Method for improving edge cracking of cold-rolled strip steel

Abstract

The invention relates to a method for improving edge cracking of cold-rolled strip steel, which comprises the following steps that steel is subjected to acid pickling and rolling treatment in sequence, in the rolling treatment, the rolling speed is below 500m / min, the number of rolling passes is larger than or equal to five, the reduction rate of each pass is smaller than or equal to 50%, the unit tension of an inlet of each pass is smaller than or equal to 20N / mm < 2 >, and the unit tension of an outlet of each pass is smaller than or equal to 20N / mm < 2 >. The method provided by the invention can effectively improve the edge cracking of the cold-rolled strip steel and improve the product quality.

Description

Technical Field

[0001] The present application relates to the technical field of steel processing, and in particular to a method for improving edge cracking of cold-rolled steel strip. Background Art

[0002] Cold-rolled steel strips are used for knives and utility knives, which require the material to have high hardness and wear resistance. Therefore, high carbon steel is used for knives and utility knives. However, high carbon steel is particularly prone to edge cracking during the production process of cold-rolled steel strips. The existence of edge cracks not only affects the quality of steel strip products, but also causes damage to production equipment, resulting in a decrease in production output, seriously affecting the smooth progress of production, and causing great economic losses to production companies. The control of edge cracks has always been a problem that technical workers in cold-rolled steel strip enterprises have paid more attention to.

[0003] Currently, there is no relevant technology that can effectively solve the problem of edge cracking of cold-rolled strip. Summary of the invention

[0004] Based on this, it is necessary to provide a method that can effectively improve the edge cracking of cold-rolled strip.

[0005] The present application provides a method for improving edge cracking of cold-rolled steel strip, comprising the following steps: sequentially performing pickling and rolling treatments on the steel,

[0006] The rolling speed in the rolling process is below 500 m / min, the number of rolling passes is ≥ 5 times, the reduction rate of each pass is ≤ 50%, and the unit tension at the entrance of each pass is ≤ 20 N / mm 2 , each exit unit tension ≤ 20N / mm 2 .

[0007] In some of the embodiments, the emulsion flow rate in the rolling process is 3000 L / min to 5300 L / min, and can further be 3200 L / min to 4300 L / min.

[0008] In some implementation modes, the rolling speed is 80 m / min to 450 m / min, and can be optionally 200 m / min to 300 m / min.

[0009] In some embodiments, the rolling passes are 5 to 10 times, and can be optionally 8 to 10 times.

[0010] In some embodiments, in the rolling process, the reduction rate of each pass is 10% to 50%, and can be optionally 10% to 20%.

[0011] In some embodiments, in the rolling process, the reduction ratio in each pass is the same.

[0012] In some embodiments, during the rolling process, the unit tension at the entrance of each pass is 5 to 20 N / mm. 2 The unit tension of each exit is 5~20N / mm 2 .

[0013] In some embodiments, when the steel is rolled to an intermediate thickness during the rolling process, the steel is taken off the machine and left for 1 to 5 days, and then put back on the machine to continue the rolling process;

[0014] The intermediate thickness is the thickness of the steel before rolling - (the thickness of the steel before rolling - the thickness of the steel after rolling) / 2.

[0015] In some embodiments, a pretreatment step is further included before the pickling step.

[0016] The pretreatment step includes checking the edge rot and edge damage of the steel and grinding the steel with edge defects.

[0017] In some embodiments, the steel strip satisfies one or more of the following conditions (1) to (2):

[0018] (1) The steel material is composed of the following chemical components in weight percentage:

[0019] C: 0.6% to 1.5%, Si: 0.1% to 0.50%, Mn: 0.1 to 1.4%, P: ≤0.02%, S: ≤0.02%, trace elements ≤2.0%, Al: ≤0.06%, and the rest are Fe and unavoidable impurities, wherein the trace elements are Cr, Ni and Mo;

[0020] (2) The thickness of the steel before rolling is 0.3 mm to 10 mm, and the width is 900 mm to 2250 mm.

