A method for continuous casting and mixed pouring of round billets with different steel grades having non-overlapping components

Abstract

The present invention discloses a process for continuous casting and mixed pouring of round billets of dissimilar steel grades with non-intersecting compositions, which is used for pouring mixed pouring liquids of dissimilar steel grades with an absolute value of a liquidus temperature difference less than or equal to a preset temperature. The process comprises: classifying the chemical compositions of the dissimilar steel grades and controlling the compositions of the mixed pouring heats according to the principle of close compositions; smelting the high-strength steel in the dissimilar steel grades and then smelting the mild steel according to the compositions of the heats; and mixing the smelted molten steel. When the remaining steel in the tundish of the last heat before mixing reaches 35%-60% of the rated weight of the tundish, the first large ladle after mixing is opened, requiring maximum flow to the tundish. When the tundish liquid level reaches the maximum allowable liquid level for normal pouring, the speed is increased as required, and the normal drawing speed is restored until the pouring is completed, thereby completing the continuous casting of round billets. The process can realize mixing short pouring times of dissimilar steel grades with non-intersecting compositions into long pouring times, reduce the length of the head and tail cuts, thereby improving the molten steel yield and production efficiency, and reducing production costs.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical industry, in particular to a process for continuous casting and mixed pouring of round billets of different steel grades with non-overlapping components. Background Art

[0002] In the global steel manufacturing industry, continuous steel casting has great competitive advantages in production efficiency and production scale. It has a higher molten steel yield than the die casting process and is an advanced method for large-scale production in steel mills.

[0003] In terms of production efficiency and steel yield, long-run continuous casting has advantages over die casting. However, short-run continuous casting reduces steel yield due to the long head and tail lengths. For example, the steel yield of Φ690mm round billets is 94.7% with 10 continuous casting runs, while the steel yield drops to 86.5% with 4 continuous casting runs. Only when the continuous casting run of Φ690mm round billets reaches 8 continuous casting runs and the steel yield reaches 92%, can it exceed the steel yield of the die casting process. For another example, when the continuous casting run of Φ800mm round billets reaches 10 or more continuous casting runs, the steel yield can exceed that of die casting. If continuous casting short-run continuous casting cannot be mixed, the steel yield will be lower than that of die-cast steel, failing to achieve the goals of continuous casting to improve steel yield and production efficiency, and the production cost of continuous casting billets will increase significantly. Summary of the Invention

[0004] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a continuous casting mixed pouring process method for round billets of different steel grades with non-overlapping compositions, which can realize the mixing of short pouring times of different steel grades with non-overlapping compositions into long pouring times, and can ensure that the chemical composition between the two meets the requirements, the purity of the molten steel meets the requirements, and the length of the cutting head and tail is reduced, so as to improve the molten steel yield and production efficiency and reduce production costs.

[0005] The technical solutions of the present invention are as follows:

[0006] The present invention provides a method for continuous casting mixed casting of round billets of different steel grades with non-overlapping compositions, which is used to cast mixed casting liquid of different steel grades with an absolute value of liquidus temperature difference being less than or equal to a preset temperature, comprising:

[0007] Classify the chemical composition of different steel grades and control the composition of mixed casting heats according to the principle of similar composition;

[0008] According to the composition of the heat, the high-strength steel in different steel grades is smelted before the soft steel is smelted;

[0009] The smelted molten steel is mixed and poured. When the remaining steel in the tundish of the last furnace before mixing reaches 35%-60% of the rated weight of the tundish, the large ladle of the first furnace after mixing is opened, and the maximum flow to the tundish is required. When the liquid level in the tundish reaches the maximum allowable liquid level for normal pouring, the speed is increased as required and the normal pulling speed is restored until the pouring is completed, thereby completing the continuous casting of the round billet.

[0010] Furthermore, the preset temperature is 10°C.

[0011] Furthermore, the liquid level in the tundish needs to be lowered during mixing and pouring, and the transition blank needs to be cut off.

[0012] Furthermore, when cutting the transition blank, the tail of the previous furnace before the mixing and the head of the next furnace after the mixing are cut as the transition blank.

[0013] Furthermore, the maximum flow rate is 70-80 kg / s and the normal flow rate is 40-45 kg / s.

