A method for controlling surface welding scar defects of a bloom high-carbon chromium bearing steel

Abstract

This invention discloses a method for controlling surface weld scar defects in large square billets of high-carbon chromium bearing steel, belonging to the field of metallurgical technology. For GCr15 steel, the method for controlling surface weld scar defects includes the following steps: molten steel enters the crystallizer, forming a solidified billet shell, and leaves the crystallizer under the action of a straightening machine. In the secondary cooling chamber, the molten steel is cooled by water spray, gradually solidifying into a large square billet. The protective slag addition rate is controlled at 58-60 g / min, the large billet drawing speed is 0.9-1.1 m / min, and the crystallizer cooling water flow rate is 142-144 m³ / min. 3 The above controls various parameters during the continuous casting process of high-carbon chromium bearing steel GCr15, ultimately reducing the surface weld scar defect rate of large billets to less than 1%. Compared with existing control methods, this significantly reduces the weld scar defect on the surface of GCr15 steel.

Description

A method for controlling surface weld scar defects in large square billet high carbon chromium bearing steel Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically, to a method for controlling surface weld scar defects on large billet high-carbon chromium bearing steel. Background Technology

[0002] Currently, the most produced bearing steel is GCr15, a high-carbon chromium bearing steel. Bearing steel is primarily used in environments with strong impact loads and alternating loads. These environments require bearing steels to exhibit good hardness and high contact fatigue strength, as well as high toughness and hardenability. Current bearing steel production processes are relatively traditional, generally utilizing continuous casting technology. Compared to ingot casting, continuous casting produces products with superior surface quality, and its yield and cost-effectiveness are also better.

[0003] However, in actual production, surface weld scars often appear on the surface of GCr15 steel. Although there are reports in the literature on controlling and improving the surface weld scar defects of GCr15 steel, the incidence of "weld scar" defects on the surface of the billet is still relatively high.

[0004] Therefore, it is necessary to develop a method for controlling surface weld scar defects in large square billet high carbon chromium bearing steel. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for controlling surface weld scar defects in large square billet high carbon chromium bearing steel.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] This invention provides a method for controlling weld scar defects on the surface of high-carbon chromium bearing steel billets, comprising the following steps: molten steel enters a crystallizer, forming a solidified billet shell; under the action of a straightening machine, it leaves the crystallizer and is cooled by water spray in a secondary cooling chamber, gradually solidifying into a large billet. The method involves controlling the addition rate of protective slag to 58-60 g / min, the billet drawing speed to 0.9-1.1 m / min, and the crystallizer cooling water flow rate to 142-144 m³ / min. 3 / h.

[0008] The present invention has the following beneficial effects:

[0009] This invention provides a method for controlling surface weld scar defects in high-carbon chromium bearing steel billets, comprising the following steps: molten steel enters a crystallizer, forming a solidified billet shell; under the action of a straightening machine, it leaves the crystallizer and is cooled by water spray in a secondary cooling chamber, gradually solidifying into a large billet. The protective slag addition rate is 58-60 g / min, the billet drawing speed is 0.9-1.1 m / min, and the crystallizer cooling water flow rate is 142-144 m³ / min. 3 By rationally configuring various parameters in the continuous casting production process, the defects of electric welding scars on the surface of high carbon chromium bearing steel in large billets can be effectively reduced, thereby improving the quality of high carbon chromium bearing steel. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 is a schematic diagram of the billet casting process;

[0012] Figure 2 is a photograph of the appearance of the cast billet obtained in the embodiment;

[0013] Figure 3 shows a photograph of the appearance of the cast billet obtained in the comparative example. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0015] The following is a detailed description of a method for controlling surface weld scar defects in high-carbon chromium bearing steel billets provided by an embodiment of the present invention.

