WO2023226813A1 - 高耐蚀镀锌热成形硬化钢及其零部件以及制备方法 - Google Patents

高耐蚀镀锌热成形硬化钢及其零部件以及制备方法 Download PDF

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WO2023226813A1
WO2023226813A1 PCT/CN2023/094304 CN2023094304W WO2023226813A1 WO 2023226813 A1 WO2023226813 A1 WO 2023226813A1 CN 2023094304 W CN2023094304 W CN 2023094304W WO 2023226813 A1 WO2023226813 A1 WO 2023226813A1
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temperature
hot
point
insulation
hardened steel
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PCT/CN2023/094304
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English (en)
French (fr)
Inventor
熊自柳
张彩东
齐建军
张雲飞
王立辉
孙力
魏元生
李建英
宋帅
陈波
卢岳
韩冰
董伊康
陈屹松
石帅
王学慧
刘洁
严文瑾
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河钢股份有限公司
河北大河材料科技有限公司
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Publication of WO2023226813A1 publication Critical patent/WO2023226813A1/zh

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    • 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
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/18—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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips

Definitions

  • the present application relates to a galvanized hot-formed steel, in particular to a highly corrosion-resistant galvanized hot-formed hardened steel and its components and preparation methods.
  • Hot-formed steel adopts austenitizing heating + high-temperature zone deformation process scheme, which not only achieves steel strength as high as 1500MPa ⁇ 2100MPa, but also solves the part quality problems of ultra-high-strength steel such as easy rebound, easy breakage, and low dimensional accuracy. It is increasingly widely used in automotive parts manufacturing. Bare plate hot-formed steel usually has shortcomings such as easy surface oxidation, decarburization, poor corrosion resistance, and the need for shot blasting, and is gradually being replaced by coated hot-formed steel. At present, commercially applied coated hot-formed steel accounts for about 70% of hot-formed steel production and is the mainstream product of hot-formed steel.
  • Coated hot-formed steel mainly includes two series: Al-based coating and Zn-based coating; among them, Al-based coating includes Al-Si, Al-Si-Cu, Al-Si-Re, Al-Si-Ni and other composition categories, Al-10 %Si coating has a high degree of commercialization and is the most widely used. It is a patented product of Arcelormittal, with a market share of 90% and almost monopolizing the domestic market.
  • Zn-based coatings include GI hot-dip pure zinc and GA alloyed hot-dip galvanizing products, which were successfully developed and put into the market by Voestalpine in 2006. Currently, only companies such as Voestalpine, ArcelorMittal, and Nippon Steel have mature product supply markets.
  • Zn-Al coating is a composite coating.
  • the forming process of coated hot-formed steel includes direct hot forming and indirect hot forming.
  • the direct hot forming process refers to heating the steel plate to the austenitizing temperature and holding it for a certain period of time, and then directly transferring it to a mold with a cooling system for stamping forming and pressure-holding quenching.
  • the indirect hot forming process means that the steel plate is first cold stamped, pre-formed to a certain amount, and then heated to the austenitizing temperature. After being kept warm for a certain period of time, it is transferred to a mold with a cooling system for final forming and processing. Quenching. Al-based coating is produced by direct hot forming, which has short production process, high output and low production cost.
  • Al-Si coating is prone to micro-cracks during heating and hot forming. Although the cracks do not extend to the substrate and do not cause brittleness of the substrate, they reduce the corrosion resistance of the coating. Al-Si coatings are prone to cracks when the cold forming amount exceeds 8%. The corrosion resistance of the coating is reduced, so the indirect hot forming process cannot be used and is only suitable for the production of parts with simple cross-sectional shapes.
  • Zn-based coatings can be produced using direct hot forming processes and indirect hot forming processes. Zn-based coated hot-formed steel is prone to liquid metal embrittlement (LMIE) and solid metal embrittlement (SMIE) when using the direct hot forming process, so the austenitic heating and hot forming process window is narrow.
  • LMIE liquid metal embrittlement
  • SMIE solid metal embrittlement
  • hot-dip galvanized hot-formed steel over aluminum-silicon-coated hot-formed steel is that it has cathodic protection capabilities.
  • the reason is that the Zn and Fe electrode potentials are -0.762V and -0.439V respectively.
  • the Zn coating electrode potential is more negative, which will protect the damaged coating part.
  • the steel base plate has good cathodic protection and has good anti-corrosion properties even at the cut.
  • hot-dip galvanized hot-formed steel undergoes austenitizing heat treatment and hot forming, the Zn content in the coating decreases, causing the electrode potential to increase and the anti-corrosion performance to decrease.
  • the Fe element in the substrate undergoes austenitizing heating and hot forming.
  • Diffusion into the zinc layer during the process increases the Fe content in the zinc layer, increases the melting point of the zinc layer, inhibits the penetration of Zn into the austenite grain boundary of the substrate, reduces the tendency of liquid metal to be brittle, and reduces the evaporation of surface Zn elements . Therefore, the diffusion of Fe and Zn elements during hot processing cannot simultaneously improve the cathodic protection capability of the coating and reduce the brittleness trend of liquid metal during hot forming.
  • European patent EP2045360A1 provides a composite coating technology.
  • the coating structure is an upper zinc layer and a lower aluminum-silicon layer.
  • the upper zinc layer contains >99% Zn and ⁇ 1% Al, and the lower structure is 90% Al-10% Si.
  • the upper zinc layer contains 80% Zn, 16% Al, and 2% Si, and the lower layer contains 40% Al, 30% Fe, 20% Zn, and 5% Si.
  • This patented technology constructs two different upper and lower coating structures through two hot-dip platings, which is difficult to produce and commercialize.
  • the coating includes 0.3 ⁇ 4.0wt% Mg, 0.05 ⁇ 6.0wt% Al, and one or more additional elements of up to 0.2wt%, and the rest are Zn and inevitable impurities.
  • the additional elements include Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr, and Bi. Among them, Sb, Pb, Sn, and Bi are used to form zinc flowers on the surface of the coating. The additional elements can improve the zinc quality. The generation of slag is not as effective in changing the corrosion resistance of the coating as Mg and Al elements, and it makes the coating more expensive.
  • Chinese patent application CN 104302802 A provides a steel plate with a sacrificial cathodic protection coating, the coating containing: 5wt% to 50wt% Zn, 0.1wt% to 15wt% Si, and optionally up to 10wt% Mg and Additional elements based on cumulative content up to 0.3 wt%.
  • the coating also contains: protective elements selected from 0.1wt% to 5wt% tin, 0.01wt% to 0.5wt% indium, and combinations thereof; wherein 0.3wt% additional elements include Sb, Pb, Ti, Ca, Mn, La, Ce, Cr, Ni, Zr or Bi; these various elements can improve in particular the corrosion resistance of the coating or its brittleness or adhesion.
  • Chinese patent application CN112011752A provides a solution for thermally hardening parts of GA coating.
  • the coating structure before thermal hardening is composed of zinc-rich ⁇ -FeZn phase and Fe-rich ⁇ -Fe(Zn) phase, among which ⁇ -FeZn phase
  • the volume ratio is 10 to 20%.
  • the patent application does not describe the composition design of the hot-dip plating bath, but only details the alloying process.
  • Chinese patent application CN110777319A provides an aluminum-based Si-Mg-Cu-REM coated steel plate.
  • the composition of the plating bath contains Si: 2.0 ⁇ 7.5%, Mg: 0.08 ⁇ 2.5%, and Cu: 0.1 ⁇ 2.0 in mass %. %, REM: 0.08 ⁇ 1.0%, the rest is Al and inevitable impurities. Its main features are excellent corrosion resistance and formability.
  • Chinese patent application CN 112139335 A adds a process of boiling water to remove the oxidation layer after the zinc layer is heated.
  • the heated sheet is transferred to a boiling water tank for high-pressure boiling water to remove the oxidation layer. After the sheet leaves the boiling water tank, it is purged with gas.
  • the disadvantage of this process is that it is difficult to control the cooling rate.
  • the technical problem to be solved by this application is to provide, on the one hand, a highly corrosion-resistant galvanized hot-formed hardened steel; and, secondly, to provide a highly corrosion-resistant galvanized hot-formed hardened steel that does not cause liquid metal brittleness or affect the crack expansion of the coating.
  • Hardened steel cannot combine corrosion resistance with the drawback of metal brittleness.
  • this application provides a highly corrosion-resistant galvanized hot-formed hardened steel, including a substrate and a coating;
  • composition and mass percentage of the substrate are: C 0.12% ⁇ 0.35%, Si 0.08% ⁇ 2.12%, Mn 0.42% ⁇ 10.00%, Al 0.03% ⁇ 0.12%, Cr 0.02% ⁇ 0.65%, Mo ⁇ 1.12%, Nb+V+Ti 0.02% ⁇ 0.25%, B 0.0003% ⁇ 0.005%, S ⁇ 0.012%, P ⁇ 0.08%, the balance is Fe and inevitable impurities;
  • composition and mass percentage of the coating are: Al 0.15% ⁇ 0.45%, Fe 0.05% ⁇ 2.50%, La 0.08% ⁇ 3.2% and/or Ce 0.12% ⁇ 5.0%, Si+Mn ⁇ 3.0%, Mg+Cr ⁇ 3.5%, the balance is Zn and inevitable impurities.
