WO2017173950A1 - 具有增强弹性模量特征的轻质钢、钢板及其制造方法 - Google Patents

具有增强弹性模量特征的轻质钢、钢板及其制造方法 Download PDF

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WO2017173950A1
WO2017173950A1 PCT/CN2017/078770 CN2017078770W WO2017173950A1 WO 2017173950 A1 WO2017173950 A1 WO 2017173950A1 CN 2017078770 W CN2017078770 W CN 2017078770W WO 2017173950 A1 WO2017173950 A1 WO 2017173950A1
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steel
rolled sheet
lightweight steel
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manufacturing
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French (fr)
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杨旗
王利
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Priority to KR1020187031733A priority Critical patent/KR102128491B1/ko
Priority to US16/092,867 priority patent/US11078554B2/en
Priority to JP2018552174A priority patent/JP6783871B2/ja
Priority to EP17778614.2A priority patent/EP3441497B1/en
Publication of WO2017173950A1 publication Critical patent/WO2017173950A1/zh
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a lightweight steel, a steel sheet and a method of manufacturing the same, and more particularly to a lightweight steel, a steel sheet having a characteristic of enhancing elastic modulus, and a method of manufacturing the same.
  • high-strength steel and advanced high-strength steel to replace the traditional low-strength steel can improve the specific strength (strength to density ratio) of the steel for automobiles and reduce the thickness of the steel plate for structural parts, thereby realizing the lightweight structure of the automobile body.
  • the aluminum-rich low-density, high-strength and toughness steel sheets currently under development can further increase the specific strength of the steel sheets to meet the potentially more stringent lightweight requirements.
  • Al-rich lightweight steel has high specific strength
  • the elastic modulus of steel decreases with increasing aluminum content (eg, Fe-8.5wt%
  • Al lightweight steel has an elastic modulus of about 170 GPa, compared with conventional C-Mn).
  • Steel has a modulus of elasticity of about 205 GPa, which is reduced by as much as 17%).
  • the rigidity requirement of the member limits the thickness reduction of the high-strength steel sheet.
  • the elastic modulus of the high-strength steel sheet material itself can be increased without changing the shape of the member, further thinning of the thickness of the steel sheet and further weight reduction of the entire body can be achieved.
  • increasing the modulus of elasticity of high-strength steel can reduce the rebound of the steel sheet during press forming, thereby contributing to the manufacture of sheet metal parts of precise shape.
  • the reduction in the elastic modulus of the aluminum-rich lightweight steel significantly impairs the weight reduction effect caused by the decrease in density and the increase in specific strength. Therefore, for aluminum-rich lightweight high-strength steel, increasing its elastic modulus is one of the important factors that must be considered in the development and promotion of steel grades.
  • the elastic modulus of the entire steel sheet material can be increased by adding hard ceramic particles such as carbides and boride such as TiC, VC and TiB 2 to the steel matrix. This is because the above ceramic particles have a high elastic modulus of about 300 to 565 GPa, which is much higher than that of a conventional steel sheet as a base material. In addition, the above ceramic particles have a relatively low density as compared with a conventional steel sheet, and thus the steel-based composite material formed by adding the reinforcing particles also has a light characteristic.
  • hard ceramic particles such as carbides and boride such as TiC, VC and TiB 2
  • TiB 2 particles are particularly suitable for use as a reinforcing phase for steel sheet substrates because it is easy to establish a direct thermodynamic equilibrium relationship between TiB 2 and iron or iron-based alloys, and the two phases (matrix and TiB 2 reinforcing phase) are in phase. A coherent relationship is formed at the interface.
  • the elastic modulus of the TiB 2 particles is significantly higher than the elastic modulus of the carbide-enhancing particles.
  • a particle-reinforced steel-based composite material (hereinafter referred to as a lightweight steel having a reinforced elastic modulus) is usually prepared by a powder metallurgy process, that is, a metal powder of different compositions is sequentially uniformly mixed, compacted, and heated. sintering. Ceramic particles such as TiB 2 are generated in situ by a chemical reaction between metal powders of different compositions.
  • this process obviously has the following disadvantages: the powder is easily contaminated and oxidized before sintering, so that the steel matrix-ceramic particle interface cannot form a good bond; the residual light inside the lightweight steel after sintering, thereby inducing the material to be easy to be used in the service process. Stress concentration and premature failure occur; the manufacturing process is only suitable for small-scale production and cannot meet the needs of mass production in the automotive industry.
  • Lightweight steel having an enhanced modulus of elasticity can be produced industrially by in-situ reaction casting.
  • the hard reinforcing particles are generated in situ by the eutectic reaction during the solidification process of the molten steel, so that the steel matrix can uniformly distribute the fine hard reinforcing particles with an appropriate volume fraction.
  • the process has the characteristics of good compatibility of the particles with the matrix and low material preparation cost.
  • TiB 2 is enhanced in the cast structure of lightweight steel prepared by using Fe-Ti-B as a main component and adding a proper amount of C, Mn, Al, and Si elements (in which the Al content is not more than 1.5%).
  • TiB 2 is enhanced.
  • the particles are easy to be continuously distributed in the form of a mesh in the ferrite grain boundary, thereby affecting the subsequent processing deformation ability of the cast slab.
  • One of the objects of the present invention is to provide a lightweight steel having enhanced elastic modulus characteristics, which has low density, high specific strength, high tensile strength and high modulus of elasticity, can be industrially produced, and can The continuous reinforcement of the hard reinforcing particles at the grain boundary of the substrate is suppressed, thereby improving the processing deformation ability of the material and having excellent ductility.
  • the present invention proposes a lightweight steel having a characteristic of enhanced elastic modulus, the chemical composition mass percentage of the lightweight steel being: 0.001% ⁇ C ⁇ 0.30%, 0.05% ⁇ Mn ⁇ 4.0%, 1.5% ⁇ Al ⁇ 3.0%, 1.5% ⁇ Ti ⁇ 7.0%, 0.5% ⁇ B ⁇ 3.6%, the rest are Fe and inevitable impurity elements; the microstructure of the lightweight steel includes a uniform dispersion in the matrix and the matrix The fine hard reinforcing particles, wherein the matrix is wholly or partially ferrite and/or bainite, and the hard reinforcing particles include at least TiB 2 .
  • the inevitable impurities are mainly S, P and N elements, wherein P is a solid solution strengthening element, but P increases the cold brittleness of the steel and reduces
  • P is a solid solution strengthening element
  • P increases the cold brittleness of the steel and reduces
  • the plasticity of the steel deteriorates the cold bending performance and the welding performance, so that P ⁇ 0.02% can be controlled;
  • C is a solid solution strengthening element, which can significantly improve the yield strength and tensile strength of the steel sheet.
  • C is also an austenite stabilizing element that can be used to control and condition the microstructure of the steel matrix, which may be partially or wholly ferrite and/or bainite.
  • C and Ti can form TiC hard particles to increase the elastic modulus of the lightweight steel.
  • an excessively high C content deteriorates the weldability of lightweight steel. Therefore, the C content in the lightweight steel is controlled to be 0.001 to 0.30%.
  • Mn increases austenite stability and promotes austenite formation, and thus can be used to control and adjust the microstructure of the steel matrix. Mn improves the hardenability of the steel matrix and the solid solution strengthened steel matrix, thereby increasing the strength of the lightweight steel. Mn can also weaken or eliminate the hot brittleness of steel caused by S, thereby improving the hot workability of lightweight steel. However, excessively high Mn content can cause Mn segregation in the cast slab and a significant band-like structure distribution in the hot rolled sheet, thereby ultimately reducing the overall mechanical properties of the lightweight steel. Therefore, the Mn content in the lightweight steel is controlled to be 0.05 to 4.0%.
  • Al is an important alloying element in the present invention.
  • the addition of Al element helps to improve the microstructure of lightweight steel slab, reduce the continuous distribution of hard reinforced particles (mainly TiB 2 particles) at the grain boundary of the matrix, and inhibit the film-like hard reinforcement phase (such as TiB 2 ). Grain boundaries, thereby increasing the subsequent processable deformability and elongation at break of the material.
  • the addition of Al reduces the density of the steel sheet, thereby further increasing the weight reduction effect of the lightweight steel.
  • the addition of excess Al reduces the castability of the cast slab. Therefore, the Al content in the lightweight steel is controlled to be within the range of 1.5 to 3.0%.
  • Ti is an important alloying element in the present invention, and combines with B to form hard particles TiB 2 which mainly enhances the elastic modulus of the lightweight steel.
  • the combination of Ti and C to form TiC hard particles can also be used to enhance the elastic modulus of lightweight steel.
  • the Ti content is less than 1.5%, the volume fraction of TiB 2 particles formed in the steel matrix is low, which is not enough to significantly improve the elastic modulus of the lightweight steel; when the Ti content is higher than 7.0%, the steel matrix is easily formed.
  • Coarse TiB 2 primary phase particles which can adversely affect the castability and subsequent processability of the composite steel material. Therefore, the Ti content in the lightweight steel is controlled to be 1.5 to 7.0%.
  • B is also an important alloying element in the present invention, and is combined with Ti to form hard particles TiB 2 which mainly enhances the elastic modulus of the composite steel material. It is known from stoichiometry that in order to form TiB 2 particles, the B content is about 0.45 times the Ti content. Adding an excessive amount of B produces a Fe 2 B hard phase, thereby reducing the ductility of the steel; adding a small amount of B causes a more solid solution of Ti in the steel, thereby reducing the economical use of Ti. Therefore, the B content in the lightweight steel is controlled to be 0.5 to 3.6%.
  • the Ti and B elements also satisfy: -1.2% ⁇ (Ti - 2.22 * B) ⁇ 1.2%.
  • Ti and B represent the mass percentages of the Ti element and the B element, respectively.
  • the value of Ti substituted into the formula is 1.6.
  • the value of B substituted into the formula is 0.6 instead of 0.006.
  • the volume fraction of the hard particles accounts for at least 3% of the entire microstructure.
  • the sum of the volume fractions of the hard reinforcing particles in the microstructure of the lightweight steel At least 3% of the total microstructure can effectively enhance the elastic modulus of lightweight steel.
  • the lower limit of the proportion of the hard reinforcing particles is mainly controlled, and there is no particularly strict requirement for the upper limit.
  • the sum of the volume fractions of the hard reinforcing particles can be controlled to account for 3-25% of the total microstructure, which is more than 25%, which is generally difficult to achieve in industrial production.