[0016] This invention provides a method for controlling weld scar defects on the surface of high-carbon chromium bearing steel billets, comprising the following steps: molten steel enters a crystallizer, forming a solidified billet shell, and leaves the crystallizer under the action of a straightening machine. In the secondary cooling chamber, the molten steel is cooled by water spray, gradually solidifying into a large billet. The protective slag addition rate is controlled at 58-60 g / min, the billet drawing speed is 0.9-1.1 m / min, and the crystallizer cooling water flow rate is 142-144 m³ / min. 3 / h.

[0017] As the name suggests, weld scar defects are named for their resemblance to the texture of an electric weld. They are a unique surface quality defect found only in high-carbon steel. Primarily located within half the distance from the center line of the surface, they appear as strip-shaped grooves along the straightening direction of the cast billet. These grooves contain weld scar textures, which appear intermittently. Weld scars are classified as surface quality defects.

[0018] High-carbon chromium bearing steel is a high-carbon, high-alloy steel, making it highly susceptible to cracking. Uneven heating and cooling can easily lead to stress cracks on its surface. The mold flux acts as a lubricant and coolant for the billet. When the mold flux is added at a reasonable rate, it melts and fills the gap between the billet shell and the crystallizer, resulting in uniform lubrication and cooling of the billet surface. At a constant addition rate, if the casting speed is too high, the mold flux cannot melt and fill the gap between the billet and the crystallizer in time, affecting the lubrication and cooling effect on the billet surface. If the casting speed is too low, the billet stays in the crystallizer for too long, resulting in excessive cooling and uneven cooling, leading to cracking. If the cooling water flow rate in the crystallizer is too high, the cooling intensity on the billet surface is too great, easily causing uneven cooling and stress cracks. If the cooling water flow rate is too low, the cooling intensity on the billet surface is too small, resulting in a thinner billet shell, which is prone to localized cracking and weld spatter defects. Therefore, only by rationally configuring the flux addition rate, casting speed, and crystallizer water flow rate can the surface of the billet be cooled uniformly, reducing the generation of weld scar defects on the billet surface. Through long-term practice, the inventors have proposed a method for controlling weld scar defects on the surface of large square billet high carbon chromium bearing steel. By rationally matching continuous casting process parameters such as flux addition rate, casting speed, and crystallizer cooling water flow rate, the proportion of weld scar defects on the surface of the continuous casting billet is controlled to within 1% during the production of large square billet high carbon chromium bearing steel, resulting in high carbon chromium bearing steel with good surface quality and no weld scar defects.

[0019] In an optional embodiment, the cross-section of the large billet is 250-320mm×250-320mm, preferably 280mm×280mm.

[0020] In an optional implementation, the high-carbon chromium bearing steel is GCr15 steel.

[0021] In an optional embodiment, the high-carbon chromium bearing steel comprises the following components by weight percentage: C: 1.0%-1.03%, Si: 0.25%-0.35%, Mn: 0.35%-0.45%, P: 0-0.015%, S: 0-0.015%, Cr: 1.48-1.6%, Mo: 0-0.1%, Ni: 0-0.3%, Cu: 0-0.25%, Ti: 0-0.003%, Al: 0.015-0.04%, As: 0-0.04%, Sn: 0-0.03%, Pb: 0-0.002%, Sb: 0-0.005%.

[0022] In an optional implementation, for the first heat of tundish casting, the superheat of the molten steel is controlled at 35-40°C; for the second to Nth heats of tundish casting, the superheat of the molten steel is controlled at 25-35°C. The superheat indirectly reflects the temperature of the molten steel in contact with the protective slag in the crystallizer. For the same protective slag, if the superheat of the molten steel is too high, the high-temperature flowing molten steel will erode the thickness of the billet shell, resulting in a thinner initial billet shell, high thermal stress, and a tendency to crack. If the superheat of the molten steel is too low, the protective slag will not melt properly, and the billet shell will not receive uniform lubrication. Therefore, the present invention's control of the superheat of the molten steel for different tundish casting heats is beneficial for stably controlling the thickness of the protective slag layer.

