A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si.

Abstract

A method for controlling transverse edge crack defects in cold-rolled non-oriented silicon steel containing ≥3.0% Si: The steel, after being smelted in a converter to a final molten steel containing no less than 3.0% Si, is cast into a billet; the billet is then subjected to conventional heating followed by conventional rough rolling; conventional finish rolling; and conventional cold rolling, annealing, and finishing processes. This invention reduces the incidence of transverse edge crack defects in cold-rolled strip from an average of at least 1.0% to no more than 0.05%, and the strip breakage rate from an average of at least 3.5% to no more than 3.0%, while maintaining good strip shape alignment and uniform strip thickness.

Description

Technical Field

[0001] This invention relates to a method for producing non-oriented silicon steel, specifically a method for controlling transverse crack defects at the edge of cold-rolled non-oriented silicon steel containing ≥3.0% Si. Background Technology

[0002] Non-oriented silicon steel with Si ≥ 3.0% is a high-grade functional metallic material, mainly used in the core manufacturing of new energy vehicles and large generator sets. It is a low-carbon and green product. The shape of hot-rolled strip is the most critical manufacturing process, and the strip edge profile is a key evaluation indicator, mainly including edge drop and local high points. By controlling the centering rolling of the strip, controlling the surface quality of the roughing mill vertical rolls, and equipping appropriate work roll shifting strategies, edge wear of the finishing mill work rolls can be improved. During cold rolling, if the edge profile of the hot-rolled strip exceeds a certain range—that is, when there are local high points or edge drop exceeding a certain degree (rapid thinning of the edge thickness), or when the edge crack depth is severe—it leads to inconsistent elongation between the surface and subsurface layers during cold rolling. The local tensile deformation resistance of the metal exceeds the tensile strength of the material itself, resulting in transverse surface crack defects (perpendicular to the rolling direction) or direct cracking at the edge. Figure 1 , 2 Sometimes, the combination and superposition of the three types of defects can further exacerbate the formation of transverse cracks on the edge surface.

[0003] Product standards typically evaluate strip profiles using C40 and W40. Statistical analysis shows that even when both typical values ​​are normal, transverse rolling defects still exist during the cold rolling process. Observational analysis of the cross-sectional profiles of coils with transverse rolling defects and those without defects revealed a close correlation between transverse crack defects and abnormal edge profiles and the depth of edge hairline cracks within a 75mm radius of the hot-rolled strip edge.

[0004] A search revealed that Jiangsu Shagang's publicly available paper, "A Preparation Method for Preventing Edge Damage and Cracks in Cold-Rolled High-Grade Silicon Steel," specifies a final rolling temperature of 840–870℃, a coiling temperature of 600–680℃, a normalizing temperature of 840–880℃, a strip temperature before rolling not lower than 40℃, and a first-pass reduction rate not exceeding 5% of the total reduction rate. This paper, by optimizing the entire process parameters, can improve the edge quality of silicon steel and prevent edge damage and cracks.

[0005] Jefu Steel Corporation's Fukushima Tatsutoshi disclosed a "cold rolling mill and cold rolling method" that can roll without causing edge cracks or plate breakage during low-speed rolling. Edge heaters that heat the two edges of the steel plate raise the temperature of the edge of the steel plate on the incoming side by 60°C, thereby improving the rolling of difficult-to-roll materials such as silicon steel plates and stainless steel plates.

[0006] Ansteel Co., Ltd. disclosed a method for preventing cold-rolled strip breakage of high-silicon electrical steel. The method involves milling operations with cutting tools on both sides of the hot-rolled steel strip. The cutting tool axis forms an angle α with the running direction of the steel strip, and the rotation direction of the cutting edge on the cutting tool is opposite to the running direction of the steel strip. The running speed of the steel strip is 5-40 m / min. When the edge crack depth is less than 10 mm, one cutting tool is set on one side of the steel strip. When the edge crack is greater than 10 mm, two or more cutting tools are used to mill the steel strip on one side at the same time, thus avoiding strip breakage caused by cracks.

[0007] Northeastern University's published method for optimizing the shape of cold-rolled non-oriented high-silicon steel sheets involves warm rolling at 100–300°C, with the total reduction controlled between 55–60%. The warm-rolled steel sheet is then held at 300–350°C in a protective atmosphere for 30–60 minutes for low-temperature recovery, followed by air cooling to room temperature, and finally cold rolling. This method results in cold-rolled non-oriented high-silicon steel sheets with minimal edge cracking and excellent sheet shape.

