Rare-earth-containing complex-phase hot rolled steel for wheel rims and preparation method thereof

Abstract

The invention discloses a rare earth-containing complex-phase hot rolled steel for a wheel rim and a preparation method thereof, and belongs to the technical field of materials and metallurgy, the rare earth-containing complex-phase hot rolled steel comprises the following components: 0.055%-0.090% of C, 0.60%-0.90% of Si, 1.00%-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.001% of S, 0.020%-0.080% of Al, 0.040%-0.080% of Nb, 0.005%-0.020% of Ti, 0.22%-0.30% of Cr, less than or equal to 0.0045% of N, less than or equal to 0.0020% of O, 0.0100%-0.0300% of RE, RE / S is greater than 3, and the balance of iron and inevitable impurities. Wherein RE comprises La and / or Ce. The hot rolled steel produced by the method consists of ferrite, pearlite and granular bainite, and has good mechanical property, broaching property, welding property and fatigue property.

Description

Technical Field

[0001] The invention relates to the technical field of materials and metallurgy, and more specifically, to a rare earth-containing complex phase hot-rolled steel for a wheel rim and a preparation method thereof. Background Art

[0002] Continuously improving "emission reduction" has become the goal of all industries. In the automotive manufacturing industry, every 10% reduction in vehicle weight can save 3% to 7% of fuel, so it is urgent to achieve lightweighting of vehicles. Wheels are an important part of the car, and the energy-saving effect achieved by reducing the weight of wheels is 1.3 times that of other automotive parts. Therefore, the development of high-strength wheel steel can not only achieve lightweighting of vehicles, but also greatly improve the safety of vehicle driving as the strength of steel increases.

[0003] At present, the main way to improve the strength of wheel steel is to increase the proportion of martensite phase in steel through process control. Although the strength of wheel steel is improved, the hole expansion performance and welding performance of wheel steel are seriously reduced, which greatly reduces the yield rate of subsequent wheel processing and forming. Therefore, how to ensure good hole expansion performance and welding performance while improving the strength of wheel steel is the key issue currently faced in the development of high-strength wheel steel.

[0004] The Chinese patent with publication number CN109536845A discloses a hot-rolled ferrite-bainite dual-phase steel strip for wheels with a tensile strength of 590MPa and a preparation method thereof, wherein the final rolling temperature is controlled to be ≤860℃, the steel plate is cooled by a front-stage continuous cooling method, and after cooling to 400~500℃, it is coiled and ventilated to obtain a ferrite-bainite dual-phase steel with a tensile strength of 590MPa. However, the improvement of the strength of the steel plate structure in this patent is small, and the comprehensive improvement of both mechanical properties and processing properties is not achieved.

[0005] Chinese patent with publication number CN108467996A discloses a ferrite-martensite dual-phase hot-rolled pickled plate for wheel spokes and a preparation method thereof. The final rolling temperature is controlled at 830°C to 860°C, and the plate is cooled to 350°C to 400°C in a two-stage cooling mode, then coiled and ventilated to obtain a ferrite-martensite dual-phase steel. The product has a tensile strength of 600-620MPa, a yield strength of 400-420MPa, and an elongation of ≥24%. Chinese patent with publication number CN110669913A discloses a hot-rolled pickled dual-phase steel for high-strength automobile wheels and a production method thereof. The structure of the finished plate is ferrite-martensite, the tensile strength is 690-730MPa, the yield ratio is 0.55-0.59, and the elongation is ≥27%. The microstructure of the steel plates in the above two patents is a ferrite-martensite dual-phase microstructure, and there is a huge difference in the deformation capacity of the dual-phase microstructure, which has fatal defects in the processing process, especially the hole expansion performance and welding performance; the wheel production process often includes rigorous cold deformation processes such as drilling, hole expansion, and flanging, which have very high requirements for hole expansion performance; at the same time, the proportion of martensite in ferrite-martensite dual-phase steel is relatively high. After flash welding, martensite phase tempering softening is likely to occur in the heat-affected zone, seriously affecting the performance of the steel.

