CN102409132B - Method for producing 25CrMnB steel through converter flow - Google Patents

Abstract

The invention discloses a method for producing 25CrMnB steel through a converter flow and belongs to the field of metallurgy. The invention aims to provide a method for enabling a continuous casting machine of small dimension to cast smoothly so as to produce 25CrMnB steel through a converter flow. The method comprises the following steps: a, carrying out converter smelting; b, adding calcium carbide during steel tapping to enable the molten steel activity to be below 0.0025; c, adding 3.5-4.5kg per ton of steel before refining and heating, and adding 0.15-0.45kg of aluminum per ton of steel during heating; stopping heating when the molten steel is heated to be 1565-1585DEG C; adding aluminum to enable the content of aluminum to be 0.011-0.016%, then adding titanium to enable the content of titanium to be 0.02-0.06%, and adding boron to enable the boron content to be 0.0005-0.003%; and d, carrying out continuous casting. The method in the invention not only is applicable to a continuous casting machine of larger dimension and can be used for casting smoothly on the continuous casting machine of small dimension.

Description

A method for producing 25CrMnB steel by a converter process

technical field

The invention belongs to the field of iron and steel metallurgy, and in particular relates to a method for producing 25CrMnB steel through a converter process.

Background technique

A small amount of boron (about 0.001%) can be adsorbed on the austenite grain boundary, reduce the grain boundary energy, inhibit the formation of ferrite nuclei, and double the hardenability of medium and low carbon steels. Therefore, medium and low carbon steels often Add 0.0005-0.003% trace amount of boron to improve hardenability of steel. However, boron is one of the most active elements, which can form stable inclusions with residual oxygen and nitrogen in steel, and lose its beneficial effect. Only boron in solid solution can play a beneficial role.

Existing studies have shown that boron has a strong affinity with oxygen and nitrogen, and boron is easily oxidized to B ₆ O or B ₂ O ₃ , or combined with nitrogen to form BN, which prevents boron in boron-containing steels from exerting Harmful substances that increase hardenability. Therefore, in order to ensure the effect of boron on improving the hardenability of boron-containing steel, it is necessary to firstly use aluminum to remove free oxygen from molten steel during steel smelting, and use titanium to fix nitrogen in molten steel to ensure the effective effect of adding boron.

25CrMnB is a new type of boron-containing structural steel, which can replace 23MnB to manufacture track shoes for bulldozers or excavators with a pitch of 228 or more. The chemical composition is: C: 0.20-0.30%, Mn: 0.80-1.40%, Si: 0.15～0.35%, P≤0.030%, S≤0.015%, Cr: 0.30～0.60%, Ni≤0.25%, Cu≤0.30%, B: 0.0005～0.0035%, usually to ensure boron element to improve hardenability It is also required to control the Ti content above 0.02%, and the Al content above 0.02%. For example:

The patent CN100519769C with the publication date of July 29, 2009 discloses a method for producing boron-containing steel by converter smelting, which is characterized in that boron-containing steel is produced by adopting the process of converter smelting → ladle deoxidation, refining → boron alloying, and the specific operation The regulations are as follows: first, add aluminum and refining slag to deoxidize the molten steel and steel slag after tapping the converter, control the acid-soluble aluminum in the molten steel within the range of 0.02% to 0.04%, and then refine in the LF furnace to control the FeO+MnO in the steel slag≤2.0 %, and the α _[O] of molten steel ≤ 10ppm, and finally adding aluminum to the ladle again for deep deoxidation, adding ferro-titanium and ferro-boron for alloying. The yield of boron using this process is high, ranging from 69.4% to 91.8%.

The patent CN101660101A published on March 3, 2010 discloses a low-carbon wear-resistant engineering machinery track shoe steel and its manufacturing method, which discloses that the track shoe steel contains 0.0005-0.0035% B, but its manufacturing method is The use of electric furnace smelting → tapping → LF refining → VD vacuum degassing treatment is a typical electric furnace process and does not involve the converter process to produce 25CrMnB steel. And the chemical composition of CN101660101A is C: 0.17-0.27%, Si: 0.17-0.37%, Mn: 0.85-1.20%, Cr: 0.10-0.30%, Al: 0.010-0.060%, Cu: 0.010-0.20%, Ni: 0.01～0.20%, P: 0.003～0.025%, S: 0.001～0.025%, Ti: 0.020～0.060%, B: 0.0005～0.0035%, [O]: 5～20× ^10-6 %, [N]: 40～90×10 ^-6 %, the remainder is Fe and unavoidable impurities, and can only produce track shoes for bulldozers or excavators with a pitch of less than 216. This patent also mentions a method to ensure the availability of boron, that is, it is required to control the Al content within the range of 0.020-0.050%.

