WO2022022692A1 - 一种扭力梁用钢板及其制造方法、扭力梁及其制造方法 - Google Patents

一种扭力梁用钢板及其制造方法、扭力梁及其制造方法 Download PDF

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WO2022022692A1
WO2022022692A1 PCT/CN2021/109665 CN2021109665W WO2022022692A1 WO 2022022692 A1 WO2022022692 A1 WO 2022022692A1 CN 2021109665 W CN2021109665 W CN 2021109665W WO 2022022692 A1 WO2022022692 A1 WO 2022022692A1
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torsion beam
steel sheet
manufacturing
torsion
steel plate
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PCT/CN2021/109665
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English (en)
French (fr)
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刘春粟
张玉龙
杨峰
倪亚平
逯若东
王金涛
韩军
于同文
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宝山钢铁股份有限公司
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Priority to EP21850736.6A priority Critical patent/EP4180548A4/en
Priority to JP2023504137A priority patent/JP2023534826A/ja
Priority to KR1020237002025A priority patent/KR20230028766A/ko
Priority to US18/017,285 priority patent/US20230295787A1/en
Publication of WO2022022692A1 publication Critical patent/WO2022022692A1/zh

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    • C—CHEMISTRY; METALLURGY
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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    • B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
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    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G21/00—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces
    • B60G21/02—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected
    • B60G21/04—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected mechanically
    • B60G21/05—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected mechanically between wheels on the same axle but on different sides of the vehicle, i.e. the left and right wheel suspensions being interconnected
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G21/00—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
    • B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
    • B60G2206/20—Constructional features of semi-rigid axles, e.g. twist beam type axles
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D2211/00—Microstructure comprising significant phases
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Definitions

  • the invention relates to the field of iron and steel, in particular to a steel plate for torsion beams, a method for manufacturing the steel plate for torsion beams, and a method for manufacturing torsion beams and torsion beams.
  • torsion beams have the advantages of simple structure, small footprint and low cost, they are widely used in A-class vehicles, MPVs and new energy vehicles.
  • the traditional torsion beam structure is an open torsion beam, the thickness of which is generally more than 6mm, and the weight of a single piece is more than 15kg.
  • a stabilizer bar is generally added inside the torsion beam, which leads to the weight of the torsion beam assembly reaching 20kg.
  • the weight of a single closed torsion beam generally does not exceed 10kg and there is no need for a stabilizer bar in the middle, which is in line with the concept of lightweight automobiles. Under the trend of environmental protection and strengthening, domestic automobile rear axles have gradually transitioned to closed torsion beams.
  • the characteristics of hot stamping are that after the steel pipe is stamped into a special-shaped section, it is heated to a high temperature of 920-940 ° C and kept warm, and then quenched. In this process, the heating temperature needs to be equal to or higher than the transformation point temperature, and an atmosphere control to prevent scale is required, so the process cost is high. At the same time, the high temperature heat treatment is easy to deform the pipe fittings, resulting in dimensional deviation, and there are problems in the subsequent assembly process. In addition, the "Comparative Study of Beam Performance of Tubular Torsion Beam" shows that compared with cold stamping materials, the heat-affected zone of the weld seam is severely softened after welding, which is easy to cause cracking.
  • the beam of a closed torsion beam will have a transition area between stretching and bending, called the fillet area, where the stress is concentrated. If a relatively low-strength steel is selected in order to reduce the stress in the fillet area, the strength and rigidity of the product cannot be guaranteed. There is a way to increase the strength and stiffness by increasing the thickness, but increasing the thickness does not meet the requirements of lightweight automobiles.
  • the present invention provides a steel plate for torsion beams and a method for manufacturing the steel plates for torsion beams, so as to solve the above technical problems.
  • the invention provides a steel plate for torsion beam, the chemical composition of which is calculated by mass percentage: C: 0.04-0.085%, Si: 0.02-0.5%, Mn: 1.3-1.8%, Cr: 0.15-0.5%, Mo: 0.12-0.30%, Nb: ⁇ 0.058%, V: ⁇ 0.15%, Ti: ⁇ 0.02%, Al: 0.02-0.1%, P ⁇ 0.02%, S ⁇ 0.005%, N ⁇ 0.005%; the balance is Fe and inevitable impurities, wherein the steel sheet contains one or both of Nb and V, and satisfies 0.096% ⁇ 2Nb+V ⁇ 0.17%.
  • Each numerical range includes endpoints unless otherwise stated.
  • the carbon content of the present invention is controlled to 0.04-0.085% .
  • Silicon in steel plays a role of solid solution strengthening and improves the strength of the steel plate.
  • the addition of silicon also increases the rate of work hardening and the uniform and total elongation at a given strength, helping to improve the elongation of the steel sheet.
  • silicon can also prevent the precipitation of carbides and reduce the appearance of pearlite phase.
  • the presence of silicon in steel tends to form surface defects such as fayalite (2FeO-SiO 2 ) scale on the surface of the steel sheet, thereby affecting the fatigue properties.
  • the silicon content of the present invention is controlled to be less than or equal to 0.5%, and further to 0.02-0.5%.
  • Manganese is a solid solution strengthening element in the present invention. Low manganese content will lead to insufficient strength, but high manganese content will reduce the plasticity of the steel plate, and at the same time easily produce segregation and MnS inclusions, which is not conducive to fatigue performance. In order to have both good formability and uniform structure on the premise of ensuring the tensile strength of the product, the manganese content of the present invention is controlled to be 1.3-1.8%.
  • Aluminum is a deoxidizing element of steel, which can reduce oxide inclusions and pure steel in steel, which is beneficial to improve the elongation and bending performance of steel plates.
  • high aluminum content will generate Al 2 O 3 inclusions, thereby affecting the continuous casting production and the fatigue performance of the steel sheet, so the aluminum content in the present invention is controlled to be 0.02-0.1%.
  • Molybdenum inhibits the formation of pearlite, which is beneficial to the formation of bainite structure. At the same time, it is added in combination with microalloys, which is beneficial to the precipitation of microalloys, and finally is beneficial to the improvement of the strength of the steel plate.
  • adding a certain content of molybdenum is beneficial to increase the tempering resistance of the material and ensure the strength of the torsion beam after annealing.
  • the molybdenum content in the present invention is controlled to be 0.12-0.3%, further 0.15-0.3%.
  • Niobium is one of the important precipitation strengthening and grain refinement strengthening elements. It exists in the form of fine precipitation during cooling after rolling or after coiling, and the strength is improved by precipitation strengthening. At the same time, the presence of niobium is beneficial to refine grains and improve strength and toughness. When the niobium content is higher than 0.058%, the strengthening effect is close to saturation, and the cost is relatively high, so the niobium content of the present invention is less than or equal to 0.058%. Further, the niobium content is in the range of 0.01-0.058%, and further, the niobium content is in the range of 0.012-0.046%.
  • Vanadium is one of the important elements for precipitation strengthening and fine-graining strengthening. In combination with niobium, it has a good effect of refining austenite grains and precipitation strengthening. During cooling after rolling Or it exists in the form of fine precipitation after coiling, and the strength is improved by precipitation strengthening. In the subsequent stress relief annealing process of the torsion beam, in order to ensure that the strength of the torsion beam does not decrease, a certain content of vanadium is added, which is beneficial to increase the strength of the material, and the vanadium content of the present invention is less than or equal to 0.15%. Further, the vanadium content is in the range of 0.01-0.15%, and further, the vanadium content is in the range of 0.025-0.10%.
  • niobium and vanadium the two elements also need to satisfy 0.096% ⁇ 2Nb+V ⁇ 0.17%.
  • niobium or vanadium there will be nano-precipitation of (Mo, Nb)C or (Mo, V)C microalloys, thereby further improving the strength of the steel sheet and obtaining better elongation and cold bending properties.
  • the chemical elements of the steel plate in the present invention may contain Nb or V alone, or both Nb and V, and the ratio of Nb and V satisfies 0.096% ⁇ 2Nb+V ⁇ 0.17%.
  • Strength can be maintained or even increased during stress relief annealing.
  • Titanium is one of the important precipitation strengthening and fine-grain strengthening elements.
  • the free nitrogen atoms in the steel are unfavorable to the impact toughness of the steel, while the impurity element nitrogen in the titanium and the steel is unfavorable.
