A method for smelting low-carbon titanium microalloy steel with controllable MnS inclusions

Abstract

The invention provides a smelting method of low-carbon titanium microalloy steel with controllable MnS inclusions, comprising the following steps: S1, converter smelting, wherein lime blocks and sintered ore are used as slag-making materials during smelting, and the lime blocks and aluminum blocks are added along with the steel flow to slag during steel tapping; S2, post-furnace treatment, silicon-manganese alloy and ferrotitanium are added, and steel is tapped after argon blowing; S3, continuous casting, molten steel is uniformly poured into a tundish, Al powder and ferrotitanium are added near a turbulent zone of the tundish, and a strong-weak-strong cooling mode is adopted at the same time; S4, heating; S5, rolling, the continuous casting billet is subjected to rough rolling and finish rolling in sequence, and the rough rolling adopts large deformation rolling; S6, the billet is coiled after rapid cooling. The present invention strictly controls the generation and growth of MnS inclusions in steel by controlling the entire process of smelting process, continuous casting process, continuous casting billet heating and post-rolling insulation, so that the MnS inclusions in steel are distributed in smaller sizes, thereby reducing the influence of the MnS inclusions on the transverse mechanics of the steel.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for smelting low-carbon titanium microalloy steel with controllable MnS inclusions. Background Art

[0002] MnS is one of the most common non-metallic plastic inclusions in steel. Its size, shape and distribution seriously affect the performance of steel. MnS inclusions are often used to improve the cutting performance of free-cutting steel. At the same time, they can also inhibit grain growth and promote the precipitation of intragranular ferrite. In addition, by increasing ω(Mn) / ω(S) so that MnS fixes sulfur, the formation of low-melting-point compounds such as FeS at the austenite grain boundary can be reduced, thereby improving the high-temperature plasticity of steel. However, due to its good deformation ability, MnS is extended into a large-sized strip along the rolling direction during the rolling process, making the mechanical properties of the steel anisotropic, significantly reducing the transverse properties of the material; and this long strip-shaped MnS inclusion is easy to become a crack source and its expansion channel during the use of the plate, reducing the service life of the material. Therefore, it is hoped that the MnS inclusions in the steel are smaller in size, less deformed during hot working, good cutting performance of the steel, and less reduction in the transverse mechanical properties of the steel.

[0003] In addition to strictly controlling the sulfur content, the traditional method for controlling MnS inclusions in the industry is to use calcium treatment technology. However, the (Mn, Ca)S inclusions formed by the calcium treatment process are easy to adhere to the oxide surface to produce new composite brittle inclusions. Therefore, it is necessary to strictly control the Al and O content in the molten steel, and blow argon for a long time in the argon blowing station to promote the full floating of the deoxidation products, which prolongs the production time and reduces the production efficiency. At the same time, a large amount of dust will be generated when the calcium treatment process is used, which worsens the working environment of the operators. In addition, a small amount of Ti can be added to the steel, and TiN will precipitate during the continuous casting process to form nucleation particles and induce the precipitation of MnS. However, on the one hand, the Ti element is very easy to be oxidized, and the yield in steel is low; on the other hand, after TiN induces the precipitation of MnS, the MnS inclusions will continue to grow, resulting in large-sized MnS inclusions, which affect the mechanical properties of the steel.

[0004] The patent with application number 202111254550.2 and patent name "A continuous casting method for controlling the distribution of manganese sulfide inclusions in medium carbon steel in the thickness direction of continuous casting slabs" discloses an unconventional continuous casting method, namely low superheat + weak cooling + strong cooling at the end of solidification mode, which reduces the difference in MnS size in the thickness direction of continuous casting slabs, promotes the uniformity of MnS distribution in the thickness direction of continuous casting slabs, and reduces the harm caused by the uneven distribution of MnS inclusion sizes. It mainly coordinates the superheat and secondary cooling water modes of the continuous casting process to improve manganese sulfide inclusions in medium carbon steel. However, the unconventional low superheat + weak cooling + strong cooling at the end of solidification continuous casting mode is adopted. The requirement of low superheat affects the smooth pouring. The complex secondary cooling water control mode also increases the difficulty of continuous casting control. It is difficult to accurately locate the end of solidification. There are practical problems such as difficulty in combining theory with practice.