  • the lightweight steel sheet has a tensile strength of >500 MPa, an elastic modulus of >200 GPa, and a density of ⁇ 7600 kg/m 3 .
  • the Ti element content is 3.0% ⁇ Ti ⁇ 6.0%
  • the B element content is 1.2% ⁇ B ⁇ 3.0%
  • the Ti and B elements also satisfy: -0.6% ⁇ ( Ti-2.22*B) ⁇ 0.6%; the volume fraction of the hard particles accounts for at least 6% of the total microstructure.
  • the content of Ti and B elements satisfies 3.0% ⁇ Ti ⁇ 6.0%, and 1.2% ⁇ B ⁇ 3.0%, so that the sum of the volume fractions of the reinforcing particles contained in the steel matrix is not less than 6%, at the same time, it is preferred that the content of Ti and B elements satisfy -0.6% ⁇ (Ti - 2.22 * B) ⁇ 0.6%, so that the reinforcing particles in the steel matrix are mainly TiB 2 to improve the hard particles to light steel The effect of the elastic modulus.
  • the lightweight steel sheet has a tensile strength of >500 MPa, an elastic modulus of >210 GPa, and a density of ⁇ 7400 kg/m 3 .
  • the hard reinforcing particles further include at least one of TiC and Fe 2 B.
  • the hard reinforcing particles have an average size of less than 15 ⁇ m.
  • the content of the alloying elements causes the hard reinforcing particles in the steel matrix to be mainly derived from the eutectic reaction which occurs when the molten steel is solidified, and the formation of the coarse primary phase is suppressed, so that the hard reinforcing particles can be uniformly fined in the steel matrix.
  • the distribution gives the lightweight steel good subsequent workability and good mechanical properties.
  • the lightweight steel has a good elongation at break.
  • the chemical composition of the lightweight steel further includes at least one of the following elements: 0.01% ⁇ Si ⁇ 1.5%, 0.01% ⁇ Cr ⁇ 2.0%, 0.01% ⁇ Mo ⁇ 1.0%, 0.01% ⁇ Nb ⁇ 0.2%, 0.01% ⁇ V ⁇ 0.5%, 0.05% ⁇ Ni ⁇ 1.0%, 0.05% ⁇ Cu ⁇ 1.0%, 0.001% ⁇ Ca ⁇ 0.2%.
  • Si is a ferrite solid solution strengthening element, which can improve the strength.
  • the addition of Si can significantly improve the mechanical stability of austenite, and contribute to the good strength and plasticity matching of lightweight steel.
  • an excessively high Si content reduces the plasticity of the lightweight steel; in addition, for a hot-dip galvanized lightweight steel plate, an excessively high Si content deteriorates the platability of the lightweight steel substrate. Therefore, the Si content in the lightweight steel is controlled to be 0.01 to 1.5%.
  • Cr:Cr can refine grain structure and inhibit grain coarsening during hot working, but too high Cr content will destroy the ductility of steel. Therefore, the Cr content in the lightweight steel is controlled to be 0.01 to 2.0%.
  • Mo has a similar effect to Cr.
  • the Mo content in the lightweight steel is controlled to be 0.01 to 1.0%.
  • Nb combines with C and N to form Nb (C, N), which can effectively suppress grain coarsening during hot working.
  • Nb strongly inhibits the occurrence of dynamic recrystallization, thereby increasing the rolling deformation resistance.
  • Nb can Refine ferrite grains.
  • the addition of excess Nb weakens the hot workability of lightweight steel and the toughness of lightweight steel sheets. Therefore, the Nb content in the lightweight steel is controlled to be 0.01 to 0.2%.
  • V:V helps to refine grain structure and improve tissue thermal stability. V can also increase the strength of lightweight steel, but adding V increases the cost of lightweight steel. Therefore, the V content in the lightweight steel is controlled to be 0.01% to 0.5%.
  • Ni is an austenite stabilizing element that hinders grain coarsening at high temperatures, but Ni is expensive and increases production costs. Therefore, the Ni content in the lightweight steel is controlled to be 0.05 to 1.0%.
  • the effect of Cu:Cu is similar to that of Ni, but when the Cu content is too high, it is disadvantageous for thermal deformation processing. Therefore, the Cu content in the lightweight steel is controlled to be 0.05 to 1.0%.
  • Ca is used to remove S to improve the hot workability of lightweight steel. Excessive Ca reduces the ductility of lightweight steel. Therefore, the Ca content in the lightweight steel is controlled to be 0.001 to 0.2%.
  • Another object of the present invention is to provide a steel sheet obtained by using the lightweight steel according to any of the above aspects.
  • the present invention also provides a steel sheet obtained by using the lightweight steel described in any of the above aspects.
  • Still another object of the present invention is to provide a manufacturing method which can be used for producing the above-mentioned steel sheet, which can produce the above-mentioned steel sheet using the lightweight steel described in any of the above aspects.
  • the present invention also provides a method of manufacturing the above steel sheet, comprising the steps of:
  • the step (3) is further performed by recrystallization annealing.
  • the recrystallization annealing treatment is performed on the hot rolled sheet to increase the ductility of the hot rolled sheet, and the hot rolled sheet has a cold rolling deformation in the subsequent order. Good rolling deformation ability. If the hot rolled sheet structure is a completely recrystallized structure and the hot rolled steel sheet has good cold rolling deformation ability and ductility, the recrystallization annealing step can be omitted.
  • the heating temperature is 1000 to 1250 ° C
  • the holding time is 0.5 to 3 h
  • the finishing temperature is ⁇ 850 ° C
  • 400 to 750 Coil under °C.
  • the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, and the heat is maintained 30. ⁇ 600s, then cooled to room temperature.
  • the reason for the selection of the relevant parameters when the step (3) adopts the continuous annealing method is: when the soaking temperature is lower than 800 ° C or the holding time is less than 30 s, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the temperature is higher than 1000 °C, the matrix structure of the steel plate will rapidly coarsen, which will affect its subsequent deformation ability. The holding time does not exceed 600s for production economic considerations.
  • the hot rolled sheet is heated to a soaking temperature of 650 to 900 ° C, The holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for the selection of the relevant parameters when the step (3) adopts the hood furnace annealing method is: when the soaking temperature is lower than 650 ° C and the holding time is less than 0.5 h, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the soaking temperature is higher than 900 °C, the microstructure of the steel sheet matrix will be significantly coarsened, which will affect its subsequent deformation ability. The holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the present invention also provides another manufacturing method of the above steel sheet, comprising the steps of:
  • the step (1) adopts a strip casting process: injecting molten steel having the light steel component between a pair of counter-rotating cooling casting rolls, The molten steel is solidified between the two rolls to form a thin strip blank having a thickness of not more than 10 mm, and the solidification cooling rate is greater than 80 ° C / s.
  • the rapid solidification of the molten steel can avoid segregation of the alloying elements and distribute the generated hard reinforcing particles finely and evenly in the thin strip blank matrix.
  • the average size of the hard reinforcing particles can be refined to less than 10 ⁇ m.
  • the fine uniform distribution of hard reinforcing particles and the uniform distribution of alloying elements are beneficial for improving the ductility of the final lightweight steel.
  • the thin strip blank prepared by the strip casting process is directly hot rolled into a hot rolled coil of a predetermined thickness without external heating, which greatly simplifies the strip production process and reduces the production cost.
  • the step (3) is further performed by recrystallization annealing.
  • the recrystallization annealing treatment is performed on the hot rolled sheet to increase the ductility of the hot rolled sheet, and the hot rolled sheet has a cold rolling deformation in the subsequent order. Good rolling deformation ability. If the hot rolled sheet structure is a completely recrystallized structure and the hot rolled steel sheet has good cold rolling deformation ability and ductility, the recrystallization annealing step can be omitted.
  • the thin strip blank is immediately hot rolled without external auxiliary heating, and the final rolling temperature is controlled to be ⁇ 850 ° C.
  • the rolling reduction is 20-60%, and then coiled at 400 to 750 °C.
  • the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, and the heat is maintained. 30 to 600 s, then cool to room temperature.
  • the reason for the selection of the relevant parameters when the step (3) adopts the continuous annealing method is: when the soaking temperature is lower than 800 ° C or the holding time is less than 30 s, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the temperature is higher than 1000 °C, the matrix structure of the steel plate will rapidly coarsen, which will affect its subsequent deformation ability. The holding time does not exceed 600s for production economic considerations.
  • the hot rolled sheet is heated to a soaking temperature of 650 to 900 ° C.
  • the holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for the selection of the relevant parameters when the step (3) adopts the hood furnace annealing method is: when the soaking temperature is lower than 650 ° C and the holding time is less than 0.5 h, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the soaking temperature is higher than 900 °C, the microstructure of the steel sheet matrix will be significantly coarsened, which will affect its subsequent deformation ability. The holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the present invention also provides a further manufacturing method of the above steel sheet, comprising the steps of:
  • the step (5) is performed after cold rolling
  • the recrystallization annealing process transforms the deformed structure of the steel sheet matrix into an equiaxed recrystallized structure to significantly improve the deformability and elongation at break of the steel sheet.
  • the step (2a) further comprises a recrystallization annealing after hot rolling.
  • the above scheme considers that if there is an unrecrystallized microstructure in the matrix of the hot rolled sheet, the recrystallization annealing treatment is performed on the hot rolled sheet to increase the ductility of the hot rolled sheet, so that the hot rolled sheet has good deformation in subsequent cold rolling deformation. Rolling deformation ability. If the hot rolled sheet structure is a completely recrystallized structure and the hot rolled steel sheet has a good cold rolling deformation ability, the recrystallization annealing step can be omitted.
  • the heating temperature is 1000 to 1250 ° C
  • the holding time is 0.5 to 3 h
  • the finishing temperature is ⁇ 850 ° C
  • step (2a) when the step (2a) is performed by continuous annealing to perform recrystallization annealing after hot rolling, the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, and the heat is maintained 30. ⁇ 600s, then cooled to room temperature.
  • the reason for the selection of the relevant parameters in the step (2a) using the continuous annealing method is: when the soaking temperature is lower than 800 ° C or the holding time is less than 30 s, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the temperature is higher than 1000 °C, the matrix structure of the steel plate will rapidly coarsen, which will affect its subsequent deformation ability. The holding time does not exceed 600s for production economic considerations.
  • the hot rolled sheet is heated to a soaking temperature of 650 to 900 ° C.
