a 1+5 rolling mode, the rough rolling mill R1 adopts 1 pass descaling, the rough rolling mill R2 adopts 1, 3, 4 and 5 passes descaling, and the thickness of the intermediate billet is 34 mm to 40 mm.

[0018] Optionally, the inlet temperature of the finishing rolling is 1050° C. to 1070° C., the final rolling temperature of the finishing rolling is 910° C. to 930° C., and the thickness of the semi-finished steel strip is 2.5 mm to 3 mm.

[0019] Optionally, the finishing rolling equipment comprises six finishing rolling stands F1 to F6, the cooling water opening ratio between the stands F1 to F3 is 50% to 80%, and the cooling water opening ratio between the stands F4 to F6 is 0% to 30%.

[0020] Optionally, the water pipes for laminar cooling are shielded at the edges to shut off the laminar cooling water at the edges.

[0021] Optionally, the coiling adopts a front-end cooling mode, and the cold water layer is not turned on for 100m at the head and tail.

[0022] Optionally, the coiling temperature is 730°C to 750°C.

[0023] Optionally, before the slow cooling, the temperature of the outer ring of the semi-finished steel strip is ≥ 600°C.

[0024] Optionally, the cold rolling reduction rate is 50% to 60%.

[0025] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0026] The present application provides a method for reducing edge cracking during cold rolling of 1300Mpa square tube steel, the method comprising: obtaining a slab with a set chemical composition; heating the slab, and then descaling it with high pressure water; rough rolling the slab after descaling it with high pressure water to obtain an intermediate slab; finishing rolling the intermediate slab to obtain a semi-finished strip; laminar cooling the semi-finished strip, and then coiling it; slow cooling the semi-finished strip after coiling; cold rolling the semi-finished strip after slow cooling to obtain a finished strip. Based on the characteristics of the steel grade component system of 1300Mpa square tube steel, by increasing the final rolling temperature, increasing the coiling temperature and performing slow cooling, the microstructure of the edge of the produced strip is ferrite and pearlite, and at the same time, combined with the process means of controlling the temperature drop of the edge too fast, there is no obvious difference in the cooling rate of the edge and the middle of the strip, avoiding the situation that the edge is cracked during the cold rolling process due to the rapid cooling of the edge to produce more hard phase structures, so that the cold rolling edge crack defect is effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0029] Figure 1 A schematic flow chart of a method for reducing edge cracking during the cold rolling process of 1300Mpa square tube steel provided in an embodiment of the present application.

[0030] Figure 2 The microstructure diagram of the edge of the hot coil provided as a comparative example of the present application.

[0031] Figure 3 This is a microstructure diagram of the edge of a hot coil provided in an embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0033] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0034] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0035] Figure 1 A schematic flow chart of a method for reducing edge cracking during cold rolling of 1300Mpa square tube steel provided in an embodiment of the present application;

[0036] like Figure 1 As shown, the embodiment of the present application provides a method for reducing edge cracking during cold rolling of 1300Mpa square tube steel, comprising:

[0037] S1. Obtaining a slab with a set chemical composition;

[0038] In some embodiments, the set chemical composition of the slab includes, by mass fraction: C: 0.22% to 0.26%, Cr: 0.75% to 0.85%, Mn: 1.65% to 1.75%, Si: 0.35% to 0.45%, Nb+Ti: 0.05% to 0.07%, wherein Nb+Ti represents the sum of the contents of Nb and Ti.

[0039] Controlling the chemical composition of the slab to meet standard requirements can reduce edge cracks caused by material problems.

[0040] The positive effects of controlling the C content to 0.22% to 0.26% are: ensuring the strength level of the steel and forming a martensitic structure after continuous quenching; too low a content leads to insufficient strength, and too high a content leads to deterioration of welding and forming properties. For example, the C content can be 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, etc.

[0041] The positive effect of controlling the Cr content to 0.75% to 0.85% is that a high Cr component system is used to ensure the hardenability during the cold rolling process. If the hardenability is too low, martensite cannot be obtained at a slow cooling rate, and there are requirements for the critical cooling rate. If the Cr content is too high, the plasticity will decrease and the alloy cost will increase. For example, the Cr content can be 0.75%, 0.77%, 0.81%, 0.83%, 0.85%, etc.