[0005] The patent with application number 201410715579.X and patent name "Method for smelting steel for yield 345MPa grade hydrogen-induced crack resistant container" has the key points of controlling aluminum and oxygen inclusions as follows: adding aluminum for strong deoxidation after the converter, using large flow argon bottom blowing to promote deoxidation reaction, LF refining to promote inclusions to float, RH no longer adjusts aluminum, RH soft blowing to promote inclusions to float, and using static method after RH treatment to promote aluminum and oxygen inclusions to float. The key points of MnS inclusion control are: two slag removal operations for molten iron pretreatment, LF deep desulfurization treatment, and RH refining using calcium treatment to fix the free sulfur element in the molten steel. The acid-resistant container steel obtained has CLR, CTR and CSR indicators of HIC resistance test all 0. However, although conventional methods such as multiple slag removal from molten iron, strong deoxidation in converters, and LF deep desulfurization processes can reduce the S content in steel, they will increase process costs, cause serious erosion of the converter lining, and the remaining sulfides in the steel will still exist in the form of stripped MnS.

[0006] The patent application number is 202211018846.9, and the patent name is "A method for controlling MnS inclusions in low-sulfur low-alloy structural steel". This invention adds Ti to the molten steel composition and reasonably configures ω(Ti) / ω(Al) to make the precipitate in the form of spherical brittle Al2O3-TiO x -MnS composite inclusions are mainly used to reduce the precipitation ratio of single MnS inclusions; at the same time, by controlling the high compression ratio rolling of MnS in the low plasticity zone, the aspect ratio of MnS is reduced, and the number of MnS inclusions with shorter lengths is increased, which effectively controls the morphology of MnS inclusions after rolling. However, due to the differences in the oxidizability of molten steel from different heats, and Ti and Al elements are both easily oxidized elements, it is difficult to control ω(Ti) / ω(Al) at a certain value.

[0007] Therefore, there is an urgent need to develop an economical method that can effectively improve the strip-type MnS inclusions in steel. Summary of the invention

[0008] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a smelting method of low-carbon titanium microalloy steel with controllable MnS inclusions, which can effectively reduce the number of MnS inclusions in the steel, reduce the level of MnS inclusions, and improve the lateral performance of the steel.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A method for smelting low-carbon titanium microalloy steel with controllable MnS inclusions comprises the following steps:

[0011] S1. Converter smelting

[0012] In converter operation, scrap steel and molten iron are added into the converter for smelting. The slag materials are lime blocks and sintered ore.

[0013] The effective ω(CaO) of the lime block 有效 ≥90%, S<0.1%, activity ≥360ml, lime blocks with a particle size of 10-30mm account for ≥90%; the basicity of the sintered ore is R2: 1.8±0.08, S in the sintered ore is <0.02%, 2.0%≤MgO≤3.0%, ω(FeO) / ω(SiO2)>1.6, and the particle size of the sintered ore is 3-5mm account for ≥80%. Specifically, the amount of lime blocks added is 40-45kg per ton of steel; the amount of sintered ore added is 10-15kg per ton of steel.

[0014] In the early stage of blowing, high lance position and high oxygen supply intensity are adopted, and medium gas supply intensity is adopted for bottom blowing. All slag materials are added at one time to make ω(FeO) / ω(SiO2)>1.5, and slag is formed quickly to avoid the formation of continuous C2S shell on the surface of lime block.

[0015] Control the endpoint composition of molten steel C: 0.06% ~ 0.08%, Si: 0.020% ~ 0.1%, P ≤ 0.030%, S ≤ 0.030%; when tapping, add lime blocks and aluminum blocks into the ladle along with the steel flow, make full use of the good molten steel dynamics to slag, promote the formation of ladle top slag, and promote ladle desulfurization. The amount of lime blocks added is 2 ~ 2.5 kg per ton of steel, and the amount of aluminum blocks added is 0.2 ~ 0.4 kg per ton of steel. When tapping, add carbon powder into the ladle to adjust the C content of molten steel: 0.15% ~ 0.20%. At the same time, strictly control the tapping time to be above 2'30" to prevent converter slag from flowing into the ladle.

[0016] S2. Post-furnace treatment

[0017] After steel is tapped, the ladle enters the argon blowing station for argon blowing. According to the final Mn content, silicon-manganese alloy is added before argon blowing, and titanium iron is added after argon blowing for 5 minutes. The steel is tapped again after argon blowing for more than 3 minutes. The Mn content is controlled to be 0.35% to 0.45%, the Ti content is 0.020% to 0.050%, the Al content is 0.020% to 0.05%, and 15≤ω(Mn) / ω(Ti)≤20; the upper steel [O] content is ≤5ppm.

[0018] The final composition of the molten steel includes the following components in weight percentage: C: 0.15% to 0.20%, Si: 0.020% to 0.1%, P≤0.030%, S≤0.030%, Mn: 0.35% to 0.45%, Ti: 0.020% to 0.050%, Al: 0.020% to 0.05%, and the rest is Fe and unavoidable inclusions. The Mn content and Ti content must also meet 15≤ω(Mn) / ω(Ti)≤20.

