WO2022042731A1 - 一种980MPa级贝氏体高扩孔钢及其制造方法 - Google Patents

一种980MPa级贝氏体高扩孔钢及其制造方法 Download PDF

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WO2022042731A1
WO2022042731A1 PCT/CN2021/115433 CN2021115433W WO2022042731A1 WO 2022042731 A1 WO2022042731 A1 WO 2022042731A1 CN 2021115433 W CN2021115433 W CN 2021115433W WO 2022042731 A1 WO2022042731 A1 WO 2022042731A1
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high hole
content
steel
steel according
980mpa
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PCT/CN2021/115433
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English (en)
French (fr)
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王焕荣
杨峰
张晨
杨阿娜
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宝山钢铁股份有限公司
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Priority to KR1020237009928A priority Critical patent/KR20230059810A/ko
Priority to JP2023513802A priority patent/JP2023539650A/ja
Priority to EP21860563.2A priority patent/EP4206351A4/en
Priority to US18/043,267 priority patent/US20230313333A1/en
Publication of WO2022042731A1 publication Critical patent/WO2022042731A1/zh

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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel

Definitions

  • the invention relates to the field of high-strength steel, in particular to a 980MPa-grade bainite high hole-expanding steel and a manufacturing method thereof.
  • the lightweight of passenger cars is not only the development trend of the automobile industry, but also the requirements of laws and regulations.
  • the fuel consumption is stipulated in the laws and regulations, in fact, it is a disguised requirement to reduce the weight of the body, which is reflected in the requirement of high strength, thinning and light weight.
  • High-strength weight reduction is an inevitable requirement for subsequent new models, which will inevitably lead to higher steel grades and changes in the chassis structure.
  • the requirements for material properties, surfaces, and molding technologies will be improved, such as Hydroforming, hot stamping, laser welding, etc., and then transform the material's high strength, stamping, flanging, springback and fatigue properties.
  • the development of domestic high-strength and high-hole-expanding steel not only has a relatively low strength level, but also has poor performance stability.
  • the high-hole-expansion steel used by domestic auto parts companies is basically high-strength steel with a tensile strength below 600MPa, and the competition for high-hole-expansion steel below 440MPa is fierce.
  • the high hole-expanding steel with a tensile strength of 780MPa is gradually being used in batches, but higher requirements are also put forward for the two important indicators of elongation and hole expansion.
  • the 980MPa-level high hole-expanding steel is still in the stage of R&D and certification, and has not yet reached the stage of mass use.
  • the hole expansion ratio of a material is closely related to many factors, the most important factors include the uniformity of the structure, the level of inclusion and segregation control, the different structure types, and the measurement of the hole expansion ratio.
  • a single homogeneous structure is beneficial to obtain a higher hole expansion ratio, while a dual-phase or multi-phase structure is usually not conducive to the improvement of the hole expansion ratio.
  • the purpose of the present invention is to provide a 980MPa grade bainite high hole-enlarging steel and a manufacturing method thereof.
  • the yield strength of the high-hole-enlarging steel is greater than or equal to 800MPa, the tensile strength is greater than or equal to 980MPa, and at the same time, it has good elongation (transverse A 50 ⁇ 11%) and hole expansion performance (hole expansion rate ⁇ 40%), it can be used in parts of passenger car chassis such as control arms and subframes that require high strength and thinning.
  • the technical scheme of the present invention is:
  • the composition design of the present invention adopts a lower C content, which can ensure that the user has excellent weldability during use, and ensures that the obtained martensite structure has good hole expansion and impact toughness;
  • the lower the carbon content the better;
  • the higher Si content is designed to match the process to obtain more retained austenite, thereby improving the plasticity of the material;
  • the higher Si content is conducive to reducing the unrecrystallized steel temperature, so that the steel can complete the dynamic recrystallization process in a wide range of finishing rolling temperature, thereby improving the structural anisotropy of the steel, refining the austenite grains and the final bainite lath size, improving the plasticity and hole expansion ratio.
  • the 980MPa grade bainite high hole-expanding steel according to the present invention has the following chemical composition weight percentages: C 0.05-0.10%, Si 0.5-2.0%, Mn 1.0%-2.0%, P ⁇ 0.02%, S ⁇ 0.003%, Al 0.02 ⁇ 0.08%, N ⁇ 0.004%, Mo ⁇ 0.1%, Ti 0.01 ⁇ 0.05%, Cr ⁇ 0.5%, B ⁇ 0.002%, O ⁇ 0.0030%, the rest are Fe and other inevitable impurities.
  • the 980MPa grade bainite high hole expanding steel according to the present invention also contains one or more elements selected from Nb ⁇ 0.06%, V ⁇ 0.05%, Cu ⁇ 0.5%, Ni ⁇ 0.5% and Ca ⁇ 0.005% .
  • the content of Mo by weight is 0.1-0.55%.
  • the 980MPa grade bainite high hole-expanding steel according to the present invention has the following chemical composition weight percentages: C 0.05-0.10%, Si 0.5-2.0%, Mn 1.0%-2.0%, P ⁇ 0.02% , S ⁇ 0.003%, Al 0.02 ⁇ 0.08%, N ⁇ 0.004%, Mo ⁇ 0.1%, Ti 0.01 ⁇ 0.05%, Cr ⁇ 0.5%, B ⁇ 0.002%, O ⁇ 0.0030%, Nb ⁇ 0.06%, V ⁇ 0.05%, Cu ⁇ 0.5%, Ni ⁇ 0.5%, Ca ⁇ 0.005%, the rest are Fe and other inevitable impurities, and the 980MPa grade bainite high hole expanding steel contains Nb, V, Cu, Ni and Ca. At least one of Cr and B, preferably at least one or both of Cr and B.
  • the Nb and V contents are preferably ⁇ 0.03%, respectively; the Cu and Ni contents are preferably ⁇ 0.3%, respectively, and the Ca content is preferably ⁇ 0.002%.
  • the yield strength of the 980MPa grade bainitic high hole-expanding steel according to the present invention is ⁇ 800MPa, preferably ⁇ 830MPa, more preferably ⁇ 850MPa, tensile strength ⁇ 980MPa, preferably ⁇ 1000MPa, more preferably ⁇ 1020MPa, transverse direction A 50 ⁇ 11%, hole expansion ratio ⁇ 40%, preferably ⁇ 50%.
  • the microstructure of the 980MPa grade bainite high hole expanding steel according to the present invention is bainite + retained austenite.
  • the content of retained austenite in the 980MPa grade bainite high hole-expanding steel is 1-5%.
  • composition design of the high hole-expanding steel of the present invention is the composition design of the high hole-expanding steel of the present invention:
  • Carbon the basic element in steel, is also one of the important elements in the present invention. Carbon expands the austenite phase region and stabilizes the austenite. As an interstitial atom in steel, carbon plays a very important role in improving the strength of steel, and has the greatest impact on the yield strength and tensile strength of steel.