[0021] Compared with the prior art, this application has at least the following beneficial effects:

[0022] The present application controls the process parameters of the rolling process without changing the equipment, increasing the cost or new process, and slowly releases the internal stress of the strip by reducing the cold rolling speed, increasing the number of rolling passes, reducing the reduction and unit tension, etc., to prevent the micro cracks at the edges from expanding and extending inward quickly, and reduce the tensile stress on the strip during the rolling process, thereby improving the problem of edge cracking of the cold-rolled strip, effectively reducing the risk of obvious cracking and strip breakage at the edges of high-carbon steel, and improving the production rhythm and yield rate. DETAILED DESCRIPTION

[0023] For ease of understanding of the present application, the present application will be described more fully below. Preferred embodiments of the present application are provided in the embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0025] In this application, "first aspect", "second aspect", "third aspect", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In the present application, "one or more" refers to any one, any two, or any two or more of the listed items.

[0028] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0029] The percentage contents involved in this application, unless otherwise specified, refer to mass percentage for solid-liquid mixing and solid-solid mixing, and refer to volume percentage for liquid-liquid mixing.

[0030] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0031] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range of instrument control.

[0032] In the present application, the method steps that do not emphasize the temperature usually refer to the method steps performed at normal temperature or room temperature. In this article, normal temperature and room temperature are equivalent and interchangeable, and the specific temperature refers to 22°C to 25°C.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0035] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0036] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0037] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] High carbon steel is particularly prone to stress concentration cracking during the cold rolling process due to its high carbon content and low ductile-brittle transition temperature. Therefore, how to release the internal stress of the strip is the key to effectively prevent edge cracking and strip breakage of cold rolled high carbon steel.

[0039] Therefore, an embodiment of the present application provides a method for improving edge cracking of cold-rolled steel strip, comprising the following steps: sequentially performing pickling and rolling treatments on the steel material;

[0040] The rolling speed in the rolling process is below 500 m / min, the number of rolling passes is ≥ 5 times, the reduction rate of each pass is ≤ 50%, and the unit tension at the entrance of each pass is ≤ 20 N / mm 2 , each exit unit tension ≤ 20N / mm2 .

[0041] The entrance unit tension of each pass is reduced to 70% to 80% of the normal entrance unit tension, and the exit unit tension of each pass is reduced to 70% to 80% of the normal exit unit tension.

[0042] The conventional inlet unit tension is 20-25 N / mm 2 The conventional export unit tension is 20-25N / mm 2 .

[0043] The present application controls the process parameters of the rolling process without changing the equipment, increasing the cost and new process, and controls the rolling speed in the rolling process to a relatively low speed below 500m / min, which is conducive to the slow release of the internal stress of the strip; increases the number of rolling passes to be greater than or equal to 5 times, and controls the reduction rate of each pass to be less than or equal to 50%, and performs rolling with multiple passes and small reduction to prevent the micro cracks at the edge from rapidly expanding and extending inward; reduces the inlet unit tension and outlet unit tension of each pass, thereby reducing the tensile stress borne by the strip during the rolling process, thereby improving the problem of edge cracking of the cold-rolled strip.

[0044] The rolling speed is lower than the conventional rolling speed. The conventional rolling speed is greater than or equal to 500m / min, and the rolling speed of the present application is less than 500m / min. Limiting the rolling speed to less than 500m / min is conducive to the slow release of the internal stress of the strip and is not easy to tear the micro cracks on the edge of the steel.

[0045] In some embodiments, the rolling speed is any value between 80m / min and 450m / min or a range therebetween. It is understandable that the rolling speed may be 80m / min, 100m / min, 150m / min, 200m / min, 250m / min, 300m / min, 350m / min, 400m / min, 450m / min, and a range between any two values. Further optionally, the rolling speed is 200m / min to 300m / min.

[0046] The number of rolling passes is greater than or equal to 5 times, and the reduction rate of each pass is less than or equal to 50%. Through multiple passes and small reductions, smooth rolling is achieved to prevent the micro cracks on the edges from expanding and extending rapidly inwards due to excessive reduction, thereby reducing the unrepairable results caused by this.

[0047] In some embodiments, the rolling passes are any value between 5 and 10 or a range therebetween. It is understandable that the rolling passes may be 5, 6, 7, 8, 9, 10, and a range between any two values. Further optionally, the rolling passes are 8 to 10.

[0048] In some embodiments, the reduction rate of each pass is any value between 10% and 50% or a range therebetween. It is understandable that the reduction rate of each pass may be 10%, 20%, 30%, 40%, 50% and a range between any two values. Further optionally, the reduction rate of each pass is 10% to 20%.