[0019] S3, continuous casting

[0020] The molten steel on the ladle turret is evenly poured from the ladle into the tundish. Al powder and ferrotitanium are added near the turbulent zone of the tundish to form a large number of fine oxide particles in the steel, which serve as nucleation points for MnS. Specifically, the amount of Al powder added is 0.3kg per ton of steel, and the amount of ferrotitanium added is 0.2kg per ton of steel.

[0021] With the increase of cooling rate, the average size of MnS decreases. When the cooling rate is greater than 100℃ / min, the cooling rate has little effect on the size of MnS. The secondary cooling of continuous casting adopts the strong cooling-weak cooling-strong cooling mode to prevent the precipitation of MnS in large quantities to form large-sized inclusions.

[0022] Therefore, the water volume in the secondary cooling section 1-3 adopts the strong cooling mode, and the water volume is controlled at 0.7-0.8L / kg. The water volume in the secondary cooling section 4-5 adopts the weak cooling mode to uniform the billet temperature, and the water volume is controlled at 0.5-0.6L / kg. The water volume in the secondary cooling section 6-9 adopts the strong cooling mode, and the water volume is controlled at 0.7-0.8L / kg.

[0023] S4, Heating

[0024] The continuous casting billet is sent to a step-beam heating furnace for heating. When the continuous casting billet is heated at a higher temperature, the MnS in the continuous casting billet will be spheroidized and dissolved. The dissolved MnS will precipitate again as the billet cools, and larger MnS inclusions may precipitate. Therefore, the heating time should be minimized while ensuring that the continuous casting billet is fully heated. The heating time is generally 100 to 160 minutes. The heating furnace is divided into three-stage heating, including heating stage 1, heating stage 2 and soaking stage, and the air-fuel ratio is 1:0.8 to 0.9;

[0025] Among them: the temperature of heating section 1 is controlled at 1180±30℃, the temperature of heating section 2 is controlled at 1260±15℃, the temperature of the soaking section is controlled at 1280±15℃, and the total heating time is controlled at 120-150min.

[0026] S5. Rolling

[0027] The heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, and the rough rolling and finishing rolling temperature is 1000℃~1050℃. (The relative plasticity of MnS is highest when the deformation temperature is 900℃, lowest when it is 1000℃, and lower when it is 1150℃. Therefore, controlling the deformation of MnS inclusions at 1000~1050℃ is beneficial to reducing the level of MnS inclusions.)

[0028] The rough rolling adopts large deformation rolling, with five rolling passes in total. The rolling deformations from the first to the fifth pass are 10%, 20%, 25%, and 45% respectively.

[0029] Then it enters the finishing rolling, which involves seven passes of rolling. The final rolling temperature is 800℃~900℃, and finally the strip steel of the target specification is obtained.

[0030] S6, cooling and coiling

[0031] The rolled steel billet is cooled by a rapid cooling process, with the final cooling temperature being 630±15°C; after being coiled, it is cooled again to room temperature to obtain a low-carbon titanium microalloy steel with low manganese sulfide inclusions.

[0032] The technical advancements achieved by the present invention are:

[0033] The invention discloses a method for controlling MnS inclusions in low-carbon titanium microalloy steel. The method strictly controls the generation and growth of MnS inclusions in the steel through full process control of smelting process, continuous casting process, continuous casting billet heating and post-rolling insulation, so that the MnS inclusions in the steel are smaller in size, thereby reducing the influence of the MnS inclusions on the transverse mechanics of the steel.

[0034] The present invention adjusts the composition of slag material in the converter smelting process. The slag material adopts lime blocks with high effective CaO and activity, and adds a certain amount of sintered ore. The Fe in the sintered ore is 2+ The components can react with O in molten steel to quickly form slag. The sintered ore has a certain basicity, so that ω(FeO) / ω(SiO2) in the slag is greater than 1.5, which can avoid the formation of continuous C2S shell on the surface of the lime block and affect further reaction, which is beneficial to the continuous desulfurization of molten steel.

[0035] The present invention particularly adds Al powder and ferrotitanium particles near the turbulent zone of the tundish during the process of pouring molten steel from the ladle into the tundish, so as to quickly deoxidize the molten steel. The deoxidation products are Al2O3 and TiO2, which have melting points above 2000 and 1800°C, respectively, and exist as oxide particles in the molten steel. In the turbulent zone, they have good dynamics, so that they can be quickly dispersed in the steel and serve as nucleation points of MnS. Adding Al powder and ferrotitanium particles at the same time can effectively avoid adding too much of the same element, which affects the final performance of the steel. Therefore, 0.3 kg of Al powder is added to a ton of steel, and 0.2 kg of Ti iron is added to a ton of steel.

