Low-carbon high-titanium high-chromium steel thin slab and method for producing the same

Abstract

This invention provides a low-carbon, high-titanium, high-chromium steel thin slab and its production method. The chemical composition and mass percentage of the low-carbon, high-titanium, high-chromium steel thin slab are: 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities. Compared with existing technologies, its Ti content is 0.07-0.13wt%, the inclusion size is smaller, and the original austenite grains in the slab are finer, providing favorable conditions for the stable rolling of high-strength, ultra-thin hot-rolled coils. This method, while ensuring the quality of the low-carbon, high-titanium, high-chromium steel thin slab, shortens the production process, significantly reduces costs, and improves efficiency.

Description

Technical Field

[0001] This invention relates to the field of metal casting, and more particularly to a low-carbon, high-titanium, high-chromium steel slab and its production method. Background Technology

[0002] Low-carbon high-chromium steel has good hardness and high resistance to atmospheric corrosion, and has a wide range of applications.

[0003] Existing technologies for producing low-carbon, high-chromium steel require the use of an LF+RH dual refining process, or a significant increase in the converter's final temperature, or the addition of vacuum refining furnace treatments such as VOD, in order to control the carbon and nitrogen content and inclusions in the molten steel and ensure the quality of the low-carbon, high-chromium steel slab.

[0004] These processes all involve relatively complex procedures, resulting in higher costs. Moreover, obtaining ultra-thin low-carbon, high-titanium, and high-chromium steel sheets requires even thinner slabs with well-structured microstructures, which necessitates more complex production processes and increases process costs accordingly. Summary of the Invention

[0005] The main objective of this invention is to provide a low-carbon, high-titanium, and high-chromium steel slab and its production method, aiming to solve the problems of complex production processes and high production costs of existing low-carbon and high-chromium steel products.

[0006] To achieve the above objectives, the present invention provides a low-carbon, high-titanium, high-chromium steel slab, wherein the chemical composition and mass percentage of the low-carbon, high-titanium, high-chromium steel slab are 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities.

[0007] The present invention also provides a method for producing low-carbon, high-titanium, and high-chromium steel thin slabs, comprising the steps of: pre-treating blast furnace molten iron with desulfurization to obtain molten iron; the S content in the treated molten iron is ≤0.003%.

[0008] The treated molten iron, copper, scrap steel, first low-carbon ferrochrome, and low-carbon ferromanganese are subjected to converter smelting to obtain crude molten steel; wherein the iron content of the treated molten iron in the converter is 72-78%; and the proportion of copper in the crude molten steel is 1.8-2.7 kg / t.

[0009] An alloy comprising second low-carbon ferrochrome and ferrotitanium is sequentially added to the crude molten steel, and the crude molten steel is subjected to LF refining to obtain refined molten steel; wherein, the refining temperature is 1580~1600℃; the slag system of the LF slag is CaO-Al2O3-SiO2 system, and the CaO / Al2O3 ratio is 1.5~1.8.

[0010] The refined molten steel is subjected to continuous casting to obtain the low-carbon, high-titanium, and high-chromium steel slab; wherein the liquid core reduction of sector 1 and sector 2 is a total of 10-15 mm; the chemical composition and mass percentage of the low-carbon, high-titanium, and high-chromium steel slab are 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities.

[0011] Furthermore, in the converter smelting process, when the steel output reaches 1 / 4, the first low-carbon ferrochrome and the low-carbon ferromanganese are added to the crude steel. The proportion of the first low-carbon ferrochrome added to the crude steel is 35-48 kg / t, and the proportion of the low-carbon ferromanganese added to the crude steel is 2.5-3.0 kg / t.

[0012] Furthermore, in the LF refining process, the amount of the second low-carbon ferrochrome added is 0.8 to 1.3 kg / t in the refined steel; and the amount of the ferrotitanium alloy added is 5.0 to 5.5 kg / t in the refined steel.

[0013] Furthermore, in the converter smelting process, the ladle lining temperature is ≥800℃, and there is no residue inside the ladle; the tapping process is carried out under an argon atmosphere.

[0014] Furthermore, during the tapping process, a double-stage tapping system with a sliding plate is used to reduce the amount of slag discharged from the converter.

