A method for controlling transverse cracks at the corners of ultra-high carbon steel billets

Abstract

This application relates to a method for controlling transverse cracks at the corners of ultra-high carbon steel billets, belonging to the field of steel preparation technology. Specifically, by optimizing the specific water volume for cooling the fan-shaped section of billets with different chemical compositions, when Alt ≥ 0.020% in the billet, the specific water volume W is controlled to satisfy: 0.6 L / kg < W < 0.83 L / kg; when Alt < 0.020% in the billet, the fan-shaped section cooling is divided into two stages, where the first specific water volume w1 and the second specific water volume w2 satisfy: w1 > w2, w1 + w2 = 0.8 L / kg ~ 0.9 L / kg. This method can reduce the occurrence of transverse cracks at the corners of ultra-high carbon steel billets with a carbon content ≥ 1.0%, and can effectively suppress periodic liquid level fluctuations in the crystallizer, thereby improving the yield of ultra-high carbon steel billets with a carbon content ≥ 1.0%.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a method for controlling transverse cracks at the corners of ultra-high carbon steel billets. Background Technology

[0002] Ultra-high carbon steel and alloy steel with a carbon content ≥1.0% are highly susceptible to cracking. When the billet is cooled in the fan-shaped section, corner transverse cracks are easily generated. As the billet temperature decreases, the width and depth of the transverse cracks further increase. Due to the easy fracture characteristics of ultra-high carbon steel billets in the cold environment, transverse crack defects cannot be cleaned offline. Once corner transverse cracks occur, they cannot be repaired and can only be scrapped, which affects the billet yield and has a significant impact on production costs. Summary of the Invention

[0003] This application provides a method for controlling transverse cracks at the corners of ultra-high carbon steel billets to improve the yield of ultra-high carbon steel billets with a carbon content ≥1.0%.

[0004] This application provides a method for controlling transverse cracks at the corner of ultra-high carbon steel billets, the method comprising:

[0005] A cast billet is obtained, wherein the mass percentage of carbon in the cast billet is ≥1.0%;

[0006] The specific water volume for cooling the billet is controlled, and the control meets the following requirements:

[0007] When the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.6L / kg < W < 0.83L / kg;

[0008] When the mass percentage of Alt in the billet is <0.020%, the specific water content includes a first specific water content and a second specific water content. The first specific water content w1 and the second specific water content w2 satisfy: w1 > w2, w1 + w2 = 0.8 L / kg ~ 0.9 L / kg, and the order in which the billet undergoes cooling with the first specific water content and the second specific water content is: first undergoing cooling with the first specific water content, and then undergoing cooling with the second specific water content.

[0009] As an optional implementation, when the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.7L / kg≤W≤0.80L / kg.

[0010] As an optional implementation, when the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.7L / kg≤W≤0.75L / kg.

[0011] As an optional implementation, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 and the second specific water content w2 satisfy: w1-w2≥0.15L / kg.

[0012] As an optional implementation, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 and the second specific water content w2 satisfy: w1-w2≥0.45L / kg.

[0013] As an optional implementation, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 ≥ 0.5 L / kg, and the second specific water content w2 ≤ 0.33 L / kg.

[0014] As an optional implementation, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 ≥ 0.66 L / kg, and the second specific water content w2 ≤ 0.17 L / kg.

[0015] As an optional implementation, when the mass percentage of Alt in the billet is <0.020%, the first specific water amount is the specific water amount of the billet in the pasty zone during cooling, and the second specific water amount is the specific water amount of the billet after passing through the pasty zone during cooling.

[0016] As an optional implementation, when the mass percentage of Alt in the billet is less than 0.020%, the switching position between the first specific water content and the second specific water content along the transport direction of the billet is 9m to 11m from the end of the fan-shaped segment.