[0036] In the molten steel composition of the present invention, the Mn content is controlled to be 0.35%-0.45%, the Ti content is 0.020%-0.050%, and 15≤ω(Mn) / ω(Ti)≤20; the addition of Mn content can enhance the mechanical strength of the steel, but excessive Mn will lead to an increase in the content of MnS inclusions. By limiting ω(Mn) / ω(Ti), the relative amounts of Mn and Ti can be controlled, so that the amount of MnS inclusions generated can be controlled.

[0037] During the continuous casting process, as the cooling rate increases, the average size of the inclusion MnS decreases; when the cooling rate is greater than 100°C / min, the cooling rate has little effect on the size of MnS. Therefore, the continuous casting process of the present invention adopts a strong cooling-weak cooling-strong cooling mode, that is, the front section of the second cooling adopts a strong cooling mode, the middle section of the second cooling adopts a weak cooling mode to ease the temperature uniformity inside and outside the billet, and the strong cooling mode is used again in the front section of the solidification end and the solidification end to reduce the center segregation of the billet, control the size of MnS, and prevent a large amount of MnS from precipitating to form large-sized inclusions. The strong cooling mode is adopted in the front section of the secondary cooling, which can make the continuous casting billet quickly form a solid billet shell, and at the same time, it can effectively reduce the size of MnS near the surface of the continuous casting billet; because there are dispersed Al2O3 and TiO2 particles in the molten steel, which act as nucleation particles to induce the precipitation of MnS, so the weak cooling mode is adopted in the middle section of the secondary cooling to make part of the MnS precipitate to form small-sized MnS inclusions, reduce its tendency to segregate to the center of the billet to form large-sized MnS inclusions, and also improve the uniformity of the billet temperature; the strong cooling mode is adopted again in the front section and the end of solidification to reduce the central segregation, control the size of MnS, and prevent a large amount of MnS from precipitating to form large-sized inclusions.

[0038] The relative plasticity of the inclusion MnS is the highest at a deformation temperature of 900℃, the lowest at 1000℃, and the lowest at 1500℃. Therefore, the MnS inclusion is controlled to deform at 1000-1050℃ to reduce the aspect ratio of MnS and improve the performance of the steel. Therefore, the rough rolling and finishing temperature is controlled at 1000-1050℃, and a large deformation rolling is used in the last pass of rough rolling, so that MnS is deformed to the maximum extent under the condition of relatively low plastic temperature, reducing the size of MnS inclusions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the metallographic structure morphology of the low-carbon titanium microalloy steel prepared in Example 1;

[0040] Figure 2 This is the metallographic structure morphology of the low-carbon titanium microalloy steel prepared in Example 2;

[0041] Figure 3 This is the metallographic structure morphology of the low carbon titanium microalloy steel prepared in Example 3;

[0042] Figure 4 This is the metallographic structure morphology of the steel of Comparative Example 1;

[0043] Figure 5 This is the metallographic structure morphology of the steel of Comparative Example 1;

[0044] Figure 6 This is the metallographic structure morphology of the steel of Comparative Example 1;

[0045] Figure 7 This is the metallographic structure morphology of the steel of Comparative Example 1;

[0046] Figure 8 This is the metallographic structure morphology of the steel of Comparative Example 1;

[0047] Fig. 9 This is the metallographic structure morphology of the steel in comparative example 1. DETAILED DESCRIPTION

[0048] The present invention will be further explained below by way of examples.

[0049] In the following examples and comparative examples, unless otherwise specified, the lime blocks used all meet the following requirements: effective ω(CaO) 有效 ≥90%, ω(S)<0.1%; activity ≥360ml; lime block 10~30mm particle size accounts for ≥90%. The sintered ore used is full of: basicity R2:1.8±0.08; ω(FeO) / ω(SiO2)>1.6, ω(S)S<0.02%, 2.0%≤ω(MgO)≤3.0%; sintered ore 3~5mm particle size accounts for ≥80%.

[0050] Example 1

[0051] A low-sulfur, low-carbon titanium microalloy steel is prepared by the following steps:

[0052] S1. Converter steelmaking

[0053] In converter smelting, 94t of molten iron and 11t of scrap steel are added to the converter for smelting, and 4242kg of lime blocks and 1035kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage, and the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200kg of lime blocks and 40kg of aluminum blocks are added with the steel flow.

[0054] S2. Post-furnace treatment

[0055] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0056]

[0057] S3, continuous casting

[0058] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.3m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. The water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg. The water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0059] S4, Heating

[0060] The temperature of heating section 1 is controlled at 1195°C, the temperature of heating section 2 is controlled at 1268°C, the temperature of the soaking section is controlled at 1283°C, and the total heating time is controlled at 125 minutes.

