Finishing method of crack sensitive square billet

Abstract

The invention discloses a finishing method for a crack-sensitive square billet, and relates to the technical field of steel production. Comprising the following steps: sampling a square billet obtained by continuous casting, heating and pickling to obtain a pickled square billet sample, observing the pickled square billet sample under a microscope, and marking the crack depth. And when the crack depth of the pickled square billet sample is smaller than or equal to 0.5 mm, the square billet obtained through continuous casting is directly rolled. And when the crack depth of the pickled square billet sample is larger than 0.5 mm, the square billet obtained through continuous casting is firstly subjected to finishing, and then rolling is conducted. Square billets obtained through continuous casting are sampled, square billet samples obtained through continuous casting are subjected to heating and acid pickling, oxide scales on the surfaces of the square billet samples can be removed, the accuracy of crack recognition is improved, then the square billet samples obtained after acid pickling are observed through a microscope, and the shape and depth of cracks can be accurately judged. And whether the square billets obtained by continuous casting in the batch need to be finished or not is determined through depth, so that unnecessary metal loss is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a finishing method for crack-sensitive square billets. Background Art

[0002] In the process of steel production, the corresponding products have different forms according to the different uses of steel products, such as wires, plates, profiles, bars and pipes. Among them, the production of wires is mainly through deformation processes such as drawing, which transforms steel billets into wires. When elements with strong crack sensitivity, such as boron, are added to the steel billets used for rolling wires, crack defects are prone to occur on the surface of the billets. If the cracks are not treated, it will directly lead to linear defects on the surface of the wires, causing the wires to crack and become scrapped during the drawing and deformation processes.

[0003] At present, the crack inspection and treatment method for steel billets is mainly through visual observation. If obvious cracks are observed, the steel billets are peeled and finished. In this process, due to the presence of iron oxide scale on the surface of the steel billets, it is not possible to fully confirm whether it is a surface crack. In addition, if the steel billets are directly peeled and finished, the steel without defects on the surface will also be removed during the peeling process, resulting in increased metal loss and increased smelting costs for steel production.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for finishing crack-sensitive billets.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a method for finishing crack-sensitive billets, comprising sampling a billet obtained by continuous casting and performing heating and pickling to obtain a pickled billet sample, and observing the pickled billet sample under a microscope and marking the depth of cracks.

[0008] When the crack depth of the pickled billet sample is ≤0.5 mm, the billet obtained by continuous casting is directly rolled.

[0009] When the crack depth of the pickled billet sample is greater than 0.5 mm, the billet obtained by continuous casting is firstly finished and then rolled.

[0010] In an optional embodiment, the finishing method includes at least one of corner peeling, edge peeling and full peeling.

[0011] In an optional embodiment, the method further includes determining a finishing method for the square billet obtained by continuous casting according to the crack position of the square billet sample after pickling.

[0012] In an optional embodiment, when the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 3 / 40 of the side length of the pickled billet sample, the billet obtained by continuous casting is first corner-skinned and then rolled.

[0013] When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is first subjected to corner peeling and edge peeling, and then rolled.

[0014] When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is greater than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is fully peeled and then rolled.

[0015] In an optional embodiment, the heating temperature of the heated pickling is 70 to 80° C., and the time is 25 to 30 minutes.

[0016] In an optional embodiment, the pickling solution for heated pickling is a hydrochloric acid solution, in which the volume ratio of hydrochloric acid to water is 1:1.

[0017] In an optional embodiment, the square billets obtained by continuous casting are sampled, and the length of the continuous casting billet samples obtained by sampling is 300-400 mm.

[0018] In an optional embodiment, the sampling method includes: sampling from different streams in each heat or every two heats of continuous casting.

[0019] In an optional embodiment, the method further includes sawing the continuous casting slab sample into at least two pieces before the heating and pickling.

[0020] In an optional embodiment, finishing further comprises locally grinding the billet obtained by continuous casting.