  • the structure to be obtained is low-carbon bainite, in order to obtain a high-strength steel with a tensile strength of 980MPa, the carbon content must be guaranteed to be above 0.05%, otherwise the carbon content is below 0.05%, even if fully quenched Even at room temperature, its tensile strength cannot reach 980MPa; however, the carbon content cannot be higher than 0.10%.
  • the carbon content should be controlled between 0.05-0.10%, preferably in the range of 0.06-0.08%.
  • Silicon the basic element in steel, is also one of the important elements in the present invention.
  • the increase of Si content not only improves the solid solution strengthening effect, but also plays the following two roles more importantly.
  • the non-recrystallization temperature of the steel is greatly reduced, so that the steel can complete dynamic recrystallization in a wide temperature range.
  • the final rolling temperature can be rolled within the final rolling temperature range of 800-920 °C, so that the difference between the transverse and longitudinal microstructures is reduced, which is not only conducive to improving the strength and plasticity, but also conducive to obtaining good
  • Another important role of Si is to inhibit the precipitation of cementite, and under appropriate rolling process conditions, especially when obtaining a structure dominated by bainite, a certain amount of retained austenite can be retained , which is beneficial to increase the elongation.
  • This effect of Si must be manifested when its content reaches more than 0.5%; but the content of Si should not be too high, otherwise the rolling force load during the actual rolling process is too large, which is not conducive to the stable production of products. Therefore, the content of Si in the steel is usually controlled between 0.5-2.0%, and the preferred range is between 0.8-1.6%.
  • Manganese the most basic element in steel, is also one of the most important elements in the present invention.
  • Mn is an important element to expand the austenite phase region, which can reduce the critical cooling rate of steel, stabilize austenite, refine grains, and delay the transformation of austenite to pearlite.
  • the effect of molybdenum on the delay of ferrite and pearlite and the reduction of the critical cooling rate is much greater than that of manganese.
  • the content of manganese in the steel can be appropriately reduced, and should generally be controlled at more than 1.0%; at the same time, the content of Mn should generally not exceed 2.0%, otherwise Mn segregation is likely to occur during steelmaking, and heat is also likely to occur during continuous slab casting. crack. Therefore, the content of Mn in the steel is generally controlled at 1.0-2.0%, preferably in the range of 1.4-1.8%.
  • Phosphorus is an impurity element in steel. P is easy to segregate on the grain boundary. When the content of P in the steel is high ( ⁇ 0.1%), Fe 2 P is formed to precipitate around the grain, reducing the plasticity and toughness of the steel, so the lower the content, the better. It is better to control within 0.02% without increasing the cost of steelmaking.
  • Sulfur is an impurity element in steel.
  • S in steel usually combines with Mn to form MnS inclusions, especially when the content of S and Mn is high, more MnS will be formed in the steel, and MnS itself has a certain plasticity.
  • the deformation in the rolling direction not only reduces the transverse plasticity of the steel, but also increases the anisotropy of the structure, which is unfavorable for the hole expansion performance. Therefore, the lower the S content in the steel, the better.
  • the Mn content in the present invention must be at a higher level, in order to reduce the MnS content, the S content should be strictly controlled, and the S content should be controlled within 0.003%.
  • the preferable range is 0.0015% or less.
  • the role of aluminum in steel is mainly deoxidation and nitrogen fixation.
  • the main role of Al is to deoxidize and refine grains.
  • the content of Al is usually controlled at 0.02-0.08%; if the content of Al is less than 0.02%, it cannot achieve the effect of refining grains; similarly, When the Al content is higher than 0.08%, the grain refinement effect is saturated. Therefore, the content of Al in the steel can be controlled between 0.02-0.08%, and the preferred range is between 0.02-0.05%.
  • Nitrogen is an impurity element in the present invention, and the lower the content, the better. But nitrogen is an inevitable element in the steelmaking process. Although its content is small, when combined with strong carbide forming elements such as Ti, the formed TiN particles have a very adverse effect on the properties of the steel, especially on the hole expansion performance. Due to the square shape of TiN, there is a large stress concentration between its sharp corners and the matrix. During the process of hole expansion and deformation, the stress concentration between TiN and the matrix is easy to form cracks, thereby greatly reducing the hole expansion performance of the material. Under the premise of controlling the nitrogen content as much as possible, the lower the content of strong carbide-forming elements such as Ti, the better. In the present invention, a trace amount of Ti is added to fix nitrogen, so as to minimize the adverse effects brought by TiN. Therefore, the nitrogen content should be controlled below 0.004%, preferably below 0.003%.
  • Titanium is one of the important elements in the present invention. Ti mainly plays two roles in the present invention: one is to combine with the impurity element N in the steel to form TiN, which plays a part of "fixing nitrogen”; the other is to form a certain amount of finely dispersed TiN in the subsequent welding process of the material , suppress the austenite grain size, refine the structure and improve the low temperature toughness. Therefore, the content of Ti in the steel is controlled in the range of 0.01-0.05%, preferably in the range of 0.01-0.03%.
  • Molybdenum is one of the important elements in the present invention.
  • the addition of molybdenum to the steel can greatly delay the transformation of ferrite and pearlite, which is beneficial to obtain bainite structure in the middle and high temperature range; at the same time, the addition of molybdenum can also improve the stability of the structure and properties of the steel and refine the grains.
  • This effect of molybdenum is beneficial to the adjustment of various processes in the actual rolling process. For example, after the end of the final rolling, it can be cooled in stages, or it can be air-cooled first and then water-cooled. In the present invention, two methods of air cooling after rolling or direct cooling are adopted.
  • the addition of molybdenum can on the one hand ensure that structures such as ferrite or pearlite will not be formed during the air cooling process;
  • the dynamic recovery of the deformed austenite during the process is beneficial to improve the uniformity of the structure and properties, and is beneficial to the hole expansion performance.
  • the effect of molybdenum on inhibiting the formation of ferrite and pearlite requires its content to be more than 0.10%. Therefore, the content of molybdenum should be controlled at ⁇ 0.10%, and the preferred range is ⁇ 0.15%. In some embodiments, the molybdenum content is 0.1-0.55%.
  • Chromium is one of the important elements in the present invention.
  • chromium is not used to improve the hardenability of steel, but to combine with B, which is conducive to the formation of acicular ferrite structure in the welding heat-affected zone after welding, which can greatly improve the low-temperature toughness of the welding heat-affected zone.
  • the final application parts involved in the present invention are passenger car chassis products, the low temperature toughness of the welded heat affected zone is an important indicator. In addition to ensuring that the strength of the welding heat-affected zone cannot be reduced too much, the low-temperature toughness of the welding heat-affected zone must also meet certain requirements.
  • chromium itself also has a certain resistance to welding softening. Therefore, a small amount of chromium element needs to be added to the steel, the range of which is generally ⁇ 0.5%, such as 0.1-0.5%, and the preferred range is 0.2-0.4%.
  • the role of boron in steel is mainly to segregate at the austenite grain boundary to inhibit the formation of pro-eutectoid ferrite; the addition of boron to steel can also greatly improve the hardenability of steel.