[0014] The main advantages of the technical solution of the present invention are as follows:

[0015] The present invention provides a mixed pouring process method for continuous casting of round billets of heterogeneous steel grades with non-overlapping components. When continuously casting round billets of heterogeneous steel grades with non-overlapping components, a mixed pouring method is adopted. Two or more heterogeneous steel grades with the absolute value of the liquidus temperature difference being less than or equal to a preset temperature are smelted and melted separately in advance. Subsequently, the separately smelted and melted heterogeneous steel grades are flowed to a ladle at the same middle position at a certain flow rate. When the liquid level in the ladle reaches a certain position and height, the flow rate is changed until all the smelted heterogeneous steel grades are completely fused, thereby achieving the purpose of continuous casting and mixed pouring of round billets. It can also achieve the mixing of short pouring times of heterogeneous steel grades with non-overlapping components into long pouring times, and can ensure that the chemical composition between the two meets the requirements, the purity of the molten steel meets the requirements, and the length of the head and tail cutting is reduced, so as to improve the molten steel yield and production efficiency and reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the embodiments of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 Schematic diagram of a process for continuous casting and mixed pouring of round billets of different steel grades with non-overlapping compositions according to an embodiment of the present invention; DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] Example 1

[0021] As attached Figure 1 As shown, an embodiment of the present invention provides a method for continuous casting mixed casting of round billets of different steel grades with non-intersecting compositions, the method comprising: casting mixed casting liquid of different steel grades having an absolute value of a liquidus temperature difference less than or equal to a preset temperature, comprising:

[0022] Classify the chemical composition of different steel grades and control the composition of mixed casting heats according to the principle of similar composition;

[0023] According to the composition of the heat, the high-strength steel in different steel grades is smelted before the soft steel is smelted;

[0024] The smelted molten steel is mixed and poured. When the remaining steel in the tundish of the last furnace before mixing reaches 35%-60% of the rated weight of the tundish, the large ladle of the first furnace after mixing is opened, and the maximum flow to the tundish is required. When the liquid level in the tundish reaches the maximum allowable liquid level for normal pouring, the speed is increased as required and the normal pulling speed is restored until the pouring is completed, thereby completing the continuous casting of the round billet.

[0025] It should be noted that, when classifying the chemical compositions of different steel grades, the components of two or more steel grades with similar compositions are consistent, and the percentages of the components are within a certain range of difference; or the components of two or more steel grades are inconsistent, but the liquidus lines of the two or more steel grades basically coincide with each other, without obvious drastic peaks and troughs, and the degree of fitting of the liquidus lines of two or more steel grades is 80% or above.

[0026] In some optional implementations of this embodiment, the maximum speed is 70-80 kg / s, the normal flow rate is 40-45 kg / s, and the allowable liquid level is the rated weight of the tundish (for example, a 40-ton tundish).

[0027] The method of the present invention can improve the yield of molten steel to a certain extent.

[0028] It should be noted that the process for continuous casting and mixed pouring of round billets of different steel grades with non-overlapping components in the present invention includes but is not limited to round continuous casting billets, and can also be used for continuous casting billets with rectangular structures.

[0029] Specifically, the preset temperature is 10° C. This setting can prevent continuous casting leakage caused by large superheat differences, which affects the success rate of mixed casting.

[0030] In some optional implementations, the preset temperature can be set to any temperature value between 6°C and 20°C, but in order to ensure the quality and performance of the round continuous casting billet during the smelting and mixing process, the preset temperature is preferably set to 10°C.

[0031] Specifically, the liquid level in the tundish needs to be lowered during mixing and pouring, and the transition blank needs to be cut off.

[0032] It should be noted that the cut transition blank is waste, and the waste is used as raw material for the next use.

[0033] Specifically, when cutting the transition blank, the tail of the furnace before the mixing and the head of the furnace after the mixing are cut as the transition blank.

[0034] Specifically, the weight of the continuous casting transition billet is calculated according to the theory of mixed molten steel, and the transition billet is judged as scrap. After the transition billet is cut off, the chemical composition of the genuine product can meet the chemical composition requirements of the steel grade.

[0035] In some optional implementations, for example: cutting the tail 3.5 meters + cutting the head 4.5 meters, 1 flow is 8 meters in total, a total of 24 meters, and this 24 meters is mixed cast molten steel.

[0036] It should be noted that when the method of the present invention is used to continuously cast round billets of different steel grades with no overlap in composition, high-strength steel is smelted first, followed by soft steel. When the chemical composition of multiple mixed steel grades is consistent, they are cast in sequence according to the carbon content in the steel grades.