[0042] The positive effect of controlling the Mn content to 1.65% to 1.75% is that Mn is a solid solution strengthening element, which dissolves in austenite during heating in the critical region, which is beneficial to improving the hardenability of austenite, obtaining martensite structure and improving the strength of martensite. For example, the Mn content can be 1.65%, 1.67%, 1.69%, 1.72%, 1.75%, etc.

[0043] The positive effect of controlling the Si content to 0.35% to 0.45% is that Si is a solid solution strengthening element that can improve hardenability, is conducive to obtaining fine and uniformly distributed martensite, and can also expand the critical zone range. However, a high Si content is not good for welding performance; but if the Si content is too low, the solid solution strengthening effect is not good, affecting the hardenability. For example, the Si content can be 0.35%, 0.37%, 0.39%, 0.42%, 0.45%, etc.

[0044] Nb+Ti represents the sum of the contents of Nb and Ti. The positive effect of controlling the content of Nb+Ti to 0.05% to 0.07% is: adding trace alloy elements for precipitation strengthening. Too low strength reduces, too high cost increases, and affects plasticity. Exemplarily, the content of Nb+Ti can be 0.05%, 0.055%, 0.06%, 0.07%, etc.

[0045] S2, heating the slab, and then descaling it with high-pressure water;

[0046] Heating is to make the slab reach a temperature suitable for rolling, improve its plasticity and reduce rolling force. At the same time, heating also helps to remove moisture and impurities on the surface of the slab. High-pressure water descaling is carried out after heating to remove iron oxide scale and other impurities on the surface of the slab to prevent them from being pressed into the steel during rolling and forming defects.

[0047] In some embodiments, the total furnace time of the heating is 160 min to 200 min.

[0048] The positive effect of controlling the total furnace time of the heating to be 160min to 200min is to ensure that Ti and Nb precipitated on the surface during the continuous casting process are completely dissolved. For example, the total furnace time of the heating can be 160min, 165min, 170min, 180min, 200min, etc.

[0049] In some embodiments, the heated furnace temperature is 1230°C to 1250°C.

[0050] The positive effect of controlling the heating furnace temperature to 1230°C to 1250°C is that since Cr+Si>1% in the slab and Cr / Si is about 2, the enrichment of Cr surface layer can inhibit the high temperature oxidation of Si element to a certain extent, so a higher furnace temperature is adopted. Exemplarily, the furnace temperature can be 1230°C, 1235°C, 1240°C, 1245°C, 1250°C, etc.

[0051] In some embodiments, the water pressure of the high-pressure water descaling is ≥30 MPa.

[0052] The positive effect of controlling the water pressure of high-pressure water descaling to ≥30Mpa: the Si content of the steel grade is high, which can effectively remove the influence of the furnace iron olivine phase and ensure the surface quality of the steel plate. For example, the water pressure of high-pressure water descaling can be 30Mpa, 31Mpa, 32Mpa, 33Mpa, 34Mpa, etc.

[0053] S3, rough rolling the slab after high-pressure water descaling to obtain an intermediate slab;

[0054] Rough rolling is the initial plastic deformation of the slab to reduce its thickness and width and make its shape closer to the final product.

[0055] In some embodiments, the rough rolling adopts a 1+5 rolling mode, the rough rolling mill R1 adopts 1 pass descaling, the rough rolling mill R2 adopts 1, 3, 4 and 5 passes descaling, and the thickness of the intermediate billet is 34 mm to 40 mm.

[0056] In some embodiments, to enhance the descaling effect, a coil box is used after rough rolling.

[0057] The coil box is mainly used in the hot rolling mill, placed between the roughing mill and the finishing mill. The intermediate billet rolled out by the roughing mill is coiled into a coil using the coreless coiling method, and then immediately unrolled in the reverse direction, cut the head and tail, and sent to the finishing mill to achieve unrolling and rolling. This technology can solve the problem of too large a temperature difference between the head and tail of the rolled piece caused by the long distance between the roughing mill and the finishing mill, a large temperature drop of the intermediate billet of the hot-rolled strip, uneven temperature over the entire length, a large load on the finishing mill, and inconsistent mechanical properties and thickness of the finished strip. The coreless coiling method is used to coil the strip head, so that the higher temperature strip head is kept warm in the center of the coil box, and then unrolled, and the lower temperature strip tail is turned into the strip head and sent to the finishing mill for rolling.