  • the main purpose of adding trace boron is not to improve the hardenability, but to combine with chromium to improve the structure of the welding heat-affected zone and obtain acicular ferrite structure with good toughness.
  • the addition of boron element in steel is generally controlled below 0.002%, and the preferred range is between 0.0005-0.0015%.
  • Calcium is an addable element in the present invention.
  • Calcium can improve the morphology of sulfides such as MnS, so that elongated sulfides such as MnS become spherical CaS, which is beneficial to improve the morphology of inclusions, thereby reducing the adverse effect of elongated sulfides on hole expansion performance.
  • the addition of calcium oxide will increase the amount of calcium oxide, which is detrimental to the hole expansion performance. Therefore, the addition amount of steel grade calcium is usually ⁇ 0.005%, and the preferred range is ⁇ 0.002%.
  • Oxygen is an unavoidable element in the steelmaking process.
  • the content of O in the steel can generally reach below 30 ppm after deoxidation, which will not cause obvious adverse effects on the performance of the steel plate. Therefore, it is sufficient to control the O content in the steel within 30 ppm.
  • Niobium is one of the elements that can be added in the present invention. Similar to titanium, niobium is a strong carbide element in steel. The addition of niobium to steel can greatly increase the unrecrystallized temperature of steel. In the finishing rolling stage, deformed austenite with higher dislocation density can be obtained. In the subsequent transformation process The final phase transition structure can be refined. However, the addition amount of niobium should not be too much. On the one hand, the addition amount of niobium exceeds 0.06%, which is easy to form relatively coarse carbonitrides of niobium in the structure, which consumes some carbon atoms and reduces the precipitation strengthening effect of carbides.
  • the high content of niobium also easily causes the anisotropy of the hot-rolled austenite structure, which is inherited to the final structure in the subsequent cooling transformation process, which is detrimental to the hole expansion performance. Therefore, the niobium content in the steel is usually controlled to be ⁇ 0.06%, and the preferred range is ⁇ 0.03%.
  • Vanadium is an addable element in the present invention. Like titanium and niobium, vanadium is also a strong carbide former. However, the carbides of vanadium have a low solid solution or precipitation temperature, and are usually all dissolved in austenite in the finishing rolling stage. It is only when the temperature is lowered that the phase transformation begins that vanadium begins to form in the ferrite. Since the solid solubility of vanadium carbides in ferrite is greater than that of niobium and titanium, the size of vanadium carbides formed in ferrite is relatively large, which is not conducive to precipitation strengthening and contributes far to the strength of steel.
  • the addition amount of vanadium in steel is usually ⁇ 0.05%, and the preferred range is ⁇ 0.03%.
  • Copper is an additive element in the present invention. Adding copper to steel can improve the corrosion resistance of steel. When it is added together with P element, the corrosion resistance effect is better; to a strong precipitation strengthening effect. However, the addition of Cu is easy to form the phenomenon of "Cu embrittlement" during the rolling process. In order to make full use of the effect of improving the corrosion resistance of Cu in some applications, and at the same time not cause significant "Cu embrittlement" phenomenon, usually Cu The content of the element is controlled within 0.5%, preferably within 0.3%.
  • Nickel is an additive element in the present invention.
  • the addition of nickel to steel has certain corrosion resistance, but the corrosion resistance effect is weaker than that of copper.
  • the addition of nickel to steel has little effect on the tensile properties of steel, but it can refine the structure and precipitation of steel, and greatly improve the low temperature toughness of steel. ; At the same time, adding a small amount of nickel can inhibit the occurrence of "Cu brittleness" in the steel added with copper.
  • the addition of higher nickel has no obvious adverse effect on the properties of the steel itself. If copper and nickel are added at the same time, it can not only improve the corrosion resistance, but also refine the structure and precipitation of the steel, greatly improving the low temperature toughness. But since copper and nickel are both relatively precious alloying elements. Therefore, in order to minimize the cost of alloy design, the addition amount of nickel is usually ⁇ 0.5%, and the preferred range is ⁇ 0.3%.
  • the manufacturing method of the 980MPa grade bainite high hole expanding steel according to the present invention comprises the following steps:
  • Rolling temperature 950 ⁇ 1100°C, under 3-5 passes above 950°C, and the accumulated deformation is ⁇ 50%, preferably ⁇ 60%, the main purpose is to refine the austenite grains; to 920-950°C, and then carry out the last 3-7 passes of rolling and the accumulated deformation is ⁇ 70%, preferably ⁇ 85%; the final rolling temperature is 800-920°C;
  • Air-cooling for 0-10s is performed first to perform dynamic recovery to make the deformed austenite more uniform, and then the strip is cooled to 400-550°C and coiled at a cooling rate of ⁇ 10°C/s, preferably ⁇ 30°C/s. Cool down to room temperature naturally after coiling;
  • the operating speed of strip pickling is adjusted within the range of 30-100m/min, the pickling temperature is controlled between 75-85°C, and the tensile correction rate is controlled within ⁇ 2% to reduce the loss of strip elongation, and then rinse, The strip surface is dried and oiled.
  • rinsing is performed at a temperature range of 35-50° C. to ensure the surface quality of the strip, and the surface of the strip is dried and oiled between 120-140° C.
  • the innovation of the present invention is:
  • the composition design of the present invention adopts a lower C content, which can ensure that the user has excellent weldability during use, and ensures that the obtained martensite structure has good hole expansion and impact toughness;
  • the lower the carbon content the better;
  • the higher Si content is designed to match the process to obtain more retained austenite, thereby improving the plasticity of the material;
  • the higher Si content is conducive to reducing the unrecrystallized steel temperature, so that the steel can complete the dynamic recrystallization process in a wide range of finishing rolling temperature, thereby improving the structural anisotropy of the steel, refining the austenite grains and the final bainite lath size, improving the plasticity and hole expansion ratio.
  • the design idea of low-carbon bainite is adopted, and high silicon is added to inhibit and reduce the formation of cementite, and at the same time, the non-recrystallization temperature is reduced, and the temperature range of final rolling is expanded.
  • direct cooling or air cooling for a certain period of time
  • a bainite structure with fine and uniform grains can be obtained, and a small amount of retained austenite is contained at the same time.
  • the bainite structure gives the steel sheet higher strength, while the retained austenite gives the steel sheet higher ductility.
  • the combination of the two can make the steel sheet show good matching of strength, ductility and hole expansion ratio.
  • the rhythm of the rolling process should be completed as quickly as possible.
  • air-cooled for a certain period of time and then water-cooled or directly water-cooled.
  • the main purpose of air cooling Due to the inclusion of a certain amount of manganese and molybdenum in the composition design, manganese is an element that stabilizes austenite, while molybdenum greatly delays the transformation of ferrite and pearlite, while promoting the transformation of bainite. Therefore, in the short-time air cooling process, the rolled deformed austenite will not undergo phase transformation, that is, the ferrite structure will not be formed, but a dynamic recovery process will occur.