  • the steel plate of the present invention contains titanium, it can cooperate with elements such as niobium to refine austenite grains; and, Titanium is added to maintain or even increase strength during stress relief annealing during the fabrication of torsion beams.
  • the mass percentage of Ti should not be too much, otherwise it is easy to form TiN with a larger size, which is unfavorable to the fatigue performance of the steel. Therefore, the present invention controls the Ti content to be ⁇ 0.02%. Further, the titanium content is in the range of 0.005-0.02%.
  • Phosphorus (P) Phosphorus in steel is generally dissolved in ferrite, which reduces the toughness of steel; high phosphorus is also unfavorable for weldability, and phosphorus segregation at grain boundaries is not conducive to the hole expansion performance of strip steel, so it should be as far as possible
  • the phosphorus content is reduced, and the content of P in the present invention is less than or equal to 0.02%.
  • S Sulfur
  • the content of sulfur and the form of sulfide are the main factors affecting the formability. The more the number of sulfides and the larger the size, the more unfavorable the hole expansion performance is. Therefore, the sulfur content in the present invention is controlled to be less than or equal to 0.005% .
  • Nitrogen (N) Nitrogen reacts with titanium to form TiN particles precipitation under high temperature conditions. Excessive TiN particles are detrimental to fatigue performance, and the nitrogen content in the steel must be controlled. Therefore, the nitrogen content in the present invention is controlled to be less than or equal to 0.005% .
  • the two elements also need to satisfy 0.3% ⁇ 0.5Cr+Mo ⁇ 0.55%, the purpose of which is to delay the transformation of pearlite, which is beneficial to the steel plate.
  • the formation of bainite phase during the manufacturing process is also conducive to improving the bending performance of the steel plate and obtaining better fatigue performance; another purpose is to ensure that the material has good tempering resistance. Basic mechanical properties are not reduced.
  • CE IIw ⁇ 0.50 in the present invention can ensure better welding performance.
  • the calculation formula of carbon equivalent is a currently recognized empirical formula, and the value substituted in the formula is the percentage content of the corresponding element, which is calculated as a dimensionless.
  • the steel sheet of the present invention does not contain nickel (Ni) and copper (Cu), or only contains a small amount of residual nickel and copper, which can be ignored in the calculation of carbon equivalent, so Ni+Cu is zero in the formula.
  • the microstructure of the above steel sheet contains bainite and ferrite, and the total content of bainite and ferrite in the steel sheet is greater than or equal to 90%, that is, the volume fraction of bainite + ferrite. and ⁇ 90%, and the volume fraction of bainite in the steel sheet is greater than 50%, for example, between 55-85%.
  • Such a microstructure is beneficial to the strength and bending properties of steel plates for torsion beams.
  • the sum of the volume fractions of bainite + ferrite is >95%, and it is expected to be as close to 100% as possible.
  • the microstructure of the steel sheet for torsion beam also includes pearlite and/or martensite, that is, the steel sheet for torsion beam may also contain pearlite, or martensite, or both pearlite and martensite. , whether it contains one or both of pearlite and martensite, the volume fraction of pearlite and martensite in the steel sheet as a whole is less than or equal to 10%. Further, the sum of the volume fractions of pearlite and martensite in the steel sheet is ⁇ 5%, and it is expected to be close to 0.
  • the obtained steel plate for torsion beam can reach longitudinal yield strength ⁇ 620Mpa, tensile strength ⁇ 760Mpa, A50 elongation ⁇ 16%, and 180° cold bending performance R/T ⁇ 1.05.
  • the uniform elongation of the steel plate is ⁇ 7.0.
  • the longitudinal yield strength is 620-720Mpa
  • the tensile strength is 760-860Mpa
  • the A50 elongation is 16-24%
  • the uniform elongation is 7.0-11.5. It is precisely because the steel sheet of the present invention satisfies the above-mentioned parameters that the excellent performance of the torsion beam is provided.
  • the present invention provides a manufacturing method of a steel plate for torsion beams, and by improving the manufacturing method, the properties of the obtained steel plate are further improved.
  • the chemical composition of the steel sheet is recorded as: C: 0.04-0.085%, Si: 0.02-0.5%, Mn: 1.3-1.8%, Cr: 0.15-0.5%, Mo: 0.12-0.30%, Nb: ⁇ 0.058%, V: ⁇ 0.15%, Ti: ⁇ 0.02%, Al: 0.02-0.1%, P ⁇ 0.02%, S ⁇ 0.005%, N ⁇ 0.005%; the balance is Fe and inevitable impurities, wherein the steel sheet contains one or both of Nb and V, and satisfies 0.096% ⁇ 2Nb+V ⁇ 0.17%.
  • smelting can be carried out by means of currently commonly used methods.
  • molten steel is subjected to RH vacuum degassing treatment and LF furnace desulfurization treatment.
  • the smelted molten steel can be continuously casted by means of the current main application.
  • the central segregation and inclusion levels of the continuous casting slab can be controlled by controlling the degree of superheat, secondary cooling water, and using appropriate light reduction processes, and the inclusion level can be controlled to be less than 1.5.
  • Hot rolling heating can fully dissolve V and/or Nb in the steel sheet.
  • the heating temperature is 1230 ⁇ 30°C. If the heating temperature exceeds 1260°C, the grains will tend to coarsen, which is not conducive to the toughness of the steel plate, and the iron oxide scale is thicker, which is not conducive to the removal of phosphorus from the iron oxide scale.
  • the cooling method of the present invention adopts laminar cooling.
  • water is used to cool the steel sheet after finishing rolling, and the laminar cooling rate is 30-70 for cooling, and the slab after finishing rolling is cooled.
  • 500-620 billets After that, it was coiled between 500-620 billets, and the microstructure was bainite + ferrite with better fatigue performance and (Mo, V)C, (Mo, Nb)C microalloy nano-precipitation, and the others were A small amount of pearlite and/or martensite, and the total volume fraction of pearlite and martensite is ⁇ 10%.
  • the microstructure and nano-precipitation further enable the steel sheet to obtain high strength and better elongation and cold bending properties.
  • the pickling step a commonly used pickling method can be used.
  • the pickling speed is controlled at 60-100m/min
  • the temperature of the last pickling tank in the pickling process is controlled at 80-90°C
  • the iron coiling ion concentration is controlled at 30-40g/L.
  • air cooling is also included between the rolling step and the cooling and coiling step, and the air cooling time is 1-8s. That is, the present invention adopts the delayed cooling control mode after rolling, and air-cools the slab after finishing rolling, and then uses cooling water for laminar cooling, cooling to 500-620° C., and then coiling. Air cooling for 1-8s after rolling is beneficial to the recovery of grains.
  • the specific operation method can control the air cooling time by controlling the speed of the finishing strip and the position of the cooling water starting valve.
  • the rolled slab of the present invention has little change in temperature after 1-8s air cooling, and the temperature will decrease by 10-50°C, mainly relying on laminar cooling to cool the slab.
  • the chemical composition of the formed steel sheet satisfies 0.3% ⁇ 0.5Cr+Mo ⁇ 0.55%.
  • the microstructure of the steel sheet formed above contains bainite and ferrite, and the total content of bainite and ferrite in the steel sheet is greater than or equal to 90%, that is, the volume of bainite + ferrite.
  • the sum of the fractions is greater than or equal to 90%, and the volume fraction of bainite in the steel sheet is greater than 50%, for example, between 55-85%.
  • Such a microstructure is beneficial to the strength and bending properties of steel plates for torsion beams. Further, the sum of the volume fractions of bainite and ferrite is >95%.
  • the microstructure of the formed steel sheet further includes pearlite and/or martensite, that is, the steel sheet may further contain pearlite, or martensite, or both pearlite and martensite. Whether it contains one or both of pearlite and martensite, the sum of the volume fractions of pearlite and martensite in the steel sheet is less than or equal to 10%. Further, the sum of the volume fractions of pearlite and martensite in the steel sheet is less than 5%.
  • the mechanical properties of the steel plate can reach the following levels: longitudinal yield strength ⁇ 620 MPa, tensile strength ⁇ 760 MPa, A50 elongation ⁇ 16%, 180° cold bending performance R/T ⁇ 1.05.
  • the present invention obtains the uniform elongation of the steel sheet ⁇ 7.0.
  • the longitudinal yield strength: 620-720Mpa the tensile strength: 760-860Mpa
  • the A50 elongation is 16%-24%
  • the uniform elongation is 7.0-11.5.