[0058] The positive effects of controlling the thickness of the intermediate billet to 34 mm to 40 mm are: increasing the rolling deformation during the rough rolling process, reducing the rolling deformation during the finishing rolling process, and avoiding excessive temperature reduction at the edge during the finishing rolling process. For example, the thickness of the intermediate billet can be 34 mm, 35 mm, 36 mm, 37 mm, 40 mm, etc.

[0059] S4, finishing rolling the intermediate billet to obtain a semi-finished steel strip;

[0060] Finish rolling is to further roll the intermediate billet to obtain the required size and surface finish. The steel after finish rolling is a semi-finished strip ready for subsequent processing. In the finishing rolling process, double-pass descaling is used to ensure the surface quality of the hot coil.

[0061] In some embodiments, the inlet temperature of the finishing rolling is 1050° C. to 1070° C., the final rolling temperature of the finishing rolling is 910° C. to 930° C., and the thickness of the semi-finished steel strip is 2.5 mm to 3 mm.

[0062] The positive effect of controlling the inlet temperature of finishing rolling to 1050°C to 1070°C is that a relatively high inlet temperature of finishing rolling can ensure that the edge temperature during hot rolling is in the temperature range of the single-phase austenite region. For example, the inlet temperature can be 1050°C, 1055°C, 1060°C, 1065°C, 1070°C, etc.

[0063] The positive effect of controlling the final rolling temperature of the finishing rolling to 910°C to 930°C is to ensure that the edge position of the hot rolling process is above the phase transition temperature to avoid the occurrence of mixed crystals induced by too low temperature. For example, the final rolling temperature can be 910°C, 915°C, 920°C, 925°C, 930°C, etc.

[0064] The positive effect of controlling the thickness of the semi-finished steel strip to 2.5mm to 3mm is that by ensuring a thinner thickness during hot rolling, the compression ratio of the cold rolling process is reduced, and the situation of severe edge hardening and cracking during the cold rolling process is avoided. For example, the thickness of the semi-finished steel strip can be 2.5mm, 2.6mm, 2.8mm, 2.9mm, 3mm, etc.

[0065] In some embodiments, the finishing rolling equipment comprises 6 finishing rolling stands F1 to F6, the cooling water opening ratio between the stands F1 to F3 is 50% to 80%, and the cooling water opening ratio between the stands F4 to F6 is 0% to 30%.

[0066] The positive effect of opening the cooling water between F1 and F3 stands at a ratio of 50% to 80% is that opening the cooling water between the stands in the front section can reduce the surface temperature, increase the rolling speed, and avoid problems such as overheating of the rolls. For example, the opening ratio of the cooling water between F1 and F3 stands can be 50%, 60%, 70%, 75%, 80%, etc.

[0067] Positive effects of the cooling water opening ratio between F4 and F6 stands being 0% to 30%: The purpose of reducing the opening ratio of the stand water in the rear stage is mainly to avoid the edge falling into the two-phase region caused by excessive surface temperature drop in the rear stage of the finishing rolling process. For example, the cooling water opening ratio between F4 and F6 stands can be 5%, 10%, 20%, 25%, 30%, etc.

[0068] S5, laminar cooling the semi-finished steel strip, and then coiling it;

[0069] Laminar cooling is to control the cooling rate and temperature distribution of steel to obtain the desired microstructure and properties. Coiling is to roll the cooled semi-finished strip into a coil for easy storage and transportation.

[0070] In some embodiments, the water pipe for laminar cooling is shielded at the edges to shut off the laminar cooling water at the edges.

[0071] During the cooling process of the strip, due to the differences in thickness and heat dissipation conditions between the edge and the center, the edge is often prone to overcooling, and edge overcooling is one of the important factors leading to cracks. Edge shielding can effectively reduce the cooling water flow in the edge area, thereby reducing the edge temperature and avoiding excessive temperature difference with the center. When implementing edge shielding, it is necessary to accurately control the range and degree of shielding to avoid adverse effects on the cooling effect of the center. When the strip width is 1200mm, edge shielding can be used to close the layer of cold water within 40mm of the edge to increase the edge temperature of the strip before coiling.