[0006] The Chinese patent with publication number CN107400824A discloses a high-strength automobile wheel steel with excellent extended flangeability and its production method. First, the metallographic structure of the patented steel is ferrite + bainite + a small amount of pearlite, in which the bainite type is lamellar bainite. Gong Shuai et al. showed in the study "The Effect of Microstructure on Cleavage Fracture Stress of High-speed Wheel Steel" in the Journal of Engineering Science that lamellar bainite is more likely to cause stress concentration than granular bainite, resulting in a higher crack propagation rate in lamellar bainite than in granular bainite; secondly, the amount of rare earth added in the patented steel plate is RE / S=1.8~2.2. According to Yu Zongsen's research in the Journal of Materials Research "New Developments in the Application of Rare Earths in Steel", when RE / S=1, 50% of MnS is denatured; when RE / S>1.5, MnS begins to disappear, and rare earth sulfides and rare earth oxysulfides such as CeS, La2O2S, and Ce2O2S are formed; when RE / S=3, rare earths can basically convert all sulfides into RE2S3; and when RE / S>3, the sulfide morphology can be thoroughly controlled. Therefore, the amount of rare earth added to the patent cannot fully deteriorate the inclusions in the steel, resulting in less rare earth that can be dissolved into the steel, and the microalloying effect of the rare earth is difficult to play; thirdly, the tensile strength of the patented steel is 590MPa, the hole expansion rate is more than 140%, and the bench bending fatigue life reaches more than 600,000 times, which does not meet current usage requirements. Summary of the invention

[0007] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a rare earth-containing complex phase hot-rolled steel for wheel rims and a preparation method thereof. Based on the C-Si-Mn steel composition, a quantitative RE element is added to ensure that it plays the role of metamorphic inclusions and microalloying; the controlled rolling and cooling temperature and the coiling temperature are designed to ensure the formation of a ferrite-pearlite-granular bainite complex phase structure; at the same time, a small amount of Nb element is added, and the strength of the steel plate is improved by utilizing the precipitation of its carbonitride, so as to prepare a rare earth-containing complex phase hot-rolled steel for wheel rims and a production method thereof that have good mechanical properties, hole expansion properties, welding properties and fatigue properties, and meet the performance requirements required for subsequent hole expansion and welding processes of the steel plate by the wheel manufacturer.

[0008] To achieve the above object, the technical solution of the present invention is as follows: A rare earth-containing complex phase hot-rolled steel for a wheel rim, comprising the following components in weight percentage: C: 0.055%-0.090%, Si: 0.60%-0.90%, Mn: 1.00%-1.60%, P≤0.010%, S≤0.001%, Al: 0.020%-0.080%, Nb: 0.040%-0.080%, Ti: 0.005%-0.020%, Cr: 0.22%-0.30%, N≤0.0045%, O≤0.0020%, RE: 0.0100-0.0300%, RE / S>3, and the balance is iron and unavoidable impurities; wherein RE comprises La and / or Ce.

[0009] The present invention also discloses a method for preparing the rare earth-containing complex phase hot-rolled steel for wheel rims as described above, comprising the following steps: molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling, cooling and coiling; In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment; During the RH refining, the molten steel treated by the LF refining is hoisted into a RH vacuum furnace for refining; In the continuous casting, the molten steel after the RH refining treatment is continuously cast to obtain a continuous casting billet; During the rolling, the continuous casting billet is sent to a heating furnace and heated to 1200°C-1280°C, and kept warm for 2h-3h; the rolling start temperature is ≥1120°C, two-stage controlled rolling is adopted, the final rolling temperature is 860°C-890°C, and the billet size after rolling is a plate with a thickness of ≤6mm; During the cooling, the rolled slab is cooled by intermittent cooling; The coiling temperature is 515°C to 555°C.

[0010] Implementing the embodiments of the present invention will have the following beneficial effects: (1) The structure of the steel plate of the present invention is "ferrite-pearlite-granular bainite". Compared with the existing "ferrite-martensite" steel and "ferrite-bainite" steel, the composite structure of the steel plate of the present invention has the advantages of both. It not only has higher mechanical properties, but also has good hole expansion performance and welding performance.

[0011] (2) After rigorous calculation and testing, the present invention adds a certain amount of RE element, which modifies inclusions while exerting its microalloying effect, refines the grain size, prolongs the phase transformation incubation period of bainite, increases the decomposition temperature of martensite, and improves the precipitation amount and dispersion degree of Nb(C,N), and finally prepares a rare earth-containing complex phase hot-rolled steel for wheel rims that takes into account both mechanical properties and processing properties.

