Steel for automobile stabilizer bar and preparation method thereof

Abstract

The invention discloses steel for an automobile stabilizer bar and a preparation method of the steel, and relates to the technical field of steel processing. The steel for the automobile stabilizer bar is prepared through the following technological processes of converter smelting, argon blowing, LF ladle furnace, RH treatment, continuous casting, finishing, hot rolling, cooling and coiling. Wherein at least three furnaces of unsmelted steel types for the automobile stabilizer bar exist in converter smelting before the converter is newly opened; and the processes of continuous casting and hot rolling are controlled and cooperate with each other, so that the high-strength and high-toughness steel for the automobile stabilizer bar is obtained. The steel for the automobile stabilizer bar is high in strength and good in toughness, no macroscopic cracks exist on the outer side face of a sample, structural integrity can be kept when the steel is impacted by external force or deforms, fracture caused by excessive deformation can be effectively avoided, and the steel is expected to become a preferred material for manufacturing high-performance parts.

Description

Technical Field

[0001] The present invention relates to the technical field of steel processing, and in particular to steel for an automobile stabilizer bar and a preparation method thereof. Background Art

[0002] As a high-strength alloy structural steel, 34MnB5 steel is widely used in automotive parts, engineering machinery, machinery manufacturing, aerospace, military, and communications due to its excellent mechanical properties. With the development of the automotive industry, the requirements for material performance in automotive parts are constantly increasing. This is especially true for key components in the vehicle's control area, such as stabilizer bars, body structures, chassis, and suspension systems, as their performance directly affects vehicle safety and stability.

[0003] As one of the core components of the automobile suspension system, the stabilizer bar's main function is to reduce body roll and improve the vehicle's stability and handling when cornering. Therefore, the stabilizer bar needs to have high strength, high toughness, and good fatigue resistance to cope with various loads, impacts, and deformations caused by high-speed driving and complex road conditions. However, in the existing technology, the traditional 34MnB5 steel has the problem of difficult to strike a balance between strength and toughness during the preparation process. When it is used to make a stabilizer bar, the car is driving at high speed or under poor road conditions, and the resulting stabilizer bar is prone to deformation, and in severe cases, it may even cause cracking or breakage (see the schematic diagram of the automobile stabilizer bar). Figure 2 , the schematic diagram of automobile stabilizer bar fracture is shown in Figure 3 ), thus affecting driving safety and making it difficult to meet increasingly stringent market application requirements.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a steel for an automobile stabilizer bar and a preparation method thereof, so as to solve the above-mentioned technical problems.

[0006] The present invention is achieved in that: In a first aspect, an embodiment of the present invention provides a method for preparing steel for an automobile stabilizer bar, the method comprising the following process flow: Converter smelting → argon blowing → LF ladle furnace → RH treatment → continuous casting → finishing → hot rolling → cooling → coiling; Among them, the converter smelts at least three furnaces of steel for automobile stabilizer bars that have not been smelted before the new furnace is opened; In the continuous casting process, the cold-charged slabs are kept in the furnace for 150-300 minutes, the hot-charged slabs are kept in the furnace for 100-250 minutes, the furnace temperature is 1170-1240°C, and the soaking time is 22-30 minutes. In the hot rolling process, the finishing rolling inlet temperature is 1000~1080℃, and the final rolling temperature is 850~900℃.

[0007] In a second aspect, an embodiment of the present invention provides a steel for an automobile stabilizer bar prepared by the aforementioned preparation method, wherein the composition of the steel for an automobile stabilizer bar comprises, by mass percentage, C 0.335%-0.360%, Si 0.17%-0.27%, Mn 1.22%-1.36%, P ≤0.018%, S ≤0.005%, Cr 0.11%-0.17%, Ti 0.022%-0.035%, Als 0.022%-0.048%, B 0.0020%-0.0030%, N ≤0.0045%, Ca 0.0008%-0.0030%, H ≤0.00025%, Ni ≤0.20%, Cu ≤0.20%, Nb+V+Ti ≤0.22%, and the balance being Fe and unavoidable impurities.

[0008] The present invention has the following beneficial effects: The method for preparing automotive stabilizer bar steel, provided in an embodiment of the present invention, achieves high-strength and high-toughness automotive stabilizer bar steel through coordinated control of the continuous casting and hot rolling processes, optimized process parameters, and the steel's chemical composition. This stabilizer bar steel exhibits both high strength and excellent toughness, with no visible cracks on the outer surface of the specimen. It maintains structural integrity when subjected to external impact or deformation, effectively preventing fracture caused by excessive deformation. It is expected to become a preferred material for the manufacture of high-performance components. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0010] Figure 1 This is a schematic diagram of the process flow for preparing steel for automobile stabilizer bars; Figure 2 This is a schematic diagram of a car stabilizer bar; Figure 3 Schematic diagram of a broken car stabilizer bar. DETAILED DESCRIPTION