[0008] The above four documents mainly adopt technical measures to prevent cold rolling edge cracks, such as low-speed rolling, load optimization, increasing plate temperature, and removing edge cracks. However, none of them involve the method proposed in this invention to control the edge profile (including edge drop and local high points) and edge hairline depth of hot-rolled strip steel to prevent cold rolling edge transverse cracks, and the control effect is not as good as that of this invention. Summary of the Invention

[0009] This invention aims to overcome the shortcomings of existing technologies and provide a method for controlling the transverse edge crack defect rate of cold-rolled non-oriented silicon steel containing Si ≥ 3.0% by controlling the thickness difference ΔH = H75-H5 in the edge section of hot-rolled strip steel to ≤ 90 μm, controlling the difference between ΔH on both sides of the strip steel to ≤ 30 μm, and controlling the local high point of the edge profile to < 10 μm.

[0010] Measures to achieve the above objectives:

[0011] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0012] 1) The molten steel, after being smelted in a converter, contains no less than 3.0% Si and is then cast into billets;

[0013] 2) After the billet is conventionally heated, it is subjected to conventional rough rolling. During the rolling process, the surface of the vertical rolls must be free of thermal cracks.

[0014] 3) During conventional finishing rolling, the following steps are taken:

[0015] D. Control the hairline depth of the strip edge to be <100um;

[0016] E. Control the wear of the work rolls F5-F7 in the finishing mill to not exceed ≤350um, and the volume concentration of the rolling oil on the work rolls to be 0.3%±0.05%;

[0017] F. Reduce the edge drop of the strip, even if the thickness difference ΔH at the two points, 75mm from the edge of the strip and 5mm from the edge, is controlled to be ≤90um, which can be expressed by the formula:

[0018] ΔH=H75-H5≤90um;

[0019] Furthermore, the difference between ΔH on both sides of the strip should be ≤30um, and the local high point of the edge profile should be <10um;

[0020] 4) Routine post-processing such as cold rolling, annealing, and finishing is carried out.

[0021] The key difference lies in the fact that the reduction in the edge drop of the strip is achieved by using work rolls made of high-speed steel with a hardness of not less than 60HRC.

[0022] The role and mechanism of each raw material and main process in this invention

[0023] The reason why this invention controls the hairline depth of the strip edge to be <100um is that, during the finishing rolling process, by improving the roll shape of the work roll edge, increasing the rolling oil concentration of the work roll, optimizing the load adjustment of the finishing rolling process parameters, and using high-speed steel work roll material, a particularly suitable roll shifting strategy is adopted to significantly reduce the wear of the finishing rolling work roll edge, reduce the degree of strip edge thickness reduction (i.e., edge drop), and avoid the generation of local high points on the edge.

[0024] The reason why this invention controls the edge wear of the work rolls F5-F7 in the finishing mill to not exceed ≤350um and the target rolling oil concentration of the work rolls to be 0.3%±0.05% is to reduce the friction coefficient of the work rolls, reduce the edge wear of the work rolls, increase the unit rolling length, and improve the degree of strip edge drop.

[0025] The reason why this invention controls the thickness difference ΔH between H75 (75mm from the edge of the steel strip) and H5 (5mm from the edge of the steel strip) to be ≤90µm, and the difference between ΔH on both sides of the strip to be ≤30µm, and controls the local high point of the edge profile to be <10µm, is that when the edge drop of the hot-rolled strip exceeds 90µm, it will easily cause the uniformity of the stress on the edge during the cold rolling process to deteriorate. The metal elongation in this area is uneven. If the local high point of the edge profile is greater than 10µm, it will further aggravate the stress difference in the local high point area. The local metal tensile deformation resistance exceeds the tensile strength of the material itself, resulting in the generation of transverse crack defects on the edge surface (perpendicular to the rolling direction) or direct cracking, and the thickness uniformity on both sides of the strip is poor.