[0012] In summary, the present invention, through the combined effects of "strictly controlling the final rolling temperature and coiling temperature", "RE element modification inclusion and microalloying", and "Nb (C, N) precipitation strengthening", produces a rare earth-containing complex phase hot-rolled steel for wheel rims, the metallographic structure of which consists of ferrite-pearlite-granular bainite, has a tensile strength of 690MPa-750MPa, a yield strength of ≥500MPa, an elongation of ≥25%, a hole expansion rate λ≥180%, and a dynamic radial rolling fatigue life of a stand after the steel plate is formed into a wheel of more than 2 million times, with stable fatigue performance, so that both the mechanical properties and processing properties of the wheel steel are taken into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 (a), (b), (c), and (d) are electron microscope images of the microstructures of the steel plates prepared in Comparative Example 1, Example 1, Example 2, and Example 3, respectively. DETAILED DESCRIPTION

[0014] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0015] 1. Chemical composition and mechanical properties The invention discloses a rare earth-containing complex phase hot-rolled steel for a wheel rim, comprising the following components in weight percentage: C: 0.055%-0.090%, Si: 0.60%-0.90%, Mn: 1.00%-1.60%, P≤0.010%, S≤0.001%, Al: 0.020%-0.080%, Nb: 0.040%-0.080%, Ti: 0.005%-0.020%, Cr: 0.22%-0.30%, N≤0.0045%, O≤0.0020%, RE: 0.0100-0.0300%, RE / S>3, and the balance is iron and unavoidable impurities; wherein RE comprises La and / or Ce.

[0016] Specifically, the mechanism of action of each alloy component in the rare earth-containing complex phase hot-rolled steel of the present invention is as follows: C: Carbon is an important strengthening element of steel, which mainly improves strength and hardness by forming iron-carbon solid solution and carbide. In wheel rim steel, an appropriate amount of carbon content helps to improve strength and wear resistance, and enhance fatigue performance. Therefore, the present invention controls the C content to 0.055%~0.090%; if it is lower than 0.055%, the strength and hardness of the steel are insufficient, which may cause the rim to deform or wear too quickly during use; if it is higher than 0.090%, the carbon content is too high, which will lead to reduced toughness, poor welding performance, easy brittle fracture, and increased cold cracking tendency.

[0017] Si: Silicon mainly acts as a deoxidizer, which can improve the strength and hardness of steel, and has a certain improvement effect on the stability and corrosion resistance of the organization. At the same time, silicon can reduce the thickness of the oxide scale of steel during hot rolling. Therefore, the present invention controls the Si content to be 0.60% to 0.90%. If it is lower than 0.60%: insufficient deoxidation will lead to an increase in inclusions in the steel, reducing the fatigue resistance and surface quality of the steel. If it is higher than 0.90%: excessive silicon content will cause the plasticity and toughness of the steel to decrease, making the cold working performance of the material worse and increasing the risk of fracture.

[0018] Mn: Manganese is an important strengthening element that can improve the hardenability and hardness of steel, and help improve the plasticity and toughness of steel. In addition, manganese can also effectively deoxidize and reduce the formation of harmful inclusions. Therefore, the present invention controls the Mn content to be 1.00%~1.60%. If it is lower than 1.00%: insufficient manganese will lead to insufficient strength and insufficient hardenability, affecting the comprehensive mechanical properties of the material. If it is higher than 1.60%: excessive manganese content is likely to cause carbide segregation, reduce the uniformity of the material, and at the same time make the welding performance worse and easily form hot cracks.

[0019] P: Phosphorus is a harmful element in steel, which will increase the cold brittleness of steel and segregate at the grain boundary, reducing the toughness of steel. Therefore, the present invention controls P≤0.010%. If it exceeds 0.010%, phosphorus segregation will cause brittle fracture of steel in low temperature environment, and will reduce fatigue performance, affecting the long-term service life of the rim.

[0020] S: Sulfur is a harmful impurity in steel, which will form sulfide inclusions, resulting in decreased plasticity and toughness of the steel and causing hot brittleness. Therefore, this application controls S≤0.001%. If it exceeds 0.001%: excessive sulfur content will lead to an increase in inclusions, reduce the fatigue performance of the steel, and affect the surface quality during hot rolling.

[0021] Al: Aluminum, as a strong deoxidizer, can effectively reduce the oxygen content in steel and reduce inclusions. At the same time, aluminum can refine the grains and improve the toughness and fatigue performance of steel. Therefore, the present invention controls Al to 0.020%~0.080%. If it is lower than 0.020%: the deoxidation effect is insufficient, resulting in an increase in inclusions in the steel and reduced fatigue strength. If it is higher than 0.080%: excessive aluminum content will form a large amount of AlN inclusions, resulting in a decrease in the toughness and plasticity of the steel at high temperatures.