[0017] As an optional implementation, the switching position between the first specific water volume and the second specific water volume is 9.5m to 10.5m from the end of the fan-shaped segment.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art:

[0019] The method provided in this application optimizes the specific water volume for cooling the fan-shaped section of billets with different chemical compositions. Specifically, when Alt ≥ 0.020% in the billet, the specific water volume W is controlled to satisfy: 0.6 L / kg < W < 0.83 L / kg; when Alt < 0.020% in the billet, the fan-shaped section cooling is divided into two cooling stages, wherein the first specific water volume w1 and the second specific water volume w2 satisfy: w1 > w2, w1 + w2 = 0.8 L / kg ~ 0.9 L / kg. This method can reduce the occurrence of transverse cracks at the corners of ultra-high carbon steel billets with a carbon content ≥ 1.0%, and can effectively suppress periodic liquid level fluctuations in the crystallizer, thereby improving the yield of ultra-high carbon steel billets with a carbon content ≥ 1.0%. Attached Figure Description

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

[0021] To more clearly illustrate the technical solutions in the embodiments of this application 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.

[0022] Figure 1 This is a flowchart illustrating the method provided in an embodiment of this application. Detailed Implementation

[0023] 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.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0025] Ultra-high carbon steel and alloy steel with a carbon content ≥1.0% are highly susceptible to cracking. During the cooling of the billet in the fan-shaped section, corner transverse cracks are easily generated (e.g., ...). Figure 1 As shown in the figure, the width and depth of transverse cracks further increase with decreasing billet temperature. For example, in the production process of ultra-high carbon steel and its alloy steel (C content ≥1%), when using a specific water volume of 0.83 L / kg and casting a billet with a width of less than 1100 mm, transverse cracks appear at the corners of the billet, with a crack depth of 5-30 mm and a width of 2-10 mm. To investigate the cause of this crack, the corner temperature of the billet was tracked at a specific water volume of 0.83 L / kg. After passing the straightening section, the corner temperature of the billet was 680-690℃. The low corner temperature suggests that the secondary cooling water volume is relatively large, resulting in stronger cooling. The billet is subjected to mechanical stress during bending and straightening, forming transverse cracks at the corners. The depth and width of the transverse crack defects are relatively large. Furthermore, this type of steel is prone to fracture at low temperatures, and at high temperatures, the billet cannot be chamfered to eliminate defects. The billets are then scrapped, which has a significant impact on production costs.

[0026] Meanwhile, the applicant discovered that when the Alt content of the steel grade was less than 0.020%, periodic fluctuations in the crystallizer liquid level occurred under a cooling mode with a specific water volume of 0.83 L / kg. This indicates that the 0.83 L / kg specific water volume provides weaker cooling for ultra-high carbon steels and their alloys with Alt < 0.020%, suggesting that the Alt content has a certain impact on the high-temperature strength of ultra-high carbon steels and their alloys. To improve the periodic liquid level fluctuations of this type of steel, the specific water volume of the secondary cooling water needs to be increased. However, with the increase of the secondary cooling water volume, the temperature at the corner of the billet further decreases, which is detrimental to controlling the formation of transverse cracks at the corner of the billet.

[0027] Therefore, this application intends to provide a cooling process for ultra-high carbon steel billets with different compositions to improve the yield of ultra-high carbon steel billets with a carbon content ≥1.0%.

[0028] Figure 1 A flowchart illustrating the method provided in the embodiments of this application, as shown below. Figure 1 As shown in the embodiment of this application, a method for controlling transverse cracks at the corner of ultra-high carbon steel billets is provided, the method comprising:

[0029] S1. Obtain a cast billet, wherein the mass percentage of carbon in the cast billet is ≥1.0%;

[0030] First, it is necessary to obtain ultra-high carbon steel billets with a carbon content of ≥1.0%.