[0015] Furthermore, in the continuous casting process, the secondary cooling adopts strong cooling control; the secondary cooling water volume is 2.2 to 2.6 L / kg.

[0016] Furthermore, prior to the LF refining process, ladle slag containing less than 1% total iron is poured into the top slag to ensure that the carbon increase of the refined steel during the LF refining process is ≤0.015% and the nitrogen increase is ≤0.003%.

[0017] Furthermore, the width of the low-carbon, high-titanium, and high-chromium steel slab is 950–1550 mm, and the thickness is 55–60 mm.

[0018] Furthermore, the melting point of the protective slag is 980–1050℃, and the viscosity is 0.09–0.1 Pa·s.

[0019] The beneficial effects achieved by this invention are as follows:

[0020] The low-carbon, high-titanium, and high-chromium steel slab provided by this invention has a Ti content of 0.07–0.13 wt% and small inclusion size, which provides favorable conditions for the stable rolling of high-strength, ultra-thin hot-rolled coils.

[0021] The production method for low-carbon, high-titanium, and high-chromium steel thin slabs provided by this invention simplifies the LF+RH double refining process, employing only the LF refining process and continuous casting on a thin slab continuous casting machine. Combined with a series of process adjustments, the carbon and nitrogen content in the molten steel is effectively controlled, resulting in steel composition that meets requirements. This refines the original grain size and TiN inclusions of the slab, improving the mechanical properties and quality of the final low-carbon, high-titanium, and high-chromium steel plate. Furthermore, the produced low-carbon, high-titanium, and high-chromium steel thin slab has a thickness of 55–60 mm, providing conditions for producing ultra-thin low-carbon, high-titanium, and high-chromium steel plates. This production method, while ensuring the quality of the low-carbon, high-titanium, and high-chromium steel thin slab, shortens the production process, significantly reduces production costs, and improves production efficiency. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 This is a low-magnification photograph of the transverse microstructure of the low-carbon, high-titanium, and high-chromium steel slab in Embodiment 1 of the present invention.

[0024] Figure 2 This is a metallographic distribution diagram of the steel plate after hot rolling of low-carbon, high-titanium, and high-chromium steel slabs in Example 1 of the present invention at 500X.

[0025] Figure 3 This is a grain structure diagram of the center of thickness of the hot-rolled coil of low-carbon, high-titanium, and high-chromium steel slab in Example 1 of the present invention at 500X.

[0026] Figure 4 This is a metallographic distribution diagram of the steel plate after hot rolling of low-carbon, high-titanium, and high-chromium steel slabs in Example 2 of the present invention at 500X.

[0027] Figure 5This is a grain structure diagram at the center of the hot-rolled coil thickness of the steel plate after hot rolling of low-carbon, high-titanium, and high-chromium steel slab in Example 2 of the present invention at 500X.

[0028] Figure 6 This is a metallographic distribution diagram of the steel plate after hot rolling of the slab in Comparative Example 1 of the present invention at 500X.

[0029] Figure 7 This is a grain structure diagram of the center of the hot-rolled coil thickness of the steel plate after hot rolling of the slab in Comparative Example 1 of the present invention at 500X.

[0030] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of this invention is for describing specific implementations and not for limiting the scope of protection of this invention.

[0033] Unless otherwise defined, all technical and scientific terms used in this invention are consistent with the prior art known to those skilled in the art and the description of this invention. This invention may also be implemented using any prior art methods, devices and materials similar to or equivalent to those described, used or made by means of methods, devices and materials in the embodiments of this invention.

[0034] When numerical ranges are given in the examples, it should be understood that, unless otherwise stated in the invention, both endpoints of each range and any value between the two endpoints may be used. Test methods in the following examples that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers. Unless otherwise specified, all materials or reagents required in the following examples are commercially available.

[0035] To address the problems of complex processes and high production costs associated with existing low-carbon, high-titanium, and high-chromium steel slabs, this invention provides a low-carbon, high-titanium, and high-chromium steel slab. The chemical composition and mass percentage of the low-carbon, high-titanium, and high-chromium steel slab are as follows: 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities.

