A method for controlling large inclusions in low alloy steel containing titanium under semi-steel smelting conditions

Abstract

The present application relates to semi-steel smelting technical field, specifically relates to a kind of based on semi-steel smelting condition under the method for controlling large-scale inclusion of titanium-containing low alloy steel, in converter process converter end point oxygen control is 320~480ppm ppm, using 80 aluminum iron deoxidation, 80 aluminum iron deoxidation ton steel addition amount is calculated according to formula:;Wherein is the oxygen activity of liquid steel;Then again carry out tapping process, refining process and continuous casting process.

Description

Technical Field

[0001] This invention relates to the field of semi-steel smelting technology, and specifically to a method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions. Background Technology

[0002] Semi-steel smelting is a unique steelmaking process in Southwest and North my country. Its raw material is semi-steel after vanadium extraction, which has the characteristics of low carbon content, extremely low silicon and manganese content, and strong oxidizing properties. When smelting titanium-containing low alloy steel, the amount of endogenous inclusions generated is much higher than in the hot metal smelting process. Moreover, the inclusions are large in size and unevenly distributed, which seriously affects the mechanical properties and processing performance of the steel.

[0003] The current status of titanium-containing low-alloy steel smelting in a 130-ton converter semi-steel mill at a certain factory: Process flow: Vanadium-extracting semi-steel → Pretreatment desulfurization → Converter → LF refining → Continuous casting Inclusion problem: Large inclusions are frequently found. The proportion of non-metallic inclusions rated ≥2.0 is 6%, mainly of type B (alumina inclusions) and type Ds (single-particle spherical inclusions). The overall pass rate of grades A, B, C, D, and Ds ≤1.0 is only 74%, which seriously restricts product quality and the development of high-quality steel.

[0004] The main reason is that the semi-steel has high oxygen and nitrogen content, high temperature and low viscosity, deoxidation imbalance, and severe slag entrapment, which makes it easy for Ti to form large TiO₂. x / TiN composite inclusions are aggregated and difficult to arrange.

[0005] In the later stages of converter blowing, the molten steel is characterized by low carbon, high oxygen, high temperature, and vigorous slag-steel reaction (C≈0.05%~0.15%, [O] high). Large inclusions in titanium-containing steel are mainly TiO2–Al2O3–SiO2 system oxides, TiN, TiC, and composite inclusions, with sizes often >50μm, and even reaching hundreds of micrometers. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions, thereby solving the technical problem of high probability of large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions in the prior art.

[0007] This invention discloses a method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions. At the converter stage, the oxygen content at the converter endpoint is controlled to 320–480 ppm. 80% aluminum-iron deoxidation is used, and the amount of 80% aluminum-iron deoxidizer added per ton of steel is calculated using the following formula: ; in Oxygen activity in molten steel; Then the steelmaking process, refining process, and continuous casting process are carried out.

[0008] Existing technologies use a fixed amount of aluminum and iron per ton of steel, which cannot dynamically change with the oxygen content at the end point. This invention has an original calculation model that correlates with oxygen activity, allowing for precise addition of deoxidizer as needed. This balances the oxygen potential of the molten steel from the deoxidation source, significantly reducing Al2O3 inclusions.

[0009] Furthermore, the specific steps of the steel tapping process are as follows: when the steel is tapped to 2 / 3 full, 4.5-5.5 kg / t steel of 25-45 mm fine lime is added, and slag-reducing agent is added at 22% of the lime mass.

[0010] Furthermore, the slag-forming agent used in the steel tapping process comprises: CaO≤14%, P≤0.18%, S≤0.18%, Al2O3:46~58%, Na2O:7±1.5%, MgO≤9%, FeO≤2.8%, SiO2≤7.5%, N≤0.45%, Cl≤0.45%, and H2O≤1.8%.

[0011] The slag-forming agent formula focuses on strictly controlling five types of impurities, which distinguishes it from general desulfurization slag-forming agents and blocks the precipitation of large titanium-based composite inclusions from the source of slag formation.

[0012] Furthermore, after all the steel tapping processes are completed, CaC2 is evenly spread on the surface of the slag in the ladle at an addition rate of 1.2–1.8 kg / t steel, without the agent penetrating into the molten steel.

