A method for improving the edge quality of cold-rolled guide rail steel

Abstract

This application relates to the field of steel rolling technology, and more particularly to a method for improving the edge quality of cold-rolled guide rail steel. The method includes the following steps: heating a steel billet to obtain a heated slab; rolling the heated slab to obtain guide rail steel, wherein during heating, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plastic low point. Guide rail steel exhibits a plastic low point in the high-temperature region. By ensuring the core temperature of the steel billet is lower than this temperature, the guide rail steel avoids the plastic low temperature zone, reducing internal cracks in the steel billet, preventing excessive deformation, controlling edge cracks, and thus improving the edge quality of the cold-rolled guide rail steel.

Description

Technical Field

[0001] This application relates to the field of steel rolling technology, and in particular to a method for improving the quality of the cold-rolled edge of guide rail steel. Background Technology

[0002] Guide rail steel has the characteristics of low pulling resistance, high load-bearing capacity, high hardness, and difficult control of plate shape and surface roughness. It is used in machining and home decoration. High-end galvanized steel is increasingly used in heavy-duty cabinets, furniture and appliance drawers.

[0003] Guide rail steel is used to make guide rails after being longitudinally cut into strips. It has high quality requirements for materials. In order to ensure high hardness, wear resistance, good impact toughness, fracture toughness, dimensional stability and other performance requirements, cracks and slag inclusions and other surface and internal defects are not allowed on the edges during production.

[0004] Currently, linear defects exist on the surface of the strip near the edge during the production of this steel grade. Research has been conducted on related defect control in other steel companies. CN201811031152.2 describes using a certain convexity pattern in the module for processing the edge of the slab on a fixed-width press to avoid linear defects. CN201710367740.2 describes using flat rolls after hot-rolled vertical rolls to reduce surface defects. CN201120059865.7 proposes designing a strip side guide device for coiling to reduce defects such as edge abrasion of the strip. However, these patents only describe the equipment and do not consider the characteristics of the steel grade, meaning that some edge quality defects in the guide rail steel cannot be solved using these technologies. Summary of the Invention

[0005] This application provides a method for improving the quality of cold-rolled edges of guide rail steel, thereby solving the technical problem of quality defects in the cold-rolled edges of guide rail steel.

[0006] In a first aspect, this application provides a method for improving the quality of the cold-rolled edge of guide rail steel, the method comprising the following steps:

[0007] The steel billet is heated to obtain a heated slab;

[0008] The heated slab is rolled to obtain guide rail steel.

[0009] During the heating process, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plasticity low point.

[0010] Optionally, during the heating process, the core temperature is <600°C.

[0011] Optionally, during the heating process, the surface temperature of the steel billet is 250-450℃.

[0012] Optionally, the heating temperature is 600-1220℃.

[0013] Optionally, the heating includes a heating section and a soaking section, wherein the temperature difference between the heating section and the soaking section is 20-60℃.

[0014] Optionally, the furnace exit temperature of the heated slab is 1180-1220℃.

[0015] Optionally, the method further includes:

[0016] The steel billet obtained after continuous casting has a wear-resistant layer hardness of 230-260 HV in the crystallizer.

[0017] Optionally, during the rolling process, when the temperature of the edge of the billet is 950-1000℃, the last vertical roll in the roughing process adopts a non-input mode to avoid lateral width reduction.

[0018] Optionally, in the roughing mill, the R1 mill and the R2 mill adopt a 3+3 rolling mode.

[0019] Optionally, the chemical composition of the steel billet includes, by mass fraction, C: 0.06%–0.12%, Mn: 0.35%–0.45%, Si: 0–0.05%, P: 0–0.015%, S: 0–0.015%, with the balance being Fe and unavoidable impurities.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art:

[0021] The method provided in this application embodiment involves heating a steel billet to obtain a heated slab; rolling the heated slab to obtain guide rail steel. During heating, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plastic low point. Since guide rail steel exhibits a plastic low point in the high-temperature region, the core temperature of the steel billet being lower than this temperature allows the guide rail steel to avoid the plastic temperature zone, reducing internal cracks in the steel billet, preventing excessive deformation, controlling edge cracks, and thus improving the cold-rolled edge quality of the guide rail steel. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic flowchart illustrating a method for improving the quality of cold-rolled edge of guide rail steel, provided in an embodiment of this application;

[0025] Figure 2 The macroscopic surface morphology of the finished roll provided for Comparative Example 1 of this application;

[0026] Figure 3 The macroscopic surface morphology of the finished roll provided in Comparative Example 2 of this application;

[0027] Figure 4 The macroscopic surface morphology of the finished roll provided in Comparative Example 3 of this application;

[0028] Figure 5 The macroscopic surface morphology of the finished roll provided in Comparative Example 4 of this application;

[0029] Figure 6 The macroscopic surface morphology of the finished roll provided in Embodiment 1 of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] This application provides a method for improving the quality of the cold-rolled edge of guide rail steel, the method comprising the following steps:

[0032] The steel billet is heated to obtain a heated slab;

[0033] The heated slab is rolled to obtain guide rail steel.

