Method for directly producing high-carbon vanadium-chromium-molybdenum die steel in short process

Abstract

The application discloses a kind of short process direct production high carbon vanadium-containing chromium molybdenum die steel method, comprising the following steps: S10, vanadium titanium magnetite concentrate is made into pellet after balling and roasting to obtain pellet;S20, using gas-based shaft furnace pre-reducing pellet to obtain metallized pellet;S30, metallized pellet and carbonaceous reducing agent are added into melting separation electric furnace to carry out deep reduction and obtain vanadium-containing molten iron;S40, vanadium-containing molten iron is added into steelmaking electric furnace, whether to add chromium alloy is determined according to the chromium content in tapping composition, after adding electric furnace slag, the temperature of molten steel is raised to greater than threshold temperature and not less than 1673K, molten steel is oxygen blown decarburization to target content, dissolved oxygen [O] content in molten steel is detected after oxygen determination, according to the content of dissolved oxygen [O], reducing agent is added to carry out deoxidation, according to the content of tapping composition, metal molybdenum and / or vanadium alloy is added, and molten steel is tapped after metal is fully melted;S50, high carbon vanadium-containing chromium molybdenum die steel is obtained by pouring and forming molten steel.

Description

Technical Field

[0001] This invention relates to the field of vanadium-titanium magnetite smelting, and more particularly to a short-process method for directly producing high-carbon vanadium-chromium-molybdenum mold steel. Background Technology

[0002] Vanadium-titanium magnetite is a composite iron ore mainly composed of iron, titanium, and vanadium, possessing very high comprehensive utilization value. As an important iron ore resource in my country, the non-blast furnace smelting of vanadium-titanium magnetite is increasingly attracting attention.

[0003] Existing long-process smelting method for vanadium-titanium magnetite (e.g.) Picture 1 As shown, vanadium-titanium magnetite concentrate (or high-chromium vanadium-titanium magnetite concentrate) and ordinary iron ore concentrate are mixed. The mixed material is processed into vanadium-titanium sinter and vanadium-titanium pellets by a sintering machine and a pelletizing machine, respectively. Then, it is smelted in a blast furnace and deeply reduced in a melting electric furnace to obtain vanadium-containing molten iron. The vanadium-containing molten iron (or vanadium-chromium-containing molten iron) is first blown in a vanadium-refining converter to obtain vanadium slag (or vanadium-chromium slag) and semi-steel. The vanadium slag (or vanadium-chromium slag) is then subjected to vanadium extraction and alloying processes to obtain vanadium-containing (vanadium-chromium-containing) alloys. The semi-steel is processed in a steelmaking converter to obtain molten steel or cast iron. Finally, the obtained molten steel or cast iron is added to a steelmaking electric furnace, and vanadium-containing (or vanadium-chromium-containing) alloys are added according to the composition requirements of the mold steel for smelting, ultimately obtaining high-carbon vanadium-chromium-molybdenum mold steel.

[0004] However, the aforementioned long blast furnace-converter smelting process involves numerous steps: vanadium-containing molten iron is processed in a vanadium-refining converter to obtain vanadium slag (or vanadium-chromium slag); this vanadium slag (or vanadium-chromium slag) then undergoes vanadium extraction and alloying processes to obtain vanadium-containing alloys and chromium-containing alloys; finally, these vanadium-containing alloys or chromium-containing alloys are added to an electric arc furnace for smelting with the molten steel. During this smelting process, valuable elements such as vanadium and chromium are significantly lost, resulting in low recovery rates. Furthermore, the large amount of vanadium or chromium alloys added during the electric arc furnace smelting process greatly increases the production cost of mold steel. Furthermore, if the blast furnace-converter long-process smelting process uses 100% vanadium-titanium magnetite or 100% high-chromium vanadium-titanium magnetite in the furnace, it will result in high TiO2 content in the blast furnace slag, excessive titanium carbonitride, poor blast furnace permeability, and difficulty in separating slag and iron, making normal smelting impossible. The inability of the blast furnace-converter long-process smelting process to smelt 100% vanadium-titanium magnetite or 100% high-chromium vanadium-titanium magnetite in the furnace will also reduce the utilization rate of vanadium-titanium magnetite and reduce the V content in vanadium-containing molten iron or the V and Cr content in vanadium-chromium molten iron.

[0005] Therefore, existing technologies still need improvement. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a short-process method for directly producing high-carbon vanadium-chromium-molybdenum mold steel. This method can solve at least one of the technical problems of severe loss and low recovery rate of valuable elements such as vanadium and chromium during the existing long-process blast furnace-converter smelting of mold steel, and high production costs due to the large amount of vanadium or chromium alloys added during the electric arc furnace smelting process.

[0007] This invention discloses a method for directly producing high-carbon vanadium-chromium-molybdenum mold steel using a short process, comprising the following steps:

[0008] S10. Vanadium-titanium magnetite concentrate is pelletized, roasted and then used to obtain pellet ore;

[0009] S20. The ore pellets are pre-reduced using a gas-based vertical shaft furnace to obtain metallized pellets;

[0010] S30. The metallized pellets and carbonaceous reducing agent are added to the melting and separation electric furnace for deep reduction. After slag and iron separation, vanadium-containing molten iron is obtained. Inert gas or reducing gas is introduced during the deep reduction process.