  • the holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for the selection of the relevant parameters when the step (2a) adopts the hood furnace annealing method is: when the soaking temperature is lower than 650 ° C and the holding time is less than 0.5 h, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the soaking temperature is higher than 900 °C, the microstructure of the steel sheet matrix will be significantly coarsened, which will affect its subsequent deformation ability. The holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the cold rolling reduction is controlled to be 25-75%.
  • the hot-rolled steel sheet after pickling is subjected to cold rolling deformation to a predetermined thickness, and the cold rolling reduction is 25 to 75%, preferably 40 to 60%.
  • Increase the amount of cold rolling reduction which can be used in the subsequent annealing process It helps to refine the microstructure of the matrix and improve the uniformity of the microstructure of the annealed steel sheet, thereby improving the ductility of the annealed steel sheet.
  • the cold rolling reduction is too large, the deformation resistance of the material due to work hardening is very high, which makes it extremely difficult to prepare a cold-rolled steel sheet having a predetermined thickness and a good shape; and too high cold rolling deformation induces the steel sheet.
  • the inside forms microcracks between the substrate and the hard reinforcing particles, which in turn causes damage to the material.
  • the step (5) when the step (5) is performed by a continuous annealing method for recrystallization annealing of a cold-rolled sheet, the cold-rolled sheet is heated to a soaking temperature of 700 to 900 ° C, and the heat is maintained. 30 to 600 s, then cool to room temperature.
  • the reason for selecting the range of relevant parameters when using the continuous annealing method in the above step (5) is that when the soaking temperature is lower than 700 ° C or the holding time is less than 30 s, the deformed structure of the steel sheet matrix does not undergo significant recrystallization; Above 900 °C, the steel substrate structure will rapidly coarsen after completion of recrystallization, which will affect the elongation at break of the annealed steel sheet.
  • the holding time does not exceed 600s for production economic considerations.
  • the step (5) when the step (5) is performed by a cover furnace annealing method for recrystallization annealing of the cold rolled sheet, the cold rolled sheet is heated to a soaking temperature of 600 to 800 ° C. The holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for selecting the range of relevant parameters when using the cover furnace annealing method in the above step (5) is that when the soaking temperature is lower than 600 ° C and the holding time is less than 0.5 h, the deformed structure of the steel sheet matrix does not undergo obvious recrystallization; When the soaking temperature is higher than 800 °C, the deformed structure of the steel sheet matrix will remarkably coarsen after completion of recrystallization, thereby affecting the elongation at break of the annealed steel sheet.
  • the holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the present invention also provides a further manufacturing method of the above steel sheet, comprising the steps of:
  • the step (1) adopts a strip casting process: injecting molten steel having the light steel component into a pair of counter-rotating cooling casting rolls, steel The water solidifies between the two rolls to form a thin strip having a thickness of not more than 10 mm, and the solidification cooling rate is greater than 80 ° C / s.
  • the rapid solidification of the molten steel can avoid segregation of the alloying elements and distribute the generated hard reinforcing particles finely and evenly in the thin strip blank matrix.
  • the average size of the hard reinforcing particles can be refined to less than 10 ⁇ m.
  • the fine uniform distribution of hard reinforcing particles and the uniform distribution of alloying elements are beneficial for improving the ductility of the final lightweight steel.
  • the thin strip blank prepared by the strip casting process is directly hot rolled into a hot rolled coil of a predetermined thickness without external heating, which greatly simplifies the strip production process and reduces the production cost.
  • the strip casting process directly casts molten steel out of the thin strip, without hot rolling or slightly hot rolling (1 to 2 passes), and then cold rolling to produce cold rolled sheets.
  • the step (5) converts the deformed structure of the steel sheet substrate into an equiaxed recrystallized structure by using a cold rolling recrystallization annealing process to significantly improve the deformation of the steel sheet. Capacity and elongation at break.
  • the step (2a) further comprises a recrystallization annealing after hot rolling.
  • the recrystallization annealing treatment is performed on the hot rolled sheet to increase the ductility of the hot rolled sheet, so that the hot rolled sheet has good deformation in subsequent cold rolling deformation. Rolling deformation ability. If the hot rolled sheet structure is a completely recrystallized structure and the hot rolled steel sheet has good cold rolling deformation ability and ductility, the recrystallization annealing step can be omitted.
  • the thin strip blank is immediately hot rolled without external auxiliary heating, and the final rolling temperature is controlled to be ⁇ 850 ° C, and the heat is controlled.
  • the rolling reduction is 20-60%, and then coiled at 400 to 750 °C.
  • the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, and the heat is maintained 30. ⁇ 600s, then cooled to room temperature.
  • the reason for the selection of the relevant parameters in the step (2a) using the continuous annealing method is: when the soaking temperature is lower than 800 ° C or the holding time is less than 30 s, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the temperature is higher than 1000 °C, the matrix structure of the steel plate will rapidly coarsen, which will affect its subsequent deformation ability. The holding time does not exceed 600s for production economic considerations.
  • the hot rolled sheet is heated to a soaking temperature of 650 to 900 ° C.
  • the holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for the selection of the relevant parameters when the step (2a) adopts the hood furnace annealing method is: when the soaking temperature is lower than 650 ° C and the holding time is less than 0.5 h, the substrate microstructure of the steel sheet does not undergo significant recrystallization; When the soaking temperature is higher than 900 °C, the microstructure of the steel sheet matrix will be significantly coarsened, which will affect its subsequent deformation ability. The holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the cold rolling reduction is controlled to be 25-75%.
  • the hot-rolled steel sheet after pickling is subjected to cold rolling deformation to a predetermined thickness, and the cold rolling reduction is 25 to 75%, preferably 40 to 60%.
  • the cold rolling reduction is 25 to 75%, preferably 40 to 60%.
  • Increasing the amount of cold rolling reduction can help to refine the matrix structure and improve the uniformity of the annealed steel sheet during the subsequent annealing process, thereby improving the ductility of the annealed steel sheet.
  • the cold rolling reduction is too large, the deformation resistance of the material due to work hardening is very high, which makes it extremely difficult to prepare a cold-rolled steel sheet having a predetermined thickness and a good shape; and too high cold rolling deformation induces the steel sheet.
  • the inside forms microcracks between the substrate and the hard reinforcing particles, which in turn causes damage to the material.
  • the step (5) when the step (5) is performed by continuous annealing to perform recrystallization annealing of the cold-rolled sheet, the cold-rolled sheet is heated to a soaking temperature of 700 to 900 ° C, and the heat is maintained. 30 to 600 s, then cool to room temperature.
  • the reason for selecting the range of relevant parameters when using the continuous annealing method in the above step (5) is that when the soaking temperature is lower than 700 ° C or the holding time is less than 30 s, the deformed structure of the steel sheet matrix does not undergo significant recrystallization; Above 900 °C, the steel substrate structure will rapidly coarsen after completion of recrystallization, which will affect the elongation at break of the annealed steel sheet.
  • the holding time does not exceed 600s for production economic considerations.
  • the step (5) when the step (5) is performed by a cover furnace annealing method for recrystallization annealing of the cold rolled sheet, the cold rolled sheet is heated to a soaking temperature of 600 to 800 ° C. The holding time is 0.5 to 48 hours, and then cooled to room temperature with the furnace.
  • the reason for selecting the range of relevant parameters when using the cover furnace annealing method in the above step (5) is that when the soaking temperature is lower than 600 ° C and the holding time is less than 0.5 h, the deformed structure of the steel sheet matrix does not undergo obvious recrystallization; When the soaking temperature is higher than 800 °C, the deformed structure of the steel sheet matrix will remarkably coarsen after completion of recrystallization, thereby affecting the elongation at break of the annealed steel sheet.
  • the holding time of no more than 48 hours is due to the long holding time affecting the production efficiency.
  • the present invention utilizes the formation of a finely dispersed hard reinforcing particle having a high modulus of elasticity in a matrix of steel to increase the overall elastic modulus of the above-mentioned steel sheet material, and to provide the steel sheet with high strength and elongation at break.
  • the microstructure and macroscopic mechanical properties of the steel sheet described above are usually achieved by controlling the above-described light-weight steel components in combination with the above-described manufacturing method.
  • the lightweight steel of the present invention mainly utilizes TiB 2 hard particles to reinforce the elastic modulus of the steel sheet.
  • a thermodynamic equilibrium relationship between TiB 2 and a lightweight steel matrix is easy to establish, and both can form a coherent relationship at the phase interface. This means that there is a strong bonding ability between the hard particles TiB 2 and the matrix, and the lightweight steel has good workability and elongation at break (the hard particles and the matrix are less prone to splitting).
  • the density of TiB 2 is lower than the density of the substrate, thereby reducing the overall density of the lightweight steel, and significantly increasing the specific elastic modulus (ratio of elastic modulus to density) of the lightweight steel.
  • the present invention utilizes the alloying element Al to effectively improve the as-cast microstructure of the lightweight steel containing the second phase hard phase, suppressing or reducing the continuous distribution of the second phase hard reinforcing particles at the grain boundary of the lightweight steel substrate, thereby Significantly improve the machinability of lightweight steel and increase the elongation at break of lightweight steel.
  • the addition of Al can reduce the density of lightweight steel and increase the specific modulus of elasticity of lightweight steel.
  • the microstructure of the lightweight steel of the present invention is partially or wholly based on ferrite and/or bainite, and the volume fraction of hard particles such as TiB 2 contained may be more than 12%, and the elasticity of the lightweight steel.
  • the modulus can be increased to 230 GPa or more, the density is reduced to 7400 kg/m 3 or less, and the tensile strength of the steel sheet is >500 MPa.
  • the steel sheet prepared by using the lightweight steel of the present invention can be used for the manufacture of automobile parts, and achieves the goal of further reducing the weight of the automobile structure.
  • the manufacturing method of the present invention can be completed on the existing high-strength steel production line without major adjustment. Therefore, the manufacturing method of the invention has a good application prospect.
  • the manufacturing method of the present invention can disperse finer hard reinforcing particles (average size less than 10 ⁇ m) in the steel sheet substrate, and The matrix structure is also refined. Similarly, the steel sheet has good thermal processing properties and elongation at break. Therefore, the manufacturing method of the invention has a good application prospect.
  • Figure 1 is a photograph of a low-magnification metallographic structure of a slab of a lightweight steel comparative example B2.
  • Figure 2 is a photograph of a high-magnification metallographic structure of a slab of a lightweight steel comparative example B2.