[0022] Nb: Niobium can refine grains, improve the organizational structure of steel, and effectively improve strength, toughness and wear resistance. Niobium can also combine with carbon and nitrogen to form stable carbonitrides to prevent grain growth. Therefore, the present invention controls the Nb content to 0.040%~0.080%. If it is lower than 0.040%: the grain refinement effect is not obvious, resulting in insufficient strength and toughness of the steel. If it is higher than 0.080%: too much niobium will cause excessive precipitation of carbonitrides, thereby reducing the plasticity of the steel and may cause crack formation during hot rolling.

[0023] Ti: Titanium can form stable TiN inclusions with nitrogen, which plays a role in refining grains. At the same time, titanium can also effectively reduce the aging sensitivity of steel. Therefore, the present invention controls the Ti content to 0.005%~0.020%. If it is lower than 0.005%, the grains cannot be effectively refined, and the strength and toughness of the material are low. If it is higher than 0.020%, the titanium content is too high, which will lead to an increase in TiN inclusions, thereby reducing the plasticity and toughness of the steel.

[0024] Cr: Chromium can improve the corrosion resistance, wear resistance and strength of steel, and improve the hardenability of steel. Therefore, the present invention controls the Cr content to 0.22%~0.30%. If it is lower than 0.22%, the wear resistance and corrosion resistance of steel cannot be significantly improved. If it is higher than 0.30%, the chromium content is too high, which will reduce the plasticity of steel and make the material more brittle.

[0025] N: Nitrogen is a strengthening element, but too much nitrogen easily forms nitride inclusions, resulting in reduced toughness of the steel. Therefore, the present invention controls N≤0.0045%. If it exceeds 0.0045%, the nitrogen content will form brittle nitride inclusions, reducing the plasticity and toughness of the steel.

[0026] O: Oxygen is a harmful impurity that will form oxide inclusions and affect the mechanical properties of steel. Therefore, the present invention controls the O content to be ≤ 0.0020%. If it exceeds 0.0020%, the excessively high oxygen content will lead to an increase in inclusions, affecting the fatigue performance and surface quality of the steel.

[0027] RE: Rare earth elements La and Ce have the function of purifying inclusions in steel, changing the morphology of inclusions, and refining grains, thereby significantly improving the fatigue resistance and toughness of steel. Therefore, the present invention controls the Cr content to be 0.0100~0.0300%. If it is lower than 0.0100%, the purification effect is not obvious, and the morphology of inclusions cannot be effectively improved. If it is higher than 0.0300%, too much rare earth elements can easily cause the precipitation of rare earth inclusions, resulting in a decrease in the plasticity and toughness of steel.

[0028] Because rare earth has a strong affinity with O and S, rare earth can transform large-sized, angular Al2O3 brittle inclusions in steel into softer ReAlO3 inclusions, and transform long strips and blocky MnS plastic inclusions into rare earth oxysulfide inclusions. Rare earth inclusions are dispersed in the molten steel in the form of small spheres or spindles, thereby improving the shape, size and number of the original inclusions in the steel, making them less likely to aggregate and grow. In addition, the thermal expansion coefficient of rare earth inclusions is similar to that of steel, which can avoid steel During the cooling of hot working, large additional stress is generated around the inclusions, which reduces the splitting effect of the inclusions on the matrix and is beneficial to improving the fatigue resistance of the steel. Studies have shown that only when the inclusions in the steel are completely metamorphosed, the rare earth solid solution increases with the increase of the rare earth addition amount. However, if the rare earth addition amount is too much, the improvement effect of the steel plate performance will gradually weaken. This is because the excessive rare earth addition leads to an increase in the precipitation amount and size of intergranular compounds and rare earth inclusions, which deteriorates the performance of the steel plate. In addition, in addition to the role of metamorphosed inclusions, the rare earth elements in the wheel steel of the present invention also have a certain microalloying effect. The microalloying effect of rare earth is believed to be due to the segregation of rare earth atoms on the grain boundaries, which interact with other elements, causing changes in the grain boundary structure, chemical composition and energy, and affecting the diffusion of other elements and the nucleation and growth of new phases, refining the grains and ultimately improving the steel structure and performance changes. During the bainite phase transformation, rare earth significantly increases the initial bainite phase transformation rate by refining austenite grains, and rare earth segregates at grain boundaries, slowing down the later bainite phase transformation rate, prolonging the bainite phase transformation incubation period, and making the temperature control range of the controlled rolling and controlled cooling process wider; at the same time, rare earth has the effect of aggravating the segregation of carbides in the bainite structure, and the bainite morphology gradually changes from feathery to granular with the increase of rare earth content, that is to say, rare earth promotes the organizational transformation of granular bainite, and granular bainite is a strong and tough matching phase. The increase in the content of this organization reduces the strength difference between each phase organization, and the soft and hard phases can be more coordinated during the deformation process, reducing the stress concentration problem caused by plastic deformation at the interface between the two phases, and its dispersion precipitation is conducive to the improvement of steel performance. In short, rare earth plays a vital role in the generation of complex phase organization. Therefore, the present invention has done a lot of calculations and experiments on the amount of rare earth addition, and further, controls RE / S>3, ensuring that rare earth can still effectively play a microalloying role after the metamorphic inclusions.

