WO2023241545A1 - 一种1000MPa级高扩孔热轧复相钢钢板及其制造方法 - Google Patents

一种1000MPa级高扩孔热轧复相钢钢板及其制造方法 Download PDF

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WO2023241545A1
WO2023241545A1 PCT/CN2023/099840 CN2023099840W WO2023241545A1 WO 2023241545 A1 WO2023241545 A1 WO 2023241545A1 CN 2023099840 W CN2023099840 W CN 2023099840W WO 2023241545 A1 WO2023241545 A1 WO 2023241545A1
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steel plate
hot
1000mpa
phase steel
rolled
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PCT/CN2023/099840
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English (en)
French (fr)
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刘春粟
杨龙
朱晓东
金鑫焱
张玉龙
罗帅
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宝山钢铁股份有限公司
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    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a multi-phase steel and a manufacturing method thereof, and in particular to a highly expanded hot-rolled multi-phase steel plate and a manufacturing method thereof.
  • the inventor hopes to further improve the strength of multi-phase steel to obtain a new 1000MPa highly expanded multi-phase steel with higher strength and ultra-high porosity, which is also the future multi-phase steel. an inevitable trend of development.
  • the publication number is CN106119702A
  • the publication date is November 16, 2016,
  • the Chinese patent document titled "A 980MPa grade hot-rolled high-strength high-hole expansion steel and its manufacturing method” discloses a 980MPa-grade hot-rolled
  • the main feature of the chemical composition design of high-strength and high-pore-expansion steel and its manufacturing method is low-carbon V-Ti micro-alloying design and contains V element.
  • the cost of this technical solution is relatively high, and the use of B element is not considered.
  • the publication number is CN114107797A
  • the publication date is March 1, 2022
  • the Chinese patent document titled "A 980MPa bainite precipitation-strengthened high hole expansion steel and its manufacturing method” discloses a 980MPa Grade bainite precipitation-strengthened high-hole expansion steel and its manufacturing method.
  • the main feature of its chemical composition design is low-carbon V-Ti microalloying design, which contains V and has a higher cost. At the same time, its structure is bainite ferrite.
  • the public number is CN113122769A
  • the public date is July 16, 2021
  • the name is The Chinese patent document "Low silicon, low carbon equivalent GiPa grade composite phase steel plate/steel strip and its manufacturing method” discloses a low silicon, low carbon equivalent GiPa grade composite phase steel plate/strip and its manufacturing method. Its chemical The composition design has low carbon content, while its structure contains ferrite, and the hot rolling and coiling temperature is high.
  • One of the purposes of the present invention is to provide a 1000MPa-level high-expansion hot-rolled multi-phase steel plate.
  • the 1000MPa-level high-expansion hot-rolled multi-phase steel plate adopts a reasonable chemical composition design and can obtain good comprehensive mechanical properties. It not only has high strength and high elongation, but also has the characteristics of high hole expansion rate. It can be used as automobile body structural parts and automobile chassis parts, and can also be used in other application fields that require high strength and weight reduction. It has good application prospects.
  • the present invention provides a 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate, which contains Fe and inevitable impurity elements, and also contains the following chemical elements in the following mass percentages:
  • the mass percentage content of N, Ti and Nb also satisfies: 0.01% ⁇ (Ti-3.43N+0.52Nb)/4 ⁇ 0.053%.
  • the mass percentage content of each chemical element is:
  • the mass percentage content of N, Ti and Nb also satisfies: 0.01% ⁇ (Ti-3.43N+0.52Nb)/4 ⁇ 0.053%.
  • C In the 1000MPa grade high-pore-expanding hot-rolled multi-phase steel plate of the present invention, considering that the level of C content largely determines the tensile strength level of the steel plate, C is used for solid solution strengthening and is combined with Nb It cooperates with Ti and other materials to form sufficient precipitation strengthening phase to ensure the strength of steel.
  • the C content in steel should not be too high. A high mass percentage of C will make the carbide particles coarse, and it is easy to form too much martensite and retained austenite, which is not conducive to hole expansion. performance.
  • the mass percentage of C element is controlled between 0.07-0.15%.
  • the Si element can play a solid solution strengthening role and improve the strength of the steel plate.
  • adding Si can increase the work hardening rate and given strength.
  • the uniform elongation and total elongation are lower, which helps to improve the elongation of the steel plate.
  • Si can also prevent the precipitation of carbides and reduce the appearance of pearlite phase.
  • the silicon content in steel can easily cause surface defects such as fayalite (2FeO-SiO 2 ) oxide scale to form on the surface of the steel plate, which has a negative impact on the surface quality. Based on this, in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention, the mass percentage content of Si element is controlled between 0.1-0.8%.
  • the Mn element is a solid solution strengthening element.
  • the mass percentage of the Mn element in the steel is low, it will lead to insufficient strength of the steel.
  • the mass percentage of Mn element is too high, the plasticity of the steel plate will be reduced.
  • Mn will also delay the pearlite transformation, improve the hardenability of the steel and reduce the bainite transformation temperature, refining the structural substructure of the steel to ensure that the lath substructure is obtained, so that the steel can obtain higher resistance.
  • high tensile strength it also has good formability. Therefore, considering the influence of Mn element content on steel properties, the mass percentage content of Mn element is controlled between 1.5-2.2% in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention.
  • Al is a deoxidizing element in the steel, which can reduce oxide inclusions in the steel, purify the steel, and help improve the forming of the steel plate. performance.
  • the content of Al element in steel should not be too high.
  • the mass percentage of Al element in steel is controlled between 0.02-0.1%.
  • Ti In the 1000MPa grade high-pore-expanding hot-rolled multi-phase steel plate of the present invention, Ti is one of the important fine grain strengthening and precipitation strengthening elements.
  • the Ti element can increase the recrystallization temperature of the steel during the hot rolling process. and refine the grain size. At the same time, the combination of Ti element and C element has a very good strengthening effect.
  • the Ti element content in the steel should not be too high. When the Ti element content in the steel is too high, it is easy to form larger TiN, which is detrimental to the impact toughness of the steel. Therefore, in order to exert the beneficial effects of Ti element, the mass percentage content of Ti element in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention is controlled between 0.05-0.18%.
  • Nb In the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention, Nb is one of the important precipitation strengthening and fine grain strengthening elements. However, when the mass percentage of Nb is higher than 0.06%, the strengthening of Nb The effect is close to saturation and the cost is high. Therefore, in order to exert the beneficial effects of Nb element and control the production cost at the same time, in the present invention, the mass percentage content of Nb element is controlled to Nb ⁇ 0.06%.
  • B In the 1000MPa-level high-pore-expanded hot-rolled multi-phase steel plate of the present invention, B is beneficial to expanding the bainite phase area and ensuring that the bainite structure can be obtained during the post-rolling cooling of the steel plate, which is important for the strength of the steel.
  • the improvement in hardness is very obvious.
  • the content of B element in steel should not be too high. Too much B element will cause excessive large-scale martensite structure in the steel plate and lead to a decrease in the hole expansion rate and elongation of the steel. Therefore, in the present invention, the mass percentage of B element is controlled to be B ⁇ 0.003%.
  • Cr and/or Mo elements can also be added to the steel.
  • Cr and Mo elements can be used individually, or they can be used in combination.
  • Cr In the 1000MPa-level high-pore-expansion hot-rolled multi-phase steel plate of the present invention, Cr is an element that inhibits the production of pearlite and is beneficial to the formation of bainite structure. It can improve the strength and hole expansion rate of the steel.