[0034] During the heating process, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plasticity low point.

[0035] In this embodiment, by using reasonable heating temperature and heating rate, deformation stress during the slab heating process is eliminated, uneven deformation of the slab is reduced, and macroscopic quality control of the hot-rolled slab is achieved.

[0036] The principle behind keeping the core temperature of the billet lower than the temperature at which the guide rail steel exhibits a plastic low point is as follows: The charging temperature of the heating furnace affects the quality of the slab. Guide rail steel falls into the peritectic steel category. High-temperature tensile testing reveals that this type of steel exhibits a plastic low point in the high-temperature ranges of 600-750℃ and 950-1000℃. Since the internal temperature of the billet is higher than its surface temperature, the surface temperature of the billet entering the hot rolling furnace is set at 250-450℃ to prevent the core temperature from exceeding 600℃, which could cause internal cracks.

[0037] In this embodiment of the application, the method may include: smelting molten steel to obtain a thin slab, heating the thin slab in a heating furnace, then rough rolling it, followed by finishing rolling, laminar flow cooling, coiling it, and then cold rolling and heat treatment to obtain the finished product, i.e., guide rail steel. The properties of the finished product include: yield strength of 280-305 MPa and tensile strength of 375-390 MPa.

[0038] In some embodiments, the core temperature is <600°C during the heating process.

[0039] In this embodiment, the temperature of the billet core is <600°C, which can prevent the billet core temperature from becoming too high and causing internal cracks.

[0040] In some embodiments, the surface temperature of the steel billet during heating is 250-450°C.

[0041] In this embodiment, controlling the surface temperature of the slab entering the heating furnace to 250-450°C can control the temperature of the slab core, thereby preventing internal cracks and also reducing the energy consumption of the heating furnace.

[0042] In some embodiments, the heating temperature is 600-1220°C.

[0043] The heating temperature is controlled at 600-1220℃, which can be the temperature in the heating furnace at the beginning of heating. The temperature of the heating section and the soaking section is between 600-1220℃, and the temperature difference between the surface and the core is 20-60℃. This prevents the temperature from rising too quickly and causing thermal stress cracks. Controlling the heating temperature range has the positive effect of effectively eliminating dendritic segregation inside the slab and ensuring good temperature uniformity of the slab.

[0044] In some embodiments, the heating includes a heating section and a soaking section, wherein the temperature difference between the steel billet and the soaking section is 20-60°C.

[0045] In this embodiment, controlling the temperature difference to 20-60℃ can prevent excessively rapid heating and thermal stress cracking of the steel billet by controlling the heating rate of the heating section and the soaking section; it can also reduce the heating load of the heating furnace and improve the service life of the heating furnace.

[0046] In some embodiments, the temperature of the heated slab is 1180-1220°C.

[0047] In this embodiment, the heating temperature of the slab is 1180-1220℃, which can be the furnace exit temperature of the steel billet. This ensures that the billet is heated evenly, eliminates casting dendrite segregation, and prevents overheating due to excessively high temperature and incomplete elimination of dendrite segregation due to excessively low temperature.

[0048] In some embodiments, the method further includes:

[0049] The steel billet obtained after continuous casting has a wear-resistant layer hardness of 230-260 HV in the crystallizer.

[0050] In this embodiment, the copper plate of the continuous casting mold uses a NiCo wear-resistant coating. The surface condition of the mold affects the quality of the narrow face of the billet. Excessive wear of the mold causes poor edge shape and severe scratches on the narrow face of the billet. During subsequent rolling, the narrow face flips to the surface, causing surface defects. Therefore, it is necessary to control the quality of the wear-resistant layer of the mold. When the hardness of the wear-resistant layer is between 230-260 HV, the quality of the narrow face is good. The narrow face of the billet is the side of the billet that contacts the mold.

[0051] In some embodiments, when the temperature of the edge of the billet is 950-1000°C during the rolling process, the last vertical roll in the roughing rolling process adopts a non-input mode to avoid lateral width reduction.

[0052] In this embodiment, the second pass of the R2 mill does not involve width reduction during the rolling process, thus avoiding lateral width reduction and reducing non-uniform deformation at the edge in the low plasticity temperature range, thereby controlling cracks at the edge of the billet. It also has a positive effect on controlling the width fluctuation of the strip.