  • Figure 3 is a photograph of a low-magnification metallographic structure of a slab of lightweight steel Example A6.
  • Figure 4 is a photograph of a high-magnification metallographic structure of a slab of lightweight steel Example A6.
  • Figure 5 is a photograph of the hot rolled profile of the steel sheet Comparative Example CS2.
  • Fig. 6 is a photograph showing the hot rolled profile of the steel sheet embodiment HM6-HM8.
  • Fig. 7 is a photograph of a low-magnification metallographic structure of the steel sheet embodiment HM6 after hot rolling.
  • Fig. 8 is a photograph of a high-magnification metallographic structure of the steel sheet embodiment after hot rolling of HM6.
  • Table 1 lists the mass ratios of the chemical elements in Examples A1-A9 and Comparative Examples B1-B3 of lightweight steel having enhanced elastic modulus characteristics.
  • Recrystallization annealing after hot rolling when recrystallization annealing is performed on the hot rolled sheet by continuous annealing, the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, kept for 30 to 600 s, and then cooled to room temperature;
  • the hot-rolled sheet is heated to a soaking temperature of 650 to 900 ° C, a holding time of 0.5 to 48 h, and then cooled to room temperature with the furnace.
  • step (3) The hot rolled sheet in the step (2) was rapidly cooled to a coiling temperature for 1 hour, and then cooled to room temperature with the furnace to simulate the coiling temperature drop of the hot rolled sheet. In some embodiments where there is no unrecrystallized microstructure in some of the hot rolled sheet substrates, step (3) may not be performed.
  • Table 2 lists the specific process parameters of the steel sheet manufacturing methods of Examples HM1-HM9 and Comparative Examples CS1-CS3.
  • the present invention can obtain low density, high tensile strength and high elastic modulus through reasonable composition and process design. A number of hot-rolled lightweight steel sheets with excellent ductility.
  • Figures 1 and 2 show the low and high as-cast microstructures of the lightweight steel comparative example B2, respectively, and Figures 3 and 4 show the low and high-old as-cast microstructures of the lightweight steel example A6, respectively.
  • the arrows in Figures 2 and 4 refer to hard reinforcing particles.
  • the ferrite matrix is surrounded by a continuously distributed hard reinforcing phase (mainly TiB 2 particles), from Fig. 3 and Fig. 3 4 It can be observed that the primary phase and the eutectic product (i.e., the hard reinforcing phase) of the lightweight steel example A6 are discretely distributed in the ferrite matrix.
  • a continuously distributed hard reinforcing phase mainly TiB 2 particles
  • Comparative Example B3 and Examples A1-A5, A7-A9 also observed similar phenomena to Comparative Example B2 and Example A6, respectively, while Comparative Examples B2-B3 did not contain Al element, and Examples A1-A9 contained The Al element, therefore, the addition of the Al element contributes to the improvement of the microstructure of the lightweight steel slab, reduces the continuous distribution of the hard reinforced particles at the grain boundary of the substrate, and inhibits the grain boundary of the hard reinforcing phase-encapsulated matrix.
  • Figures 5 and 6 show the hot rolled profile of the steel sheet comparative example CS2 and the steel sheet example HM6-HM8, respectively.
  • Figures 7 and 8 show the low and high power microstructures of the steel sheet embodiment HM6 after hot rolling, respectively.
  • the arrows in Figures 7 and 8 are referred to as hard reinforcing particles.
  • the distribution of hard reinforcing particles in the ferrite matrix in the hot rolled sheet can be observed from Fig. 7 and Fig. 8.
  • the figure shows that the elongated hard reinforcing phase in the as-cast microstructure is broken and fined due to thermal deformation. Chemical.
  • the molten steel is cast and rolled into a thin strip blank having a thickness of not more than 10 mm by means of thin strip continuous casting, wherein S, P and N are inevitable impurities.
  • the balance is Fe; the solidification cooling rate of the molten steel is about 320 ° C / s;
  • Hot rolling obtaining a hot-rolled sheet of 1.3 mm thickness: hot-rolling the strip blank immediately without external auxiliary heating, controlling the finishing rolling temperature ⁇ 850 ° C, and the hot rolling reduction is 20-60% Then, it is taken up at 400 to 750 °C.
  • Recrystallization annealing after hot rolling when recrystallization annealing is performed on the hot rolled sheet by continuous annealing, the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, kept for 30 to 600 s, and then cooled to room temperature;
  • the hot-rolled sheet is heated to a soaking temperature of 650 to 900 ° C, a holding time of 0.5 to 48 h, and then cooled to room temperature with the furnace.
  • the metallographic observation of the above embodiment HM10-HM13 revealed that the hot-rolled sheet substrate is an equiaxed ferrite structure, and the average size of the TiB 2 -based hard reinforcing particles distributed in the matrix is about 3 ⁇ . 5 ⁇ m.
  • Examples HM14-HM18 respectively smelt and continuously cast light steel materials having A1, A3, A5, A6 and A9 in Table 1 to obtain slabs having a thickness of 120 to 300 mm, wherein S, P and N Is an inevitable impurity, the balance is Fe;
  • heating temperature is 1000 ⁇ 1250 ° C, holding time is 0.5-3 h, finishing rolling temperature ⁇ 850 ° C, and then coiling at 400-750 ° C;
  • Recrystallization annealing after hot rolling when recrystallization annealing is performed on the hot rolled sheet by continuous annealing, the hot rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, kept for 30 to 600 s, and then cooled to room temperature;
  • the hot-rolled sheet is heated to a soaking temperature of 650 to 900 ° C, the holding time is 0.5 to 48 h, and then cooled to room temperature with the furnace;
  • Recrystallization annealing of cold-rolled sheet After cold rolling and recrystallization annealing by continuous annealing, the cold-rolled sheet is heated to a soaking temperature of 700-900 ° C, kept for 30-600 s, and then cooled to room temperature; In the furnace annealing method, after cold rolling and recrystallization annealing, the cold rolled sheet is heated to a soaking temperature of 600 to 800 ° C, a holding time of 0.5 to 48 h, and then cooled to room temperature with the furnace.
  • Table 6 lists the specific process parameters of the steel sheet manufacturing method of Example HM14-HM18.
  • the steel sheet has a tensile strength of >500 MPa and an elastic modulus of >200 GPa. Therefore, the present invention can obtain a hot-rolled lightweight steel sheet having low density, high tensile strength, high elastic modulus, and excellent ductility.
  • the steel material with the light steel material in Table 1 is smelted and then cast by thin strip casting Casting and rolling into a thin strip blank having a thickness of not more than 10 mm, wherein S, P and N are unavoidable impurities, the balance being Fe; the solidification cooling rate of the molten steel is about 200 ° C / s;
  • Hot rolling, obtaining hot-rolled sheet hot strip rolling is carried out immediately without external auxiliary heating, controlling the final rolling temperature ⁇ 850 ° C, the hot rolling reduction is 20-60%, and then at 400 Coiling at ⁇ 750 °C;
  • Recrystallization annealing after hot rolling when re-crystallization annealing is performed by continuous annealing, the hot-rolled sheet is heated to a soaking temperature of 800 to 1000 ° C, kept for 30 to 600 s, and then cooled to room temperature; When the furnace is annealed, the hot-rolled sheet is heated to a soaking temperature of 650 to 900 ° C, the holding time is 0.5 to 48 h, and then cooled to room temperature with the furnace;
  • Recrystallization annealing of cold-rolled sheet After cold rolling and recrystallization annealing by continuous annealing, the cold-rolled sheet is heated to a soaking temperature of 700-900 ° C, kept for 30-600 s, and then cooled to room temperature; In the furnace annealing method, after cold rolling and recrystallization annealing, the cold rolled sheet is heated to a soaking temperature of 600 to 800 ° C, a holding time of 0.5 to 48 h, and then cooled to room temperature with the furnace.
  • Table 8 lists the specific process parameters of the steel sheet manufacturing method of Example HM19-HM22.

