A method for determining the correlation between surface porosity of continuously cast billets and carbon enrichment behavior of protective slag.

Abstract

This invention discloses a method for determining the correlation between porosity on the surface of continuously cast billets and the carburization behavior of the protective slag, comprising the following steps: S1, acquiring metallographic images of the porosity defect region and the non-porosity defect region on the surface of the continuously cast billet; S2, calculating the ferrite content in the porosity defect region and the non-porosity defect region; S3, calculating the original austenite grain size in the porosity defect region and the non-porosity defect region; S4, comparing the ferrite content in the porosity defect region and the non-porosity defect region, and comparing the original austenite grain size in the porosity defect region and the non-porosity defect region; S5, if the ferrite content in the porosity defect region is less than that in the non-porosity defect region, and the original austenite grain size in the porosity defect region is greater than that in the non-porosity defect region, then the correlation between porosity defects on the surface of the continuously cast billet and the carburization behavior of the protective slag is strong; otherwise, the correlation is weak. This invention solves the problem of porosity defects on the surface of continuously cast billets.

Description

Technical Field

[0001] This invention relates to continuous casting production technology, and more specifically, to a method for determining the correlation between surface porosity of continuously cast billets and carbonization behavior of protective slag. Background Technology

[0002] As users' requirements for steel quality continue to increase, the quality requirements for continuously cast billets are also becoming more stringent. The quality of continuously cast billets can be mainly divided into three parts: surface quality, internal quality, and cleanliness. Among these, surface porosity is a relatively common defect in the surface quality of continuously cast billets, so analyzing the causes of porosity defects is of great significance.

[0003] Currently, common causes of porosity include poor deoxidation, foreign gas elements, secondary oxidation, and mold flux in continuous casting molds. However, in actual production, tracing the source of porosity defects often involves many uncertainties, making accurate judgment difficult. While poor deoxidation, foreign gas elements, and secondary oxidation can often be reflected in the steel composition, effective methods for addressing mold flux are often lacking. Mold flux has a direct impact on the surface quality control of continuously cast billets, and its role is crucial in the stable production of high-quality steel. The functions of mold flux typically include five aspects: heat insulation, prevention of secondary oxidation, absorption of inclusions, lubrication of the billet, and control of heat transfer. Improper use of mold flux can easily lead to surface defects such as sticking, cracks, and porosity. Therefore, ensuring the proper functioning of mold flux and avoiding its negative effects is of great significance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for determining the correlation between surface porosity of continuously cast billets and carbon-increasing behavior of protective slag, thereby solving the problem of surface porosity defects in continuously cast billets and avoiding potential negative effects during the use of protective slag. This approach is beneficial for steadily improving the surface quality of continuously cast billets and better leveraging the role of protective slag.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for determining the correlation between surface porosity of continuously cast billets and carbon-increasing behavior of protective slag includes the following steps:

[0007] S1. Obtain metallographic images of the porosity defect area and the non-porosity defect area on the surface of the continuously cast billet.

[0008] S2. Calculate the ferrite content in the porosity defect region and the non-porosity defect region;

[0009] S3. Calculate the original austenite grain size in the porosity defect region and the non-porosity defect region;

[0010] S4. Compare the ferrite content in the porosity defect region and the non-porosity defect region, and compare the original austenite grain size in the porosity defect region and the non-porosity defect region.

[0011] S5. If the ferrite content in the porosity defect region is less than that in the region without porosity defects, and the original austenite grain size in the porosity defect region is greater than that in the region without porosity defects, then the porosity defects on the surface of the continuously cast billet are strongly correlated with the carbon increase behavior of the protective slag; otherwise, the correlation is weak.

[0012] Preferably, before obtaining the metallographic image in step S1, the surface of the continuously cast billet needs to be processed:

[0013] After grinding and polishing the porosity defect area and the non-porosity defect area on the surface of the continuously cast billet, the surface is etched with nitric acid alcohol.

[0014] Preferably, in steps S2 and S3, the ferrite content in the porosity defect region and the non-porosity defect region are calculated using image processing software Image Pro Plus, and the original austenite grain size in the porosity defect region and the non-porosity defect region is calculated.