[0061] S5. Rolling

[0062] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1048°C and the final rolling temperature of the finish rolling being 850°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0063] S6. Cooling

[0064] The rolled steel is cooled by a rapid cooling process, and the steel is rapidly cooled to 630° C. by using multiple laminar flows, and then coiled into a coil to obtain a low-carbon hot-rolled strip steel with low manganese sulfide inclusions.

[0065] Example 2

[0066] A low-sulfur, low-carbon titanium microalloy steel is prepared by the following steps:

[0067] S1. Converter steelmaking

[0068] In converter smelting, 88 tons of molten iron and 15 tons of scrap steel are added to the converter for smelting. 4223 kg of lime blocks and 1339 kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage. At the same time, the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200 kg of lime blocks and 40 kg of aluminum blocks are added with the steel flow.

[0069] S2. Post-furnace treatment

[0070] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0071]

[0072] S3, continuous casting

[0073] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.2m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0074] S4, Heating

[0075] The temperature of heating section 1 is controlled at 1190°C, the temperature of heating section 2 is controlled at 1265°C, the temperature of the soaking section is controlled at 1283°C, and the total heating time is controlled at 128 minutes.

[0076] S5. Rolling

[0077] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1046°C and the final rolling temperature of the finish rolling being 846°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0078] S6. Cooling

[0079] The rolled steel is cooled by a rapid cooling process, and the steel is rapidly cooled to 635° C. by using multiple laminar flows, and then coiled into a coil to obtain a low-carbon hot-rolled strip steel with low manganese sulfide inclusions.

[0080] Example 3

[0081] S1. Converter steelmaking

[0082] In converter smelting, 96 tons of molten iron and 8 tons of scrap steel are added to the converter for smelting. 4472 kg of lime blocks and 1450 kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage. At the same time, the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200 kg of lime blocks and 40 kg of aluminum blocks are added with the steel flow.

[0083] S2. Post-furnace treatment

[0084] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0085]

[0086] S3, continuous casting

[0087] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.25m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0088] S4, Heating

[0089] The temperature of heating section 1 is controlled at 1193°C, the temperature of heating section 2 is controlled at 1266°C, the temperature of the soaking section is controlled at 1285°C, and the total heating time is controlled at 122 minutes.

[0090] S5. Rolling

[0091] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1047°C and the final rolling temperature of the finish rolling being 851°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0092] S6. Cooling

[0093] The rolled steel is cooled by a rapid cooling process, and the steel is rapidly cooled to 636° C. by using multiple laminar flows, and then coiled into a coil to obtain a low-carbon hot-rolled strip steel with low manganese sulfide inclusions.

[0094] Comparative Example 1

[0095] This comparative example is a comparative example of Example 1, except that the slag-making material used is lime block.

[0096] A low-sulfur, low-carbon titanium microalloy steel is prepared by the following steps:

[0097] S1. Converter steelmaking

[0098] In converter smelting, 90t of molten iron and 8t of scrap steel are added to the converter for smelting, and 4135kg of lime blocks are added at one time. The gun position is high in the early stage, the oxygen supply intensity is large, and the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200kg of lime blocks and 40kg of aluminum blocks are added with the steel flow.

[0099] S2. Post-furnace treatment

[0100] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0101]

[0102] S3, continuous casting

[0103] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added to the casting impact zone. A total of 29.4kg Al powder and 19.6kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.3m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. The water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg. The water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0104] S4, Heating

[0105] The temperature of heating section 1 is controlled at 1195°C, the temperature of heating section 2 is controlled at 1268°C, the temperature of the soaking section is controlled at 1283°C, and the total heating time is controlled at 125 minutes.

[0106] S5. Rolling

[0107] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1045°C and the final rolling temperature of the finish rolling being 848°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0108] S6. Cooling

[0109] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 637°C, and then coiled into coils.

[0110] Comparative Example 2

[0111] This comparative example is a comparative example of Example 1, except that when the molten steel is poured into the tundish, no aluminum powder and ferrotitanium particles are added.

[0112] A low-sulfur, low-carbon titanium microalloy steel is prepared by the following steps:

[0113] S1. Converter steelmaking

[0114] In converter smelting, 93t of molten iron and 12t of scrap steel are added to the converter for smelting, and 4246kg of lime blocks and 995kg of sintered ore are added at one time. The gun position is high in the early stage, the oxygen supply intensity is large, and the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200kg of lime blocks and 40kg of aluminum blocks are added with the steel flow.

[0115] S2. Post-furnace treatment

[0116] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0117]

[0118] S3, continuous casting

[0119] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. The water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. The water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg. The water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0120] S4, Heating

[0121] The temperature of heating section 1 is controlled at 1195°C, the temperature of heating section 2 is controlled at 1268°C, the temperature of the soaking section is controlled at 1283°C, and the total heating time is controlled at 125 minutes.