  • the plating layer includes a zinc plating layer and a diffusion layer, the diffusion layer contains an inhibition layer; the zinc plating layer is mainly composed of eta phase, and the diffusion layer is mainly composed of ⁇ Fe and ⁇ phases. Composition, the main component of the suppression layer is Fe 2 Al 5 .
  • the composition of the galvanized layer contains: solid solution Fe 0.08% ⁇ 2.20%, Al 0.08% ⁇ 0.45%, La 0.08% ⁇ 1.4% and/or Ce 0.12% ⁇ 2.0%, Si+Mn ⁇ 3.0%, Mg+Cr ⁇ 3.5%.
  • Si/Mn ⁇ 1.1 and Mg/Cr ⁇ 0.8 are examples of the components of the galvanized layer.
  • ⁇ Fe in the diffusion layer is ⁇ 80%, and the average content of the main solid solution elements is: Al 0.34% ⁇ 1.45%, La 0.1% ⁇ 2.5% and/or Ce 0.2% ⁇ 3.1 %, Si+Mn ⁇ 15.0%, Mg+Cr ⁇ 2.4%.
  • this application provides a method for preparing highly corrosion-resistant galvanized hot-formed hardened steel in the first aspect and any possible implementation of the first aspect, including: hot-dip plating the hardened steel plate; the composition and quality of the plating solution
  • the percentage content is: Al 0.12% ⁇ 0.35%, Fe 0.005% ⁇ 0.06%, La 0.08% ⁇ 3.2% and/or Ce 0.12% ⁇ 5.0%, Si+Mn ⁇ 3.0%, Mg+Cr ⁇ 3.5%, Si /Mn ⁇ 1.1, Mg/Cr ⁇ 0.8, and the rest are Zn and inevitable impurities.
  • the hot-dip plating process is: the temperature of the hardened steel plate entering the zinc pot is Ts 410°C ⁇ 475°C, the temperature of the plating solution Tz is 420°C ⁇ 475°C, and the hot-dip plating time is 3s ⁇ 10s; Ts, The temperature of Tz satisfies the condition ⁇ Ts-Tz ⁇ 40°C.
  • the application provides a galvanized hot-formed hardened steel component, which is prepared from the above-mentioned highly corrosion-resistant galvanized hot-formed hardened steel, including a substrate and a coating; the coating is surface oxidized in sequence from the outer surface to the substrate. layer, Zn-Fe alloy matrix layer and diffusion layer;
  • the main component of the surface oxide layer is one or more of Al 2 O 3 , MgO, MnO, SiO 2 , ZnO, CeO, and La 2 O 3 ;
  • the Zn-Fe alloy matrix layer includes ⁇ Fe, ⁇ phase and an intermediate alloy phase.
  • the intermediate alloy phase includes Zn x Si y Fez , Zn x Mny Fez and ZnMg 2 ;
  • the Zn-Fe alloy matrix layer Ingredients: Fe 40% ⁇ 70%, Zn 20% ⁇ 50%;
  • the diffusion layer is mainly composed of ⁇ Fe with solid solution Zn, Si, Mn, Ce and/or Re elements, and its composition is: Fe ⁇ 80%, Zn ⁇ 5%.
  • this application provides a method for preparing galvanized hot-formed hardened steel parts, which includes: cold stamping preforming, trimming, and austenitizing heat treatment of galvanized hot-formed hardened steel; The part blank is transferred to the cooling device for cooling and oxidation layer removal; the part blank after cooling and oxidation layer removal is then transferred to the mold for shaping or low-temperature thermoforming.
  • the cooling and oxide layer removal process is: using water cooling or air cooling to reduce the temperature of the billet to 10°C to 20°C above the precipitation temperature of ferrite or bainite.
  • the shaping or low-temperature thermoforming process is: holding time 4s to 8s, quenching cooling rate ⁇ 27°C/s; when Mn in the substrate is ⁇ 3.0wt%, hot stamping temperature range is 450°C ⁇ 760°C; when 3.0wt% ⁇ Mn ⁇ 10.0wt% in the substrate, the hot stamping temperature range is 350°C ⁇ 660°C.
  • the beneficial effect of adopting the above technical solution is that: the structure and composition design of the substrate and its coated zinc layer meet the wide heating process window of complete austenitization (Ac3) or above, and the thermal state of the hot-formed steel of the substrate is austenitized.
  • the stability of the body is relatively high, with a lower martensitic transformation starting temperature (Ms), and the precipitation temperature of bainite (Bs) and ferrite (Fs) shifts to the right, which will not occur during low-temperature hot forming. Bainite, ferrite or martensite phases precipitate, and mixed crystal or multi-phase structures will not appear, causing Zn to easily penetrate into grain boundaries and cause brittleness.
  • a hot forming and cooling process window with a low critical cooling rate and a temperature about 50°C to 200°C lower than the traditional hot forming temperature can be used to avoid the precipitation of ferrite (Fs) and bainite (Bs), and Under this process window condition, no liquid metal brittleness or coating crack propagation that affects the fatigue performance of the substrate will occur.
  • the manufactured parts have a high degree of cathodic protection and anti-corrosion performance, welding performance, mechanical performance, bending performance, fatigue performance, etc.
  • thermoforming temperature range is significantly lower than the traditional thermoforming process by 50°C to 200°C.
  • the deformation is limited to ⁇ 20% of the total deformation of the part, or even does not occur. In the case of deformation, hot forming will not easily cause cracks in the zinc layer.
  • Figure 1 shows the morphology distribution of the coating inhibition layer after hot dip plating in this application
  • Figure 2 shows the coating structure morphology of the hot-dip plated steel plate in Example 4 of the present application
  • Figure 3 shows the heating process window in this application with Mn content ⁇ 3.0wt%, 0.7mm ⁇ thickness ⁇ 1.4mm;
  • Figure 4 shows the heating process window in this application with Mn content ⁇ 3.0wt% and 1.4mm ⁇ thickness ⁇ 3.0mm;
  • Figure 5 shows the heating process window in this application with Mn content ⁇ 3.0wt%, 3.0mm ⁇ thickness ⁇ 4.0mm;
  • Figure 6 shows the heating process window of 3.0wt% ⁇ Mn content ⁇ 10.0wt%, 0.7mm ⁇ thickness ⁇ 1.4mm in this application;
  • Figure 7 shows the heating process window of 3.0wt% ⁇ Mn content ⁇ 10.0wt%, 1.4mm ⁇ thickness ⁇ 3.0mm in this application;
  • Figure 8 shows the heating process window of 3.0wt% ⁇ Mn content ⁇ 10.0wt% and 3.0mm ⁇ thickness ⁇ 4.0mm in this application;
  • Figure 9 is a comparison diagram of the process principles of low-temperature hot shaping/forming quenching and traditional hot forming in this application.
  • the austenitic heating and hot forming process window during parts manufacturing will be very narrow, that is, the heating temperature, heating rate, holding time and other parameters can be The control range is very small, and the fatigue performance, cathodic protection anti-corrosion performance and welding performance of the parts produced are low. Evaporation/melting/oxidation of the zinc layer can also affect production equipment.
  • the design of the plating solution and coating composition of the highly corrosion-resistant galvanized hot-formed hardened steel in this application is as follows.
  • the following plating bath composition and coating composition are designed for galvanized hot forming hardened steel in this application.
  • Plating solution composition (wt): Al 0.12% ⁇ 0.35%, Fe 0.005% ⁇ 0.06%, La 0.08% ⁇ 3.2% and/or Ce 0.12% ⁇ 5.0%, Si+Mn ⁇ 3.0%, Mg+Cr ⁇ 3.5% , Si/Mn ⁇ 1.1, Mg/Cr ⁇ 0.8, and the rest are Zn and inevitable impurities.
  • the Al element is mainly used to control the formation of the Fe 2 Al 5 inhibition layer in the coating.
  • the inhibition layer controls the generation of the brittle phase of the Zn-Fe alloy and the thickness of the diffusion layer.
  • the hot dip plating process can usually achieve the formation of a continuous Fe 2 Al 5 suppression layer, but the composition, thickness, size and distribution of the suppression layer are affected by the annealing temperature, annealing dew point/ The influence of hydrogen and other atmospheres, hot dip plating temperature/time and other processes.
  • the Al in the zinc layer can diffuse to the surface of the zinc layer through the austenitizing heating process to form a dense Al 2 O 3 film, which reduces the evaporation and oxidation of Zn, but the content of Al 2 O 3 is too high.
  • the film is detrimental to coating and welding properties, and is removed through a pre-cooling process in this preparation method.
  • La and Ce elements can effectively purify the components of the plating solution and achieve uniform distribution of Zn, Al and other elements in the plating solution.
  • the evenly distributed Al reacts with the substrate during hot dip plating, helping to form continuous and straight Fe 2 Al 5 inhibition layer to inhibit the brittleness of liquid metal; in addition, La and Ce can refine the grain size of the zinc layer in the original coating layer and refine the Zn, Fe, Si, Mn alloy phases formed during the austenitizing heating process.