[0013] By adding CaC2 after all the steel tapping processes are completed and before the LF furnace is powered on and heated, the function is to reduce the FeO and MnO in the slag system, reduce the oxidizability of the slag, and avoid the secondary oxidation of titanium at the steel-slag interface during the refining stage to generate TiO2 and TiN clusters. This is completely different from the existing calcium carbide desulfurization process in molten steel in terms of mechanism and application.

[0014] Furthermore, the refining process specifically involves adding 3.5–4.5 kg / t of lime and 1.2–1.8 kg / t of 75 ferrosilicon during the LF heating stage to stabilize the alkalinity of the refining slag. After the alloying is completed, the composite titanium wire made of low-carbon steel sheet is wrapped and then titanium alloyed. Before titanium alloying, supplement with aluminum wire, and strictly control the interval between aluminum and titanium alloying to be 5.5 to 6.5 minutes.

[0015] This promotes the full removal of aluminum inclusions generated during aluminum wire feeding, thus preventing the formation of large amounts of titanium-aluminum composite inclusions.

[0016] The coated titanium wire delays the instantaneous oxidation of titanium; the narrow time sequence of 5.5 to 6.5 minutes is a parameter specific to semi-steel high oxygen, ensuring that the deoxidation products in the early stage are fully floated before adding titanium, thus inhibiting the formation of titanium aluminum spinel.

[0017] Furthermore, after the titanium alloying is completed in the refining process, the titanium alloy is modified in steps: first, the angular hard titanium inclusions are broken down, then the inclusions are spheroidized and refined, and finally the inclusions are promoted to float.

[0018] Furthermore, the specific method for breaking up angular hard titanium inclusions involves first feeding 0.35–0.45 kg / t of iron-calcium wire into steel, followed by soft blowing for 3.5–4.5 minutes to break up the angular hard titanium inclusions.

[0019] Furthermore, the spheroidizing and refining of inclusions specifically involves feeding 0.06–0.10 kg / t of steel with high-purity cerium-rich rare earth wire containing ≥60% Ce, followed by soft blowing for 9–11 minutes to spheroidize and refine the inclusions.

[0020] Furthermore, by mass ratio, the total rare earth element RE of the high-purity cerium-rich rare earth wire is ≥98.5, of which Ce: 58~62, La: 35~40, Pr: 0.5~1.2, Nd: 0.5~1.2, and the remainder is impurities.

[0021] Furthermore, the specific steps for promoting inclusion flotation are as follows: after all modification is completed, the molten steel is allowed to stand for 18-22 minutes to promote inclusion flotation.

[0022] The unique design abandons the combination of mixed rare earth elements and the sequence of first calcium short blowing followed by cerium-rich long blowing, thus eliminating the inclusion of large particles of high-melting-point rare earth titanates.

[0023] Furthermore, the continuous casting process specifically includes: during the initial casting stage, the liquid level in the tundish is ≥ 52% of the total volume of the tundish; during steady-state casting, the liquid level in the tundish is ≥ 82% of the total volume; the casting speed is 1.25~1.35m / min, and the casting speed fluctuation per minute is ≤ ±1.8%.

[0024] Furthermore, by mass ratio, the titanium-containing low-alloy steel contains 0.06-0.12% carbon, ≤1.2% manganese, and 0.05-0.08% titanium.

[0025] Compared with the prior art, the beneficial effects of the present invention are: 1. Existing technologies use a fixed amount of aluminum and iron per ton of steel, which cannot dynamically change with the oxygen content at the end point; This invention has an original calculation model that correlates with oxygen activity, which accurately adds deoxidizer as needed, balances the oxygen potential of the molten steel from the deoxidation source, and significantly reduces Al2O3 inclusions. 2. The slag-forming agent formula of this invention focuses on strictly controlling five types of impurities, which distinguishes it from general desulfurization slag-forming agents and blocks the precipitation of large titanium-based composite inclusions from the source of slag formation; 3. By adding CaC2 after the steel tapping process is completed and before the LF furnace is powered on and heated, the function is to reduce FeO and MnO in the slag system, reduce the oxidizing properties of the slag, and avoid the secondary oxidation of titanium at the steel-slag interface during the refining stage to generate TiO2 and TiN clusters. This is completely different from the existing calcium carbide desulfurization process in molten steel in terms of mechanism and application. 4. Coated titanium wire delays the instantaneous oxidation of titanium; the narrow time sequence of 5.5 to 6.5 minutes is a parameter specific to semi-steel high oxygen, ensuring that the deoxidation products in the early stage are fully floated before adding titanium, thus inhibiting the formation of titanium aluminum spinel; 5. The unique design abandons the combination of mixed rare earth elements and first calcium short blowing followed by cerium-rich long blowing, thus eliminating the inclusion of large particles of high-melting-point rare earth titanates. 6. The occurrence rate of refractory inclusions and slag inclusions in this invention is ≤1%, while the original proportion in the prior art is about 5.7%. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] The composition of the semi-steel (raw material) used in the examples is as follows: Semi-steel (raw material) composition: 3.51% C, 0.040% Mn, 0.063% P, 0.007% S, 0.03% V and trace amounts of Cr, Si and Ti, with the balance being iron and unavoidable impurities.