  • the inventor's research found that when the mass percentage of Cr element in steel is less than 0.15%, its impact on the phase transformation curve is not significant; and when the mass percentage of Cr element in steel is too high, it will not only cause The increase in alloy cost also tends to produce more martensite structures. Based on this, in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention, when added, the mass percentage of Cr element is controlled between 0.2% and 1.5%.
  • the Mo element can not only inhibit the production of pearlite, but also facilitate the formation of bainite structure and a small amount of martensite austenite islands. .
  • the Mo element can also promote the transformation of bainite microstructure at higher temperatures, thus allowing steel to be coiled at higher temperatures. This higher coiling temperature provides sufficient precipitation kinetics, thereby stimulating significant precipitation strengthening.
  • Mo element also plays a very important role in the composite precipitation process with Nb and Ti, which can also reduce the possibility of coarse particle size of precipitated particles.
  • the content of Mo element in steel should not be too high.
  • the mass percentage of the Mo element is controlled between 0.05% and 0.5%.
  • the inventor while controlling the mass percentage of a single chemical element in the substrate, the inventor also further controlled the mass percentage of N, Ti, and Nb in the steel plate.
  • the content also satisfies: 0.01% ⁇ (Ti-3.43N+0.52Nb)/4 ⁇ 0.053%.
  • N is the impurity element in the steel plate.
  • the inventor adopts a high-Ti and high-Nb design, which can mainly play the following three roles of grain refinement and one precipitation strengthening: (1) During the heating process of the slab, Nb, The precipitates of Ti can prevent the growth of original austenite grains; (2) During the hot rolling process, (Nb, Ti) (C, N) is conducive to increasing the recrystallization temperature and further refining the austenite grains. ; (3) The precipitated (Nb, Ti) (C, N) or (Nb, Ti) (Mo, Cr) (C, N) is conducive to the refinement of phase transformation bainite and a small amount of martensite crystals. particles; (4) During the laminar cooling process, nanoscale precipitates of (Nb, Ti) (C, N) or (Nb, Ti) (Mo, Cr) (C, N) can play a strong role Precipitation strengthening effect.
  • the present invention in order to ensure that Ti and Nb compounds are fully separated, in addition to the design of the C element that needs to be coordinated with the Ti and Nb content, it is also necessary to control the quality of N, Ti and Nb through reasonable Nb and Ti compounding.
  • the content satisfies the relationship of "0.01% ⁇ (Ti-3.43N + 0.52Nb) / 4 ⁇ 0.053%" and cooperates with the optimized design of the manufacturing process to obtain 1000MPa high-density bainite grain size ⁇ 6um. Hole hot rolled composite phase steel plate.
  • P, S and N are all impurity elements in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention.
  • the content of impurity elements in the steel plate should be reduced as much as possible.
  • the P element is controlled
  • the element content is P ⁇ 0.02%
  • the S element content is controlled to be S ⁇ 0.005%
  • the N element content is controlled to be N ⁇ 0.005%.
  • the Cr and Mo contents of the steel type satisfy one of the following:
  • Cr and Mo elements can be used individually, or they can be used in combination. Adding an appropriate amount of Cr or Mo elements is to obtain the bainite structure and smaller martensite and austenite islands during the hot rolling and coiling process to ensure that there is no pearlite and massive particles that affect the hole expansion performance. martensite.
  • the inventor designed the Cr and Mo contents in the steel. Further optimization design has been carried out, and in actual application, any one of the Cr and Mo component ratios designed in (1)-(4) above can be preferably added.
  • the main body of the microstructure matrix is bainite, and there are nanoscale precipitates on the matrix.
  • the microstructure matrix of the 1000MPa high-expansion hot-rolled multi-phase steel plate designed by the present invention has nanoscale precipitates.
  • These microalloy nanoscale precipitates include TiC, (Ti, Nb)C , its specific precipitation size can be controlled between 3-20nm.
  • the bainite volume fraction is ⁇ 85%.
  • the matrix of the microstructure also includes martensite and/or retained austenite. Further, in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention, the total fraction of martensite and retained austenite is ⁇ 15%.
  • the size of the nanoscale precipitates is 3-20nm.
  • the microstructure of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention contains martensite with a volume fraction of 85 to 96% and a total martensite with a volume fraction of 4 to 15%. And retained austenite, where the grain size of bainite is between 3.2-5um, and the grain size of martensite is between 0.5-3um.
  • the yield strength of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 780MPa. In some embodiments, the yield strength of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 800MPa. In some embodiments, the yield strength of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is 750-960MPa.
  • the tensile strength of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is 980-1150MPa.
  • the punching expansion rate of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 50%. In some embodiments, the punching expansion rate of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 55%.
  • the reaming hole expansion rate of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 70%. In some embodiments, the reaming hole expansion rate of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of the present invention is ⁇ 75%.
  • another object of the present invention is to provide the manufacturing method of the above-mentioned 1000MPa-grade high-pore-expanding hot-rolled multi-phase steel plate of the present invention.
  • the 1000MPa-grade high-pore-expanding hot-rolled multi-phase steel plate obtained by the manufacturing method is equipped with It not only has high strength and high elongation, but also has the characteristics of high hole expansion rate, which has good application prospects.
  • the present invention proposes a manufacturing method for the above-mentioned 1000MPa grade high-expansion hot-rolled multi-phase steel plate, which includes the steps:
  • Hot rolling The slab is heated to 1200-1300°C and kept warm; then rolled, in which the rough rolling outlet temperature is controlled to be 1000-1080°C, and the finishing rolling temperature is 840-950°C;
  • each chemical element in the formula has the value before the mass percentage of the corresponding chemical element is substituted;
  • the heating temperature of the slab is particularly important for performance.
  • Ti will have a large number of large-sized (Ti, Nb) (Ti, Nb) during the continuous casting process.
  • C, N) precipitates are precipitated, and the heating temperature is set to ⁇ 1200°C.
  • the main purpose is to ensure that Ti and other alloying elements are dissolved as much as possible during the heating process of the slab to ensure that subsequent micro-alloys such as Ti are coiled during hot rolling. Nanoscale precipitation during the process.
  • the heating temperature should not be too high. When the heating temperature exceeds 1300°C, there will be a tendency for grain coarsening, which is not conducive to the toughness of the steel plate. Therefore, in the hot rolling process of the present invention, the heating temperature is preferably controlled between 1200°C and 1300°C.
  • the rough rolling temperature control in the hot rolling process has a greater impact on microalloys such as Ti.
  • Ti carbides and carbonitrides will precipitate at lower rough rolling temperatures and during the finishing rolling process.
  • the larger precipitated size is not conducive to the improvement of final strength, but the precipitated (Nb, Ti) (C, N) is conducive to the refinement of austenite grains. Therefore, in the hot rolling process of the present invention, the rough rolling outlet temperature is controlled to 1000-1080°C. In some embodiments, the rough rolling outlet temperature is controlled to be 1050-1080°C. In some embodiments, the finishing rolling temperature is controlled to be 880-950°C.
  • the laminar cooling time, cooling speed and tape threading speed of step (3) In order to control the cooling time from the midpoint temperature to the coiling temperature ⁇ 4.5s, preferably ⁇ 6.5s, the average cooling rate of the first section before the midpoint temperature is ⁇ 100°C/s, and the average cooling rate after the midpoint temperature is ⁇ 3°C. /s, control the belt threading speed 7-12m/s.
  • the coiling temperature is also necessary to control bainite transformation and microalloy precipitation.