Based on the above disclosed technologies, in order to ensure the effect of boron on improving hardenability, there must be more than 0.02% aluminum in the steel to ensure the effective effect of adding boron. According to production practice, it is found that CN100519769C and CN101660101A mentioned controlling aluminum or acid-soluble aluminum not less than 0.02%, which has certain limitations. Specifically, molten steel with more _than 0.02% aluminum or acid-soluble aluminum will produce a certain amount of Al ₂ O ₃ in the _casting process. The nozzle of the casting machine crystallizer, especially on the continuous casting machine with a section of 200×200mm or below 200×200mm, is particularly serious, making it impossible for the small-sized continuous casting machine to cast.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for producing 25CrMnB steel through a converter process that ensures the hardenability of the boron-containing steel and enables a small-size continuous casting machine to cast smoothly.

The technical solution adopted by the present invention to solve its technical problems is:

A method for converter flow process to produce 25CrMnB steel, comprising the steps:

a. Add molten iron to the converter for smelting;

b. The molten steel is tapped to the ladle, and calcium carbide is added to keep the oxygen activity of the molten steel below 0.0025% when tapping;

c. The ladle is moved into the LF furnace for refining. Add 3.5-4.5kg of calcium carbide per ton of molten steel before refining and heating, and add 0.15-0.45kg of metal aluminum per ton of molten steel during heating. When the temperature of molten steel is heated to 1565-1585°C, stop heating and add adding aluminum to the water so that the acid-soluble aluminum content in the molten steel is 0.011-0.016% by weight, then adding titanium to make the titanium content in the molten steel 0.02-0.06% by weight, and adding boron to make the boron content in the molten steel 0.0005-0.003% by weight;

d. Continuous casting after refining.

Wherein, in step a of the above method, while adding molten iron into the converter, scrap steel is also added, and the weight of scrap steel does not exceed 15% of the weight of the molten iron.

Further, the molten steel is tapped into a ladle when the composition of the molten steel is initially smelted to a weight percentage of C of 0.05% to 0.15%, P≤0.015%, and S≤0.015%.

Wherein, in step b of the above method, the amount of calcium carbide to be added is based on the carbon content at the end point of the primary smelting of the converter. %, less than 0.15%, 2.5-3.5kg per ton of molten steel is input; when the carbon weight percentage at the end of the converter is above 0.15%, 1.5-2.5kg per ton of molten steel is input.

Wherein, adding calcium carbide in step b of the above method, ferrosilicon is also added to make the silicon content in molten steel 0.15-0.35% by weight; ferromanganese is added to make the manganese content in molten steel 0.80-1.10% by weight; The chromium content is 0.30-0.60% by weight, and the carburizer is added to make the carbon content 0.20-0.30% by weight.

The carburant mainly refers to asphalt glue containing more than 98% of fixed carbon or anthracite coal containing more than 92% of fixed carbon.

Wherein, in step c of the above method, 3.8-4.2 kg of calcium carbide is added per ton of molten steel before refining and heating, and 0.2-0.4 kg of metallic aluminum is added per ton of molten steel during heating.

Wherein, the method of adding titanium in step c of the above method is to feed the cored wire containing titanium through a wire feeding machine, and the method of adding boron is to feed the cored wire containing boron through a wire feeding machine.

Wherein, the temperature of the tundish of the continuous casting machine during continuous casting in step d of the above method is 1530±20° C.

Wherein, the calcium carbide in the above method contains more than 70% of CaC ₂ .

The present invention can specifically be implemented in the following manner: a method for producing 25CrMnB steel by a converter flow process, comprising the steps:

a. Add molten iron and steel scrap to the converter for smelting. The weight of scrap steel shall not exceed 15% of the weight of molten iron. When the composition of molten steel is initially smelted to a ratio of C of 0.05% to 0.15% by weight, P≤0.015%, and S≤0.015% Tap the molten steel into the ladle;