[0021] The present invention has the following beneficial effects:

[0022] The present invention provides a finishing method for crack-sensitive square billets. The method comprises the following steps: sampling square billets obtained by continuous casting, heating and pickling the continuously cast square billet samples, thereby removing iron oxide scale on the surface thereof and improving the accuracy of crack identification; and observing the pickled square billet samples by a microscope to accurately judge the shape and depth of the cracks, and determining whether the square billets obtained by continuous casting in this batch need to be finished according to the depth, thereby avoiding unnecessary metal loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 A schematic diagram of edge cracks of a square billet sample after pickling provided in Example 1 of the present invention;

[0025] Figure 2 A metallographic microscope image of edge cracks of a square billet sample after pickling provided in Example 1 of the present invention;

[0026] Figure 3 This is a metallographic microscope image of edge cracks of a square billet sample after pickling provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0028] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0029] In a first aspect, the present invention provides a method for finishing crack-sensitive square billets, comprising sampling square billets obtained by continuous casting and performing heating and pickling to obtain pickled square billet samples, observing crack defects of the pickled square billet samples under a microscope and marking the depth of the cracks.

[0030] By sampling the billets obtained by continuous casting and heating and pickling the billet samples, the iron oxide scale on the surface can be removed and the accuracy of crack identification can be improved.

[0031] When the crack depth of the pickled billet sample is ≤0.5 mm, the billet obtained by continuous casting is directly rolled.

[0032] When the crack depth of the pickled billet sample is greater than 0.5 mm, the billet obtained by continuous casting is firstly finished and then rolled.

[0033] By observing the crack defects of the billet samples after pickling under a microscope, the shape and depth of the cracks can be accurately determined, and according to the crack conditions of the billet samples after pickling, it can be determined whether the billets obtained by continuous casting in this batch need to be finished, thereby avoiding unnecessary metal loss.

[0034] In an optional embodiment, the finishing method includes at least one of corner peeling, edge peeling and full peeling.

[0035] In an optional embodiment, the method further includes determining a finishing method for the square billet obtained by continuous casting according to the crack position of the square billet sample after pickling.

[0036] In an optional embodiment, when the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 3 / 40 of the side length of the pickled billet sample, the billet obtained by continuous casting is first corner-skinned and then rolled.

[0037] When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is first subjected to corner peeling and edge peeling, and then rolled.

[0038] When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is greater than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is fully peeled and then rolled.

[0039] The four surfaces of the square billet sample except the two end faces are divided into an inner arc surface, an outer arc surface and two side surfaces according to the orientation of the continuous casting process. According to the location of the crack, the distance between the crack and each edge of the plane where the crack is located is measured. The distance with the smallest numerical value is the minimum distance between the crack position of the square billet sample after pickling and the edge of the square billet sample after pickling.

[0040] In an optional embodiment, in order to better remove the iron oxide scale on the surface of the billet without damaging the morphology of the billet, the heating temperature of the heating pickling is 70-80° C. and the time is 25-30 min.

[0041] For example, the temperature of the heated pickling can be any value among 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, or a range value between any two of the above values ​​or any point value within the range value.

[0042] For example, the time for heated pickling can be any value among 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, or a range value between any two of the above values ​​or any point value within the range value.

[0043] In an optional embodiment, the pickling solution for heated pickling is a hydrochloric acid solution, in which the volume ratio of hydrochloric acid to water is 1:1.

[0044] In an optional embodiment, the square billets obtained by continuous casting are sampled, and the length of the continuous casting billet samples obtained by sampling is 300-400 mm.

[0045] For example, the length of the continuous casting billet sample can be any value among 300 mm, 350 mm or 400 mm, or a range value between any two of the above values ​​or any point value within the range value.

[0046] By cutting the billet obtained by continuous casting according to the above length, it is possible to quickly determine whether the continuous casting process of the billet meets the product requirements, and quickly confirm the further processing method of the billet. This method is easy to operate and can quickly and accurately process the actual situation of the billet, reducing unnecessary metal losses without affecting production efficiency. In addition, the parameters of the continuous casting process can be adjusted according to the crack detection situation to reduce the number of cracks on the surface of the billet obtained by subsequent continuous casting of molten steel, as well as the depth and length of the cracks.

[0047] In an optional embodiment, the sampling method includes: sampling in different streams of each furnace or every two furnaces of continuous casting. That is, each sampling can be performed in each furnace continuously, or sampling can be performed at intervals of one furnace, such as sampling the 1st furnace, the 3rd furnace, the 5th furnace, and the 7th furnace; each furnace of continuous casting also has different streams, such as stream I, stream II, stream III, stream IV, and stream V of the first furnace. In order to ensure that the continuous casting billet samples are representative, different streams should be sampled, such as sampling stream I of the 1st furnace, stream II of the 2nd furnace, stream III of the 3rd furnace, and stream IV of the 4th furnace for crack detection.