[0023] In an optional embodiment, the total salt content of the cooling water used in the crystallizer is ≤500mg / l, and the turbidity is ≤10ntu.

[0024] In an optional implementation, the total cooling water flow rate of the secondary cooling zone is 200.2-203.7 m³ / h. 3 / h.

[0025] In an optional implementation, the secondary cooling zone is divided into six cooling zones, with water flow rates for each zone as follows: Zone 1: 30-30.6 L / min; Zone 2: 30-30.6 L / min; Zone 3: 33-33.6 L / min; Zone 4: 33-33.6 L / min; Zone 5: 46.2-46.8 m³ / min. 3 / h and Zone 6 28-28.5m 3 / h. In this embodiment of the invention, the secondary cooling zone is divided into 6 cooling zones. The front section of the secondary cooling zone is subjected to ultra-strong cooling by increasing the water flow rate gradient, which is more conducive to the rapid growth of the billet shell and reduces the risk of steel leakage under high drawing speed conditions. The rear section of the secondary cooling zone is subjected to a warming method by decreasing the water flow rate, which makes the temperature gradient distribution from the surface of the billet to the center position uniform and is conducive to quality control during the rolling process.

[0026] In an optional implementation, the total salt content of the cooling water used in the secondary cooling zone is ≤1000 mg / L, and the turbidity is ≤20 ntu.

[0027] In an optional implementation, the surface weld scar defects of the large billet high carbon chromium bearing steel are inspected, and the surface weld scars account for less than 1%.

[0028] As can be seen from the above, the embodiments of the present invention provide a method for controlling surface weld scar defects of high carbon chromium bearing steel in large billets. By reasonably configuring various parameters in the continuous casting process, the surface weld scar defect rate of high carbon chromium bearing steel in large billets can be effectively reduced. Compared with the 33% surface weld scar defect rate obtained by traditional continuous casting production, the method provided by the embodiments of the present invention can reduce the surface weld scar defect rate to less than 1%.

[0029] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0030] A schematic diagram of the billet casting process is shown in Figure 1. This invention provides a method for controlling surface weld scar defects in large square billets of high-carbon chromium bearing steel, comprising the following steps:

[0031] With 280 2 Taking GCr15 steel as an example, its composition is as follows: C: 1.0%-1.03%, Si: 0.25%-0.35%, Mn: 0.35%-0.45%, P: 0-0.015%, S: 0-0.015%, Cr: 1.48-1.6%, Mo: 0-0.1%, Ni: 0-0.3%, Cu: 0-0.25%, Ti: 0-0.003%, Al: 0.015-0.04%, As: 0-0.04%, Sn: 0-0.03%, Pb: 0-0.002%, Sb: 0-0.005%. Control during continuous casting:

[0032] The rate of adding protective slag is 58-60 g / min.

[0033] The pulling speed is 0.9-1.1 m / min.

[0034] The cooling water flow rate for the crystallizer is 142-144 m³ / h. 3 / h, total salt content of cooling water ≤500mg / l, turbidity ≤10ntu.

[0035] The total cooling water flow rate of the secondary cooling zone is 200.2-203.7 m³ / h. 3 The cooling water quality has a total salt content ≤1000mg / l and turbidity ≤20ntu. The secondary cooling zone is divided into six sections: Zone 1, Zone 2, Zone 3, Zone 4, Zone 5, and Zone 6. The cooling water flow rate for Zones 1 and 2 is 30-30.6L / min, for Zones 3 and 4 it is 33-33.6L / min, and for Zone 5 it is 46.2-46.8m³ / min. 3 The cooling water flow rate in Zone 6 is 28-28.5 m³ / h. 3 / h.

[0036] After continuous casting is completed, the surface of the large billet after cooling is inspected for weld scars.

[0037] Table 1 below is 280 2 The main production process parameters for large square billets.