b. When the molten steel is tapped to the ladle, calcium carbide containing 70% of CaC ₂ is added to make the oxygen activity of the molten steel below 0.0025%. 3.5-4.5kg per ton of molten steel when the % is below; 2.5-3.5kg per ton of molten steel when the carbon weight percentage at the end of the converter is greater than 0.10% but less than 0.15%; Add 1.5-2.5kg per ton of molten steel; add calcium carbide and also add ferrosilicon to make the silicon weight percentage in the steel 0.15-0.35%, add ferromanganese to make the manganese weight percentage in the steel 0.80-1.10%, add ferrochrome to make the steel The chromium content in water is 0.30-0.60% by weight, and the carburant is added to make the carbon content in 0.20-0.30% by weight;

c. Move the ladle into the LF furnace for refining. Add 3.8-4.2kg of calcium carbide containing 70% CaC ₂ per ton of molten steel before refining and heating. During the heating process, add 0.2-0.4kg of metal aluminum per ton of molten steel. When the temperature of molten steel is heated to 1565-1585℃ Stop heating at this time, add aluminum to the molten steel, so that the weight percentage of acid-soluble aluminum in the molten steel is 0.011-0.016%, and then use the wire feeder to feed the titanium-containing cored wire so that the weight percentage of titanium in the molten steel is 0.02-0.06% , use the wire feeder to feed the boron-containing cored wire so that the boron weight percentage in the molten steel is 0.0005-0.003%;

d. Continuous casting is carried out after refining. During continuous casting, the temperature of the tundish of the continuous casting machine is 1530±20°C.

The beneficial effects of the present invention are: the blockage of the nozzle of the crystallizer during the casting process of the continuous casting machine is caused by the excessive aluminum content in the molten steel. According to the actual production situation, if the casting slab size is Molten steel containing more than 0.02% aluminum may block the nozzle of the mold of the continuous casting machine, resulting in the inability of the continuous casting machine to cast. However, in order to ensure that the boron element in boron-containing steel can improve hardenability, boron-containing steel must first use aluminum to remove free oxygen from molten steel during steel smelting, and use titanium to fix nitrogen in molten steel to ensure the addition of boron. effective effect. Analyzing the key points of boron-containing steel production, more than 0.02% of aluminum is just to remove free oxygen in the molten steel as much as possible. The method of the present invention does not use aluminum for pre-deoxidation in the tapping process after the initial smelting of molten steel, but uses calcium carbide. According to the relationship between carbon and equilibrium oxygen in the converter smelting process, which is usually a constant, the technology of the present invention adopts the method of adding different amounts of calcium carbide correspondingly according to different end points of the converter to carry out pre-deoxidation. After the above-mentioned pre-deoxidation, the molten steel oxygen Degree α _[O] can be controlled below 0.0025%. The ladle is moved to the LF refining furnace to refine the molten steel for further deoxidation. Calcium carbide is added before heating, and metal aluminum is added during the heating process to achieve enhanced diffusion and deoxidation effects. Before heating in the LF furnace, calcium carbide is added to replace part of the aluminum, thereby reducing the acid-soluble aluminum content in molten steel. . The added calcium carbide and metal aluminum have light specific gravity and will not enter the molten steel. After diffusion deoxidation, the molten steel α _[O] can be controlled below 0.0015%, and the oxidizing properties of steel slag FeO+MnO can be controlled below 1.5%. If only calcium carbide is used in the refining process of the LF furnace, it is difficult to control the oxidizing properties of FeO+MnO to less than 1.5%, and it can only reach the level of 1.5-2.0%. Therefore, it is very necessary to add 0.2-0.4kg of metal aluminum shot per ton of molten steel of. When the temperature of the molten steel is heated to 1565-1585°C, the heating is stopped, and aluminum is added to the molten steel so that the weight percentage of acid-soluble aluminum in the molten steel is 0.011-0.016%. The phenomenon of Al ₂ O ₃ , after a lot of practice, it is known that 0.006-0.011% of Als is oxidized to Al ₂ O ₃ in the continuous casting process. In this process, aluminum must be added to control the acid-soluble aluminum at 0.011-0.016%, so as to ensure the final casting There is also 0.005-0.010% acid-soluble aluminum in the molten steel. After the molten steel is completely deoxidized, the aluminum added basically forms AlN, which has the effect of fixing nitrogen, can reduce the amount of titanium used, and avoid the occurrence of large TiN inclusions. In addition, AlN is also beneficial to the grain refinement of steel. The method of the invention ensures that the free oxygen in the molten steel is removed, the yield of boron is high, and the hardenability of the 25CrMnB steel is good, but the aluminum content in the molten steel is not too high. Therefore, the method of the present invention is not only applicable to large-sized continuous casting machines, but also suitable for small-sized continuous casting machines below 200×200 mm, so as to ensure that the small-sized continuous casting machines can cast smoothly.