[0028] Example 1 This embodiment discloses a method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions, including the following steps: 1. Converter process The oxygen content at the converter endpoint is controlled at 400 ppm, and 80% aluminum-iron deoxidation is used, with an addition rate of 1.29 kg / t per ton of steel.

[0029]

[0030] =(1.15*400+260) / (810*(0.91-0.00055*400) =1.29 2. Steel tapping process When the steel is tapped to 2 / 3 full, add 5.0 kg / t of fine lime and simultaneously add 1.10 kg / t of slag-reducing agent for semi-steel. Slag-reducing agent composition: CaO≤14%, P≤0.18%, S≤0.18%, Al2O3:46~58%, Na2O:7±1.5%, MgO≤9%, FeO≤2.8%, SiO2≤7.5%, N≤0.45%, Cl≤0.45%, H2O≤1.8%.

[0031] After tapping, 1.5 kg / t of calcium carbide (CaC2) is added to the slag surface.

[0032] 3. Refining process During the heating process, 4.0 kg / t of lime and 1.5 kg / t of 75% ferrosilicon are added. After the alloy composition was adjusted to the appropriate level, titanium alloying was carried out using sponge titanium cored wire; The interval between titanium alloying and aluminum supplementation is 6.0 min; After titanium alloying, feed iron-calcium wire at a rate of 0.40 kg / t and gently blow it for 4 min. Then feed 0.08 kg / t of cerium-rich rare earth wire and blow it softly for 10 minutes; The total rare earth element (RE) content of the high-purity cerium-rich rare earth wire is ≥98.5%, of which Ce: 58~62, La: 35~40, Pr: 0.5~1.2, Nd: 0.5~1.2, and the remainder is impurities. The molten steel is allowed to stand for 20 minutes before being sent to continuous casting.

[0033] 4. Continuous casting process The initial pouring level in the tundish is 55% of the capacity, and the process pouring level is ≥87% of the capacity. The casting speed was 1.30 m / min, and there was no change throughout the furnace.

[0034] Results: No large inclusions larger than 20μm, and the overall pass rate for all types of inclusions with a rating of ≤1.0 is 96%.

[0035] Example 2: 1. Converter process The oxygen content at the converter endpoint is controlled at 480 ppm, and 80% aluminum-iron deoxidation is used with an addition rate of 1.55 kg / t per ton of steel.

[0036]

[0037] =(1.15*480+260) / (810*(0.91-0.00055*480) =1.55 2. Steel tapping process When the steel is tapped to 2 / 3 full, add 5.5 kg / t of fine lime and simultaneously add 1.21 kg / t of slag-reducing agent for semi-steel. Slag-reducing agent composition: CaO≤14%, P≤0.18%, S≤0.18%, Al2O3:46~58%, Na2O:7±1.5%, MgO≤9%, FeO≤2.8%, SiO2≤7.5%, N≤0.45%, Cl≤0.45%, H2O≤1.8%.

[0038] After tapping, 1.8 kg / t of calcium carbide (CaC2) is added to the slag surface.