  • the dislocations inside the austenite grains will be greatly reduced, the austenite structure will be more uniform, and the bainite structure formed in the subsequent transformation process will be more uniform.
  • the water cooling rate of the strip is required to be ⁇ 10°C/s.
  • the strip steel needs to be cooled to the bainite transformation temperature range.
  • the bainite transformation temperature range is 400-550°C.
  • the bainitic lath becomes smaller, the structure is relatively more uniform, the strength increases and the plasticity decreases; on the contrary, as the coiling temperature increases, the bainitic lath in the structure decreases.
  • the body can be partially transformed into granular bainite, resulting in a decrease in strength and an increase in plasticity.
  • Theoretical calculations and experiments have confirmed that the bainite structure with excellent comprehensive properties can be obtained when the strip is cooled to the range of 400-550 °C.
  • the coiling temperature is ⁇ 550°C
  • relatively coarse upper bainite will be formed in the structure, which cannot meet the strength requirement above 980MPa; when the coiling temperature is ⁇ 400°C, the structure will be transformed into martensite.
  • the coiling temperature needs to be controlled between 400-550 °C. It is precisely based on this innovative composition and process design idea that the present invention can obtain 980MPa-level high hole-expanding steel with excellent strength, plasticity and hole-expanding performance. After coiling, the steel coil is naturally cooled slowly, and the microstructure of bainite + retained austenite can be obtained.
  • the cooling rate of natural slow cooling is less than or equal to 20°C/h, preferably less than or equal to 15°C/h.
  • the steel coil or steel plate has excellent matching of strength, plasticity and hole expansion and flanging, its yield strength is ⁇ 800MPa, tensile strength is ⁇ 980MPa, and it has good elongation (transverse A 50 ⁇ 11%) and expansion.
  • Hole performance (hole expansion ratio ⁇ 40%), it can be used in the manufacture of parts such as automobile chassis and sub-frames that require high-strength thinning and hole-enlarging and flanging, and has a very broad application prospect.
  • FIG. 1 is a process flow diagram of the method for manufacturing 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 2 is a schematic diagram of the rolling process in the manufacturing method of 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 3 is a schematic diagram of the cooling process in the manufacturing method of the 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 4 is a photo of a typical metallographic structure of Example 2 of the 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 5 is a photo of typical metallographic structure of Example 4 of the 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 6 is a photo of a typical metallographic structure of Example 6 of the 980MPa grade bainite high hole-expanding steel according to the present invention.
  • FIG. 7 is a photo of typical metallographic structure of Example 8 of the 980MPa grade bainite high hole-expanding steel according to the present invention.
  • the manufacturing method of 980MPa grade bainite high hole expanding steel according to the present invention includes the following steps:
  • Rolling temperature 950 ⁇ 1100°C, under 3-5 passes above 950°C and the accumulated deformation is ⁇ 50%, then the intermediate billet is warmed to 920-950°C, and then the last 3-7 passes are rolled and the accumulated deformation is ⁇ 70%; the final rolling temperature is 800-920°C;
  • the operating speed of strip pickling is adjusted within the range of 30-100m/min, the pickling temperature is controlled between 75-85°C, the pull-straightening rate is controlled within ⁇ 2%, the rinsing is carried out in the temperature range of 35-50°C, and the Dry the surface between 120-140°C and apply oil.
  • Tables 1-3 are the production process parameters of the steel embodiments of the present invention for the composition of the high hole-enlarging steel embodiments of the present invention, wherein the thickness of the billet in the rolling process is 120 mm;
  • Table 4 is the mechanical properties of the steel plates of the embodiments of the present invention.
  • the tensile properties yield strength, tensile strength, elongation
  • the hole expansion ratio was tested according to the ISO16630-2017 international standard.
  • the yield strength of the steel coil is ⁇ 800MPa
  • the tensile strength is ⁇ 980MPa
  • the elongation is between 10-13%
  • the hole expansion rate is ⁇ 40%.
  • Figures 4 to 7 show typical metallographic photographs of Examples 2, 4, 6 and 8, respectively. It can be seen that the typical microstructure is bainite with a small amount of retained austenite.
  • the 980MPa high hole expanding steel of the present invention has good matching of strength, plasticity and hole expanding performance, and is especially suitable for parts such as automobile chassis structures that require high strength thinning and hole expanding and flanging forming, such as control arms It can also be used for parts that need to be turned, such as wheels, and has broad application prospects.

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Abstract

一种980MPa级贝氏体高扩孔钢及其制造方法，其化学成分重量百分比为：C 0.05～0.10％，Si 0.5～2.0％，Mn 1.0％～2.0％，P≤0.02％，S≤0.003％，Al 0.02～0.08％，N≤0.004％，Mo≥0.1％，Ti 0.01～0.05％，Cr≤0.5％，B≤0.002％，O≤0.0030％，其余为Fe以及其它不可避免的杂质。本发明所述高扩孔钢的屈服强度≥800MPa，抗拉强度≥980MPa，同时且具有良好的延伸率(横向A 50≥11％)和扩孔性能(扩孔率≥40％)，可应用在乘用车底盘零件如控制臂以及副车架等需要高强减薄的部位。

Description

一种980MPa级贝氏体高扩孔钢及其制造方法 技术领域：
本发明涉及高强钢领域，特别涉及一种980MPa级贝氏体高扩孔钢及其制造方法。
背景技术
随着国民经济的发展，汽车的生产也大幅增加，板材的使用量不断提高。国内汽车行业许多车型的零部件原设计要求使用热轧或酸洗板，如汽车的底盘件、扭力梁、轿车的副车架、车轮轮辐和轮辋、前后桥总成、车身结构件、座椅、离合器、安全带、卡车箱板、防护网、汽车大梁等零配件。其中，底盘用钢占轿车总用钢量的比例可达24-34％。
乘用车的轻量化不仅是汽车行业的发展趋势，而且还是法律法规的要求。法律法规中规定了油耗，实际上是变相地要求降低车身重量，反映到材料上的要求是高强减薄轻量化。高强减重是后续新车型的必然要求，这势必造成用钢级别更高，底盘结构上也必然带来变化：如零件更复杂，造成在材料性能、表面等要求上以及成型技术上进步，如液压成形、热冲压、激光焊接等，进而转化材料的高强、冲压、翻边、回弹以及疲劳等性能上。
国内高强度高扩孔钢的开发与国外相比不仅强度级别相对较低，而且性能稳定性也不好。如国内汽车零部件企业使用的高扩孔钢基本是抗拉强度600MPa以下的高强钢，440MPa以下级别的高扩孔钢竞争白热化。抗拉强度780MPa级别的高扩孔钢目前正在逐渐开始批量使用，但是对于延伸率和扩孔率两个成形的重要指标也提出了较高要求。而980MPa级别的高扩孔钢目前还处于研发认证阶段，尚未到达批量使用阶段。但更高强度更高扩孔率的980高扩孔钢是未来的必然发展趋势。为了更好的满足用户的未来潜在需求，需要开发具有良好扩孔性能的980MPa级高扩孔钢。
目前绝大部分相关专利文献均是780MPa及以下级别的高扩孔钢。有关980MPa级高扩孔钢涉及的文献极少。中国专利申请CN106119702A公开了一种 980MPa级热轧高扩孔钢，其成分设计主要特点为低碳V-Ti微合金化设计，微观组织为粒状贝氏体和少量马氏体，同时添加微量Nb和Cr。在成分、工艺和组织等方面与本发明利存在很大不同。
由文献可知，在通常情况下，材料的延伸率与扩孔率呈反比关系，即延伸率越高，扩孔率越低；反之，延伸率越低，扩孔率越高。那么要获得高延伸高扩孔，同时又具有高强度的高扩孔钢就显得非常困难。此外，在相同或相似的强化机制下，材料的强度越高，扩孔率越低。
为了获得具有良好的塑性和扩孔翻边性能的钢材，需要更好的平衡两者之间的关系。当然，材料的扩孔率与许多因素密切相关，最主要的因素包括组织的均匀性、夹杂物和偏析控制水平、不同的组织类型以及扩孔率的测量等。通常来说，单一均匀的组织有利于获得更高的扩孔率，而双相或多相组织通常不利于扩孔率的提高。
发明内容
本发明的目的在于提供一种980MPa级贝氏体高扩孔钢及其制造方法，该高扩孔钢的屈服强度≥800MPa，抗拉强度≥980MPa，同时且具有良好的延伸率(横向A 50≥11％)和扩孔性能(扩孔率≥40％)，可应用在乘用车底盘零件如控制臂以及副车架等需要高强减薄的部位。
为达到上述目的，本发明的技术方案是：