Detailed ways

The specific embodiments of the present invention are as follows: a method for producing 25CrMnB steel by a converter flow process, comprising the steps:

a. Add molten iron to the converter for smelting;

b. The molten steel is tapped to the ladle, and calcium carbide is added to keep the oxygen activity of the molten steel below 0.0025% when tapping;

c. The ladle is moved into the LF furnace for refining. Add 3.5-4.5kg of calcium carbide per ton of molten steel before refining and heating, and add 0.15-0.45kg of metal aluminum per ton of molten steel during heating. When the temperature of molten steel is heated to 1565-1585°C, stop heating and add adding aluminum to the water so that the acid-soluble aluminum content in the molten steel is 0.011-0.016% by weight, then adding titanium to make the titanium content in the molten steel 0.02-0.06% by weight, and adding boron to make the boron content in the molten steel 0.0005-0.003% by weight;

d. Continuous casting after refining.

Preferably, in step a of the above method, while adding molten iron into the converter, scrap steel is also added, and the weight of scrap steel does not exceed 15% of the weight of the molten iron. Scrap steel can come from scrap recycling stations or from within steel mills. There is no external heat source in converter steelmaking, and all rely on carbon in oxidized iron water and a small amount of silicon and manganese to release heat, so that molten steel is heated. Compared with molten iron, the carbon content of scrap steel is generally very low, and scrap steel added in converter smelting can act to lower the temperature. At the same time, in order to save resources and produce qualified finished steel, because the residual Ni and Cu in the scrap steel are uncontrollable, in order to avoid excessive addition of scrap steel, the phenomenon of Ni>0.25% and Cu>0.30% in molten steel can occur, and the weight of scrap steel Can not exceed 15% of the weight of molten iron.

Further, the molten steel is tapped into a ladle when the composition of the molten steel is initially smelted to a weight percentage of C of 0.05% to 0.15%, P≤0.015%, and S≤0.015%. The steelmaking process is actually a process of oxidation first and then reduction. In converter steelmaking, only the oxidation reaction is carried out in the converter, and the reduction reaction is carried out in the ladle. When C is 0.05% to 0.15%, it means that the oxidation reaction has ended, and the steel should be tapped for reduction reaction.

Preferably, in step b of the above method, the amount of calcium carbide to be added is based on the carbon content at the end point of the primary smelting of the converter. When 0.10% and less than 0.15%, 2.5-3.5kg per ton of molten steel is input; when the carbon weight percentage at the end of the converter is above 0.15%, 1.5-2.5kg per ton of molten steel is input. The method of the present invention does not use aluminum for pre-deoxidation in the tapping process after the initial smelting of molten steel, but uses calcium carbide, and according to the relationship between carbon and equilibrium oxygen in the converter smelting process, which is usually a constant, the technology of the present invention adopts different end points according to the converter. Carbon, the method of adding different amounts of calcium carbide to carry out pre-deoxidation can not only achieve the effect of deoxidation, but also avoid excessive carbon and control the carbon within a suitable range. After the molten steel is through the above-mentioned pre-deoxidation, the oxygen activity α _[O] of the molten steel can be controlled below 0.0025%, which ensures that the method of the present invention can finally obtain qualified 25CrMnB steel, and can control the acid-soluble aluminum in a relatively small range, so that Small size continuous casting machines can cast smoothly.

In order to be able to produce qualified 25CrMnB steel, add calcium carbide in the above method step b and also add ferrosilicon to make the silicon weight percentage content in the molten steel be 0.15～0.35%, add ferromanganese so that the manganese weight percentage content in the molten steel is 0.80～1.10% 1. Add ferrochromium to make the chromium content in molten steel be 0.30-0.60% by weight, and add carburant to make the carbon content in 0.20-0.30% by weight.

Preferably, in step c of the above method, 3.8-4.2 kg of calcium carbide is added per ton of molten steel before refining and heating, and 0.2-0.4 kg of metallic aluminum is added per ton of molten steel during heating. Calcium carbide is added before heating, and metal aluminum is added during the heating process to achieve the effect of strengthening the diffusion deoxidation effect. The added calcium carbide and metal aluminum have light specific gravity and will not enter the molten steel. After diffusion deoxidation, the molten steel α _[O] can be controlled below 0.0015%, ensuring Hardenability of boron-containing steel, steel slag oxidation FeO+MnO can be controlled below 1.5%. If only calcium carbide is used in the refining process of the LF furnace, it is difficult to control the oxidizing properties of FeO+MnO to less than 1.5%, and it can only reach the level of 1.5-2.0%. Therefore, it is very necessary to add 0.2-0.4kg of metal aluminum shot per ton of molten steel Yes, you can't just add calcium carbide.