[0031] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements:

[0032] When the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.6L / kg < W < 0.83L / kg;

[0033] When the mass percentage of Alt in the billet is <0.020%, the specific water content includes a first specific water content and a second specific water content. The first specific water content w1 and the second specific water content w2 satisfy: w1 > w2, w1 + w2 = 0.8 L / kg ~ 0.9 L / kg, and the order in which the billet undergoes cooling with the first specific water content and the second specific water content is: first undergoing cooling with the first specific water content, and then undergoing cooling with the second specific water content.

[0034] Chemical composition analysis was performed on the cast billet, particularly the content of Alt. The Alt content directly affects the control of the subsequent cooling water ratio. Controlling the cooling water ratio:

[0035] When the mass percentage of Alt in the billet is ≥0.020%, the specific water content W during the cooling process should be controlled between 0.6 L / kg and 0.83 L / kg. This range of specific water content helps reduce internal stress and hot cracks generated in the billet during cooling.

[0036] When the mass percentage of Alt in the billet is less than 0.020%, the cooling process is divided into two stages: a first specific water volume w1 and a second specific water volume w2. The first specific water volume w1 is controlled to be greater than the second specific water volume w2, and the sum of the two, w1 + w2, is between 0.8 L / kg and 0.9 L / kg. The billet first undergoes cooling with the first specific water volume, and then with the second specific water volume. This segmented cooling method can more effectively reduce the incidence of transverse cracks at the corners of the billet.

[0037] In some embodiments, when the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.7L / kg≤W≤0.80L / kg.

[0038] Furthermore, when the mass percentage of Alt in the billet is ≥0.020%, the specific water content W satisfies: 0.7L / kg≤W≤0.75L / kg.

[0039] In some embodiments, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 and the second specific water content w2 satisfy: w1-w2≥0.15L / kg.

[0040] Furthermore, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 and the second specific water content w2 satisfy: w1-w2≥0.45L / kg.

[0041] In some embodiments, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 ≥ 0.5 L / kg, and the second specific water content w2 ≤ 0.33 L / kg.

[0042] Furthermore, when the mass percentage of Alt in the billet is <0.020%, the first specific water content w1 ≥ 0.66 L / kg, and the second specific water content w2 ≤ 0.17 L / kg.

[0043] In some embodiments, when the mass percentage of Alt in the billet is <0.020%, the first specific water amount is the specific water amount of the billet in the pasty region during cooling, and the second specific water amount is the specific water amount of the billet after passing through the pasty region during cooling.

[0044] Furthermore, when the mass percentage of Alt in the billet is less than 0.020%, the switching position between the first specific water content and the second specific water content along the transport direction of the billet is 9m to 11m from the end of the fan-shaped segment.

[0045] Furthermore, the switching position between the first specific water volume and the second specific water volume is 9.5m to 10.5m from the end of the fan-shaped segment.

[0046] In summary, the proposed method provides a method for controlling transverse cracks at the corners of ultra-high carbon steel billets, which has the following advantages:

[0047] Reducing the incidence of transverse cracks: By precisely controlling the specific water volume during the cooling process, this method can significantly reduce the incidence of transverse cracks at the corners of ultra-high carbon steel billets.

[0048] Improved yield: By reducing the occurrence of transverse cracks, the scrap rate of the cast billet will be reduced in subsequent processing, thereby improving the yield.

[0049] Improve production efficiency: This method is simple and easy to implement, and can achieve significant technical results without large-scale modification of existing production equipment.

[0050] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0051] To study the cooling process of ultra-high carbon steel billets with a mass percentage of Alt ≥ 0.020%, the following study investigates the cooling process of billets with the following composition by mass fraction: C: 1.05%, Si: 0.3%, Mn: 0.65%, Alt: 0.035%.

[0052] Comparative Example 1

[0053] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0054] S1. Obtain the cast billet;

[0055] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.83 L / kg.

[0056] Example 1

[0057] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0058] S1. Obtain the cast billet;

[0059] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.80 L / kg.

[0060] Example 2

[0061] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0062] S1. Obtain the cast billet;

[0063] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.75 L / kg.