  • Magnesium alloy phase MgZn 2 the alloy phase is a high melting point phase, which can significantly delay the formation of liquid zinc and zinc-iron phases, and inhibit their penetration into the matrix and matrix grain boundaries; the refined coating structure and intermediate phase significantly increase the density of the zinc layer , thereby improving the corrosion resistance of the coating.
  • the alloy phase is a high melting point phase, which can significantly delay the formation of liquid zinc and zinc-iron phases, and inhibit their penetration into the matrix and matrix grain boundaries; the refined coating structure and intermediate phase significantly increase the density of the zinc layer , thereby improving the corrosion resistance of the coating.
  • Ce, La, etc. are added as additional elements, and the content is less than 0.3wt%.
  • This galvanized steel achieves precise control of the continuity of the inhibition layer and control of the surface state during the hot dip plating process by adding a higher content of La and/or Ce.
  • Si and Mn elements in the plating solution increases the melting point of the Zn layer and reduces the evaporation of Zn during the austenitizing heating process.
  • Si and Mn form a ternary or quaternary intermediate alloy phase with Zn and Fe in the coating, which is extremely The earth blocks the penetration of liquid zinc into the matrix grain boundaries.
  • the composite addition of Si and Mn makes the distribution of the intermediate alloy phase more uniform, and the ratio of Si to Mn, Si/Mn ⁇ 1.1, enables the intermediate alloy phase to obtain the best uniform distribution state.
  • the patent application CN104302802A adds Si between 0.1wt% and 15wt%, with a preferred Si content ranging from 1wt% to 15wt%, and adds an additional element Mn with a content of less than 0.3wt%, preferably 0.01wt%.
  • This technology is mainly passed Si improves the high-temperature oxidation resistance of the coating, reduces coating peeling above 650°C, and reduces excessively thick zinc-iron alloy layers during hot-dip plating.
  • this technology uses a higher content of Si, which increases production costs.
  • This galvanized steel is designed to use two elements, Si+Mn, together to form an intermediate alloy phase.
  • the total content of the two elements is less than 3wt%, which reduces production costs.
  • Si and Mn interact with each other to improve the distribution uniformity of the intermediate alloy phase.
  • Ce and La rare earth elements refines the grain size of the master alloy and improves the corrosion resistance of the zinc layer.
  • the Mg content in the plating bath improves the corrosion resistance of the Zn layer's cathodic protection and notch protection, but the corrosion resistance rate decreases rapidly when the content exceeds 3wt%; in addition, Mg and Zn precipitate the MgZn 2 phase during the solidification process of the plating bath, and this phase Uniform distribution in the coating can improve the hardness of the coating and the surface friction state.
  • the Cr element in the coating diffuses to the surface of the Zn layer during the austenitizing heating process to form a Cr 2 O 3 oxide film, which prevents Zn from evaporating and also inhibits the formation of Al 2 O 3 .
  • Patent application CN 104302802 A adds 10wt% Mg, and preferably uses the range of 3wt% to 6wt%, which is mainly used to improve the cathodic protection performance of the zinc layer.
  • Patent applications WO2008102012A1 and CN110777319A use 0.3wt% ⁇ 4.0wt%Mg and 0.08% ⁇ 2.5%Mg respectively, which can improve the corrosion resistance of the cathodic protection of the coating.
  • rough oxide MgO is easily formed on the surface of the coating during the austenitizing heating process.
  • ZnO which increases the friction coefficient of the coating surface, is not conducive to the hot stamping process, and may cause the solid metal brittleness of the zinc layer.
  • This galvanized steel is designed to be used together with two elements, Mg+Cr, which not only improves the corrosion resistance of the cathode of the coating, but also removes the rough ZnO and MgO oxide layers through the pre-cooling process, retaining the fine Zn, Mg, Cr, and Al
  • the mixed oxide layer reduces the thermal surface friction coefficient, improves the stability of hot stamping, improves coating crack expansion, and improves performance.
  • the Fe content in the plating bath is controlled at 0.005wt% ⁇ 0.06wt%, and the iron content in the plating bath is controlled to be low to reduce the generation of zinc dross.
  • the hot-dip plating process promotes the diffusion of Fe in the steel plate to the zinc layer. After hot-dip plating, the Fe content reaches 0.05wt% to 2.50wt%.
  • the higher Fe content in the coating increases the melting point of the coating and reduces the tendency of liquid metal brittleness.
  • Fe continues to expand into the zinc layer.
  • the higher the Fe content in the coating the better the welding performance and the higher the hardness of the coating. However, excessive Fe content will cause the zinc layer to The Fe content in the zinc layer is low, thereby reducing the cathodic protection ability of the coating.
  • the Fe content in the zinc layer of the parts is controlled at 40wt% to 70wt%.
  • Factors affecting the austenitization and hot forming process windows of zinc-based coated steel sheets also include the control of chemical elements of the substrate.
  • the substrate can be austenitized at a lower temperature, and at the same time, the zinc layer can be heat treated at a lower temperature to achieve Fe diffusion and reduce Zn evaporation and oxidation.
  • the precipitation temperature of ferrite and bainite can be reduced, so that hot forming can be performed at a lower temperature, thereby reducing the brittleness of liquid metal, especially the brittleness of solid metal.
  • alloy elements in the substrate has an important impact on the mechanical properties after hot dip plating and hot forming.
  • the addition of these alloy elements should not only improve the cold forming performance after hot dip plating, but also improve the mechanical properties after hot forming. and fatigue performance.
  • Substrate alloy composition design (wt): C 0.12% ⁇ 0.35%, Si 0.08% ⁇ 2.12%, Mn 0.42% ⁇ 10.00%, Al 0.03% ⁇ 0.12%, Cr 0.02% ⁇ 0.65%, Mo ⁇ 1.12%, Nb+ V+Ti 0.02% ⁇ 0.25%, B 0.0003% ⁇ 0.005%, S ⁇ 0.012%, P ⁇ 0.08%, the balance is Fe and inevitable impurities.
  • the C element has a great influence on Ac3, Fs, and Bs.
  • Increasing 0.1wt% C content can reduce the complete austenitization temperature (Ac3) by 20°C, and reduce the bainite precipitation temperature (Bs) by 27°C during the cooling process. , delaying the precipitation of ferrite.
  • Increasing the C content can effectively expand the window range of the austenitizing heating process and hot forming process.
  • the C content affects the mechanical properties of galvanized hot-formed steel. It greatly improves the strength of martensite after hot-forming through solid solution strengthening.
  • C is also a strong austenite stabilizing element, which helps to obtain a certain amount of retained austeni after annealing. body content to improve the toughness and fatigue properties of the steel plate.
  • the Mn element can significantly reduce the Ac3 and Bs temperatures. 1wt% Mn can reduce the Ac3 temperature by 20.7°C.
  • the hot forming process reduces the Bs point by 90°C, delaying ferrite transformation. Therefore, increasing the Mn content can very effectively expand the window range of the austenitizing heating process and hot forming process.
  • the Mn element helps to obtain a certain amount of stable retained austenite on the steel plate substrate of the part, thereby improving the mechanical properties of galvanized steel plate parts.
  • the Mn content is increased to the range of 5wt% to 10wt%, the Q&P structure of martensite + austenite will be obtained.
  • Si element in adjusting the temperature of Ac3 is not significant, but it can reduce the Bs and Fs points, realize the heat treatment process at a lower temperature, and help reduce the occurrence of liquid metal brittleness and solid metal brittleness.
  • Si has a strong solid solution strengthening effect, which can inhibit the production of pearlite, increase the austenite carbon content and retained austenite volume content, and improve the toughness and fatigue performance of hot-formed steel parts.
  • the Al element has a similar effect to the Si element. It can inhibit the production of pearlite and improve the stability of austenite. Excessively high Al content greatly increases the Ac3 temperature.
  • Cr and Mo are mainly used to improve the hardenability of hot-formed steel when the Mn content in the steel is low, and the overall martensite content can be obtained at a cooling rate of 25°C/s.
  • Nb, V, and Ti are mainly used to improve the strength of hot-formed steel substrates through precipitation strengthening and fine-grain strengthening. This is achieved by adding one, two or three elements to this galvanized steel.
  • the element control range is 0.02wt% ⁇ 0.25 wt%.
  • B element within 50ppm can greatly improve the hardenability of hot formed steel.
  • P and S are impurity elements. Within the reasonable range limited by the above, it is conducive to smooth production, reducing production costs and improving the fatigue performance of steel plates.
  • the substrate thickness is 0.70mm ⁇ 4.00mm.
  • the hot-dip plated mechanical properties of the substrate yield strength 350MPa ⁇ 500MPa, tensile strength 500MPa ⁇ 780MPa, elongation 10 ⁇ 25%, tensile strain hardening index n value ⁇ 0.12, plastic strain ratio r value ⁇ 0.70.
  • this galvanized steel plate has precise design and control of the hot-dip galvanized layer and parts alloy zinc layer.
  • Coating structure design at least one side of the substrate is coated; both sides are coated with equal or differential thickness; the thickness of the coating (single side) is 8.0 ⁇ m to 24 ⁇ m, and the weight of the coating (single side) is 50g/m 2 to 200g/ m2 .
  • the coating structure from the surface to the substrate includes: surface layer (oil film or passivation film, etc.); galvanized layer with solid solution of Al, Fe, Ce, La, Si, Mn, Mg and/or Cr elements; diffusion layer; diffusion layer Contains an inhibitory layer.