[0029] In a specific embodiment, the metallographic structure of the rare earth-containing complex phase hot-rolled steel is a three-phase composite of ferrite-pearlite-granular bainite.

[0030] In a specific embodiment, the tensile strength of the rare earth-containing complex phase hot-rolled steel is 690MPa-750MPa, the yield strength is ≥500MPa, the elongation is ≥25%, and the hole expansion ratio λ is ≥180%.

[0031] Specifically, in the structure of steel, the ferrite phase is a soft phase, which ensures the plasticity of wheel steel; pearlite reduces the performance difference between different microstructures, and its strength is higher than ferrite but lower than bainite. This structure not only makes the wheel steel have higher strength, but also makes the steel plate have good hole expansion and welding performance; the bainite phase improves the strength of the steel plate, and according to research, fatigue cracks cannot pass through bainite, and are forced to change the crack propagation path, so that the crack propagation energy is increased, the crack propagation is delayed, and the fatigue resistance of the steel is improved. And the granular bainite structure has higher fatigue strength than the equal strength lamellar bainite structure; 2. Production technology The present invention also discloses a method for preparing rare earth-containing complex phase hot-rolled steel for wheel rims as in any embodiment of the present invention, comprising the following steps: molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling, cooling and coiling.

[0032] Further, the method specifically includes the following steps: S1. In the pretreatment of molten iron, the molten iron is pretreated and desulfurized by the KR (Kambara Reactor) method or the injection method, and the molten iron after the desulfurization pretreatment is slag-scraped to ensure that the mass fraction of sulfur in the molten iron is ≤0.0020%.

[0033] S2. During converter smelting, the molten iron is decarburized, desiliconized and desulfurized by top and bottom combined blowing converter. During the steel tapping process, 4kg / t-steel to 8kg / t-steel of lime and 1kg / t-steel to 3kg / t-steel of pre-melted refined slag are added to the first molten steel.

[0034] In S3 and LF refining, the molten steel discharged from the converter is sent to the LF furnace for refining.

[0035] In a specific embodiment, during LF refining, the mass fraction of total oxygen in the molten steel is ≤0.0015%, and the mass fraction of sulfur is ≤0.0010% when the LF leaves the station.

[0036] In S4 and RH refining, the molten steel treated by LF refining is hoisted into the RH vacuum furnace for refining.

[0037] In a specific embodiment, in RH refining, rare earth iron alloy is added through a silo for rare earth treatment after vacuum treatment for 10 min to 20 min, and the static stirring time is ≥15 min.

[0038] In a specific embodiment, the mass content of the rare earth element in the rare earth iron alloy is 10% to 50%.

[0039] In a specific embodiment, the rare earth element in the rare earth iron alloy is one or both of lanthanum and cerium.

[0040] S5. During continuous casting, the molten steel after RH refining treatment is continuously cast to obtain a continuous casting ingot.

[0041] In a specific embodiment, during continuous casting, the temperature of the molten steel in the tundish is 1545° C. to 1585° C., and argon sealing is used during the continuous casting process.

[0042] S6. During rolling, the continuous casting billet is sent to a heating furnace and heated to 1200℃~1280℃, and kept warm for 2h~3h; the rolling start temperature is ≥1120℃, two-stage controlled rolling is adopted, the final rolling temperature is 860℃~890℃, and the billet size after rolling is a plate with a thickness of ≤6mm.

[0043] S7. During cooling, the rolled billet is cooled by intermittent cooling.

[0044] S8, coiling, the coiling temperature is 515℃~555℃.

[0045] The following are specific embodiments Example 1 In this embodiment, the alloy composition of the rare earth-containing "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims is, by weight percentage, C: 0.064%, Si: 0.76%, Mn: 1.46%, P: 0.0009%, S: 0.0008%, Al: 0.046%, Nb: 0.051%, Ti: 0.016%, Cr: 0.26%, N: 0.0031%, O: 0.0009%, Ce: 0.011%, and the remainder is iron and unavoidable impurities.