[0011] S40. The vanadium-containing molten iron is added to the steelmaking electric furnace. Whether to add chromium alloy is determined according to the chromium content requirement in the steel composition. After adding the electric furnace slag, the slag is formed and the temperature of the molten steel rises to a temperature greater than the threshold temperature and not lower than 1673K. The molten steel is decarburized by blowing oxygen to the target content. After oxygen determination, the dissolved oxygen [O] content in the molten steel is detected. A reducing agent is added according to the dissolved oxygen [O] content for deoxidation. Molybdenum metal and / or vanadium alloy are added according to the steel composition requirements. The steel is tapped after the metal is fully melted.

[0012] S50. The molten steel is poured into molds to obtain the high-carbon vanadium-chromium-molybdenum mold steel.

[0013] According to one embodiment of the present invention, the method further includes: in step S10, adding a calcium flux to the vanadium-titanium magnetite concentrate and then pelletizing and roasting it to obtain an alkaline pellet, wherein the alkalinity of the alkaline pellet is in the range of 0.3 to 0.6, and the calcium flux is any one of quicklime, limestone or hydrated lime;

[0014] Alternatively, in step S10, the vanadium-titanium magnetite concentrate is pelletized and roasted to obtain pellets with natural basicity. In step S30, a calcium flux is added to the melting furnace to control the slag basicity to be 0.3 to 0.6. The calcium flux is any one of quicklime, limestone, or hydrated lime.

[0015] According to one embodiment of the present invention, in step S10, the roasting preheating temperature is 850℃~950℃, the roasting preheating time is 10min~20min, the roasting temperature is 1200℃~1300℃, the roasting time is 15min~25min, and the average compressive strength of the obtained pellet is 2000~2600N.

[0016] According to one embodiment of the present invention, in step S20, the reducing gas used for pre-reduction includes H2, CO, impurity N2 and / or CO2, wherein the volume fraction of each gas in the reducing gas satisfies: H2 / CO≥6, H2+CO≥90%, CO2<5% and / or N2<5%.

[0017] According to one embodiment of the present invention, in step S20, the reduction temperature is 1000-1100°C, the reduction time is 2-4 hours, and the metallization rate of the pre-reduced metallized pellets is controlled to be 85%-95%.

[0018] According to one embodiment of the present invention, in step S30, the carbonaceous reducing agent is one or more of coking coal, coal or activated carbon, the total fixed carbon content of the carbonaceous reducing agent is ≥80%, and the mass of the carbonaceous reducing agent is 2 to 5% of the mass of the metallized pellets.

[0019] According to one embodiment of the present invention, in step S30, the temperature of the melting furnace is controlled to be 1500-1600°C, and the inert gas is argon or the reducing gas is any one or two of CO and H2.

[0020] According to one embodiment of the present invention, in step S30, the mass percentages of each component in the vanadium-containing molten iron are: C: 0.5-2.5%, V: 0.3-0.6%, Cr: 0-1.0%, Si: 0.1-0.5%, Ti: 0.1-0.3%, S: 0.005-0.05%, P: 0.005-0.03%.

[0021] According to one embodiment of the present invention, in step S40, the mass ratio of the electric furnace slag to the vanadium-containing molten iron is 0.1 to 0.3, the electric furnace slag is composed of limestone and fluorite, wherein the mass ratio of limestone to fluorite is 2.6:1 to 3:1; the threshold temperature is calculated using the following formula:

[0022]

[0023] Wherein, [Cr] and [C] are the values ​​before the percentage sign for the chromium content w[Cr]% and carbon content w[C]% in the steel composition, respectively.

[0024] According to one embodiment of the present invention, the mass percentage of some components in the high-carbon vanadium-chromium-molybdenum mold steel is: C: 0.6% to 2.0%, V ≥ 0.3%, Cr ≥ 0.5%.

[0025] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0026] This invention provides a short-process method for directly producing high-carbon vanadium-chromium-molybdenum mold steel. The method uses a gas-based vertical shaft furnace to reduce metallized pellets, which are then subjected to a deep reduction process in a melting electric furnace to obtain vanadium-containing molten iron. This vanadium-containing molten iron is directly fed into a steelmaking electric furnace. Appropriate amounts of chromium alloy, metallic molybdenum, and vanadium alloy are added according to the required steel composition, ultimately yielding high-carbon vanadium-chromium-molybdenum mold steel. The vanadium-containing molten iron obtained by this method has high vanadium and chromium content, low carbon and sulfur content, and a high molten iron temperature, meeting the requirements for direct feeding into a steelmaking electric furnace for smelting high-carbon vanadium-chromium-molybdenum mold steel. Furthermore, the method provided by this invention effectively avoids severe losses of vanadium and chromium during smelting, significantly improving the recovery rate of vanadium and chromium, and greatly reducing the amount of vanadium or chromium alloy used in the smelting process, thus helping to reduce the production cost of mold steel.

[0027] Furthermore, by using vanadium-titanium magnetite with a 100% furnace feed ratio, this invention significantly improves the utilization rate of vanadium-titanium magnetite and increases the V content (or V and Cr content in vanadium-chromium ferrometallurgical water). The method provided by this invention for preparing vanadium-titanium pellets eliminates the high costs and pollution associated with sintering processes. By using a gas-based vertical shaft furnace to reduce the pellets, it achieves clean metallurgical separation of vanadium-titanium magnetite and high-value utilization of mold steel through a short-process smelting process. The method provided by this invention avoids the use of coke resources required for long-process blast furnace operations, eliminates sintering and coking processes, meets current carbon reduction requirements, and possesses sustainable development capabilities. Attached Figure Description

[0028] 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 these drawings without creative effort.

[0029] Picture 1 This is a schematic diagram of the existing long-process smelting process for vanadium-titanium magnetite.