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Abstract

一种具有增强弹性模量特征的轻质钢及其制造方法，轻质钢的化学成分质量百分数为：0.001％≤C≤0.30％，0.05％≤Mn≤4.0％，1.5％＜Al＜3.0％，1.5％≤Ti≤7.0％，0.5％≤B≤3.6％，其余为Fe和不可避免的杂质元素；轻质钢的微观组织包括基体和基体中均匀弥散分布的细小的硬质增强颗粒，其中基体全部地或部分地为铁素体和/或贝氏体，硬质增强颗粒至少包括TiB 2。

Description

具有增强弹性模量特征的轻质钢、钢板及其制造方法 技术领域
本发明涉及一种轻质钢、钢板及其制造方法，尤其涉及一种具有增强弹性模量特征的轻质钢、钢板及其制造方法。
背景技术
应用高强钢和先进高强钢替代传统低强度级别钢材，可以提高汽车用钢的比强度(强度与密度之比)和减小结构件用钢板的厚度，实现汽车车身结构轻量化。目前正在研发的富铝低密度、高强韧性钢板可以进一步提高钢板的比强度，从而能满足潜在的更为严苛的轻量化需求。
然而，尽管富铝轻质钢具有高比强度，但是随铝含量增加，钢的弹性模量不断降低(如Fe-8.5wt％Al轻质钢的弹性模量约为170GPa，与常规C-Mn钢所具有约205GPa的弹性模量相比较，降低达17％之多)。由材料力学理论可知，在钢板材料的弹性模量一定的条件下，构件刚度需求限制了高强钢钢板的厚度减薄。因此，为满足构件刚度需求，在不改变构件形状的前提下，如能增加高强度钢板材料本身的弹性模量，则可以实现钢板厚度进一步减薄和车身整体的进一步减重。另外，提高高强钢的弹性模量可以减少钢板在冲压成型时的回弹，从而有助于制造形状精确的钣金件。富铝轻质钢弹性模量的降低显著削弱了由密度降低和比强度升高而带来的减重效果。所以，针对富铝轻质高强钢，提高其弹性模量是钢种开发和推动钢种应用所必须要考虑的重要因素之一。
通过在钢的基体中添加碳化物和硼化物等硬质陶瓷颗粒(如TiC、VC和TiB2)可以提高钢板材料整体的弹性模量。这是由于上述陶瓷颗粒具有约300～565GPa的高弹性模量，远高于作为基体材料的常规钢板的弹性模量。另外，与常规钢板相比较，上述陶瓷颗粒具有相对低的密度，因此通过添加增强颗粒而形成的钢铁基复合材料同样具有轻质的特征。研究表明，TiB2颗粒尤其适用于做钢板基体的增强相，这是因为TiB2与铁或铁基合金之间易于建立直接的热力学平衡关系，并且两相(基体和TiB2增强相)在相界面处形成共格关系。另外，TiB2 颗粒的弹性模量要显著高于碳化物增强颗粒的弹性模量。
现有技术中，颗粒增强钢铁基复合材料(以下称之为具有增强弹性模量的轻质钢)通常通过粉末冶金工艺来制备,即将不同成分的金属粉末依次经均匀混合、压实成形和高温烧结。TiB2等陶瓷颗粒通过不同成分的金属粉末之间的化学反应而原位生成。然而这种工艺明显具有以下缺点：粉末在烧结前容易被污染和氧化，从而使钢质基体-陶瓷颗粒界面无法形成良好结合；烧结后轻质钢内部残留孔隙，从而诱发材料在服役过程中易于发生应力集中和过早破坏；制造工艺只适合少量生产，无法满足汽车工业中大批量生产制造的需求。
通过原位反应铸造法可以工业规模化生产具有增强弹性模量的轻质钢。该技术方法中，硬质增强颗粒在钢水凝固过程中通过共晶反应原位生成，因而钢质基体中能均匀弥散分布适量体积分数的细小硬质增强颗粒。并且，该工艺还具有颗粒与基体相容性好以及材料制备成本低等特点。然而，目前以Fe-Ti-B为主要成分并适量添加C、Mn、Al和Si元素的成分体系(其中Al含量不超过1.5％)所制备的轻质钢的铸造组织中，TiB2等增强颗粒易于在铁素体晶界呈网状连续分布，从而影响铸坯的后序加工变形能力。
发明内容
本发明的目的之一在于提供一种具有增强弹性模量特征的轻质钢，其具有低密度、高比强度、高抗拉强度以及高弹性模量的特性，可以工业规模化生产，且能抑制硬质增强颗粒在基体晶界处连续分布，从而改善材料的加工变形能力，具有优良延展性。
为了实现上述目的，本发明提出了一种具有增强弹性模量特征的轻质钢，所述轻质钢的化学成分质量百分数为：0.001％≤C≤0.30％，0.05％≤Mn≤4.0％，1.5％＜Al＜3.0％，1.5％≤Ti≤7.0％，0.5％≤B≤3.6％，其余为Fe和不可避免的杂质元素；所述轻质钢的微观组织包括基体和基体中均匀弥散分布的细小的硬质增强颗粒，其中所述基体全部地或部分地为铁素体和/或贝氏体，所述硬质增强颗粒至少包括TiB2。
在本发明所述的具有增强弹性模量特征的轻质钢中，不可避免的杂质主要是S、P和N元素，其中，P是固溶强化元素，但是P会增加钢的冷脆性，降低钢的塑性，使冷弯性能和焊接性能变坏，因此，可以控制P≤0.02％；S使钢 产生热脆性，降低钢的延展性和韧性，使焊接性能变坏，降低钢的耐蚀性，因此，可以控制S≤0.01％；N与Al形成AlN，过量粗大AlN会降低钢的热塑性，因此，可以控制N≤0.01％。
本发明所述的具有增强弹性模量特征的轻质钢中的各化学元素的设计原理为：
C：C是固溶强化元素，可以显著提高钢板的屈服强度和抗拉强度。C还是奥氏体稳定化元素，可以用来控制和调节钢质基体的显微组织，该显微组织可以部分或全部为铁素体和(或)贝氏体。另外，C和Ti可以形成TiC硬质颗粒以提高轻质钢的弹性模量。然而，过高的C含量会恶化轻质钢的焊接性能。因此，所述轻质钢中C含量控制为：0.001～0.30％。
Mn：Mn增加奥氏体稳定性和促进奥氏体生成，因而能用来控制和调节钢质基体的显微组织。Mn能提高钢质基体的淬透性和固溶强化钢质基体，从而增加轻质钢的强度。Mn还可以减弱或消除S所引起的钢的热脆性，从而改善轻质钢的热加工性能。但是，过高Mn含量会引起铸造板坯中Mn偏析以及热轧板中明显的带状组织分布，从而最终降低轻质钢的综合力学性能。因此，所述轻质钢中Mn含量控制为：0.05～4.0％。
Al：Al在本发明中是重要合金元素。添加Al元素有助于改善轻质钢铸坯的微观组织，减少硬质增强颗粒(主要指TiB2颗粒)在基体晶界处连续分布，抑制薄膜状硬质增强相(如TiB2)包裹基体晶界，从而增加材料的后续可加工变形能力和断裂延伸率。另外添加Al可降低钢板密度，从而进一步增加轻质钢的减重效果。然而，添加过量Al会降低铸造板坯的可铸造性。因此，所述轻质钢中Al含量控制为：1.5～3.0％的范围以内。
Ti：Ti在本发明中是重要合金元素，与B结合形成主要增强轻质钢弹性模量的硬质颗粒TiB2。另外，Ti与C结合形成TiC硬质颗粒同样可以用来增强轻质钢的弹性模量。当Ti含量低于1.5％时，钢质基体中形成的TiB2颗粒体积分数较低，不足以显著改善轻质钢的弹性模量；当Ti含量高于7.0％时，钢质基体中容易生成粗大的TiB2初生相颗粒，这会给复合钢质材料的可铸造性和后续可加工性带来不利影响。因此，所述轻质钢中Ti含量控制为：1.5～7.0％。
B：B在本发明中同样是重要合金元素，与Ti结合形成主要增强复合钢质材料弹性模量的硬质颗粒TiB2。由化学计量可知，为生成TiB2颗粒，B含量约 为Ti含量的0.45倍。添加过量的B会生成Fe2B硬质相，从而降低钢的延展性；添加过少量的B会使钢中固溶较多的Ti，从而降低Ti的使用经济性。因此，所述轻质钢中B含量控制为：0.5～3.6％。
进一步地，本发明所述的轻质钢中，Ti和B元素还满足：-1.2％≤(Ti-2.22*B)≤1.2％。
在该限定公式中，Ti和B分别表示Ti元素和B元素的质量百分含量，例如，当Ti的含量为1.6％，B的含量为0.6％时，代入公式中的Ti的值为1.6，而不是0.016，代入公式中的B的值为0.6，而不是0.006。
上述轻质钢中，Ti和B元素的含量需要同时满足-1.2％≤(Ti-2.22*B)≤1.2％。当(Ti-2.22*B)＞1.2％时，钢质基体中固溶较多的Ti而降低Ti的使用经济性；当(Ti-2.22*B)＜-1.2％时，钢质基体中会形成过多的Fe2B硬质相而显著降低钢的延展性。
更进一步地，在上述轻质钢中，所述硬质颗粒的体积分数占全部微观组织的至少3％。
上述轻质钢中，当Ti和B元素的含量满足-1.2％≤(Ti-2.22*B)≤1.2％时，所述轻质钢的显微组织结构中硬质增强颗粒的体积分数之和占全部微观组织的至少3％，可以有效地增强轻质钢的弹性模量。在本技术方案中，主要是控制硬质增强颗粒所占比例的下限，对于上限并没有特别严格的要求。一般来说，可以控制硬质增强颗粒的体积分数之和占全部微观组织的3-25％，该比例超过25％，一般在工业生产中是难以实现的。
更进一步地，在上述轻质钢中，所述轻质钢板的抗拉强度＞500MPa、弹性模量＞200GPa、密度＜7600kg/m3。
优选地，在前述轻质钢中，所述Ti元素含量为3.0％≤Ti≤6.0％，所述B元素含量为1.2％≤B≤3.0％，Ti和B元素还满足：-0.6％≤(Ti-2.22*B)≤0.6％；所述硬质颗粒的体积分数占全部微观组织至少6％。
上述轻质钢中，在含有适量C的情况下，当0.6％＜(Ti-2.22*B)≤1.2％时，钢质基体中会形成较多TiC颗粒，从而影响轻质钢的弹性模量增强效果。当-1.2％≤(Ti-2.22*B)＜-0.6％时，钢质基体中的Fe2B硬质相会降低轻质钢的延展性。本发明优选轻质钢的化学成分中Ti和B元素的含量满足3.0％≤Ti≤6.0％，1.2％≤B≤3.0％，使钢质基体中所包含的增强颗粒的体积分数之和不 小于6％，同时，优选Ti和B元素的含量满足-0.6％≤(Ti-2.22*B)≤0.6％，使钢质基体中的增强颗粒主要为TiB2，以提高硬质颗粒对轻质钢弹性模量的增强效果。
更进一步地，在上述轻质钢中，所述轻质钢板的抗拉强度＞500MPa、弹性模量＞210GPa、密度＜7400kg/m3。
进一步地，本发明所述的或以上更进一步的任一方案所述的轻质钢中，所述硬质增强颗粒还包括TiC和Fe2B的至少其中之一。
进一步地，本发明所述的或以上更进一步的任一方案所述的轻质钢中，所述硬质增强颗粒的平均尺寸小于15μm。
本发明中，合金元素含量使钢质基体中硬质增强颗粒主要来源于钢水在凝固时发生的共晶反应，粗大初生相的形成受到抑制，因而硬质增强颗粒能够在钢质基体中均匀细小分布，进而使轻质钢具有良好的后续可加工性以及良好的机械性能。当硬质增强颗粒的平均尺寸不超过15μm时，轻质钢具有良好的断裂延伸率。
进一步地，本发明所述的或以上更进一步的任一方案所述的轻质钢中，所述轻质钢的化学成分还包括如下元素的至少其中之一：0.01％≤Si≤1.5％，0.01％≤Cr≤2.0％，0.01％≤Mo≤1.0％，0.01％≤Nb≤0.2％，0.01％≤V≤0.5％，0.05％≤Ni≤1.0％，0.05％≤Cu≤1.0％，0.001％≤Ca≤0.2％。
上述具有增强弹性模量特征的轻质钢中的各化学元素的设计原理为：
Si：Si是铁素体固溶强化元素，可提高强度；另外，添加Si可以显著提高奥氏体的力学稳定性，有助于轻质钢获取良好强度和塑性的匹配。但是，过高Si含量会降低轻质钢的塑性；另外，对于热镀锌轻质钢钢板来说，过高Si含量使轻质钢基板的可镀性变差。因此，所述轻质钢中Si含量控制为：0.01～1.5％。
Cr：Cr可以细化晶粒组织和抑制热加工时晶粒粗化，但是过高Cr含量会破坏钢的延展性。因此，所述轻质钢中Cr含量控制为：0.01～2.0％。
Mo：Mo的作用与Cr相似。Mo元素含量过高时会增加生产成本。因此，所述轻质钢中Mo含量控制为：0.01～1.0％。
Nb：Nb与C、N结合会形成Nb(C，N)，可有效地抑制热加工过程中晶粒粗化。Nb会强烈抑制动态再结晶的发生，从而增加轧制变形抗力。Nb可以 细化铁素体晶粒。但添加过量的Nb会减弱轻质钢的热加工性能和轻质钢钢板的韧性。因此，所述轻质钢中Nb含量控制为：0.01～0.2％。