[0037] In summary, the principle of the process method for continuous casting and mixed pouring of round billets of different steel grades with non-intersecting compositions of the present invention is as follows: after the smelting of the steel grades is completed, the high-strength steel first flows into the tundish for normal continuous casting. After the ladle has flowed out, the liquid level of the tundish begins to drop. When it drops to 35-60% of the rated weight of the tundish, the molten steel of the mild steel is flowed into the tundish. The tundish is filled to the rated weight at a flow rate of 70-80kg / s. There is mixed molten steel in the tundish. The continuous casting billets formed by the mixed molten steel are judged as transition billets and scrapped. The remaining continuous casting billets are the finished billets with the required compositions, thus completing the mixed pouring process of different steel grades with non-intersecting compositions. If mixed pouring is not required, two short pouring times are required for production. At this time, the two head cuts and two tail cuts need to be judged as scrap. The two mixed pouring times require 3-4 hours of preparation and waiting time, which makes production impossible and has low production efficiency. If mixed pouring is used, only one head and one tail need to be trimmed, which saves one head and one tail, reduces the weight of the head and tail, and improves the molten steel yield. One pouring saves 3-4 hours of preparation and waiting time, saving production time and improving production efficiency.

[0038] Example 2

[0039] Using the method of Example 1 above, mixed casting was performed on 16 continuous pours of 42CrMo and 4 continuous pours of 40Cr, each with a diameter of 690 mm. The D1200840 heat, which produced 42CrMo, and the D1200841 heat, which produced 40Cr, were mixed castings. Without mixed casting, the combined steel yield of the two pours was low. After mixed casting, the yield was 97.3%. The process is as follows:

[0040] (1) Design a mixed casting scheme. The chemical element Mo of 40Cr is ≤ 0.12%, and the chemical element Mo of 42CrMo is 0.17-0.24%. There is no intersection in the Mo chemical composition, and the Mo content should be as close as possible. 40Cr is controlled at 0.10-0.12%, and 42CrMo is controlled at 0.17-0.19%, to reduce the difference in Mo content between the mixed casting steels.

[0041] (2) There are 16 furnaces of 42CrMo in total. The first 15 furnaces of 42CrMo are in normal production according to the process operation procedures. When there are 15 tons of molten steel remaining in the tundish of the 16th furnace of 42CrMo, the ladle of the 1st furnace of 40Cr is opened, and the maximum flow is required to fill the tundish with steel.

[0042] (3) The length of the 42CrMo tail cut is 3.5 meters + the 40Cr blank after casting is 4.5 meters, which is considered as the transition blank, totaling 8 meters.

[0043] (4) Samples were taken at the head and tail of the transition billet to represent the chemical composition of the finished billet before and after. The chemical composition of the head of the transition billet was in line with the internal control of the chemical composition of 42CrMo, and the chemical composition of the tail of the transition section was in line with the internal control of the chemical composition of 40Cr. Except for the three flow cutting heads of 1.0m / 1.0m / 1.0m, the cutting tails of 3.9m / 4.3m / 4.4m, and the transition section of 8m, all the others were judged as finished billets.

[0044] The method of Example 1 was used to perform multiple mixed casting production on the continuous casting round billets of the above specifications. Before the mixed casting was implemented, the yield of molten steel in 4 continuous castings was about 86.0%. After the mixed casting was implemented, the yield of molten steel in 8 continuous castings was about 94.0%, and the yield of molten steel could be increased by 8%.

[0045] Example 3

[0046] Using the method of Example 1 of the present invention, mixed casting was performed on continuous casting round billets with a diameter of 690 mm (Ø). Mixed casting was performed on furnaces 25# (D1203458) and 20# (D1203459). Without mixed casting, the combined molten steel yield for the two castings was 94.1%, while after mixed casting, the yield was 97.1%. The process was as follows:

[0047] (1) Design a mixed casting scheme. The chemical elements of 20# steel are 0.18% ≤ C ≤ 0.22%, and the chemical elements of 25# steel are 0.23% ≤ C ≤ 0.27%. There is no overlap in the C element in the chemical composition. The carbon content is required to be as close as possible, and both are controlled within 0.22-0.23% to reduce the difference in carbon composition of the mixed cast steel types.