  • the coiling temperature is too high, it will lead to higher ferrite content and larger secondary martensite and retained austenite sizes. If the coiling temperature is large, it is not conducive to improving the hole expansion rate; when the coiling temperature is low, a primary martensite structure may appear, resulting in a lower elongation of the steel. Therefore, in the present invention, controlling the coiling temperature between 430-600°C can solve the matching problem between elongation and hole expansion rate. Of course, in order to obtain better implementation effects, the coiling temperature can also be further controlled between 430-580°C.
  • cooling to room temperature with a cooling rate of ⁇ 0.1°C/s can not only promote further transformation of bainite, but also facilitate the tempering of martensite and further precipitation of microalloys. It can effectively improve the strength, hole expansion rate and elongation of steel.
  • the present invention has no special limitations on the pickling process, but in some embodiments, when actually implementing pickling, it can be specifically: control the pickling tensile straightening elongation to 0.2-2%; The washing speed is controlled at 60-150m/min, the temperature of the last pickling tank in the pickling process is controlled at 80-90°C, and the iron ion concentration is controlled at 30-40g/L. The finished steel plate is obtained after pickling.
  • the total rolling reduction rate is controlled to be ⁇ 80%, and the total finishing rolling reduction rate is ⁇ 50%.
  • the total rolling reduction ratio is 90%-95%, and the total finishing rolling reduction ratio is 85%-90%. It is further preferred that the thickness of the finished steel plate is no more than 5mm.
  • the heat preservation time is 1 to 3 hours.
  • step (3) the cooling time from the intermediate point temperature to the coiling temperature is controlled to be ⁇ 8 s.
  • the average cooling rate of the first stage is 100-160°C/s, preferably 120-160°C/s.
  • the average cooling rate of the second stage is 3-25°C/s, preferably 3-22°C/s.
  • step (4) the coiling temperature is controlled to be 430-580°C. In some embodiments, in step (4), the coiling temperature is controlled to be 430-550°C.
  • the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate and its manufacturing method according to the present invention have the following advantages and beneficial effects:
  • the invention adopts an economical and reasonable chemical composition design, and at the same time cooperates with the existing hot continuous rolling production line to produce a new type of ultra-high strength and hole expansion rate of 1000MPa high hole expansion heat Rolled composite phase steel plate.
  • the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate prepared by the invention has a high hole expansion rate and high Strength, high formability and other characteristics, its yield strength ⁇ 750MPa, tensile strength 950-1150MPa, elongation A50 ⁇ 12%, punching expansion rate ⁇ 45%, reaming expansion rate ⁇ 65%, it can be It is used as automobile body structural parts and automobile chassis parts, and can also be used in other application fields that require high strength and weight reduction, and has good application prospects.
  • Figure 1 is a photo of the metallographic structure of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate in Example 3.
  • Figure 2 is a photo of the metallographic structure of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate in Example 5.
  • Figure 3 is a photo of the metallographic structure of the comparative steel in Comparative Example 6.
  • Table 1-1 lists the mass percentage proportions of each chemical element in the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of Examples 1-13 and the comparative steel plate of Comparative Examples 1-11.
  • Table 1-2 lists the coordination between each chemical element in the steel plates of Examples 1-13 and Comparative Examples 1-11.
  • Hot rolling The slab obtained through smelting and continuous casting is heated to 1200-1300°C and kept for 1-3 hours; then rolling is performed, in which the outlet temperature of rough rolling is controlled to 1000-1080°C, and the final rolling The temperature is 840-950°C, the total rolling reduction rate is controlled to be ⁇ 80%, and the total finishing rolling reduction rate is ⁇ 50%.
  • the average cooling speed of the first stage is ⁇ 100°C/s
  • the average cooling speed of the second stage is ⁇ 3°C/s
  • the average cooling speed of the first stage is ⁇ 3°C/s.
  • the intermediate point temperature between the first stage cooling and the second stage cooling is the bainite transformation temperature Bs ⁇ 30°C, and the threading speed is controlled to 7-12m/s; the cooling time from the intermediate point temperature to the coiling temperature is controlled to ⁇ 4.5s.
  • the cooling time from the midpoint temperature to the coiling temperature can be controlled to be ⁇ 6 seconds.
  • Coiling Coil the water-cooled steel plate, and control the coiling temperature to 430-600°C, preferably 430-580°C. After coiling, use a cooling speed of ⁇ 0.1°C/s. to room temperature.
  • the chemical composition design and related processes of the 1000MPa grade high-expansion hot-rolled multi-phase steel plates of Examples 1-13 meet the specification requirements designed by the present invention.
  • the steps used in the comparative steel plate of Comparative Example 1-11 are also prepared in the above steps (1)-(5), there are some problems in the chemical composition design and/or related manufacturing process of the comparative steel plate in Comparative Example 1-11. Parameters that do not meet the design requirements of the present invention.
  • Table 2-1 and Table 2-2 list the specific process parameters of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of Examples 1-13 and the comparative steel plate of Comparative Examples 1-11.
  • the inventor took samples of the 1000MPa grade highly expanded hot-rolled multi-phase steel plates of finished product Examples 1-13 obtained through the above process steps and the comparative steel plates of Comparative Examples 1-11, respectively, and conducted a comparison of each Example and The microstructure of the comparative steel plate was observed and analyzed.
  • the results of the relevant observation and analysis are listed in Table 3 below.
  • Table 3 lists the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plates and comparative examples of Examples 1-13. Observation and analysis results of microstructure of comparative steel plates 1-11.
  • the microstructure matrix of the 1000MPa grade highly expanded hot-rolled multi-phase steel plates prepared in Examples 1-13 is all bainite + a small amount of martensite and retained austenite. body, and the volume fraction of bainite is between 85%-96%, the volume fraction of martensite and/or retained austenite is between 4-15%, and the grain size of bainite is between 3.2-5um time, the grain size of martensite is between 0.5-3um.
  • nanoscale precipitates on the phase steel plate matrix including TiC and (Ti, Nb)C.
  • the diameter of these nanoscale precipitates is between 3-20nm.
  • Hole expansion test The hole expansion rate is measured by the hole expansion test. Use a punch mold to press the specimen with a hole in the center into the concave mold to expand the center hole of the specimen until necking or penetration cracks appear at the edge of the plate hole. Since the preparation method of the original hole in the center of the specimen has a great influence on the hole expansion rate test results, punching and reaming were used to prepare the original hole in the center of the specimen. Subsequent tests and testing methods were in accordance with the ISO/DIS 16630 standard. The hole expansion rate test method was implemented, and the test results are shown in Table 4.
  • Table 4 lists the mechanical property testing results of the 1000MPa grade highly expanded hot-rolled multi-phase steel plate of Examples 1-11 and the comparative steel plate of Comparative Examples 1-111.
  • Examples 1-13 adopt the reasonable Cr and Mo ratios in Table 1-1 and Table 1-2, and add Ti and Nb at the same time to increase the precipitation strengthening effect during the annealing process, while meeting the requirements of Table 2- 1 and the hot rolling process in Table 2-2, the finished 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of Example 1-13 finally obtained obtained the microstructure shown in Table 3.
  • the yield strength of the designed 1000MPa grade highly expanded hot-rolled multi-phase steel plates of Examples 1-13 is between 755-953MPa, and the tensile strength is between 982-1150MPa.
  • the elongation A50 is between 12-18.5%, the punching expansion rate is between 45-65%, and the reaming expansion rate is between 65-81%.
  • Comparative Example 1-2 uses the same type A steel grade, but uses different hot rolling coiling temperatures. Among them, Comparative Example 1 adopts a lower coiling temperature, and the coiling temperature is 380°C, and the martensite content in the final microstructure reaches 80%, which ultimately leads to high tensile strength and low elongation. . Comparative Example 2 uses a higher coiling temperature, and the coiling temperature is 620°C. The ferrite content in the microstructure is low, resulting in low bainite content and insufficient tensile strength of the steel.