  • the surface layer is oil film or passivation film + oil film.
  • the oil film thickness is 500mg/m 2 ⁇ 800mg/m 2 ;
  • the passivation film thickness is 20mg/m 2 ⁇ 50mg/m 2 and the oil film thickness is 500mg/m 2 ⁇ 800mg/m 2 ;
  • the thickness of the galvanized layer is 6 ⁇ m ⁇ 20 ⁇ m, mainly composed of eta phase.
  • eta phase mainly composed of eta phase.
  • the zinc layer with the above composition and thickness can ensure a sufficiently high melting point and high-temperature oxidation resistance during the subsequent austenitic heating and hot forming process, which helps to effectively control the evaporation and oxidation of surface Zn and obtain good surface conditions and friction. coefficient.
  • the thickness of the diffusion layer is 2 ⁇ m ⁇ 4 ⁇ m, accounting for ⁇ 40% of the thickness of the galvanized layer. It is mainly composed of ⁇ Fe and ⁇ phases, of which ⁇ Fe content is ⁇ 80%; average content of solid solution elements (wt): Al 0.34% ⁇ 1.45%, La 0.1 % ⁇ 2.5% and/or Ce 0.2% ⁇ 3.1%, Si+Mn ⁇ 15.0%, Mg+Cr ⁇ 2.4%; among them, Si/Mn ⁇ 1.1, Mg/Cr ⁇ 0.8.
  • the suppression layer is located in the diffusion layer.
  • the thickness of the suppression layer is 100 nm to 200 nm.
  • the thickness of the suppression layer accounts for 5% to 10% of the thickness of the diffusion layer, and is mainly Fe 2 Al 5 .
  • the inhibition layer is straight (that is, parallel to the interface between the substrate and the coating), continuous, and dense, ensuring that Fe can effectively diffuse into the galvanized layer during subsequent heat treatment and effectively inhibiting Zn from penetrating into the austenite grain boundary of the substrate. .
  • the diffusion layer and inhibition layer with this structure help control the diffusion of Fe and Zn elements during austenitizing heating and hot forming processes, thereby controlling the brittleness and cathodic protection performance of liquid metal.
  • thermo-hardened steel component is, in order from the outer surface to the substrate: surface oxide layer, Zn-Fe alloy matrix, and diffusion layer.
  • the surface oxide layer is mainly composed of one or more oxides among Al 2 O 3 , MgO, MnO, SiO 2 , ZnO, CeO, and La 2 O 3 , with a thickness of 1.0 ⁇ m to 2.0 ⁇ m.
  • the oxides are fine and uniform, and the particle size is Less than 3 ⁇ m; the depth (thickness) of the surface oxide layer is less than 2 ⁇ m, and the roughness is low, which does not affect the normal coating performance.
  • the oxide layer can also be removed by shot peening to further improve the coating performance.
  • the Zn-Fe alloy matrix layer is composed of ⁇ Fe, ⁇ phase and intermediate alloy phase.
  • the intermediate alloy phase includes Zn x Si y Fe z , Zn x Mn y Fe z , ZnMg 2 ; the Fe content in the Zn-Fe alloy matrix layer is 40wt% ⁇ 70wt%, Zn content 20wt% ⁇ 50wt%, thickness 10 ⁇ m ⁇ 35 ⁇ m, and has good cathodic protection performance and welding performance.
  • the diffusion layer is composed of ⁇ Fe with solid solution Zn, Si, Mn, Ce and/or Re elements, wherein the Fe content is ⁇ 80wt%, the Zn content is ⁇ 5wt%, and the thickness is 4 ⁇ m to 6 ⁇ m.
  • thermo-hardened steel parts The mechanical properties of this galvanized hot-formed thermo-hardened steel parts are: yield strength ⁇ 1100MPa, tensile strength ⁇ 1300MPa, elongation ⁇ 4%, bending angle ⁇ 55°.
  • the preparation method of this highly corrosion-resistant galvanized hot-formed hardened steel is: iron-making, steel-making, continuous casting, hot rolling, pickling or pickling, and continuous annealing and galvanizing to obtain a galvanized hot-formed hardened steel plate or galvanized steel plate.
  • Zinc hot formed hardened steel coil is: iron-making, steel-making, continuous casting, hot rolling, pickling or pickling, and continuous annealing and galvanizing to obtain a galvanized hot-formed hardened steel plate or galvanized steel plate.
  • the key process parameters of continuous hot dip plating the temperature Ts of the steel plate entering the zinc pot: 410°C ⁇ 475°C, the temperature of the zinc liquid Tz: 420°C ⁇ 475°C, the hot dip plating time 3s ⁇ 10s; the temperatures of Ts and Tz meet the conditions ⁇ Ts-Tz ⁇ 40°C; plating solution composition (wt): Al 0.12% ⁇ 0.35%, Fe 0.005% ⁇ 0.06%, La 0.08% ⁇ 3.2% and/or Ce 0.12% ⁇ 5.0%, Si+Mn ⁇ 3.0 %, Mg+Cr ⁇ 3.5%, the rest is Zn and inevitable impurities.
  • the above-mentioned galvanized hot-formed hardened steel plate or galvanized hot-formed hardened steel coil is blanked by swing shear, and preferably punched by swing shear blanking to obtain part blanks with the required size and shape for manufacturing the final parts.
  • the part blanks are further processed to obtain the final parts products.
  • the deep processing process is as follows:
  • Cold stamping preforming cold stamping the part blank to preform; compared with the total deformation of the component parts in the following step f) during deep processing, cold stamping preforming accounts for 70% of the total deformation during deep processing ⁇ 100%; in order to ensure the size of the formed parts, it is preferred that cold stamping preforming accounts for 90% to 100% of the total deformation.
  • the steel plate insulation temperature and heating time are limited to the range ABCD; the heating rate Vr in the temperature range from room temperature to T1 is controlled at 3°C/s ⁇ 7°C/ s, the heating rate Vr in the T 1 temperature to holding temperature range is controlled at 6°C/s to 18°C/s; the T 1 temperature range is 500°C to 620°C; the ABCD range is shown in Figure 3, which is point A and point B.
  • point A is kept at 850°C for 190s
  • point B is kept at 850°C for 750s
  • point C is kept at 940°C for 550s
  • point D is kept at 940°C for 150s
  • the steel plate insulation temperature and heating time are limited to the range of EFGH;
  • the heating rate Vr in the temperature range from room temperature to T1 is controlled at 3°C/s ⁇ 7°C/ s, the heating rate Vr in the T 1 temperature to holding temperature range is controlled at 6°C/s to 18°C/s;
  • the T 1 temperature range is 520°C to 640°C;
  • the EFGH range is shown in Figure 4, which is point E and point F.
  • point E is insulated at 870°C for 240s
  • point F is insulated at 870°C for 850s
  • point G is insulated at 955°C for 600s
  • point H is insulated at 955°C for 200s;
  • the steel plate insulation temperature and heating time are limited to the IJKL range; the heating rate Vr in the temperature range from room temperature to T1 is controlled at 3°C/s ⁇ 7°C/ s, the heating rate Vr in the T 1 temperature to holding temperature range is controlled at 6°C/s to 18°C/s; the T 1 temperature range is 540°C to 660°C; the IJHK range is shown in Figure 5, which is point I and point J.
  • point I is insulated at 890°C for 270s
  • point J is insulated at 890°C for 880s
  • point K is insulated at 960°C for 630s
  • point L is insulated at 960°C for 230s.
  • the steel plate insulation temperature and heating time are limited to the range A 1 B 1 C 1 D 1 ; the heating rate Vr in the temperature range from room temperature to T 1 is controlled at 3 °C/s ⁇ 7°C/s, the heating rate Vr in the range of T 1 temperature to holding temperature is controlled at 6°C/s ⁇ 18°C/s; among them, T 1 temperature range is 500°C ⁇ 620°C; A 1 B 1 C 1 D
  • the 1 range is shown in Figure 6, which is a box-shaped range surrounded by point A 1 , point B 1 , point C 1 and point D 1 ; among them, point A 1 is insulated at 750°C for 200s, and point B 1 is insulated at 750°C. 930s, point C is 840°C for 630s, point D is 840°C for 180s;
  • the steel plate insulation temperature and heating time are limited to the range of E 1 F 1 G 1 H 1 ;
  • the heating rate Vr in the temperature range from room temperature to T 1 is controlled at 3 °C ⁇ 7 °C / s, the heating rate Vr in the T 1 temperature ⁇ holding temperature range is controlled at 6 °C / s ⁇ 18 °C / s; among them, T 1 temperature range is 520 °C ⁇ 640 °C;
  • E 1 F 1 G 1 H 1 range As shown in Figure 7, it is a box-shaped range surrounded by point E 1 , point F 1 , point G 1 and point H 1 ; among them, point E 1 is maintained at 770°C for 270s, point F 1 is kept at 770°C for 980s, G 1 point is kept at 855°C for 680s, H 1 point is kept at 855°C for 230s;
  • the steel plate insulation temperature and heating time are limited to the range of I 1 J 1 K 1 L 1 ; the heating rate Vr in the temperature range from room temperature to T 1 is controlled at 3 °C/s ⁇ 7°C/s, the heating rate Vr in the range of T 1 temperature to holding temperature is controlled at 6°C/s ⁇ 18°C/s; among which T 1 temperature range is 540°C ⁇ 660°C; I 1 J 1 K 1 L
  • the range 1 is shown in Figure 8, which is a box-shaped range surrounded by point I 1 , point J 1 , point K 1 and point L 1 ; among them, point I 1 is insulated at 790°C for 330s, and point J 1 is insulated at 790°C. 1010s, K 1 point is 870°C insulation for 710s, L 1 point is 870°C insulation 260s.