[0048] In an optional embodiment, in order to ensure that the surface of the continuous casting billet sample can be completely immersed in the hydrochloric acid solution during the heating and pickling process, the continuous casting billet sample is further sawed into at least two pieces before the heating and pickling.

[0049] Preferably, each sawn continuous casting billet sample should be of similar size, for example, the continuous casting billet sample can be sawed into two halves along the inner and outer arc center lines of the entire continuous casting billet sample.

[0050] In an optional embodiment, finishing also includes local grinding of the billet obtained by continuous casting to remove surface defects such as scars, slag pits, indentations and scratches to ensure product quality.

[0051] Example 1

[0052] This embodiment provides a method for finishing a crack-sensitive billet, comprising the following steps:

[0053] The steel is smelted in a 120t converter, followed by LF furnace refining and RH vacuum treatment to obtain refined molten steel. 2 Billet continuous casting produces 15 furnaces of boron wire steel billets in one pour.

[0054] Take one continuous casting billet sample with a length of 400 mm from each of the 1st furnace I stream, the 3rd furnace II stream, the 5th furnace III stream, the 7th furnace IV stream, the 9th furnace V stream, the 11th furnace VI stream, the 13th furnace I stream and the 15th furnace I stream of the above casting, for a total of 8 pieces. Use a sawing machine to saw each of the above continuous casting billet samples along the center line of the inner and outer arcs into two identical halves for standby use.

[0055] Hydrochloric acid and water were added into the hot acid tank in a volume ratio of 1:1 as the etching liquid. The etching liquid was heated to 75°C, and then the continuous casting billet sample was placed in the hot acid tank. After etching for 25 minutes with the sawn surface facing down, the etching liquid was drained, the continuous casting billet sample was rinsed with water, and dried with compressed air to obtain the pickled square billet sample.

[0056] The upper surface and side surface (non-sawed surface) of the pickled billet sample were inspected with the naked eye and microscope, and a total of 7 edge cracks and 4 corner cracks were found, as follows:

[0057] There are two edge cracks on the side of the first stream of the first furnace (such as Figure 1 to Figure 3 As shown in the figure, there are 1 edge crack and 1 corner crack on the outer arc surface of the V stream of the 9th furnace; there is 2 edge cracks and 1 corner crack on the inner arc surface of the I stream of the 13th furnace; there is 1 edge crack and 1 corner crack on the inner arc surface of the I stream of the 15th furnace; there is 1 edge crack and 1 corner crack on the outer arc surface of the I stream of the 15th furnace.

[0058] Among them, the minimum distances of the two edge cracks on the side of the first furnace I stream from the edge of the pickled billet sample are 64mm and 35mm respectively, and the length of the edge crack on the inner arc surface of the 15th furnace I stream is 9mm. It is preliminarily judged that the cracks are relatively serious and cannot be eliminated by heating, oxidation and burning. Therefore, the edge cracks with a minimum distance of 35mm on the side of the first furnace I stream, the corner cracks on the inner arc surface of the first furnace I stream, and the edge cracks on the inner arc surface of the 15th furnace I stream were selected for metallographic analysis.

[0059] The metallographic analysis results show that the depth of the edge cracks in the first and fifteenth furnaces is 1.518 mm (as shown in Figure 2). Figure 3 As shown) and 0.91mm, the depth of the corner crack of the first furnace is 0.65mm, and the depth of the above cracks are all greater than 0.5mm, requiring finishing.

[0060] According to the 8 continuous casting billet samples, the total length of the 8 continuous casting billet samples is 3.2m, and the crack occurrence probability is 3.4 / m, indicating that the crack occurrence probability of the continuous casting billet in this casting is high. According to the above crack parameters, it is determined that all the billets obtained by continuous casting in this casting are fully peeled, and the metal loss of the full peeling treatment is 1.75%. There are 15 furnaces of billets in this casting, a total of 1875t of steel, and the peeling metal loss is 32.8t. The wire rod rolled after the billet is peeled in this casting has no quality problem of cracking due to billet defects during the processing process.

[0061] Example 2

[0062] This embodiment provides a method for finishing a crack-sensitive billet, comprising the following steps:

[0063] The steel is smelted in a 120t converter, followed by LF furnace refining and RH vacuum treatment to obtain refined molten steel. 2 Billet continuous casting produces 15 furnaces of boron wire steel billets in one pour.

