A process for improving the cleanliness of molten steel of 20crmnTi

Abstract

The present application belongs to the technical field of steel metallurgy, and particularly relates to a molten steel cleanliness improvement process for 20CrMnTi, which adopts carbon pre-deoxidization + carbon-containing chromium iron deoxidization alloying when the converter is tapped, and performs refining slag modification in the LF furnace, so that the oxidized chromium element is reduced and reenters the molten steel. Compared with the traditional Al deoxidization process, the process can greatly reduce the Al consumption, thereby reducing the generation amount of alumina inclusions, and further reducing the calcium wire feeding amount, and has good metallurgical effect.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically a process for improving the cleanliness of molten steel for 20CrMnTi. Background Technology

[0002] 20CrMnTi gear steel is a high-performance carburizing steel with high hardenability, high strength and toughness, especially high low-temperature impact toughness. It also has good machinability, minimal deformation during machining, and excellent fatigue resistance. After normalizing, it exhibits good machinability. It is used to manufacture important parts subjected to high speeds, medium or heavy loads, impacts, and friction, such as gears, gear rings, and gear shaft crosses. Currently, the main deoxidizer used in the smelting of gear steel both domestically and internationally is aluminum granules. The resulting deoxidation product, Al2O3 inclusions, has a high melting point and low deformability. These high-melting-point inclusions are difficult to deform and tend to accumulate at the nozzle during tundish casting, causing nozzle blockage, reducing nozzle life, and even affecting production. Furthermore, during subsequent rolling, the difficult-to-deform nature of Al2O3 inclusions can cause scratches on the steel matrix, and stress tends to concentrate around the inclusions, forming voids or cracks. This can lead to damage and fracture during use, reducing fatigue performance. Summary of the Invention

[0003] To address the problems existing in the prior art, the main objective of this invention is to propose a process for improving the cleanliness of molten steel for 20CrMnTi.

[0004] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0005] A process for improving the cleanliness of molten steel for 20CrMnTi involves carbon pre-deoxidation and carbon-containing ferrochrome deoxidation alloying during converter tapping, followed by refining slag modification during LF refining, which reduces the oxidized chromium element and allows it to re-enter the molten steel.

[0006] As a preferred embodiment of the steel cleanliness improvement process for 20CrMnTi according to the present invention, the smelting process includes the following steps:

[0007] S1. Oxygen determination at the end of converter smelting;

[0008] S2. Converter tapping;

[0009] S3. Carbon pre-deoxidation;

[0010] S4. Carbon-containing ferrochrome deoxidized and initially alloyed;

[0011] S5. Upgrading of refining slag;

[0012] S6.LF secondary alloying;

[0013] S7. Microcalcium treatment;

[0014] S8. Soft blow.

[0015] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S1, before tapping the steel from the converter, an oxygen analyzer is used to determine the oxygen content.

[0016] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S2, the tapping temperature is 1610~1650℃ and the tapping time is 3~4min.

[0017] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi as described in this invention, in step S3, during the tapping process, carbon powder is added to pre-deoxidize the molten steel. The carbon reacts with free oxygen in the molten steel to generate CO, which then leaves the molten steel system. The deoxidation products do not contaminate the molten steel. The amount of carbon powder added is 0.70–0.95 kg / t. 钢 Add the steel when the output reaches 1 / 4.

[0018] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S4, carbon-containing ferrochrome is added for deoxidation and alloying when the steel output reaches 1 / 2; when the carbon-containing ferrochrome is low-carbon ferrochrome, the amount of low-carbon ferrochrome added is 17.5~18.8kg / t. 钢 When the carbon-containing ferrochrome is either high-carbon or low-carbon, the amount of low-carbon ferrochrome added is 10–12 kg / t. 钢 The amount of high-carbon ferrochrome added is 4-5 kg / t 钢 Additionally, 0.3–0.5 kg / t of toner needs to be added. 钢 .

[0019] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S4, after deoxidation and alloying, a slagging agent is added through a silo. The slagging agent is selected as synthetic refining slag + lime; the amount of synthetic refining slag added is 5-6 kg / t. 钢 The amount of lime added is 2-3 kg / t 钢 The synthetic refining slag includes: CaO: 40-50 wt%, Al2O3: 30-45 wt%; CaO in lime ≥ 95 wt%; the basicity of the final refining slag at the end of LF smelting is 5-7, CaO: 50-60 wt%, SiO2: 9-13 wt%, Al2O3: 25-35 wt%, MgO: 3-5 wt%, ∑(FeO+MnO) ≤ 1 wt%.