  • the hot-rolled coiling temperature can be 560-620°C, combined with air cooling after rolling for more than 2s (including 2s), not only the longitudinal direction of the steel sheet can be satisfied.
  • Yield strength ⁇ 620MPa, tensile strength ⁇ 760MPa can further improve the forming performance, that is, A50 elongation ⁇ 18%, 180° cold bending performance 1.25 ⁇ R/T ⁇ 1.05, and uniform elongation ⁇ 8.0.
  • the present invention also provides a torsion beam, the torsion beam is made by the above-mentioned steel plate for the torsion beam.
  • the torsion beam obtained by the invention can achieve a longitudinal yield strength of ⁇ 680 MPa, a tensile strength of ⁇ 800 MPa, and a bench fatigue of 500,000 to 1.8 million times.
  • the present invention also provides a method for manufacturing a torsion beam, wherein the steel plate obtained by the above-mentioned method for manufacturing a steel plate for a torsion beam is used as a processing material in combination with the chemical composition ratio of the steel plate for a torsion beam, to manufacture a torsion beam with excellent performance .
  • the closed torsion beam mainly has two methods: hot stamping and cold forming.
  • the torsion beam manufacturing method of the present invention adopts the cold forming method to manufacture the torsion beam.
  • the manufacturing method of the torsion beam of the present invention adopts the method of cold forming, and includes the following steps: welding the pipe: welding the steel plate through the torsion beam to form a circular pipe; forming: hydraulically or punching the circular pipe to form a special-shaped pipe, the
  • the special-shaped tube is U-shaped or V-shaped and has an inner fillet, wherein the ratio of the inner fillet R to the thickness T of the special-shaped tube satisfies R/T ⁇ 1.05; after that, stress relief annealing and/or shot peening are performed to form a torsion beam .
  • the torsion beam manufacturing method of the present invention may directly perform the shot peening step after forming, or directly perform the stress relief annealing step, or perform both the stress relief annealing step and the shot peening step.
  • the stress relief annealing step may be performed first and then the shot peening step may be performed.
  • a high-strength steel plate is welded into a round pipe by laser welding or high-frequency welding, and is cut into a preset size. Since the C content of the present invention is 0.04-0.085%, and one or both of Nb and V are contained, it has the effect of refining grains, so that in the pipe welding step, the hardness of the welded seam is excessively stable, and the microstructure is smaller.
  • a stress relief annealing step or a shot peening step, or a stress relief annealing and shot peening step is performed.
  • the shaped special-shaped tube is put into a heating furnace, heated with the furnace, kept at 475-610 ° C for 20 to 90 minutes, and then cooled to 300 ° C with the furnace and then air-cooled.
  • the internal structure of the steel has more residual stress, especially the tensile stress state on the surface, which leads to a short fatigue life of the torsion beam.
  • Stress relief annealing can remove the stress state in the forming process, and at the same time keep the mechanical properties of the annealed special-shaped tube from decreasing or even increasing.
  • the surface shot peening treatment is performed on the stress concentration area of the pipe fitting, that is, the fillet position by the shot peening equipment.
  • the shot peening may be performed on either the inner surface or the outer surface of the fillet position, or the shot peening may be performed on both the inner and outer surfaces of the fillet position.
  • the shot peening step can ensure that the surface of the torsion beam beam is in a state of compressive stress, thereby improving the fatigue performance of the torsion beam.
  • the manufacturing method of the torsion beam of the present invention from the perspective of improving elongation and bending performance, the surface state of the R angle is improved to improve the fatigue of the finally formed torsion beam.
  • the fatigue performance of the torsion beam is improved. Accordingly, in order to achieve the above two effects at the same time, the chemical composition ratio, microstructure and manufacturing method of the steel plate will be improved.
  • the structure of the formed torsion beam is also designed to match the properties of the obtained steel plate (for example, through the composition design of the steel plate for torsion beam of the present invention)
  • the manufacturing method the obtained 180° cold bending performance R/T ⁇ 1.05, correspondingly, when manufacturing the torsion beam, the ratio of the inner fillet of the torsion beam to the thickness T is required to be R/T ⁇ 1.05, to ensure that the manufactured torsion beam structure and the original torsion force
  • the performance of the beam steel plate is matched, thereby significantly reducing the occurrence of folding, wrinkling, fracture and other problems that reduce the fatigue performance).
  • the core hardness of the torsion beam formed by the manufacturing method of the present invention is above 260HV, and the microhardness at 0.05mm of the inner and outer surfaces is 30-80HV higher than that of the core, so that the effect of external strength and internal toughness can be achieved, and the torsion beam can also be avoided. Internal folding occurs, increasing fatigue strength.
  • the formed torsion beam can achieve the excellent performance of longitudinal yield strength ⁇ 680MPa, tensile strength ⁇ 800MPa, and bench fatigue of 500,000-1.8 million times.
  • Fig. 1 shows the metallographic microstructure of the steel sheet of Example 2 of the present invention
  • FIG. 3 is a schematic diagram showing the change of microhardness of Example 1, Example 11 and the torsion beam without destressing annealing of the present invention.
  • Table 1 is the mass percentage of each chemical element in Examples 1-10 and Comparative Examples 1-7 of the present invention.
  • Table 2 shows the steel sheet manufacturing methods of the corresponding Examples 1-10 and Comparative Examples 1-7, and lists the properties of the manufactured steel sheets.
  • the manufacturing method of the steel sheet for torsion beams of the present invention includes the steps of smelting, continuous casting, hot rolling and pickling.
  • converter steel is first used, and molten steel is subjected to RH vacuum degassing treatment and LF furnace desulfurization treatment.
  • the specific method can refer to the existing smelting method.
  • Continuous casting is then carried out.
  • the central segregation and inclusion levels of the continuous casting slab can be controlled, and the inclusion level can be controlled to be less than 1.5.
  • the inclusion grade refers to the standard of GB/T 10561-2005.
  • the hot rolling step includes hot rolling heating, rolling, cooling and coiling.
  • the heating temperature and holding time of hot rolling heating in the following examples and comparative examples are shown in Table 2.
  • the rolling process includes rough rolling and finishing rolling, and Table 2 also lists the rough rolling outlet temperature and finishing rolling temperature in each example.
  • the cooling method adopts laminar cooling.
  • the coiling temperature in Table 2 represents the temperature when the slab is coiled.
  • the air-cooling time represents the time for air-cooling the slab after rolling, and when the air-cooling time is 0 s, it means that the embodiment directly performs laminar cooling without air-cooling.
  • the steel sheets formed in the following Examples 1-10 and Comparative Examples 1-7 were subjected to property tests.
  • the mechanical property test is performed according to the GB/T228.1-2010 standard
  • the 180° cold bending performance R/T is performed according to the GB/T232-2010 standard.
  • the longitudinal yield strength, tensile strength, uniform elongation, A50 Elongation and 180° cold bending performance results.
  • Table 2 there is a column of 180° cold bending properties, no wrinkle on the cold-formed surface is indicated as "OK”, and wrinkle on the cold-formed surface is indicated as "NG”.
  • Fig. 1 is a metallographic microstructure diagram of the steel sheet of Example 2. It can be seen from the figure that the obtained steel sheet microstructure includes bainite, ferrite, and a small amount of pearlite. In this embodiment, bainite + ferrite The sum of the volume fractions is greater than 90%.
  • Table 3 shows the calculation parameters and properties of torsion beams made from the steel plates of the above embodiments.
  • the manufacturing method of the torsion beam of the present invention adopts the cold forming method to manufacture the torsion beam, including welding the pipe, forming, and then performing the steps of stress relief annealing and/or shot peening, thereby forming the torsion beam.
  • the steel plate in the above embodiment is welded into a round tube, and then the round tube is hydraulically or stamped to form a special-shaped tube.
  • the special-shaped tube is U-shaped or V-shaped and has inner fillets.
  • the final torsion beam structure is shown in Figure 2 shown.
  • Figure 2 shows the radius R at the fillet of the torsion beam and the thickness T of the torsion beam.
  • the fillet is manufactured so that R/T is greater than or equal to 1.05, for example
  • the radius R of the fillet is 4.61
  • the forming method is, for example, putting the round tube into the lower mold, closing the upper mold for stamping and forming, or after the mold is closed, the liquid is pressurized and inflated in the tube after the hydroforming method.
  • Examples 11-21 and Comparative Examples 8-14 respectively use different methods to make steel plates into torsion beams.