  • Comparative Example 3-6 uses the same Class B steel type, but its process does not meet the design requirements. Among them, in Comparative Example 3, due to the lower intermediate point temperature, the cooling time from the intermediate point temperature to the coiling temperature in the laminar cooling process is shorter, and the phase transformation of bainite during the laminar cooling process is incomplete, resulting in overcooled aerosol. The proportion of phase transformation in the coiling process is higher, and the martensite content in the final microstructure is higher. The elongation and hole expansion rate of the obtained comparative steel are relatively low.
  • Comparative Example 4 due to the low total rolling reduction of only 20%, the recrystallization was insufficient, resulting in relatively coarse grains and relatively low elongation and hole expansion rates.
  • Comparative Example 5 is due to the fact that during the hot rolling process in step (2), the rough rolling outlet temperature and the finishing rolling temperature are relatively low, and relatively coarse microalloy particles have precipitated during the rolling process, which does not contribute significantly to the strength. , ultimately leading to insufficient tensile strength of the steel.
  • Comparative Example 6 is because the heating temperature used in the hot rolling process of step (2) is low, only 1120°C, resulting in insufficient Nb and Ti content, and coarse (Ti, Nb )(C, N) particles are not completely solid-solubilized and contribute little to the strength, which also shows insufficient tensile strength of the steel plate.
  • Comparative Example 7 uses the same type C steel, but the cooling rate after hot rolling and coiling in Comparative Example 7 is too fast, and the cooling rate after hot rolling and coiling is 0.2°C/s. As a result, the supercooled austenite undergoes a larger proportion of martensite transformation and a smaller proportion of bainite transformation after coiling, which ultimately leads to lower elongation and hole expansion ratio of the steel.
  • Comparative Examples 8-11 are because the chemical composition does not meet the requirements of the present invention, resulting in poor performance of the final steel.
  • Figure 1 is a photo of the metallographic structure of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate in Example 3.
  • the microstructure of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of Example 3 is 92% bainite + 8% martensite and retained austenite, where, The grain size of bainite is 4.3um, and the grain size of martensite and retained austenite is between 0.5-2um.
  • Figure 2 is a photo of the metallographic structure of the 1000MPa grade high-expansion hot-rolled multi-phase steel plate in Example 5.
  • the microstructure of the 1000MPa grade high-hole expansion hot-rolled multi-phase steel plate of Example 5 is 85% bainite + 15% martensite and retained austenite, where, The grain size of bainite is 5.0um, and the grain size of martensite and retained austenite is between 0.5-3um.
  • Figure 3 is a photo of the metallographic structure of the comparative steel in Comparative Example 6.
  • the microstructure of the comparative steel in Comparative Example 6 is 20% bainite + 80% martensite, in which the bainite grain size is 3.0um and the martensite grain size is 3.0um. Size>3um.

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Abstract

本发明公开了一种1000MPa级高扩孔热轧复相钢钢板及其制作方法，该钢板含有Fe和不可避免的杂质元素，其还含有质量百分含量如下的下述各化学元素：C：0.07-0.15％，Si：0.1-0.8％，Mn：1.5-2.2％，Al：0.02-0.1％，Ti：0.05-0.18％，Nb≤0.06％，B≤0.003％，以及0.2％≤Cr≤1.5％、0.05％≤Mo≤0.5％中的至少其中之一；其中N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。。该1000MPa级高扩孔热轧复相钢钢板可用做汽车底盘以及结构件，满足汽车复杂零件翻边、冲压及汽车轻量化的技术要求。

Description

一种1000MPa级高扩孔热轧复相钢钢板及其制造方法 技术领域
本发明涉及一种复相钢及其制造方法，尤其涉及一种高扩孔热轧复相钢钢板及其制造方法。
背景技术
近年来，随着汽车行业的迅速发展，市场和用户对汽车的轻量化要求也随之变得越来越高，轻量化已成为汽车行业发展的趋势，高强度钢板在汽车结构件中所占的比例也越来越大。
为了提高强度，当前很多车型采用80kg级别的钢板生产汽车底盘件，但是，目前市场上常见的复相钢强度普遍不能达到1000MPa水平，在已公布的专利技术方案中，多数复相钢的抗拉强度在800MPa级别。
因此，为了满足轻量化要求，发明人期望进一步提高复相钢的强度，以获得一种新的具有更高强度以及超高孔率的1000MPa高扩孔复相钢，这同时也是未来复相钢发展的必然趋势。
研究发现，现有技术中具有一些1000MPa级高扩孔复相钢。
例如：公开号为CN106119702A，公开日为2016年11月16日，名称为“一种980MPa级热轧高强度高扩孔钢及其制造方法”的中国专利文献，公开了一种980MPa级热轧高强度高扩孔钢及其制造方法，其化学成分分设计主要特点为低碳V-Ti微合金化设计，并含有V元素，该技术方案的成本较高，同时没有考虑B元素的使用。
又例如：公开号为CN114107797A，公开日为2022年3月1日，名称为“一种980MPa级贝氏体析出强化型高扩孔钢及其制造方法”的中国专利文献，公开了一种980Mpa级贝氏体析出强化型高扩孔钢及其制造方法，其化学成分设计主要特点为低碳V-Ti微合金化设计，含有V，成本较高。同时其组织为贝氏体铁素体。