[0020] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S5, after the ladle enters the LF refining process, a modifier is added to the ladle to reduce the oxidizing properties of the refining slag and create reducing white slag. The slag-forming modifier is selected as calcium carbide + silicon carbide + aluminum granules; wherein the amount of calcium carbide added is 0.95~1.2 kg / t. 钢 The amount of silicon carbide added is 0.6–0.85 kg / t. 钢 The addition amount of calcium carbide and silicon carbide is ≥1.8 kg / t 钢 Simultaneously, spread 0.23–0.35 kg / t of fertilizer onto the slag surface. 钢 Aluminum particles assist in rapid deoxidation and alloying of aluminum.

[0021] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S6, after the slag modification is completed in the LF refining process of the ladle, ferrosilicon and ferrotitanium are added through the feeding bin for secondary alloying.

[0022] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi as described in this invention, in step S7, after alloying, the composition meets the target requirements; considering that a high-basicity, high-alumina refining slag system is still used, to ensure the castability of the molten steel, the molten steel is subjected to micro-calcium treatment, with a calcium wire feed rate of 0.35~0.60m / t. 钢 .

[0023] As a preferred embodiment of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention, in step S8, after the calcium feeding line, the ladle is subjected to a soft blowing operation for at least 10 minutes before being hoisted to the continuous casting.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention proposes a process to improve the cleanliness of molten steel for 20CrMnTi. It employs a converter-based carbon pre-deoxidation followed by carbon-containing ferrochrome deoxidation and alloying, replacing the traditional Al deoxidation process. This reduces Al consumption and the amount of inclusions generated. Some of the chromium in the carbon-containing ferrochrome is oxidized during tapping; after entering the LF (sulfurized ferrochrome) reducing slag, the oxidized chromium is reduced and re-enters the molten steel. This method can produce high-cleanliness 20CrMnTi gear steel and reduces the amount of calcium added, saving costs and improving metallurgical efficiency. Attached Figure Description

[0026] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the process for improving the cleanliness of molten steel for 20CrMnTi according to the present invention.

[0028] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a process for improving the cleanliness of molten steel for 20CrMnTi (e.g. Figure 1 As shown, the method of pre-deoxidation of carbon steel produced from converter and deoxidation alloying with carbon-containing ferrochrome is used instead of Al deoxidation process. This not only reduces the consumption of deoxidation alloy, but also reduces the amount of calcium wire fed in and the generation of inclusions, resulting in good metallurgical effect.

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0032] Example 1

[0033] This embodiment describes a process for improving the cleanliness of molten steel for 20CrMnTi, using a 100t top-and-bottom blowing converter, and includes the following steps:

[0034] S1. Oxygen content determined at the end of converter smelting, with a value of 484 ppm.

[0035] S2. Converter tapping: After the oxygen fixation is completed, the converter rotates to begin tapping steel.

[0036] S3. Carbon pre-deoxidation: Add 65kg of carbon powder when the steel output is 1 / 4;

[0037] S4. Carbon-containing ferrochrome deoxidation and alloying: When the steel output is 1 / 2, add 1795 kg of low-carbon ferrochrome for deoxidation and alloying, then add 520 kg of synthetic refining slag (CaO: 45 wt%, Al2O3: 39 wt%) through the silo, and add 240 kg of lime.

[0038] S5. Refining slag modification: After the ladle enters the LF station, it is powered on to start smelting. 105 kg of calcium carbide and 75 kg of silicon carbide are added to the slag surface, and 26 kg of aluminum granules are spread on the slag surface at the same time.

[0039] S6.LF secondary alloying: After slag modification, 890 kg of silicon manganese and 86 kg of titanium ferroalloy are added for secondary alloying.

[0040] S7. Calcium treatment: After the alloy composition meets the requirements, in order to ensure the smooth casting of molten steel, a calcium wire of 45m is fed in.

[0041] S8. Soft blowing: After wire feeding, the ladle is transferred to the soft blowing area for 12 minutes. The inclusions in the molten steel after soft blowing are shown in Table 1, based on on-site sampling.

[0042] Table 1. Inclusions in molten steel after soft blowing.

[0043] type Al-O CaO Ca-Al-O Contains CaS <![CDATA[Quantity (pcs / (50mm 2 ))]]> 28 6 25 165 Average size (μm) 3.78 3.66 4.02 3.52

[0044] Example 2

[0045] This embodiment describes a process for improving the cleanliness of molten steel for 20CrMnTi, using a 100t top-and-bottom blowing converter, and includes the following steps:

[0046] S1. Oxygen level is determined at the end of converter smelting, with a value of 520 ppm.

[0047] S2. Converter tapping: After the oxygen fixation is completed, the converter rotates to begin tapping steel.

[0048] S3. Carbon pre-deoxidation: Add 75kg of carbon powder when the steel output reaches 1 / 4.