[0049] In some embodiments, the reduction rate is the same for each pass.

[0050] In some embodiments, during the rolling process, the unit tension at the entrance of each pass is 5 to 20 N / mm. 2 The unit tension of each exit is 5~20N / mm 2 The unit tension during the rolling process is reduced by an average of 20% to 30% compared to the conventional unit tension.

[0051] The unit tension of each entrance can be 5N / mm 2 , 15N / mm 2 , 20N / mm 2 And the range between any two values. The unit tension of each entrance is reduced by 20% to 30% compared with the conventional entrance unit tension.

[0052] The unit tension of each exit can be 5N / mm 2 , 15N / mm 2 , 20N / mm 2 And the range between any two values. The unit tension of each pass is reduced by 20% to 30% compared with the conventional unit tension of each pass.

[0053] In some embodiments, the emulsion flow rate during the rolling process is reduced to 60% to 75% of the conventional emulsion flow rate. It is understandable that the emulsion flow rate during the rolling process can be reduced to 60%, 62%, 65%, 68%, 70%, 71%, 75% and the range between any two values ​​of the conventional emulsion flow rate. Appropriately reducing the emulsion flow rate during the rolling process can further improve the edge cracking problem of cold-rolled strip. Excessive emulsion flow rate can easily cause the edge of the strip to be overcooled, and for high carbon steel, it is easy for the edge structure to transform into brittle and hard martensite. If the edge contains martensitic structure, it is easy to produce microcracks at harder positions during the rolling process due to the unevenness of the edge structure, which can easily cause cracking problems. The conventional emulsion flow rate is 5000L / min to 7500L / min.

[0054] In some embodiments, the emulsion flow rate in the rolling process is 3000L / min to 5300L / min and any value therebetween. It is understandable that the emulsion flow rate in the rolling process may be 3000L / min, 3500L / min, 4000L / min, 4500L / min, 5000L / min, 5100L / min, 5300L / min and a range between any two values. Further optionally, the emulsion flow rate in the rolling process is 3200L / min to 4300L / min.

[0055] The temperature of the emulsion is not particularly limited and can be any temperature known to those skilled in the art. For example, in some embodiments, the temperature of the emulsion is 35 to 65° C. The components of the emulsion are not particularly limited and can be any components known to those skilled in the art. For example, in some embodiments, the components of the emulsion include base oil, emulsifier, additives and water.

[0056] In some embodiments, when the steel is rolled to an intermediate thickness during the rolling process, the steel is taken off the machine and left for 1 to 5 days, such as 1 day, 2 days, 3 days, 4 days, or 5 days, and then put back on the machine to continue the rolling process. It should be noted that the intermediate thickness refers to the thickness of the steel before rolling - (the thickness of the steel before rolling - the thickness of the steel after rolling) / 2.

[0057] In some embodiments, a pretreatment step is further included before pickling. The method for improving edge cracking of cold-rolled steel strip comprises the following steps: pretreatment, pickling and rolling treatment are performed in sequence.

[0058] The pretreatment step includes checking the rotten edge and edge damage of the steel and grinding the steel with edge defects. Specifically, the method for checking the rotten edge and edge damage of the steel is a conventional method known to those skilled in the art, such as observation by several relevant technicians. The judgment standard for steel with edge defects is the conventional judgment standard in the field. Further, the grinding treatment is also any conventional method in the field, and the grinding treatment is performed until the rotten edge and edge damage visible to the naked eye are not visible on the end face of the steel.

[0059] The pickling process is not particularly limited, and can be a conventional method and process parameters known to those skilled in the art. For example, a typical process can be: straightening and uncoiling → inlet shearing → welding → descaling → clamping machine → looper → pickling → acid return tank → cleaning tank → purging → rinsing tank → neutralization tank → purging → drying → outlet pinching → outlet shearing → coiling.

[0060] In some embodiments, the steel material is composed of the following chemical components in weight percentage:

[0061] C: 0.6% to 1.5%, Si: 0.1% to 0.50%, Mn: 0.1 to 1.4%, P: ≤0.02%, S: ≤0.02%, trace elements ≤2.0%, Al: ≤0.06%, and the rest are Fe and unavoidable impurities, wherein the trace elements are Cr, Ni and Mo.