本发明成分设计采用较低的C含量，可保证用户在使用时具有优异的焊接性、保证所获得的马氏体组织具有良好的扩孔性和冲击韧性；在满足抗拉强度≥980MPa的基础上，碳含量越低越好；设计较高的Si含量，与工艺匹配获得较多的残余奥氏体，从而提高材料的塑性；同时，较高的Si含量，有利于降低钢的未再结晶温度，使钢在较宽的终轧温度范围内即可完成动态再结晶过程，从而改善钢的组织各向异性，细化奥氏体晶粒和最终的贝氏体板条尺寸，改善塑性和扩孔率。
具体的，本发明所述的980MPa级贝氏体高扩孔钢，其化学成分重量百分比为：C 0.05～0.10％，Si 0.5～2.0％，Mn 1.0％～2.0％，P≤0.02％，S≤0.003％，Al 0.02～0.08％，N≤0.004％，Mo≥0.1％，Ti 0.01～0.05％，Cr≤0.5％，B≤0.002％，O≤0.0030％，其余为Fe以及其它不可避免的杂质。
进一步，本发明所述的980MPa级贝氏体高扩孔钢还包含Nb≤0.06％，V≤0.05％，Cu≤0.5％，Ni≤0.5％，Ca≤0.005％中的一种或一种以上元素。
在一些实施方式中，Mo的重量百分比含量为0.1～0.55％。
在一些实施方案中，本发明所述的980MPa级贝氏体高扩孔钢，其化学成分重量百分比为：C 0.05～0.10％，Si 0.5～2.0％，Mn 1.0％～2.0％，P≤0.02％，S≤0.003％，Al 0.02～0.08％，N≤0.004％，Mo≥0.1％，Ti 0.01～0.05％，Cr≤0.5％，B≤0.002％，O≤0.0030％，Nb≤0.06％，V≤0.05％，Cu≤0.5％，Ni≤0.5％，Ca≤0.005％，其余为Fe以及其它不可避免的杂质，且所述980MPa级贝氏体高扩孔钢含有Nb、V、Cu、Ni和Ca中的至少一种，优选至少含有Cr和B中的至少一种或全部两种。
所述Nb、V含量分别优选为≤0.03％；所述Cu、Ni含量分别优选为≤0.3％，所述Ca的含量优选为≤0.002％。
在一些实施方案中，本发明所述的980MPa级贝氏体高扩孔钢的屈服强度≥800MPa、优选≥830MPa、更优选≥850MPa，抗拉强度≥980MPa、优选≥1000MPa、更优选≥1020MPa，横向A 50≥11％，扩孔率≥40％、优选≥50％。
优选地，本发明所述的980MPa级贝氏体高扩孔钢的显微组织为贝氏体+残余奥氏体。以体积比计，所述980MPa级贝氏体高扩孔钢中残余奥氏体的含量为1～5％。
在本发明所述高扩孔钢的成分设计中：
碳，是钢中的基本元素，也是本发明中的重要元素之一。碳扩大奥氏体相区，稳定奥氏体。碳作为钢中的间隙原子，对提高钢的强度起着非常重要的作用，对钢的屈服强度和抗拉强度影响最大。在本发明中，由于要获得的组织为低碳贝氏体，为获得抗拉强度达980MPa级的高强钢，必须保证碳的含量在0.05％以上，否则碳含量在0.05％以下，即使完全淬火至室温，其抗拉强度也达不到980MPa；但是碳的含量也不能高于0.10％。碳的含量太高，形成的贝氏体强度太高，且组织中容易出现较多的马奥岛，对延伸率和扩孔率均不利。因此，碳含量应控制在0.05-0.10％之间，优选范围在0.06-0.08％。
硅，是钢中的基本元素，同时也是本发明中的重要元素之一。Si含量提高，不仅提高了固溶强化效果，更重要的是起到以下两个作用。一是大大降低了钢的未再结晶温度，使钢在很宽的温度范围内即可完成动态再结晶。这样，在实际轧制过程中，终轧温度可在800-920℃的终轧温度范围内进行轧制，使横纵向组织差异减小，既有利于提高强度和塑性，同时也有利于获得良好的扩孔率；Si的另一个重要作用是可以抑制渗碳体析出，在适当的轧制工艺条件下，尤其是在获得以贝氏体为主的组织时，可保留一定量残余奥氏体，有利于提高延伸率。Si的这种作用必须在 其含量达到0.5％以上时才表现出来；但Si的含量也不宜太高，否则实际轧制过程中轧制力负荷过大，不利于产品稳定生产。因此，钢中Si的含量通常控制在0.5-2.0％之间，优选范围在0.8-1.6％之间。
锰，是钢中最基本的元素，同时也是本发明中最重要的元素之一。Mn是扩大奥氏体相区的重要元素，可以降低钢的临界冷却速度，稳定奥氏体，细化晶粒，推迟奥氏体向珠光体的转变。但在本发明中，由于加入了一定的钼，而钼对铁素体和珠光体的推迟以及降低临界冷速的作用远大于锰。因此，钢中锰的含量可以适当减少，一般应控制在1.0％以上；同时，Mn的含量一般也不宜超过2.0％，否则炼钢时容易发生Mn偏析，同时板坯连铸时也容易发生热裂。因此，钢中Mn的含量一般控制在1.0-2.0％，优选范围在1.4-1.8％。
磷，是钢中的杂质元素。P极易偏聚到晶界上，钢中P的含量较高(≥0.1％)时，形成Fe 2P在晶粒周围析出，降低钢的塑性和韧性，故其含量越低越好，一般控制在0.02％以内较好且不提高炼钢成本。
硫，是钢中的杂质元素。钢中的S通常与Mn结合形成MnS夹杂，尤其是当S和Mn的含量均较高时，钢中将形成较多的MnS，而MnS本身具有一定的塑性，在后续轧制过程中MnS沿轧向发生变形，不仅降低了钢的横向塑性，而且增加了组织的各项异性，对扩孔性能不利。故钢中S含量越低越好，考虑到本发明中Mn的含量必须在较高的水平上，为了减少MnS的含量，故对S含量要加以严格控制，要求S含量控制在0.003％以内，优选范围在0.0015％以下。
铝，在钢中的作用主要是脱氧和固氮。在有强碳化物形成元素如Ti等存在的前提下，Al的主要作用是脱氧和细化晶粒。在本发明中，Al作为常见的脱氧元素和细化晶粒的元素，其含量通常控制在0.02-0.08％即可；Al含量低于0.02％，起不到细化晶粒的作用；同样，Al含量高于0.08％时，其细化晶粒效果达到饱和。因此，钢中Al的含量控制在0.02-0.08％之间即可，优选范围在0.02-0.05％之间。
氮，在本发明中属于杂质元素，其含量越低越好。但是氮在炼钢过程中是不可避免的元素。虽然其含量较少，但是与强碳化物形成元素如Ti等结合，形成的TiN颗粒对钢的性能带来非常不利的影响，尤其对扩孔性能非常不利。由于TiN呈方形，其尖角与基体之间存在很大的应力集中，在扩孔变形的过程中，TiN与基体之间的应力集中容易形成裂纹，从而大大降低材料的扩孔性能。在尽量控制氮含量的前提下，Ti等强碳化物形成元素含量越低越好。在本发明中，加入微量的Ti以固定氮， 尽量减少TiN带来的不利影响。因此，氮的含量应控制在0.004％以下，优选范围在0.003％以下。
钛，是本发明中的重要元素之一。Ti在本发明中主要起两个作用：一是与钢中的杂质元素N结合形成TiN，起到一部分“固氮”的作用；二是在材料后续的焊接过程中形成一定数量的弥散细小的TiN，抑制奥氏体晶粒尺寸，细化组织和改善低温韧性。因此，钢中Ti的含量范围控制在0.01-0.05％，优选范围为0.01-0.03％。
钼，是本发明中的重要元素之一。钼加入钢中可以大大推迟铁素体和珠光体相变，有利于在中高温区间获得贝氏体组织；同时，钼的加入还可以提高钢的组织和性能稳定性以及细化晶粒。钼的这种作用有利于在实际的轧制过程中多种工艺的调整，如在终轧结束之后既可以进行分段冷却，也可以先进行空冷再进行水冷等。在本发明中，采用轧后空冷或直接冷却两种方式，在空冷的过程中，钼的加入一方面可以确保在空冷过程中不会形成铁素体或珠光体等组织；另一方面在空冷过程中变形的奥氏体发生动态回复有利于提高组织和性能的均匀性，对扩孔性能有利。钼抑制铁素体和珠光体形成的作用需要其含量达到0.10％以上。因此，钼的含量应控制在≥0.10％，优选范围≥0.15％。在一些实施方案中，钼的含量为0.1～0.55％。
铬，是本发明中的重要元素之一。铬在本发明中并非为了提高钢的淬透性，而是为了与B相结合，有利于焊接后在焊接热影响区形成针状铁素体组织，可大大提高焊接热影响区的低温韧性。由于本发明所涉及的最终应用零件为乘用车底盘类产品，因此，其焊接热影响区的低温韧性是很重要的指标。除了要保证焊接热影响区的强度不能降低太多外，焊接热影响区的低温韧性也要满足一定要求。此外，铬本身也有一定的抗焊接软化作用。因此，钢中需要加入少量的铬元素，其范围一般≤0.5％，如0.1-0.5％，优选范围在0.2-0.4％。
硼，在钢中的作用主要是偏聚在奥氏体晶界处，抑制先共析铁素体的形成；硼加入钢中还可以大大提高钢的淬透性。但在本发明中，微量硼元素的加入主要目的不是为了提高淬透性，而是为了与铬相结合，改善焊接热影响区组织，获得韧性良好的针状铁素体组织。钢中硼元素的加入一般控制在0.002％以下，优选范围在0.0005-0.0015％之间。