[0064] Take one continuous casting billet sample with a length of 400 mm from each of the 1st furnace I stream, the 1st furnace II stream, the 4th furnace III stream, the 4th furnace IV stream, the 8th furnace V stream, the 8th furnace VI stream, the 12th furnace I stream, the 12th furnace II stream, the 15th furnace III stream and the 15th furnace IV stream of the above casting, for a total of 10 pieces. Use a sawing machine to saw each of the above continuous casting billet samples along the center line of the inner and outer arcs into two identical halves for standby use.

[0065] Hydrochloric acid and water were added into the hot acid tank in a volume ratio of 1:1 as the etching liquid. The etching liquid was heated to 78°C, and then the continuous casting billet sample was placed in the hot acid tank. After etching for 28 minutes with the sawn surface facing down, the etching liquid was drained, the continuous casting billet sample was rinsed with water, and dried with compressed air to obtain the pickled square billet sample.

[0066] The upper surface and side surface (non-sawed surface) of the pickled billet sample were inspected with the naked eye and microscope, and a total of 3 edge cracks and 4 corner cracks were found, as follows:

[0067] There is 1 edge crack on the inner arc surface of the Ⅰ stream of the 1st furnace; there is 1 edge crack on the inner arc surface of the Ⅱ stream of the 1st furnace; there is 1 edge crack and 1 corner crack on the inner arc surface of the Ⅰ stream of the 12th furnace; there is 1 corner crack on the inner arc surface of the Ⅱ stream of the 12th furnace; there is 1 corner crack on the inner arc surface of the Ⅲ stream of the 15th furnace; there is 1 corner crack on the outer arc surface of the Ⅳ stream of the 15th furnace.

[0068] Among them, the minimum distance between an edge crack on the inner arc surface of stream I of the 12th furnace and the edge of the pickled billet sample is 28 mm. The edge cracks of the 1st furnace with relatively serious cracks and the corner cracks of streams III and IV of the 15th furnace were subjected to metallographic analysis.

[0069] From the metallographic analysis results, it can be seen that the depth of the edge cracks of the first furnace is 0.73mm, and the depths of the corner cracks of the third and fourth streams of the fifteenth furnace are 0.57mm and 0.64mm respectively. The depths of the above cracks are all greater than 0.5mm and need to be refined.

[0070] According to the 10 continuous casting billet samples, the total length of the 10 continuous casting billet samples is 4m, and the probability of crack occurrence is 1.75 / m, indicating that the probability of crack occurrence of the continuous casting billet in this casting is relatively low. Based on the above crack parameters, it is determined that all the billets obtained by continuous casting in this casting are subjected to corner peeling, and the metal loss of the corner peeling treatment is 0.9%. There are 15 furnaces of billets in this casting, a total of 1890t of steel, and the metal loss of peeling is 16.9t. The wire rod rolled after the billet is peeled in this casting has no quality problem of cracking due to billet defects during the processing process.

[0071] Example 3

[0072] This embodiment provides a method for finishing a crack-sensitive billet, comprising the following steps:

[0073] The steel is smelted in a 120t converter, followed by LF furnace refining and RH vacuum treatment to obtain refined molten steel. 2 Billet continuous casting produces 16 furnaces of boron wire steel billets in one pour.

[0074] Take one continuous casting billet sample with a length of 400 mm from each of the 1st furnace I stream, the 1st furnace II stream, the 4th furnace III stream, the 4th furnace IV stream, the 8th furnace V stream, the 8th furnace VI stream, the 12th furnace I stream, the 12th furnace II stream, the 16th furnace III stream and the 16th furnace IV stream of the above casting, for a total of 10 pieces. Use a sawing machine to saw each of the above continuous casting billet samples along the center line of the inner and outer arcs into two identical halves for standby use.

[0075] Hydrochloric acid and water were added into the hot acid tank in a volume ratio of 1:1 as the etching liquid. The etching liquid was heated to 80°C, and then the continuous casting billet sample was placed in the hot acid tank. After etching for 30 minutes with the sawn surface facing down, the etching liquid was drained, the continuous casting billet sample was rinsed with water, and dried with compressed air to obtain the pickled square billet sample.