Preferably, the method of adding titanium in step c of the above method is to feed the titanium-containing cored wire with a wire feeder, and the method of adding boron is to feed the boron-containing cored wire with a wire feeder.

Preferably, the temperature of the tundish of the continuous casting machine during continuous casting in step d of the above method is 1530±20°C. The liquidus temperature of 25CrMnB is 1500℃, and the superheat degree of the tundish of the continuous casting machine is controlled to be 30±20℃. Therefore, the temperature of the tundish of the continuous casting machine is controlled to be 1530±20℃, which is achieved by the electric heating of the front LF furnace. Achieved.

Preferably, the calcium carbide in the above method contains more than 70% of CaC ₂ . To facilitate operation and avoid adding too many impurities.

The present invention will be further described by the following examples, but the present invention is not limited to the scope of the description of the examples.

Embodiment one

The technology of the present invention is used to produce 25CrMnB steel on the converter process with a nominal capacity of 120 tons and an actual steel output within the range of 120 to 140 tons. The production process is 120 tons of converter primary molten steel → 120 tons of LF furnace refining molten steel → 6 A 6-strand billet continuous casting machine casts a 280mm×380mm billet.

First, add 130 tons of molten iron and 10 tons of steel scrap into the converter, and use the function of the converter to blow oxygen to remove C, and initially smelt the molten iron and scrap steel into molten steel. , 0.01% Si and 0.05% Mn are tapped into the ladle. At this time, the actual tapping amount is 133 tons, and about 5% of the raw materials are burned during the converter smelting process. Add calcium carbide 530kg (containing CaC ₂ 75%) to molten steel in tapping process, and add FeSi, FeMn, FeCr alloy and anthracite simultaneously and carry out Si, Mn, Cr and C element alloying, wherein the Si content in the FeSi alloy that adds is 74%, Mn content in FeMn alloy is 82%, Cr content in FeCr alloy is 52%, fixed C in anthracite is 92%, Si content in controlled molten steel is 0.16%, Mn content is 1.40%, Cr content is 0.31%, The C content is 0.20%. After the steel is tapped, the oxygen activity α[O] of the molten steel is measured with an oxygen meter to be 0.0025%.

After the molten steel reaches the LF furnace, add 530kg of calcium carbide containing more than 70% CaC ₂ before heating, then start heating, and add 26kg of metal aluminum pellets after heating for 3 minutes. Stop heating when the temperature of the molten steel reaches 1565°C, and feed 22kg of φ10 aluminum wire into the ladle with a wire feeder, at this time, the aluminum yield of the fed aluminum wire is about 60%, and then feed φ12 Ti-containing 90kg of cored wire (90kg at this time is the weight of the core powder, excluding the weight of the outer layer of the cored wire, the core powder is all FeTi40, that is, an iron alloy containing 40% Ti), and 10kg of φ12 cored wire containing B (10kg at this time is the core powder weight, excluding the iron sheet weight of the outer layer of the cored wire, the core powder is all FeB23, that is, an iron alloy containing 23% B), measure the oxygen activity α[O] of molten steel after feeding the wire It is 0.0012%, and the steel slag oxidizing FeO+MnO is 1.3%. In addition, the chemical composition Als of the molten steel was determined to be 0.011%, Ti to be 0.02%, and B to be 0.0014%, and the yield of B was 80% at this time.

Finally, 280mm×380mm slab was cast on a 6-machine 6-strand billet continuous casting machine. The temperature of the tundish during continuous casting was 1520°C. The chemical composition of molten steel was sampled and analyzed in the continuous casting machine as 0.20% C and 0.15% C. Si, 1.40% of Mn, 0.015% of P, 0.014% of S, 0.35% of Cr, 0.06% of Ni, 0.10% of Cu, 0.0012% of B, and 0.02% of Ti and 0.005% of Als (casting process Als burning loss 0.006%), the rest is Fe and other unavoidable impurities.

Embodiment two

The technology of the present invention is used to produce 25CrMnB steel on the converter process with a nominal capacity of 120 tons and an actual steel output within the range of 120 to 140 tons. The production process is 120 tons of converter primary molten steel → 120 tons of LF furnace refining molten steel → 6 A 6-strand billet continuous casting machine casts a 200mm×200mm billet.