[0011] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0012] The automobile stabilizer bar is an important part of the automobile suspension system and needs to have good mechanical properties and reliability. It is crucial to protect the passenger space. To ensure the safety and stability of the vehicle and prevent excessive deformation of the components during a collision, the embodiment of the present invention obtains a steel for automobile stabilizer bar with high strength and high toughness. The process flow diagram of the preparation of automobile stabilizer bar steel is shown in FIG. Figure 1 The specific implementation methods are as follows: In a first aspect, an embodiment of the present invention provides a method for preparing steel for an automobile stabilizer bar, the method comprising the following process flow: Converter smelting → argon blowing → LF ladle furnace → RH treatment → continuous casting → finishing → hot rolling → cooling → coiling; Among them, the converter smelts at least three furnaces of steel for automobile stabilizer bars that have not been smelted before the new furnace is opened; In the continuous casting process, the cold-charged slabs are kept in the furnace for 150-300 minutes, the hot-charged slabs are kept in the furnace for 100-250 minutes, the furnace temperature is 1170-1240°C, and the soaking time is 22-30 minutes. In the hot rolling process, the finishing rolling inlet temperature is 1000~1080℃, and the final rolling temperature is 850~900℃.

[0013] It should be noted that through the coordinated control of the continuous casting and hot rolling processes, as well as the optimization of process parameters and the chemical composition of the steel, a high-strength and high-toughness steel for automotive stabilizer bars has been obtained. This steel not only has high strength but also good toughness. It can maintain structural integrity when subjected to external impact or deformation, effectively avoiding fracture caused by excessive deformation, and is expected to become the material of choice for the manufacture of high-performance components.

[0014] The raw material for converter smelting is desulfurized hot metal. Prior to the start-up of a new converter, at least three unsmelted furnaces of steel grades used for automotive stabilizer bars must have been used. This is crucial for the following reasons: A new furnace lining can rapidly wear out during initial high-temperature operation due to thermal stress or chemical erosion (e.g., chemical reactions between the molten steel and the slag). By smelting steel grades with lower lining requirements (e.g., ordinary carbon steel) in these first few furnaces, the refractory material can gradually adapt to the high temperatures and chemical reactions, reducing the risk of thermal shock cracking or localized spalling. This also avoids drastic temperature fluctuations and prevents thermal shock cracking of the lining. It also promotes the formation of a "slag glaze" (a protective film formed by the reaction of slag and refractory material) on the lining surface, reducing erosion during subsequent smelting.

[0015] Generally speaking, three furnaces can basically complete the lining stabilization and parameter debugging. In other embodiments of the present invention, the specific number of furnace bodies may be adjusted due to differences in furnace type and steel grade to ensure production compliance.

[0016] In an optional embodiment, [S] in the molten iron entering the converter is ≤0.005%; in the converter smelting process, the smelting bottom blowing is controlled by N2 / Ar switching; and the steel tapping time of the converter smelting is 4~5 min.

[0017] It's important to note that sulfur in hot metal easily combines with manganese to form MnS inclusions, which expand into banded inclusions during the hot rolling process, significantly reducing the steel's transverse impact toughness and resistance to hydrogen-induced cracking (HIC). Furthermore, high-sulfur hot metal can also cause subcutaneous porosity and hot brittleness in the ingot. Improper control of the sulfur content in hot metal can increase steel brittleness, cause surface defects in cold-rolled sheets, and clog the continuous casting nozzles. Therefore, controlling the sulfur content in the hot metal entering the converter helps reduce inclusions, improve steel strength and toughness, reduce the refining burden, and shorten the smelting cycle.

[0018] In the converter smelting process, switching between N2 and Ar in bottom blowing promotes metallurgical efficiency, cost-effectiveness, and high-end products. N2 partially dissolves nitrogen in the molten steel, providing strong stirring capacity and low cost, accelerating decarburization and reducing costs. Ar, which does not participate in the reaction, prevents nitrogen accumulation in the molten steel and promotes the floating of deoxidation products or inclusions. It is important to note that the nitrogen content must be properly controlled to avoid cold brittleness caused by high nitrogen content.

[0019] In the converter smelting process, the ladle only requires normal turnover, which can maintain the stability of the molten steel temperature and reduce heat energy loss; ensure the purity of the molten steel, optimize the production rhythm and improve equipment utilization, which is conducive to ensuring efficient, stable and low-cost production operation.

[0020] The tapping time of converter smelting needs to be reasonably adjusted according to the actual amount of material processed, temperature and smelting target composition, for example, the phosphorus content and sulfur content reach the target value, and the molten steel temperature meets the standard.

[0021] Calculated per furnace, the raw materials include 580~620kg / furnace of recarburizer, 1950~2100kg / furnace of silicon manganese and 300~450kg / furnace of aluminum iron.

[0022] Among them, the recarburizer is a substance that adds carbon element to molten steel. It is not particularly limited in the present invention and can be reasonably selected according to actual needs, such as 90 carbon (carbon content above 90%).

[0023] In an optional embodiment, the target composition of LF ladle furnace desulfurization [S] is ≤ 0.005%; In the white slag making process of LF ladle furnace, the target composition is adjusted to C: 0.340%~0.350%, Si: 0.21%~0.23%, Mn: 1.25%~1.30%, Als: 0.030%~0.040%, Cr: 0.13%~0.15%, and Ti: 0.025%~0.030%.