[0030] Picture 2 This is a schematic flowchart of a method for directly producing high-carbon vanadium-chromium-molybdenum mold steel using a short process, as disclosed in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0032] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0033] like Picture 2 As shown, one embodiment of the present invention discloses a method for directly producing high-carbon vanadium-chromium-molybdenum mold steel in a short process, comprising the following steps:

[0034] S10. Vanadium-titanium magnetite concentrate is pelletized, roasted and then used to obtain pellet ore;

[0035] S20. Metallized pellets are obtained by pre-reducing ore using a gas-based vertical shaft furnace.

[0036] S30. Metallized pellets and carbonaceous reducing agent are added to a melting furnace for deep reduction. After slag and iron separation, vanadium-containing molten iron is obtained. Inert gas or reducing gas is introduced during the deep reduction process.

[0037] S40. Add vanadium-containing molten iron to the steelmaking electric furnace. Determine whether to add chromium alloy according to the chromium content requirement in the steel composition. After adding electric furnace slag, slag is formed and the temperature of the molten steel rises to a temperature greater than the threshold temperature and not lower than 1673K. The molten steel is decarburized by blowing oxygen to the target content. After oxygen determination, the dissolved oxygen [O] content in the molten steel is detected. A reducing agent is added for deoxidation according to the dissolved oxygen [O] content. Molybdenum metal and / or vanadium alloy are added according to the steel composition requirements. The steel is tapped after the metal is fully melted.

[0038] S50 is a high-carbon vanadium-chromium-molybdenum mold steel obtained by casting molten steel into molds.

[0039] In the embodiments disclosed in this invention, the vanadium-containing molten iron obtained by the method of this invention has high vanadium and chromium content, low carbon and sulfur content, and a high molten iron temperature. It meets the requirements for direct entry into a steelmaking electric furnace for the smelting of high-carbon vanadium-chromium-molybdenum mold steel. Furthermore, the method provided by this invention effectively avoids severe losses of vanadium and chromium during the smelting process, greatly improving the recovery rate of vanadium and chromium, and significantly reducing the amount of vanadium or chromium alloys used in the smelting process, thus helping to reduce the production cost of mold steel. In the embodiments of this invention, the vanadium-titanium magnetite concentrate includes high-chromium vanadium-titanium magnetite concentrate.

[0040] Furthermore, by using 100% vanadium-titanium magnetite or 100% high-chromium vanadium-titanium magnetite in the furnace, the embodiments of the present invention significantly improve the utilization rate of vanadium-titanium magnetite or high-chromium vanadium-titanium magnetite and increase the V content (or V and Cr content in vanadium-chromium ferrometallurgical) in vanadium-containing molten iron. The method provided by the embodiments of the present invention for preparing vanadium-titanium pellets eliminates the high cost and high pollution caused by the sintering process. It uses a gas-based vertical shaft furnace to reduce the pellets, achieving clean metallurgical separation of vanadium-titanium magnetite or high-chromium vanadium-titanium magnetite and high-value utilization of die steel through a short-process smelting. The method provided by the embodiments of the present invention avoids the use of coke resources required for the long-process blast furnace process, eliminates sintering and coking processes, meets current carbon reduction requirements, and has sustainable development capabilities.

[0041] In this embodiment of the invention, the principle of slag and molten iron separation during the deep reduction process in the electric furnace is that the two have different specific gravities in the electric furnace, resulting in stratification, thereby achieving slag-iron separation.

[0042] In this embodiment of the invention, in step S30, an inert gas or reducing gas is introduced during the deep reduction process. This can prevent vanadium oxides from being difficult to reduce into the molten iron due to the entry of oxygen, thus accelerating the deep reduction process and reducing the C content in the molten iron.

[0043] In this embodiment of the invention, in step S40, adding electric furnace slag to the steelmaking electric furnace can further remove impurities such as TiO2, SiO2 and Al2O3 remaining in the molten iron, which is beneficial to ensuring the quality of the final high-carbon vanadium-chromium-molybdenum mold steel.

[0044] In this embodiment of the invention, in step S40, the temperature of the molten steel is raised to a temperature greater than the threshold temperature and not lower than 1673K to ensure that the V and Cr elements in the molten steel are not oxidized in the subsequent oxygen blowing decarbonization process.

[0045] In this embodiment of the invention, in step S40, since molybdenum and vanadium are more easily oxidized than chromium, adding metallic molybdenum and / or vanadium alloys after oxygen blowing decarburization of molten steel helps to prevent the oxidation loss of molybdenum and / or vanadium added during the electric arc furnace smelting process.

[0046] In this embodiment of the invention, the mass percentage of carbon in the high-carbon vanadium-chromium-molybdenum mold steel is ≥0.6%.

[0047] In some embodiments, in step S10, a calcium flux is added to vanadium-titanium magnetite concentrate or high-chromium vanadium-titanium magnetite concentrate, followed by pelletizing and roasting to obtain alkaline pellets. The alkalinity range of the alkaline pellets is 0.3 to 0.6. The calcium flux is any one of quicklime, limestone, or hydrated lime. That is, if the alkaline pellets are pre-reduced in step S20, then it is not necessary to add calcium flux to the melting furnace in step S30. Alternatively, in step S10, vanadium-titanium magnetite concentrate or high-chromium vanadium-titanium magnetite concentrate is pelletized and roasted to obtain pellets with natural alkalinity. In step S30, a calcium flux is added to the melting furnace to control the slag alkalinity to be 0.3 to 0.6. The calcium flux is any one of quicklime, limestone, or hydrated lime. In this embodiment of the invention, adjusting the basicity of the pellets or adding calcium flux to the melting furnace are both ways to adjust the melting point of the slag, preventing the slag from being too hot to melt and thus affecting the slag-iron separation.