[0053] In some embodiments, the roughing mills R1 and R2 employ a 3+3 rolling pattern.

[0054] In this embodiment, the roughing mill can be two roughing mills, RI and R2. Each mill can have a vertical roll for lateral widening. The 3+3 pass rolling mode is beneficial to reduce the temperature drop of the slab during the rolling process. However, due to the large temperature drop at the edge of the slab, the edge temperature is lower than the middle temperature during the rolling process. During the roughing stage, the edge enters the plastic low point of 950-1000℃, resulting in poor metal flow at the edge and easy to generate edge defects. In particular, during the second pass of R2, the edge enters the 950-1000℃ temperature. At this time, the last vertical roll in the roughing mill should adopt the vertical roll non-input mode to avoid lateral widening.

[0055] In some embodiments, the chemical composition of the billet comprises, by mass fraction, C: 0.06%–0.12%, Mn: 0.35%–0.45%, Si: 0–0.05%, P: 0–0.015%, S: 0–0.015%, with the balance being Fe and unavoidable impurities.

[0056] In this embodiment, the guide rail steel needs to meet requirements such as noiselessness and smooth operation during the support of heavy objects and the pulling process. Therefore, the guide rail steel has few inclusions and high purity. Thus, during steelmaking, the composition, especially the content of residual elements, needs to be strictly controlled. Controlling the carbon content can affect the formation of pearlite structure. Controlling the carbon content to 0.06-0.12% can obtain 85%-95% ferrite structure and 5%-15% pearlite structure, ensuring that the guide rail steel has good hardness. A content exceeding 0.12% leads to poor impact toughness and difficulty in maintaining hardness. Adding a certain amount of Si and M to the steel... Nitrogen (N) is mainly used for solid solution strengthening to ensure strength. The strength cannot be too high, and the yield strength is controlled at 280-305 MPa. Si (Si) content is generally less than 0.05%, and Mn content is less than 0.45%. In addition, Si and Mn are good deoxidizers, which can ensure the purity of steel. Mn is also a desulfurizer, and the Mn content needs to be greater than 0.35%, which can effectively reduce the harmful FeS content in steel. Residual phosphorus (P) and sulfur (S) affect the purity and plasticity of steel. Especially for guide rail steel, the plasticity requirement is that the elongation after fracture (A80) should not be less than 30%, and it needs to be strictly required to be less than 0.015%.

[0057] This application embodiment, by controlling the composition of the billet, ensures the cleanliness and appropriate strength of the molten steel. Through continuous casting crystallizer, heating furnace and rough rolling process control, it reduces the wear on the edge of the billet and avoids excessive deformation in the plastic zone of the steel grade. It solves the product quality problems caused by unreasonable control of equipment process parameters and improper use in many ways. This method is simple, economical and efficient. Using this invention, the surface defects on the edge of the guide rail steel can be solved relatively easily without affecting production and performance.

[0058] The method of the present invention will now be described in detail with reference to embodiments, comparative examples and experimental data.

[0059] Example 1

[0060] A method for improving the edge quality of cold-rolled guide rail steel, the method comprising the following steps:

[0061] The steel billet is heated to obtain a heated slab;

[0062] The heated slab is rolled to obtain guide rail steel.

[0063] During the heating process, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plasticity low point.

[0064] The chemical composition of the steel billet includes, by mass percentage: C: 0.10%, Mn: 0.36%, Si: 0.04%, P: 0.007%, S: 0-0.009%, with the balance being Fe and unavoidable impurities. The process includes: the surface temperature of the steel billet is 250-450℃; during heating, the temperature of the core of the steel billet is <600℃.

[0065] The NiCo wear-resistant coating on the copper plate of the continuous casting crystallizer has a hardness value of 240HV. The billet enters the hot rolling furnace at a temperature of 380℃. The temperature difference between the billet in the heating section and the soaking section is 30℃. The exit temperature is 1190℃. The roughing mill adopts a 3+3 rolling mode, and the second pass of the R2 mill does not involve width reduction on the vertical rolls.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is as follows:

[0068] The chemical composition of the steel billet includes, by mass percentage: C: 0.08%, Mn: 0.43%, Si: 0.03%, P: 0.005%, S: 0–0.012%, with the balance being Fe and unavoidable impurities. Specifically, it includes:

[0069] The surface temperature of the steel billet is 250-450℃; during heating, the temperature of the billet core is <600℃; the hardness value of the NiCo wear-resistant coating on the copper plate of the continuous casting crystallizer is 230HV; the temperature of the billet entering the hot rolling furnace is 260℃; the temperature difference between the billet in the casting heating section and the soaking section is 50℃; and the furnace exit temperature is 1220℃. The roughing rolling adopts a 3+3 rolling mode, with the second pass of the R2 mill using a width reduction vertical roll.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is as follows:

[0072] The chemical composition of the steel billet includes, by mass percentage: C: 0.12%, Mn: 0.38%, Si: 0.02%, P: 0.007%, S: 0-0.009%, with the balance being Fe and unavoidable impurities. The process includes: the surface temperature of the steel billet is 250-450℃; during heating, the temperature of the billet core is <600℃; the hardness value of the NiCo wear-resistant coating on the copper plate of the continuous casting crystallizer is 200HV; the temperature of the billet entering the hot rolling furnace is 400℃; the temperature difference between the billet in the heating section and the soaking section is 40℃; and the furnace exit temperature is 1200℃. The roughing rolling adopts a 3+3 rolling mode, and the second pass of the R2 mill does not involve width reduction on the vertical rolls.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 1 is as follows:

[0075] The chemical composition of the steel billet includes, by mass percentage: C: 0.11%, Mn: 0.39%, Si: 0.03%, P: 0.010%, S: 0-0.005%, with the balance being Fe and unavoidable impurities. The process includes: a surface temperature of 250-450℃ for the steel billet; a core temperature of ≤600℃ during heating; a NiCo wear-resistant coating hardness of 235HV on the copper plate of the continuous casting crystallizer; a billet temperature of 550℃ entering the hot rolling furnace; a temperature difference of 30℃ between the heating section and the soaking section; and a furnace exit temperature of 1190℃. The roughing rolling adopts a 3+3 rolling pattern, and the second pass of the R2 mill does not involve width reduction on the vertical rolls.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 1 is as follows:

[0078] The second vertical roll of the R2 mill is not used for width reduction. The temperature difference between the heating section and the soaking section is 70°C.

[0079] Performance testing

[0080] The surface of the finished guide rail steel coil was inspected, and the macroscopic surface morphology of the finished coil was examined. Figure 2-6 It can be seen that the surface quality of the guide rail steel prepared in the embodiments of the present invention and the comparative examples differs. For example... Figure 2 As shown in the figure, the crack is 150-200mm long and 15-20mm wide. In Comparative Example 1, the surface linear defects caused by the use of vertical rolls to reduce the strip width in the second pass of the R2 rolling mill are severe and far from the edge of the strip. Figure 3 As shown in the figure, the cracks are 50-100mm long and 6-10mm wide. In Comparative Example 2, due to the softness of the wear-resistant layer of the crystallizer, multiple linear defects appear on the surface. Figure 4As shown in the figure, the crack is 30-50mm long and 2-3mm wide. In Comparative Example 3, the high furnace temperature of the slab caused cracks in the cast slab, which then propagated to longitudinal cracks in the center of the strip. Figure 5 As shown in the figure, the cracks are 100-200mm long and 3-4mm wide. Comparative Example 4 shows that due to a large temperature difference, cracks appear in the cast billet, which then propagate to longitudinal cracks in the center of the strip. Figure 6 As shown in the figure, no cracks appear on the edge, indicating that the relative edge quality of Example 1 is better.

[0081] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0082] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for improving the edge quality of cold-rolled guide rail steel, characterized in that, The method includes the following steps: The steel billet is heated to obtain a heated slab; The heated slab is rolled to obtain guide rail steel. During the heating process, the core temperature of the steel billet is lower than the temperature at which the guide rail steel exhibits a plasticity low point. During the heating process, the furnace entry temperature of the core is <600℃; During the heating process, the surface temperature of the steel billet entering the furnace is 250-450℃. The heating temperature is 600-1220℃; The heating process includes a heating section and a soaking section, wherein the temperature difference between the heating section and the soaking section is 20-60℃. The furnace exit temperature of the heated slab is 1180-1220℃; The chemical composition of the steel billet includes, by mass fraction, C: 0.06%–0.12%, Mn: 0.35%–0.45%, Si: 0–0.05%, P: 0–0.015%, S: 0–0.015%, with the balance being Fe and unavoidable impurities; The method further includes: obtaining a continuously cast steel billet, wherein the wear-resistant layer of the crystallizer has a hardness of 230-260 HV during the continuous casting process; When the temperature of the edge of the heated slab is 950-1000℃, the last vertical roll in the roughing process adopts the mode of not putting the vertical roll in order to avoid lateral width reduction. The R1 and R2 mills adopt a 3+3 rolling mode.

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