[0026] Compared with the prior art, this invention reduces the incidence of transverse crack defects at the edge of the hot-rolled strip from an average of at least 1.0% to no more than 0.05%, and the strip breakage rate from an average of at least 3.5% to no more than 3.0%, by controlling the thickness difference of ΔH = H75-H5 in the edge section of the hot-rolled strip to ≤90µm, controlling the difference of ΔH between the two sides of the strip to ≤30µm, and controlling the local high point of the edge profile to <10µm. In addition, the strip has good shape alignment and good thickness uniformity. Attached Figure Description

[0027] Figure 1 Images showing transverse cracks at the cold-rolled edge of the non-oriented silicon steel with Si ≥ 3.0% produced by this invention;

[0028] Figure 2 Images showing transverse cracks at the edge of cold-rolled non-oriented silicon steel with Si ≥ 3.0% produced using existing technology. Detailed Implementation

[0029] The present invention will now be described in detail:

[0030] Example 1

[0031] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0032] 1) The molten steel containing 3.15% Si after being smelted in a converter is cast into billets;

[0033] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0034] 3) During conventional finishing rolling, the following steps are taken:

[0035] A. Control the hairline depth of the strip edge to 83µm;

[0036] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 190-270µm, and the volume concentration of rolling oil on the work rolls to be 0.35%.

[0037] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75). 传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5 工 For 2120um, enter the following formulas respectively.

[0038] ΔH 传 =H75-H5=60umΔH 工 =H75-H5=75um, which shows that ΔH on both sides of the steel strip is ≤90um;

[0039] And |ΔH 传 -ΔH 工 |=|-15|≤30um indicates good strip alignment; the local high points of the edge profile are all 0um, indicating good uniformity of strip thickness.

[0040] 4) Routine post-processing such as cold rolling, annealing, and finishing is carried out.

[0041] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.05%, and the strip breakage rate is 2.4%.

[0042] Example 2

[0043] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0044] 1) The molten steel, which contains 3.22% Si after being smelted in a converter, is then cast into billets;

[0045] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0046] 3) During conventional finishing rolling, the following steps are taken:

[0047] A. Control the hairline depth of the strip edge to 73µm;

[0048] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 180-330µm, and the volume concentration of rolling oil on the work rolls to be 0.33%.

[0049] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75).传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5 工 For 2120um, enter the following formulas respectively.

[0050] ΔH 传 =H75-H5=66umΔH 工 =H75-H5=84um, which shows that ΔH on both sides of the steel strip is ≤90um;

[0051] And |ΔH 传 -ΔH 工 |=|-18|≤30um indicates good strip alignment; the local high point of the edge profile is 4um, indicating good uniformity of strip thickness.

[0052] 1) Conventional post-processing such as cold rolling, annealing, and finishing is carried out.

[0053] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.06%, and the strip breakage rate is 2.5%.

[0054] Example 3

[0055] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0056] 1) The molten steel containing 3.07% Si after being smelted in a converter is cast into billets;

[0057] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0058] 3) During conventional finishing rolling, the following steps are taken:

[0059] A. Control the hairline depth of the strip edge to 86µm;

[0060] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 210-350 μm, and the volume concentration of rolling oil on the work rolls to be 0.30%.

[0061] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75). 传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5工 For 2120um, enter the following formulas respectively.

[0062] ΔH 传 =H75-H5=60umΔH 工 =H75-H5=85um, which shows that ΔH on both sides of the steel strip is equal.

[0063] ≤90um;

[0064] And |ΔH 传 -ΔH 工 |=|-25|≤30um indicates good plate alignment; the local high point of the edge profile is 6um, indicating good uniformity of strip thickness.

[0065] 2) Conventional post-processing such as cold rolling, annealing, and finishing is carried out.

[0066] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.11%, and the strip breakage rate is 2.8%.

[0067] Example 4

[0068] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0069] 1) The molten steel containing 3.02% Si after being smelted in a converter is cast into billets;

[0070] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0071] 3) During conventional finishing rolling, the following steps are taken:

[0072] A. Control the hairline depth of the strip edge to 88µm;

[0073] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 150-240 μm, and the volume concentration of rolling oil on the work rolls to be 0.34%.

[0074] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75). 传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5 工 For 2120um, enter the following formulas respectively.

[0075] ΔH 传 =H75-H5=88umΔH工 =H75-H5=75um, which shows that ΔH on both sides of the steel strip is ≤90um;

[0076] And |ΔH 传 -ΔH 工 |=|13|≤30um indicates good plate alignment; the local high points of the edge profile are all 3um, indicating good uniformity of strip thickness;

[0077] 3) Routine post-processing such as cold rolling, annealing, and finishing is carried out.