[0048] In some embodiments, in step S40, the chromium alloy is a 70 ferrochrome alloy (in which the mass fraction of chromium is 70%), and the vanadium alloy is a 70 ferrovanadium alloy (in which the mass fraction of vanadium is 70%).

[0049] In some embodiments, in step S40, a reducing agent is added for deoxygenation based on the dissolved oxygen [O] content. The reducing agent is, for example, FeSi or Al blocks, and the amount of reducing agent can be calculated based on the dissolved oxygen [O] content.

[0050] In some embodiments, in step S10, alkaline pellets are obtained by adding calcium flux to vanadium-titanium magnetite concentrate or high-chromium vanadium-titanium magnetite concentrate, followed by pelletizing and roasting. The alkalinity range of the alkaline pellets is 0.3 to 0.6, and the calcium flux is any one of quicklime, limestone or hydrated lime.

[0051] In some embodiments, during the preparation of pellets in step S10, bentonite is added to the vanadium-titanium magnetite concentrate or the high-chromium vanadium-titanium magnetite concentrate to increase the cohesiveness of the pellets.

[0052] In some embodiments, in step S10, the calcination preheating temperature is 850℃~950℃, the calcination preheating time is 10min~20min, the calcination temperature is 1200℃~1300℃, and the calcination time is 15min~25min, resulting in an average compressive strength of 2000~2600N for the obtained pellets. This is beneficial for improving the structural strength of the pellets and for ensuring the metallization rate of the pellets during subsequent reduction.

[0053] In some embodiments, in step S20, the reducing gas used for pre-reduction includes H2, CO, impurity N2, and / or CO2, wherein the volume fraction of each gas in the reducing gas satisfies: H2 / CO≥6, H2+CO≥90%, CO2<5%, and / or N2<5%. Using clean, hydrogen-rich gas achieves clean reduction of vanadium-titanium magnetite concentrate or high-chromium vanadium-titanium magnetite concentrate, reducing environmental pollution and ensuring the metallization rate of the pellets.

[0054] In some embodiments, in step S20, the reduction temperature is 1000–1100°C, the reduction time is 2–4 h, and the metallization rate of the pre-reduced metallized pellets is controlled to be 85%–95%. A high metallization rate can further reduce the time required for subsequent deep reduction and reduce the amount of carbonaceous reducing agent used in the deep reduction process, thereby helping to reduce the carbon content in the vanadium-containing molten iron obtained after slag-iron separation.

[0055] In some embodiments, in step S30, the carbonaceous reducing agent is one or more of coke, coal, or activated carbon, the total fixed carbon content of the carbonaceous reducing agent is ≥80%, and the mass of the carbonaceous reducing agent is 2-5% of the mass of the metallized pellets.

[0056] In some embodiments, in step S30, the temperature of the melting furnace is controlled at 1500–1600°C, and the inert gas is argon or the reducing gas is any one or both of CO and H2. Introducing Ar, CO, H2, or a mixture of CO and H2 into the melting furnace avoids the entry of vanadium into the molten iron due to the difficulty in reducing vanadium oxides caused by oxygen entering the furnace. This accelerates the deep reduction process, reduces the C content in the molten iron, and prevents the formation of high-melting-point TiN or titanium carbonitride (Ti(C,N)) solids from N2 in the air reacting with over-reduced Ti. These solids, mixed in the slag, affect the slag's fluidity and the separation of slag from the molten iron. This reduces the amount of carbonaceous reducing agent used, shortens smelting time, reduces power consumption, and lowers graphite electrode oxidation losses, thereby significantly reducing smelting costs.

[0057] Experiments show that, under air atmosphere, it takes 2 hours to reduce vanadium-containing molten iron to obtain the same V recovery rate. However, if Ar is used as a protective gas, the time to obtain the same V recovery rate of vanadium-containing molten iron is 1 to 1.5 hours, which can shorten the melting time (deep reduction time) by 25-50% compared to air atmosphere.

[0058] In some embodiments, in step S30, the mass percentages of each component in the vanadium-containing molten iron are: C: 0.5–2.5%, V: 0.3–0.6%, Cr: 0–1.0%, Si: 0.1–0.5%, Ti: 0.1–0.3%, S: 0.005–0.05%, P: 0.005–0.03%.

[0059] In some embodiments, in step S40, the mass ratio of electric furnace slag to vanadium-containing molten iron is 0.1 to 0.3, and the electric furnace slag is composed of limestone and fluorite, wherein the mass ratio of limestone to fluorite is 2.6:1 to 3:1; the threshold temperature is calculated using the following formula:

[0060]

[0061] Wherein, [Cr] and [C] are the values ​​before the percentage sign for the chromium content w[Cr]% and carbon content w[C]% in the steel composition, respectively.

[0062] In some embodiments, the mass percentages of certain components in the high-carbon vanadium-chromium-molybdenum mold steel are: C: 0.6%–2.0%, V ≥ 0.3%, Cr ≥ 0.5%.

