A steel for welding and a method for producing the same

Abstract

The application discloses a kind of steel for welding and preparation method thereof, belong to steel smelting process control technical field.The phosphorus content of tapping is controlled to be ≤0.008% by dephosphorization in converter early stage, and the oxygen content of tapping is controlled in suitable range, then the molten steel is continuously dephosphorized in ladle, and the dephosphorized slag is removed after dephosphorization, and the ladle is lifted into LF refining station for refining after slag removal;Through thermodynamic calculation, suitable refining slag system and deoxidation process are determined, lime, synthetic slag and the like are added in refining station for slagging operation, calcium carbide and aluminum particles are used for diffusion deoxidation in refining process, and the refining slag with strong desulfurization is used for desulfurization operation of molten steel, while the deoxidation intensity is controlled, to ensure that the silicon content is ≤0.05%, and the steel with P, S, Si and other element compositions fully meets the requirements.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically to a welding steel and its preparation method. Background Technology

[0002] As the economy and society enter a stage of high-quality development, the performance requirements of steel materials in various industries are becoming increasingly stringent, especially the requirements for the content of phosphorus, sulfur and other residual elements in steel. Many steel grades also impose restrictions on the content of elements such as silicon, aluminum and titanium, requiring them to be as low as possible. Moreover, some of these requirements are contradictory from the basic principles of metallurgical reactions. Therefore, it is necessary to find the optimal balance point in the production process to resolve these contradictions.

[0003] Welding steels have high requirements for four interrelated yet contradictory elements: phosphorus, sulfur, silicon, and aluminum. The lower the content of these elements, the higher the welding quality. However, in normal production processes, it is difficult to control the content of a single phosphorus element in the steel to below 0.005%. In the production process, dephosphorization must be carried out under strong oxidizing conditions, while desulfurization must be carried out under strong reducing conditions. Strong reducing conditions require sufficient deoxidation reaction to be achieved. However, welding steels also require that the aluminum and silicon contents not be too high. Achieving ultra-low sulfur requirements under low aluminum content conditions is quite difficult, while high aluminum conditions may cause the silicon content to exceed the standard. In other words, controlling these elements, which are contradictory in metallurgical control principles, is even more difficult to achieve.

[0004] To address the aforementioned issues, providing a reasonable smelting method to effectively control the content of the four elements is a technical challenge that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a welding steel and a method for preparing the same, which yields welding steel with a phosphorus content not exceeding 0.005%, a sulfur content not exceeding 0.003%, and a silicon content not exceeding 0.05%.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] First, the present invention provides a welding steel comprising the following components by weight percentage:

[0008] C 0.06%–0.08%, Si ≤0.05%, Mn 0.35%–0.55%, P ≤0.005%, S ≤0.003%, Al ≤0.010%, Ca ≤0.0015%, balance being Fe and unavoidable impurities.

[0009] The present invention also provides a method for preparing welding steel as described above, comprising the following steps:

[0010] (1) Add desulfurizing agent to molten iron for KR desulfurization until S < 0.0015wt% in molten iron, remove desulfurization slag, and control the temperature of molten iron ≥ 1300℃;

[0011] (2) Step (1) The desulfurized molten iron and scrap steel are fed into the converter, and then lime and dolomite are added to form slag and dephosphorize until P < 0.006 wt%. The final molten steel in the converter has O = 400-600 ppm, C ≤ 0.05 wt%, P ≤ 0.008 wt%, S ≤ 0.008 wt%, and the final molten steel temperature ≥ 1600℃.

[0012] (3) After smelting (2), the steel is tapped. The thickness of the slag during the tapping process is ≤30mm. After tapping, lime and pre-melted refining slag are added to the ladle. Argon gas is used to stir the molten steel to remove phosphorus until P <0.003wt% in the molten steel. The dephosphorized slag is then removed.

[0013] (4) The dephosphorized steel liquid in step (3) is refined. During the refining process, lime and refining synthetic slag are added to form slag and the slag basicity is controlled at 5.0 to 6.5. Then, an appropriate amount of calcium carbide and aluminum particles are added to diffuse deoxidize the refining slag to ensure that Si in the steel liquid is ≤0.05wt%. After the refining and slag formation is completed, the steel liquid is desulfurized to S≤0.0025wt% to obtain steel liquid with the required composition. Then, the steel liquid is continuously cast to obtain the welding steel.

[0014] Preferably, the desulfurizing agent in step (1) is lime and granular magnesium, with the amount of lime added being 13-15 kg / t of molten iron and the amount of granular magnesium added being 2-5 kg / t of molten iron.

[0015] Preferably, the converter in step (2) is a 120-ton top-and-bottom blown converter.

[0016] Preferably, the mass ratio of molten iron to scrap steel in step (2) is (75-80):(15-20).