  • Table 3 lists the specific parameters such as the R/T value at the fillet formed by different examples and comparative examples, the process after forming, that is, the temperature and time of stress relief annealing, and the position of the shot peening step.
  • the torsion beams formed in the following Examples 11-20 and Comparative Examples 8-14 were tested for performance, and the mechanical performance test of this embodiment was performed according to the GB/T 228.1-2010 standard.
  • the longitudinal yield strength and tensile strength of the inner fillet cannot be measured.
  • the core hardness at the inner fillet and the microhardness difference between the surface and the core can be detected.
  • the microhardness test method is in accordance with GB/T 4342-1991 implement.
  • Examples 1-10 in Table 1 and Table 2 and Examples 11-21 in Table 3 adopt the design method of the present invention, and finally obtain a high-strength and high-formation steel plate and a torsion beam with high-strength and high fatigue performance.
  • Example 1 and Examples 3-10 all adopt air cooling in the steel plate manufacturing process.
  • the coiling temperature is 500-620 ° C
  • the carbon equivalent is less than 0.50, it can have good formability and elongation. Rate.
  • Comparative Example 1 resulted in poor bending performance, which further led to the occurrence of micro-cracks on the surface of the R angle in the hydraulic process of Comparative Example 8 in Table 3, and cracking at the weld, which eventually led to the failure of the bench fatigue. reached 500,000 times.
  • the process parameters of the manufacturing method of the steel plate of Example 4 and Comparative Example 1 are similar (for example, the coiling temperature and air cooling time are the same), while the carbon equivalent of Comparative Example 1 is higher, and the carbon equivalent of Example 4 is lower, so the steel plate of Example 4 Welding performance is better.
  • Comparative Example 2 and Comparative Example 3 do not satisfy the condition of 0.096% ⁇ 2Nb+V ⁇ 0.17%, resulting in lower yield strength and tensile strength of the sheet.
  • the steel plates of Comparative Example 2 and Comparative Example 3 are used to make torsion beams, that is, the strength of the torsion beams obtained in Comparative Examples 9 and 10 is also low, which eventually leads to weaker fatigue resistance of the material and cannot achieve weight reduction. quantified effect.
  • the carbon content in Comparative Example 4 is low, and at the same time, due to the excessively high hot-rolling and coiling temperature, the strength of the sheet is low, and the tensile strength of the steel sheet cannot meet the requirement of ⁇ 760MPa, which eventually leads to the torsion force of Comparative Example 11 in Table 3.
  • the tensile strength of the beam is also less than 800Mpa, which cannot achieve the effect of weight reduction and weight reduction.
  • microalloy in Comparative Example 5 is relatively high, which does not satisfy the condition of 0.096% ⁇ 2Nb+V ⁇ 0.17%, resulting in high strength of the sheet, and the bending performance cannot satisfy R/T ⁇ 1.05, which further leads to the comparative example in Table 3. 12 During the hydraulic process, micro-cracks appeared on the surface of the R angle, which eventually led to the fatigue of the bench not reaching 500,000 times.
  • Comparative Example 6 The relatively low Cr content of Comparative Example 6 resulted in a lower strength of the plate, which ultimately resulted in the poor bench fatigue capacity of the torsion beam of Comparative Example 13. Due to the low Cr content and the high annealing temperature when making the torsion beam, the strength decreases, and the effect of high strength and weight reduction cannot be achieved.
