A sulphur-containing steel and a method for electroslag remelting thereof

Abstract

This invention provides a method for electroslag remelting sulfur-containing steel. Specifically, it relates to a production control method for ensuring that the sulfur content (S) in the electroslag ingot meets the requirement of "0.010-0.035%" during the electroslag remelting process of free-machining steels with low S content, such as 42CrMoS, belonging to the field of electroslag remelting technology. The method involves first selecting electroslag base material with simultaneously controlled sulfur and aluminum content, performing surface treatment, and coating with aluminum powder; then remelting the electroslag base material with a binary slag system under gas protection to reduce desulfurization at the arc initiation end; after a certain amount of electroslag base material has been remelted, gas protection is stopped, and deoxidation is increased by applying aluminum powder to the surface to enhance desulfurization at the feeding end, until the remelting is completed, resulting in remelted sulfur-containing steel. The obtained remelted sulfur-containing steel (electroslag ingot) meets the requirement of "0.010-0.035%" for S. The method for electroslag remelting of sulfur-containing steel has solved the problems of [S] < 0.010% at the arc-starting end (tail) and [S] > 0.035% at the feeding end (head) of the electroslag ingot. The method effectively controls the sulfur content of the sulfur-containing steel.

Description

Technical Field

[0001] This invention belongs to the field of electroslag remelting technology, specifically relating to a sulfur-containing steel and a method for electroslag remelting therein. Background Technology

[0002] Sulfur (S) has a significant impact on slag desulfurization and gas-phase volatilization desulfurization during electroslag remelting, making S element control during this process difficult. Free-cutting steels are generally produced in electric furnaces or converters and are typically not subjected to electroslag remelting. However, in recent years, with increasing market demands for the cleanliness and uniformity of metal materials, some S-containing free-cutting steels require initial production of base materials in electric furnaces or converters, followed by electroslag remelting, specifically in a gas-protected electroslag furnace.

[0003] 42CrMoS steel requires a sulfur content of 0.010-0.035%. While the sulfur content in the electroslag remelting base material can be controlled within a certain range, during production using the electroslag remelting process, the arc-starting end (tail end) of the electroslag ingot is prone to low sulfur content due to 60-70% direct desulfurization of the slag, resulting in sulfur content <0.010% in the tail end of the ingot, which is unacceptable. As remelting progresses, the desulfurization efficiency of the slag gradually decreases, and due to the influence of the protective gas partial pressure in the gas-protected electroslag furnace, almost no sulfur is removed at the feeding end (head) of the electroslag ingot in the later stages of remelting. This results in high sulfur content, exceeding 0.035%, which is also unacceptable.

[0004] However, there are no reports on how to control the desulfurization of free-cutting steel with low sulfur content during electroslag remelting under gas protection to ensure that the sulfur content in each part is up to standard. Summary of the Invention

[0005] The present invention aims to provide a method for electroslag remelting of sulfur-containing steel to solve the above-mentioned problems, so that the sulfur content of each part of the electroslag ingot after remelting of free-machining steel with low S content is qualified.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for electroslag remelting of sulfur-containing steel, comprising:

[0008] First, select electroslag base material with controlled sulfur and aluminum content, perform surface treatment, and coat with aluminum powder; then remelt the electroslag base material with binary slag system and blow gas for protection to reduce desulfurization at the arc initiation end; after a certain amount of electroslag base material has been remelted, stop the gas protection and increase deoxidation by adding aluminum powder to the surface to increase desulfurization at the feeding end until the remelting is completed, and obtain remelted sulfur-containing steel.

[0009] Furthermore, in the electroslag matrix, the sulfur content is 0.040% to 0.050% and the aluminum content is 0.040% to 0.060% by mass percentage of chemical composition.

[0010] Furthermore, the surface treatment is either peeling or shot blasting.

[0011] Furthermore, the coating amount of the aluminum powder accounts for 0.02 to 0.05% of the total weight of the electroslag matrix.

[0012] Furthermore, the area of ​​the aluminum powder coating accounts for less than 50% of the surface area of ​​the electroslag matrix.