[0062] In some embodiments, the steel material has a thickness of 0.3 mm to 10 mm and a width of 900 mm to 2250 mm before rolling.

[0063] Example

[0064] The following are specific embodiments. The purpose is to further explain the present application in detail to help the technical personnel and researchers in the field to further understand the present application. The relevant technical conditions do not constitute any limitation to the present application. Any form of modification made within the scope of the claims of the present application is within the scope of protection of the claims of the present application.

[0065] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods. Experimental methods without specific conditions specified in the examples are carried out according to conventional conditions, such as those described in literature or books or methods recommended by manufacturers.

[0066] Example 1

[0067] The raw material is 75CR1 continuous casting slab. The chemical composition and mass percentage of the strip steel are: C: 0.74%, Si: 0.28%, Mn: 0.83%, S: 0.005%, P: 0.013%, Al: 0.03%, Cr: 0.43%, Cu: 0.08%, Ni: 0.03%, and the rest is Fe and unavoidable impurities. The finished strip steel specification is 1.1mm×2250mm×full length.

[0068] The above steel is sequentially subjected to pretreatment, pickling and rolling treatment to prepare a cold-rolled steel strip with a thickness of 1.1 mm, as follows:

[0069] (1) Pretreatment: Carefully check whether there are rotten edges and edge damage on the end surface, and grind the strip with edge defects until there is no visible rotten edge and edge damage on the end surface of the steel.

[0070] (2) Pickling: straightening and uncoiling → inlet shearing → welding → descaling → clamping machine → looper → pickling → acid return tank → cleaning tank → purging → rinsing tank → neutralization tank → purging → drying → outlet clamping → outlet shearing → coiling. The process parameters of each link are conventional parameters known to those skilled in the art.

[0071] (3) Rolling treatment: The rolling speed is limited to 300m / min, and 5 passes are used, with each pass rolling at a 20% reduction rate. The unit tension at the inlet and outlet is 14N / mm 2 Compared with the conventional inlet and outlet, the unit tension is reduced by 30%, and the emulsion flow rate is reduced to 3200L / min. During the rolling process, when the strip is rolled to 2.0mm, it is taken off the machine and placed for 3 days before continuing to be rolled on the machine.

[0072] Example 2

[0073] The chemical composition and mass percentage of the strip steel are as follows: C: 0.83%, Si: 0.16%, Mn: 0.35%, S: 0.0025%, P: 0.013%, Al: 0.03%, Cr: 0.15%, Cu: 0.03%, Ni: 0.15%, and the rest are Fe and unavoidable impurities. The finished strip steel specifications are 1.8mm×2250mm×full length.

[0074] The above steel is sequentially subjected to pretreatment, pickling and rolling treatment to prepare a cold-rolled steel strip with a thickness of 1.8 mm, as follows:

[0075] (1) Pretreatment: Carefully check whether there are rotten edges and edge damage on the end surface, and grind the strip with edge defects until there is no visible rotten edge and edge damage on the end surface of the steel.

[0076] (2) Pickling: straightening and uncoiling → inlet shearing → welding → descaling → clamping machine → looper → pickling → acid return tank → cleaning tank → purging → rinsing tank → neutralization tank → purging → drying → outlet clamping → outlet shearing → coiling. The process parameters of each link are conventional parameters known to those skilled in the art.

[0077] (3) Rolling treatment: The rolling speed is limited to 200m / min, and 8 passes are used for rolling, with each pass being rolled at a 10% reduction rate. The unit tension at the inlet and outlet is 18N / mm 2 Compared with the conventional inlet and outlet, the unit tension is reduced by 20% on average, and the emulsion flow rate is reduced to 4300L / min. During the rolling process, when the strip is rolled to 3.2mm, it is taken off the machine and placed for 1 day before continuing to be rolled on the machine.

[0078] Embodiment 3-4

[0079] The preparation methods of Examples 3 to 4 are basically the same as the preparation method of Example 1, except that: when preparing the cold-rolled steel strip, at least one of the rolling speed, rolling passes, reduction rate per pass, unit tension, emulsion flow rate and placement days in the rolling process is different, as shown in Table 1 below.