[0015] Preferably, step S5 further includes:

[0016] If the ratio of ferrite content in the porosity defect region to ferrite content in the non-porosity defect region is less than 80%, and the ratio of the original austenite grain size in the porosity defect region to the original austenite grain size in the non-porosity defect region is greater than 110%, then the porosity defects on the surface of the continuously cast billet are strongly correlated with the carbon-increasing behavior of the protective slag; otherwise, the correlation is weak.

[0017] This invention provides a method for determining the correlation between surface porosity of continuously cast billets and the carbon-increasing behavior of the protective slag. This method is simple, accurate, and highly applicable, and is of great significance for the stable improvement of the surface quality of continuously cast billets. When the correlation between surface porosity of continuously cast billets and the carbon-increasing behavior of the protective slag is significant, the formation of porosity defects on the surface of the continuously cast billets can be suppressed by reducing the carbon-increasing behavior of the protective slag. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the method for determining the present invention;

[0019] Figure 2 This is a schematic diagram of the morphology of the porosity defect area on the surface of the continuously cast billet;

[0020] Figure 3 This is a schematic diagram of the metallographic structure of the porosity defect area on the surface of the continuously cast billet;

[0021] Figure 4This is a schematic diagram of the metallographic structure of the area without porosity defects on the surface of the continuously cast billet. Detailed Implementation

[0022] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] Combination Figure 1 As shown, the method for determining the correlation between surface porosity of continuously cast billets and carbon enrichment behavior of protective slag provided by the present invention includes the following steps:

[0024] S1. Obtain metallographic images of the porosity defect area and the non-porosity defect area on the surface of the continuously cast billet.

[0025] S2. Calculate the ferrite content in the porosity defect region and the non-porosity defect region;

[0026] S3. Calculate the original austenite grain size in the porosity defect region and the non-porosity defect region;

[0027] S4. Compare the ferrite content in the porosity defect region and the non-porosity defect region, and compare the original austenite grain size in the porosity defect region and the non-porosity defect region.

[0028] S5. If the ferrite content in the porosity defect region is significantly less than that in the region without porosity defects, and the original austenite grain size in the porosity defect region is significantly greater than that in the region without porosity defects, then the porosity defects on the surface of the continuously cast billet are strongly correlated with the carbonization behavior of the protective slag; otherwise, the correlation is weak.

[0029] Before obtaining the metallographic image in step S1, the surface of the continuously cast billet needs to be processed:

[0030] After grinding and polishing the areas with porosity defects and areas without porosity defects on the surface of the continuously cast billet, the surface is etched with 4% nitric acid alcohol.

[0031] In steps S2 and S3, the ferrite content in the porosity defect region and the non-porosity defect region are calculated using the image processing software Image Pro Plus, as well as the original austenite grain size in the porosity defect region and the non-porosity defect region.

[0032] Step S5 further includes:

[0033] If the ratio of ferrite content in the porosity defect region to ferrite content in the non-porosity defect region is less than 80%, and the ratio of the original austenite grain size in the porosity defect region to the original austenite grain size in the non-porosity defect region is greater than 110%, then the correlation between porosity defects on the surface of the continuously cast billet and the carbonization behavior of the protective slag is strong; otherwise, the correlation is weak.

[0034] The carbon increase phenomenon in molten steel leads to a relatively high carbon content in the vicinity of the porosity, resulting in a lower ferrite content. At the same time, the increase in carbon content in the early stage of liquid-solid transformation leads to a widening of the two-phase region, which in turn increases the initial austenite grain size. Therefore, the above characteristics are the key basis for determining the correlation between porosity on the surface of continuously cast billets and carbon increase in the protective slag.

[0035] Example 1

[0036] Taking the surface porosity defect of SCM435 cold heading steel (carbon content of 0.35%) continuously cast billet as an example, the method for determining the correlation between surface porosity of continuously cast billet and carbon increase behavior of protective slag in Example 1 is adopted, including the following steps:

[0037] S1. Use a 4% nitric acid alcohol solution to treat the porosity defect areas on the surface of the continuously cast billet (such as...). Figure 2 The samples (shown) and those in the non-porosity defect area (normal area) were etched, and their corresponding metallographic images were obtained, as shown. Figure 3 and Figure 4 As shown;

[0038] S2. Calculate the ferrite content in the porosity defect region and the non-porosity defect region, which are 17.6% and 24.8%, respectively.