[0017] Preferably, the amount of lime added in step (2) is 21 kg / t of total loading, and the amount of dolomite added is 8 kg / t of total loading.

[0018] Preferably, in step (3), the amount of lime added is 2 kg / t of molten steel, and the amount of pre-melted refining slag added is 1 kg / t of molten steel.

[0019] Preferably, in step (4), an LF furnace is used for refining, and the amount of lime added during the refining process is 6 kg / t of molten steel, and the amount of refining slag added is 6 kg / t of molten steel.

[0020] Preferably, in step (4), the amount of calcium carbide added is 1 kg / t of molten steel, and the amount of aluminum particles added is 0.5 kg / t of molten steel.

[0021] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a welding steel and its preparation method, which has the following beneficial effects:

[0022] This invention addresses the chemical composition characteristics of ultra-low phosphorus, ultra-low sulfur, and ultra-low silicon welding steel. Through thermodynamic calculations, it seeks a suitable balance point in processes such as desulfurization, aluminum deoxidation, and aluminum reduction of silicon. It selects appropriate refining slag systems and reasonable slag-making processes, and combines them with hot metal pretreatment processes and converter dephosphorization and endpoint control. This achieves both desulfurization and control of aluminum and silicon content to meet requirements, realizing an effective balance of phosphorus, sulfur, silicon, and aluminum. This results in a stable chemical composition required for welding steel, achieving the required composition control for welding steel. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 The diagram shows the sulfur content control during the smelting process in Examples 1 and 2 of this invention.

[0025] Figure 2 The diagram shows the phosphorus content control during the smelting process in Examples 1 and 2 of this invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] The molten iron fed into the converter needs to undergo pretreatment. Before pretreatment, the molten iron has a phosphorus content of P = 0.153 wt%, a sulfur content of S = 0.032 wt%, a carbon content of C = 4.19 wt%, a Si content of Si = 0.41 wt%, and a temperature of 1358℃. 76 tons of molten iron and 16 tons of scrap steel are added to the converter for smelting.

[0029] (1) First, add 1064 kg of lime and 228 kg of granular magnesium to the molten iron entering the furnace. Use the KR method for pretreatment and desulfurization. The sulfur content of the molten iron after pretreatment and desulfurization is 0.0012 wt%. Then, remove the desulfurization slag and measure the temperature of the molten iron after pretreatment to 1317℃.

[0030] (2) Step (1) The desulfurized molten iron and scrap steel are fed into the converter. In the early stage of converter smelting, 1932 kg of lime is added, and 736 kg of dolomite is added according to the fluidity of the slag to create a converter slag with high alkalinity, strong oxidizing properties, and good fluidity, which is conducive to dephosphorization. The molten steel is dephosphorized. After dephosphorization, a sample is taken. The phosphorus content in the molten steel is 0.0048 wt%. At the end of the converter, the oxygen content in the molten steel is O = 430 ppm, the carbon content is C = 0.048 wt%, the phosphorus content is P = 0.0067 wt%, the sulfur content is S = 0.0076 wt%, and the end temperature is 1633℃.

[0031] (3) No deoxidation and alloying operations are performed during the tapping process. The slag thickness is required to be 25mm during the tapping process. After the tapping is completed, lime and pre-melted refining slag are added to the ladle at a rate of 2kg / t of molten steel and 1kg / t of molten steel. The molten steel is stirred with large argon gas to carry out dephosphorization operation. During the dephosphorization process, the molten steel is sampled. When the phosphorus content in the molten steel is P = 0.0027wt%, the dephosphorization operation is stopped, the dephosphorization slag is removed, and the ladle is then hoisted to the LF refining station for refining operation.

[0032] (4) In the LF refining process, 6 kg / t of lime and 6 kg / t of refining synthetic slag are added based on the weight of the refined steel liquid to form slag. The basicity of the slag is 5.6. In the refining process, 1 kg / t of calcium carbide and 0.5 kg / t of aluminum particles are added to the refining slag for diffusion deoxidation. After the refining slag is formed, desulfurization operation is carried out. After the desulfurization operation is completed, a sample is taken. The sulfur content in the steel is S = 0.0021 wt% and Si = 0.038 wt%. The specific composition is shown in Table 1. Then the molten steel is continuously cast to obtain the welding steel.

[0033] Table 1

[0034]

[0035] Example 2

[0036] The molten iron fed into the converter needs to undergo pretreatment. Before pretreatment, the molten iron has a phosphorus content of P = 0.149 wt%, a sulfur content of S = 0.029 wt%, a carbon content of C = 4.41 wt%, a Si content of Si = 0.43 wt%, and a temperature of 1363℃. 78 tons of molten iron and 15 tons of scrap steel are added to the converter for smelting.