[0063] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0064] Example 1

[0065] Process flow for smelting H13 steel using vanadium-titanium magnetite concentrate:

[0066] (1) Bentonite (the mass of bentonite is 1.5% of the mass of vanadium-titanium magnetite concentrate) was added to vanadium-titanium magnetite concentrate (the composition is shown in Table 1 below). The preheating temperature was 900℃, the preheating time was 15min, the roasting temperature was 1220℃, and the roasting time was 20min to obtain pellets (the composition is shown in Table 2). The average compressive strength of the pellets was 2080N.

[0067] Table 1. Composition of vanadium-titanium magnetite concentrate (wt%)

[0068] TFe FeO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> CaO MgO <![CDATA[Al2O3]]> MnO <![CDATA[V2O5]]> <![CDATA[TiO2]]> <![CDATA[Cr2O3]]> 56.53 33.67 43.35 3.14 0.34 3.28 3.33 0.20 0.710 10.153 0.2

[0069] Table 2. Pellet composition (wt%)

[0070] TFe <![CDATA[SiO2]]> CaO MgO <![CDATA[Al2O3]]> MnO <![CDATA[V2O5]]> <![CDATA[TiO2]]> <![CDATA[Cr2O3]]> S P 54.71 3.94 0.51 3.21 3.36 0.19 0.69 9.82 0.18 0.014 0.194

[0071] (2) The above-mentioned pellets were pre-reduced using a gas-based vertical shaft furnace to ensure that the volume fraction of the gas in the reducing gas met the following conditions: H2 / CO=8, H2+CO=95%, CO2=2%, N2=3%, and the reduction temperature was 1050℃. After 3 hours of pre-reduction in the vertical shaft furnace, the average metallization rate of the pellets was about 95%.

[0072] (3) The pre-reduced metallized pellets were subjected to high-temperature smelting and slag-iron separation using a smelting electric furnace. Coking coal (5% of the mass of the metallized pellets) and quicklime (2% of the mass of the metallized pellets) were added. The smelting temperature (temperature of the smelting electric furnace) was 1500℃, and the slag basicity was controlled at 0.4. During the smelting process (deep reduction process), Ar gas was introduced into the electric furnace as a protective gas. The composition of the vanadium-containing molten iron after slag-iron separation is shown in Table 3 below.

[0073] Table 3 Composition of vanadium-containing molten iron (wt%)

[0074] C Si P S V Ti Cr Fe 1.8 0.45 0.02 0.03 0.55 0.15 0.05 96.95

[0075] In the gas-based vertical shaft furnace-electric furnace smelting process, the recovery rate of vanadium from vanadium-titanium magnetite concentrate to vanadium-containing molten iron is about 75-80%. The obtained vanadium-containing molten iron does not need to be extracted for vanadium removal, and the vanadium in the vanadium-containing molten iron can be fully utilized for steelmaking.

[0076] (4) 23t of vanadium-containing molten iron and 2t of ferrochrome alloy (with a chromium mass fraction of 70%) were mixed into a 30t electric furnace. 2500kg of electric furnace slag was added, with a slag composition of limestone:fluorite (mass ratio) = 3:1. The slag was then inserted and the molten steel was heated to 1770K (threshold temperature 1720K). Oxygen was blown to reduce the C content to 0.4% (mass fraction). After oxygen determination, the dissolved oxygen content in the molten steel was measured to be: [O] = 6.2 × 10⁻⁶. -5 Atm, then according to the dissolved oxygen [O] content, 140 kg of FeSi alloy (with a Si mass fraction of 90%) was added for deoxidation. After standing for 6 minutes, 300 kg of metallic Mo and 100 kg of 70 vanadium-iron alloy (with a vanadium mass fraction of 70%) were added. After the alloy was fully melted, the steel was tapped (the steel composition is shown in Table 4 below). The next refining process was to cast the tapped steel into shape to obtain H13 steel.

[0077] Table 4. Steel composition (wt%)

[0078] C Si P S V Mo Cr Fe 0.4 0.9 0.02 0.01 0.8 1.2 5.2 91.47

[0079] The vanadium yield in the steelmaking process is close to 100%. In summary, using this process to smelt vanadium-titanium magnetite can achieve a vanadium yield of approximately 75-80%, which is beneficial for vanadium recovery.

[0080] Comparative Example 1

[0081] Currently, the furnace charge structure used for blast furnace smelting of vanadium-titanium magnet ore is vanadium-titanium sinter + vanadium-titanium pellets (+ a small amount of lump ore or none). One furnace charge structure used is 60% vanadium-titanium sinter + 40% vanadium-titanium pellets, and the composition is shown in Table 5 below.

[0082] Table 5. Charge Structure (wt%)

[0083]

[0084]

[0085] The composition of the vanadium-containing molten iron obtained after blast furnace smelting is shown in Table 6.

[0086] Table 6. Composition (wt%) of vanadium-containing molten iron obtained from blast furnace smelting

[0087]

[0088] In the blast furnace smelting process, the vanadium recovery rate from vanadium-titanium magnetite concentrate to vanadium-containing molten iron is approximately 65%. This vanadium-containing molten iron is then subjected to converter vanadium extraction to obtain semi-steel (composition shown in Table 7) and vanadium slag (composition shown in Table 8). The vanadium recovery rate from the vanadium-containing molten iron to the vanadium slag is approximately 78%; the vanadium recovery rate from the vanadium slag extraction process (roasting and leaching) is approximately 80%. The obtained vanadium pentoxide can be alloyed to produce 70 ferrovanadium alloy, with a vanadium recovery rate of approximately 95%. Therefore, the total recovery rate of ferrovanadium produced from vanadium-titanium magnetite concentrate is less than 40%.