[0036] This low-carbon, high-titanium, and high-chromium steel slab has a Ti content of 0.07–0.13 wt% and small inclusion size, which provides favorable conditions for the stable rolling of high-strength, ultra-thin hot-rolled coils.

[0037] It should be noted that to obtain low-carbon, high-titanium, and high-chromium steel slabs, the high chromium content leads to increased nitrogen content, making nitrogen control difficult. Existing technologies generally require vacuum treatment (RH, VOD, and other vacuum refining furnaces) for denitrification, which is a complex and costly process. Furthermore, while high-titanium slabs have high strength, they are prone to unstable rolled dimensions and more susceptible to Ti precipitation, affecting slab quality. Large TiN inclusions can also cause product cracking. Without vacuum treatment for nitrogen control in existing technologies, nitrogen levels frequently fluctuate during production, resulting in significant strength fluctuations for high-titanium steel, and the precipitated TiN further impacts product quality.

[0038] The present invention also provides a method for producing low-carbon, high-titanium, and high-chromium steel thin slabs, comprising the steps of: desulfurizing molten iron in a blast furnace; the sulfur content in the molten iron after treatment is ≤0.003%.

[0039] The treated molten iron, copper, scrap steel, first low-carbon ferrochrome, and low-carbon ferromanganese are smelted in a converter to obtain crude molten steel; wherein the iron content of the treated molten iron in the converter is 72-78%; and the proportion of copper in the scrap steel is 1.8-2.7 kg / t.

[0040] Specifically, the processed molten iron, copper, and scrap steel are added together to a converter for smelting to obtain refined molten steel. The refined molten steel is then poured into a ladle, and simultaneously, low-carbon ferrochrome and low-carbon ferromanganese are added to the ladle for further converter smelting. The iron content in the ladle is 72-78%. Clean scrap steel is used, and cathode copper at a concentration of 1.8-2.7 kg / t steel is added at the front end of the scrap steel trough to control the alloying of the molten iron. The clean scrap steel can be rolled coil trimmings or low-magnification samples of cast billets from within the plant.

[0041] An alloy consisting of second low-carbon ferrochrome and ferrotitanium is added sequentially to the crude steel, and the crude steel is subjected to LF refining to obtain refined steel; wherein, the refining temperature is 1580~1600℃; the slag system of the LF slag is CaO-Al2O3-SiO2 system, and the CaO / Al2O3 ratio is 1.5~1.8.

[0042] The refined molten steel is continuously cast to obtain a low-carbon, high-titanium, and high-chromium steel slab. The liquid core reduction of the first and second fan-shaped sections is a total of 10-15 mm. The chemical composition and mass percentage of the low-carbon, high-titanium, and high-chromium steel slab are as follows: 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities.

[0043] In existing technologies, only the first fan-shaped section is typically pressed down, and the reduction amount of the first fan-shaped section is 5-10 mm. In this invention, when using a thin slab continuous casting machine to continuously cast refined molten steel, the liquid core of the first and second fan-shaped sections of the thin slab continuous casting machine is pressed down by a total of 10-15 mm. This setting can improve the center segregation of the cast billet and facilitate the subsequent stable rolling of thin specifications (e.g., 1.5 mm specifications, which can improve the unstable rolling situation of this specification due to the high strength of the steel grade).

[0044] This production method simplifies the LF+RH dual refining process, employing only the LF refining step and continuous casting on a thin slab casting machine. Combined with a series of process adjustments, it effectively controls the carbon and nitrogen content in the molten steel, obtaining steel composition that meets requirements. It refines the original grain size and TiN inclusions of the slab, improving the mechanical properties and quality of the final low-carbon, high-titanium, high-chromium steel plate. Furthermore, the produced low-carbon, high-titanium, high-chromium steel thin slab has a thickness of 55–60 mm, providing conditions for producing ultra-thin low-carbon, high-titanium, high-chromium steel plates. This production method, while ensuring the quality of the low-carbon, high-titanium, high-chromium steel thin slab, shortens the production process, significantly reduces production costs, and improves production efficiency.