[0037] (1) First, add 1014 kg of lime and 390 kg of granular magnesium to the molten iron entering the furnace. Use the KR method for pretreatment and desulfurization. The sulfur content of the molten iron after pretreatment and desulfurization is 0.0009 wt%. Then remove the desulfurization slag and measure the temperature of the molten iron after pretreatment to 1309℃.

[0038] (2) Step (1) The desulfurized molten iron and scrap steel are fed into the converter. In the early stage of converter smelting, 1953 kg of lime is added, and 744 kg of dolomite is added according to the fluidity of the slag to create a converter slag with high alkalinity, strong oxidizing properties, and good fluidity, which is conducive to dephosphorization. The molten steel is dephosphorized. After dephosphorization, a sample is taken. The phosphorus content in the molten steel is 0.0056 wt%. At the end of the converter, the oxygen content in the molten steel is O = 560 ppm, the carbon content is C = 0.039 wt%, the phosphorus content is P = 0.0078 wt%, the sulfur content is S = 0.0066 wt%, and the end temperature is 1653℃.

[0039] (3) No deoxidation and alloying operations are performed during the tapping process. The slag thickness is required to be 28 mm during the tapping process. After the tapping is completed, lime and pre-melted refining slag are added to the ladle at a rate of 2 kg / t of molten steel and 1 kg / t of molten steel. The molten steel is stirred with large argon gas to carry out dephosphorization operation. During the dephosphorization process, the molten steel is sampled. When the phosphorus content in the molten steel is P = 0.0029 wt%, the dephosphorization operation is stopped, the dephosphorization slag is removed, and the ladle is then hoisted to the LF refining station for refining operation.

[0040] (4) In the LF refining process, 6 kg / t of lime and 6 kg / t of refining synthetic slag are added by weight of the refined steel liquid to form slag. The basicity of the slag is 6.1. In the refining process, 1 kg / t of calcium carbide and 0.5 kg / t of aluminum particles are added to the refining slag for diffusion deoxidation. After the refining slag is formed, desulfurization operation is carried out. After the desulfurization operation is completed, a sample is taken. The sulfur content in the steel is S = 0.0028 wt% and Si = 0.046 wt%. The specific composition is shown in Table 2. Then the molten steel is continuously cast to obtain the welding steel.

[0041] Table 2

[0042]

[0043] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0044] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A type of welding steel, characterized in that, Includes the following components by weight percentage: C 0.06%~0.08%, Si ≤0.05%, Mn 0.35%~0.55%, P ≤0.005%, S ≤0.003%, Al ≤0.010%, Ca ≤0.0015%, balance Fe and unavoidable impurities; The method for preparing the welding steel includes the following steps: (1) Add desulfurizing agent to molten iron for KR desulfurization until S < 0.0015wt% in molten iron, remove desulfurization slag, and control the temperature of molten iron ≥ 1300℃; (2) Step (1) The desulfurized molten iron and scrap steel are fed into the converter, and then lime and dolomite are added to form slag and dephosphorize until P < 0.006 wt%. The final molten steel in the converter has O = 400~600 ppm, C ≤ 0.05 wt%, P ≤ 0.008 wt%, S ≤ 0.008 wt%, and the final molten steel temperature ≥ 1600℃. (3) After smelting in step (2), the steel is tapped. The thickness of the slag during the tapping process is ≤30mm. After tapping, lime and pre-melted refining slag are added to the ladle. Argon gas is used to stir the molten steel to remove phosphorus until P <0.003wt% in the molten steel. The dephosphorized slag is then removed. (4) The dephosphorized steel liquid in step (3) is refined. During the refining process, lime and refining synthetic slag are added to form slag and the slag basicity is controlled at 5.0~6.

5. Then, an appropriate amount of calcium carbide and aluminum particles are added to diffuse deoxidize the refining slag to ensure that Si in the steel liquid is ≤0.05wt%. After the refining and slag forming is completed, the steel liquid is desulfurized to S≤0.0025wt% to obtain steel liquid with the required composition. Then, the steel liquid is continuously cast to obtain the welding steel. The desulfurizing agent in step (1) is lime and granular magnesium. The amount of lime added is 13-15 kg / t of molten iron, and the amount of granular magnesium added is 2-5 kg / t of molten iron. In step (2), the mass ratio of molten iron to scrap steel is (75~80):(15~20). In step (2), the amount of lime added is 21 kg / t of total loading, and the amount of dolomite added is 8 kg / t of total loading. In step (3), the amount of lime added is 2 kg / t of molten steel, and the amount of pre-melted refining slag added is 1 kg / t of molten steel; In step (4), LF furnace refining is used. During the refining process, the amount of lime added is 6 kg / t of molten steel, the amount of refining slag added is 6 kg / t of molten steel, the amount of calcium carbide added is 1 kg / t of molten steel, and the amount of aluminum particles added is 0.5 kg / t of molten steel.

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