再例如：公开号为CN113122769A，公开日为2021年7月16日，名称为 “低硅低碳当量吉帕级复相钢板/钢带及其制造方法”的中国专利文献，公开了一种低硅低碳当量吉帕级复相钢板/带钢及其制造方法，其化学成分设计低碳含量较低，同时其组织含有铁素体，并且热轧卷取温度较高。
综上所述可以看出，在通常情况下，材料的延伸率、扩孔率、强度之间是呈现一种反比的关系。为此，本发明为了获得一种兼具有高强度、高扩孔、高延伸率的1000MPa级高扩孔热轧复相钢钢板，在设计时，需要合金元素、相变规律、显微组织的良好匹配。
发明内容
本发明的目的之一在于提供一种1000MPa级高扩孔热轧复相钢钢板，该1000MPa级高扩孔热轧复相钢钢板采用了合理的化学成分设计，可以获得良好的综合力学性能，其在具有高强度、高延伸率的同时，还具有高扩孔率的特点，其既可以用做汽车车身结构件及其汽车底盘件，也可以用于其他需要高强、减重等应用领域，具有良好的应用前景。
为了实现上述目的，本发明提供了一种1000MPa级高扩孔热轧复相钢钢板，其含有Fe和不可避免的杂质元素，其还含有质量百分含量如下的下述各化学元素：
C：0.07-0.15％，Si：0.1-0.8％，Mn：1.5-2.2％，Al：0.02-0.1％，Ti：0.05-0.18％，Nb≤0.06％，B≤0.003％，以及0.2％≤Cr≤1.5％、0.05％≤Mo≤0.5％中的至少其中之一；
其中N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其各化学元素质量百分含量为：
C：0.07-0.15％，Si：0.1-0.8％，Mn：1.5-2.2％，Al：0.02-0.1％，Ti：0.05-0.18％，Nb≤0.06％，B≤0.003％，以及0.2％≤Cr≤1.5％和0.05％≤Mo≤0.5％中的至少其中之一；余量为Fe和不可避免的杂质元素；优选地，0.015％≤Nb≤0.06％；
其中N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。
在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，各化学元素的设 计原理如下所述：
C：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，考虑到C含量的高低很大程度上决定了钢板的抗拉强度级别，C用于固溶强化，以及与Nb和Ti等配合形成足够的析出强化相，能够保证钢的强度。但需要注意的是，钢中C含量也不宜过高，C的质量百分含量较高时会使碳化物颗粒粗大，同时容易形成过多的马氏体和残余奥氏体，不利于扩孔性能。因此，为了在保证钢种强度的前提下，既能或高扩孔率，又可以获得良好的成形和焊接性能，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，将C元素的质量百分含量控制在0.07-0.15％之间。
Si：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Si元素能够起到固溶强化作用，并提高钢板的强度，同时添加Si可加大加工硬化速率和给定强度下的均匀延伸率和总延伸率，有助于改善钢板的延伸率。此外，Si还可以阻止碳化物的析出，减少珠光体相的出现。但需要注意的是，钢中含硅容易使钢板表面形成铁橄榄石(2FeO-SiO2)氧化铁皮的表面缺陷，对表面质量有不良影响。基于此，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，将Si元素的质量百分含量控制在0.1-0.8％之间。
Mn：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Mn元素是固溶强化元素，当钢中Mn元素的质量百分含量较低时，会导致钢材的强度不足，但是当Mn元素的质量百分含量过高时，则又会导致钢板的塑性降低。此外，Mn同时会推迟珠光体转变，提高钢的淬透性并降低贝氏体转变温度，使钢的组织亚结构细化，以保证获得板条亚结构组织，从而使钢材在获得较高抗拉强度的前提下，同时具备良好的成形性。因此，考虑到Mn元素含量对钢材性能的影响，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，将Mn元素的质量百分含量控制在1.5-2.2％之间。
Al：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Al是钢中的脱氧元素，其能够减少钢中的氧化物夹杂、纯净钢质，并有利于提高钢板的成形性能。但需要注意的是，钢中Al元素的含量也不宜过高，当钢中Al元素的质量百分含量过高时，会产生氧化，从而进一步影响连铸生产。因此，考虑到Al元素对钢板性能的影响，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，将Al的质量百分含量控制在0.02-0.1％之间。
Ti：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Ti是重要的细晶强化和析出强化元素之一，Ti元素在热轧过程中可以提高钢材的再结晶温度，并细化晶粒尺寸。同时，Ti元素与C元素的结合有着很好的强化作用。但需要注意的是，钢中Ti元素含量同样不宜过高，当钢中Ti元素含量过高时，容易形成尺寸较大的TiN，对钢的冲击韧性不利。因此，为了发挥Ti元素的有益效果，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，将Ti元素的质量百分含量控制在0.05-0.18％之间。
Nb：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Nb是重要的析出强化和细晶强化元素之一，但当Nb的质量百分比高于0.06％时，Nb的强化效果接近饱和，并且成本较高。因此，为了发挥Nb元素的有益效果，同时控制生产成本，在本发明中，将Nb元素的质量百分含量控制为Nb≤0.06％。
B：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，B有利于扩大贝氏体相区，并保证钢板在轧后冷却中可以得到贝氏体组织，其对于钢材强度和硬度的提升十分明显。但需要注意的是，钢中B元素的含量也不宜过高，过多的B元素会导致钢板中出现过多的大块状马氏体组织，并导致钢材扩孔率延伸率下降。因此，在本发明中，将B元素的质量百分含量控制为B≤0.003％。
相应地，除上述元素外，在本发明设计的这种1000MPa级高扩孔热轧复相钢钢板中，钢中还可以添加有Cr和/或Mo元素。其中，Cr、Mo元素可以分别单独使用，也可以二者复合使用。
Cr：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Cr是抑制珠光体的产生，有利于贝氏体组织的形成元素，其可以提升钢材的强度和扩孔率。发明人研究发现，当钢中Cr元素的质量百分含量小于0.15％时，其对于相变曲线的影响并不显著；而当钢中Cr元素的质量百分含量过高时，其不仅会导致合金成本的提高，还容易产生较多的马氏体组织。基于此，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，当添加时，将Cr元素的质量百分含量控制在0.2％-1.5％之间。
Mo：在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，Mo元素不仅能够抑制珠光体产生，其同时还有利于贝氏体组织以及少量马氏体奥氏体岛的形成。此外，Mo元素还可以在较高的温度下促进贝氏体显微组织转变，因而允许在较高的温度下对钢材进行卷取，这种较高的卷取温度提供了充足的析 出动力学，从而能够刺激显著的析出强化。在本发明中，Mo元素在与Nb，Ti的复合析出过程也起到了十分重要的作用，其同时可以降低析出颗粒的粒径粗大的可能性。但需要注意的是，钢中Mo元素含量也不宜过高，钢中Mo元素含量过高时，不仅会导致合金成本的提高，还容易形成较多的马氏体和奥氏体，不利于钢材的性能。因此，为了发挥Mo元素的有益效果，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，当添加时，将Mo元素的质量百分含量控制在0.05％-0.5％之间。
此外，需要注意的是，在本发明所设计的这种技术方案中，发明人在控制基板单一化学元素质量百分含量的同时，还进一步地控制了钢板中的N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。其中，N为钢板中的杂质元素。
在本发明中，发明人采用了高Ti、高Nb的设计，其主要可以起到以下三点细化晶粒的作用和一点析出强化的作用：(1)在板坯加热过程中，Nb，Ti的析出物能够阻止原始奥氏体晶粒的长大；(2)在热轧过程中，(Nb，Ti)(C，N)有利于提高再结晶温度，进一步细化奥氏体晶粒；(3)已经析出的(Nb，Ti)(C，N)或者(Nb，Ti)(Mo，Cr)(C，N)有利于细化相变的贝氏体，以及少量马氏体晶粒；(4)在进行层流冷却的过程中，(Nb，Ti)(C，N)或者(Nb，Ti)(Mo，Cr)(C，N)的纳米级析出物可以起到强烈的析出强化效果。
因此，在本发明中，为了保证Ti，Nb的化合物充分析出，除了C元素的设计需要与Ti，Nb含量配合外，还需要通过合理的Nb，Ti复合，控制N、Ti、Nb的质量百分含量满足“0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％”这一关系，并配合优化设计的制造工艺，方可得到贝氏体晶粒尺寸≤6um的1000MPa级高扩孔热轧复相钢钢板。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，在不可避免的杂质元素中，P≤0.02％，S≤0.005％，N≤0.005％。
在上述技术方案中，P、S和N均是本发明所述的1000MPa级高扩孔热轧复相钢钢板中的杂质元素，在技术条件允许情况下，为了获得性能更好且质量更优的钢材，应尽可能降低钢板中杂质元素的含量。
由此，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，控制P元 素含量为P≤0.02％，控制S元素含量为S≤0.005％，控制N元素含量为N≤0.005％。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，钢种的Cr与Mo含量满足下述其中一项：