[0013] Furthermore, the binary slag system comprises, by mass percentage: CaF2: 68%–72%, Al2O3: 28%–32%.

[0014] Furthermore, before the electroslag base material is remelted, gas is first introduced into the remelting device for 10-15 minutes, and then electricity is supplied to add a binary slag system to start the remelting process.

[0015] Furthermore, the amount of electroslag base material remelted is such that the weight of the remelted ingot reaches 8-10% of the weight of the electroslag base material before remelting.

[0016] Furthermore, before a certain amount of the electroslag base material is remelted, the remelting positive pressure is guaranteed to be ≥0.2KPa.

[0017] Furthermore, the gas is argon.

[0018] Secondly, the present invention provides a sulfur-containing steel, which is obtained by remelting using the above-described method.

[0019] Furthermore, the sulfur content of the sulfur-containing steel is 0.010-0.035%.

[0020] Furthermore, the sulfur-containing steel is 42CrMoS steel.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The method of this invention achieves a [S] content of 0.010-0.035% in free-machining steel (such as 42CrMoS) with low S content after electroslag remelting through the following three key controls: First, in addition to controlling the [S] content in the electroslag base material, the [Al] content is also controlled to stabilize desulfurization during the remelting process; second, gas protection and the use of a binary slag system are implemented from the start of the electroslag base material remelting until a specific melting amount is reached, reducing desulfurization at the tail end of the electroslag ingot and solving the problem of [S] < 0.010% at the arc-starting end (tail end) of the electroslag ingot; third, aluminum powder is coated on the surface of the base material to increase deoxidation, and gas protection is stopped after a specific amount of electroslag base material is remelted, increasing the desulfurization during the remelting process and solving the problem of [S] > 0.035% at the feeding end (head) of the electroslag ingot.

[0023] 2. The electroslag remelting method for free-cutting steel of the present invention is stable and effective, and can stabilize the [S] content of 42CrMoS steel after electroslag remelting at 0.010-0.035%. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of aluminum powder coating on the surface of the base material in an embodiment.

[0025] Figure 2 This is a schematic diagram of the installation of the base material in an example. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The embodiments of this invention are implemented based on the technical solutions of this invention, and detailed implementation methods and processes are given. However, the scope of protection of this invention is not limited to the following embodiments. Those skilled in the art should understand that the embodiments are merely helpful in understanding this invention and should not be considered as specific limitations on this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0028] In this invention, unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are "by weight or weight percentage" throughout. Process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions. The raw materials described in the following examples are all available from publicly available commercial sources.

[0029] The inventors explored the desulfurization process of free-cutting steels with low sulfur content, such as 42CrMoS, in electroslag remelting under gas protection. By combining continuous sampling and analysis of the changes in sulfur content from the beginning to the end of the electroslag ingot, they studied the composition of the electroslag base material, the remelting slag system, and the gas protection of free-cutting steels with low sulfur content, such as 42CrMoS, and clarified the desulfurization law during the electroslag remelting process of free-cutting steels with low sulfur content, such as 42CrMoS.

[0030] This invention is specifically for 42CrMoS type steel, which has a low S content. After electroslag remelting, the S content in the steel should meet the requirement of "0.010-0.035%".

[0031] This invention controls the desulfurization of 42CrMoS-type steel electroslag ingots by controlling factors such as the composition of Al and S, surface peeling, shot blasting, coating, etc., the remelting slag system (selected binary slag), and the protective gas. This reduces desulfurization at the arc-starting end (tail) and increases desulfurization at the feeding end (head) of the ingot. This achieves the preparation of free-cutting steel with a low S content (0.010-0.035%). The S content of the ingot obtained after electroslag remelting of the base material meets the requirement of "0.010-0.035%" at the head, middle, and tail.

[0032] The technical solution adopted in this invention is:

[0033] According to a first aspect of the present invention, a method for electroslag remelting of sulfur-containing steel includes:

[0034] First, select electroslag base material with controlled sulfur and aluminum content, perform surface treatment, and coat with aluminum powder; then remelt the electroslag base material with binary slag system and blow gas for protection to reduce desulfurization at the arc initiation end; after a certain amount of electroslag base material has been remelted, stop the gas protection and increase deoxidation by adding aluminum powder to the surface to increase desulfurization at the feeding end until the remelting is completed, and obtain remelted sulfur-containing steel.