[0046] In this embodiment, the production method of the "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims includes the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → rolling → controlled cooling → coiling. Specifically, the following steps are included: 1) Hot metal pretreatment: The hot metal is pretreated and desulfurized by the KR (Kambara Reactor) method or the injection method. The hot metal after desulfurization pretreatment is slag-scraped to ensure that the mass fraction of sulfur in the hot metal is ≤0.0020%.

[0047] 2) Converter smelting: The molten iron is decarburized, desiliconized and desulfurized through a top and bottom double-blown converter. During the steelmaking process, 5.3 kg / t of lime and 2.6 kg / t of pre-melted refined slag are added to the first molten steel.

[0048] 3) LF refining is carried out with deep deoxidation and desulfurization. When LF leaves the station, the mass fraction of total oxygen in the molten steel is 0.0011%, and the mass fraction of sulfur is 0.0009%.

[0049] 4) After RH refining is vacuum treated for 17 minutes, rare earth iron alloy is added through the silo for rare earth treatment. The rare earth-iron alloy is ferrocerium alloy, in which the mass fraction of rare earth is 20%, and the static stirring time is 16 minutes.

[0050] 5) During continuous casting, the temperature of the molten steel in the tundish is 1568°C. The argon seal is strengthened during the continuous casting process to prevent secondary oxidation and ensure the cleanliness of the molten steel.

[0051] 6) Rolling: The continuous casting ingot is sent to a heating furnace and heated to 1280°C and kept warm for 2 hours; the starting rolling temperature is 1133°C, two-stage controlled rolling is adopted, the final rolling temperature is 871°C, and the size of the ingot after rolling is a plate with a thickness of 3 mm.

[0052] 7) The steel plate is cooled to the coiling temperature by intermittent cooling and then coiled. The coiling temperature is 529°C.

[0053] Example 2 In this embodiment, the alloy composition of the rare earth-containing "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims is, by weight percentage, C: 0.076%, Si: 0.87%, Mn: 1.19%, P: 0.0008%, S: 0.0009%, Al: 0.064%, Nb: 0.061%, Ti: 0.009%, Cr: 0.24%, N: 0.0040%, O: 0.0008%, La: 0.019%, and the remainder is iron and unavoidable impurities.

[0054] In this embodiment, the production method of the "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims includes the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → rolling → controlled cooling → coiling. Specifically, the following steps are included: 1) Hot metal pretreatment: The hot metal is pretreated and desulfurized by the KR (Kambara Reactor) method or the injection method. The hot metal after desulfurization pretreatment is slag-scraped to ensure that the mass fraction of sulfur in the hot metal is ≤0.0020%.

[0055] 2) Converter smelting: The molten iron is decarburized, desiliconized and desulfurized through a top and bottom double-blown converter. During the steelmaking process, 6.1 kg / t of lime and 2.4 kg / t of pre-melted refined slag are added to the first molten steel.

[0056] 3) LF refining carries out deep deoxidation and desulfurization. When LF leaves the station, the mass fraction of total oxygen in the molten steel is 0.0013%, and the mass fraction of sulfur is 0.0009%.

[0057] 4) After RH refining is vacuum treated for 18 minutes, rare earth iron alloy is added through the silo for rare earth treatment. The rare earth-iron alloy is lanthanum iron alloy, in which the mass fraction of rare earth is 40%, and the static stirring time is 16 minutes.

[0058] 5) During continuous casting, the temperature of the molten steel in the tundish is 1549°C. The argon seal is strengthened during the continuous casting process to prevent secondary oxidation and ensure the cleanliness of the molten steel.

[0059] 6) Rolling: The continuous casting ingot is sent to a heating furnace and heated to 1250°C, and kept warm for 2.5 hours; the starting rolling temperature is 1122°C, and two-stage controlled rolling is adopted. The final rolling temperature is 886°C, and the size of the ingot after rolling is a plate with a thickness of 6 mm.

[0060] 7) The steel plate is cooled to the coiling temperature by intermittent cooling and then coiled. The coiling temperature is 541°C.

[0061] Example 3 In this embodiment, the alloy composition of the rare earth-containing "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rim is, by weight percentage, C: 0.084%, Si: 0.69%, Mn: 1.31%, P: 0.0008%, S: 0.0008%, Al: 0.076%, Nb: 0.079%, Ti: 0.013%, Cr: 0.25%, N: 0.0029%, O: 0.0009%, La+Ce: 0.026%, of which La: 0.0078%, Ce: 0.0182%, and the remainder is iron and unavoidable impurities.