[0039] 3. Refining process During the heating process, 4.5 kg / t of lime and 1.8 kg / t of 75% ferrosilicon are added. After the alloy composition is adjusted to the appropriate level, titanium alloying is carried out. The interval between titanium alloying and aluminum supplementation is 6.5 min; After titanium alloying, feed iron-calcium wire at a rate of 0.45 kg / t and gently blow it for 4.5 min. Then feed 0.10 kg / t of cerium-rich rare earth wire and blow it softly for 11 min; The total rare earth element (RE) content of the high-purity cerium-rich rare earth wire is ≥98.5%, of which Ce: 58~62, La: 35~40, Pr: 0.5~1.2, Nd: 0.5~1.2, and the remainder is impurities. The molten steel was allowed to stand for 22 minutes before being sent to continuous casting.

[0040] 4. Continuous casting process The initial pouring level in the tundish is 62.3% of the capacity, and the process pouring level is ≥83% of the capacity. The pulling speed is 1.25 m / min, and the pulling speed fluctuation is ≤±1.7%.

[0041] Results: No large inclusions larger than 20μm, and the overall pass rate of various inclusions rated ≤1.0 is 95%.

[0042] Example 3: 1. Converter process The oxygen concentration at the converter endpoint is controlled at 320 ppm. 80% aluminum ferrode oxidation is used, with an addition rate of 1.06 kg / t per ton of steel.

[0043]

[0044] =(1.15*480+260) / (810*(0.91-0.00055*480) =1.06 2. Steel tapping process When the steel is tapped to 2 / 3 full, add 4.5 kg / t of fine lime and simultaneously add 0.99 kg / t of slag-reducing agent for semi-steel. Slag-reducing agent composition: CaO≤14%, P≤0.18%, S≤0.18%, Al2O3:46~58%, Na2O:7±1.5%, MgO≤9%, FeO≤2.8%, SiO2≤7.5%, N≤0.45%, Cl≤0.45%, H2O≤1.8%.

[0045] After tapping, 1.2 kg / t of calcium carbide (CaC2) is added to the slag surface.

[0046] 3. Refining process During the heating process, 3.5 kg / t of lime and 1.2 kg / t of 75% ferrosilicon are added. After the alloy composition is adjusted to the appropriate level, titanium alloying is carried out. The interval between titanium alloying and aluminum supplementation is 5.5 min; After titanium alloying, feed 0.35 kg / t of iron-calcium wire and blow it softly for 3.5 min; Then feed 0.06 kg / t of cerium-rich rare earth wire and blow it softly for 9 minutes; The total rare earth element (RE) content of the high-purity cerium-rich rare earth wire is ≥98.5%, of which Ce: 58~62, La: 35~40, Pr: 0.5~1.2, Nd: 0.5~1.2, and the remainder is impurities. The molten steel was allowed to stand for 18 minutes before being sent to continuous casting.

[0047] 4. Continuous casting process The initial pouring level in the tundish is 72% of the capacity, and the process pouring level is ≥ 82% of the capacity. The pulling speed was 1.35 m / min, with no fluctuations in pulling speed.

[0048] Results: No large inclusions larger than 20μm, and the overall pass rate for all types of inclusions with a rating of ≤1.0 is 97%.

[0049] Comparative Example 1 The only change from Example 1 is that the oxygen content was changed from 480 ppm to 640 ppm, while the rest remained unchanged.

[0050] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions with a rating of ≤1.0 was 88%.

[0051] Comparative Example 2 The only change from Example 1 is that aluminum is added in a fixed amount, at a rate of 1.72 kg / t of steel; all other aspects remain unchanged.

[0052] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions with a rating of ≤1.0 was 92%.

[0053] Comparative Example 3 The only change from Example 1 is that no slag remover or calcium carbide was added; everything else remains the same.

[0054] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions with a rating of ≤1.0 was 87%.

[0055] Comparative Example 4 The only changes made to Example 1 were that the aluminum-titanium interval time (1.7 min) was not strictly controlled, and titanium cored wire was not used; titanium iron was used directly instead. All other changes remained the same.

[0056] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions rated ≤1.0 was 83%.

[0057] Comparative Example 5 The only change from Example 1 was that only calcium wire was fed, and no rare earth treatment was performed; everything else remained the same.

[0058] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions with a rating of ≤1.0 was 92%.

[0059] Comparative Example 6 The only change from Example 1 is that after feeding calcium wire, composite rare earth wire is used for rare earth treatment (RE(La+Ce+Pr+Nd)≥98.5, La: 43~48, Ce: 50~55, Pr: 0.5~1.5, Nd: 0.5~1.5, the rest are impurities), and the rest remain unchanged.