(1)当0.2％≤Cr≤0.7％时，Mo质量百分含量满足0.2％≤Mo≤0.35％；
(2)当0.7％＜Cr≤1.0％时，Mo质量百分含量满足0.05％≤Mo＜0.2％；
(3)当1.0％＜Cr≤1.5％时，不含有Mo；
(4)当0.35％＜Mo≤0.5％时，不含有Cr。
在本发明上述的技术方案中，在化学成分设计上，Cr、Mo元素可以分别单独使用，也可以二者复合使用。加入适量的Cr元素或者Mo元素是为了在热轧卷取过程中得到贝氏体组织以及尺寸较少的马氏体和奥氏体岛，确保不含有影响扩孔性能的珠光体和块状的马氏体。
因此，为了进一步适配所设计的制造工艺，获得综合力学能更优异的1000MPa级高扩孔热轧复相钢钢板，从而满足用户和市场需求，发明人对钢中的Cr、Mo的含量设计进行了进一步的优化设计，在实际应用时，其可以优选地添加上述(1)-(4)所设计的Cr、Mo成分配比中的任意一种。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其微观组织的基体的主体为贝氏体，所述基体上具有纳米级析出物。
在本发明中，本发明所设计的这种1000MPa级高扩孔热轧复相钢钢板的微观组织基体上具有纳米级析出物，这些微合金纳米级析出物包括TiC、(Ti，Nb)C，其具体析出尺寸可以控制在3-20nm之间。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其中贝氏体体积分数≥85％。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其微观组织的基体还包括马氏体和/或残余奥氏体。进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，所述马氏体和残余奥氏体的总体积分数≤15％。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，所述纳米级析出物的尺寸为3-20nm。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其中 贝氏体的晶粒尺寸≤6um，马氏体和/或残余奥氏体的晶粒尺寸≤3um。
在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的微观组织含有体积分数为85～96％的马氏体和总体积分数为4～15％的马氏体和残余奥氏体，其中，贝氏体的晶粒尺寸在3.2-5um之间，马氏体的晶粒尺在0.5-3um之间。
进一步地，在本发明所述的1000MPa级高扩孔热轧复相钢钢板中，其性能满足：屈服强度≥750MPa，抗拉强度为950-1150MPa，延伸率A50≥12％，冲孔扩孔率≥45％，铰孔扩孔率≥65％。
在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的屈服强度≥780MPa。在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的屈服强度≥800MPa。在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的屈服强度为750～960MPa。
在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的抗拉强度为980～1150MPa。
在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的冲孔扩孔率≥50％。在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的冲孔扩孔率≥55％。
在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的铰孔扩孔率≥70％。在一些实施方案中，本发明所述的1000MPa级高扩孔热轧复相钢钢板的铰孔扩孔率≥75％。
相应地，本发明的另一目的在于提供本发明上述1000MPa级高扩孔热轧复相钢钢板的制造方法，采用该制造方法所获得的1000MPa级高扩孔热轧复相钢钢板，在具备高强度、高延伸率的同时，还具有高扩孔率的特点，其具有良好的应用前景。
为了实现上述目的，本发明提出了上述1000MPa级高扩孔热轧复相钢钢板的制造方法，其包括步骤：
(1)冶炼和铸造；
(2)热轧：板坯被加热至1200-1300℃并保温；然后进行轧制，其中控制粗轧出口温度为1000-1080℃，精轧终轧温度为840-950℃；
(3)进行两阶段层流冷却以将钢板水冷到卷取温度：其中第一段的平均 冷速≥100℃/s，第二段的平均冷速≥3℃/s，第一段冷却和第二段冷却的中间点温度为贝氏体相变温度Bs±30℃，控制穿带速度为7-12m/s；控制从中间点温度冷却至卷取温度的时间≥4.5s，优选≥6s，更优选≥6.5s，其中Bs＝844-597×C+127×C2-92×Mn+8×Mn2-32×Cr+2.2×Cr2-42×Mo，式中各化学元素具代入相应化学元素质量百分含量百分号前的数值；
(4)卷取：控制卷取温度为430-600℃，卷取后采用冷速≤0.1℃/s的冷速冷到室温；
(5)酸洗。
在本发明上述技术方案中，在步骤(2)中，对于含Ti钢来说，板坯的加热温度对于性能尤其重要，Ti在连铸过程会有大量的大尺寸的(Ti，Nb)(C，N)析出物析出，将加热温度设定为≥1200℃，主要目的是为了板坯在加热过程中，Ti等合金元素尽可能固溶，以确保后续Ti等微合金在热轧卷取过程中的纳米级析出。但加热温度也不宜过高，当加热温度超过1300℃时，会有晶粒粗化的趋势，不利于钢板的韧性。因此，在本发明的热轧过程中，优选地将加热温度控制在1200-1300℃之间。
此外，热轧过程的粗轧温度控制对于Ti等微合金的影响较大，Ti在较低的粗轧温度和精轧过程中，会有Ti的碳化物以及碳氮化物的析出，此过程的析出尺寸较大，不利于最终强度的提升，但是析出的(Nb，Ti)(C，N)有利于奥氏体晶粒的细化。因此，在本发明的热轧过程中，控制粗轧出口温度1000-1080℃。在一些实施方案中，控制粗轧出口温度1050-1080℃。在一些实施方案中，控制精轧终轧温度为880-950℃。
另外，虽然钢中添加的Cr和/或Mo元素已经较好抑制了铁素体和珠光体的形成，但是也仍然很容易形成块状的二次马氏体和残余奥氏体，其在步骤(3)的热轧层流冷却过程中，对贝氏体相变的体积分数影响较大。因此，在本发明中，为了得到合适的贝氏体相变和尺寸较小的马氏体奥氏体岛，需控制步骤(3)的层流冷却时间、冷却速度和穿带速度，并具体为控制从中间点温度冷却至卷取温度的时间≥4.5s，优选≥6.5s，中间点温度之前第一段的平均冷速≥100℃/s，中间点温度之后的平均冷速≥3℃/s，控制穿带速度7-12m/s。
需要注意的是，在本发明中还需要控制贝氏体转变和微合金析出，其中卷取温度过高时，会导致铁素体含量较多以及二次马氏体和残余奥氏体尺寸较 大，不利于扩孔率的提升；而当卷取温度较低时，则有可能出现一次马氏体组织，并致使钢材的延伸率较低。因而，在本发明中，将卷取温度控制在430-600℃之间可以解决延伸率和扩孔率之间的匹配问题。当然，为了获得更优的实施效果，也可以进一步将卷取温度控制在430-580℃之间。
相应地，在卷取之后，采用冷速≤0.1℃/s的冷速冷到室温，不仅可以促进贝氏体进一步转变，还有利于马氏体的回火、以及微合金的进一步析出，其可以有效提升钢材的强度、扩孔率和延伸率。
此外，需要注意的是，本发明对于酸洗工艺并无特殊限定，但是在某些实施方式中，在实际实施酸洗时，可以具体：控制酸洗拉矫延伸率为0.2-2％；酸洗速度速度控制在60-150m/min，酸洗过程最后的一个酸洗酸槽温度控制80-90℃、铁离子浓度控制为30-40g/L，酸洗后得到成品钢板。
进一步地，在本发明所述的制造方法中，在步骤(2)中，控制轧制总压下率≥80％，精轧总压下率≥50％。优选地，轧制总下压率为90％-95％，精轧总下压率为85％-90％。进一步优选地，所得成品钢板厚度不大于5mm。
进一步地，在本发明所述的制造方法中，在步骤(2)中，保温时间为1～3小时。
进一步地，在本发明所述的制造方法中，在步骤(3)中，控制从中间点温度冷却至卷取温度的时间≥8s。
进一步地，在本发明所述的制造方法中，在步骤(3)中，第一段的平均冷速为100～160℃/s，优选为120～160℃/s。
进一步地，在本发明所述的制造方法中，在步骤(3)中，第二段的平均冷速为3～25℃/s，优选为3～22℃/s。
进一步地，在本发明所述的制造方法中，在步骤(4)中，控制卷取温度为430-580℃。在一些实施方案中，在步骤(4)中，控制卷取温度为430-550℃。
相较于现有技术，本发明所述的1000MPa级高扩孔热轧复相钢钢板及其制造方法具有如下所述的优点以及有益效果：
在本发明中，本发明采用了经济合理的化学成分设计，其同时配合现有的热连轧产线，就可以生产出一种新型的超高强度和扩孔率的1000MPa级高扩孔热轧复相钢钢板。
本发明所制备的1000MPa级高扩孔热轧复相钢钢板具有较高扩孔率，高 强度，高成形性等特点，其屈服强度≥750MPa，抗拉强度为950-1150MPa，延伸率A50≥12％，冲孔扩孔率≥45％，铰孔扩孔率≥65％，其既可以用做汽车车身结构件及其汽车底盘件，也可以用于其他需要高强、减重等应用领域，具有良好的应用前景。
附图说明
图1为实施例3的1000MPa级高扩孔热轧复相钢钢板的金相组织照片。
图2为实施例5的1000MPa级高扩孔热轧复相钢钢板的金相组织照片。
图3为对比例6的对比钢材的金相组织照片。
具体实施方式
下面将结合具体的实施例和说明书附图对本发明所述的1000MPa级高扩孔热轧复相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。
实施例1-13和对比例1-11
表1-1列出了实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例1-11的对比钢板的各化学元素的质量百分配比。
表1-1.(wt％，余量为Fe和除P、S和N以外其他不可避免的杂质)
表1-2列出了实施例1-13和对比例1-11钢板中的各化学元素之间的配合。
表1-2.