[0062] In this embodiment, the production method of the "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims includes the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → rolling → controlled cooling → coiling. Specifically, the following steps are included: 1) Hot metal pretreatment: The hot metal is pretreated and desulfurized by the KR (Kambara Reactor) method or the injection method. The hot metal after desulfurization pretreatment is slag-scraped to ensure that the mass fraction of sulfur in the hot metal is ≤0.0020%.

[0063] 2) Converter smelting: The molten iron is decarburized, desiliconized and desulfurized through a top and bottom double-blown converter. During the steelmaking process, 6.9 kg / t of lime and 2.4 kg / t of pre-melted refined slag are added to the first molten steel.

[0064] 3) LF refining is carried out with deep deoxidation and desulfurization. When LF leaves the station, the mass fraction of total oxygen in the molten steel is 0.0012%, and the mass fraction of sulfur is 0.0009%.

[0065] 4) After RH refining was vacuum treated for 19 minutes, rare earth iron alloy was added through the silo for rare earth treatment. The rare earth-iron alloy was lanthanum-cerium-iron alloy, in which La:Ce was added in a ratio of 1:2, the mass fraction of rare earth was 30%, and the static stirring time was 16 minutes.

[0066] 5) During continuous casting, the temperature of the molten steel in the tundish is 1576°C. The argon seal is strengthened during the continuous casting process to prevent secondary oxidation and ensure the cleanliness of the molten steel.

[0067] 6) Rolling: The continuous casting ingot is sent to a heating furnace and heated to 1220°C and kept warm for 3 hours; the starting rolling temperature is 1127°C, two-stage controlled rolling is adopted, the final rolling temperature is 877°C, and the size of the ingot after rolling is a plate with a thickness of 6 mm.

[0068] 7) The steel plate is cooled to the coiling temperature by intermittent cooling and then coiled. The coiling temperature is 552°C.

[0069] Comparative Example 1 In this comparative example, the alloy composition of the "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims is, by weight percentage, C: 0.061%, Si: 0.82%, Mn: 1.49%, P: 0.0009%, S: 0.0009%, Al: 0.039%, Nb: 0.046%, Ti: 0.012, Cr: 0.28%, N: 0.0035%, O: 0.0009%, and the remainder is iron and unavoidable impurities.

[0070] In this comparative example, the production method of the "ferrite-pearlite-granular bainite" complex phase hot-rolled steel plate for wheel rims includes the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → rolling → controlled cooling → coiling. Specifically, the following steps are included: 1) Hot metal pretreatment: same as in Example 1.

[0071] 2) Converter smelting: same as in Example 1.

[0072] 3) LF refining is carried out with deep deoxidation and desulfurization. When LF leaves the station, the mass fraction of total oxygen in the molten steel is 0.0012%, and the mass fraction of sulfur is 0.0009%.

[0073] 4) After RH refining is vacuum treated for 16 minutes, rare earth iron alloy is added through the silo for rare earth treatment. The rare earth-iron alloy is lanthanum-iron alloy, cerium-iron alloy or lanthanum-cerium-iron alloy. The static stirring time is 16 minutes.

[0074] 5) During continuous casting, the temperature of the molten steel in the tundish is 1553°C, and the argon seal during the continuous casting process is strengthened to prevent secondary oxidation and ensure the cleanliness of the molten steel; 6) Rolling: The continuous casting ingot is sent to a heating furnace and heated to 1280°C and kept warm for 2 hours; the rolling start temperature is 1126°C, two-stage controlled rolling is adopted, the final rolling temperature is 869°C, and the size of the ingot after rolling is a plate with a thickness of 3 mm.

[0075] 7) Controlled cooling: The steel plate is cooled to the coiling temperature by intermittent cooling for coiling, and the coiling temperature is controlled at 527°C.

[0076] Table 1 shows the properties of the wheel steel of the present invention; Table 2 shows the different tissue contents of the wheel steel of the present invention; Table 3 shows the bench dynamic radial rolling fatigue properties of the wheel steel of the present invention.