[0064] Example 3

[0065] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0066] S1. Obtain the cast billet;

[0067] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.70 L / kg.

[0068] Comparative Example 2

[0069] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0070] S1. Obtain the cast billet;

[0071] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.60 L / kg.

[0072] The cooling processes of Examples 1 to 3 and Comparative Examples 1 to 2, as well as the crack conditions and corner temperatures of the final cast slabs, are as follows:

[0073]

[0074] The table above shows that when the specific water volume is reduced to 0.70 L / kg, the transverse cracks at the corners of the cast billet disappear. However, when the secondary cooling water volume reaches 0.6 L / kg, the fluctuation in the crystallizer liquid level shows an increasing trend. This indicates that using a secondary cooling water volume of 0.70 L / kg is effective in improving the reduction of transverse cracks at the corners of ultra-high carbon and alloy steel billets with an Alt content ≥ 0.020%. Compared to the original process, the secondary cooling water volume is reduced by 0.13 L / kg, and the corner temperature of the cast billet increases by 60℃.

[0075] As shown in the table above, the method provided in this application embodiment can improve the yield of billets with a mass percentage of C ≥ 1.0% and a mass percentage of Alt ≥ 0.020%, control the crack incidence rate to below 54%, and control the fluctuation of the liquid level in the crystallizer.

[0076] To study the cooling process of ultra-high carbon steel billets with a mass percentage of Alt < 0.020%, the following study investigates the cooling process of billets with the following composition by mass fraction: C: 1.05%, Si: 0.3%, Mn: 0.65%, Alt: 0.008%.

[0077] Example 4

[0078] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0079] S1. Obtain the cast billet;

[0080] S2. Control the specific water volume for cooling the billet, wherein the control satisfies the following requirements: the specific water volume includes a first specific water volume and a second specific water volume, wherein the first specific water volume w1 and the second specific water volume w2 satisfy: w1 > w2, w1 + w2 = 0.83 L / kg, w1 = 0.5 L / kg, w2 = 0.33 L / kg, and the order in which the billet undergoes cooling with the first specific water volume and the second specific water volume is: first undergoing cooling with the first specific water volume, and then undergoing cooling with the second specific water volume. Along the transport direction of the billet, the switching position of the first specific water volume and the second specific water volume is 10m from the end of the fan-shaped segment.

[0081] Example 5

[0082] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0083] S1. Obtain the cast billet;

[0084] S2. Control the specific water volume for cooling the billet, wherein the control satisfies the following requirements: the specific water volume includes a first specific water volume and a second specific water volume, wherein the first specific water volume w1 and the second specific water volume w2 satisfy: w1 > w2, w1 + w2 = 0.83 L / kg, w1 = 0.66 L / kg, w2 = 0.17 L / kg, and the order in which the billet undergoes cooling with the first specific water volume and the second specific water volume is: first undergoing cooling with the first specific water volume, and then undergoing cooling with the second specific water volume. Along the transport direction of the billet, the switching position of the first specific water volume and the second specific water volume is 10m from the end of the fan-shaped segment as the starting position.

[0085] Comparative Example 3

[0086] A method for controlling transverse cracks at the corners of ultra-high carbon steel billets, the method comprising:

[0087] S1. Obtain the cast billet;

[0088] S2. The specific water volume for cooling the billet is controlled, and the control meets the following requirements: the specific water volume W is 0.83 L / kg.

[0089] The cooling process, crack conditions, and corner temperatures of the final cast billets in Examples 4 and 5 and Comparative Example 3 are as follows:

[0090]

[0091] As shown in the table above, the method provided in this application redistributes the secondary cooling water flow rate in each zone. Specifically, it increases the secondary cooling water flow rate before the mushy zone, thereby increasing the billet shell thickness, enhancing its resistance to the static pressure of molten steel, and eliminating periodic liquid level fluctuations in the crystallizer. After the mushy zone, it reduces the secondary cooling water flow rate, decreasing the cooling intensity, allowing the billet to reheat, increasing the corner temperature of the billet, and preventing the formation of transverse cracks.