[0045] Furthermore, during the converter smelting process, when the steel output reaches 1 / 4, a first low-carbon ferrochrome and a low-carbon ferromanganese are added to the crude steel. The proportion of the first low-carbon ferrochrome added to the crude steel is 35-48 kg / t, and the proportion of the low-carbon ferromanganese added to the crude steel is 2.5-3.0 kg / t.

[0046] Specifically, when the steel output reaches 1 / 4, 35–48 kg / t of low-carbon ferrochrome and 2.5–3.0 kg / t of low-carbon ferromanganese are added to the molten steel. There is no need to add aluminum blocks or ferroaluminum after tapping. It should be noted that in conventional converter smelting, deoxidation is often achieved by adding aluminum after tapping. This invention, to control the nitrogen content in the molten steel, adopts a process without adding aluminum after tapping. Utilizing the surface-active element O, when the steel output reaches 1 / 4, 35–48 kg / t of low-carbon ferrochrome and 2.5–3.0 kg / t of low-carbon ferromanganese are added to the molten steel. At this point, the oxygen content in the molten steel is high, and O and FeO will accumulate on the surface of the molten steel, thus reducing the gas-liquid reaction interface, lowering the nitrogen absorption rate, and hindering nitrogen absorption by the molten steel.

[0047] Furthermore, in LF refining, the proportion of the second low-carbon ferrochrome added to the refined steel is 0.8–1.3 kg / t; the proportion of the ferrotitanium alloy added to the refined steel is 5.0–5.5 kg / t. The first and second low-carbon ferrochromes can be of the same carbon content or different carbon contents. In the embodiments of this invention, both the first and second low-carbon ferrochromes used are low-carbon ferrochromes with a carbon content of 0.15%. Adding 5.0–5.5 kg / t of ferrotitanium alloy to the steel during LF refining helps to achieve the tensile strength requirement of >800 MPa for this steel grade.

[0048] Furthermore, in the converter smelting process, the ladle lining temperature is ≥800℃, and there is no residue inside the ladle; the tapping process is carried out under an argon atmosphere.

[0049] Specifically, in the converter smelting process, a ladle with a lining temperature of ≥800℃ is used, the ladle is free of slag, the argon gas at the bottom of the ladle is turned on 2 minutes before tapping, and the argon gas is turned off immediately after the alloying materials and slag-forming materials are added.

[0050] Furthermore, a double-stage tapping system with a sliding plate is used during the tapping process to reduce the amount of slag discharged from the converter.

[0051] Furthermore, in the continuous casting process, secondary cooling is controlled by strong cooling; the secondary cooling water volume is 2.2–2.6 L / kg. Because this process has a high titanium content and omits RH refining, it is difficult to control the nitrogen content at extremely low levels. This results in the precipitation of a significant amount of titanium nitrides (Ti) during continuous casting, affecting the quality of the low-carbon, high-titanium, high-chromium steel slab. When strong cooling is used for secondary cooling, the TiN precipitates in the slab are finer, generally below 3 μm, and dispersed. Simultaneously, strong cooling helps refine the original austenite grains in the slab, improving strength and reducing the likelihood of product cracking due to large-sized TiN inclusions.

[0052] Furthermore, prior to LF refining, ladle slag containing less than 1% total iron in the slag is poured into the top slag to ensure that the carbon increase in the refined steel during the LF refining process is ≤0.015% and the nitrogen increase is ≤0.003%. Specifically, in the LF refining process, before smelting begins, ladle slag containing less than 1% total iron in the cast slag is poured into the top slag to improve the submerged arc effect during power transmission, thereby controlling the carbon increase to ≤0.015% and the nitrogen increase to ≤0.003%.

[0053] Furthermore, the slab width of the low-carbon, high-titanium, and high-chromium steel thin slab is 950–1550 mm, and the slab thickness is 55–60 mm. When the slab width is 950–1550 mm and the slab thickness is 55–60 mm, it is beneficial to stably roll out high-strength, thin-gauge hot-rolled coils of low-carbon, high-titanium, and high-chromium steel.

[0054] Furthermore, the melting point of the protective slag is 980–1050℃, and the viscosity is 0.09–0.1 Pa·s. When the melting point of the protective slag is 980–1050℃ and the viscosity is 0.09–0.1 Pa·s, the low-carbon high-chromium steel can be cast stably and at high casting speeds with very little slag entrapment.