[0035] The method of this invention ensures that the sulfur content of the remelted sulfur-containing steel (electroslag ingot) after electroslag remelting of low-sulfur free-machining steel (such as 42CrMoS) meets the requirement of "0.010-0.035%" in the head, middle, and tail sections through the following three key controls: First, in addition to controlling the sulfur content in the electroslag base material, the Al content is also controlled to stabilize desulfurization during the remelting process; second, gas protection and the use of a binary slag system in the early stage of remelting reduce desulfurization at the tail section of the electroslag ingot, solving the problem of sulfur content <0.010% at the tail section; third, aluminum powder is coated on the surface of the base material to increase deoxidation, and argon protection is stopped, which increases the desulfurization during the remelting process, solving the problem of sulfur content >0.035% at the head section of the electroslag ingot.

[0036] In this invention, the shrinkage end refers to the part that is last remelted into an ingot, i.e., the head of the electroslag ingot; the arc-starting end refers to the part that is first remelted into an ingot, i.e., the tail of the electroslag ingot.

[0037] As an optional embodiment of the present invention, the electroslag parent material, by mass percentage of chemical composition, has the following sulfur content: 0.040% to 0.050% (e.g., 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049%), and the aluminum content: 0.040% to 0.060% (e.g., 0.041%, 0.043%, 0.045%, 0.047%, 0.049%, 0.051%, 0.053%, 0.057%, 0.059%).

[0038] In the above technical solution, additional control of the Al content in the base material can result in a lower O content, thereby ensuring smooth desulfurization. The lower the O content in the steel, the easier it is to desulfurize.

[0039] As an optional embodiment of the present invention, the surface treatment is peeling or shot blasting.

[0040] In the above technical solutions, peeling or shot blasting is performed on the entire surface to remove the oxide layer or other impurities from the entire surface.

[0041] As an optional embodiment of the present invention, the coating area of ​​the aluminum powder accounts for less than 50% of the surface area of ​​the electroslag matrix (e.g., 45%, 35%, 25%, 15%, 10%, 5%, 2%).

[0042] In the above technical solution, the aluminum powder coating area only occupies a portion of the side surface of the base material, not the entire surface. This is mainly to consider operability in actual production, facilitating on-site aluminum powder application. Preferably, the aluminum powder is applied from the coating start position along the height direction of the electroslag base material to the end of the electroslag base material (i.e., the last remelted part) or near the end. The method for determining the starting position of the aluminum powder coating on the side surface of the electroslag base material is as follows: starting from the starting end of the electroslag base material (the first remelted part), calculate a height position accounting for 8-10% of the total weight of the base material. No aluminum powder is applied between the starting end of the electroslag base material and the coating start position. Specifically, the aluminum powder coating area on the base material surface can be as follows: the steel base material is a Ф400mm bar, 2800mm in length; the aluminum powder coating is 100mm wide and 2500mm long, accounting for approximately 7.1% of the side surface area of ​​the base material.

[0043] As an optional embodiment of the present invention, the coating amount of aluminum powder accounts for 0.02 to 0.05% of the total weight of the electroslag matrix (e.g., 0.021%, 0.023%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.047%, 0.049%).

[0044] In the above technical solution, controlling the amount of aluminum powder coating within the specified range ensures both surface oxidation and deoxidation of the base material and avoids Al2O3 inclusions that could affect the purity of the steel. Specifically, for example: the steel base material is a Ф400mm bar, 2800mm in length, weighing approximately 2900kg, with an Al content of 0.04-0.06%, and 800-1000g of aluminum powder is applied to the surface. During remelting, argon gas is first purged, followed by electric remelting. After melting approximately 280kg, argon purging is stopped (i.e., argon purging stops when the aluminum powder coating begins). The purpose of applying aluminum powder is: since there is no argon protection after melting approximately 280kg, the base material surface is oxidized. The pre-coated aluminum powder ensures deoxidation of the surface oxide layer, thereby achieving desulfurization.