First, add 120 tons of molten iron and 20 tons of scrap steel into the converter, and use the function of oxygen blowing and de-C of the converter to initially smelt the molten iron and scrap steel into molten steel. , 0.01% Si and 0.05% Mn are tapped into the ladle. At this time, the actual tapping amount is 133 tons, and about 5% of the raw materials are burned during the converter smelting process. Add calcium carbide 400kg (containing CaC ₂ 75%) to molten steel in tapping process, and add FeSi, FeMn, FeCr alloy and anthracite simultaneously and carry out Si, Mn, Cr and C element alloying, wherein the Si content in the FeSi alloy that adds is 74%, Mn content in FeMn alloy is 82%, Cr content in FeCr alloy is 52%, fixed C in anthracite is 92%, Si content in controlled molten steel is 0.35%, Mn content is 0.80%, Cr content is 0.45%, The C content is 0.30%. After the steel is tapped, the oxygen activity α[O] of the molten steel is measured with an oxygen meter to be 0.0020%.

After the molten steel reaches the LF furnace, add 530kg of calcium carbide containing more than 70% CaC ₂ before heating, then start heating, and add 40kg of metal aluminum pellets after heating for 3 minutes. When the molten steel temperature is heated to 1585°C, stop heating, feed 33kg of φ10 aluminum wire into the ladle with a wire feeder (at this time, the yield of aluminum fed into the aluminum wire is about 60%), and then feed φ12 aluminum wire into the ladle. Ti cored wire 130kg (130kg at this time is the weight of the core powder, not including the weight of the outer layer of the cored wire, the core powder is all FeTi40, that is, an iron alloy containing 40% Ti), and φ12 B cored wire 15kg (the 15kg at this time is the core powder weight, does not include the iron sheet weight of the outer layer of the cored wire, and the core powder is all FeB23, that is, an iron alloy containing 23% B), measure the oxygen activity of molten steel α [O ] is 0.0014%, and steel slag oxidizing FeO+MnO is 1.0%. In addition, the chemical composition Als of the molten steel was determined to be 0.015%, Ti to be 0.03%, and B to be 0.0020%, and the yield of B was 75%.

Finally, 200mm×200mm slabs were cast on a 6-machine 6-strand billet continuous casting machine. The temperature of the tundish during continuous casting was 1550°C. The chemical components of the molten steel were sampled and analyzed in the continuous casting machine as 0.30% C and 0.35% C. Si, 0.81% of Mn, 0.015% of P, 0.009% of S, 0.45% of Cr, 0.06% of Ni, 0.16% of Cu, 0.0020% of B, and 0.03% of Ti and 0.009% of Als (casting process Als burning loss 0.006%), the rest is Fe and other unavoidable impurities.

Embodiment Three

The technology of the present invention is used to produce 25CrMnB steel on the converter flow process with a nominal capacity of 80 tons and an actual steel tapping within the range of 80 to 82 tons. The production process is as follows: 80 tons of converter primary molten steel → 80 tons of LF furnace refining molten steel → 5 A 150mm×150mm billet is cast by a 5-strand billet continuous casting machine.

First, 84 tons of molten iron are added to the converter, and the molten iron is initially smelted into molten steel by using the function of the converter to remove C by blowing oxygen. When the Mn content is 0.05%, the steel is tapped into the ladle. At this time, the actual tapping amount is 80 tons, and about 5% of the raw materials are burned during the converter smelting process. Add 320kg of calcium carbide (containing 75% CaC ₂ ) to the molten steel during tapping, and simultaneously add FeSi, FeMn, FeCr alloy and anthracite to alloy Si, Mn, Cr and C elements, wherein the Si content in the FeSi alloy is 74% , the Mn content in the FeMn alloy is 82%, the Cr content in the FeCr alloy is 52%, the fixed C in anthracite is 92%, the Si content in the control molten steel is 0.25%, the Mn content is 1.01%, the Cr content is 0.60%, and the C content is 0.60%. It is 0.23%, and the oxygen activity α[O] of the molten steel measured by an oxygen meter is 0.0024% after the steel is tapped.