  • Cooling and oxidation layer removal The heat-treated part blank is transferred to the cooling device for cooling, and then the oxide layer is removed; the cooling process is: water cooling or air cooling is used to cool the part blank at a cooling rate of 20°C/s ⁇ 100°C/s Cool, cool to 10°C to 20°C above the temperature at which ferrite (Fs) or bainite (Bs) begins to precipitate, that is, 10°C to 20°C above the higher phase transformation point temperature of F phase or B phase, ensuring No ferrite or bainite phase precipitates before hot stamping.
  • Fs ferrite
  • Bs bainite
  • the mechanism of this cooling process After the zinc layer hot-formed steel billet undergoes austenitizing heat treatment, the temperature difference between the hot-forming temperature and the hot-forming temperature reaches 300°C to 400°C. If the traditional hot-forming process is used, air cooling will occur during the conveyor belt and hot-forming stages. Reduce production efficiency, and cooling in the mold will lead to uneven cooling; this application sets up a water cooling or air cooling process after the austenitizing and heating of the billet, which can effectively shorten the subsequent hot stamping holding time, improve production efficiency, and improve the cooling process.
  • the uniformity of temperature control in addition, the water cooling or air cooling process can effectively remove the loose Al 2 O 3 , MgO, Cr 2 O 3 and other oxides on the surface of the zinc layer of the billet after high temperature heating.
  • Mold placement transfer the cooled part blank to the mold.
  • both the low-temperature hot forming process and the shaping process are: when Mn ⁇ 3.0wt% in the substrate, the hot stamping temperature range is 450°C ⁇ 760°C; when 3.0wt% ⁇ Mn ⁇ 10.0wt% in the substrate, the hot stamping temperature range is 350°C ⁇ 660°C; holding time 4s ⁇ 8s; quenching cooling rate ⁇ 27°C/s, preferably 27°C/s ⁇ 60°C/s.
  • the line represented by Ms represents the temperature curve of martensitic phase transformation starting in the traditional hot forming process
  • Ms' refers to The line represents the temperature curve at which martensitic transformation begins in the low-temperature hot forming process.
  • B represents the bainite phase transformation area in the traditional hot forming process
  • B' represents the bainite phase transformation area in the low-temperature hot forming process.
  • P represents the pearlite phase change transition area in the traditional thermoforming process
  • P' represents the pearlite phase change transition area in the low-temperature thermoforming process.
  • F represents the ferrite phase transformation region in the traditional hot forming process.
  • Critical cooling is reduced from 30°C/s in the traditional hot forming process to 15°C/s.
  • this method can accurately shape the shape of parts, or hot-form components with complex shapes with small deformations, which can effectively improve the forming accuracy of parts.
  • the hot forming temperature range of the low-temperature hot forming process is significantly lower than that of the traditional hot forming process by 50°C to 200°C. This is mainly due to: first, the stability of the austenite in the thermal state of the substrate in this method It has high sex ratio, lower Ms, Bs and Fs precipitation temperature shifts to the right.
  • bainite, ferrite or martensite phase will not precipitate, and mixed crystal or multi-phase will not occur.
  • the structure causes Zn to easily penetrate into the grain boundaries and cause brittleness; secondly, under lower temperature conditions, the deformation is limited to ⁇ 20% of the total deformation of the part, and even when no deformation occurs, hot forming does not easily cause zinc The generation of layer cracks.
  • Example 1-30 The highly corrosion-resistant galvanized hot-formed hardened steel and its parts and preparation methods of this application are as follows.
  • Galvanized hot-formed hardened steel sheets or steel coils are prepared through the processes of ironmaking, steelmaking, continuous casting, hot rolling, pickling or pickling, and continuous annealing and galvanizing.
  • the chemical composition of the substrate is as described in Table 1.