[0045] As an optional embodiment of the present invention, the binary slag system comprises, by mass percentage: CaF2: 68%–72% (e.g., 68.5%, 69%, 69.5%, 70%, 70.5%, 71%, 71.5%), and Al2O3: 28%–32% (e.g., 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%).

[0046] In the above technical solution, the binary slag system may also include a small amount of SiO2, generally not exceeding 1%, which can be ignored. Specifically, the binary slag system includes: CaF2: 68%–71% (e.g., 68.5%, 69%, 69.5%, 70%, 70.5%), Al2O3: 28%–31% (e.g., 28.5%, 29%, 29.5%, 30%, 30.5%), and SiO2: 0.5–1.0% (e.g., 0.6%, 0.7%, 0.8%, 0.9%), totaling 100%.

[0047] As an optional embodiment of the present invention, before the electroslag base material is remelted, gas is first introduced into the remelting device for 10-15 minutes (e.g., 11 minutes, 12 minutes, 13 minutes, 14 minutes), and then electricity is supplied to add a binary slag system to start remelting.

[0048] In the above technical solution, the remelting device, such as the electroslag remelting crystallizer, is first filled with protective gas -Ar, which can reduce the desulfurization in the early stage of remelting and avoid the low S content at the tail of the electroslag ingot, thus preventing it from being unqualified.

[0049] As an optional embodiment of the present invention, the amount of electroslag base material remelted is 8-10% (e.g., 8.1%, 8.3%, 8.5%, 8.7%, 8.9%, 9.1%, 9.3%, 9.5%, 9.7%, 9.9%) of the weight of the remelted ingot before remelting.

[0050] In this invention, for ease of description, the process of electroslag remelting is divided into two stages: the remelted ingot weight is defined as 8-10% of the original electroslag base material weight before remelting, and the ingot weight is defined as the early stage of remelting before remelting.

[0051] As an optional embodiment of the present invention, during the early stage of remelting, a protective gas is continuously supplied to ensure that the positive pressure during the early stage of remelting is ≥0.2KPa (e.g., 0.2KPa, 0.5KPa, 1KPa, 1.5KPa, 2KPa, 3KPa, 4KPa), so as to avoid an increase in the desulfurization rate and resulting in low sulfur content.

[0052] In an optional embodiment of the present invention, the protective gas is argon.

[0053] Other remelting electrostatic processes in this invention, such as remelting rate, smelting current, voltage, and the size of the electroslag base material and electroslag ingot, are related to the size of the electroslag base material and the size of the electroslag ingot. They are no different from general production and can be set as needed, such as a melting rate of 7.0-6.0 kg / min.

[0054] According to a second aspect of the invention, a sulfur-containing steel is obtained by remelting as described above.

[0055] As an optional embodiment of the present invention, the sulfur content of the sulfur-containing steel is 0.010-0.035%.

[0056] In an optional embodiment of the present invention, the sulfur-containing steel is 42CrMoS steel.

[0057] In a specific embodiment of the present invention, 42CrMoS steel, a free-machining steel with a low S content, is used as an example for illustration.

[0058] In the specific embodiments and comparative examples of this invention, the 42CrMoS steel electroslag base material is obtained by "20-ton electric furnace + VD refining". Each heat of steel can yield 6 pieces of base material with a diameter of 400mm and a length of 2800mm. One piece of base material is remelted into one electroslag ingot. That is, each piece of electroslag base material obtained from each heat of steel is remelted into one electroslag ingot in a crystallizer (top opening Ф490mm / bottom opening Ф530mm).

[0059] It should be noted that the composition of each batch of 42CrMoS steel electroslag remelting base material was analyzed by sampling in the molten steel state, and only one component was analyzed. That is, the sulfur content and aluminum content of all six batches of electroslag base material from the same batch were identical. During the "20-ton electric arc furnace + VD refining" process, the sulfur and aluminum content of the 42CrMoS steel electroslag base material can be controlled within the aforementioned requirements using existing technologies. For example, appropriate amounts of sulfur and aluminum source raw materials can be selected before smelting, and sulfur-containing and aluminum-containing substances can be added during smelting to control the elemental content of sulfur and aluminum in the molten steel. Alternatively, sulfur-containing steel that has passed sulfur and aluminum content tests can be directly selected as the electroslag base material before remelting.