[0072] In some embodiments, the coiling adopts a front-end cooling mode, and the cold water layer is not turned on for 100 m at the head and tail.

[0073] Since the head and tail are easily affected by various factors during the rolling process, the final rolling temperature is different from that of the middle part. By not opening the layer cooling water at the head and tail, the temperature of these areas can be prevented from dropping too fast due to overcooling. Overcooled head and tail are prone to thermal stress concentration during the coiling process, thereby increasing the risk of cracks. Not opening the layer cooling water can reduce the cooling rate of these areas, reduce thermal stress concentration, and thus avoid cracks.

[0074] In some embodiments, the coiling temperature is 730°C to 750°C.

[0075] The positive effect of controlling the coiling temperature to 730°C to 750°C is that a higher coiling temperature can avoid the formation of bainite or martensite at the edge, which affects the structure and causes cracking of the structure during the cold rolling process. For example, the coiling temperature can be 730°C, 735°C, 740°C, 745°C, 750°C, etc.

[0076] S6, slowly cooling the semi-finished steel strip after coiling;

[0077] After the strip comes off the line, it is bundled to prevent the head and tail from loosening, and then sent to the slow cooling pit for slow cooling.

[0078] The slow cooling pit is an important device for reducing thermal residual stress and improving the mechanical properties of metal parts. During the cold rolling process, the temperature of the steel is still high after final rolling and coiling. If it is cooled directly at this time, it may cause large thermal stress and structural stress inside the steel, which will cause cracks. The slow cooling pit provides a relatively slow and uniform cooling environment, so that the internal stress of the steel can be fully released during the cooling process to avoid the generation of cracks.

[0079] In some embodiments, before the slow cooling, the temperature of the outer ring of the semi-finished steel strip is ≥ 600°C.

[0080] The positive effect of controlling the outer ring temperature of the semi-finished strip steel to be ≥600°C is to avoid the generation of hardened structure, and 600°C or above is conducive to the generation of ferrite + pearlite structure. Exemplarily, the outer ring temperature can be 600°C, 610°C, 620°C, 625°C, 630°C, etc.

[0081] S7, cold rolling the semi-finished steel strip after slow cooling to obtain a finished steel strip;

[0082] Cold rolling is a rolling process carried out at room temperature or below, which can further reduce the thickness of steel and improve its surface finish and dimensional accuracy. The steel after cold rolling is the finished strip steel, which meets the specific mechanical properties and dimensional requirements.

[0083] In some embodiments, the cold rolling reduction ratio is 50% to 60%.

[0084] Positive effects of controlling the cold rolling reduction rate to 50% to 60%: The cold rolling reduction rate is one of the important factors affecting edge cracking. Controlling the cold rolling reduction rate within a reasonable range can effectively reduce the occurrence of edge cracking. Too high a reduction rate will increase the internal stress and deformation resistance of the material, thereby causing edge cracking. Exemplarily, the reduction rate can be 50%, 52%, 54%, 58%, 60%, etc.

[0085] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples that do not specify specific conditions are usually measured according to industry standards; if there are no corresponding industry standards, they are carried out according to common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0086] The following is a detailed description of a method for reducing edge cracking during cold rolling of 1300Mpa square tube steel provided by the present application in combination with embodiments, comparative examples and experimental data. The method comprises:

[0087] S11, obtaining a slab with a set chemical composition;

[0088] S21, heating the slab, and then descaling it with high-pressure water;

[0089] S31, rough rolling the slab after high-pressure water descaling to obtain an intermediate slab;

[0090] S41, finishing rolling the intermediate billet to obtain a semi-finished steel strip;

[0091] S51, laminar cooling the semi-finished steel strip, and then coiling it;

[0092] S61, slowly cooling the semi-finished steel strip after coiling;

[0093] S71. Cold-roll the semi-finished steel strip after slow cooling to obtain a finished steel strip. The process parameters of each embodiment and each comparative example are listed in Table 1.