[0024] In the optimal embodiment, after fine-tuning, the target composition is C: 0.345%, Si: 0.22%, Mn: 1.28%, Als: 0.030%, Cr: 0.14%, Ti: 0.028%, and the temperature is 1601~1621℃.

[0025] It should be noted that in LF ladle furnaces, the ladle must be well-blown with argon from the bottom, with no noticeable cold steel at the bottom or ladle opening. Bottom-blown argon bubbles rise, creating a "pumping effect" that drives vertical circulation in the molten steel. This promotes the rise of inclusions, improving steel cleanliness, and helps break up localized concentrations of alloying elements (such as Mn) and deoxidation products (such as Al2O3), which can form "dead zones."

[0026] In order to obtain highly uniform molten steel, avoid secondary oxidation of the molten steel caused by high-flow argon blowing; ensure that the added alloy is fully dissolved, and the stirring time can be appropriately extended; in addition, regularly check the blockage of the argon pipeline air bricks to ensure the uniformity and effectiveness of argon blowing.

[0027] In an optional embodiment, the vacuum degree of the RH treatment is less than 0.27 kPa, and the time of the RH treatment is 15 to 18 minutes.

[0028] During the RH treatment, the target composition was adjusted to C: 0.340%~0.350%, Si: 0.21%~0.23%, Mn: 1.25%~1.30%, Als: 0.030%~0.040%, Cr: 0.13%~0.15%, Ti: 0.025%~0.030%, B: 0.0022%~0.0024%, Ca: 0.0014%~0.0016%, and H ≤ 2.5 ppm.

[0029] In the optimal embodiment, the target composition is fine-tuned to C: 0.345%, Si: 0.22%, Mn: 1.28%, Als: 0.030%, Cr: 0.14%, Ti: 0.028%, B: 0.0023%, Ca: 0.0015%, and H≤2.5ppm.

[0030] The time required for homogenizing the molten steel is 6 to 10 minutes between the addition of the last batch of alloy and the completion of the RH treatment.

[0031] Before the end of RH treatment, calcium line feeding treatment is carried out, and the speed of calcium line feeding is 5~8 m / s; after feeding silicon calcium line, the soft blowing time of molten steel before leaving the station is 7~10 minutes; the time from the end of refining to the start of continuous casting ladle pouring (calming time) is 10~15 minutes.

[0032] It should be noted that the uniformity of molten steel in the RH treatment process is guaranteed, which can optimize production efficiency and reduce production costs.

[0033] Soft blowing is more effective in removing inclusions from molten steel by floating them up. The molten steel surface must be kept clear during soft blowing, which helps to facilitate the floating and removal of inclusions, thereby reducing their impact on molten steel quality, improving steel purity, and promoting uniformity of composition and temperature. Soft blowing also reduces secondary oxidation, preventing atmospheric oxygen from entering the molten steel when the steel surface is exposed, which can lead to a decrease in steel purity. Soft blowing also achieves a more uniform composition and temperature within the molten steel, which helps improve its overall quality.

[0034] In an optional embodiment, the continuous casting process has the following characteristics: The number of continuous casting furnaces is ≤7, the liquidus temperature TL is 1450~1550℃, and the target temperature of the tundish molten steel is 18~25℃ higher than TL.

[0035] It should be noted that continuous casting technology eliminates the repeated mold opening and demolding processes of traditional mold casting through continuous casting and cooling, thereby significantly improving production efficiency.

[0036] In an optional embodiment, the heating furnace process has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0-3.60 mm, the furnace time of cold-charged slab is 170-240 min, the furnace time of hot-charged slab is 140-200 min, and the furnace discharge temperature is 1180-1240°C. Feature 2: When the slab rolling thickness is 3.61~10.50 mm, the cold-charged slab in the furnace time is 170~240 min, the hot-charged slab in the furnace time is 140~200 min, and the furnace outlet temperature is 1170~1230℃.

[0037] It should be noted that the setting of the slab rolling thickness is reasonably adjusted according to the actual situation. During the setting process, at least one of the following factors needs to be referred to: material strength, load requirements (such as static load, dynamic load, wind load or earthquake load), structural form, environmental factors and economy.

[0038] Cold-charged slabs in the furnace are reheated after the continuous casting slabs have cooled. They need to be heated from room temperature, which consumes a lot of gas. This is the "heat recovery" stage, which has high energy consumption and is flexible. Hot-charged slabs in the furnace utilize the waste heat of continuous casting and belong to the "heat connection" stage. It is energy-saving but has high requirements for production continuity. The temperature settings of cold-charged slabs in the furnace and hot-charged slabs in the furnace are reasonably adjusted according to the specific steel type and chemical composition.

[0039] The slab out of the furnace is the "rolling outpost" stage after the heating is completed. All process paths must pass through this node before entering hot rolling.

[0040] The liquidus temperature is the critical temperature at which molten steel changes from liquid to solid. If the temperature of the molten steel is lower than the liquidus, cold steel will form in the tundish or crystallizer, leading to nozzle blockage or surface defects on the ingot. Controlling the superheat of the molten steel is beneficial to optimizing the solidification structure, refining the grains, and reducing segregation.