[0060] In the specific embodiments and comparative examples of the present invention, the binary slag system used, by mass percentage, includes: CaF2: 68%–71%, Al2O3: 28%–31%, SiO2: 0.5–1.0%, totaling 100%.

[0061] The present invention will now be described in further detail with reference to specific embodiments.

[0062] Examples 1-6

[0063] The electroslag remelting method for 42CrMoS steel in Examples 1-6 includes the following steps:

[0064] (1) Mass percentage of S and Al in the parent material: S: 0.045%, Al: 0.055%;

[0065] (2) The Ф400mm*2800mm base material is subjected to full-surface shot blasting or peeling treatment, and aluminum powder is coated on part of the side surface of the base material (the coating area is about 100mm wide and 2500mm long, accounting for about 7.1% of the side surface area of ​​the base material). Partial coating facilitates the coating operation and is applied to the part of the base material that is to be remelted later, so that after a certain amount of base material is remelted, the gas protection is stopped (the starting point of aluminum powder coating is reached when the gas protection is stopped). The aluminum powder on the surface can increase deoxidation and thus enhance the desulfurization at the feeding end. The schematic diagram of aluminum powder coating on the base material surface is shown below. Figure 1 As shown.

[0066] (3) Directly install the base material and remelt the slag. A schematic diagram of the base material installation is shown below. Figure 2 As shown.

[0067] (4) Before electro-slag charging, purge argon gas through a rapid charging pipe for 10-15 minutes, then charge and add slag, using 90 kg of binary slag per pipe. In the early stage of remelting, ensure a positive pressure ≥ 0.2 kPa inside the protective cover and continuously charge with argon gas for protection. Charge the electro-remelting gas for 80-90 minutes. When the ingot weight reaches 280 kg (the weight of the remelted ingot is 8-10% of the weight of the electroslag base material before remelting), the middle and late stages of remelting are entered. Turn off the protective gas (Ar) until the remelting is completed, and obtain a 42CrMoS steel electroslag ingot.

[0068] The six masterbatches from the same furnace in Examples 1-6 were remelted into ingots, and the relevant specific parameters are shown in Table 1 below:

[0069] Table 1

[0070]

[0071] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 2 below:

[0072] Table 2

[0073]

[0074]

[0075] In Table 2 above, each base material produced in the same furnace contains 0.045% sulfur (S) and 0.055% aluminum (Al). This type of sulfur-containing steel only requires a certain amount of sulfur (S) and not a certain amount of aluminum (Al). Table 2 lists the Al content for comparison with the base material's Al composition, but in reality, the Al content in the electroslag ingot is affected by both the Al composition of the base material and the amount of aluminum powder coating. Because the distribution of S content on the sulfur-containing steel electroslag ingot follows a pattern of "low → high" from the tail end to the head end, to ensure that the S content of the electroslag ingot steel meets the requirement of "0.010-0.035%", it is only necessary to analyze that the S content at the tail end of the electroslag ingot is ≥0.010% and the S content at the head end is ≤0.035%. As shown in Table 2 above, the [S] and [Al] contents of the six electroslag ingots obtained from the remelting of the six parent materials were all within acceptable limits, but there were some slight differences. The main reasons include: 1) there are analytical deviations in the composition of S and Al elements; 2) the quality of the six parent materials themselves varies, and there are slight differences in the cleanliness of their surfaces; 3) although they are all 90 kg of binary slag, their slag compositions are not completely the same. In addition, the sealing state of the gas-protected electroslag furnace during the remelting of each parent material also differed.

[0076] Examples 7 and 8

[0077] The only difference from Example 1 is the different mass percentages of S and Al in the parent material, as shown in Table 3 below:

[0078] Table 3

[0079] project Base material composition Example 7 0.040% [S], 0.040% [Al] Example 8 0.050%

S

Al

[0080] All other settings are the same as in Example 1.