[0038] Table 1

[0039]

[0040] Table 2 below is 2802 The proportion of internal cracks in large billets.

[0041] Table 2

[0042]

[0043] As can be seen from Table 2 above: In this embodiment of the invention, a suitable continuous casting process is adopted to control the 280°C of GCr15 steel. 2 By rationally configuring the flux addition rate, casting speed, crystallizer water flow rate, and cooling process in the production of large billets, the proportion of weld scar defects on the surface of high-carbon chromium bearing steel billets can be stably controlled to within 1%. The appearance of the resulting product is shown in Figure 2, indicating good surface quality, smoothness, and no defects. In contrast, in the comparative example, changes in the flux addition rate, casting speed, crystallizer water flow rate, and cooling parameters during continuous casting significantly increased the weld scar defects on the surface of the high-carbon chromium bearing steel billets. The appearance of the resulting product is shown in Figure 3, where micro-cracks are visible under the surface of the billet after grinding, and obvious weld scar defects appear on the billet surface, severely affecting surface quality and leading to a reduction in billet performance and price. Specifically:

[0044] Comparative Example 1

[0045] Similar to the steps in Example 1, the only difference is that the addition rate of the protective slag is 54 g / min, resulting in a weld scar defect rate of 10%. When the addition rate of the protective slag is too low, the melting rate of the protective slag cannot keep up with the casting speed of the billet, resulting in intermittent unevenness on the surface of the billet. This causes the molten steel to seep out and solidify after the surface shell cracks, forming weld scar defects.

[0046] Comparative Example 2

[0047] Similar to the steps in Example 1, the only difference is that the flux addition rate is 65 g / min, resulting in a weld spatter defect rate of 26%. When the flux addition rate is too high, the flux cannot melt in time, resulting in poor lubrication between the billet surface and the crystallizer, and poor cooling of the billet surface. When the billet surface cools unevenly, weld spatter defects are easily generated.

[0048] Comparative Example 3

[0049] Similar to the steps in Example 1, the only difference is that the casting speed of the large billet is 0.7 m / min, resulting in a weld scar defect rate of 15%. When the casting speed is slow, the cooling intensity obtained by the billet in the same time is too large, which makes the surface of the billet prone to uneven cooling and stress cracks, forming weld scar defects.

[0050] Comparative Example 4

[0051] Similar to the steps in Example 1, the only difference is that the casting speed of the large billet is 1.3 m / min, resulting in a weld scar defect rate of 20%. When the casting speed is high, the protective slag of the molten layer on the surface of the billet cannot fill the gap between the billet and the crystallizer in time, resulting in poor cooling effect on the surface of the billet, thin billet shell, and easy cracking to form weld scar defects.

[0052] Comparative Example 5

[0053] The steps are similar to those in Example 1, except that the cooling water flow rate of the crystallizer is 135 m³ / h. 3 / h, the result showed that the proportion of weld scar defects was 25%. When the water flow rate of the crystallizer is low, the cooling efficiency of the crystallizer is low, resulting in a thin shell on the surface of the billet, which is prone to cracking and forming weld scar defects.

[0054] Comparative Example 6

[0055] The steps are similar to those in Example 1, except that the cooling water flow rate of the crystallizer is 150 m³ / h. 3 / h, the result showed that the proportion of weld scar defects was 22%. When the water flow rate of the crystallizer is large, the cooling intensity of the billet surface is too high, which makes the billet surface prone to uneven cooling and stress cracks, forming weld scar defects.

[0056] Comparative Example 7

[0057] Similar to the steps in Example 1, the only difference is that the cooling water flow rate in the secondary cooling zone is 217.5 L / min, resulting in a weld scar defect rate of 14%. When the water flow rate in the secondary cooling zone is large, the cooling intensity on the surface of the billet is too high, which makes the surface of the billet prone to uneven cooling and stress cracks, forming weld scar defects.