  • Comparative Example 7 the strength of the plate and the final torsion beam (Comparative Example 14) can reach more than 800 MPa by microalloying strengthening with high Ti, but the final bench fatigue performance of the torsion beam in Comparative Example 14 is only 290,000 times. Because of the larger TiN precipitation, there is no precipitation of Nb and V which are beneficial to the fatigue properties. In addition, the coiling temperature of Comparative Example 7 was only 480°C, resulting in poor formability of the material.
  • Example 11-Example 21 the steps of stress relief annealing or shot peening in processing the torsion beam can improve the fatigue resistance of the torsion beam, and the stress relief annealing process and/or shot peening process can maintain or even improve the fatigue resistance of the torsion beam. Longitudinal yield strength of torsion beams.
  • Example 11 Compared with Example 11 and Example 21, the yield strength of the torsion beam after stress relief annealing increases more obviously.
  • FIG. 3 shows the microhardness change in the thickness direction of the steel plate in Example 1, that is, the microhardness change of the plate in the figure.
  • the steel plate in Example 1 is welded and formed to form a special-shaped tube, and the microhardness change in the thickness direction of the fillet is detected without the stress relief annealing step. Microhardness changes.
  • the steel plate in Example 1 is also welded, formed, and subjected to a stress relief annealing step to form a torsion beam, that is, Example 11 of the present invention. Microhardness change of fillet annealed. It can be seen that after stress relief annealing, the microhardness of the surface of Example 11 is higher, and the hardness of the core at the fillet is lower, achieving the effect of external strength and internal toughness.

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Abstract

本发明公开了一种扭力梁用钢板及其制造方法，以及扭力梁及其制造方法，其中扭力梁用钢板的化学成分按质量百分含量计为：C：0.04-0.085％，Si：0.02-0.5％，Mn：1.3-1.8％，Cr：0.15-0.5％，Mo：0.12-0.30％，Nb：≤0.058％，V：≤0.15％，Ti：≤0.02％，Al：0.02-0.1％，P≤0.02％，S≤0.005％，N≤0.005％；余量为Fe和不可避免杂质，其中，所述钢板中含有Nb、V中的一种或者两种，且满足0.096％≤2Nb+V≤0.17％。本发明的扭力梁用钢板能够在保证高强度的同时获得优异的延伸率和冷弯性能，符合制作扭力梁轻量化的要求。

Description

一种扭力梁用钢板及其制造方法、扭力梁及其制造方法 技术领域
本发明涉及钢铁领域，特别涉及一种扭力梁用钢板、扭力梁用钢板的制造方法，以及扭力梁和扭力梁的制造方法。
背景技术
由于扭力梁具有结构简单、占用空间小、成本低等优点，因此在A级车、MPV以及新能源汽车中得到广泛的应用。传统扭力梁结构为开口型扭力梁，其板厚一般为6mm以上，单件重量15kg以上。为了提高车型刚度要求，一般要在扭力梁内部增加一根稳定杆，这导致扭力梁总成重量达到20kg。然而，封闭式扭力梁单件重量一般不超过10kg且中间无需稳定杆，符合汽车轻量化理念，在环保和强量化的趋势下，国内汽车后桥已逐步向封闭式扭力梁过度。
目前封闭式扭力梁主要有热冲压和冷成型两种路径：
热冲压的特点是将钢管冲压成型成异形截面后，加热到高温920-940℃并进行保温，再进行淬火处理。在该过程中，加热温度需要达到相变点温度以上，而且需要使用防止氧化皮的气氛控制，因此工序成本较高。同时，高温热处理容易使管件变形，产生尺寸偏差，在后续装配过程中存在问题。此外，《管状扭力梁横梁性能的对比研究》表明，与冷冲压材料相比，热冲压材料焊接后焊缝热影响区域软化严重，容易引起开裂。
在冷成型过程中，封闭式扭力梁的横梁会有一个拉伸和折弯的过渡区域，称为圆角区域，该区域应力集中。若为了降低圆角区域的应力而选择强度相对较低的钢材，则产品的强度和刚度得不到保障。有一种办法是通过增加厚度来增加强度和刚度，但是增加厚度又不满足汽车轻量化的要求。
发明内容
本发明提供了一种扭力梁用钢板、扭力梁用钢板的制造方法，用以解决上述技术问题。
本发明提供了一种扭力梁用钢板，其化学成分按质量百分含量计为：C：0.04-0.085％，Si：0.02-0.5％，Mn：1.3-1.8％，Cr：0.15-0.5％，Mo：0.12-0.30％，Nb：≤0.058％，V：≤ 0.15％，Ti：≤0.02％，Al：0.02-0.1％，P≤0.02％，S≤0.005％，N≤0.005％；余量为Fe和不可避免杂质，其中，所述钢板中含有Nb、V中的一种或者两种，且满足0.096％≤2Nb+V≤0.17％。各数值范围除非特别说明均包括端点。
本发明化学成分设计中：
碳(C)：碳含量的高低很大程度上决定了钢板的抗拉强度级别。碳用于固溶强化和形成足够的微合金析出相以保证钢的强度，碳含量太低会使钢板的强度降低；碳含量太高，则折弯性能和延伸率不好，会影响后续扭力梁圆角度的设计。本发明的钢板中C含量相对较低，有利于提高钢板的折弯性能，提高焊缝疲劳性能。在本发明所限定的钢板成分的情况下，为了保证钢种既达到较高的纵向抗拉强度，又能获得期望的折弯性能、成型以及焊接性能，本发明碳含量控制为0.04-0.085％。
硅(Si)：钢中硅起到固溶强化作用，提高钢板的强度。添加硅还可加大加工硬化速率以及给定强度下的均匀延伸率和总延伸率，有助于改善钢板的延伸率。此外，硅还可以阻止碳化物的析出，减少珠光体相的出现。但是钢中含硅容易使钢板表面形成铁橄榄石(2FeO-SiO 2)氧化铁皮等表面缺陷，从而影响疲劳性能。本发明硅含量控制为小于或等于0.5％，进一步为0.02-0.5％。
锰(Mn)：本发明中锰是固溶强化元素，锰含量低会导致强度不足，但是锰含量高会导致钢板的塑性降低，同时容易产生偏析和MnS夹杂，不利于疲劳性能。为在保证产品抗拉强度的前提下，兼具良好的成型性和均匀化组织，因此本发明锰含量控制为1.3-1.8％。
铝(Al)：铝是钢的脱氧元素，能减少钢中的氧化物夹杂、纯净钢质，有利于提高钢板的延伸率和折弯性能。但是铝含量高，会产生Al 2O 3夹杂物，进而影响连铸生产和钢板的疲劳性能，因此本发明铝含量控制为0.02-0.1％。
铬(Cr)：铬抑制珠光体的形成，有利于贝氏体组织的形成，最终有利于强度的提升。铬含量小于0.15％时对CCT曲线(冷奥氏体连续冷却转变曲线)影响不显著，含量高时成本高，因此本发明铬含量控制为0.15-0.5％。进一步地，铬含量为0.15-0.43％。