[0081] After the electroslag ingots cooled, two ingots were randomly selected, and powder-steel chips were drilled from both ends (tail and head). The content of [S] was detected using a CS instrument, and the content of [Al] was detected using an ICP (inductively coupled plasma optical emission spectrometer). The results are shown in Table 4 below:

[0082] Table 4

[0083]

[0084]

[0085] As can be seen from Table 4 above, the electroslag ingot steel [S] obtained by the method of the present invention meets the requirement of "0.010-0.035%".

[0086] Examples 9 and 10

[0087] The only difference from Example 1 is the amount of aluminum powder used for coating, as detailed in Table 5 below:

[0088] Table 5

[0089] project Total weight of parent material (kg) Aluminum powder mass (g) Example 9 2900 580 Example 10 2900 1450

[0090] All other settings are the same as in Example 1.

[0091] After the electroslag ingots cooled, two ingots were randomly selected, and powder-steel chips were drilled from both ends (tail and head). The content of [S] was detected using a CS instrument, and the content of [Al] was detected using an ICP (inductively coupled plasma optical emission spectrometer). The results are shown in Table 6 below:

[0092] Table 6

[0093]

[0094] As can be seen from Table 6 above, the electroslag ingot steel [S] obtained by the method of the present invention meets the requirement of "0.010-0.035%".

[0095] Comparative Examples 1-6

[0096] The main difference between Comparative Examples 1-6 and Example 1 is that the aluminum content in the parent material was not controlled. Specifically, the steps include the following:

[0097] (1) S mass percentage in the base material: 0.044%, Al content is not controlled (actual Al content in the base material steel is 0.015%).

[0098] (2) The entire surface of the Ф400mm*2800mm base material is shot blasted, and aluminum powder is applied to some side surfaces of the base material (the coating area is about 100mm wide and 2500mm long).

[0099] (3) Directly install the base material and remelt the slag.

[0100] (4) Before electro-slag charging, purge argon gas for 15 minutes using a rapid charging pipe, then charge and add slag, using 90 kg of binary slag per pipe. In the early stage of remelting, ensure a positive pressure ≥ 0.2 kPa inside the protective cover and continuously charge with argon gas for protection. Charge the gas for electro-remelting for 85-90 minutes. When the ingot weight reaches 280 kg (the weight of the remelted ingot is 8-10% of the weight of the electroslag base material before remelting), the middle and late stages of remelting are entered. Turn off the protective gas (Ar) until the remelting is completed, and obtain a 42CrMoS steel electroslag ingot.

[0101] The six masterbatches from the same furnace in Comparative Examples 1-6 were remelted into ingots, and the relevant parameters are shown in Table 7 below:

[0102] Table 7

[0103]

[0104] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 8 below:

[0105] Table 8

[0106]

[0107] As can be seen from Table 8 above, the content of Al in the base material of Comparative Examples 1-6 was not controlled, resulting in a higher S content at the head of the electroslag ingot. Some steel ingots had unqualified S content. Compared with Examples 1-6, the pass rate of electroslag ingots prepared by remelting steel from the same furnace decreased.

[0108] Comparative Examples 7-12

[0109] The main difference between Comparative Examples 7-12 and Example 5 is that the base material was not subjected to surface shot blasting treatment. Specifically, the steps include:

[0110] (1) Mass percentage of S and Al in the parent material: S: 0.044%, Al: 0.053%.

[0111] (2) The surface of the Ф400mm*2800mm base material was not shot blasted, and aluminum powder was directly applied to part of the side surface of the base material (the coating area is about 100mm wide and 2500mm long).

[0112] (3) Directly install the base material and remelt the slag.