After the molten steel reaches the LF furnace, add 320kg of calcium carbide containing more than 70% CaC ₂ before heating, then start heating, and add 32kg of metal aluminum pellets after heating for 3 minutes. When the molten steel temperature is heated to 1570°C, stop heating, feed 20kg of φ10 aluminum wire into the ladle with a wire feeder (at this time, the yield of aluminum fed into the aluminum wire is about 60%), and then feed φ12 aluminum wire into the ladle. Ti cored wire 145kg (145kg at this time is the core powder weight, excluding the iron sheet weight of the outer layer of the cored wire, the core powder is all FeTi40, that is, an iron alloy containing 40% Ti), and φ12 B cored wire 10kg (10kg at this time is the weight of the core powder, excluding the weight of the iron sheet on the outer layer of the cored wire, and the core powder is all FeB23, that is, an iron alloy containing 23% B), measure the oxygen activity of molten steel α[O ] is 0.0011%, and steel slag oxidizing FeO+MnO is 1.4%. In addition, the chemical composition Als of the molten steel was determined to be 0.015%, Ti to be 0.06%, and B to be 0.0019%, and the yield of B was 65% at this time.

Finally, 150mm×150mm slabs were cast on a 5-machine, 5-strand billet continuous casting machine. The temperature of the tundish during continuous casting was 1530°C. The chemical components of molten steel were sampled and analyzed in the continuous casting machine as 0.23% C and 0.25% C. Si, 1.09% of Mn, 0.013% of P, 0.009% of S, 0.60% of Cr, 0.06% of Ni, 0.05% of Cu, 0.0019% of B, and 0.06% of Ti and 0.006% of Als (casting process Als burning loss of 0.009%), the rest is Fe and other inevitable impurities.

comparative example

The technology of the present invention is used to produce 25CrMnB steel on the converter flow process with a nominal capacity of 80 tons and an actual steel tapping within the range of 80 to 82 tons. The production process is as follows: 80 tons of converter primary molten steel → 80 tons of LF furnace refining molten steel → 5 A 150mm×150mm billet is cast by a 5-strand billet continuous casting machine.

First, 84 tons of molten iron are added to the converter, and the molten iron is initially smelted into molten steel by using the function of the converter to remove C by blowing oxygen. When the Mn content is 0.05%, the steel is tapped into the ladle. At this time, the actual tapping amount is 80 tons, and about 5% of the raw materials are burned during the converter smelting process. Add FeAl 167kg (containing Al 40%, the rest is Fe) to molten steel in tapping process, and simultaneously add FeSi, FeMn, FeCr alloy and anthracite to carry out alloying of Si, Mn, Cr and C element, wherein Si content in FeSi alloy The Mn content in the FeMn alloy is 82%, the Cr content in the FeCr alloy is 52%, the fixed C in anthracite is 92%, and the Si content in the controlled molten steel is 0.25%, the Mn content is 1.01%, and the Cr content is 0.60%. , C content is 0.23%, is 0.0021% with measuring molten steel oxygen activity α [O] with oxygen meter after tapping out steel, and the Als of sampling test molten steel is 0.05% (yield rate is 60%).

The molten steel starts heating after reaching the LF furnace, and stops heating when the temperature of the molten steel reaches 1570°C. The Als of the molten steel is 0.025% by sampling and testing. At this time, 0.025% of Als in the molten steel is burnt because the slag is not deoxidized. Feed φ 10 aluminum wire 22kg (because steel slag does not carry out deoxidation in steel ladle with wire feeder, the higher slag layer that feeds aluminum wire needs to pass through oxidation, the recovery rate of aluminum is lower than 60% of the present invention technology, It is about 55%), and then feed 145kg of φ12 Ti-containing cored wire (145kg at this time is the weight of the core powder, not including the weight of the iron sheet on the outer layer of the cored wire, and the core powder is all FeTi40, that is, the Ti content is 40 % iron alloy), and 10kg of φ12 cored wire containing B (10kg at this time is the weight of the core powder, excluding the weight of the iron sheet on the outer layer of the cored wire, and the core powder is all FeB23, that is, an iron alloy containing 23% B) After feeding the line, the chemical composition of molten steel measured acid-soluble aluminum (Als) was 0.040%, Ti was 0.06%, and B was 0.0019%. At this moment, the yield of B was 65%.

Finally, 150mm×150mm slabs were cast on a 5-machine, 5-strand billet continuous casting machine. The temperature of the tundish during continuous casting was 1530°C. The chemical components of molten steel were sampled and analyzed in the continuous casting machine as 0.23% C and 0.25% C. Si, 1.09% of Mn, 0.013% of P, 0.009% of S, 0.60% of Cr, 0.06% of Ni, 0.05% of Cu, 0.0019% of B, and 0.06% of Ti and 0.030% of Als (casting process Als burning loss 0.010%), the rest is Fe and other inevitable impurities. During molten steel casting, the 1st and 4th streams have serious variable flow (that is, the nozzle of the continuous casting machine becomes smaller), and they are all blocked after 12 minutes, and the remaining flow channels also have variable flow phenomena.