  • the balance is Fe and unavoidable impurities;
  • the steel type of the comparative example is 22MnB5, where the number 22 represents the carbon content, that is, 0.22wt% carbon.
  • the balance of the average coating content in Table 4 is Zn and inevitable impurities.
  • the first heating rate is the heating rate in the temperature range from room temperature to T 1
  • the second heating rate is the heating rate in the temperature range from T 1 temperature to the holding temperature.
  • Examples 1, 2, 10, 11, and 12 correspond to Figure 3; Examples 3, 4, 13, 14, and 15 correspond to Figure 4; Examples 5, 16, 17, 18, and 19 correspond to Figure 5; Implementation Examples 8, 9, 20, 21, and 22 correspond to Figure 6; Examples 23, 24, 25, 26, and 27 correspond to Figure 7; Examples 6, 7, 28, 29, and 30 correspond to Figure 8.

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Abstract

本申请公开了一种高耐蚀镀锌热成形硬化钢及其零部件以及制备方法，包括基板和镀层；基板的成分及其质量百分含量为：C0.12％～0.35％，Si0.08％～2.12％，Mn0.42％～10.00％，Al0.03％～0.12％，Cr0.02％～0.65％，Mo≤1.12％，Nb+V+Ti 0.02％～0.25％，B 0.0003％～0.005％，S≤0.012％，P≤0.08％，余量为Fe和不可避免的杂质；镀层的成分及其质量百分含量为：Al0.15％～0.45％，Fe0.05％～2.50％，La0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，余量为Zn及不可避免的杂质。本基板及锌层组织和成分设计满足完全奥氏体化(Ac3)以上宽加热工艺窗口，基板热成形钢热状态奥氏体的稳定性比较高，具有较低的Ms，及Bs和Fs析出温度右移，在低温热成形过程中不会析出贝氏体、铁素体或马氏体相，不会出现混晶或多相组织导致Zn容易渗透进晶界导致脆性。

Description

高耐蚀镀锌热成形硬化钢及其零部件以及制备方法
本专利申请要求于2022年05月27日提交的中国专利申请No.CN202210594111.4的优先权。在先申请的公开内容通过整体引用并入本申请。
技术领域
本申请涉及一种镀锌热成形钢，尤其是一种高耐蚀镀锌热成形硬化钢及其零部件以及制备方法。
背景技术
热成形钢采用奥氏体化加热+高温区变形的工艺方案，不仅实现了高达1500MPa～2100MPa的钢强度，而且解决了超高强钢的易回弹、易破裂、尺寸精度低等零件质量问题，在汽车零部件制造中获得了越来越广泛的应用。裸板热成形钢通常存在表面易氧化、脱碳、耐腐蚀性差、需要抛丸处理等缺点，逐渐被镀层热成形钢所替代。目前商业化应用的镀层热成形钢占热成形钢产量的70％左右，是热成形钢的主流产品。
镀层热成形钢主要有Al基镀层、Zn基镀层两大系列；其中Al基镀层包括Al-Si、Al-Si-Cu、Al-Si-Re、Al-Si-Ni等成分类别，Al-10％Si镀层的商业化程度较高、应用最广，是安赛乐米塔尔(Arcelormittal)的专利产品，市场份额占90％，几乎垄断国内市场。Zn基镀层包括GI热镀纯锌和GA合金化热镀锌产品，2006年时奥钢联(Voestalpine)研发成功并投入市场。目前仅有奥钢联、安赛乐米塔尔、新日铁等公司有成熟的产品供应市场。德国蒂森克虏伯(ThyssenKrupp)成功开发了电镀锌Zn-Ni产品，并进行了应用，但成本过高，耐蚀性能不及GI和GA产品，还未到大规模应用阶段。此外，国内外学者还在实验室开发了Zn-Al、Zn-Al-Mg等镀层，Zn-Al镀层为复合镀层。
镀层热成形钢的成形工艺包括直接热成形和间接热成形两种工艺。直接热成形工艺是指将钢板加热到奥氏体化温度并保温一定时间后，直接转移到带有冷却系统的模具内进行冲压成形和保压淬火。间接热成形工艺是指将钢板先经过冷冲压加工，预成形一定的量，然后再加热到奥氏体化温度，保温一定时间后，转移至带有冷却系统的模具内进行最终的成形加工和淬火。Al基镀层采用直接热成形的方式进行生产，生产流程短、产量高、生产成本低。Al-Si镀层在加热和热成形过程中容易产生微裂纹，裂纹虽然不扩展到基板，不造成基板脆性，但降低了镀层耐腐蚀性能；铝硅镀层在冷成形量超过8％时容易出现裂纹而降低镀层耐腐蚀性能，因而不能采用间接热成形工艺，只适合截面形状简单的零部件的生产。Zn基镀层可采用直接热成形工艺和间接热成形工艺进行生产。Zn基镀层热成形钢采用直接热成形工艺时容易发生液态金属脆性(LMIE)和固态金属脆性(SMIE)，因此奥氏体加热和热成形工艺窗口窄。Zn基镀层热成形钢采用间接热成形工艺时可以将大部分变形分配到冷成形过程中进行，并且由于其良好的冷成形性能而不易产生裂纹，因此在后续奥氏体化工艺和热成形工艺时有较宽的工艺窗口，可以生产截面形状复杂的零部件产品。
热镀锌热成形钢对于铝硅镀层热成形钢另外一个优势是具有阴极保护能力，原因在于Zn和Fe电极电位分别为-0.762V和-0.439V，Zn镀层电极电位更负，对破损镀层部分钢板基板有很好的阴极保护作用，即使切口处也有良好的防腐性能。热镀锌热成形钢经过奥氏体化热处理和热成形后镀层中Zn含量降低，导致电极电位升高，防腐性能降低；与此同时，基板中的Fe元素在奥氏体化加热、热成形过程中向锌层扩散，提高了锌层中Fe含量、提高了锌层熔点，抑制了Zn向基板奥氏体晶界的渗透，减少了液态金属脆性的倾向，并且减少了表面Zn元素的蒸发。因此，通过热加工过程中Fe、Zn元素扩散并不能同时提高镀层阴极保护能力和减少热成形过程中液态金属脆性趋势。
欧洲专利EP2045360A1提供了一种复合镀层技术，镀层结构为上层锌层和下层铝硅层，上层锌层含有＞99％Zn、＜1％Al，下层结构为90％Al-10％Si。该镀层热成形后上层锌层含有80％Zn、16％Al、2％Si，下层含有40％Al、30％Fe、20％Zn、5％Si。该专利技术通过两次热浸镀构造上下两种不同的涂层结构，生产难度大，商业化难度大。
国际专利申请WO 2008102012 A1提供了一种Zn+Mg+Al镀层，镀层包括0.3～4.0wt％Mg、0.05～6.0wt％Al，还包括至多0.2wt％的1种或多种附加元素，其余为Zn及不可避免的杂质。其中附加元素包括Sb、Pb、Ti、Ca、Mn、Sn、La、Ce、Cr、Ni、Zr、Bi，其中Sb、Pb、Sn、Bi用于在镀层表面形成锌花，附加元素可以改善锌渣的产生，但是对镀层耐腐蚀性能的改变效果不如Mg和Al元素，并且使得镀层更加昂贵。
中国专利申请CN 104302802 A提供了牺牲阴极保护的涂层的钢板，该涂层包含：5wt％至50wt％的Zn、0.1wt％至15wt％的Si、以及任选的最高达10wt％的Mg和根据累积含量最高达0.3wt％的附加元素。该涂层还包含：选自0.1wt％至5wt％的锡、0.01wt％至0.5wt％的铟、及其组合的保护元素；其中0.3wt％的附加元素包括Sb、Pb、Ti、Ca、Mn、La、Ce、Cr、Ni、Zr或Bi；这些不同元素尤其可以改善涂层的耐腐蚀性或者它的脆性或粘附性。
中国专利申请CN112011752A提供了一种GA镀层的热硬化零件解决方案，其热硬化前镀层组织由富锌的Г-FeZn相、以及富Fe的α-Fe(Zn)相组成，其中Г-FeZn相的体积占比为10～20％。该专利申请在热浸镀镀液成分设计方面没有进行描述，只对合金化工艺进行了详细说明。
中国专利申请CN110777319A提供了一种铝基Si-Mg-Cu-REM镀层钢板，镀液的组成成分以质量％计，含有Si：2.0～7.5％、Mg：0.08～2.5％、Cu：0.1～2.0％、REM：0.08～1.0％，其余为Al和不可避免的杂质，主要特点是优异的耐腐蚀性能和成形性能。
中国专利申请CN 112139335 A在锌层加热后增加了沸水除氧化层工序，加热后的板料转移至沸水箱中进行高压沸水除氧化层，板料出沸水箱后进行气体吹扫。该工艺缺点是冷却速度控制难度大。
发明概述
技术问题
本申请要解决的技术问题是一方面提供一种高耐蚀镀锌热成形硬化钢；第二方面提供一种不发生液态金属脆性或影响镀层裂纹扩展的高耐蚀镀锌热成形硬化钢的制备方法；第三方面提供一种高耐蚀镀锌热成形硬化钢零部件；第四方面提供一种高耐蚀镀锌热成形硬化钢零部件的制备方法，以解决现有技术中热成形硬化钢不能兼顾耐腐蚀性能和金属脆性的缺陷。
技术解决方案
为解决上述技术问题，本申请采用的技术方案是：
第一方面，本申请提供一种高耐蚀镀锌热成形硬化钢，包括基板和镀层；
所述基板的成分及其质量百分含量为：C 0.12％～0.35％，Si 0.08％～2.12％，Mn 0.42％～10.00％，Al 0.03％～0.12％，Cr 0.02％～0.65％，Mo≤1.12％，Nb+V+Ti 0.02％～0.25％，B 0.0003％～0.005％，S≤0.012％，P≤0.08％，余量为Fe和不可避免的杂质；