注：在上表1-2之中，Bs＝844-597×C+127×C2-92×Mn+8×Mn2-32×Cr+2.2×Cr2-42×Mo，该计算式中的各化学元素代入质量百分含量的百分号之前的数值；TiCeq＝(Ti-3.43N+0.52Nb)/4，式中的N、Ti、Nb均代入各化学元素对应的质量百分含量。
本发明所述实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例1-11的对比钢板均采用以下步骤制得：
(1)按照表1-1和表1-2所示的化学成分进行冶炼和铸造。
(2)热轧：将经过冶炼和连铸获得的板坯被加热至1200-1300℃并保温1-3h；然后进行轧制，其中控制粗轧出口温度为1000-1080℃，精轧终轧温度为840-950℃，控制轧制总压下率≥80％，精轧总压下率≥50％。
(3)精轧后进行两阶段层流冷却以将钢板水冷到卷取温度：其中第一段的平均冷速≥100℃/s，第二段的平均冷速≥3℃/s，第一段冷却和第二段冷却的中间点温度为贝氏体相变温度Bs±30℃，控制穿带速度为7-12m/s；控制从中间点温度冷却至卷取温度的时间≥4.5s，优选地可以控制从中间点温度冷却至卷取温度的时间≥6s。
(4)卷取：对水冷后的钢板进行卷取，控制卷取温度为430-600℃，优选地可以控制为430-580℃，卷取后采用冷速≤0.1℃/s的冷速冷到室温。
(5)酸洗：控制酸洗拉矫延伸率为0.2-2％；酸洗速度速度控制在60-150m/min，酸洗过程最后的一个酸洗酸槽温度控制80-90℃、铁离子浓度控制为30-40g/L，酸洗后得到厚度≤5mm的钢板。
在本发明中，实施例1-13的1000MPa级高扩孔热轧复相钢钢板的化学成分设计以及相关工艺均满足本发明所设计的规范要求。而对比例1-11的对比钢板所采用的步骤虽然也是上述步骤(1)-(5)进行制备，但在对比例1-11的对比钢板的化学成分设计和/或相关制造工艺中，存在不满足本发明设计要求的参数。
表2-1和表2-2列出了实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例1-11的对比钢板的具体工艺参数。
表2-1.

表2-2.
在本发明中，发明人将经过上述工艺步骤得到的成品实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例1-11的对比钢板分别取样，进行对各实施例和对比例钢板的微观组织进行观察和分析，相关观察分析所得的结果列于下述表3之中。
表3列出了实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例 1-11的对比钢板的微观组织观察分析结果。
表3.
通过观察可以看出，在本发明中，所制备的实施例1-13的1000MPa级高扩孔热轧复相钢钢板的微观组织基体均为贝氏体+少量的马氏体和残余奥氏体，且贝氏体体积分数在85％-96％之间，马氏体和/或残余奥氏体的体积分数在4-15％之间，贝氏体的晶粒尺寸在3.2-5um之间，马氏体的晶粒尺在0.5-3um之间。
需要注意的是，在实际制备时，实施例1-13的1000MPa级高扩孔热轧复 相钢钢板基体上还具有纳米级析出物，其包括TiC、(Ti，Nb)C，这些纳米级析出物的直径在3-20nm之间。
相应地，在完成微观组织的分析后，进一步将经过上述工艺步骤得到的成品实施例1-13的1000MPa级高扩孔热轧复相钢钢板和对比例1-11的对比钢板分别取样，并对各实施例和对比例样品钢板的力学性能进行检测，相关力学性能检测结果列于下述表4中。
相关性能检测手段如下所述：
(1)拉伸性能测试：取沿纵向JIS 5#拉伸试样，采用GB/T 228.1-2010《金属材料拉伸试验第1部分：室温实验方法》标准进行拉伸试验，以测试获得各实施例和对比例钢板的屈服强度、抗拉强度和延伸率。
(2)扩孔试验：扩孔率采用扩孔试验测定，用凸模把中心带孔的试件压入凹模，使试件中心孔扩大，直到板孔边缘出现颈缩或贯穿裂纹为止。由于试件中心原始孔的制备方式对扩孔率测试结果存在较大影响，因此，分别采用冲孔和铰孔制备试件中心原始孔，后续试验及测试方法按ISO/DIS 16630标准中规定的扩孔率测试方法执行，测试结果见表4。
表4列出了实施例1-11的1000MPa级高扩孔热轧复相钢钢板和对比例1-111的对比钢板的力学性能检测结果。
表4.