[0089] Table 7. Main components of semi-steel (wt%)

[0090]

[0091] Table 8. Composition of vanadium slag (wt%)

[0092]

[0093] Semi-steel is processed in a steelmaking converter to obtain qualified molten steel (or cooled into pig iron billets). The carbon content in the molten steel is 0.45% (mass percentage), and the [O] content is 60 ppm. The molten steel or pig iron billets are then added to a steelmaking electric furnace to produce H13 steel. 23t of molten steel (or pig iron billets) and 2t of ferrochrome alloy (containing 70% chromium by mass) are added to a 30t electric furnace, along with 2500 kg of electric furnace slag. The slag composition is limestone:fluorite (mass ratio) = 3:1. Electrode electrodes are inserted to neutralize the slag. The molten steel is heated to 1770K, and oxygen is blown to reduce the carbon content to 0.4% (mass percentage). After oxygen determination, the dissolved oxygen content in the molten steel is measured to be: [O] = 6.2 × 10⁻⁶. -5 Atm, then according to the dissolved oxygen [O] content, 140 kg of FeSi alloy (with a Si mass fraction of 90%) was added. After standing for 6 minutes, 300 kg of metallic Mo and 270 kg of 70 vanadium-iron alloy (with a vanadium mass fraction of 70%) were added. After the alloy was fully melted, the steel was tapped (the steel composition is shown in Table 9 below). The next refining process involves casting the tapped steel into molds to obtain H13 steel. The V yield in the steelmaking process is close to 100%.

[0094] Table 9 Steel composition (wt%)

[0095] C Si P S V Mo Cr Fe 0.4 0.9 0.02 0.01 0.8 1.2 5.2 91.47

[0096] Using this long process, the recovery rate of V is less than 40%.

[0097] A comparison of the data from Example 1 and Comparative Example 1 shows that the mass of ferrovanadium alloy used in the short-process direct smelting method for H13 steel disclosed in this invention is much smaller than the mass of ferrovanadium alloy used in the existing long-process blast furnace-converter smelting of H13 steel. This indicates that the short-process direct smelting method for H13 steel disclosed in this invention greatly improves the recovery rate of vanadium, significantly reduces the amount of ferrovanadium alloy used, lowers production costs, and has a shorter production process, which is beneficial to improving production efficiency.

[0098] Example 2

[0099] Process flow for producing Cr5Mo1V steel from high-chromium vanadium-titanium magnetite concentrate:

[0100] (1) Bentonite (1.5% of the mass of vanadium-titanium magnetite concentrate) and slaked lime (2.5% of the mass of vanadium-titanium magnetite concentrate) were added to high-chromium vanadium-titanium magnetite concentrate (the composition of which is shown in Table 10 below). The preheating temperature was 920℃, the preheating time was 10min, the roasting temperature was 1250℃, and the roasting time was 25min to obtain pellets (the composition of which is shown in Table 11). The average compressive strength of the pellets was 2493N.

[0101] Table 10 Composition of high-chromium vanadium-titanium magnetite concentrate (wt%)

[0102] TFe FeO CaO <![CDATA[SiO2]]> MgO <![CDATA[Al2O3]]> <![CDATA[TiO2]]> <![CDATA[V2O5]]> <![CDATA[Cr2O3]]> 51.12 25.73 1.03 5.87 3.56 3.23 12.02 0.53 0.76

[0103] Table 11 Composition of high-chromium vanadium-titanium magnetite pellets (wt%)

[0104] TFe <![CDATA[SiO2]]> CaO MgO <![CDATA[Al2O3]]> <![CDATA[V2O5]]> <![CDATA[Cr2O3]]> <![CDATA[TiO2]]> S P 49.94 6.37 2.53 3.43 3.09 0.49 0.91 11.54 0.02 0.03

[0105] (2) The above-mentioned high-chromium vanadium-titanium magnetite pellets were pre-reduced using a gas-based vertical shaft furnace to ensure that the volume fraction of the gas in the reducing gas met the following conditions: H2 / CO=10, H2+CO=92%, CO2=4%, N2=4%, and the reduction temperature was 1000℃. After 2.5 hours of pre-reduction in the vertical shaft furnace, the average metallization rate of the pellets was about 92%.

[0106] (3) The pre-reduced metallized pellets were subjected to high-temperature smelting and slag-iron separation using a smelting electric furnace, with 8% pulverized coal added (the mass of the pulverized coal was 5% of the mass of the metallized pellets). No slag conditioner was added. The smelting temperature was 1550℃. During the smelting process (deep reduction process), CO gas was introduced into the electric furnace as a protective gas. The composition of the vanadium-chromium molten iron after slag-iron separation is shown in Table 12 below.

[0107] Table 12 Composition of Vanadium-Chromium Molten Iron (wt%)

[0108] Fe C Si V Ti Cr P S 96.594 1.2 0.50 0.477 0.20 0.962 0.058 0.009

[0109] In the gas-based vertical shaft furnace-electric furnace smelting process, the recovery rates of vanadium from vanadium-titanium magnetite concentrate to vanadium-containing molten iron are approximately 75-80% and 70-75%, respectively. The obtained vanadium-chromium molten iron does not require vanadium and chromium extraction, and the vanadium and chromium in the vanadium-chromium molten iron can be fully utilized for steelmaking.