所述镀层的成分及其质量百分含量为：Al 0.15％～0.45％，Fe 0.05％～2.50％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，余量为Zn及不可避免的杂质。
在一种可能的实现方式中，所述镀层包括镀锌层和扩散层，所述扩散层中含有抑制层；所述镀锌层主要由η相组成，所述扩散层主要由αFe和Г相组成，所述抑制层的主要成分为Fe2Al5。
在一种可能的实现方式中，所述镀锌层的成分含有：固溶Fe 0.08％～2.20％，Al 0.08％～0.45％，La 0.08％～1.4％和/或Ce 0.12％～2.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％。优选的，所述镀锌层的成分中，Si/Mn≥1.1、Mg/Cr≥0.8。
在一种可能的实现方式中，所述扩散层中αFe≥80％，主要固溶元素的平均含量为：Al0.34％～1.45％，La 0.1％～2.5％和/或Ce 0.2％～3.1％，Si+Mn≤15.0％，Mg+Cr≤2.4％。
第二方面，本申请提供上述第一方面以及第一方面任一可能的实现方式中高耐蚀镀锌热成形硬化钢的制备方法，包括：将硬化钢板进行热浸镀；镀液成分及其质量百分含量为：Al 0.12％～0.35％，Fe 0.005％～0.06％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，Si/Mn≥1.1，Mg/Cr≥0.8，其余为Zn及不可避免的杂质。
在一种可能的实现方式中，所述热浸镀工艺为：硬化钢板入锌锅温度Ts 410℃～475℃，镀液温度Tz 420℃～475℃，热浸镀时间3s～10s；Ts、Tz的温度满足条件∣Ts-Tz∣≤40℃。
第三方面，本申请提供一种镀锌热成形硬化钢零部件，采用上述高耐蚀镀锌热成形硬化钢制备而成，包括基板和镀层；所述镀层由外表面到基板依次为表面氧化层、Zn-Fe合金基体层和扩散层；
所述表面氧化层主要成分为Al2O3、MgO、MnO、SiO2、ZnO、CeO、La2O3中的一种或多种；
所述Zn-Fe合金基体层包括αFe、Г相和中间合金相，所述中间合金相包括ZnxSiyFez、ZnxMnyFez和ZnMg2；所述Zn-Fe合金基体层的成分中：Fe 40％～70％、Zn 20％～50％；
所述扩散层主要由固溶Zn、Si、Mn、Ce和/或Re元素的αFe组成，在其成分中：Fe≥80％、Zn≤5％。
第四方面，本申请提供一种镀锌热成形硬化钢零部件的制备方法，包括：镀锌热成形硬化钢经冷冲压预成形、修整、奥氏体化热处理；将奥氏体化热处理后的零件坯料转移到冷却装置，进行冷却和去氧化层；将冷却和去氧化层后的零件坯料再转移到模具，进行整形或低温热成形。
在一种可能的实现方式中，所述冷却和去氧化层工艺为：采用水冷或者气冷方式将坯料温度降至铁素体或贝氏体的析出温度以上10℃～20℃。
在一种可能的实现方式中，所述整形或低温热成形工艺为：保压时间4s～8s，淬火冷速≥27℃/s；当基板中Mn≤3.0wt％，热冲压温度范围450℃～760℃；当基板中3.0wt％＜Mn≤10.0wt％时，热冲压温度范围350℃～660℃。
有益效果
采用上述技术方案所产生的有益效果在于：本申请所述基板及其涂覆的锌层组织和成分设计满足完全奥氏体化(Ac3)以上宽加热工艺窗口，基板热成形钢热状态奥氏体的稳定性比较高，具有较低的马氏体相变开始转变温度(Ms)，及贝氏体(Bs)和铁素体(Fs)析出温度右移，在低温热成形过程中不会析出贝氏体、铁素体或马氏体相，不会出现混晶或多相组织，导致Zn容易渗透进晶界导致脆性。生产零件时可采用低临界冷却速度和低于传统热成形温度50℃～200℃左右的温度的热成形和冷却工艺窗口，避开铁素体(Fs)和贝氏体(Bs)析出，并在该工艺窗口条件下不发生液态金属脆性或影响基板疲劳性能的镀层裂纹扩展，所制造的零件具有高度的阴极保护防腐蚀性能、焊接性能、机械性能、弯曲性能、疲劳性能等。
本申请零部件采用低温热成形工艺，热成形温度范围明显比传统热成形工艺低50℃～200℃，在较低的温度条件下，变形量限制在≤20％零件总变形量，甚至不发生变形的情况下，热成形不容易导致锌层裂纹的产生。
附图说明
下面结合附图和具体实施方式对本申请作进一步详细的说明。
图1为本申请热浸镀后镀层抑制层形貌分布；
图2为本申请实施例4热浸镀钢板镀层组织形貌；
图3为本申请中Mn含量≤3.0wt％、0.7mm≤厚度≤1.4mm加热工艺窗口；
图4为本申请中Mn含量≤3.0wt％、1.4mm＜厚度≤3.0mm加热工艺窗口；
图5为本申请中Mn含量≤3.0wt％，3.0mm＜厚度≤4.0mm加热工艺窗口；
图6为本申请中3.0wt％＜Mn含量≤10.0wt％、0.7mm≤厚度≤1.4mm加热工艺窗口；
图7为本申请中3.0wt％＜Mn含量≤10.0wt％、1.4mm＜厚度≤3.0mm加热工艺窗口；
图8为本申请中3.0wt％＜Mn含量≤10.0wt％、3.0mm＜厚度≤4.0mm加热工艺窗口；
图9为本申请低温热整形/成形淬火与传统热成形工艺原理对比图。
本发明的实施方式
影响锌基镀层钢板奥氏体化加热工艺窗口范围宽窄的限制条件有3个，(1)，液态金属脆性，即加热过程中锌或锌铁液相渗透入奥氏体晶界，造成锌层和基板开裂；(2)锌层熔化、蒸发、氧化；(3)锌层Fe、Zn含量的控制以实现阴极保护防腐性能和焊接性能匹配。如果热镀锌热成形钢镀层成分、镀层结构、基板及镀层厚度等设计不当，则零件制造时的奥氏体加热和热成形工艺窗口非常窄，即加热温度、加热速率、保温时间等参数可控范围很小，所生产的零件疲劳性能、阴极保护防腐性能和焊接性能合格率偏低。锌层蒸发/熔化/氧化也会对生产设备造成影响。基于上述原理，本申请高耐蚀镀锌热成形硬化钢的镀液及镀层成分设计如下所述。
(1)为了扩大奥氏体加热工艺窗口和热成形工艺窗口，提高零件性能，本申请镀锌热成形硬化钢设计了下述镀液成分和镀层成分。
镀液成分(wt)：Al 0.12％～0.35％，Fe 0.005％～0.06％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，Si/Mn≥1.1，Mg/Cr≥0.8，其余为Zn及不可避免的杂质。
镀层成分(wt)：Al 0.15％～0.45％，Fe 0.05％～2.50％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，其余为Zn及不可避免的杂质。
镀层中各元素的作用机理如下：
Al元素主要用于控制镀层中Fe2Al5抑制层的形成，通过抑制层控制Zn-Fe合金脆性相的生成和扩散层的厚度。当镀液中Al含量超过0.15wt％时，通常热浸镀工艺就能实现连续的Fe2Al5抑制层的生成，但抑制层的成分、厚度、尺寸和分布等受退火温度、退火露点/氢气等气氛、热浸镀温度/时间等工艺的影响。为了增加热浸镀锌层的冷成形性能，避免在冷成形过程中产生微裂纹或缺陷，需要控制合金层的厚度和Zn-Fe脆性相的生成，因此在热浸镀过程中控制生成连续、致密、厚度均匀(100nm～200nm)的抑制层很关键。此外，更关键的是需要在奥氏体化加热过程450℃～700℃范围，通过抑制层控制Fe和Zn元素的相互扩散进程，抑制Zn或Zn-Fe液相向基体晶粒晶界渗透，减少液态金属脆性的产生；此外，锌层中Al经过奥氏体化加热过程可扩散到锌层表面形成致密的Al2O3膜，减轻Zn的蒸发和氧化，但过高含量Al2O3膜对涂镀和焊接性能不利，本制备方法通过预冷却工艺进行了去除。
La、Ce元素能够有效净化镀液成分，实现镀液中Zn、Al等元素的均匀分布，在热浸镀时均匀分布的Al与基板发生反应，有助于形成连续、平直的Fe2Al5抑制层，抑制液态金属脆性；此外，La、Ce能够细化原始涂覆层中锌层晶粒尺寸，细化奥氏体化加热过程中形成的Zn、Fe、Si、Mn合金相，锌镁合金相MgZn2，合金相为高熔点相，能明显延迟液态锌、锌铁相的形成，并抑制其向基体及基体晶界渗透；细化的镀层组织和中间相明显提升了锌层密度，从而提升了镀层耐腐蚀性能。专利申请WO2008102012A1、CN104302802A中Ce、La等作为附加元素添加，含量低于0.3wt％，在该成分范围内达不到控制抑制层形貌和有效细化镀层中合金相尺寸的目的。而本镀锌钢通过添加较高含量的La和/或Ce实现了热浸镀过程中抑制层连续性的精准控制及表面状态的控制。
镀液中Si、Mn元素的添加提升了Zn层的熔点，在奥氏体化加热过程中减少Zn的蒸发，另外Si、Mn与镀层中Zn、Fe形成三元或四元中间合金相，极大地阻滞液态锌向基体晶界渗透。Si和Mn复合添加使得中间合金相分布更加均匀，并且Si与Mn的比例Si/Mn≥1.1使中间合金相获得了最佳的均匀分布状态。专利申请CN104302802A中添加了0.1wt％至15wt％之间的Si，优选Si含量范围1wt％至15wt％，并添加了含量小于0.3wt％的附加元素Mn，优选的0.01wt％，该技术主要通过Si提高镀层抗高温氧化特性，减少650℃以上镀层剥离，减少热浸镀过程中过厚的锌铁合金层。该技术采用较高含量的Si一方面增加了生产成本，另外，容易形成过于粗大的中间合金相，且分布均匀性控制难度大，不利于耐腐蚀性提升。本镀锌钢设计了Si+Mn两种元素配合使用形成中间合金相，两种元素总含量低于3wt％，降低了生产成本，同时Si与Mn相互作用，提高了中间合金相的分布均匀性。更重要的通过配合Ce、La稀土元素的使用细化了中间合金的晶粒尺寸，提升了锌层耐腐蚀性能。