钼(Mo)：钼抑制珠光体的形成，有利于贝氏体组织的形成，同时和微合金复合添加，有利于微合金析出，最终有利于钢板强度的提升。在扭力梁后续的去应力退火过程中，为了保证扭力梁强度不降低，添加一定含量的钼有利于增加材料的回火抗力，保证退火后扭力梁的强度。但其含量高时成本高，因此本发明钼含量控制为0.12-0.3％，进一步为0.15-0.3％。
铌(Nb)：铌是重要的析出强化和细晶强化元素之一，在轧制结束后的冷却中或卷取 后以细小析出的形式存在，利用析出强化来提高强度。同时铌的存在有利于细化晶粒，提高强度和韧性。当铌含量高于0.058％时强化效果接近饱和，并且成本较高，因此本发明铌含量≤0.058％。进一步地，铌含量范围在0.01-0.058％，更进一步地，铌含量范围在0.012-0.046％。
钒(V)：钒是重要的析出强化和细晶强化元素之一，与铌配合，起到较好的细化奥氏体晶粒的作用和析出强化作用，在轧制结束后的冷却中或卷取后以细小析出的形式存在，利用析出强化来提高强度。在扭力梁后续的去应力退火过程中，为了保证扭力梁强度不降低，添加一定含量的钒，有利于增加材料的强度，本发明钒含量≤0.15％。进一步地，钒含量范围在0.01-0.15％，更进一步地，钒含量范围在0.025-0.10％。
除了上述对于铌和钒两种元素自身范围的限定外，该两种元素还需满足0.096％≤2Nb+V≤0.17％。铌或者钒元素的加入，会有(Mo，Nb)C或(Mo，V)C微合金纳米析出，从而进一步提高钢板的强度，并获得更好的延伸率和冷弯性能。本发明中钢板的化学元素中可以单独含有Nb或V，或者同时含有Nb和V，并且Nb和V的配比关系满足0.096％≤2Nb+V≤0.17％，在后续制造扭力梁的过程中，在去应力退火时能够保持甚至增加强度。
钛(Ti)：钛是重要的析出强化和细晶强化元素之一，对于本发明的钢板，一方面由于钢中游离的氮原子对钢的冲击韧性不利，而钛与钢中的杂质元素氮结合形成TiN，因此加入微量钛可将游离的氮固定；另一方面当本发明的钢板中含有钛元素时，能够与铌等元素配合，起到细化奥氏体晶粒的作用；并且，钛的加入为在制造扭力梁的过程中，在去应力退火时能够保持甚至增加强度。但在本发明中Ti的质量百分比不宜太多，否则容易形成尺寸较大的TiN，对钢的疲劳性能不利。因此，本发明控制Ti含量≤0.02％。进一步地，钛含量范围在0.005-0.02％。
磷(P)：钢中磷一般固溶在铁素体中，降低钢的韧性；高磷对焊接性也不利，同时晶界处磷偏聚，不利于带钢的扩孔性能，故应尽量减少磷含量，本发明中P的含量小于或等于0.02％。
硫(S)：硫含量和硫化物的形态是影响成型性的主要因素，硫化物的数量越多，尺寸越大，对扩孔性能越不利，因此本发明中硫含量控制小于或等于0.005％。
氮(N)：氮在高温条件下就与钛反应形成TiN颗粒析出，过大的TiN颗粒对疲劳性能不利，必须对钢中氮含量进行控制，因此本发明中氮含量控制小于或等于0.005％。
可选地，除了上述对于铬和钼两种元素自身范围的限定外，该两种元素还需满足0.3％≤0.5Cr+Mo≤0.55％，其目的是推迟珠光体的转变，有利于在钢板制造过程中贝氏体相的 形成，同时也有利于提高钢板的折弯性能，获得更好的疲劳性能；另一目的是保证材料有较好的回火抗力，在去应力退火后，管材的基础力学性能不降低。
可选地，上述钢板化学成分满足碳当量CE Ⅱw≤0.50，其中CE Ⅱw＝％C+％Mn/6+％(Cr+Mo+V)/5+％(Ni+Cu)/15。本发明CE Ⅱw≤0.50能够保证较好的焊接性能。其中碳当量的计算公式为目前公认的经验公式，式中代入的数值为相应元素的百分比含量，作为无量纲计算。本发明的钢板中不含有镍(Ni)和铜(Cu)，或者只含有少量且残余的镍和铜，在碳当量的计算中可忽略不计，因此公式中Ni+Cu为零。
可选地，上述钢板的微观组织含有贝氏体和铁素体，贝氏体和铁素体在钢板中总的含量为大于或等于90％，即贝氏体+铁素体的体积分数之和≥90％，并且贝氏体在钢板中的体积分数大于50％，具体例如在55-85％之间。这样的微观组织有利于扭力梁用钢板的强度和折弯性能。进一步地，贝氏体+铁素体的体积分数之和＞95％，并期待其尽可能接近100％。
可选地，扭力梁用钢板的微观组织还包括珠光体和/或马氏体，即扭力梁用钢板中还可含有珠光体，或者含有马氏体，或者既含有珠光体也含有马氏体，其中无论是含有珠光体和马氏体的一种还是两种，珠光体和马氏体作为整体在钢板中的体积分数≤10％。进一步地，珠光体和马氏体在钢板中的体积分数之和＜5％，并期待其接近于0。
通过本发明的化学成分配比，获得的扭力梁用钢板能够达到纵向屈服强度≥620Mpa，抗拉强度≥760Mpa，A50延伸率≥16％，180°冷弯性能R/T≥1.05。同时，钢板的均匀延伸率≥7.0。进一步地，纵向屈服强度在620-720Mpa，抗拉强度在760-860Mpa，A50延伸率为16-24％，均匀延伸率在7.0-11.5。正是由于本发明的钢板满足上述参数，为扭力梁的优异性能提供了基础。
本发明提供了一种扭力梁用钢板的制造方法，通过对制造方法的改进，从而进一步提高了获得的钢板的性能。具体地，本发明的制造方法中，钢板的化学成分按质量百分含量记为：C：0.04-0.085％，Si：0.02-0.5％，Mn：1.3-1.8％，Cr：0.15-0.5％，Mo：0.12-0.30％，Nb：≤0.058％，V：≤0.15％，Ti：≤0.02％，Al：0.02-0.1％，P≤0.02％，S≤0.005％，N≤0.005％；余量为Fe和不可避免杂质，其中，钢板中含有Nb、V中的一种或者两种，且满足0.096％≤2Nb+V≤0.17％。本发明的制造方法包括冶炼、连铸、热轧和酸洗。其中，热轧步骤包括热轧加热、轧制以及冷却卷取。其中，热轧加热中，经过冶炼和连铸获得的板坯被加热至1200-1260℃并保温1-3小时；之后进行轧制，轧制包括粗轧和精轧，其中控制粗轧出口温度在1020-1100℃，控制终轧出口温度在840-920℃，控制总压下率≥80％； 上述冷却卷取包括将轧制后的钢板进行层流冷却，以30-70却，秒的速率，冷却到500-620包后进行卷取。
关于冶炼步骤，可采用目前常用的手段进行冶炼。例如，采用转炉炼钢，钢水经过RH真空脱气处理、LF炉脱硫处理。
关于连铸步骤，可采用目前主要应用的手段对冶炼后的钢水进行连铸。例如，在连铸过程中可通过控制过热度、二冷水、以及采用适当的轻压下等工艺，来控制连铸坯的中心偏析和夹杂物等水平，控制夹杂物等级小于1.5级。
热轧加热能够使得钢板中的V和/或Nb充分固溶。加热温度为1230±30℃，若加热温度超过1260℃，会有晶粒粗化的趋势，不利于钢板的韧性，并且氧化铁皮较厚，不利于氧化铁皮除磷。
在热轧步骤中，控制粗轧出口温度在1020-1100℃，能够保证粗轧在再结晶区域轧制，避免奥氏体区的微合金析出；终轧温度控制为840-920℃之间，能在未再结晶区域轧制，用于细化晶粒；卷取温度在500-620轧之间，控制贝氏体转变和微合金析出，从而控制钢板的强度，以及延伸率和冷弯性能。
在精轧之后进行冷却，本发明的冷却采用层流冷却的方式，例如采用水对精轧后的钢板进行冷却，层流冷却冷速为30-70进行冷，将精轧后的板坯冷却到500-620坯。之后在500-620坯之间卷取，得到显微组织为疲劳性能较好的贝氏体+铁素体组织和(Mo，V)C，(Mo，Nb)C微合金纳米析出，其他为少量珠光体和/或马氏体组织，并且珠光体和马氏体整体的体积分数之和≤10％。显微组织和纳米析出进一步使钢板获得了高强度以及更好的延伸率和冷弯性能。
关于酸洗步骤，可采用目前常用的酸洗方法。例如，酸洗速度控制在60-100m/min，酸洗过程最后的一个酸洗酸槽温度控制80-90℃、铁卷取离子浓度控制为30-40g/L。
可选地，在进行上述轧制步骤以及冷却卷取步骤之间还包括空冷，空冷时间为1-8s。即本发明在轧制后采用豫迟冷却控制模式，将精轧后的板坯进行空冷，之后再采用开启冷却水进行层流冷却，冷却到500-620℃，再进行卷取。轧制后空冷1-8s有利于晶粒的回复，具体操作方式可以通过控制精轧带钢的速度和冷却水起始阀门的位置来控制空冷时间。本发明经过轧制后的板坯在进行1-8s的空冷后其温度变化不大，温度会降低10-50℃，主要是依靠层流冷却对板坯进行降温。
可选地，形成的钢板化学成分满足0.3％≤0.5Cr+Mo≤0.55％。
可选地，本发明的扭力梁用制造方法中，形成的钢板化学成分满足碳当量CE Ⅱw≤0.50， 其中CE Ⅱw＝％C+％Mn/6+％(Cr+Mo+V)/5+％(Ni+Cu)/15。
可选地，上述形成的钢板的微观组织含有贝氏体和铁素体，贝氏体和铁素体在钢板中总的含量为大于或等于90％，即贝氏体+铁素体的体积分数之和≥90％，并且贝氏体在钢板中的体积分数大于50％，具体例如在55-85％之间。这样的微观组织有利于扭力梁用钢板的强度和折弯性能。进一步地，贝氏体+铁素体的体积分数之和＞95％。
可选地，形成的钢板的微观组织还包括珠光体和/或马氏体，即钢板中还可含有珠光体，或者含有马氏体，或者既含有珠光体也含有马氏体。无论是含有珠光体和马氏体中的一种还是两种，珠光体和马氏体在钢板中的体积分数之和≤10％。进一步地，珠光体和马氏体在钢板中的体积分数之和＜5％。