[0041] Setting the target temperature of the molten steel in the tundish helps to offset temperature fluctuations of the molten steel and ensure stable continuous casting.

[0042] In addition, the continuous casting process also has at least one of the following characteristics: (1) the tundish covering agent is universal; (2) the mold protective slag uses a special protective slag for high carbon steel; (3) the mold taper is 0.95%; (4) it is not allowed to be continuously cast with other steel grades in the same tundish; when using the tundish quick-change continuous casting, in order to prevent the quick-change head billet and / or quick-change tail billet from being incompatible in composition, its fixed length shall not be less than 9.5 m.

[0043] It should be noted that tundish coating agents reduce heat loss from the molten steel in the tundish during the metallurgical process, maintaining a stable temperature. They also adsorb non-metallic inclusions (such as oxides and sulfides) in the molten steel, improving its cleanliness. They also form a physical barrier to isolate the air, preventing secondary oxidation of the molten steel from oxygen. These coating agents are general-purpose and can be selected from polymer coating agents, polyurethane coating agents, low-silicon and ultra-low-carbon coating agents, and surfactants, depending on actual needs.

[0044] Pol slag specifically designed for high-carbon steel typically has a low bulk density and excellent thermal insulation properties, effectively maintaining the temperature of the mold meniscus and reducing the formation or excessive growth of slag rings. During this process, the mold level remains stable, preventing secondary oxidation of the molten steel and the inclusion of slag in the primary shell.

[0045] As a mold protective slag, the special protective slag for high carbon steel has the following significance: (1) It has an insulating and heat-insulating effect on the molten steel, prevents the molten steel from contacting with the air, and avoids secondary oxidation; (2) It has a good ability to absorb and dissolve inclusions, and can prevent non-metallic inclusions in the molten steel from floating to the meniscus and being drawn into the solidified shell, thereby reducing inclusion defects on the surface or under the skin of the ingot; (3) The protective slag forms a layer of lubricating slag film in the crystallizer, reducing the friction between the ingot shell and the crystallizer wall, reducing the resistance to billet drawing, and preventing the solidified shell from bonding with the copper plate and causing billet leakage accidents; (4) The liquid slag film of the protective slag fills the air gap between the primary billet shell and the crystallizer, reducing thermal resistance, improving heat transfer effect, making the solidified billet shell grow evenly, and effectively reducing the generation of billet cracks.

[0046] Electromagnetic stirring is not used in the continuous casting process to avoid the appearance of multi-layer segregation bands in the cross section of the finished product.

[0047] It shall not be cast in the same tundish as other steel grades; when using tundish quick-change continuous casting, in order to prevent the composition of the quick-change head billet and / or quick-change tail billet from being incompatible, the fixed length shall not be less than 9.5m.

[0048] The automotive stabilizer bar steel produced in accordance with the present invention has high requirements for surface decarburization, requiring strict control of the slab's furnace time in the high-temperature section. During normal production, in principle, the furnace time for directly heated slabs should not exceed 200 minutes, and for cold-charged slabs, it should not exceed 240 minutes. Products with long heating times or high tapping temperatures should not be scheduled before or after this product. The air-fuel ratio in the soaking section should be appropriately adjusted (0.95-1.05), and accumulated water in the gas pipeline should be drained to minimize moisture in the gas. These measures can mitigate slab surface decarburization.

[0049] In addition, when heating the cold billet, in order to prevent the occurrence of surface crack defects, the rolling rhythm and heating speed of the slab should be appropriately reduced when the slab is at 500~800℃, or the roll changing time should be used for preheating in the middle and later stages of the preheating section.

[0050] In an optional embodiment, the slabs after continuous casting are subjected to finishing, specifically, direct loading and hot loading should be arranged, and the slabs off the line need to be slowly cooled.

[0051] In an optional embodiment, the hot rolling process has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0~2.99 mm, the finishing rolling inlet temperature is 1020~1080℃, and the final rolling temperature is 850~890℃; Feature 2: When the slab rolling thickness is 3.00-5.60 mm, the finishing rolling inlet temperature is 1020-1060°C, and the final rolling temperature is 860-900°C; Feature 3: When the slab rolling thickness is 5.61~7.50 mm, the finishing rolling entrance temperature is 1020~1060℃, and the final rolling temperature is 860~900℃; Feature 4: When the slab rolling thickness is 7.51~10.50 mm, the finishing rolling entrance temperature is 1020~1060℃, and the final rolling temperature is 850~890℃.

[0052] It should be noted that the reference factors for setting the slab rolling thickness remain the same as those mentioned above and will not be repeated here.

[0053] The finishing rolling entrance temperature refers to the surface temperature of the strip before it enters the finishing rolling unit. If the temperature is higher, the deformation resistance of the steel will be lower, the rolling force will be reduced, and the mill load and energy consumption can be reduced; but too high a temperature may cause thermal fatigue of the rolls or increase in iron oxide scale; too low a temperature will increase the rolling force, which may cause mill vibration or dimensional deviation; ensure that the temperature of the strip is uniform before finishing rolling to avoid local uneven deformation (such as edge cracks or wave defects) caused by temperature differences; and provide a basis for the subsequent final rolling temperature.