V：V有助于细化晶粒组织和提高组织热稳定性，V还可以提高轻质钢的强度，但是添加V增加了轻质钢的成本。因此，所述轻质钢中V含量控制为：0.01％～0.5％。
Ni：Ni是奥氏体稳定化元素，可阻碍高温下晶粒粗化，但是Ni的价格昂贵从而增加生产成本。因此，所述轻质钢中Ni含量控制为：0.05～1.0％。
Cu：Cu的作用和Ni相近，但Cu含量过高时对热变形加工不利。因此，所述轻质钢中Cu含量控制为：0.05～1.0％。
Ca：Ca用来脱S以改善轻质钢的热加工性能，过量的Ca会降低轻质钢的延展性。因此，所述轻质钢中Ca含量控制为：0.001～0.2％。
本发明的另一目的在于提供一种采用以上任一方案所述的轻质钢制得的钢板。
为了达到上述发明目的，本发明还提出了一种钢板，其采用以上任一方案所述的轻质钢制得。
本发明的再一目的还在于提供一种可用于制造上述钢板的制造方法，该方法可以采用以上任一方案所述的轻质钢生产上述钢板。
为了达到上述发明目的，本发明还提出了上述钢板的一种制造方法，包括步骤：
(1)冶炼并连铸，得到板坯，板坯厚度为120～300mm；
(2)热轧，得到热轧板。
可选地，本发明所述的一种制造方法中，在所述步骤(2)后还具有步骤(3)再结晶退火。
上述方案考虑到若热轧板基体存在未再结晶显微组织时，对热轧板实施再结晶退火处理，以增加热轧板的延展性，并使热轧板在后序冷轧变形时具有良好的轧制变形能力。若热轧板组织为完全再结晶组织，热轧钢板已具有良好的冷轧变形能力和延展性时，该再结晶退火步骤可以省略。
进一步地，本发明所述的一种制造方法中，在所述步骤(2)中，加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取。
更进一步地，在前述的一种制造方法中，当所述步骤(3)采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
上述方案中，步骤(3)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于800℃或保温时间少于30s时，钢板基体组织未发生明显的再结晶；当均热温度高于1000℃时，钢板基体组织会迅速粗化，进而影响其后续变形能力。保温时间不超出600s是出于生产经济性考虑。
更进一步地，在前述的一种制造方法中，当所述步骤(3)采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案中，步骤(3)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于650℃和保温时间少于0.5h时，钢板基体组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织会发生显著粗化，进而影响其后续变形能力。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
此外，为了达到上述发明目的，本发明还提出了上述钢板的另一种制造方法，包括步骤：
(1)冶炼并薄带连铸，得到厚度不超过10mm的薄带坯；
(2)热轧，得到热轧板。
本发明提出的上述钢板的另一种制造方法中，所述步骤(1)采用薄带连铸工艺：将具有所述轻质钢成分的钢水注入一对反向旋转的冷却铸辊之间，钢水在两辊间凝固形成厚度不超过10mm的薄带坯，凝固冷却速率大于80℃/s。薄带连铸工艺制造过程中，钢水快速凝固可以避免合金元素偏析，以及使生成的硬质增强颗粒细小均匀地分布在薄带坯基体中。通常硬质增强颗粒的平均尺寸可以细化至10μm以下。细小均匀分布的硬质增强颗粒以及合金元素均匀分布对改善最终轻质钢的延展性有益。此外，采用薄带连铸工艺制备的薄带坯在无需外部加热的条件下直接被热轧成规定厚度的热轧卷，大大简化带钢生产工艺，从而降低生产成本。
可选地，本发明所述的另一种制造方法中，在所述步骤(2)后还具有步骤(3)再结晶退火。
上述方案考虑到若热轧板基体存在未再结晶显微组织时，对热轧板实施再结晶退火处理，以增加热轧板的延展性，并使热轧板在后序冷轧变形时具有良好的轧制变形能力。若热轧板组织为完全再结晶组织，热轧钢板已具有良好的冷轧变形能力和延展性时，该再结晶退火步骤可以省略。
进一步地，本发明所述的另一种制造方法中，在所述步骤(2)中，将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取。
更进一步地，在前述的另一种制造方法中，当所述步骤(3)采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
上述方案中，步骤(3)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于800℃或保温时间少于30s时，钢板基体组织未发生明显的再结晶；当均热温度高于1000℃时，钢板基体组织会迅速粗化，进而影响其后续变形能力。保温时间不超出600s是出于生产经济性考虑。
更进一步地，在前述的另一种制造方法中，当所述步骤(3)采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案中，步骤(3)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于650℃和保温时间少于0.5h时，钢板基体组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织会发生显著粗化，进而影响其后续变形能力。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
此外，为了达到上述发明目的，本发明还提出了上述钢板的又一种制造方法，包括步骤：
(1)冶炼并连铸，得到板坯，板坯厚度为120～300mm；
(2)热轧；
(3)酸洗；
(4)冷轧，得到冷轧板；
(5)冷轧板再结晶退火。
本发明提出的上述钢板的又一种制造方法中，所述步骤(5)利用冷轧后 再结晶退火工艺，将钢板基体的变形组织转变为等轴状再结晶组织，以显著提高钢板的变形能力和断裂延伸率。
可选地，本发明所述的又一种制造方法中，在所述步骤(2)后还具有步骤(2a)热轧后再结晶退火。
上述方案考虑到若热轧板基体存在未再结晶显微组织时，对热轧板实施再结晶退火处理，以增加热轧板的延展性，使热轧板在后序冷轧变形时具有良好的轧制变形能力。若热轧板组织为完全再结晶组织，热轧钢板已具有良好的冷轧变形能力时，该再结晶退火步骤可以省略。
进一步地，本发明所述的又一种制造方法中，在所述步骤(2)中，加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取。
更进一步地，在前述的又一种制造方法中，当所述步骤(2a)采用连续退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
上述方案中，步骤(2a)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于800℃或保温时间少于30s时，钢板基体组织未发生明显的再结晶；当均热温度高于1000℃时，钢板基体组织会迅速粗化，进而影响其后续变形能力。保温时间不超出600s是出于生产经济性考虑。
更进一步地，在前述的又一种制造方法中，当所述步骤(2a)采用罩式炉退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案中，步骤(2a)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于650℃和保温时间少于0.5h时，钢板基体组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织会发生显著粗化，进而影响其后续变形能力。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
进一步地，本发明所述的又一种制造方法中，在所述步骤(4)中，控制冷轧压下量为25-75％。
上述方案步骤(4)中，对酸洗后的热轧钢板实施冷轧变形至规定厚度，冷轧压下量为25～75％，优选40～60％。增加冷轧压下量，可以在后续退火过程 中有助于细化基体显微组织以及提高退火钢板的组织均匀性，从而提高退火钢板的延展性。但是冷轧压下量如果过大，因加工硬化导致材料的变形抗力非常高，会使得制备规定厚度和良好板形的冷轧钢板变得异常困难；并且，过高冷轧变形量会诱发钢板内部在基体和硬质增强颗粒之间形成微裂纹，进而使材料发生破坏。
进一步地，本发明所述的又一种制造方法中，当所述步骤(5)采用连续退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温。
上述方案步骤(5)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于700℃或保温时间少于30s时，钢板基体变形组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织在完成再结晶后会迅速粗化，进而影响退火钢板的断裂延伸率。保温时间不超出600s是出于生产经济性考虑。
进一步地，本发明所述的又一种制造方法中，当所述步骤(5)采用罩式炉退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案步骤(5)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于600℃和保温时间少于0.5h时，钢板基体变形组织未发生明显的再结晶；当均热温度高于800℃时，钢板基体变形组织在完成再结晶后会发生显著粗化，进而影响退火钢板的断裂延伸率。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
此外，为了达到上述发明目的，本发明还提出了上述钢板的再一种制造方法，包括步骤：
(1)冶炼并薄带连铸，得到厚度不超过10mm的薄带坯；
(2)热轧；
(3)酸洗；
(4)冷轧，得到冷轧板；
(5)冷轧板再结晶退火。
本发明提出的上述钢板的再一种制造方法中，所述步骤(1)采用薄带连铸工艺：将具有所述轻质钢成分的钢水注入一对反向旋转的冷却铸辊之间，钢 水在两辊间凝固形成厚度不超过10mm的薄带坯，凝固冷却速率大于80℃/s。薄带连铸工艺制造过程中，钢水快速凝固可以避免合金元素偏析，以及使生成的硬质增强颗粒细小均匀地分布在薄带坯基体中。通常硬质增强颗粒的平均尺寸可以细化至10μm以下。细小均匀分布的硬质增强颗粒以及合金元素均匀分布对改善最终轻质钢的延展性有益。此外，采用薄带连铸工艺制备的薄带坯在无需外部加热的条件下直接被热轧成规定厚度的热轧卷，大大简化带钢生产工艺，从而降低生产成本。薄带连铸工艺将钢水直接浇注出薄带坯，不经热轧或稍经热轧(1～2个道次)，然后再经冷轧便可生产冷轧薄板。
本发明提出的上述钢板的再一种制造方法中，所述步骤(5)利用冷轧后再结晶退火工艺，将钢板基体的变形组织转变为等轴状再结晶组织，以显著提高钢板的变形能力和断裂延伸率。
可选地，本发明所述的再一种制造方法中，在所述步骤(2)后还具有步骤(2a)热轧后再结晶退火。
上述方案考虑到若热轧板基体存在未再结晶显微组织时，对热轧板实施再结晶退火处理，以增加热轧板的延展性，使热轧板在后序冷轧变形时具有良好的轧制变形能力。若热轧板组织为完全再结晶组织，热轧钢板已具有良好的冷轧变形能力和延展性时，该再结晶退火步骤可以省略。
进一步地，本发明所述的再一种制造方法中，在所述步骤(2)中，将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取。