[0122] S5. Rolling

[0123] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1045°C and the final rolling temperature of the finish rolling being 856°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0124] S6. Cooling

[0125] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 634°C, and then coiled into coils.

[0126] Comparative Example 3

[0127] This comparative example is a comparative example of Example 2, except that: ω(Mn) / ω(Ti) in molten steel is lower than the range of 15≤ω(Mn) / ω(Ti)≤20. The specific smelting process is as follows:

[0128] S1. Converter steelmaking

[0129] In converter smelting, 89 tons of molten iron and 16 tons of scrap steel are added to the converter for smelting. 4357 kg of lime blocks and 1240 kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage. At the same time, the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200 kg of lime blocks and 40 kg of aluminum blocks are added with the steel flow.

[0130] S2. Post-furnace treatment

[0131] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0132]

[0133] It can be seen that in this comparative example, the contents of each element in the molten steel are within the limited range, but ω(Mn) / ω(Ti)=0.450 / 0.0351=12.963, <15.

[0134] S3, continuous casting

[0135] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.25m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0136] S4, Heating

[0137] The temperature of heating section 1 is controlled at 1190°C, the temperature of heating section 2 is controlled at 1265°C, the temperature of the soaking section is controlled at 1285°C, and the total heating time is controlled at 125 minutes.

[0138] S5. Rolling

[0139] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1046°C and the final rolling temperature of the finish rolling being 853°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0140] S6. Cooling

[0141] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 632°C, and then coiled into coils.

[0142] Comparative Example 4

[0143] This comparative example is a comparative example of Example 2, and the difference is that: the ω(Mn) / ω(Ti) in the molten steel is higher than the range of 15≤ω(Mn) / ω(Ti)≤20. The specific smelting process is:

[0144] S1. Converter steelmaking

[0145] In converter smelting, 91t of molten iron and 15t of scrap steel are added to the converter for smelting, and 4367kg of lime blocks and 1320kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage, and the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200kg of lime blocks and 40kg of aluminum blocks are added with the steel flow.

[0146] S2. Post-furnace treatment

[0147] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0148]

[0149] It can be seen that in this comparative example, the contents of each element in the molten steel are within the limited range, but ω(Mn) / ω(Ti)=0.450 / 0.0201=22.388,>20.

[0150] S3, continuous casting

[0151] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.25m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0152] S4, Heating

[0153] The temperature of heating section 1 is controlled at 1193°C, the temperature of heating section 2 is controlled at 1266°C, the temperature of the soaking section is controlled at 1289°C, and the total heating time is controlled at 122 minutes.

[0154] S5. Rolling

[0155] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1042°C and the final rolling temperature of the finish rolling being 851°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0156] S6. Cooling

[0157] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 627°C, and then coiled into coils.

[0158] Comparative Example 5

[0159] This comparative example is a comparative example of Example 3, and the difference is that the continuous casting cooling method is different. This comparative example adopts strong cooling-weak cooling-weak cooling. The specific smelting method is:

[0160] S1. Converter steelmaking

[0161] In converter smelting, 95t of molten iron and 9t of scrap steel are added to the converter for smelting, and 4502kg of lime blocks and 1463kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage, and the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200kg of lime blocks and 40kg of aluminum blocks are added with the steel flow.

[0162] S2. Post-furnace treatment

[0163] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0164]

[0165] S3, continuous casting

[0166] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.25m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the weak cooling mode, and the water content is controlled at 0.60L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0167] S4, Heating

[0168] The temperature of heating section 1 is controlled at 1191°C, the temperature of heating section 2 is controlled at 1268°C, the temperature of the soaking section is controlled at 1287°C, and the total heating time is controlled at 120 minutes.

[0169] S5. Rolling

[0170] The heated continuous casting billet is subjected to five passes of rough rolling and seven passes of finish rolling in sequence, with the final rolling temperature of the rough rolling being 1049°C and the final rolling temperature of the finish rolling being 855°C; the rough rolling deformations are 10%, 20%, 25%, and 45% respectively;

[0171] S6. Cooling

[0172] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 639°C, and then coiled into coils.

[0173] Comparative Example 6

[0174] This comparative example is a comparative example of Example 3, in which different steel billets of the same heat of Example 3 are rolled, and the difference is that the rough rolling deformation is different. The specific smelting process is:

[0175] S1. Converter steelmaking

[0176] In converter smelting, 96 tons of molten iron and 8 tons of scrap steel are added to the converter for smelting. 4472 kg of lime blocks and 1450 kg of sintered ore are added at one time. The gun position is high and the oxygen supply intensity is large in the early stage. At the same time, the bottom blowing adopts medium gas supply intensity. After the blowing composition is appropriate, the steel is tapped, and 200 kg of lime blocks and 40 kg of aluminum blocks are added with the steel flow.