如表4所示，相较于对比例1-11的对比钢板，本案实施例1-13的1000MPa级高扩孔热轧复相钢钢板的综合力学性能更加优异。
在本发明中，实施例1-13采用了表1-1和表1-2中合理的Cr，Mo配比，同时添加Ti，Nb以增加在退火过程的析出强化效果，同时满足表2-1和表2-2的热轧工艺，最终获得的实施例1-13的成品1000MPa级高扩孔热轧复相钢钢板获得了表3所示的显微组织。
参阅表4不难看出，在本实施方式中，所设计的实施例1-13的1000MPa级高扩孔热轧复相钢钢板的屈服强度在755-953MPa之间，抗拉强度在982-1150MPa之间，延伸率A50在12-18.5％之间，冲孔扩孔率在45-65％之间，铰孔扩孔率在65-81％之间。
与实施例1-5相比，对比例1-2采用了相同的A类钢种，但其采用了不同的热轧卷取温度。其中，对比例1采用了较低的卷取温度，其卷取温度选用为380℃，且最终显微组织中马氏体含量达到80％，并最终导致抗拉强度较高，延伸率较低。而对比例2采用了较高的卷取温度，其卷取温度选用为620℃，其显微组织中铁素体含量较低，导致贝氏体含量较低，钢材的抗拉强度不足。
与实施例6-8相比，对比例3-6采用了相同的B类钢种，但其工艺不满足设计要求。其中，对比例3由于中间点温度较低，导致层流冷却过程的从中间点温度冷却至卷取温度的冷却时间较短，贝氏体在层流冷却过程相变不完全，导致过冷奥氏体在卷取过程中相变的比例较多，最终显微组织中的马氏体含量较高，所得的对比钢材的延伸率和扩孔率相对较低。
而对比例4则由于精轧总压下率较低，仅为20％，其再结晶不充分，导致晶粒相对粗大，延伸率和扩孔率相对较低。对比例5是由于在步骤(2)的热轧过程中，粗轧出口温度以及精轧终轧温度较低，其在轧制过程中有较为粗大的微合金颗粒已经析出，对强度贡献不明显，最终导致钢材的抗拉强度不足。 而对比例6则是因为在步骤(2)的热轧过程中，所采用的加热温度较低，仅为1120℃，导致Nb，Ti含量不充分，固溶连铸过程粗大的(Ti，Nb)(C，N)的颗粒没有完全固溶，对强度的贡献较小，从而也表现出钢板的抗拉强度不足。
与实施例9相比，对比例7采用了相同的C类钢种，但是对比例7由于热轧卷取后的冷却速度过快，其热轧卷取后的冷却速度为0.2℃/s，导致过冷奥氏体在卷取后发生了马氏体相变比例较多，贝氏体相变比例较少，从而最终导致钢材的延伸率和扩孔率较低。
不同于上述对比例1-7，对比例8-11则是因为化学成分不满足本发明的要求，导致最终钢材的性能不佳。
在对比例8中，由于钢中的Cr，Mo配比不合理，导致在贝氏体相变较低，马氏体和残余奥氏体相变比例较高，对强度贡献较大，反而降低了延伸率和扩孔率。
在对比例9中，由于钢中的Ti含量较低，其所产生的析出强化效果较弱，对钢材的强度贡献较小，从而导致最终所得的钢板强度不足。
在对比例10中，由于钢中的N含量较高，消耗了大量的Ti，导致大量块状TiN的析出，5-20umTiN对强度的贡献较小，降低了钢板的强度。
在对比例11中，由于钢中的C，Mn含量较低，其所产生的固溶强化和贝氏体相变强化效果较弱，导致最终的钢板强度较低。
图1为实施例3的1000MPa级高扩孔热轧复相钢钢板的金相组织照片。
如图1所示，在本实施方式中，实施例3的1000MPa级高扩孔热轧复相钢钢板的微观组织为92％贝氏体+8％马氏体和残余奥氏体，其中，贝氏体晶粒尺寸为4.3um，马氏体和残余奥氏体的晶粒尺寸在0.5-2um之间。
图2为实施例5的1000MPa级高扩孔热轧复相钢钢板的金相组织照片。
如图2所示，在本实施方式中，实施例5的1000MPa级高扩孔热轧复相钢钢板的微观组织为85％贝氏体+15％马氏体和残余奥氏体，其中，贝氏体晶粒尺寸5.0um，马氏体和残余奥氏体的晶粒尺寸在0.5-3um之间。
图3为对比例6的对比钢材的金相组织照片。
如图3所示，在该实施方式中，对比例6的对比钢材的微观组织为20％贝氏体+80％马氏体，其中，贝氏体晶粒尺寸3.0um，马氏体晶粒尺寸＞3um。
需要说明的是，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或是具体实施例所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
还需要注意的是，以上所列举的实施例仅为本发明的具体实施例。显然本发明不局限于以上实施例，随之做出的类似变化或变形是本领域技术人员能从本发明公开的内容直接得出或者很容易便联想到的，均应属于本发明的保护范围。

Claims (15)

  1. 一种1000MPa级高扩孔热轧复相钢钢板，其含有Fe和不可避免的杂质元素，其特征在于，其还含有质量百分含量如下的下述各化学元素：
    C：0.07-0.15％，Si：0.1-0.8％，Mn：1.5-2.2％，Al：0.02-0.1％，Ti：0.05-0.18％，Nb≤0.06％，B≤0.003％，以及0.2％≤Cr≤1.5％、0.05％≤Mo≤0.5％中的至少其中之一；
    其中N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。
  2. 如权利要求1所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，其各化学元素质量百分含量为：
    C：0.07-0.15％，Si：0.1-0.8％，Mn：1.5-2.2％，Al：0.02-0.1％，Ti：0.05-0.18％，Nb≤0.06％，B≤0.003％，以及0.2％≤Cr≤1.5％、0.05％≤Mo≤0.5％中的至少其中之一；余量为Fe和不可避免的杂质元素；优选地，0.015％≤Nb≤0.06％；
    其中N、Ti、Nb的质量百分含量还满足：0.01％≤(Ti-3.43N+0.52Nb)/4≤0.053％。
  3. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，在不可避免的杂质元素中，P≤0.02％，S≤0.005％，N≤0.005％。
  4. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，钢种的Cr与Mo含量满足下述其中一项：
    (1)当0.2％≤Cr≤0.7％时，Mo的质量百分含量满足0.2％≤Mo≤0.35％；
    (2)当0.7％＜Cr≤1.0％时，Mo的质量百分含量满足0.05％≤Mo＜0.2％；
    (3)当1.0％＜Cr≤1.5％时，不含有Mo；
    (4)当0.35％＜Mo≤0.5％时，不含有Cr。
  5. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，其微观组织的基体主体为贝氏体，所述基体上具有纳米级析出物。
  6. 如权利要求5所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于， 其中贝氏体体积分数≥85％。
  7. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，其微观组织的基体还包括马氏体和/或残余奥氏体。
  8. 如权利要求5所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，所述纳米级析出物的尺寸为3-20nm。
  9. 如权利要求7所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，其中贝氏体的晶粒尺寸≤6um；马氏体和/或残余奥氏体的晶粒尺寸≤3um。
  10. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，所述1000MPa级高扩孔热轧复相钢钢板的微观组织含有体积分数为85～96％的马氏体和总体积分数为4～15％的马氏体和残余奥氏体，其中，贝氏体的晶粒尺寸在3.2-5um之间，马氏体的晶粒尺在0.5-3um之间。
  11. 如权利要求1或2所述的1000MPa级高扩孔热轧复相钢钢板，其特征在于，其性能满足：屈服强度≥750MPa，抗拉强度为950-1150MPa，延伸率A50≥12％，冲孔扩孔率≥45％，铰孔扩孔率≥65％。
  12. 如权利要求1-11中任意一项所述的1000MPa级高扩孔热轧复相钢钢板的制造方法，其特征在于，其包括步骤：
    (1)冶炼和铸造；
    (2)热轧：板坯被加热至1200-1300℃并保温；然后进行轧制，其中控制粗轧出口温度为1000-1080℃，精轧终轧温度为840-950℃；
    (3)进行两阶段层流冷却以将钢板水冷到卷取温度：其中第一段的平均冷速≥100℃/s，第二段的平均冷速≥3℃/s，第一段冷却和第二段冷却的中间点温度为贝氏体相变温度Bs±30℃，控制穿带速度为7-12m/s；控制从中间点温度冷却至卷取温度的时间≥4.5s，其中Bs＝844-597×C+127×C2-92×Mn+8×Mn2-32×Cr+2.2×Cr2-42×Mo，式中各化学元素具代入相应化学元素质量百分含量百分号前的数值；
    (4)卷取：控制卷取温度为430-600℃，卷取后采用冷速≤0.1℃/s的冷速冷到室温；
    (5)酸洗。
  13. 如权利要求12所述的制造方法，其特征在于，在步骤(2)中，控制轧制 总压下率≥80％，精轧总压下率≥50％；优选地，轧制总下压率为90％-95％，精轧总下压率为85％-90％；进一步优选地，所得成品钢板厚度不大于5mm。
  14. 如权利要求12所述的制造方法，其特征在于，在步骤(3)中，控制从中间点温度冷却至卷取温度的时间≥6s。
  15. 如权利要求12所述的制造方法，其特征在于，在步骤(4)中，控制卷取温度为430-580℃。
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