[0077] Table 1 Properties of the wheel steels of Examples 1-3 of the present invention and Comparative Example 1

[0078] Table 2 Different tissue contents of wheel steels in Examples 1-3 of the present invention and Comparative Example 1

[0079] Table 3 Dynamic radial rolling fatigue properties of the wheel steels of Examples 1-3 of the present invention and Comparative Example 1

[0080] Figure 1 (a), (b), (c), and (d) are electron microscope images of the microstructures of the steel plates of the comparative example, embodiment 1, embodiment 2, and embodiment 3 of the present invention, respectively. Figure 1 It can be seen that the microstructures in the comparative example, Example 1, Example 2, and Example 3 are all ferrite-pearlite-granular bainite, but with the addition of RE and the increase in its content, the degree of microstructure refinement continues to increase. Grain refinement is the only strengthening method that can improve both the strength and plastic toughness of steel plates, which undoubtedly highlights the importance of rare earths.

[0081] As can be seen from Table 1, the performance of the complex phase hot rolled steel plate without RE in Comparative Example 1 is lower than that of the complex phase hot rolled steel plate with RE in Examples 1, 2 and 3, indicating that rare earth plays a vital role in improving the performance of wheel steel plates. As can be seen from Table 2, with the addition of RE and the increase in content: the content of granular bainite continues to increase, the strength difference between the organizations is reduced, and the hole expansion performance of the steel plate is improved; as can be seen from Table 3, before RE is added, the dynamic radial rolling fatigue life of the rig after the steel plate is formed into a wheel is 840,000 times; after RE is added, the dynamic radial rolling fatigue life of the rig after the steel plate is formed into a wheel is significantly improved, all greater than 2 million times, and the fatigue performance is stable.

[0082] In the embodiment of the method of the present invention, the tensile strength of the rare earth-containing composite hot-rolled finished steel plate is 690MPa~750MPa, the yield strength is ≥500MPa, the elongation is ≥25%, the hole expansion rate (λ) is ≥180%, and the dynamic radial rolling fatigue life of the stand after the steel plate is formed into a wheel is significantly improved, all of which are greater than 2 million times, and the fatigue performance is stable. It not only has high mechanical properties, but also has good hole expansion performance, welding performance and fatigue performance.

[0083] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A rare earth-containing complex phase hot-rolled steel for wheel rims, characterized in that: The composition includes the following weight percentages: C: 0.055%~0.090%, Si: 0.60%~0.90%, Mn: 1.00%~1.60%, P≤0.010%, S≤0.001%, Al: 0.020%~0.080%, Nb: 0.040%~0.080%, Ti: 0.005%~0.020%, Cr: 0.22%~0.30%, N≤0.0045%, O≤0.0020%, RE: 0.0100~0.0300%, and RE / S>3, and the balance is iron and unavoidable impurities; wherein RE includes La and / or Ce.

2. The rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 1, characterized in that: The metallographic structure of the rare earth-containing complex phase hot-rolled steel is a three-phase composite of ferrite, pearlite and granular bainite.

3. The rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 1, characterized in that: The rare earth-containing complex phase hot-rolled steel has a tensile strength of 690 MPa to 750 MPa, a yield strength of ≥500 MPa, an elongation of ≥25%, and a hole expansion rate λ of ≥180%.

4. A method for preparing rare earth-containing complex phase hot-rolled steel for wheel rims as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling, cooling and coiling; In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment; During the RH refining, the molten steel treated by the LF refining is hoisted into a RH vacuum furnace for refining; In the continuous casting, the molten steel after the RH refining treatment is continuously cast to obtain a continuous casting billet; During the rolling, the continuous casting billet is sent to a heating furnace and heated to 1200°C-1280°C, and kept warm for 2h-3h; the rolling start temperature is ≥1120°C, two-stage controlled rolling is adopted, the final rolling temperature is 860°C-890°C, and the billet size after rolling is a plate with a thickness of ≤6mm; During the cooling, the rolled slab is cooled by intermittent cooling; The coiling temperature is 515°C to 555°C.

5. The method for preparing rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 4, characterized in that: In the LF refining, the mass fraction of total oxygen in the molten steel is ≤0.0015%, and the mass fraction of sulfur is ≤0.0010% when the LF leaves the station.

6. The method for preparing rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 4, characterized in that: In the RH refining, after vacuum treatment for 10 minutes to 20 minutes, rare earth iron alloy is added through the silo for rare earth treatment, and the static stirring time is ≥15 minutes.

7. The method for preparing rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 6, characterized in that: In the rare earth iron alloy, the mass content of rare earth elements is 10% to 50%; The rare earth element in the rare earth iron alloy is one or both of lanthanum and cerium.

8. The method for preparing rare earth-containing complex phase hot-rolled steel for wheel rim according to claim 4, characterized in that: In the continuous casting, the temperature of the molten steel in the tundish is 1545° C. to 1585° C., and argon sealing is used in the continuous casting process.

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