[0055] To further illustrate the present invention, the following examples are provided:

[0056] Example 1

[0057] This embodiment provides a method for producing low-carbon, high-titanium, and high-chromium steel thin slabs. The chemical composition is: C: 0.045%, Si: 0.15%, Mn: 0.45%, Cu: 0.26%, Ti: 0.075%, Cr: 2.3%, N: 0.0055%, with the remainder being Fe and unavoidable impurities. The process involves KR desulfurization pretreatment, converter primary refining, LF refining, and continuous casting of the thin slab.

[0058] The molten iron enters the KR desulfurization pretreatment, and the exposed area of ​​the molten iron after desulfurization and slag removal is >95%, and the S content in the treated molten iron is 0.0015%.

[0059] Converter smelting: The iron-to-metal ratio is 75%, and clean scrap steel is used. Cathode copper at 1.9 kg / t steel is added to the front of the scrap trough. When 1 / 4 of the steel is tapped, low-carbon ferrochrome at 38 kg / t steel and low-carbon ferromanganese at 2.7 kg / t steel are added. No aluminum blocks or ferrosilicon are added. A ladle with a lining temperature ≥800℃ is used, and the ladle is free of slag. Argon gas is turned on at the bottom of the ladle 2 minutes before tapping, and immediately turned off after the alloying and slag-forming materials are added. During tapping, a double-stage tapping system with a sliding plate is used to reduce the amount of slag falling into the converter.

[0060] LF Refining: Before smelting begins, the ladle slag with less than 1% total iron in the cast slag is poured into the top slag to improve the submerged arc effect during power transmission, resulting in a carbon increase of 0.010% and a nitrogen increase of 0.0012% in the molten steel throughout the LF refining process. The power transmission heating temperature is raised to 1585℃, and 0.9 kg / t of low-carbon ferrochrome is added. Ferrotitanium is added last, at a rate of 5.0–5.5 kg / t of steel. No strong argon stirring is performed during the entire LF refining process. The slag system of the LF furnace slag is CaO-Al2O3-SiO2, with the CaO / Al2O3 ratio controlled at 1.6.

[0061] Casting on a thin slab continuous casting machine: a total of 10mm is applied using a fan-shaped section 1 and a fan-shaped section 2 liquid core for pressing, resulting in a slab thickness of 60mm; the melting point of the protective slag is 1000℃, and the viscosity is 0.09Pa·s. Secondary cooling is achieved using strong cooling control with a specific water volume of 2.3L / kg steel, which causes the fine and dispersed precipitation of Ti carbonitrides during solidification.

[0062] The final low-magnification microstructure of the obtained low-carbon, high-titanium, high-chromium steel slab is shown in the following image. Figure 1 As shown, the center segregation is grade C1.0.

[0063] The metallographic distribution of the hot-rolled low-carbon, high-titanium, high-chromium steel slab at 500X is shown in the figure below. Figure 2 As shown; Figure 2 The dot-shaped inclusions are TiN inclusions.

[0064] The grain structure diagram of the center thickness of the hot-rolled coil of this low-carbon, high-titanium, high-chromium steel slab at 500X is shown below. Figure 3 As shown.

[0065] Example 2

[0066] This embodiment provides a method for producing low-carbon, high-titanium, and high-chromium steel thin slabs. The chemical composition is: C: 0.055%, Si: 0.25%, Mn: 0.5%, Cu: 0.28%, Ti: 0.135%, Cr: 2.9%, N: 0.0070%, with the remainder being Fe and unavoidable impurities. The process involves KR desulfurization pretreatment, converter primary refining, LF refining, and continuous casting of the thin slab.

[0067] The molten iron enters the KR desulfurization pretreatment, and the exposed area of ​​the molten iron after desulfurization and slag removal is >95%, and the S content in the treated molten iron is 0.0015%.