[0076] The upper surface and side surface (non-sawed surface) of the pickled billet sample were inspected with the naked eye and microscope, and a total of 1 edge crack and 2 corner cracks were found, as follows:

[0077] There is one edge crack on the inner arc surface of stream I of the first furnace; there is one corner crack on the inner arc surface of stream II of the first furnace; there is one corner crack on the inner arc surface of stream III of the 16th furnace. Metallographic analysis was performed on the above three cracks.

[0078] The metallographic analysis results show that the depth of the edge cracks of the first furnace is 0.5mm, the depth of the corner cracks of the first furnace is 0.46mm, and the depth of the corner cracks of the 16th furnace is 0.39mm. The total length of the 10 continuous casting billet samples is 4m, and the probability of crack occurrence is 0.75 / m, indicating that the probability of crack occurrence of the continuous casting billet in this casting is low. The depth of the edge cracks and corner cracks of the continuous casting billet samples does not exceed the burn loss of 0.5mm caused by heating the billet. Therefore, no finishing is required. The wire rod rolled from the billet in this casting has no quality problem of cracking due to billet defects during the processing.

[0079] Comparative Example 1

[0080] This comparative example provides a finishing method for crack-sensitive billets, and adopts the same process as Example 1 to produce 15 heats of boron-containing wire steel billets in 1 casting, and the billets are directly rolled without finishing. The produced wires are used for drawing and deformation processing by users, among which 5 rolls of steel have cracking problems, the weight of the quality objection steel is 8.16t, and the quality objection rate is 4.5‰.

[0081] Comparative Example 2

[0082] This comparative example provides a finishing method for crack-sensitive square billets, and adopts the same process as Example 2 to produce 16 furnaces of boron wire steel square billets in one casting. The number and depth of cracks observed by naked eyes after pickling of the billets are relatively high, so they are directly subjected to full stripping treatment. The metal loss from stripping is 32.9 tons, which is 16 tons more than that of Example 2.

[0083] Comparative Example 3

[0084] This comparative example provides a finishing method for crack-sensitive square billets, in which 16 furnaces of boron wire steel square billets are produced in one casting by the same process as in Example 3. The number and depth of cracks observed by naked eyes after pickling of the billets are relatively high, and the corners are directly stripped, with a metal loss of 17 tons, which is 17 tons more than that in Example 3.

[0085] In summary, the method of determining the finishing method by naked eye observation may cause unnecessary increase in metal loss, thereby increasing smelting costs. The method provided by the embodiment of the present invention can determine the processing technology of the square billet according to the crack state of the square billet, obtain better quality wire at a lower cost, and prevent defects such as cracking during wire processing.

[0086] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for finishing crack-sensitive billets, characterized in that: The method comprises: sampling a square billet obtained by continuous casting and performing heating and pickling to obtain a pickled square billet sample, and observing the pickled square billet sample under a microscope and marking the depth of cracks; When the crack depth of the pickled billet sample is ≤0.5 mm, directly rolling the billet obtained by continuous casting; When the crack depth of the pickled billet sample is greater than 0.5 mm, the billet obtained by continuous casting is firstly finished and then rolled.

2. The method according to claim 1, characterized in that The finishing method includes at least one of corner peeling, edge peeling and full peeling.

3. The method according to claim 2, characterized in that The method also includes determining a finishing method for the square billet obtained by continuous casting according to the crack position of the square billet sample after pickling.

4. The method according to claim 3, characterized in that When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 3 / 40 of the side length of the pickled billet sample, the billet obtained by continuous casting is first subjected to corner peeling and then subjected to rolling; When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is less than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is first subjected to corner peeling and edge peeling, and then subjected to rolling; When the minimum distance between the crack position of the pickled billet sample and the edge of the pickled billet sample is greater than 1 / 10 of the side length of the pickled billet sample, the billet obtained by continuous casting is first fully peeled and then rolled.

5. The method according to claim 1, characterized in that: The heating temperature of the heated pickling is 70-80° C. and the time is 25-30 minutes.

6. The method according to claim 1 or 5, characterized in that: The pickling liquid for the heated pickling is a hydrochloric acid solution, in which the volume ratio of hydrochloric acid to water is 1:

1.

7. The method according to claim 1, characterized in that The square billets obtained by continuous casting are sampled, and the length of the continuous casting billet samples obtained by sampling is 300 to 400 mm.

8. The method according to claim 7, characterized in that The method further comprises sawing the continuous casting slab sample into at least two pieces before the heating and pickling.

9. The method according to claim 1, characterized in that: Finishing also includes local grinding of the billets obtained from continuous casting.

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