[0049] S4. Carbon-containing ferrochrome deoxidation and alloying: When the steel output is 1 / 2, add 1820 kg of low-carbon ferrochrome for deoxidation and alloying; then add 545 kg of synthetic refining slag (CaO: 45 wt%, Al2O3: 39 wt%) through the silo, and add 250 kg of lime.

[0050] S5. Refining slag modification: After the ladle enters the LF station, it is powered on to start smelting. 110 kg of calcium carbide and 75 kg of silicon carbide are added to the slag surface, and 25 kg of aluminum granules are spread on the slag surface at the same time.

[0051] S6.LF secondary alloying: After slag modification, 880 kg of silicon manganese and 80 kg of titanium ferrometallurgy are added for secondary alloying.

[0052] S7. Calcium treatment: After the alloy composition meets the requirements, in order to ensure the smooth casting of molten steel, 50m of calcium wire is fed in.

[0053] S8. Soft blowing: After wire feeding, the ladle is transferred to the soft blowing area for 13 minutes. The inclusions in the molten steel after soft blowing are shown in Table 1, based on on-site sampling.

[0054] Table 2. Inclusions in molten steel after soft blowing.

[0055] type Al-O CaO Ca-Al-O Contains CaS <![CDATA[Quantity (pieces / (50mm 2 ))]]> 35 6 28 174 Average size (μm) 3.74 3.76 4.04 3.48

[0056] Comparative Example 1

[0057] A smelting process for 20CrMnTi gear steel, using a 100t top-and-bottom blown converter, includes the following steps:

[0058] S1. Oxygen concentration, oxygen value 498ppm;

[0059] S2. After the oxygen fixation is completed, the converter rotates to begin tapping steel.

[0060] S3. Deoxidation and alloying: When the steel output reaches 1 / 3, add 100 kg of aluminum blocks and then add 1373 kg of low-carbon ferrochrome and 889 kg of silicon manganese sequentially through the alloy hopper.

[0061] S4. Slag making: After adding deoxidizer, add 395 kg of lime and 310 kg of synthetic refining slag (CaO: 45 wt%, Al2O3: 40 wt%) through the hopper. After tapping, the ladle car leaves the tapping position and enters the LF position.

[0062] S5. Slag modification: After the ladle enters the LF station, the power is turned on to start smelting. 95 kg of calcium carbide and 60 kg of silicon carbide are added to the slag surface.

[0063] S6. Alloy fine-tuning: After completing the modification of the refining slag, add 100 kg of low-carbon ferrochrome, 78 kg of silicon manganese and 80 kg of titanium ferrochrome to the molten steel through the alloy hopper to adjust the composition of the molten steel to the target range of the process card.

[0064] S7. Wire feeding: After alloying, in order to ensure the smooth casting of molten steel, 110m of calcium wire is fed in.

[0065] S8. Soft blowing: After wire feeding, the ladle is transferred to the soft blowing area for 10 minutes. Table 3 shows the inclusions in the molten steel after soft blowing, obtained from on-site sampling.

[0066] Table 3. Inclusions in molten steel after soft blowing.

[0067] type Al-O CaO Ca-Al-O Contains CaS <![CDATA[Quantity (pieces / (50mm 2 ))]]> 70 38 87 367 Average size (μm) 4.05 4.07 3.96 4.74

[0068] Comparative Example 2

[0069] A smelting process for 20CrMnTi gear steel, using a 100t top-and-bottom blown converter, includes the following steps:

[0070] S1. Oxygen concentration, oxygen value 533 ppm;

[0071] S2. After the oxygen fixation is completed, the converter rotates to begin tapping steel;

[0072] S3. Deoxidation and alloying: When the steel output reaches 1 / 3, add 100 kg of aluminum blocks and then add 1388 kg of low-carbon ferrochrome and 878 kg of silicon manganese through the alloy hopper.

[0073] S4. Slag making: After adding deoxidizer, add 400 kg of lime and 315 kg of synthetic refining slag (CaO: 44 wt%, Al2O3: 37 wt%) through the silo. After tapping, the steel truck leaves the tapping position and enters the LF station.

[0074] S5. Slag modification: After the ladle enters the LF station, the power is turned on to start smelting. 90 kg of calcium carbide and 65 kg of silicon carbide are added to the slag surface.

[0075] S6. Alloy fine-tuning: After completing the modification of the refining slag, add 105 kg of low-carbon ferrochrome, 85 kg of silicon manganese and 80 kg of titanium ferrochrome to the molten steel through the alloy hopper to adjust the composition of the molten steel to the target range of the process card.

[0076] S7. Wire feeding: After alloying, in order to ensure the smooth casting of molten steel, 110m of calcium wire is fed in.