[0177] S2. Post-furnace treatment

[0178] After steel is tapped, the ladle enters the argon blowing station. According to the Mn content of the molten steel, silicon-manganese alloy is added. After blowing argon for 5 minutes, ferrotitanium is added, and argon is blown again for more than 3 minutes to tap the steel. The final composition of the molten steel is:

[0179]

[0180] S3, continuous casting

[0181] After the ladle is hoisted to the turntable, it is transferred to the casting station to start casting. At the same time, Al powder and ferrotitanium particles are evenly added in the casting turbulent zone. A total of 30kg Al powder and 20kg ferrotitanium particles are added during the casting process. During the continuous casting process, the continuous casting speed is 1.25m / min; the water content of the second cooling section 1-3 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg, the water content of the second cooling section 4-5 adopts the weak cooling mode, and the water content is controlled at 0.55L / kg, and the water content of the second cooling section 6-9 adopts the strong cooling mode, and the water content is controlled at 0.75L / kg. Finally, a continuous casting billet with a thickness of 200mm is obtained.

[0182] S4, Heating

[0183] The temperature of heating section 1 is controlled at 1193°C, the temperature of heating section 2 is controlled at 1266°C, the temperature of the soaking section is controlled at 1285°C, and the total heating time is controlled at 122 minutes.

[0184] S5. Rolling

[0185] The heated continuous casting billet is subjected to five rough rolling passes and seven finish rolling passes in sequence, the rough rolling final rolling temperature is 1041°C, the deformation amounts of the first to fifth passes are 15%, 30%, 30%, 25% respectively; the finish rolling final rolling temperature is 853°C;

[0186] S6. Cooling

[0187] The rolled steel is cooled by a rapid cooling process, and multiple groups of laminar flows are used to rapidly cool the steel to 631°C, and then coiled into coils.

[0188] The performance of the strip steels prepared in Examples 1 to 3 and Comparative Examples 1 to 6 was measured. The test method is based on GB / T228.1-2021 Metallic Material Tensile Test Part 1: Room Temperature Test Method. The test data are as follows:

[0189]

[0190] The steel samples prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were subjected to metallographic analysis (using a Leica DMI3000M metallographic microscope), and were rated according to the relevant requirements of GB / T 10561-2023 Microscopic Examination Method for Determination of Non-Metallic Inclusion Content in Steel - Standard Rating Chart.

[0191]

[0192]

[0193] It can be seen from the above data that the steels of Examples 1 to 3 using the method of the present invention have significantly better yield strength and tensile strength than the control examples, and have high impact absorption energy; at the same time, the number of inclusions is small, the length is short, and the inclusion rating is within AT1.0.

[0194] The steels smelted by the methods of Comparative Examples 1 to 6 have different performance differences to varying degrees. Comparative Example 1 uses lime blocks as slag making materials, and no sintering ore is added during the steelmaking process, resulting in poor desulfurization effect of molten steel, and the final S content of molten steel is high, resulting in large size of MnS inclusions. Comparative Example 2 does not add aluminum powder and ferrotitanium particles to the tundish, so a large number of dispersed Al2O3 and TiO2 small particles are not formed in the molten steel during pouring as nucleation points of MnS, and the size of MnS inclusions in the steel is large, and no small point-shaped inclusions are precipitated. Comparative Example 3 Since ω(Mn) / ω(Ti) in the molten steel is lower than the range of 15≤ω(Mn) / ω(Ti)≤20, the relative amount of Ti element in the steel is relatively high, so the molten steel is very easy to form TiN particles and precipitate during solidification, and at the same time, because its morphology is angular pink particles, it is very easy to be wrapped by the precipitated MnS, forming super-long inclusions during rolling. In Comparative Example 4, since ω(Mn) / ω(Ti) in the molten steel is higher than the range of 15≤ω(Mn) / ω(Ti)≤20, the relative amount of Mn element in the steel is relatively high, so the MnS content in the molten steel is relatively high, resulting in the final MnS inclusions being too long. In Comparative Example 5, the continuous casting cooling method is strong cooling-weak cooling-weak cooling. Since the weak cooling mode is used in the latter stage of continuous casting, a large amount of MnS segregates to the center of the ingot when the continuous casting ingot solidifies, forming large-sized inclusions. In Comparative Example 6, since there is no large reduction rolling in the MnS low plasticity temperature range during the rough rolling process, the MnS inclusions are relatively large in size.