[0113] (4) Before electro-slag charging, purge argon gas through a rapid charging pipe for 10-15 minutes, then charge the slag, using 90 kg of binary slag per pipe. During the early stage of remelting, ensure a positive pressure ≥ 0.2 kPa inside the protective shield and continuously charge with argon gas for protection. Charge the electro-remelting gas for 85-90 minutes. When the ingot weight reaches 280 kg (the weight of the remelted ingot is 8-10% of the weight of the electroslag base material before remelting), the middle and late stages of remelting are entered. Turn off the protective gas (Ar) until the remelting is completed, and obtain a 42CrMoS steel electroslag ingot.

[0114] The six masterbatches from the same furnace in Comparative Examples 7-12 were remelted into ingots, and the relevant parameters are shown in Table 9 below:

[0115] Table 9

[0116]

[0117] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 10 below:

[0118] Table 10

[0119]

[0120]

[0121] As can be seen from Table 10 above, comparative examples 7-12 did not perform surface treatment such as shot blasting or peeling on the surface of the base material before coating with aluminum powder, resulting in a high [S] at the head of the electroslag ingot, which is unqualified.

[0122] Comparative Examples 13-18

[0123] The main difference between Comparative Examples 13-18 and Example 5 is that the base material was not coated with aluminum powder. Specifically, the steps include:

[0124] (1) Mass percentage of S and Al in the parent material: S: 0.044%, Al: 0.054%.

[0125] (2) Perform full-surface shot blasting on the Ф400mm*2800mm base material, but do not apply aluminum powder to the surface of the base material.

[0126] (3) Directly install the base material and remelt the slag.

[0127] (4) Before electro-slag charging, purge argon gas through a rapid charging pipe for 10-15 minutes, then charge the slag, using 90 kg of binary slag per pipe. During the early stage of remelting, ensure a positive pressure ≥ 0.2 kPa inside the protective shield and continuously charge with argon gas for protection. Charge the electro-remelting gas for 85-90 minutes. When the ingot weight reaches 280 kg (the weight of the remelted ingot is 8-10% of the weight of the electroslag base material before remelting), the middle and late stages of remelting are entered. Turn off the protective gas (Ar) until the remelting is completed, and obtain a 42CrMoS steel electroslag ingot.

[0128] The six masterbatches from the same furnace in Comparative Examples 13-18 were remelted into ingots, and the relevant parameters are shown in Table 11 below:

[0129] Table 11

[0130]

[0131] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 12 below:

[0132] Table 12

[0133]

[0134]

[0135] As can be seen from Table 12 above, comparative examples 13-18 did not coat the base material with aluminum powder, resulting in a high [S] at the head of the electroslag ingot, which is unqualified.

[0136] Comparative Examples 19-24

[0137] The main difference between Comparative Examples 19-24 and Example 1 is that argon protection was not stopped during the later stages of remelting. Specifically, the steps included are as follows:

[0138] (1) Mass percentage of S and Al in the parent material: S: 0.045%, Al: 0.054%.

[0139] (2) The entire surface of the Ф400mm*2800mm base material is shot blasted, and aluminum powder is applied to some side surfaces of the base material (the coating area is about 100mm wide and 2500mm long).

[0140] (3) Directly install the base material and remelt the slag.

[0141] (4) Before electro-slag charging, argon gas is purged through a rapid charging pipe for 15 minutes, and then electricity is supplied to add slag. The binary slag is 90 kg / piece. In the early stage of remelting, the positive pressure inside the protective cover is kept ≥0.2 kPa and argon gas is continuously supplied for protection. Even when the ingot weight is 280 kg (the weight of the remelted ingot is 8-10% of the weight of the electroslag base material before remelting), the protective gas (Ar) is not turned off in the middle and late stages of remelting. The entire electro-remelting process is purged for more than 500 minutes until the remelting is completed, and 42CrMoS steel electroslag ingot is obtained.

[0142] The six masterbatches from the same furnace in Comparative Examples 19-24 were remelted into ingots, and the relevant parameters are shown in Table 13 below:

[0143] Table 13

[0144]

[0145] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 14 below:

[0146] Table 14

[0147]

[0148] As can be seen from Table 14 above, the remelting process of Comparative Examples 19-24 was protected by argon blowing throughout (argon was not stopped in the middle and late stages of remelting), which resulted in high [S] at the head of the electroslag ingot, which was unqualified, and the [Al] at the head was also too high.