[0058] Comparative Example 8

[0059] Similar to the steps in Example 1, the only difference is that the cooling water flow rate in the secondary cooling zone is 184.4 L / min, resulting in a weld scar defect rate of 15%. When the water flow rate in the secondary cooling zone is low, the cooling intensity of the billet surface is low, making the billet surface susceptible to the influence of unsolidified molten steel inside, resulting in surface reheating. This leads to uneven heating and cooling of the billet, causing stress cracks and weld scar defects.

[0060] As can be seen from the above, the embodiments of the present invention provide a method for controlling surface weld scar defects in high-carbon chromium bearing steel billets, due to the continuous casting 280 2The weld scar defects on large billets are determined by factors such as the addition rate of mold flux, continuous casting speed, and cooling water volume of the mold. To eliminate these defects, the inventors, through long-term practice, rationally configured the addition rate of mold flux, the casting speed of large billets, and the cooling water volume of the mold, thereby improving the continuous casting process of large billets. Ultimately, they controlled the proportion of weld scars on the surface of high-carbon chromium bearing steel GCr15 in large billets to within 1%, resulting in a smooth and defect-free surface. This significantly improved the surface quality of the product, leading to good appearance and performance.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling surface weld scar defects in large square billet high-carbon chromium bearing steel, characterized in that, Includes the following steps: liquid Molten steel enters the crystallizer, forming a solidified billet shell. Under the action of the straightening machine, it leaves the crystallizer and is cooled by water spray in the secondary cooling chamber. The liquid steel gradually solidifies into a large square billet. The control measures are: the addition rate of the protective slag is 58-60 g / min, the billet drawing speed is 0.9-1.1 m / min, and the crystallizer cooling water flow rate is 142-144 m³ / min. 3 For the first heat of tundish casting, the superheat of the molten steel is controlled at 35-40℃; for the second to Nth heats of tundish casting, the superheat of the molten steel is controlled at 25-35℃, and the total cooling water flow rate in the secondary cooling zone is 200.2-203.7 m³ / h. 3 The two cooling zones are divided into six cooling zones, with water flow rates of: Zone 1 30-30.6 L / min, Zone 2 30-30.6 L / min, Zone 3 33-33.6 L / min, Zone 4 33-33.6 L / min, and Zone 5 46.2-46.8 m³ / min. 3 / h and Zone 6 28-28.5m 3 / h, the water flow rate gradient is increased in the front section of the secondary cooling zone for ultra-strong cooling, which is more conducive to the rapid growth of the billet shell and reduces the risk of steel leakage under high drawing speed conditions; the water flow rate is decreased in the rear section of the secondary cooling zone for reheating, which makes the temperature gradient distribution from the surface to the center of the billet uniform, which is beneficial to the quality control of the rolling process; the high carbon chromium bearing steel contains the following composition by mass percentage: C: 1.0%-1.03%, Si: 0.25%-0.35%, Mn: 0.35%-0.45%, P: 0-0.015%, S: 0-0.015%, Cr: 1.48-1.6%, Mo: 0-0.1%, Ni: 0-0.3%, Cu: 0-0.25%, Ti: 0-0.003%, Al: 0.015-0.04%, As: 0-0.04%, Sn: 0-0.03%, Pb: 0-0.002%, Sb: 0-0.005%; The surface weld scar defects of the large square billets of high carbon chromium bearing steel produced were detected, and the surface weld scar ratio was less than 1%.

2. The control method according to claim 1, characterized in that, The cross-section of the large square billet is 250-320mm × 250-320mm.

3. The control method according to claim 1, characterized in that, The high-carbon chromium bearing steel is GCr15 steel.

4. The control method according to claim 1, characterized in that, The total salt content of the cooling water used in the crystallizer is ≤500mg / l, and the turbidity is ≤10ntu.

5. The control method according to claim 1, characterized in that, The total salt content of the cooling water used in the second cooling zone is ≤1000mg / l, and the turbidity is ≤20ntu.

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