[0195] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for smelting low-carbon titanium microalloy steel with controllable MnS inclusions, characterized in that The following steps are involved: S1. Converter smelting Scrap steel and molten iron are added to the converter for smelting. During smelting, lime blocks and sintered ore are used as slag-making materials. In the early stage of blowing, high gun position and large oxygen supply intensity are used, and medium gas supply intensity is used for bottom blowing. All slag-making materials are added at one time to make ω(FeO) / ω(SiO2)>1.5; At the end of smelting, the final components of the molten steel are controlled to be C: 0.06%~0.08%, Si: 0.020%~0.1%, P≤0.030%, S≤0.030%; when tapping, lime blocks and aluminum blocks are added into the ladle along with the steel flow, and carbon powder is added into the ladle to adjust the C content of the molten steel to 0.15%~0.20%; S2. Post-furnace treatment After steel is tapped, the ladle enters the argon blowing station for argon blowing, and silicon-manganese alloy and ferro-titanium are added at the same time to adjust the Mn content in the molten steel to 0.35%-0.45%, the Ti content to 0.020%-0.050%, the Al content to 0.020%-0.05%, and 15≤ω(Mn) / ω(Ti)≤20; S3, continuous casting The molten steel on the ladle turret is evenly poured from the ladle into the tundish, and Al powder and ferrotitanium are added near the turbulent area of ​​the tundish; then the molten steel enters the continuous casting unit for continuous casting; S4, Heating The continuous casting billet is sent into a walking beam heating furnace for heating at a temperature of 1280±15℃; S5. Rolling The heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, the rough rolling final rolling temperature is 1000℃~1050℃, and then enters the finish rolling, the finish rolling final rolling temperature is 800℃~900℃; S6, cooling and coiling The rolled steel billet is cooled by a rapid cooling process, with the final cooling temperature being 630±15°C; after being coiled, it is cooled again to room temperature to obtain a low-carbon titanium microalloy steel with low manganese sulfide inclusions.

2. The smelting method of low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 1, characterized in that: In the slag-making material of step S1, the effective ω (CaO) of the lime block 有效 ≥90%, S<0.1%, activity ≥360ml, lime blocks with a particle size of 10-30mm account for ≥90%; basicity of sintered ore R2:1.8±0.08, S in sintered ore<0.02%, 2.0%≤MgO≤3.0%, ω(FeO) / ω(SiO2)>1.6, and sintered ore with a particle size of 3-5mm accounts for ≥80%.

3. The smelting method of low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 2, characterized in that: The amount of lime blocks added to the slag-making material is 40-45 kg per ton of steel, and the amount of sintered ore added is 10-15 kg per ton of steel.

4. The smelting method of low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 1, characterized in that: When the steel is discharged in step S1, the amount of lime blocks added is 2-2.5 kg per ton of steel, and the amount of aluminum blocks added is 0.2-0.4 kg per ton of steel.

5. The smelting method of low-carbon titanium microalloy steel with controllable MnS inclusions according to claim 1, characterized in that: The specific process of step S2 is as follows: after steel is tapped, the ladle enters an argon blowing station for argon blowing, and according to the final Mn content, silicon-manganese alloy is added before argon blowing, and titanium iron is added after argon blowing for 5 minutes to adjust the composition of the molten steel, and argon is blown again for more than 3 minutes to tap the steel.

6. The smelting method of low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 1, characterized in that: In step S3, the amount of Al powder added near the turbulent zone of the tundish is 0.3 kg per ton of steel, and the amount of Ti iron is 0.2 kg per ton of steel.

7. The method for smelting low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 2, characterized in that: The step S2 adopts a strong cooling-weak cooling-strong cooling mode during continuous casting cooling; wherein, the water content of the second cooling section 1-3 adopts a strong cooling mode, and the water content is controlled at 0.7-0.8L / kg, the water content of the second cooling section 4-5 adopts a weak cooling mode, and the water content is controlled at 0.5-0.6L / kg, and the water content of the second cooling section 6-9 adopts a strong cooling mode, and the water content is controlled at 0.7-0.8L / kg.

8. The method for smelting low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 1, characterized in that: The step S4 adopts a three-stage heating method, including heating stage 1, heating stage 2 and soaking stage; wherein the temperature of heating stage 1 is controlled at 1180±30°C, the temperature of heating stage 2 is controlled at 1260±15°C, the temperature of soaking stage is controlled at 1280±15°C, and the total heating time is controlled at 120 to 150 minutes.

9. The method for smelting low-carbon titanium microalloyed steel with controllable MnS inclusions according to claim 1, characterized in that: In step S5, the rough rolling adopts five rolling passes, and the finish rolling adopts seven rolling passes; the rough rolling adopts large deformation rolling, and the deformations of the first to fifth rolling passes are 10%, 20%, 25%, and 45% respectively.

Images