更进一步地，在前述的再一种制造方法中，当所述步骤(2a)采用连续退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
上述方案中，步骤(2a)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于800℃或保温时间少于30s时，钢板基体组织未发生明显的再结晶；当均热温度高于1000℃时，钢板基体组织会迅速粗化，进而影响其后续变形能力。保温时间不超出600s是出于生产经济性考虑。
更进一步地，在前述的再一种制造方法中，当所述步骤(2a)采用罩式炉退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案中，步骤(2a)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于650℃和保温时间少于0.5h时，钢板基体组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织会发生显著粗化，进而影响其后续变形能力。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
进一步地，本发明所述的再一种制造方法中，在所述步骤(4)中，控制冷轧压下量为25-75％。
上述方案步骤(4)中，对酸洗后的热轧钢板实施冷轧变形至规定厚度，冷轧压下量为25～75％，优选40～60％。增加冷轧压下量，可以在后续退火过程中有助于细化基体组织以及提高退火钢板的组织均匀性，从而提高退火钢板的延展性。但是冷轧压下量如果过大，因加工硬化导致材料的变形抗力非常高，会使得制备规定厚度和良好板形的冷轧钢板变得异常困难；并且，过高冷轧变形量会诱发钢板内部在基体和硬质增强颗粒之间形成微裂纹，进而使材料发生破坏。
进一步地，本发明所述的再一种制造方法中，当所述步骤(5)采用连续退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温。
上述方案步骤(5)采用连续退火方式时相关参数选择范围的理由是：当均热温度低于700℃或保温时间少于30s时，钢板基体变形组织未发生明显的再结晶；当均热温度高于900℃时，钢板基体组织在完成再结晶后会迅速粗化，进而影响退火钢板的断裂延伸率。保温时间不超出600s是出于生产经济性考虑。
进一步地，本发明所述的再一种制造方法中，当所述步骤(5)采用罩式炉退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
上述方案步骤(5)采用罩式炉退火方式时相关参数选择范围的理由是：当均热温度低于600℃和保温时间少于0.5h时，钢板基体变形组织未发生明显的再结晶；当均热温度高于800℃时，钢板基体变形组织在完成再结晶后会发生显著粗化，进而影响退火钢板的断裂延伸率。保温时间不超过48小时是出于保温时间过长影响生产效率考虑。
本发明利用在钢的基体中形成细小弥散分布的具有高弹性模量的硬质增强颗粒，来提高上述钢板材料的整体弹性模量，并使上述钢板具有较高的强度和断裂延伸率。上述钢板具有的微观组织特征和宏观力学性能通常除了通过控制上述轻质钢成分外，还需要结合上述制造方法来实现。
本发明的增强弹性模量特征的轻质钢、钢板及其制造方法有益效果如下：
1)本发明的轻质钢主要利用TiB2硬质颗粒来增强钢板的弹性模量。TiB2与轻质钢基体之间易于建立热力学平衡关系，并且两者在相界面处能形成共格关系。这意味着硬质颗粒TiB2与基体之间存在强结合能力，轻质钢具有良好的可加工性和断裂延伸率(硬质颗粒与基体之间不易发生分裂)。另外，TiB2的密度低于基体的密度，从而降低轻质钢整体的密度，显著提高轻质钢的比弹性模量(弹性模量与密度之比)。
2)本发明利用合金元素Al来有效地改善含有第二相硬质相的轻质钢的铸态组织，抑制或减少第二相硬质增强颗粒在轻质钢基体晶界处连续分布，从而显著改善轻质钢的可加工性能和提高轻质钢的断裂延伸率。另外，添加Al能降低轻质钢的密度和提高轻质钢的比弹性模量。
3)本发明轻质钢的显微组织部分或全部以铁素体和/或贝氏体为基体，所包含的TiB2等硬质颗粒的体积分数可达12％以上，轻质钢的弹性模量可增加到230GPa以上，密度降低至7400kg/m3以下，钢板的抗拉强度＞500MPa。利用本发明轻质钢制备的钢板可以用于汽车零部件的制造，实现汽车结构进一步轻量化的目标。
4)当采用连铸工艺制备板坯时，本发明的制造方法可以在现有高强钢生产线上完成而无需做较大调整。因此，本发明的制造方法具有很好的推广应用前景。
5)当采用快速凝固的方式(即薄带连铸工艺)制备薄带坯时，本发明的制造方法可以使钢板基体弥散分布着更为细小的硬质增强颗粒(平均尺寸小于10μm)，并且基体组织也得到细化。同样地，钢板具有良好的热力加工性能和断裂延伸率。因此，本发明的制造方法具有很好的推广应用前景。
附图说明
图1为轻质钢对比例B2的板坯低倍金相组织照片。
图2为轻质钢对比例B2的板坯高倍金相组织照片。
图3为轻质钢实施例A6的板坯低倍金相组织照片。
图4为轻质钢实施例A6的板坯高倍金相组织照片。
图5为钢板对比例CS2的热轧后形貌照片。
图6为钢板实施例HM6-HM8的热轧后形貌照片。
图7钢板实施例HM6热轧后的低倍金相组织照片。
图8钢板实施例HM6热轧后的高倍金相组织照片。
具体实施方式
下面将结合附图说明和具体的实施例对本发明所述的具有增强弹性模量特征的轻质钢、钢板及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
轻质钢成分实施例A1-A9及对比例B1-B3
表1列出了具有增强弹性模量特征的轻质钢的实施例A1-A9及对比例B1-B3中的化学元素的质量百分配比。
表1.(wt％)
  C Mn Al B Ti Nb V Cr Mo Ni Cu Si Ca N S P Ti-2.22*B
A1 0.15 2.1 2.0 0.5 1.5 - 0.4 - 0.9 - - - 0.2 0.003 0.005 0.004 0.39
A2 0.05 4.0 2.4 1.2 3.5 0.2 - 1.4 - - - - - 0.003 0.004 0.010 0.84
A3 0.10 0.8 2.8 2.1 4.8 - - - - 1.0 1.0 - - 0.008 0.001 0.006 0.14
A4 0.15 3.0 2.3 1.1 3.0 - - - - - - 1.2 - 0.003 0.002 0.008 0.56
A5 0.26 1.0 2.0 2.6 6.9 - - - - - - - - 0.004 0.002 0.007 1.13
A6 0.04 0.05 2.5 2.0 4.2 - - - - - - - - 0.002 0.005 0.003 -0.24
A7 0.005 0.1 1.6 2.3 4.9 - - - - - - - - 0.003 0.001 0.009 -0.21
A8 0.08 0.5 2.9 2.2 4.3 - - 0.4 0.1 - - - - 0.003 0.002 0.008 -0.58
A9 0.06 0.1 1.8 3.6 6.8 - - - - - - - - 0.007 0.009 0.01 -1.19
B1 0.006 0.2 2.5 - - - - - - - - - - 0.004 0.003 0.014 0.0
B2 0.04 0.05 - 2.3 4.0 - - - - - - - - 0.003 0.004 0.012 -1.11
B3 0.1 0.1 - 1.9 5.2 - - - - - - - - 0.003 0.008 0.007 0.98
钢板及其制造方法实施例HM1-HM9及对比例CS1-CS3
上述实施例及对比例中的钢板采用以下步骤制得：
(1)实施例HM1-HM9分别对具有表1中A1-A9的轻质钢材料进行冶炼并连铸，对比例CS1-CS3分别对具有表1中B1-B3的轻质钢材料进行冶炼并连铸，得到厚度为120～300mm的板坯，其中S、P和N是不可避免的杂质，余量为Fe；
(2)热轧，得到3.2mm厚的热轧板：该步骤中，加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取。
(3)热轧后再结晶退火：采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
将步骤(2)中的热轧板快速冷却至卷取温度下保温1小时，然后随炉冷却至室温，用以模拟热轧板的卷取温降过程。在某些热轧板基体不存在未再结晶显微组织的实施例中，可以不进行步骤(3)。
表2列出了实施例HM1-HM9及对比例CS1-CS3的钢板制造方法的具体工艺参数。
表2.
Figure PCTCN2017078770-appb-000001
Figure PCTCN2017078770-appb-000002
对上述实施例HM1-HM9及对比例CS1-CS3的钢板取样后，进行包括力学性能在内的各项测试，将测得的相关数据列于表3中。
表3.
Figure PCTCN2017078770-appb-000003
由表3可知，钢板的抗拉强度＞500MPa、密度＜7600kg/m3、弹性模量＞200GPa，因此，本发明通过合理的成分和工艺设计可以获取低密度、高抗拉强度、高弹性模量以及优良延展性的热轧轻质钢板。
图1和图2分别显示了轻质钢对比例B2的低倍和高倍铸态组织，图3和图4分别显示了轻质钢实施例A6的低倍和高倍铸态组织。图2和图4中箭头所指为硬质增强颗粒。
从图1和图2可以观察到，轻质钢对比例B2的板坯微观组织中，铁素体基体被连续分布的硬质增强相(主要是TiB2颗粒)所包裹，从图3和图4可以观察到，轻质钢实施例A6的初生相和共晶产物(即硬质增强相)离散分布在铁素体基体中。实际上，对比例B3和实施例A1-A5、A7-A9也分别观察到与上述对比例B2和实施例A6相似的现象，而对比例B2-B3不含有Al元素，实施例A1-A9含有Al元素，因此，添加Al元素有助于改善轻质钢铸坯的微观组织，减少硬质增强颗粒在基体晶界处连续分布，抑制薄膜状硬质增强相包裹基体晶界。
图5和图6分别显示了钢板对比例CS2和钢板实施例HM6-HM8的热轧后形貌。
从图5可以观察到，钢板对比例CS2无法进行良好的热轧变形，从图6可以观察到，钢板实施例HM6-HM8可以被热轧成所需厚度的钢板。实际上，对比例CS3和实施例HM1-HM5、HM9也分别观察到与上述对比例CS2和实施例HM6-HM8相似的现象，而对比例CS2-CS3不含有Al元素，实施例HM1-HM9含有Al元素，因此，添加Al元素有益于钢板的热轧变形能力。
图7和图8分别显示了钢板实施例HM6热轧后的低倍和高倍显微组织。图7和图8中箭头所指为硬质增强颗粒。
从图7和图8可以观察到热轧板中硬质增强颗粒在铁素体基体中的分布情况，图中显示铸态组织中细长的硬质增强相由于热力变形的缘故被破碎和细化。
钢板制造方法实施例HM10-HM13
上述实施例中的钢板采用以下步骤制得：
(1)具有表1中的轻质钢材料经冶炼后通过薄带连铸的方式将钢水浇注压轧制成厚度为不超过10mm的薄带坯，其中S、P和N是不可避免的杂质，余量为Fe；钢水凝固冷却速度约为320℃/s；
(2)热轧，得到1.3mm厚的热轧板：将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取。
(3)热轧后再结晶退火：采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
表4.列出了实施例HM10-HM13的钢板制造方法的具体工艺参数。
表4.