[0078] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.06%, and the strip breakage rate is 2.5%.

[0079] Example 5

[0080] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0081] 1) The molten steel, which contains 3.18% Si after being smelted in a converter, is then cast into billets;

[0082] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0083] 3) During conventional finishing rolling, the following steps are taken:

[0084] A. Control the hairline depth of the strip edge to 82µm;

[0085] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 130-220 μm, and the volume concentration of rolling oil on the work rolls to be 0.35%.

[0086] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75). 传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5 工 For 2120um, enter the following formulas respectively.

[0087] ΔH 传 =H75-H5=60umΔH 工 =H75-H5=75um, which shows that ΔH on both sides of the steel strip is ≤90um;

[0088] And |ΔH 传 -ΔH 工|=|15|≤30um indicates good plate alignment; all local high points on the edge profile are 0um, indicating good uniformity of strip thickness.

[0089] 4) Routine post-processing such as cold rolling, annealing, and finishing is carried out.

[0090] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.07%, and the strip breakage rate is 2.7%.

[0091] Example 6

[0092] A method for controlling transverse edge cracks in cold-rolled non-oriented silicon steel containing ≥3.0% Si, comprising the following steps:

[0093] 1) The molten steel containing 3.25% Si after being smelted in a converter is cast into billets;

[0094] 2) After conventional heating of the billet, conventional rough rolling was carried out. During the rolling process, the quality of the vertical roll surface was tested and no thermal cracking was found.

[0095] 3) During conventional finishing rolling, the following steps are taken:

[0096] A. Control the hairline depth of the strip edge to 90µm;

[0097] B. Control the edge wear of work rolls F5-F7 in the finishing mill to be between 230-330 μm, and the volume concentration of rolling oil on the work rolls to be 0.25%.

[0098] C. Reduce the edge drop of the strip, at a distance of 75mm from the edge of the strip on the drive side (H75). 传 and working side H75 工 The thicknesses are H75 and H75, respectively. 传 2190um and H75 工 It is 2195um, H5 传 For 2130um and H5 工 For 2120um, enter the following formulas respectively.

[0099] ΔH 传 =H75-H5=88umΔH 工 =H75-H5=65um, which shows that ΔH on both sides of the steel strip is equal.

[0100] ≤90um;

[0101] And |ΔH 传 -ΔH 工 |=|23|≤30um indicates good plate alignment; the local high points of the edge profile are all 4um, indicating good thickness uniformity of the strip.

[0102] 5) Routine post-processing such as cold rolling, annealing, and finishing is carried out.

[0103] According to the test and statistics of this embodiment, the incidence of transverse crack defects at the edge of the cold-rolled section is 0.09%, and the strip breakage rate is 2.6%.

[0104] Note: The working rolls in Examples 3 and 6 above are made of high-speed steel with a hardness of not less than 60HRC.

[0105] This specific embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.

Claims

1. A method for controlling the cold-rolled edge transverse crack defects of non-oriented silicon steel containing Si≥3.0%, comprising the steps of: 1) pouring the steel containing not less than 3.0% Si into a billet after smelting the final molten steel in a converter; 2) performing conventional rough rolling after conventional heating of the cast billet, and in the rolling process, requiring no thermal cracks on the surface of the vertical roll; 3) performing conventional finish rolling, and in the rolling process: A, controlling the edge line depth of the strip to be <100 um; B, controlling the wear of the edge of the work roll in the F5-F7 finish rolling mill to be ≤350 um, and the volume concentration of the rolling oil of the work roll to be 0.3%±0.05%; C, reducing the edge drop degree of the strip, i.e. controlling the thickness difference ΔH between the thickness H75 at 75 mm from the edge of the strip and the thickness H5 at 5 mm from the edge of the strip to be ≤90 um, which is expressed by the formula: ΔH=H75-H5≤90 um; and controlling the difference between the ΔH of the two sides of the strip to be ≤30 um, and controlling the local high point of the edge profile of the strip to be <10 um; 4) performing conventional cold rolling, annealing and finishing after the process. The reduction of the edge drop degree of the strip is achieved by using a work roll made of high-speed steel with a hardness not less than 60HRC. ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. A method of controlling the cold-rolled edge transverse crack defects of Si≥3.0% non-oriented silicon steel according to claim 1, characterized in that: ​

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