[0092] Compared with Comparative Example 3, under the condition of constant secondary cooling water specific volume of 0.83 L / kg, by adjusting the surface temperature of the billet in the secondary automatic water distribution model, the cooling of the fan-shaped billet is divided into two control segments. When the length of the fan-shaped billet is ≤10m, the specific water volume is increased, the billet shell thickness is increased, and the ability of the billet shell to resist the static pressure of molten steel is improved, thus alleviating the periodic liquid level fluctuations in the crystallizer. When the length of the fan-shaped billet is >10m, the specific water volume is reduced, the billet reheats, and the temperature of the billet corner is increased, thus solving the transverse crack defect at the corner of the billet. After optimizing the specific water volume distribution, the periodic liquid level fluctuations in the crystallizer are significantly improved, and there are no transverse cracks at the corner of the billet.

[0093] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0094] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely 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. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" 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 both mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0095] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. 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 this application. Therefore, this application 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 of controlling corner transverse cracking of ultra-high carbon steel slabs, characterized by, The method comprises: obtaining a casting blank, wherein the mass percentage of C in the casting blank is greater than or equal to 1.0%; controlling the specific water quantity of the casting blank cooling, wherein the control satisfies the following requirements: when the mass percentage of Alt in the casting blank is greater than or equal to 0.020%, the specific water quantity W satisfies 0.6L / kg when the mass percentage of Alt in the casting blank is less than 0.020%, the specific water quantity comprises a first specific water quantity and a second specific water quantity, the first specific water quantity w1 and the second specific water quantity w2 satisfy w1 > w2, w1 + w2 = 0.8L / kg ~ 0.9L / kg, and the sequence of the casting blank experiencing the first specific water quantity and the second specific water quantity cooling is: first experiencing the first specific water quantity cooling, and then experiencing the second specific water quantity cooling.

2. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 1, characterized in that, when the mass percentage of Alt in the casting blank is greater than or equal to 0.020%, the specific water quantity W satisfies 0.7L / kg 3. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 2, characterized in that, when the mass percentage of Alt in the casting blank is greater than or equal to 0.020%, the specific water quantity W satisfies 0.7L / kg 4. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 1, characterized in that, when the mass percentage of Alt in the casting blank is less than 0.020%, the first specific water quantity w1 and the second specific water quantity w2 satisfy w1 - w2 greater than or equal to 0.15L / kg.

5. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 4, characterized in that, when the mass percentage of Alt in the casting blank is less than 0.020%, the first specific water quantity w1 and the second specific water quantity w2 satisfy w1 - w2 greater than or equal to 0.45L / kg.

6. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 1, characterized in that, when the mass percentage of Alt in the casting blank is less than 0.020%, the first specific water quantity w1 is greater than or equal to 0.5L / kg, and the second specific water quantity w2 is less than or equal to 0.33L / kg.

7. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 6, characterized in that, when the mass percentage of Alt in the casting blank is less than 0.020%, the first specific water quantity w1 is greater than or equal to 0.66L / kg, and the second specific water quantity w2 is less than or equal to 0.17L / kg.

8. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 1, characterized in that, when the mass percentage of Alt in the casting blank is less than 0.020%, the first specific water quantity is the specific water quantity of the casting blank in the pasty zone cooling, and the second specific water quantity is the specific water quantity of the casting blank after the pasty zone cooling.

9. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 1, wherein when the mass percentage of Alt in the casting blank is less than 0.020%, the switching position of the first specific water quantity and the second specific water quantity is 9m ~ 11m from the starting position of the sector segment end.

10. The method of controlling corner transverse cracking of ultra-high carbon steel slabs according to claim 9, wherein the switching position of the first specific water quantity and the second specific water quantity is 9.5m ~ 10.5m from the starting position of the sector segment end.

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