钙，是本发明中的可添加元素。钙能够改善硫化物如MnS形态，使长条形的MnS等硫化物变为球形CaS，有利于改善夹杂物形态，进而减小长条形硫化物对扩孔性能的不利影响，但过多钙的加入会增加氧化钙的数量，对扩孔性能不利。因此， 钢种钙的添加量通常≤0.005％，优选范围在≤0.002％。
氧，是炼钢过程中不可避免的元素，对本发明而言，钢中O的含量通过脱氧之后一般都可以达到30ppm以下，对钢板的性能不会造成明显不利影响。因此，将钢中的O含量控制在30ppm以内即可。
铌，是本发明的可添加元素之一。铌与钛相似，是钢中的强碳化物元素，铌加入钢中可以大大提高钢的未再结晶温度，在精轧阶段可获得位错密度更高的形变奥氏体，在后续转变过程中可细化最终的相变组织。但铌的加入量不可太多，一方面铌的加入量超过0.06％，易在组织中形成比较粗大的铌的碳氮化物，消耗了部分碳原子，降低了碳化物的析出强化效果。同时，铌的含量较多，还容易造成热轧态奥氏体组织的各向异性，在后续的冷却相变过程中遗传给最终的组织，对扩孔性能不利。因此，钢中铌含量通常控制在≤0.06％，优选范围在≤0.03％。
钒，是本发明中的可添加元素。钒与钛、铌类似，也是一种强碳化物形成元素。但钒的碳化物固溶或析出温度低，在精轧阶段通常全部固溶在奥氏体中。只有当温度降低开始相变是，钒才开始在铁素体中形成。由于钒的碳化物在铁素体中的固溶度大于铌和钛的固溶度，故钒的碳化物在铁素体中形成的尺寸较大，不利于析出强化，对钢的强度贡献远小于钛，但由于钒的碳化物形成也消耗了一定的碳原子，对钢的强度提高不利。因此，钢中钒的添加量通常≤0.05％，优选范围≤0.03％。
铜，是本发明中的一种可添加元素。铜加入钢中可提高钢的耐蚀性，当其与P元素共同加入时，耐蚀效果更佳；当Cu加入量超过1％时，在一定条件下，可形成ε-Cu析出相，起到较强的析出强化效果。但Cu的加入容易在轧制过程中形成“Cu脆”现象，为了在某些应用场合下充分利用Cu的改善耐蚀性效果，同时又不至于引起显著的“Cu脆”现象，通常将Cu元素的含量控制在0.5％以内，优选范围在0.3％以内。
镍，是本发明中的一种可添加元素。镍加入钢中具有一定的耐蚀性，但耐蚀效果较铜弱，镍加入钢中对钢的拉伸性能影响不大，但可以细化钢的组织和析出相，大大提高钢的低温韧性；同时在添加铜元素的钢中，添加少量的镍可以抑制“Cu脆”的发生。添加较高的镍对钢本身的性能无明显不利影响。若铜和镍同时添加，不仅可以提高耐蚀性，而且对钢的组织和析出相进行细化，大大提高低温韧性。但由于铜和镍均属于比较贵重的合金元素。因此，为了尽量降低合金设计的成本，镍的添加量通常≤0.5％，优选范围≤0.3％。
本发明所述的980MPa级贝氏体高扩孔钢的制造方法，其包括如下步骤：
1)冶炼、浇铸
按所述成分采用转炉或电炉冶炼、真空炉二次精炼后浇铸成铸坯或铸锭；
2)铸坯或铸锭再加热，加热温度1100-1200℃，保温时间1～2小时；
3)热轧
开轧温度：950～1100℃，在950℃以上3-5道次大压下且累计变形量≥50％、优选≥60％，主要目的是细化奥氏体晶粒；随后中间坯待温至920-950℃，然后进行最后3-7个道次轧制且累计变形量≥70％、优选≥85％；终轧温度800-920℃；
4)冷却
先进行0-10s的空冷，以进行动态回复，使变形奥氏体更加均匀，再以≥10℃/s、优选≥30℃/s的冷速将带钢水冷至400-550℃卷取，卷取后自然冷却至室温；
5)酸洗
带钢酸洗运行速度在30～100m/min的区间内调整，酸洗温度控制在75～85℃之间，拉矫率控制在≤2％，以减小带钢延伸率损失，然后漂洗、带钢表面烘干，涂油。
优选的，步骤5)酸洗后，在35-50℃温度区间进行漂洗，以保证带钢表面质量，并在120-140℃之间进行带钢表面烘干，涂油。
本发明的创新点在于：
本发明成分设计采用较低的C含量，可保证用户在使用时具有优异的焊接性、保证所获得的马氏体组织具有良好的扩孔性和冲击韧性；在满足抗拉强度≥980MPa的基础上，碳含量越低越好；设计较高的Si含量，与工艺匹配获得较多的残余奥氏体，从而提高材料的塑性；同时，较高的Si含量，有利于降低钢的未再结晶温度，使钢在较宽的终轧温度范围内即可完成动态再结晶过程，从而改善钢的组织各向异性，细化奥氏体晶粒和最终的贝氏体板条尺寸，改善塑性和扩孔率。
在组织设计上采用低碳贝氏体设计思路、加入较高的硅以抑制和减少渗碳体形成，同时降低未再结晶温度，扩大终轧温度范围，通过轧后直接冷却或空冷一定时间后再冷却，可获得晶粒细小均匀的贝氏体组织，同时含有少量残余奥氏体。贝氏体组织赋予钢板更高的强度，而残余奥氏体则赋予钢板更高的塑性，二者相结合可 使钢板表现出良好的强度、塑性和扩孔率匹配。
在轧制工艺设计上，在粗轧和精轧阶段，轧制过程的节奏应尽量快速完成。在终轧结束后，先进行一定时间的空冷后水冷或直接进行水冷。空冷主要目的：由于在成分设计中含有一定的锰和钼，锰是稳定奥氏体的元素，而钼则大大推迟铁素体和珠光体相变，同时促进贝氏体转变。因此，在短时空冷过程中，经过轧制的变形奥氏体不会发生相变，即不会形成铁素体组织，而是发生动态回复过程。经过动态回复之后的奥氏体晶粒内部的位错会大大减少，奥氏体组织更加均匀，在后续的相变过程中形成的贝氏体组织也更加均匀。为了避免在连续冷却过程中形成铁素体，要求带钢水冷速度≥10℃/s。
为了获得单相均匀的贝氏体组织，需要将带钢冷却至贝氏体相变温度区间，在本发明中，根据成分不同，贝氏体转变温度区间在400-550℃。在此温度范围内，随着卷取温度降低，贝氏体板条更细小，组织相对更均匀，强度增加而塑性有所降低；反之，随着卷取温度升高，组织中板条贝氏体可部分转变为粒状贝氏体，使得强度降低而塑性增加。理论计算和实验已经证实，带钢冷却至400-550℃范围内，可获得综合性能优异的贝氏体组织。当卷取温度≥550℃时，组织中会形成比较粗大的上贝氏体，不能满足980MPa以上的强度要求；当卷取温度≤400℃时，组织会转变为马氏体。基于上述原因，卷取温度需控制在400-550℃之间。正是基于这种创新的成分和工艺设计思路，本发明可获得强度、塑性和扩孔性能优异的980MPa级高扩孔钢。卷取之后，使钢卷自然缓慢冷却，可获得贝氏体+残余奥氏体的显微组织。通常，自然缓冷的冷速≤20℃/h，优选≤15℃/h。
本发明的有益效果：
(1)采用相对经济的成分设计思路，如不添加或少添加贵重金属元素，同时采用创新性的冷却工艺路径，可获得强度、塑性、韧性、冷弯以及扩孔性能优异的980MPa级高扩孔钢；
(2)钢卷或钢板具有优异的强度、塑性和扩孔翻边性能匹配，其屈服强度≥800MPa，抗拉强度≥980MPa，同时且具有良好的延伸率(横向A 50≥11％)和扩孔性能(扩孔率≥40％)，可应用于汽车底盘、副车架等需要高强减薄和扩孔翻边的零部件制造，具有非常广阔的应用前景。
附图说明
图1为本发明所述980MPa级贝氏体高扩孔钢制造方法的工艺流程图。
图2为本发明所述980MPa级贝氏体高扩孔钢制造方法中轧制工艺的示意图。
图3为本发明所述980MPa级贝氏体高扩孔钢制造方法中冷却工艺的示意图。
图4为本发明所述980MPa级贝氏体高扩孔钢实施例2典型金相组织照片。
图5为本发明所述980MPa级贝氏体高扩孔钢实施例4典型金相组织照片。
图6为本发明所述980MPa级贝氏体高扩孔钢实施例6典型金相组织照片。
图7为本发明所述980MPa级贝氏体高扩孔钢实施例8典型金相组织照片。
具体实施方式
参见图1～图3，本发明所述的980MPa级贝氏体高扩孔钢的制造方法，其包括如下步骤：
1)冶炼、浇铸
按所述成分采用转炉或电炉冶炼、真空炉二次精炼后浇铸成铸坯或铸锭；
2)铸坯或铸锭再加热，加热温度1100-1200℃，保温时间1～2小时；
3)热轧
开轧温度：950～1100℃，在950℃以上3-5道次大压下且累计变形量≥50％，随后中间坯待温至920-950℃，然后进行最后3-7个道次轧制且累计变形量≥70％；终轧温度800-920℃；
4)冷却
先进行0-10s的空冷，以进行动态回复，使变形奥氏体更加均匀，再以≥10℃/s的冷速将带钢水冷至400-550℃卷取，卷取后自然冷却至室温；
5)酸洗