[0110] (4) 26t of vanadium-chromium molten iron was added to a 30t electric furnace, along with 3200kg of electric furnace slag. The slag composition was limestone:fluorite (mass ratio) = 2.6:1. Electrode-polarized slag was inserted, and the molten steel was heated to 1700K (threshold temperature 1612K). Oxygen was blown to reduce C to 0.4% (mass fraction). After oxygen determination, the dissolved oxygen content in the molten steel was measured to be: [O] = 2.8 × 10⁻⁶. -5 Atm, then add Al block 300g according to the dissolved oxygen [O] content, add electrolytic Mo 230g, let stand for 6 minutes and then tap the steel (the steel composition is shown in Table 13 below). The next refining process will cast the tapped steel into a mold to obtain Cr5Mo1V steel.

[0111] Table 13 Steel composition (wt%)

[0112] Fe C Si V Cr P S Mo 96.248 0.95 0.46 0.47 0.919 0.05 0.003 0.9

[0113] Comparative Example 2

[0114] Currently, the furnace charge structure used for blast furnace smelting of high-chromium vanadium-titanium magnet ore is vanadium-titanium sinter + high-chromium vanadium-titanium pellets. One furnace charge structure used is 65% vanadium-titanium sinter + 35% high-chromium vanadium-titanium pellets, and the composition is shown in Table 14.

[0115] Table 14 Charge Structure (wt%)

[0116]

[0117]

[0118] The composition of the molten iron obtained after blast furnace smelting is shown in Table 15.

[0119] Table 15 Composition (wt%) of vanadium-chromium molten iron obtained from blast furnace smelting

[0120]

[0121] In the blast furnace smelting process, the vanadium recovery rate from high-chromium vanadium-titanium magnetite concentrate to vanadium-containing molten iron is approximately 60%, and the chromium recovery rate is approximately 70%. The molten iron is then subjected to converter vanadium and chromium extraction to obtain semi-steel (composition shown in Table 16 below) and vanadium-chromium slag (composition shown in Table 17 below). The vanadium recovery rate from the vanadium-chromium molten iron to the vanadium-chromium slag is approximately 78%, and the chromium recovery rate is approximately 75%. After vanadium and chromium extraction (roasting and leaching) from the vanadium-chromium slag, the yields are both approximately 80%. The obtained vanadium oxide and chromium oxide can be alloyed to produce 70% ferrovanadium alloy and 70% ferrochrome alloy, with yields of 95% and 90%, respectively. The overall yields of vanadium and chromium from high-chromium vanadium-titanium magnetite to ferrovanadium alloy and vanadium-chromium alloy are approximately 35% and 38%, respectively.

[0122] Table 16 Semi-steel composition (wt%)

[0123]

[0124] Table 17 Composition of Vanadium-Chromium Slag (wt%)

[0125]

[0126] The semi-steel is processed in a steelmaking converter to obtain qualified molten steel (or cooled into pig iron billets). The carbon content in the molten steel is 0.45% (mass percentage), and the [O] content is 60 ppm. The molten steel or pig iron billets are then added to a steelmaking electric furnace to produce Cr5Mo1V steel. 26t of molten steel is added to a 30t electric furnace, along with 3200 kg of electric furnace slag. The slag composition is limestone:fluorite (mass ratio) = 2.6:1. The slag is then inserted and the molten steel is heated to 1700K (threshold temperature 1612K). Oxygen is blown to reduce the carbon content to 0.4% (mass fraction). After oxygen determination, the dissolved oxygen content in the molten steel is measured to be: [O] = 2.8 × 10⁻⁶. -5 Atm, then according to the dissolved oxygen [O] content, add Al block: 300g, electrolytic Mo: 230g, 70 vanadium ferroalloy: 180Kg, 70 chromium ferroalloy: 350Kg, and let stand for 6 minutes before tapping (steel composition is shown in Table 18 below). The next refining process involves casting the tapped steel into Cr5Mo1V steel. The V and Cr yields during the steelmaking process are close to 100%.

[0127] Table 18 Steel Composition (wt%)

[0128] Fe C Si V Cr P S Mo 96.248 0.95 0.46 0.47 0.919 0.05 0.003 0.9

[0129] Using this long process, the recovery rate of V is less than 40%.

[0130] A comparison of the data from Example 2 and Comparative Example 2 shows that the short-process direct smelting method for Cr5Mo1V steel disclosed in this invention does not require the addition of ferrovanadium alloy and ferrochrome alloy, while the existing long-process blast furnace-converter smelting method for Cr5Mo1V steel uses a large amount of ferrovanadium alloy and ferrochrome alloy. This indicates that the short-process direct smelting method for Cr5Mo1V disclosed in this invention can greatly improve the recovery rate of ferrovanadium and greatly reduce the amount of ferrovanadium alloy and ferrochrome alloy used, thereby reducing production costs. Furthermore, the short production process is beneficial for improving production efficiency.

[0131] In summary, the method for directly producing high-carbon vanadium-chromium-molybdenum mold steel using a short-process method provided by this invention involves reducing metallized pellets in a gas-based vertical shaft furnace, then performing a deep reduction process in a melting electric furnace to obtain vanadium-containing molten iron. This vanadium-containing molten iron is directly fed into a steelmaking electric furnace, where appropriate amounts of chromium alloy, metallic molybdenum, and vanadium alloy are added based on the required steel composition, ultimately yielding high-carbon vanadium-chromium-molybdenum mold steel. The vanadium-containing molten iron obtained by this method has high vanadium and chromium content, low carbon and sulfur content, and a high molten iron temperature, meeting the requirements for direct feeding into a steelmaking electric furnace for smelting high-carbon vanadium-chromium-molybdenum mold steel. Furthermore, the method provided by this invention effectively avoids severe losses of vanadium and chromium during smelting, significantly improving the recovery rate of vanadium and chromium, and greatly reducing the amount of vanadium or chromium alloy used in the smelting process, thus helping to reduce the production cost of mold steel.