[0054] The final rolling temperature refers to the temperature of the strip when it leaves the finishing mill, which directly affects the performance of the final product. If the temperature is too high, it will aggravate the formation of iron oxide scale and cause surface defects; if the temperature is too low, it may cause rolling cracks. In addition, the final rolling temperature needs to be coordinated with the laminar cooling rate to ensure that the coiling temperature meets the standard.

[0055] In an optional embodiment, the cooling and coiling process adopts laminar cooling and slow cooling coiling, which has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0~2.99 mm, the front section cooling and coiling temperature are 620~660℃; Feature 2: When the slab rolling thickness is 3.00~5.60 mm, the rear cooling stage and the coiling temperature are 620~660℃; Feature 3: When the slab rolling thickness is 5.61~7.50 mm, the rear cooling stage and the coiling temperature are 610~650℃; Feature 4: When the slab rolling thickness is 7.51~10.50 mm, the coiling temperature is 600~640℃.

[0056] It should be noted that the reference factors for setting the slab rolling thickness remain the same as those mentioned above and will not be repeated here.

[0057] Laminar cooling is a process that uses a uniform, high-speed water flow (or a mixed flow of air and mist) to rapidly cool steel plates. It has the following benefits: rapid cooling inhibits austenite grain growth, promotes uniform precipitation of ferrite and pearlite, and improves steel strength; controls phase transformation to meet the demand for high-strength steel; uniform cooling eliminates banded segregation after hot rolling, improving weldability and formability; the oxide film formed by laminar water cooling is uniform and dense, resulting in high efficiency in subsequent pickling and reduced surface defects; and it helps shorten cooling time and improve production efficiency.

[0058] Slow-cooling coiling involves cooling rolled steel plates to room temperature at a low rate, or by holding them in a specific temperature range before slowly cooling them. This approach has the following benefits: It prevents thermal stress in high-strength steel or thick plates caused by rapid cooling, minimizing warping or cracking during subsequent processing; slow cooling also promotes dislocation realignment, restoring plastic deformation capacity, and ultimately reducing surface roughness and improving toughness during cold rolling or stamping.

[0059] In the embodiment of the present invention, through the synergistic effect of laminar cooling and slow cooling coiling, the full chain demand from ordinary structural steel to ultra-high strength steel can be covered, and the steel products can be upgraded towards high performance and high added value.

[0060] In an optional embodiment, the coiled steel coil should enter the slow cooling pit as soon as possible, and the slow cooling time should be controlled to be ≥48 hours.

[0061] In an optional embodiment, the hot rolling further includes a hot tail process having at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.00~4.80 mm, the tail lifting temperature is 8~12℃, and the tail heating length is 13~17 m; Feature 2: When the slab rolling thickness is 4.81~10.50 mm, the tail lifting temperature is 8~12℃, and the tail heating length is 8~12 m.

[0062] It should be noted that the reference factors for setting the slab rolling thickness remain the same as those mentioned above and will not be repeated here.

[0063] At the end of rolling, the tail of the strip is exposed to heat for a longer period after leaving the mill, dissipating heat quickly and typically cooling it lower than the middle section. This can lead to increased strength, decreased elongation, loose coiling, and surface scratches. A hot tail process is needed to address these issues. The "hot tail process" generally refers to the tail temperature control technology used in hot-rolled strip production. It primarily addresses uneven performance issues caused by a sudden temperature drop at the tail of the strip (the final coiling section). By adjusting parameters, fluctuations in mechanical properties or surface defects caused by a rapid temperature drop at the tail can be effectively avoided.

[0064] In an optional embodiment, descaling is normally carried out after the hot rolling furnace, and the actual operation is aimed at strictly ensuring the surface quality of the strip and the final rolling temperature. Specifically, the number of rough rolling descaling passes can be appropriately adjusted according to the finishing rolling entrance temperature.

[0065] It should be noted that phosphorus segregation can easily lead to cold brittleness. Descaling can prevent phosphorus from segregating at grain boundaries, causing low-temperature brittleness of steel, and improve the welding performance and toughness of steel.

[0066] In an optional embodiment, the crown control in the process flow has at least one of the following characteristics: Feature 1: The target convexity is 15-65 μm at a thickness of 2.0-3.60 mm; Feature 2: The target convexity is 20-70 μm at a thickness of 3.61-10.50 mm.

[0067] It should be noted that the reference factors for setting the slab rolling thickness remain the same as those mentioned above and will not be repeated here.

[0068] Crown control is a core technology in the production process, ensuring uniform thickness distribution across the cross-section of the plate and strip. It plays a crucial role in product quality, production efficiency, and cost control. Crown affects the distribution of rolling deformation, which in turn alters grain size and texture (for example, uneven crown leads to differences in mechanical properties between the edge and the center), impacting production efficiency and equipment life. Good crown control reduces the number of cold rolling passes, reduces trimming width, and improves yield. Excessive crowning can result in "tapered" or "heart-shaped" coils during coiling, impacting subsequent cold rolling. Excessive crowning can lead to insufficient edge extension during rolling, causing edge ripples or cracks.