[0094] Table 1 Process parameters for reducing edge cracking during cold rolling of 1300Mpa square tube steel

[0095]

[0096] It can be seen from the data in Table 1 that the process parameters of the embodiment are within the required range of the present invention, and the microstructure of the edge of the hot coil is ferrite + pearlite type, and the microhardness is below 300 HV.

[0097] Attached Figure 2-3 Detailed description:

[0098] Figure 2 The microstructure diagram of the edge of the hot coil provided as a comparative example of this application; Figure 2 As shown, the microstructure of the edge of the hot coil provided in the comparative example is bainite.

[0099] Figure 3 The microstructure diagram of the edge of the hot coil provided in the embodiment of the present application; Figure 3 As shown, the microstructure of the edge of the hot coil provided in the embodiment is ferrite+pearlite.

[0100] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0101] 1. Improve product quality: Edge cracking is one of the main problems affecting the surface quality of cold-rolled steel. By solving the edge cracking problem, the surface finish and consistency of square tubes can be significantly improved, and the generation of defects and unqualified products can be reduced.

[0102] 2. Improve production efficiency: Edge cracking often leads to production line interruptions, increasing scrap rates and repair costs. By solving the edge cracking problem, downtime and repetitive work caused by product defects can be reduced, thereby improving overall production efficiency.

[0103] 3. Reduce production costs: Solving the edge crack problem not only reduces the scrap rate and downtime, but also reduces the raw material and labor costs caused by handling scrap and repeated production.

[0104] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features applied for by the present application.

Claims

1. A method for reducing edge cracking during cold rolling of 1300Mpa square tube steel, characterized in that: The method comprises: A slab with a set chemical composition is obtained; The slab is heated and then descaled with high pressure water; Rough rolling the slab after high-pressure water descaling to obtain an intermediate slab; Finish rolling the intermediate billet to obtain a semi-finished steel strip; laminar cooling the semi-finished steel strip and then coiling it; Slowly cooling the semi-finished steel strip after coiling; The semi-finished steel strip after slow cooling is cold rolled to obtain a finished steel strip.

2. The method according to claim 1, characterized in that In terms of mass fraction, the set chemical composition of the slab includes: C: 0.22% to 0.26%, Cr: 0.75% to 0.85%, Mn: 1.65% to 1.75%, Si: 0.35% to 0.45%, Nb+Ti: 0.05% to 0.07%, wherein Nb+Ti represents the sum of the contents of Nb and Ti.

3. The method according to claim 1, characterized in that The total furnace time of the heating is 160min to 200min, and the furnace outlet temperature of the heating is 1230°C to 1250°C.

4. The method according to claim 1, characterized in that: The water pressure of the high-pressure water descaling is ≥30Mpa.

5. The method according to claim 1, characterized in that The rough rolling adopts a 1+5 rolling mode, the rough rolling mill R1 adopts 1 pass descaling, the rough rolling mill R2 adopts 1, 3, 4 and 5 passes descaling, and the thickness of the intermediate billet is 34 mm to 40 mm.

6. The method according to claim 1, characterized in that The inlet temperature of the finishing rolling is 1050° C. to 1070° C., the final rolling temperature of the finishing rolling is 910° C. to 930° C., and the thickness of the semi-finished steel strip is 2.5 mm to 3 mm.

7. The method according to claim 1, characterized in that The finishing rolling equipment comprises 6 finishing rolling stands F1-F6, the cooling water opening ratio between the stands F1-F3 is 50%-80%, and the cooling water opening ratio between the stands F4-F6 is 0%-30%.

8. The method according to claim 1, characterized in that The water pipes for laminar cooling are shielded at the edges, and the laminar cooling water at the edges is closed.

9. The method according to claim 1, characterized in that: The coiling adopts the front section cooling mode, and the cold water layer is not opened for 100m at the head and tail; and / or, The coiling temperature is 730°C to 750°C; and / or, Before the slow cooling, the temperature of the outer ring of the semi-finished steel strip is ≥ 600°C.

10. The method according to claim 1, characterized in that The cold rolling reduction ratio is 50% to 60%.

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