[0048] (2) There are 8 furnaces in total for 25#. The first 7 furnaces are in normal production according to the process operation procedures. When there are 15 tons of molten steel remaining in the tundish of the 8th furnace 25#, the ladle water inlet of the 1st furnace 20# is opened, and the maximum flow is required to pour steel into the tundish until the ladle is full.

[0049] (3) The length of the 25# cut tail is 3.5 meters + the 20# cast blank is 4.5 meters after casting, which is considered as the transition blank, totaling 8 meters.

[0050] (4) Samples were taken at the head and tail of the transition billet to represent the chemical composition of the finished billet before and after. The chemical composition of the head of the transition billet was in line with the internal control of the chemical composition of 25#, and the chemical composition of the tail of the transition section was in line with the internal control of the chemical composition of 20#. Except for the three flow cutting heads of 1.0m / 1.0m / 1.0m, the cutting tail of 3.8m / 4.0m / 4.1m, and the transition section of 8m, all the others were judged to be finished billets.

[0051] By adopting the method of the above-mentioned embodiment 1, the continuous casting round billets of the above-mentioned specifications are mixed and cast multiple times. Before the mixed casting is implemented, the molten steel yield of 4 continuous castings is about 83.0%, and after the mixed casting is implemented, the molten steel yield of 8 continuous castings is about 95.0%, and the molten steel yield can be increased by 12%.

[0052] In summary, the main technical features of this process are that when different steel grades with non-overlapping chemical compositions are mixed, the liquid level of the tundish is lowered, the weight of the mixed molten steel is reduced, the degree of influence of the mixed steel on the chemical composition is reduced, the length of the transition billet is accurately calculated during the mixed casting, and after the transition billet is judged to be scrapped, the chemical composition of the finished billet meets the composition requirements of the different steel grades.

[0053] The present invention provides a method for continuous casting and co-casting of round billets of dissimilar steel grades with non-overlapping compositions. This method enables co-casting of dissimilar steel grades when the liquidus difference between the steel grades is ≤10°C. By first continuously casting the high-strength steel grade and then the mild steel grade, the tundish liquid level in the first furnace prior to co-casting must be lowered to 35-60% of the rated weight of the tundish before the ladle of the next furnace can begin pouring. This reduces the weight of the co-cast molten steel and the length of the transition section. Before co-casting, the molten steel yield for four consecutive casts is approximately 85.0%, while after co-casting, the molten steel yield for eight consecutive casts is approximately 95.0%, an increase of at least 10%. If multiple co-casting operations are performed, the molten steel yield can approach 98%.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this document are all referenced to the placement states shown in the accompanying drawings.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for continuous casting and mixing round billets of different steel grades with non-overlapping compositions, characterized in that: Used to pour mixed slurry of different steel grades whose absolute value of liquidus temperature difference is less than or equal to the preset temperature, including: Classify the chemical composition of different steel grades and control the composition of mixed casting heats according to the principle of similar composition; According to the composition of the heat, the high-strength steel in different steel grades is smelted before the soft steel is smelted; The smelted molten steel is mixed and poured. When the remaining steel in the tundish of the last heat before mixing reaches 35%-60% of the rated weight of the tundish, the first large ladle after mixing is opened and the opening of the first large ladle is opened to the maximum, and the molten steel flows to the tundish at the maximum flow rate. When the liquid level in the tundish reaches the maximum allowable liquid level for normal pouring, the molten steel flow rate is adjusted to the normal flow rate until the pouring is completed. The short pours are mixed into long pours to complete the continuous casting of round billets. The preset temperature is 10°C; the maximum flow rate is 70-80 kg / s, and the normal flow rate is 40-45 kg / s; During mixing and pouring, the tundish liquid level needs to be lowered and the transition piece needs to be cut off; When classifying the chemical composition of different steel grades, the components of two or more steel grades with similar compositions are consistent, and the percentage content between the components is within a certain range of difference, or the components of two or more steel grades are inconsistent, but the liquidus lines of two or more steel grades basically coincide with each other, without obvious drastic peaks and troughs, and the fitting degree of the liquidus lines of two or more steel grades is 80% or above.

2. The method for continuous casting and mixed pouring of round billets of non-intersecting different steel grades according to claim 1, characterized in that: When cutting the transition blank, cut the tail of the furnace before mixing and the head of the furnace after mixing as the transition blank.

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