[0069] In a second aspect, an embodiment of the present invention provides a steel for an automobile stabilizer bar prepared by the aforementioned preparation method, wherein the composition of the steel for an automobile stabilizer bar comprises, by mass percentage, C: 0.335%~0.360%, Si: 0.17%~0.27%, Mn: 1.22%~1.36%, P ≤0.018%, S ≤0.005%, Cr: 0.11%~0.17%, Ti: 0.022%~0.035%, Als: 0.022%~0.048%, B: 0.0020%~0.0030%, N: ≤0.0045%, Ca: 0.0008%~0.0030%, H: ≤0.00025%, Ni ≤0.20%, Cu ≤0.20%, Nb+V+Ti ≤0.22%, and the balance being Fe and unavoidable impurities.

[0070] It should be noted that hydrogen is a primary cause of weld cold cracking (such as delayed cracking) and can also lead to localized strength anomalies. Hydrogen atoms diffuse in steel and accumulate at grain boundaries or defects, causing a local decrease in the material's plasticity and, under stress, inducing brittle fracture. Therefore, reducing hydrogen content can significantly reduce the risk of hydrogen embrittlement and improve the steel's reliability in dynamic load or high-strength applications. In an optional embodiment of the present invention, the composition of the automotive stabilizer bar steel is effectively controlled to ≤0.00025%, which helps reduce the occurrence of cold cracking and improves the strength and stability of the resulting automotive stabilizer bar steel.

[0071] In an optional embodiment, the composition of the steel for an automobile stabilizer bar includes, by mass percentage, C 0.345%, Si 0.22%, Mn 1.28%, P ≤0.015%, S ≤0.004%, Cr 0.14%, Ti 0.028%, Als 0.030%, B 0.0023%, N ≤0.0040%, Ca 0.0015%, H ≤0.00025%, Ni ≤0.20%, Cu ≤0.20%, Nb+V+Ti ≤0.22%, and the balance being Fe and unavoidable impurities.

[0072] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0073] Example 1 This embodiment provides a method for preparing steel for an automobile stabilizer bar, which includes the following steps: 1 Smelting process 1.1 Raw material preparation (1) Desulfurization of molten iron: The molten iron entering the converter [S] is ≤ 0.005%. After desulfurization, the desulfurization slag is scraped off.

[0074] (2) Scrap steel: Ordinary scrap steel is used.

[0075] (3) Ferroalloys and material types: Based on furnaces, the raw materials are as follows: 90 carbon 500kg / furnace, silicon manganese 2000kg / furnace, aluminum iron 400kg / furnace; the alloys and materials must be clean and dry, and no mixing is allowed.

[0076] 1.2 Converter smelting (1) The first three furnaces of a newly opened furnace shall not smelt this type of steel.

[0077] (2) Ladle requirements: normal turnover ladle.

[0078] (3) Bottom blowing: The bottom blowing of smelting is controlled by switching between N2 and Ar.

[0079] (4) Steel tapping time: 4 min; steel tapping is performed with slag blocking, and the amount of slag discharged from the converter is strictly controlled.

[0080] 1.3 Argon Station Arrive at the station and add 300kg of aluminum iron for deoxidation, then hoist the package to the LF furnace.

[0081] 1.4 LF furnace (1) The ladle requires good argon blowing at the bottom; there is no obvious cold steel at the bottom and mouth of the ladle.

[0082] (2) Desulfurization in ladle furnace to target composition.

[0083] (3) Make white slag, and fine-tune the composition according to the target composition of C: 0.345%, Si: 0.22%, Mn: 1.28%, Als: 0.030%, Cr: 0.14%, Ti: 0.028% and adjust the temperature to 1601~1621℃.

[0084] 1.5 RH treatment (1) RH adopts this treatment, and the treatment time is 16 min at a vacuum degree below 0.27 kPa.

[0085] (2) RH was fine-tuned according to the target composition. The pure degassing time (the time between the addition of the last batch of alloy and the end of the treatment, simply to homogenize the molten steel) was 7 min. The alloy composition after fine-tuning was C: 0.345%, Si: 0.22%, Mn: 1.28%, Als: 0.030%, Cr: 0.14%, Ti: 0.028%, B: 0.0023%, Ca: 0.0015%, and H ≤ 2.5 ppm.

[0086] (3) Before the end of the treatment, the calcium wire is fed at a speed of 5.5 m / s. After adding alloy and feeding the silicon calcium wire, the molten steel is soft-blown (the steel surface must not be exposed) for 8 minutes before leaving the station.

[0087] (4) The time from the end of refining to the start of pouring in the continuous casting ladle is 11 minutes.

[0088] 1.6 Continuous Casting (1) The liquidus temperature TL is 1496℃, the target temperature of the tundish molten steel is TL+20℃; the control range is 1509~1523℃.

[0089] (2) Middle bag covering agent: general type.

[0090] (3) Mold protection slag: special protection slag for high carbon steel.

[0091] (4) Crystallizer taper: 0.95%.

[0092] (5) Electromagnetic stirring: not used (if used, multi-layer segregation bands may easily appear on the cross section of the finished product).