[0132] Furthermore, by using 100% vanadium-titanium magnetite or 100% high-chromium vanadium-titanium magnetite in the furnace, this invention significantly improves the utilization rate of vanadium-titanium magnetite or high-chromium vanadium-titanium magnetite and increases the V content (or V and Cr content) in vanadium-containing molten iron. The method provided by this invention for preparing vanadium-titanium pellets eliminates the high cost and pollution caused by the sintering process. It uses a gas-based vertical shaft furnace to reduce the pellets, achieving clean metallurgical separation of vanadium-titanium magnetite or high-chromium vanadium-titanium magnetite and high-value utilization of die steel through a short-process smelting process. The method provided by this invention avoids the long-process use of coke resources required for blast furnace operations, eliminates sintering and coking processes, meets current carbon reduction requirements, and possesses sustainable development capabilities.

[0133] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0134] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0135] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A short process for direct production of high carbon vanadium chromium molybdenum die steel characterized by, Includes the following steps: S10. Vanadium-titanium magnetite concentrate is pelletized, roasted and then used to obtain pellet ore; S20. The ore pellets are pre-reduced using a gas-based vertical shaft furnace to obtain metallized pellets; S30. The metallized pellets and carbonaceous reducing agent are added to the melting and separation electric furnace for deep reduction. After slag and iron separation, vanadium-containing molten iron is obtained. Inert gas or reducing gas is introduced during the deep reduction process. S40. The vanadium-containing molten iron is directly added to the steelmaking electric furnace. Whether to add chromium alloy is determined according to the chromium content requirement in the steel composition. After adding the electric furnace slag, the slag is formed and the temperature of the molten steel rises to a temperature greater than the threshold temperature and not lower than 1673K. The molten steel is decarburized by blowing oxygen to the target content. After oxygen determination, the dissolved oxygen [O] content in the molten steel is detected. A reducing agent is added according to the dissolved oxygen [O] content for deoxidation. Molybdenum metal and / or vanadium alloy are added according to the steel composition requirements. The steel is tapped after the metal is fully melted. S50. The molten steel is poured into molds to obtain the high-carbon vanadium-chromium-molybdenum mold steel. In step S10, after adding a calcium flux to the vanadium-titanium magnetite concentrate, the pellets are pelletized and roasted to obtain alkaline pellets. The alkalinity of the alkaline pellets is in the range of 0.3 to 0.

6. The calcium flux is any one of quicklime, limestone or hydrated lime. Alternatively, in step S10, the vanadium-titanium magnetite concentrate is pelletized and roasted to obtain pellets with natural basicity. In step S30, a calcium flux is added to the melting furnace to control the slag basicity to be 0.3 to 0.

6. The calcium flux is any one of quicklime, limestone, or hydrated lime. In step S40, the mass ratio of the electric furnace slag to the vanadium-containing molten iron is 0.1 to 0.3, the electric furnace slag is composed of limestone and fluorite, and the mass ratio of the limestone to fluorite is 2.6:1 to 3:1; the threshold temperature is calculated using the following formula: Wherein, [Cr] and [C] are the values ​​before the percentage sign for the chromium content w[Cr]% and carbon content w[C]% in the steel composition, respectively; In step S30, the mass percentages of each component in the vanadium-containing molten iron are as follows: C: 0.5–2.5%, V: 0.3–0.6%, Cr: 0–1.0%, Si: 0.1–0.5%, Ti: 0.1–0.3%, S: 0.005–0.05%, P: 0.005–0.03%.

2. The method of short process direct production of high carbon vanadium chromium molybdenum die steel according to claim 1, characterized in that, In step S10, the roasting preheating temperature is 850℃~950℃, the roasting preheating time is 10min~20min, the roasting temperature is 1200℃~1300℃, the roasting time is 15min~25min, and the average compressive strength of the obtained pellet is 2000~2600N.

3. The method of claim 1, wherein the short process direct production of high carbon vanadium-chromium-molybdenum die steel is characterized by, In step S20, the reducing gas used for pre-reduction includes H2, CO, impurity N2 and / or CO2, wherein the volume fraction of each gas in the reducing gas satisfies: H2 / CO≥6, H2+CO≥90%, CO2<5% and / or N2<5%.

4. The short process direct production of high carbon vanadium chromium molybdenum die steel of claim 1, wherein, In step S20, the reduction temperature is 1000-1100℃, the reduction time is 2-4h, and the metallization rate of the pre-reduced metallized pellets is controlled to be 85%-95%.

5. The method for direct production of high-carbon vanadium-chromium-molybdenum mold steel via a short process according to claim 1, characterized in that, In step S30, the carbonaceous reducing agent is one or more of coke, coal or activated carbon, the total fixed carbon content of the carbonaceous reducing agent is ≥80%, and the mass of the carbonaceous reducing agent is 2 to 5% of the mass of the metallized pellets.

6. The short process direct production of high carbon vanadium chromium molybdenum die steel of claim 1, wherein, In step S30, the temperature of the melting furnace is controlled to be 1500-1600°C, and the inert gas is argon or the reducing gas is any one or both of CO and H2.

7. The short process direct production of high carbon vanadium chromium molybdenum die steel of claim 1, wherein, The mass percentages of some components in the high-carbon vanadium-chromium-molybdenum mold steel are: C: 0.6%~2.0%, V≥0.3%, Cr≥0.5%.

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