通过以上成分设计和钢板的制造工艺，钢板力学性能可达到如下水平：纵向屈服强度≥620MPa，抗拉强度≥760MPa，A50延伸率≧16％，180°冷弯性能R/T≧1.05。另外，本发明获得钢板的均匀延伸率≥7.0。进一步地，纵向屈服强度：620-720Mpa，抗拉强度：760-860Mpa，A50延伸率为16％-24％，180°冷弯性能R/T≧1.05，均匀延伸率在7.0-11.5。
进一步地，当钢板成分满足0.3％≤0.5Cr+Mo≤0.55％，且热轧卷取温度可在560-620℃，再配合轧制后空冷2s以上(包括2s)，不仅能够满足钢板的纵向屈服强度≥620MPa，抗拉强度≥760MPa，还能使得成型性能进一步提升，即A50延伸率≧18％，180°冷弯性能1.25≥R/T≥1.05，均匀延伸率≥8.0。
本发明还提供一种扭力梁，该扭力梁为通过上述的扭力梁用钢板制得。
本发明获得的扭力梁，能够达到纵向屈服强度≥680MPa，抗拉强度≥800MPa，台架疲劳为50-180万次。
另外，本发明采用上述的扭力梁用钢板的制造方法制得钢板，将此钢板作为板材，制成扭力梁。
本发明还提供了一种扭力梁的制造方法，将结合上述扭力梁用钢板的化学成分配比，将采用上述扭力梁用钢板的制造方法获得的钢板作为加工材料，制造成性能优异的扭力梁。目前封闭式扭力梁主要有热冲压和冷成型两种方式，本发明的扭力梁的制造方法采用冷成型的方式制造扭力梁。
本发明的扭力梁的制造方法采用冷成型的方式，包括以下步骤：焊管：将通过上述的扭力梁用钢板焊接成圆管；成型：将所述圆管液压或者冲压成型，形成异形管，该异形管为U形或V形，并具有内圆角，其中该内圆角R与异形管的厚度T的比值满足R/T≥1.05；之后进行去应力退火和/或喷丸，形成扭力梁。也即本发明的扭力梁的制造方法可以在成型 后直接进行喷丸步骤，也可以直接进行去应力退火步骤，或者既进行去应力退火步骤又进行喷丸步骤。在进行去应力退火和喷丸步骤时，可以是先采用去应力退火步骤之后再进行喷丸步骤。
焊管步骤中，例如，将高强度钢板通过激光焊接或者高频焊接成圆管，并切割成预设的尺寸。由于本发明C含量在0.04-0.085％，并且含有Nb和V中的一种或两种，具有细化晶粒的效果，使得在焊管步骤中，焊缝的硬度过度较为平稳，且显微组织较为细小。
成型步骤中，例如，通过冲压或者液压的成型方式将圆管成型成所需的异形管断面，要求扭力梁内圆角和厚度T的比值R/T≥1.05，保证圆角的内表面无折叠或者外表面无起皱等缺陷。
之后会进行去应力退火步骤，或者进行喷丸步骤，或者进行去应力退火和喷丸步骤。
其中，去应力退火步骤中，例如，将成型后的异形管放入加热炉，采用随炉升温，并在475-610℃下保温20～90min，然后随炉降温到300℃后空冷。钢板制成焊管以及管件成型为异形管的过程中，钢材内部结构有较多的残余应力，特别是表面的拉应力状态，导致扭力梁的疲劳寿命较短。去应力退火可以去除成型过程的应力状态，同时保持退火后的异形管的力学性能不降低甚至增加，纵向屈服强度≥680Mpa，抗拉强度≥800Mpa，A50延伸率≥16％。
其中，喷丸步骤中，例如，通过喷丸设备对管件的应力集中区域，即圆角位置进行表面喷丸处理。可以是对内圆角位置的内表面或外表面之一进行喷丸处理，也可以是对内圆角位置的内表面和外表面都进行喷丸处理。喷丸步骤能够保证扭力梁横梁的表面处于压应力状态，从而提高扭力梁的疲劳性能。
另外，在本发明的扭力梁的制造方法中，可对成型后的异形管分别进行去应力退火和喷丸步骤，即先对异形管进行去应力退火，去除成型过程的应力状态，再对退火后的管件的表面进行喷丸处理，能够进一步提高形成的扭力梁的疲劳性能。
为了获得高强度以及优异疲劳性能的扭力梁，本发明的扭力梁的制造方法中，首先从改善延伸率和折弯性能的角度出发，改善R角表面状态，来提高最终形成的扭力梁的疲劳性能，其次从提高钢板强度的角度出发，以及提高最终形成的扭力梁的纵向屈服强度以及抗拉强度，来提高扭力梁的疲劳性能。相应地，为同时实现上述两点效果会对钢板的化学成分配比、微观组织以及钢板制造方法等方面进行改进。
另外，在将获得的钢板制造成扭力梁的过程中，也会对成型的扭力梁的结构进行设计，从而与获得的钢板的性能相匹配(例如，通过本发明的扭力梁用钢板的成分设计以及制造 方法，获得的180°冷弯性能R/T≥1.05，相应在制造扭力梁时，要求扭力梁内圆角和厚度T的比值R/T≥1.05，保证制造的扭力梁结构与原扭力梁钢板的性能匹配，从而明显降低发生折叠、起皱、断裂等降低疲劳性能的问题出现)。
更令人惊喜的是，在制造扭力梁的过程中，由于之前在制造钢板时Nb和/或V元素的加入，在进行去应力退火时，扭力梁的强度相比于原材料扭力梁用钢板的强度能够得到保持，甚至会提高。另外，Ti元素的加入也能起到保持甚至提高扭力梁强度的作用。本发明获得的扭力梁用钢板的纵向屈服强度≥620MPa，抗拉强度≥760MPa，在制造成扭力梁后，其屈服强度≥680MPa，抗拉强度≥800MPa。
本发明的制造方法形成的扭力梁的心部硬度为260HV以上，其内外表面0.05mm处的显微硬度比心部高30-80HV，从而可以达到外强内韧的效果，也能避免扭力梁发生内部折叠，提高疲劳强度。
通过本发明的扭力梁的制造方法，形成的扭力梁能够达到纵向屈服强度≥680MPa、抗拉强度≥800MPa以及台架疲劳为50-180万次的优异性能。
附图说明
图1示出本发明实施例2的钢板的金相显微组织图；
图2示出本发明实施例的扭力梁内圆角横截面形貌示意图；
图3示出本发明实施例1、实施例11以及未经过去应力退火的扭力梁的显微硬度变化示意图。
具体实施方式
以下由特定的具体实施例说明本发明的实施方式，本领域技术人员可由本说明书所揭示的内容轻易地了解本发明的其他优点及功效。虽然本发明的描述将结合较佳实施例一起介绍，但这并不代表此发明的特征仅限于该实施方式。恰恰相反，结合实施方式作发明介绍的目的是为了覆盖基于本发明的权利要求而有可能延伸出的其它选择或改造。为了提供对本发明的深度了解，以下描述中将包含许多具体的细节。本发明也可以不使用这些细节实施。此外，为了避免混乱或模糊本发明的重点，有些具体细节将在描述中被省略。需要说明的是，在不冲突的情况下，本发明中的实施例及实施例中的特征可以相互组合。
应注意的是，在本说明书中，相似的标号和字母在下面的附图中表示类似项，因此，一旦某一项在一个附图中被定义，则在随后的附图中不需要对其进行进一步定义和解释。
为使本发明的目的、技术方案和优点更加清楚，下面将结合附图对本发明的实施方式作进一步地详细描述。
表1为本发明实施例1-10以及对比例1-7的各化学元素的质量百分比。表2为相应的实施例1-10以及对比例1-7的钢板制造方法，并列出了制造的钢板的性能。
本发明的扭力梁用钢板的制造方法包括冶炼、连铸、热轧和酸洗步骤。下述实施例和对比例首先采用转炉炼钢，钢水经过RH真空脱气处理、LF炉脱硫处理，具体方法可参照现有冶炼方法。接着进行连铸。在连铸过程中例如可通过控制过热度、二冷水，以及采用适当的轻压下等工艺，控制连铸坯的中心偏析和夹杂物等水平，控制夹杂物等级小于1.5级。本实施例中夹杂物等级参照GB/T 10561-2005的标准。
连铸后对获得的板坯进行热轧。热轧步骤包括热轧加热、轧制、冷却卷取。下述实施例和对比例中热轧加热的加热温度和保温时间如表2所示。轧制过程包括粗轧和精轧，表2还列出了各实施例中粗轧出口温度和终轧温度。轧制之后形成钢板，接着对钢板进行冷却卷取，冷却的方式采用层流冷却，表2中卷取温度代表对板坯进行卷取时的温度。空冷时间代表进行轧制后对板坯进行空冷的时间，当空冷时间为0s时代表该实施例未进行空冷而直接进行层流冷却。
将下述实施例1-10和对比例1-7中形成的钢板进行性能测试。本实施例力学性能测试按照GB/T228.1-2010标准执行，180°冷弯性能R/T按照GB/T232-2010标准执行，相应地获得纵向屈服强度、抗拉强度、均匀延伸率、A50延伸率以及180°冷弯性能结果。在表2中，180°冷弯性能一列，冷弯表面无起皱表示为“OK”，冷弯表面起皱表示为“NG”。
图1为实施例2的钢板的金相显微组织图，图中可知获得的钢板显微组织中包括贝氏体和铁素体，以及少量的珠光体，本实施例中贝氏体+铁素体的体积分数之和大于90％。
表3展示了采用上述实施例的钢板制成扭力梁的计算参数以及性能。本发明的扭力梁的制造方法采用冷成型的方式制造扭力梁，包括焊管、成型、之后进行去应力退火和/或喷丸步骤，从而形成扭力梁。
将上述实施例中的钢板焊接成圆管，之后将圆管液压或者冲压成型，形成异形管，该异形管为U形或V形，并具有内圆角，最后形成的扭力梁结构如图2所示。图2中表示出了扭力梁中内圆角处的半径R以及扭力梁的厚度T，本发明在扭力梁的制造过程中，会将内圆角制造成R/T满足大于或等于1.05，例如图2中内圆角的半径R为4.61，厚度T为3，形成的R/T＝1.537。成型的方式例如将圆管放入下模，闭合上模冲压成型，或者合模后，在管内液体加压胀成型的液压成型方式。实施例11-21以及对比例8-14分别采用不同的方 式将钢板制成扭力梁。表3中列出了不同实施例和对比例等形成的内圆角处的R/T值、成型后的工艺，即去应力退火的温度和时间，喷丸步骤的位置等具体参数。