[0077] S8. Soft blowing: After wire feeding, the ladle is transferred to the soft blowing area for 10 minutes. Table 4 shows the inclusions in the molten steel after soft blowing, obtained from on-site sampling.

[0078] Table 4. Inclusions in molten steel after soft blowing.

[0079] type Al-O CaO Ca-Al-O Contains CaS <![CDATA[Quantity (pieces / (50mm 2 ))]]> 71 35 86 603 Average size (μm) 4.08 4.06 3.98 4.86

[0080] As can be seen from the above embodiments and comparative examples, at the end of the 20CrMnTi converter smelting process, the oxygen content in the molten steel is still around 500ppm. Using the traditional Al deoxidation process, aluminum blocks are added to the molten steel during tapping (Comparative Examples 1-2). The combination of aluminum and oxygen forms a large amount of Al2O3 inclusions. Although the refining slag can adsorb and remove most of the alumina inclusions, some remain in the molten steel, affecting its castability. Currently, calcium treatment is commonly used to deform and treat Al2O3 inclusions, but excessive calcium treatment affects the cleanliness of the molten steel. Excessive calcium combines with sulfur in the molten steel to generate excessive CaS-type inclusions, especially for 20CrMnTi gear steel, where CaS-type inclusions are difficult to control. This invention uses a converter tapping carbon pre-deoxidation + carbon-containing ferrochrome deoxidation alloying method to replace the traditional Al deoxidation process. This significantly reduces the amount of Al2O3 inclusions and also greatly reduces the amount of calcium wire used to modify the Al2O3 inclusions. This invention enables the production of high-purity 20CrMnTi gear steel while reducing the consumption of aluminum blocks and calcium wire, thereby lowering production costs and improving enterprise efficiency.

[0081] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A process for improving the cleanliness of molten steel for 20CrMnTi, characterized in that, Carbon pre-deoxidation + carbon-containing ferrochrome deoxidation alloying is carried out during the converter tapping process to replace the traditional Al deoxidation process. The refining slag is modified in LF refining so that the oxidized chromium element is reduced and re-enters the molten steel. The process includes the following steps: S1. Oxygen determination at the end of converter smelting; S2. Converter tapping; S3. Carbon pre-deoxidation: During the tapping process, carbon powder is added to pre-deoxidize the molten steel. The addition begins when 1 / 4 of the steel has been tapped. S4. Deoxidation and initial alloying of carbon-containing ferrochrome; when the steel output reaches 1 / 2, carbon-containing ferrochrome is added for deoxidation and alloying. S5. Refining slag modification: After the ladle enters the LF refining process, a modifier is added to the ladle to reduce the oxidizing properties of the refining slag and create reducing white slag. The modifier is selected as calcium carbide + silicon carbide + aluminum granules. S6.LF secondary alloying; S7. Micro-calcium treatment; Micro-calcium treatment is applied to the molten steel, with a calcium wire feed rate of 0.35~0.6 m / t. 钢 ; S8. Soft blow.

2. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S2, the tapping temperature is 1610~1650℃ and the tapping time is 3~4 minutes.

3. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S3, the amount of toner added is 0.70~0.95 kg / t. 钢。 4. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S4, when the carbon-containing ferrochrome is low-carbon ferrochrome, the amount of low-carbon ferrochrome added is 17.5~18.8 kg / t. 钢 When the carbon-containing ferrochrome is high-carbon ferrochrome or low-carbon ferrochrome, the amount of low-carbon ferrochrome added is 10~12 kg / t. 钢 The amount of high-carbon ferrochrome added is 4~5 kg / t 钢 Additionally, 0.3~0.5 kg / t of toner needs to be added. 钢 .

5. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S4, after deoxidation and alloying, a slag-forming agent is added through the silo. The slag-forming agent is selected as a mixture of synthetic refining slag and lime, and the amount of synthetic refining slag added is 5-6 kg / t. 钢 The amount of lime added is 2-3 kg / t 钢 .

6. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S5, the amount of calcium carbide added is 0.95~1.2 kg / t. 钢 The silicon carbide addition amount is 0.6~0.85 kg / t 钢 The amount of calcium carbide and silicon carbide added is ≥1.8 kg / t 钢 Simultaneously, spread 0.23~0.35 kg / t of fertilizer onto the slag surface. 钢 Aluminum granules.

7. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S6, after the refining slag is used to make reducing white slag, ferrosilicon and ferrotitanium are added through the alloy silo for secondary alloying.

8. The process for improving the cleanliness of molten steel for 20CrMnTi according to claim 1, characterized in that, In step S8, after the calcium feed line is fed, the ladle undergoes a soft blowing operation for at least 10 minutes before being hoisted to the continuous casting station.

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