Figure PCTCN2017078770-appb-000004
对上述实施例HM10-HM13的钢板取样后，进行包括力学性能在内的各项测试，将测得的相关数据列于表5中。
表5.
Figure PCTCN2017078770-appb-000005
同时，对上述实施例HM10-HM13进行金相观察，发现热轧板基体为等轴状铁素体组织，分布在基体中的以TiB2为主的硬质增强颗粒的平均尺寸约为3～5μm。
钢板制造方法实施例HM14-HM18
上述实施例中的钢板采用以下步骤制得：
(1)实施例HM14-HM18分别对具有表1中A1、A3、A5、A6以及A9的轻质钢材料进行冶炼并连铸，得到厚度为120～300mm的板坯，其中S、P和N是不可避免的杂质，余量为Fe；
(2)热轧，得到热轧板：加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取；
(3)热轧后再结晶退火：采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温；
(4)酸洗；
(5)冷轧：控制冷轧压下量为25-75％；
(6)冷轧板再结晶退火：采用连续退火方式进行冷轧后再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式进行冷轧后再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
表6列出了实施例HM14-HM18的钢板制造方法的具体工艺参数。
表6.
Figure PCTCN2017078770-appb-000006
Figure PCTCN2017078770-appb-000007
表6.(续)
Figure PCTCN2017078770-appb-000008
对上述实施例HM14-HM18的钢板取样后，进行包括力学性能在内的各项测试，将测得的相关数据列于表7中。
表7.
Figure PCTCN2017078770-appb-000009
由表7可知，钢板的抗拉强度＞500MPa、弹性模量＞200GPa，因此，本发明可以获取低密度、高抗拉强度、高弹性模量以及优良延展性的热轧轻质钢板。
钢板制造方法实施例HM19-HM22
上述实施例中的钢板采用以下步骤制得：
(1)具有表1中的轻质钢材料经冶炼后通过薄带连铸的方式将钢水 浇注压轧制成厚度为不超过10mm的薄带坯，其中S、P和N是不可避免的杂质，余量为Fe；钢水凝固冷却速度约为200℃/s；
(2)热轧，得到热轧板：将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取；
(3)热轧后再结晶退火：采用连续退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温；
(4)酸洗；
(5)冷轧。该步骤中，冷轧压下量为25-75％；
(6)冷轧板再结晶退火：采用连续退火方式进行冷轧后再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温；采用罩式炉退火方式进行冷轧后再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
表8列出了实施例HM19-HM22的钢板制造方法的具体工艺参数。
表8.
Figure PCTCN2017078770-appb-000010
表8.(续)
Figure PCTCN2017078770-appb-000011
Figure PCTCN2017078770-appb-000012
对上述实施例HM19-HM22的钢板取样后，进行包括力学性能在内的各项测试，将测得的相关数据列于表9中。
表9.
Figure PCTCN2017078770-appb-000013
对上述实施例HM19-HM22进行金相观察，发现冷轧板经退火后基体为等轴状铁素体组织，分布在基体中的以TiB2为主的硬质增强颗粒的平均尺寸约为3～6μm。
需要注意的是，以上列举的仅为本发明的具体实施例，显然本发明不限于以上实施例，随之有着许多的类似变化。本领域的技术人员如果从本发明公开的内容直接导出或联想到的所有变形，均应属于本发明的保护范围。

Claims (36)

  1. 一种具有增强弹性模量特征的轻质钢，其特征在于：
    所述轻质钢的化学成分质量百分数为：0.001％≤C≤0.30％，0.05％≤Mn≤4.0％，1.5％＜Al＜3.0％，1.5％≤Ti≤7.0％，0.5％≤B≤3.6％，其余为Fe和不可避免的杂质元素；
    所述轻质钢的微观组织包括基体和基体中均匀弥散分布的细小的硬质增强颗粒，其中所述基体全部地或部分地为铁素体和/或贝氏体，所述硬质增强颗粒至少包括TiB2。
  2. 如权利要求1所述的轻质钢，其特征在于，Ti和B元素还满足：-1.2％≤(Ti-2.22*B)≤1.2％。
  3. 如权利要求2所述的轻质钢，其特征在于，所述硬质颗粒的体积分数占全部微观组织的至少3％。
  4. 如权利要求3所述的轻质钢，其特征在于，所述轻质钢板的抗拉强度＞500MPa、弹性模量＞200GPa、密度＜7600kg/m3。
  5. 如权利要求2所述的轻质钢，其特征在于，所述Ti元素含量为3.0％≤Ti≤6.0％，所述B元素含量为1.2％≤B≤3.0％，Ti和B元素还满足：-0.6％≤(Ti-2.22*B)≤0.6％；所述硬质颗粒的体积分数占全部微观组织的至少6％。
  6. 如权利要求5所述的轻质钢，其特征在于，所述轻质钢板的抗拉强度＞500MPa、弹性模量＞210GPa、密度＜7400kg/m3。
  7. 如权利要求1-6中任意一项所述的轻质钢，其特征在于，所述硬质增强颗粒还包括TiC和Fe2B的至少其中之一。
  8. 如权利要求1-6中任意一项所述的轻质钢，其特征在于，所述硬质增强颗粒的平均尺寸小于15μm。
  9. 如权利要求1-6中任意一项所述的轻质钢，其特征在于，所述轻质钢的化学成分还包括如下元素的至少其中之一：0.01％≤Si≤1.5％，0.01％≤Cr≤2.0％，0.01％≤Mo≤1.0％，0.01％≤Nb≤0.2％，0.01％≤V≤0.5％，0.05％≤Ni≤1.0％，0.05％≤Cu≤1.0％，0.001％≤Ca≤0.2％。
  10. 一种钢板，其采用如权利要求1-9中任意一项所述的轻质钢制得。
  11. 如权利要求10所述的钢板的制造方法，其特征在于，包括步骤：
    (1)冶炼并连铸，得到板坯，板坯厚度为120～300mm；
    (2)热轧，得到热轧板。
  12. 如权利要求11所述的制造方法，其特征在于，在所述步骤(2)后还具有步骤(3)再结晶退火。
  13. 如权利要求11所述的制造方法，其特征在于，在所述步骤(2)中，加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取。
  14. 如权利要求12所述的制造方法，其特征在于，当所述步骤(3)采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
  15. 如权利要求12所述的制造方法，其特征在于，当所述步骤(3)采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
  16. 如权利要求10所述的钢板的制造方法，其特征在于，包括步骤：
    (1)冶炼并薄带连铸，得到厚度不超过10mm的薄带坯；
    (2)热轧，得到热轧板。
  17. 如权利要求16所述的制造方法，其特征在于，在所述步骤(2)后还具有步骤(3)再结晶退火。
  18. 如权利要求16所述的制造方法，其特征在于，在所述步骤(2)中，将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取。
  19. 如权利要求17所述的制造方法，其特征在于，当所述步骤(3)采用连续退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
  20. 如权利要求17所述的制造方法，其特征在于，当所述步骤(3)采用罩式炉退火方式对热轧板进行再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
  21. 如权利要求10所述的钢板的制造方法，其特征在于，包括步骤：
    (1)冶炼并连铸，得到板坯，板坯厚度为120～300mm；
    (2)热轧；
    (3)酸洗；
    (4)冷轧，得到冷轧板；
    (5)冷轧板再结晶退火。
  22. 如权利要求21所述的制造方法，其特征在于，在所述步骤(2)后还具有步骤(2a)热轧后再结晶退火。
  23. 如权利要求21所述的制造方法，其特征在于，在所述步骤(2)中，加热温度为1000～1250℃，保温时间为0.5～3h，终轧温度≥850℃，然后在400～750℃下卷取。
  24. 如权利要求22所述的制造方法，其特征在于，当所述步骤(2a)采用连续退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
  25. 如权利要求22所述的制造方法，其特征在于，当所述步骤(2a)采用罩式炉退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
  26. 如权利要求21所述的制造方法，其特征在于，在所述步骤(4)中，控制冷轧压下量为25-75％。
  27. 如权利要求21所述的制造方法，其特征在于，当所述步骤(5)采用连续退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温。
  28. 如权利要求21所述的制造方法，其特征在于，当所述步骤(5)采用罩式炉退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
  29. 如权利要求10所述的钢板的制造方法，其特征在于，包括步骤：
    (1)冶炼并薄带连铸，得到厚度不超过10mm的薄带坯；
    (2)热轧；
    (3)酸洗；
    (4)冷轧，得到冷轧板；
    (5)冷轧板再结晶退火。
  30. 如权利要求29所述的制造方法，其特征在于，在所述步骤(2)后还具有 步骤(2a)热轧后再结晶退火。
  31. 如权利要求29所述的制造方法，其特征在于，在所述步骤(2)中，将薄带坯在无外部辅助加热的情况下立刻进行热轧，控制终轧温度≥850℃，热轧压下量为20-60％，然后在400～750℃下卷取。
  32. 如权利要求30所述的制造方法，其特征在于，当所述步骤(2a)采用连续退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度800～1000℃，保温30～600s，然后冷却至室温。
  33. 如权利要求30所述的制造方法，其特征在于，当所述步骤(2a)采用罩式炉退火方式进行热轧后再结晶退火时，将热轧板加热至均热温度650～900℃，保温时间0.5～48h，然后随炉冷却至室温。
  34. 如权利要求29所述的制造方法，其特征在于，在所述步骤(4)中，控制冷轧压下量为25-75％。
  35. 如权利要求29所述的制造方法，其特征在于，当所述步骤(5)采用连续退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度700～900℃，保温30～600s，然后冷却至室温。
  36. 如权利要求29所述的制造方法，其特征在于，当所述步骤(5)采用罩式炉退火方式进行冷轧板再结晶退火时，将冷轧板加热至均热温度600～800℃，保温时间0.5～48h，然后随炉冷却至室温。
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