[0060] Cerium-rich and composite rare earth elements have the following advantages over semi-steel smelting of titanium-containing high-strength steel: 1. Stronger deoxidation and desulfurization capabilities The semi-steel final product exhibits high oxygen and residual sulfur content, with Ce showing a significantly higher affinity for O and S than La. At the same addition amount, cerium-rich rare earth elements can further reduce free oxygen and active sulfur in the molten steel, decreasing the need for TiO2 during subsequent titanium alloying. x The explosive generation of endogenous hybrids reduces the base number of large hybrid nuclei from the source.

[0061] 2. Superior resistance to slag entrapment and foreign inclusions. Semi-steel tapping is prone to slag entrapment, and refractory corrosion introduces oxide inclusions. Ce preferentially reacts with the slag phase, external Al2O3, and SiO2, preferentially encapsulating external inclusion particles and inhibiting their role as core adsorption sites for TiO2. x TiN grows into large-scale composite inclusions Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions rated ≤1.0 was 86%.

[0062] Comparative Example 7 The only change from Example 1 is the removal of process liquid level control (38%), while the rest remain unchanged.

[0063] Results: Large inclusions larger than 20μm were found, and the overall pass rate for all types of inclusions with a rating of ≤1.0 was 93%.

[0064] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions, characterized in that: In the converter process, the oxygen content at the converter endpoint is controlled at 320–480 ppm. 80% aluminum-iron deoxidation is used, and the amount of 80% aluminum-iron deoxidizer added per ton of steel is calculated using the following formula: ； in Oxygen activity in molten steel; Then the steelmaking process, refining process, and continuous casting process are carried out.

2. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 1, characterized in that: The specific steps of the steel tapping process are as follows: when the steel is tapped to 2 / 3, 4.5-5.5 kg / t steel of 25-45 mm fine lime is added, and slag-dissolving agent is added at 22% of the lime mass.

3. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 2, characterized in that: The slag-forming agent used in the steel tapping process has the following composition: CaO≤14%, P≤0.18%, S≤0.18%, Al2O3:46~58%, Na2O:7±1.5%, MgO≤9%, FeO≤2.8%, SiO2≤7.5%, N≤0.45%, Cl≤0.45%, H2O≤1.8%.

4. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 1, characterized in that: After all the steel tapping processes are completed, CaC2 is evenly spread on the surface of the slag in the ladle at an addition rate of 1.2–1.8 kg / t steel, without the agent penetrating into the molten steel.

5. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 1, characterized in that: The refining process specifically involves adding 3.5–4.5 kg / t of lime and 1.2–1.8 kg / t of 75 ferrosilicon during the LF heating stage to stabilize the alkalinity of the refining slag. After the alloying process is completed, the composite titanium wire made of low-carbon steel sheet is coated and then titanium alloyed.

6. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 1, characterized in that: In the refining process, after titanium alloying is completed, step-by-step modification is carried out: first, the angular hard titanium inclusions are broken, then the inclusions are spheroidized and refined, and finally the inclusions are promoted to float.

7. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 6, characterized in that: Specifically, the angular hard titanium inclusions are broken by first feeding 0.35-0.45 kg / t of iron-calcium wire into steel and then soft blowing for 3.5-4.5 min.

8. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 6, characterized in that: The spheroidizing and refining of inclusions specifically involves feeding 0.06–0.10 kg / t of steel with high-purity cerium-rich rare earth wire (Ce ≥ 60%) and then gently blowing it for 9–11 minutes to spheroidize and refine the inclusions.

9. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 6, characterized in that: The specific steps for promoting inclusion flotation are as follows: after all modification is completed, the molten steel is allowed to stand for 18-22 minutes to promote inclusion flotation.

10. The method for controlling large inclusions in titanium-containing low-alloy steel under semi-steel smelting conditions according to claim 1, characterized in that: The continuous casting process is as follows: during the initial casting stage, the liquid level in the tundish is ≥ 52% of the total volume of the tundish; during steady-state casting, the liquid level in the tundish is ≥ 82% of the total volume; the casting speed is 1.25~1.35m / min, and the casting speed fluctuation per minute is ≤ ±1.8%.

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