[0068] Converter smelting: The iron-to-metal ratio is 73%, and clean scrap steel is used. 2.1 kg / t steel of cathode copper is added to the front of the scrap trough. When 1 / 4 of the steel is tapped, 43 kg / t steel of low-carbon ferrochrome and 3.0 kg / t steel of low-carbon ferromanganese are added. No aluminum blocks or ferrosilicon are added. A ladle with a lining temperature ≥800℃ is used, and the ladle is free of slag. Argon gas is turned on at the bottom of the ladle 2 minutes before tapping, and immediately turned off after the alloying and slag-forming materials are added. During tapping, a double-stage tapping system with a sliding plate is used to reduce the amount of slag falling into the converter.

[0069] LF Refining: Before smelting begins, the ladle slag with less than 1% total iron in the cast slag is poured into the top slag to improve the submerged arc effect during power transmission, resulting in a 0.013% increase in carbon and a 0.002% increase in nitrogen in the molten steel throughout the LF refining process. The power transmission heating temperature is raised to 1585℃, and 1.2 kg / t of low-carbon ferrochrome is added. Ferrotitanium is added last, at a rate of 5.0–5.5 kg / t of steel. No strong argon stirring is performed during the entire LF refining process. The slag system of the LF furnace slag is CaO-Al2O3-SiO2, with the CaO / Al2O3 ratio controlled at 1.5.

[0070] Casting on a thin slab continuous casting machine: a total of 15mm is applied using a fan-shaped section 1 and a fan-shaped section 2 liquid core for pressing, resulting in a slab thickness of 50mm; the melting point of the protective slag is 1020℃, and the viscosity is 0.09Pa·s. Secondary cooling is achieved using strong cooling control with a specific water volume of 2.5L / kg steel, which causes the fine and dispersed precipitation of Ti carbonitrides during solidification.

[0071] The metallographic distribution of the hot-rolled low-carbon, high-titanium, high-chromium steel slab at 500X is shown in the figure below. Figure 4 As shown; Figure 4 The dot-shaped objects are TiN inclusions in the low-carbon, high-titanium, and high-chromium steel slab.

[0072] The grain structure diagram of the hot-rolled steel sheet after hot rolling of the low-carbon, high-titanium, and high-chromium steel slab at 500X is shown below. Figure 5 As shown.

[0073] Comparative Example 1

[0074] The slab processing method provided in this comparative example has the following chemical composition: C: 0.068%, Si: 0.2%, Mn: 0.5%, Cu: 0.27%, Ti: 0.09%, Cr: 2.8%, N: 0.0095%, with the remainder being Fe and unavoidable impurities. The slab processing technology employs KR desulfurization pretreatment – ​​converter primary refining – LF refining – thin slab continuous casting.

[0075] The molten iron enters the KR desulfurization pretreatment, and the exposed area of ​​the molten iron after desulfurization and slag removal is >95%, and the S content in the treated molten iron is 0.0015%.

[0076] Converter smelting: The iron-to-metal ratio is 73%, and clean scrap steel is used. 2.1 kg / t steel of cathode copper is added to the front of the scrap trough. When 1 / 4 of the steel is tapped, 43 kg / t steel of low-carbon ferrochrome and 2.5 kg / t steel of low-carbon ferromanganese are added, along with 1.5 kg / t steel of aluminum blocks. A ladle with a lining temperature ≥800℃ is used, and the ladle is free of slag. Argon gas is turned on at the bottom of the ladle 2 minutes before tapping, and immediately turned off after the alloying and slag-forming materials are added. During tapping, a double-stage tapping system with a sliding plate is used to reduce the amount of slag carried over from the converter.

[0077] LF Refining: Before smelting begins, the total iron content in the slag not yet poured into the casting ladle is less than 1%, and the carbon increase in the molten steel is 0.025% and the nitrogen increase is 0.0045% throughout the LF refining process. The electric heating temperature is raised to 1585℃, and 1.2 kg / t of low-carbon ferrochrome and 5.0-5.5 kg / t of ferrotitanium are added as the last alloys. No strong argon stirring is performed during the entire LF refining process. The slag system of the LF slag is CaO-Al2O3-SiO2, with the CaO / Al2O3 ratio controlled at 1.5.

[0078] Casting on a thin slab continuous casting machine: A fan-shaped single-stage liquid core is used to reduce the slab thickness by 5mm, resulting in a slab thickness of 65mm; the melting point of the protective slag is 1020℃, and the viscosity is 0.09 Pa·s. Secondary cooling is controlled with a medium cooling intensity, and the specific water volume is 1.8 L / kg steel.