The above examples illustrate that the technology of the present invention is used to produce 25CrMnB steel. The oxygen activity of molten steel and the content of acid-soluble aluminum are effectively controlled throughout the whole process. Aluminum is not used for pre-deoxidation in the tapping process, but calcium carbide is used, and strong diffusion deoxidation is carried out in the LF furnace. , use calcium carbide to replace part of the aluminum, reduce the acid-soluble aluminum content in molten steel, and the yield of boron after adding ferroboron is above 65%, which not only ensures the role of boron in improving hardenability, but also in casting 200mm×200mm and 150mm In the process of ×150mm square billet, the phenomenon that the nozzle of the continuous casting machine becomes smaller is avoided, and the casting is smooth. Therefore, the method of the present invention is not only applicable to large-sized continuous casting machines, but also suitable for small-sized continuous casting machines below 200×200 mm, so as to ensure smooth casting of small-sized continuous casting machines.

Claims (9)

1. a converter flow process produces the method for 25CrMnB steel, is characterized in that comprising the steps: a. Add molten iron to the converter for smelting; b. The molten steel is tapped to the ladle, and calcium carbide is added to keep the oxygen activity of the molten steel below 0.0025% when tapping; c. The ladle is moved into the LF furnace for refining. Add 3.5-4.5kg of calcium carbide per ton of molten steel before refining and heating, and add 0.15-0.45kg of metal aluminum per ton of molten steel during heating. When the temperature of molten steel is heated to 1565-1585°C, stop heating and add adding aluminum to the water so that the acid-soluble aluminum content in the molten steel is 0.011-0.016% by weight, then adding titanium to make the titanium content in the molten steel 0.02-0.06% by weight, and adding boron to make the boron content in the molten steel 0.0005-0.003% by weight; d. Continuous casting after refining. 2. The method for producing 25CrMnB steel by the converter flow process according to claim 1 is characterized in that: in step a, steel scrap is also added while adding molten iron in the converter, and the weight of scrap steel is no more than 15% of the molten iron weight. 3. The method for producing 25CrMnB steel according to the converter flow process according to claim 2, characterized in that: when the molten steel composition is initially refined to C being 0.05% to 0.15% by weight percentage, P≤0.015%, and S≤0.015%, the The molten steel is tapped into the ladle. 4. The method for producing 25CrMnB steel according to the converter flow process according to claim 1 is characterized in that: in step b, the amount of calcium carbide added is based on the carbon content at the end point of the converter, and when the carbon weight percentage at the end point of the converter is below 0.10%, it is calculated as per ton 3.5-4.5kg of molten steel is input; when the weight percentage of carbon at the end of the converter is greater than 0.10% and less than 0.15%, 2.5-3.5 kg per ton of molten steel is input; when the weight percentage of carbon at the end of the converter is above 0.15%, 1.5-2.5 kg per ton of molten steel put in. 5. The method for producing 25CrMnB steel by the converter flow process according to claim 1 is characterized in that: while adding calcium carbide in step b, ferrosilicon is also added to make the silicon weight percentage content in the molten steel 0.15～0.35%, and ferromanganese is added to make the steel The manganese content in water is 0.80-1.10% by weight, the ferrochrome is added to make the chromium content in the molten steel 0.30-0.60% by weight, and the carburant is added to make the carbon content in 0.20-0.30% by weight. 6. The method for producing 25CrMnB steel according to claim 1, characterized in that: in step c, 3.8-4.2 kg of calcium carbide is added per ton of molten steel before refining and heating, and 0.2-0.4 kg of metallic aluminum is added per ton of molten steel during heating . 7. The method for producing 25CrMnB steel by the converter flow process according to claim 1 is characterized in that: the method of adding titanium in the step c is to feed the titanium-containing cored wire with a wire feeder, and the method of adding boron is to use a wire feeder The machine feeds boron-containing cored wire. 8. The method for producing 25CrMnB steel with a converter process according to claim 1, characterized in that: the temperature of the tundish of the continuous casting machine during continuous casting in step d is 1530±20°C. 9. The method for producing 25CrMnB steel according to claim 1, characterized in that the calcium carbide contains more than 70% of CaC ₂ .