带钢酸洗运行速度在30～100m/min的区间内调整，酸洗温度控制在75～85℃之间，拉矫率控制在≤2％，在35-50℃温度区间进行漂洗，并在120-140℃之间进行表面烘干，涂油。
本发明所述高扩孔钢实施例的成分参见表1-3为本发明钢实施例的生产工艺参数，其中，轧制工艺中钢坯厚度120mm；表4为本发明实施例钢板的力学性能。实施例中，拉伸性能(屈服强度、抗拉强度、延伸率)按照ISO6892-2-2018国际标准进行检测；扩孔率按照ISO16630-2017国际标准进行检测。
从表4可以看出，钢卷屈服强度≥800MPa，抗拉强度≥980MPa，延伸率在10-13％之间，扩孔率≥40％。
图4～图7分别给出了实施例2、4、6和8典型金相照片。从中可以看出，典型微观组织为贝氏体并含有少量残余奥氏体。
从上述实施例可以看出，本发明所述980MPa高扩孔钢具有良好的强度、塑性和扩孔性能匹配，特别适合汽车底盘结构等需要高强减薄和扩孔翻边成形的零件如控制臂等，也可用于车轮等需要翻孔的零件，具有广阔的应用前景。
表1(单位：重量百分比)
实施例 C Si Mn P S Al N Mo Ti Cr B Ca Nb V Cu Ni O
1 0.077 0.95 1.75 0.009 0.0026 0.043 0.0038 0.11 0.019 0.42 0.0008 / 0.030 / / / 0.0025
2 0.084 1.89 1.13 0.011 0.0020 0.035 0.0028 0.22 0.050 0.11 / 0.002 / 0.025 / / 0.0024
3 0.099 0.50 1.04 0.013 0.0012 0.079 0.0032 0.55 0.015 0.28 0.0015 / 0.033 / / 0.12 0.0028
4 0.061 1.98 1.98 0.009 0.0028 0.022 0.0035 0.18 0.033 / 0.0010 0.003 0.025 / 0.20 0.21 0.0025
5 0.080 1.60 1.85 0.008 0.0011 0.065 0.0029 0.24 0.011 / / 0.005 / 0.033 / 0.50 0.0023
6 0.065 1.77 1.40 0.015 0.0023 0.058 0.0034 0.42 0.023 0.36 0.0018 / / 0.048 0.25 0.43 0.0020
7 0.090 1.24 1.94 0.013 0.0005 0.028 0.0029 0.31 0.018 0.31 0.0005 0.001 0.059 / / / 0.0027
8 0.051 1.40 1.80 0.012 0.0024 0.071 0.0040 0.37 0.029 0.50 0.0011 / / / 0.50 0.30 0.0029
表2
Figure PCTCN2021115433-appb-000001
Figure PCTCN2021115433-appb-000002
表3
Figure PCTCN2021115433-appb-000003
表4：钢板的力学性能
Figure PCTCN2021115433-appb-000004

Claims (15)

  1. 一种980MPa级贝氏体高扩孔钢，其化学成分重量百分比为：C 0.05～0.10％，Si 0.5～2.0％，Mn 1.0％～2.0％，P≤0.02％，S≤0.003％，Al 0.02～0.08％，N≤0.004％，Mo≥0.1％，Ti 0.01～0.05％，Cr≤0.5％，B≤0.002％，O≤0.0030％，其余为Fe以及其它不可避免的杂质，其中，所述高扩孔钢的显微组织为贝氏体+残余奥氏体。
  2. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，还包含Nb≤0.06％，V≤0.05％，Cu≤0.5％，Ni≤0.5％，Ca≤0.005％中的一种或一种以上元素；其中，所述Nb、V含量分别优选为≤0.03％；所述Cu、Ni含量分别优选为≤0.3％，所述Ca含量优选为≤0.002％。
  3. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，其化学成分重量百分比为：C 0.05～0.10％，Si 0.5～2.0％，Mn 1.0％～2.0％，P≤0.02％，S≤0.003％，Al 0.02～0.08％，N≤0.004％，Mo≥0.1％，Ti 0.01～0.05％，Cr≤0.5％，B≤0.002％，O≤0.0030％，Nb≤0.06％，V≤0.05％，Cu≤0.5％，Ni≤0.5％，Ca≤0.005％，其余为Fe以及其它不可避免的杂质，其中所述980MPa级贝氏体高扩孔钢含有Nb、V、Cu、Ni和Ca中的至少一种。
  4. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述C含量为0.06-0.08％。
  5. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Si含量为0.8-1.6％。
  6. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Mn含量为1.4-1.8％。
  7. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述S含量控制在0.0015％以下，和/或所述N含量控制在0.003％以下。
  8. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Al含量为0.02-0.05％。
  9. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Ti含量为0.01-0.03％。
  10. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Mo含量为≥0.15％。
  11. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述Cr含量为 0.2～0.4％，和/或所述B含量为0.0005-0.0015％，和/或Mo含量为0.1～0.55％。
  12. 如权利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述高扩孔钢的屈服强度≥800MPa，抗拉强度≥980MPa，延伸率横向A 50≥10％，扩孔率≥40％。
  13. 利要求1所述的980MPa级贝氏体高扩孔钢，其特征在于，所述高扩孔钢的屈服强度更优选≥850MPa，抗拉强度≥1000MPa，横向A 50≥11％，扩孔率≥50％。
  14. 如权利要求1～13中任何一项所述的980MPa级贝氏体高扩孔钢的制造方法，其特征是：包括如下步骤：
    1)冶炼、浇铸
    按权利要求1～11所述成分采用转炉或电炉冶炼、真空炉二次精炼后浇铸成铸坯或铸锭；
    2)铸坯或铸锭再加热，加热温度1100-1200℃，保温时间1～2小时；
    3)热轧
    开轧温度：950～1100℃，在950℃以上3-5道次大压下且累计变形量≥50％、优选≥60％；随后中间坯待温至920-950℃，然后进行最后3-7个道次轧制且累计变形量≥70％、优选≥85％；终轧温度800-920℃；
    4)冷却
    先进行0-10s的空冷，再以≥10℃/s、优选≥30℃/s的冷速将带钢水冷至400-550℃卷取，卷取后自然冷却至室温；
    5)酸洗
    带钢酸洗运行速度在30～100m/min的区间内调整，酸洗温度控制在75～85℃之间，拉矫率控制在≤2％，然后漂洗、带钢表面烘干，涂油。
  15. 如权利要求14所述的980MPa级贝氏体高扩孔钢的制造方法，其特征是，步骤5)酸洗后，在35-50℃温度区间进行漂洗，并在120-140℃之间进行表面烘干，涂油。
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