[0079] The metallographic distribution of the hot-rolled steel plate after the slab is shown in the figure at 500X. Figure 6 As shown; Figure 6 The lumpy material is TiN inclusion in the thin slab of this low-carbon, high-titanium, and high-chromium steel.

[0080] The grain structure diagram of the hot-rolled steel plate after hot rolling at 500X is shown below. Figure 7 As shown.

[0081] Combination Figure 6 and Figure 7 Compared with this embodiment Figures 2-5 It can be seen that the grain refinement of the final product low-carbon high-titanium high-chromium steel plate obtained in Examples 1 and 2 is significantly higher than that of the final product hot-rolled coil obtained in Comparative Example 1; and the inclusion size is smaller, significantly smaller than the inclusions in the product obtained in Comparative Example 1.

[0082] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for producing low-carbon, high-titanium, high-chromium steel thin slabs, characterized in that, Including the following steps: Desulfurization pretreatment is performed on blast furnace molten iron; the sulfur content in the molten iron after treatment is ≤0.003%. The treated molten iron, copper, scrap steel, first low-carbon ferrochrome, and low-carbon ferromanganese are subjected to converter smelting to obtain crude molten steel; wherein, the iron ratio of the treated molten iron in the converter is 72~78%; and the proportion of copper in the crude molten steel is 1.8~2.7 kg / t. An alloy comprising second low-carbon ferrochrome and ferrotitanium is sequentially added to the crude molten steel, and the crude molten steel is subjected to LF refining to obtain refined molten steel; wherein, the refining temperature is 1580~1600℃; the slag system of the LF slag is CaO-Al2O3-SiO2 system, and the CaO / Al2O3 ratio is 1.5~1.

8. The refined molten steel is continuously cast to obtain the low-carbon, high-titanium, high-chromium steel slab; wherein the liquid core reduction of sector 1 and sector 2 is a total of 10-15 mm; the chemical composition and mass percentage of the low-carbon, high-titanium, high-chromium steel slab are 0.04wt%≤C≤0.065wt%, 0.1wt%≤Si≤0.3wt%, 0.4wt%≤Mn≤0.8wt%, 0.2wt%≤Cu≤0.4wt%, 0.07wt%≤Ti≤0.15wt%, 2wt%≤Cr≤3wt%, N≤0.008wt%, with the remainder being iron and other unavoidable impurities; In the converter smelting process, when the steel output reaches 1 / 4, the first low-carbon ferrochrome and the low-carbon ferromanganese are added to the crude steel. The proportion of the first low-carbon ferrochrome added to the crude steel is 35~48 kg / t, and the proportion of the low-carbon ferromanganese added to the crude steel is 2.5~3.0 kg / t. The width of the low-carbon, high-titanium, and high-chromium steel slab is 950~1550mm; the thickness of the slab is 55~60mm.

2. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 1, characterized in that, In the LF refining process, the amount of the second low-carbon ferrochrome added is 0.8~1.3 kg / t of the refined steel; the amount of the ferrotitanium alloy added is 5.0~5.5 kg / t of the refined steel.

3. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 1, characterized in that, In the converter smelting process, the ladle lining temperature is ≥800℃ and there is no residue inside the ladle; the tapping process is carried out under an argon atmosphere.

4. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 3, characterized in that, During the tapping process, a double-stage tapping system with a sliding plate is used to reduce the amount of slag discharged from the converter.

5. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 1, characterized in that, In the continuous casting process, the secondary cooling adopts strong cooling control; the secondary cooling water volume is 2.2~2.6L / kg.

6. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 1, characterized in that, Before the LF refining process, the ladle residue with less than 1% total iron in the slag is poured into the top slag to ensure that the carbon increase of the refined steel during the LF refining process is ≤0.015% and the nitrogen increase is ≤0.003%.

7. The method for producing low-carbon, high-titanium, high-chromium steel thin slabs according to claim 1, characterized in that, The melting point of the protective slag is 980~1050℃, and the viscosity is 0.09~0.1 Pa·s.

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