[0039] S3. Calculate the original austenite grain size in the porosity defect region and the non-porosity defect region, which are 430.3 μm and 379.2 μm, respectively;

[0040] S4. Comparing the ferrite content in the porosity defect region with that in the non-porosity defect region, the proportion of ferrite content less than that in the porosity defect region is 29.0%. Comparing the original austenite grain size in the porosity defect region with that in the non-porosity defect region, the proportion of ferrite content greater than that in the porosity defect region is 13.5%.

[0041] Therefore, the ferrite content in the porosity defect region / the ferrite content in the non-porosity defect region is <80%, and the original austenite grain size in the porosity defect region / the original austenite grain size in the non-porosity defect region is >110%.

[0042] S5. If both of these conditions are met, then the porosity defects on the surface of the continuously cast billet are strongly correlated with the carbonization behavior of the protective slag. The occurrence of surface porosity defects can be suppressed by weakening the carbonization behavior of the protective slag.

[0043] Example 2

[0044] Taking the surface porosity defect of SCM435 cold heading steel (carbon content of 0.35%) continuously cast billet as an example, the method for determining the correlation between surface porosity of continuously cast billet and carbon increase behavior of protective slag in Example 1 is adopted, including the following steps:

[0045] S1. Using a 4% nitric acid alcohol solution, samples with porosity defects and non-porosity defects (normal areas) on the surface of continuously cast billets were etched, and their corresponding metallographic images were obtained.

[0046] S2. Calculate the ferrite content in the porosity defect region and the non-porosity defect region, which are 21.3% and 22.5%, respectively;

[0047] S3. Calculate the original austenite grain size in the porosity defect region and the non-porosity defect region, which are 375.4 μm and 370.5 μm, respectively;

[0048] S4. Comparing the ferrite content in the porosity defect region with that in the non-porosity defect region, the proportion of ferrite content in the porosity defect region is less than 5.3%. Comparing the original austenite grain size in the porosity defect region with that in the non-porosity defect region, the proportion of ferrite content in the porosity defect region is greater than 1.3%.

[0049] Therefore, the ratio of ferrite content in the porosity defect region to ferrite content in the non-porosity defect region is significantly greater than 80%, and the original austenite grain size in the porosity defect region is very close to that in the non-porosity defect region.

[0050] S5. If neither of the two conditions is met, it indicates that the correlation between porosity defects on the surface of the continuously cast billet and the carbonization behavior of the protective slag is weak.

[0051] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for determining the correlation between surface porosity of continuously cast billets and carbon-increasing behavior of protective slag, characterized in that, Includes the following steps: S1. Obtain metallographic images of the porosity defect area and the non-porosity defect area on the surface of the continuously cast billet. S2. Calculate the ferrite content in the porosity defect region and the non-porosity defect region; S3. Calculate the original austenite grain size in the porosity defect region and the non-porosity defect region; S4. Compare the ferrite content in the porosity defect region and the non-porosity defect region, and compare the original austenite grain size in the porosity defect region and the non-porosity defect region. S5. If the ferrite content in the porosity defect area / the ferrite content in the non-porosity defect area is <80%, and the original austenite grain size in the porosity defect area / the original austenite grain size in the non-porosity defect area is >110%, then the porosity defects on the surface of the continuously cast billet are strongly correlated with the carbon increase behavior of the protective slag, and vice versa.

2. The method for determining the correlation between surface porosity of continuously cast billets and carbon-increasing behavior of protective slag according to claim 1, characterized in that, Before obtaining the metallographic image in step S1, the surface of the continuously cast billet needs to be processed: After grinding and polishing the porosity defect area and the non-porosity defect area on the surface of the continuously cast billet, the surface is etched with nitric acid alcohol.

3. The method for determining the correlation between surface porosity of continuously cast billets and carbon increase behavior of protective slag according to claim 1, characterized in that: In steps S2 and S3, the ferrite content in the porosity defect region and the non-porosity defect region are calculated using the image processing software Image Pro Plus, and the original austenite grain size in the porosity defect region and the non-porosity defect region is calculated.

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