[0093] (6) The liquid level in the crystallizer should be kept stable to prevent secondary oxidation of the molten steel and the inclusion of protective slag.

[0094] 1.7 Finishing The slabs should be directly loaded and hot loaded, and the slabs off the line need to be cooled slowly.

[0095] 1.8 Hot rolling (1) The slab out-of-furnace temperature and the time the cold / hot loaded slab is in the furnace are shown in Table 1: Table 1 Slab out-of-furnace temperature and cold / hot loaded slab in-furnace time

[0096] (2) Rolling process temperature requirements are shown in Table 2: Table 2 Rolling process temperature

[0097] (3) The requirements for hot tail process are shown in Table 3 below: Table 3 Hot tail process requirements

[0098] (4) The descaling process after the furnace is normally put into operation. The actual operation is aimed at strictly ensuring the surface quality of the strip and the final rolling temperature. The operator can appropriately adjust the rough rolling descaling pass according to the finishing rolling entrance temperature.

[0099] (5) Convexity control requirements: target convexity 15~65 μm.

[0100] The finished steel product obtained in this embodiment is recorded as N34MnB5.

[0101] Example 2 This embodiment provides a method for preparing steel for automobile stabilizer bars, which differs from Example 1 only in that: 1.5 RH treatment (1) RH adopts this treatment, and the treatment time is 17 min at a vacuum degree below 0.27 kPa.

[0102] (2) RH is fine-tuned according to the target composition. The pure degassing time (the time between the addition of the last batch of alloy and the end of the treatment, simply to make the molten steel uniform) is 8 min.

[0103] (3) Before the end of the treatment, the calcium wire is fed at a speed of 5.5 m / s. After adding alloy and feeding the silicon calcium wire, the molten steel is soft-blown (the steel surface must not be exposed) for 8 minutes before leaving the station.

[0104] (4) The time from the end of refining to the start of pouring in the continuous casting ladle is 12 minutes.

[0105] 1.8 Hot rolling (1) The slab discharge temperature and the cold / hot charged slab in the furnace time are shown in Table 4: Table 4 Slab out-of-furnace temperature and cold / hot loaded slab in-furnace time

[0106] (2) Rolling process temperature requirements are shown in Table 5: Table 5 Rolling process temperature

[0107] (3) The requirements for hot tail process are shown in Table 6 below: Table 6 Hot tail process requirements

[0108] (5) Convexity control requirements: target convexity 20~70μm.

[0109] Test Example 1 In this test example, the mechanical and process performance tests were conducted on the steel strips obtained in Examples 1-2. The sampling quantity, sampling method, and test method for the inspection items required for each batch of steel strips should comply with the requirements of Table 7. The relevant test results are shown in Table 8.

[0110] Table 7 Sampling standards for samples required for testing

[0111] Table 8 Mechanical and process performance test results

[0112] The data in Table 8 demonstrates that the automotive stabilizer bar steels produced in Examples 1-2 of the present invention achieved 100% compliance with mechanical and process performance standards, meeting the yield strength requirements of 330-500 MPa, tensile strength ≥550 MPa, and elongation ≥20%. The average yield strength was 421 MPa, the average tensile strength was 699.5 MPa, and the average elongation was 31.75%. Furthermore, after the bending test, no visible cracks were observed on the outer surfaces of any of the steel strips.

[0113] According to the test items in Table 7, the test results of other items are as follows: (1) The results of decarburization are shown as follows: the depth of decarburization layer is ≤ 0.02 mm / surface.

[0114] (2) The test result of grain size is: the grain size is not less than grade 8.5.

[0115] (3) In the inclusion detection, the detection of non-metallic inclusions refers to GB / T 10561, and the results are shown in Table 9.

[0116] Table 9 Non-metallic inclusions meet the category

[0117] (4) The organization of the steel coils at delivery status was inspected in accordance with GB / T 34474.1. The test results are as follows: Among them, the metallographic structure of the steel is ferrite, troostite and pearlite, and the ferrite band width in the steel is ≤20 μm.

[0118] In summary, the automobile stabilizer bar steel provided by the embodiment of the present invention is obtained by coordinated control of continuous casting process control, hot rolling process control, optimization of process parameters and chemical composition of steel, thereby obtaining automobile stabilizer bar steel with high strength and high toughness. The mechanical and process performance compliance rate of automobile stabilizer bar steel is 100%, meeting the requirements of yield strength of 330~500 MPa, tensile strength ≥550MPa and elongation ≥20%. The automobile stabilizer bar steel not only has high strength, but also good toughness, and there are no cracks visible to the naked eye on the outer side of the sample. It can maintain the integrity of the structure when subjected to external impact or deformation, and can effectively avoid fracture caused by excessive deformation. It is expected to become the preferred material for the manufacture of high-performance components.

[0119] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing steel for automobile stabilizer bars, characterized in that: The preparation method includes the following process flow: Converter smelting → argon blowing → LF ladle furnace → RH treatment → continuous casting → finishing → hot rolling → cooling → coiling; Among them, the converter smelts at least three furnaces of steel for automobile stabilizer bars that have not been smelted before the new furnace is opened; In the continuous casting process, the furnace time of cold-charged slabs is 150-300 min, the furnace time of hot-charged slabs is 100-250 min, the furnace temperature is 1170-1240°C, and the soaking time is 22-30 min. In the hot rolling process, the finishing rolling inlet temperature is 1000~1080℃, and the final rolling temperature is 850~900℃.