[0080] Comparative Examples 1 to 4

[0081] The preparation methods of Comparative Examples 1 to 4 are basically the same as the preparation method of Example 1, except that: when preparing the cold-rolled steel strip, at least one of the rolling speed, rolling passes, reduction rate per pass, unit tension, emulsion flow rate and placement days in the rolling process is different, as shown in Table 1 below.

[0082] The process parameters in the preparation methods of Examples 1 to 4 and Comparative Examples 1 to 4 are listed in Table 1 below. The edge cracking conditions are also listed in Table 1. The edge cracking conditions are determined by relevant technicians in the field using conventional methods:

[0083] Table 1

[0084]

[0085]

[0086] As shown in Table 1 above, the edge cracking and strip breaking of cold-rolled high carbon steel can be improved by reducing the cold rolling speed, increasing the number of rolling passes, reducing the reduction and unit tension, etc., and can be further improved by checking the edge rot of the incoming hot-rolled coil, reducing the emulsion flow rate, and rolling the strip to the middle thickness and leaving it for a period of time before re-rolling it on the machine. Through the adjustment of the above measures, the tensile stress on the strip during the rolling process is reduced, and the probability of brittle and hard martensite appearing on the edge is reduced. Even if micro cracks appear during the rolling process, they will not continue to extend inward due to excessive tensile stress and tension, thereby effectively reducing the risk of obvious cracking and strip breaking on the edge of high carbon steel, and improving the production rhythm and yield rate.

[0087] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for improving edge cracking of cold-rolled strip steel, It is characterized in that The following steps are involved: The steel is pickled and rolled in sequence. The rolling speed in the rolling process is below 500 m / min, the number of rolling passes is ≥ 5 times, the reduction rate of each pass is ≤ 50%, and the unit tension at the entrance of each pass is ≤ 20 N / mm 2 , each exit unit tension ≤ 20N / mm 2 .

2. The method for improving edge cracking of cold-rolled strip according to claim 1, It is characterized in that The emulsion flow rate in the rolling process is 3000L / min to 5300L / min, and can be optionally 3200L / min to 4300L / min.

3. The method for improving edge cracking of cold-rolled strip according to claim 2, It is characterized in that The rolling speed is 80m / min to 450m / min, and can be optionally 200m / min to 300m / min.

4. The method for improving edge cracking of cold-rolled strip according to claim 1, It is characterized in that The rolling passes are 5 to 10 times, and can be optionally 8 to 10 times.

5. The method for improving edge cracking of cold-rolled strip according to claim 1, It is characterized in that In the rolling process, the reduction rate of each pass is 10% to 50%, and can be optionally 10% to 20%.

6. The method for improving edge cracking of cold-rolled strip according to claim 1 or 5, It is characterized in that In the rolling process, the reduction ratio in each pass is the same.

7. The method for improving edge cracking of cold-rolled strip according to claim 1, It is characterized in that During the rolling process, the unit tension at the entrance of each pass is 5 to 20 N / mm. 2 The unit tension of each exit is 5~20N / mm 2 .

8. The method for improving edge cracking of cold-rolled steel strip according to any one of claims 1 to 7, It is characterized in that When the steel is rolled to an intermediate thickness during the rolling process, the steel is taken off the machine and left for 1 to 5 days, and then put back on the machine to continue the rolling process; The intermediate thickness is the thickness of the steel before rolling - (the thickness of the steel before rolling - the thickness of the steel after rolling) / 2.

9. The method for improving edge cracking of cold-rolled steel strip according to any one of claims 1 to 7, It is characterized in that A pretreatment step is also included before the pickling step. The pretreatment step includes checking the edge rot and edge damage of the steel and grinding the steel with edge defects.

10. The method for improving edge cracking of cold-rolled steel strip according to any one of claims 1 to 7, It is characterized in that The steel strip satisfies one or more of the following conditions (1) to (2): (1) The steel material has the following chemical components in weight percentage: composition: C: 0.6% to 1.5%, Si: 0.1% to 0.50%, Mn: 0.1 to 1.4%, P: ≤0.02%, S: ≤0.02%, trace elements ≤2.0%, Al: ≤0.06%, and the rest are Fe and unavoidable impurities, wherein the trace elements are Cr, Ni and Mo; (2) The thickness of the steel before rolling is 0.3 mm to 10 mm, and the width is 900 mm to 2250 mm.

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