将下述实施例11-20和对比例8-14中形成的扭力梁进行性能测试，本实施例力学性能测试按照GB/T 228.1-2010标准执行。内圆角处的纵向屈服强度和抗拉强度无法测得，可检测内圆角处的心部硬度以及表面与心部的显微硬度差，显微硬度的测试方法按照GB/T 4342-1991执行。
扭力梁台架的试验条件为位移控制±50mm，频率为1.5HZ。
下面结合表1，表2和表3中的实施例以及对比例进行详细说明：
表1和表2实施例1-10以及表3的实施例11-21，采用了本发明的设计方法，最终得到一种高强度高成型钢板，以及高强度高疲劳性能的扭力梁。
实施例1、实施例3-10在钢板制造工艺上均采用了空冷的方式，实施例中当卷取温度在500-620℃，且满足碳当量小于0.50，能够有较好的成型性和延伸率。
对比例1中碳含量较高导致折弯性能不好，进一步导致表3中的对比例8在液压过程中，R角表面出现微裂纹，在焊缝处还会开裂，最终导致台架疲劳不能达到50万次。实施例4与对比例1的钢板的制造方法工艺参数相近(例如卷取温度、空冷时间相同)，而对比例1碳当量较高，实施例4中碳当量较低，因此实施例4的钢板焊接性能更好。
对比例2中Cr和Mo含量较低，导致回火抗力较低(即强度较低)。对比例2和对比例3不满足0.096％≤2Nb+V≤0.17％的条件，导致板材的屈服强度和抗拉强度较低。相应地采用对比例2和对比例3的钢板制作成扭力梁，即对比例9和对比例10获得的扭力梁的强度也较低，最终导致材料抗疲劳能力较弱，并且不能达到减重轻量化的效果。
对比例4中的碳含量较低，同时由于热轧卷取温度过高，导致板材的强度较低，达不到钢板的抗拉强度≥760MPa的要求，最终导致表3中对比例11的扭力梁的抗拉强度也达不到800Mpa，不能达到减重轻量化的效果。
对比例5的微合金含量较高，不满足0.096％≤2Nb+V≤0.17％的条件，导致板材的强度较高，折弯性能不能满足R/T≥1.05，进一步导致表3中的对比例12在液压过程中，R角表面出现微裂纹，最终导致台架疲劳不能达到50万次。
对比例6的Cr含量相对较低，导致板材的强度较低，最终导致对比例13的扭力梁的台架疲劳能力较差。由于Cr含量低，加之在制作扭力梁时退火温度高，使得强度下降，不能达到高强减重轻量化的效果。
对比例7通过高Ti进行微合金强化，其板材和最终扭力梁(对比例14)的强度分别 能够达到800MPa以上，但是对比例14的扭力梁最终的台架疲劳性能仅为29万次，主要因为有较大的TiN析出，没有对疲劳性能有利的Nb和V的析出。另外，对比例7的卷取温度只有480℃，导致材料的成型性能不良。
实施例11-实施例21中，在加工成扭力梁中采用去应力退火或喷丸的步骤均能提高扭力梁的抗疲劳性能，其中采用去应力退火工艺和/或喷丸工艺能够保持甚至提高扭力梁的纵向屈服强度。
其中实施例11和实施例21相比，经过去应力退火后的扭力梁屈服强度增加的更加明显。
图3展示了实施例1中钢板厚度方向的显微硬度变化，即图中板材的显微硬度变化。本发明将实施例1中的钢板进行焊管、成型，形成异形管，在未进行去应力退火步骤的情况下检测其圆角厚度方向的显微硬度变化，即图3中圆角未退火的显微硬度变化。本发明还将实施例1中的钢板进行焊管、成型，并进行去应力退火步骤，形成扭力梁，即本发明的实施例11，并检测其圆角处的显微硬度变化，即图3中的圆角退火的显微硬度变化。可以看出，经过去应力退火后，实施例11表面的显微硬度较高，圆角处的心部硬度较低，达到了外强内韧的效果。
Figure PCTCN2021109665-appb-000001
Figure PCTCN2021109665-appb-000002
Figure PCTCN2021109665-appb-000003
虽然通过参照本发明的某些优选实施方式，已经对本发明进行了图示和描述，但本领域的普通技术人员应该明白，以上内容是结合具体的实施方式对本发明所作的进一步详细说明，不能认定本发明的具体实施只局限于这些说明。本领域技术人员可以在形式上和细节上对其作各种改变，包括做出若干简单推演或替换，而不偏离本发明的精神和范围。

Claims (20)

  1. 一种扭力梁用钢板，其化学成分按质量百分含量计为：
    C：0.04-0.085％，Si：0.02-0.5％，Mn：1.3-1.8％，Cr：0.15-0.5％，Mo：0.12-0.30％，Nb：≤0.058％，V：≤0.15％，Ti：≤0.02％，Al：0.02-0.1％，P≤0.02％，S≤0.005％，N≤0.005％，余量为Fe和不可避免杂质，
    其中，所述钢板中含有Nb、V中的一种或者两种，且满足0.096％≤2Nb+V≤0.17％。
  2. 如权利要求1所述的扭力梁用钢板，其特征在于，所述钢板化学成分满足0.3％≤0.5Cr+Mo≤0.55％。
  3. 如权利要求1所述的扭力梁用钢板，其特征在于，所述钢板化学成分满足碳当量CE Ⅱw≤0.50，其中CE Ⅱw＝％C+％Mn/6+％(Cr+Mo+V)/5+％(Ni+Cu)/15。
  4. 如权利要求1所述的扭力梁用钢板，其特征在于，所述钢板的微观组织含有贝氏体和铁素体，所述贝氏体和铁素体的总体积分数≥90％，所述贝氏体的体积分数>50％。
  5. 如权利要求4所述的扭力梁用钢板，其特征在于，所述钢板的微观组织还包括珠光体和/或马氏体。
  6. 如权利要求1-5任一项所述的扭力梁用钢板，其特征在于，所述钢板的纵向屈服强度≥620MPa，抗拉强度≥760MPa，A50延伸率≥16％，180°冷弯性能R/T≥1.05。
  7. 一种扭力梁用钢板的制造方法，所述钢板的化学成分按质量百分含量计为：
    C：0.04-0.085％，Si：0.02-0.5％，Mn：1.3-1.8％，Cr：0.15-0.5％，Mo：0.12-0.30％，Nb：≤0.058％，V：≤0.15％，Ti：≤0.02％，Al：0.02-0.1％，P≤0.02％，S≤0.005％，N≤0.005％；余量为Fe和不可避免杂质，其中，所述钢板中含有Nb、V中的一种或者两种，且满足0.096％≤2Nb+V≤0.17％；
    所述制造方法包括冶炼、连铸、热轧和酸洗，其中，
    所述热轧包括热轧加热、轧制以及冷却卷取，所述热轧加热中，经过冶炼和连铸的板坯被加热至1200-1260℃并保温1-3小时；所述轧制包括粗轧和精轧，其中控制粗轧出口温度在1020-1100℃，控制终轧出口温度在840-920℃，控制总压下率≥80％；所述冷却卷取中，对轧制后的钢板进行层流冷却，以30-70℃/秒的速率冷却到500-620℃后进行卷取。
  8. 如权利要求7所述的扭力梁用钢板的制造方法，其特征在于，在进行所述轧制和所述冷却卷取之间还包括空冷，所述空冷时间为1-8秒。
  9. 如权利要求7所述的扭力梁用钢板的制造方法，其特征在于，所述钢板化学成分满足0.3％≤0.5Cr+Mo≤0.55％。
  10. 如权利要求7所述的扭力梁用钢板的制造方法，其特征在于，所述钢板化学成分满足碳当量CE Ⅱw≤0.50，其中CE Ⅱw＝％C+％Mn/6+％(Cr+Mo+V)/5+％(Ni+Cu)/15。
  11. 如权利要求6所述的扭力梁用钢板的制造方法，其特征在于，形成的所述扭力梁用钢板的微观组织含有贝氏体和铁素体，所述贝氏体和铁素体的总体积分数≥90％，所述贝氏体的体积分数>50％。
  12. 如权利要求8所述的扭力梁用钢板的制造方法，其特征在于，形成的所述钢板的微观组织还包括珠光体和/或马氏体。
  13. 如权利要求7-12任一项所述的扭力梁用钢板的制造方法，其特征在于，形成的所述钢板的纵向屈服强度≥620MPa，抗拉强度≥760MPa，A50延伸率≥16％，180°冷弯性能R/T≥1.05。
  14. 一种扭力梁，其使用如权利要求1-6任一项所述的扭力梁用钢板制得。
  15. 如权利要求14所述的扭力梁，其特征在于，所述扭力梁的纵向屈服强度≥680MPa，抗拉强度≥800MPa，台架疲劳为50-180万次。
  16. 一种扭力梁的制造方法，其特征在于，包括以下步骤：
    焊管：将如权利要求1-6中任一项所述的扭力梁用钢板焊接成圆管；
    成型：将所述圆管液压或者冲压成型为异形管，所述异形管为U形或V形，并具有内圆角，其中所述内圆角R与所述异形管的厚度T的比值满足R/T≥1.05；
    之后进行去应力退火和/或喷丸，形成所述扭力梁。
  17. 如权利要求16所述的扭力梁的制造方法，其特征在于，所述去应力退火步骤中，将所述异形管加热，在475-610℃下保温20～90min，然后降温到300℃后空冷。
  18. 如权利要求16所述的扭力梁的制造方法，其特征在于，所述喷丸步骤中，对所述异形管的内圆角位置的内表面或外表面进行喷丸处理。
  19. 如权利要求16所述的扭力梁的制造方法，其特征在于，所述内圆角处的心部硬度为260HV以上，所述内圆角的内外表面0.05mm处的显微硬度比心部高30-80HV。
  20. 如权利要求16-19所述的扭力梁的制造方法，其特征在于，所述扭力梁的纵向屈服强度≧680MPa，抗拉强度≥800MPa，台架疲劳为50-180万次。
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