2. The preparation method according to claim 1, characterized in that [S] in the molten iron entering the converter is ≤0.005%; in the converter smelting process, the bottom blowing is controlled by switching between N2 / Ar; the tapping time of the converter smelting is 4~5 minutes; Calculated per furnace, the raw materials include 580~620kg / furnace of recarburizer, 1950~2100kg / furnace of silicon manganese and 300~450kg / furnace of aluminum iron.

3. The preparation method according to claim 1, characterized in that Target composition of LF ladle furnace desulfurization [S] ≤ 0.005%; In the white slag making process of LF ladle furnace, the target composition is adjusted to C: 0.340%~0.350%, Si: 0.21%~0.23%, Mn: 1.25%~1.30%, Als: 0.030%~0.040%, Cr: 0.13%~0.15%, and Ti: 0.025%~0.030%.

4. The preparation method according to claim 1, characterized in that The vacuum degree of RH treatment was <0.27 kPa, and the time of RH treatment was 15–18 min; The target composition in the RH treatment was adjusted to C: 0.340%~0.350%, Si: 0.21%~0.23%, Mn: 1.25%~1.30%, Als: 0.030%~0.040%, Cr: 0.13%~0.15%, Ti: 0.025%~0.030%, B: 0.0022%~0.0024%, Ca: 0.0014%~0.0016%, H ≤ 2.5 ppm; The time required for homogenizing the molten steel is 6 to 10 minutes between the addition of the last batch of alloy and the completion of the RH treatment. Before the end of RH treatment, calcium line feeding treatment is carried out, and the speed of calcium line feeding is 5~8 m / s; after feeding silicon calcium line, the soft blowing time of molten steel before leaving the station is 7~10 minutes; the time from the end of refining to the start of continuous casting ladle pouring is 10~15 minutes.

5. The preparation method according to claim 1, characterized in that The continuous casting process has the following characteristics: The number of continuous casting furnaces is ≤7, the liquidus temperature TL is 1450~1550℃, and the target temperature of the tundish molten steel is 18~25℃ higher than TL.

6. The preparation method according to claim 1, characterized in that The heating furnace process has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0-3.60 mm, the furnace time of cold-charged slab is 170-240 min, the furnace time of hot-charged slab is 140-200 min, and the furnace discharge temperature is 1180-1240°C. Feature 2: When the slab rolling thickness is 3.61~10.50 mm, the cold-charged slab in the furnace time is 170~240 min, the hot-charged slab in the furnace time is 140~200 min, and the furnace outlet temperature is 1170~1230℃.

7. The preparation method according to claim 1, characterized in that The hot rolling process has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0~2.99 mm, the finishing rolling inlet temperature is 1020~1080℃, and the final rolling temperature is 850~890℃; Feature 2: When the slab rolling thickness is 3.00-5.60 mm, the finishing rolling inlet temperature is 1020-1060°C, and the final rolling temperature is 860-900°C; Feature 3: When the slab rolling thickness is 5.61~7.50 mm, the finishing rolling entrance temperature is 1020~1060℃, and the final rolling temperature is 860~900℃; Feature 4: When the slab rolling thickness is 7.51~10.50 mm, the finishing rolling entrance temperature is 1020~1060℃, and the final rolling temperature is 850~890℃.

8. The preparation method according to claim 1, characterized in that The cooling and coiling process adopts laminar cooling and slow cooling coiling, and has at least one of the following characteristics: Feature 1: When the slab rolling thickness is 2.0~2.99 mm, the front section cooling and coiling temperature are 620~660℃; Feature 2: When the slab rolling thickness is 3.00~5.60 mm, the rear cooling stage and the coiling temperature are 620~660℃; Feature 3: When the slab rolling thickness is 5.61~7.50 mm, the rear cooling stage and the coiling temperature are 610~650℃; Feature 4: When the slab rolling thickness is 7.51~10.50 mm, sparse cooling and coiling temperature are 600~640℃.

9. The preparation method according to claim 1, characterized in that The crown control in the process flow has at least one of the following characteristics: Feature 1: The target convexity is 15-65 μm at a thickness of 2.0-3.60 mm; Feature 2: The target convexity is 20-70 μm at a thickness of 3.61-10.50 mm.

10. A steel for an automobile stabilizer bar produced by the method according to any one of claims 1 to 8, characterized in that: The steel for an automobile stabilizer bar comprises, by mass percentage, C: 0.335% to 0.360%, Si: 0.17% to 0.27%, Mn: 1.22% to 1.36%, P ≤ 0.018%, S ≤ 0.005%, Cr: 0.11% to 0.17%, Ti: 0.022% to 0.035%, Al: 0.022% to 0.048%, B: 0.0020% to 0.0030%, N ≤ 0.0045%, Ca: 0.0008% to 0.0030%, H ≤ 0.00025%, and the balance being Fe and unavoidable impurities.

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