[0149] Comparative examples 25-30

[0150] The main difference between Comparative Examples 25-30 and Example 1 is that argon protection was not used during remelting. Specifically, the steps included are as follows:

[0151] (1) Mass percentage of S and Al in the parent material: S: 0.045%, Al: 0.053%.

[0152] (2) The entire surface of the Ф400mm*2800mm base material is shot blasted, and aluminum powder is applied to some side surfaces of the base material (the coating area is about 100mm wide and 2500mm long).

[0153] (3) Directly install the base material and remelt the slag.

[0154] (4) No argon protection is used; slag is added directly by power supply, with 90 kg of binary slag per piece. 42CrMoS steel base material is remelted into electroslag ingots.

[0155] Six masterbatches from the same furnace were remelted into ingots according to comparative examples 25-30. The relevant parameters are shown in Table 15 below:

[0156] Table 15

[0157]

[0158]

[0159] (5) After the electroslag ingot cools, powder-steel chips are drilled at both ends (tail and head). The content of [S] is detected using a CS instrument, and the content of [Al] is detected using an ICP (inductively coupled plasma atomic emission spectrometer). The results are shown in Table 16 below:

[0160] Table 16

[0161]

[0162] As can be seen from Table 16 above, the comparative example 25-30 did not undergo argon protection during the early stage of remelting, resulting in low [S] at the tail end of the electroslag ingot, which is unqualified.

[0163] In summary, this invention controls the S and Al content of the base material, and after peeling or shot blasting the surface of the electroslag base material, coats a portion of the base material surface with aluminum powder, the amount of which accounts for 0.02-0.005% of the total weight of the base material. A commonly used binary slag system is used, and gas protection during remelting is controlled. This achieves reduced desulfurization at the arc-starting end (tail) of 42CrMoS type steel electroslag ingots, while increasing desulfurization at the feeding end (head). This ensures that the S content of free-cutting steel with a low S content (S: 0.010-0.035%) meets the "0.010-0.035%" requirement at the head, middle, and tail of the electroslag ingot after electroslag remelting.

[0164] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for electroslag remelting of sulfur-containing steel, characterized in that, include: First, select electroslag base material with controlled sulfur and aluminum content, perform surface treatment, and coat with aluminum powder; then remelt the electroslag base material with binary slag system and blow gas for protection to reduce desulfurization at the arc initiation end; when the electroslag base material remelts to the starting position of aluminum powder coating, stop the gas protection and increase deoxidation by surface aluminum powder to increase desulfurization at the feeding end until the remelting is completed, and obtain remelted sulfur-containing steel; The coating starts along the height of the electroslag substrate and continues to the end or near the end of the electroslag substrate. The method for determining the starting position of aluminum powder coating on the side surface of the electroslag substrate is as follows: starting from the starting end of the electroslag substrate, calculate the height position that accounts for 8-10% of the total weight of the substrate. No aluminum powder is applied between the starting end of the electroslag substrate and the starting position of coating. In the electroslag matrix, the sulfur content is 0.040% to 0.050% and the aluminum content is 0.040% to 0.060% by mass percentage of chemical composition. The amount of aluminum powder coated accounts for 0.02 to 0.05% of the total weight of the electroslag matrix.

2. The method as described in claim 1, characterized in that, The surface treatment is either peeling or shot blasting.

3. The method as described in claim 1, characterized in that, The area of ​​the aluminum powder coating accounts for less than 50% of the side surface area of ​​the electroslag matrix.

4. The method as described in claim 1, characterized in that, The binary slag system comprises, by mass percentage: CaF2: 68%–72%, Al2O3: 28%–32%.

5. The method as described in claim 1, characterized in that, Before remelting the electroslag base material, gas is first introduced into the remelting device for 10-15 minutes, and then electricity is supplied to add a binary slag system to start the remelting process.

6. The method as described in claim 1, characterized in that, Before a certain amount of electroslag base material is remelted, the remelting positive pressure is guaranteed to be ≥0.2 kPa; And / or, the gas is argon.

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