镀液中Mg含量提升了Zn层阴极保护和切口保护耐腐蚀性能，但含量超过3wt％时耐腐蚀速率降低很快；此外，Mg与Zn在镀液凝固过程中析出MgZn2相，该相在镀层中均匀分布可提高镀层硬度和表面摩擦状态。镀层中Cr元素在奥氏体化加热过程中扩散到Zn层表面形成Cr2O3氧化膜，防止Zn蒸发，此外也可以抑制Al2O3的形成。Cr与Mg和Al元素复合作用，控制高温下镀层表面摩擦状态，能够有效减少高温状态Zn层的摩擦系数，减低热冲压过程中液态金属脆性(LIME)或固态金属脆性(SIME)的产生。Mg和Cr元素复合添加使Mg与Cr的比例控制在Mg/Cr≥0.8可以获得良好的表面状态效果，获得最佳的高温表面摩擦系数，可将700℃时高温摩擦系数降至0.2～0.3之间。专利申请CN 104302802 A中添加了10wt％Mg，并优选的使用3wt％～6wt％范围，主要用于提升锌层阴极保护性能，实际上当锌层中Mg含量超过3wt％时，其耐腐蚀性能呈现降低的趋势。专利申请WO2008102012A1和CN110777319A分别采用0.3wt％～4.0wt％Mg和0.08％～2.5％Mg，可以提高镀层阴极保护耐腐蚀性能，但是奥氏体化加热过程中易于在镀层表面形成粗糙的氧化物MgO和ZnO，增加了镀层表面摩擦系数，不利于热冲压过程，并有可能导致锌层的固态金属脆性问题。本镀锌钢设计了Mg+Cr两种元素配合应用，不仅提升了镀层阴极耐腐蚀性能，而且通过预冷却工艺去除了粗糙的ZnO和MgO氧化层，保留了细密的Zn、Mg、Cr、Al混合氧化层，降低了热状态表面摩擦系数，提升了热冲压成形的稳定性，改善了镀层裂纹扩展，提升了性能。
镀液中Fe含量控制在0.005wt％～0.06wt％，控制镀液中低铁含量以减少锌渣产生。热浸镀工艺促进钢板中Fe向锌层扩散，热浸镀后Fe含量达到0.05wt％～2.50wt％，镀层中较高的Fe含量提高了镀层熔点，降低了液态金属脆性的产生的趋势。镀锌热成形钢在后续奥氏体化加热或者热成形过程中Fe继续向锌层扩展，镀层中Fe含量越高镀层焊接性能越好，硬度越高，但是过高的Fe含量将导致锌层中Fe含量低，从而降低镀层的阴极保护能力，零件锌层中Fe含量控制在40wt％～70wt％。
(2)影响锌基镀层钢板奥氏体化及热成形工艺窗口的因素还包括基板化学元素控制。通过合金元素的控制适当降低镀层钢板Ac3点温度，这样基板可以在较低的温度条件下实现奥氏体化，同时满足锌层在较低温度下热处理实现Fe扩散，减少Zn蒸发和氧化。通过合金元素的设计可以降低铁素体、贝氏体析出温度，这样可以在较低的温度下进行热成形，从而降低液态金属脆性，特别是固态金属脆性的产生。此外基板中合金元素的添加对热浸镀后和热成形后机械性能有重要的影响，这些合金元素的添加应该既能提升热浸镀后的冷成形性能，又能提升热成形后的机械性能和疲劳性能。
基板合金成分设计(wt)：C 0.12％～0.35％，Si 0.08％～2.12％，Mn 0.42％～10.00％，Al 0.03％～0.12％，Cr 0.02％～0.65％，Mo≤1.12％，Nb+V+Ti 0.02％～0.25％，B 0.0003％～0.005％，S≤0.012％，P≤0.08％，余量为Fe和不可避免的杂质。
基板中各元素的作用机理如下：
C元素对Ac3、Fs、Bs有较大的影响，增加0.1wt％C含量可以将完全奥氏体化温度(Ac3)降低20℃，冷却过程中将贝氏体析出温度(Bs)降低27℃，推迟铁素体的析出。提高C含量能够有效扩大奥氏体化加热工艺、热成形工艺窗口范围。同时C含量影响镀锌热成形钢力学性能，通过固溶强化大幅提升热成形后马氏体的强度，另外C还是强烈的奥氏体稳定性元素，有助于退火后获得一定的残余奥氏体含量，提高钢板的韧性、疲劳性能等。
Mn元素可以大幅降低Ac3、Bs温度，1wt％Mn可以将Ac3温度降低20.7℃，热成形过程将Bs点降低90℃，推迟铁素体转变。因此，提高Mn含量能够非常有效扩大奥氏体化加热工艺、热成形工艺窗口范围。同时Mn元素有助于在零件钢板基板获得一定数量的稳定残余奥氏体，提升镀锌钢板零件力学性能。当Mn含量提升到5wt％～10wt％范围时，将获得马氏体+奥氏体的Q&P组织，其抗拉强度能够达到1500MPa以上，伸长率达到15％以上，并且Ac3温度低至740℃，在此温度下就可以实现完全奥氏体化，在此温度下进行热处理将大幅减少Zn的蒸发和氧化。
Si元素调节Ac3温度的效果不显著，但是能够降低Bs和Fs点，在较低的温度下实现热处理工艺，有助于减少液态金属脆性和固态金属脆性的产生。Si有较强的固溶强化效果，能够抑制珠光体的产生，提高奥氏体碳含量和残余奥氏体体积含量，提升热成形钢零件韧性和疲劳性能。
Al元素与Si元素的作用类似，能抑制珠光体产生，提高奥氏体稳定性，过高的Al含量极大提升Ac3温度。
Cr和Mo主要用于在钢中Mn含量偏低的时候，提高热成形钢的淬透性，在25℃/s冷却速度时能够获得全面马氏体含量。
Nb、V、Ti主要用于通过析出强化、细晶强化提高热成形钢基板强度，本镀锌钢中选用一种、两种或三种元素的添加来实现，元素控制范围0.02wt％～0.25wt％。
B元素在50ppm以内可以极大提高热成形钢淬透性。
P、S属于杂质元素，在上述限定的合理范围之内，有利于生产顺利进行、降低生产成本和提高钢板疲劳性能。
基板厚度为0.70mm～4.00mm。基板的热浸镀态机械性能：屈服强度350MPa～500MPa，抗拉强度500MPa～780MPa，伸长率10～25％，拉伸应变硬化指数n值≥0.12，塑性应变比r值≥0.70。
(3)本镀锌钢板为了保证具有较宽的奥氏体化加热工艺窗口、热成形工艺窗口，对热浸镀锌层、零件合金锌层进行了精确设计和控制。
镀层组织结构设计：基板至少一个面有镀层；双面等厚或差厚镀层；镀层以厚度计(单面)为8.0μm～24μm，以重量计(单面)为50g/m2～200g/m2。
镀层结构从表面至基体包括：表面层(油膜或者钝化膜等)；镀锌层，并固溶Al、Fe、Ce、La、Si、Mn、Mg和/或Cr元素；扩散层；扩散层中含有抑制层。
表面层为油膜或钝化膜+油膜。采用油膜时，油膜厚度500mg/m2～800mg/m2；采用钝化膜+油膜处理时，钝化膜厚度20mg/m2～50mg/m2，油膜厚度500mg/m2～800mg/m2；镀层表面粗糙度Ra 0.6μm～1.5μm。该表面层保证冷冲压后能够获得比较好的表面状态和高温状态下的摩擦系数。
镀锌层厚度6μm～20μm，主要由η相组成，其成分中(wt)：固溶Fe 0.08％～2.20％，Al 0.08％～0.45％，La 0.08％～1.4％和/或Ce 0.12％～2.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，Si/Mn≥1.1、Mg/Cr≥0.8。具有上述成分及厚度的锌层在随后奥氏体加热和热成形过程能够保证有足够高的熔点和抗高温氧化性能，有助于有效控制表面Zn的蒸发和氧化，获得良好的表面状态和摩擦系数。
扩散层厚度为2μm～4μm，占镀锌层厚度≤40％，主要由αFe、Г相组成，其中αFe含量≥80％；固溶元素平均含量(wt)：Al 0.34％～1.45％、La 0.1％～2.5％和/或Ce 0.2％～3.1％、Si+Mn≤15.0％、Mg+Cr≤2.4％；其中，Si/Mn≥1.1、Mg/Cr≥0.8。
抑制层位于扩散层中，抑制层厚度100nm～200nm，抑制层厚度占扩散层厚度的5％～10％，主要为Fe2Al5。如图1所示，抑制层平直(即与基板和镀层界面平行)、连续、致密，确保后续热处理过程中Fe能有效向镀锌层中扩散，有效抑制Zn向基板奥氏体晶界渗透。具有该结构的扩散层和抑制层，有助于控制奥氏体化加热和热成形过程中Fe、Zn元素的扩散，从而控制液态金属脆性和阴极保护性能。
(4)本镀锌热成形热硬化钢零部件的镀层设计，由外表面到基板依次为：表面氧化层、Zn-Fe合金基体、扩散层。
表面氧化层主要由Al2O3、MgO、MnO、SiO2、ZnO、CeO、La2O3中的一种或多种氧化物构成，厚度1.0μm～2.0μm，氧化物细密均匀，颗粒尺寸小于3μm；表面氧化层深度(厚度)小于2μm，粗糙度较低，不影响正常的涂镀性能，也可以喷丸去掉该氧化层进一步提升涂覆性能。
Zn-Fe合金基体层由αFe、Г相以及中间合金相组成，中间合金相包括ZnxSiyFez、ZnxMnyFez、ZnMg2；Zn-Fe合金基体层中Fe含量40wt％～70wt％、Zn含量20wt％～50wt％，厚度10μm～35μm，具有良好的阴极保护性能和焊接性能。
扩散层由固溶Zn、Si、Mn、Ce和/或Re元素的αFe组成，其中Fe含量≥80wt％、Zn含量≤5wt％，厚度4μm～6μm。
本镀锌热成形热硬化钢零部件的机械性能为：屈服强度≥1100MPa，抗拉强度≥1300MPa，伸长率≥4％，弯曲角度≥55°。
(5)本高耐蚀镀锌热成形硬化钢的制备方法为：炼铁、炼钢、连铸、热轧、酸洗或酸轧、连续退火镀锌，得到镀锌热成形硬化钢板或镀锌热成形硬化钢卷。
其中，连续热浸镀关键工艺参数：钢板入锌锅温度Ts：410℃～475℃，锌液温度Tz：420℃～475℃，热浸镀时间3s～10s；Ts、Tz的温度满足条件∣Ts-Tz∣≤40℃；镀液成分(wt)：Al 0.12％～0.35％，Fe 0.005％～0.06％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，其余为Zn及不可避免的杂质。
(6)本高耐蚀镀锌热成形硬化钢零部件的制备方法如下所述。
将上述镀锌热成形硬化钢板或镀锌热成形硬化钢卷采用摆剪落料，并优先采用摆剪落料的方式进行冲裁等，获得制造最终零部件所要求的尺寸形状的零件坯料。将零件坯料进行深加工，得到最终的零部件产品。深加工过程如下所述：
a)冷冲压预成形：对零件坯料进行冷冲压以预成形；与下述步骤f)组成零件在深加工过程中的总变形量相比，冷冲压预成形占深加工过程中总变形量的70％～100％；为了保证成形后零件尺寸，优选冷冲压预成形占总变形量的90％～100％。
b)修整：冷冲压预成形后的零件坯料采用冲裁方式进行修整，包括冲孔、翻边、修边等。
c)奥氏体化热处理：对零件坯料进行热处理；
Ⅰ)当镀锌成形热硬化钢板的基板中0.42wt％≤Mn含量≤3.0wt％时，采用如下加热工艺：
①当镀锌成形热硬化钢板厚度0.7mm≤T≤1.4mm时，钢板保温温度和加热时间限定在ABCD范围内；室温～T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围500℃～620℃；ABCD范围如图3所示，为A点、B点、C点和D点围成的方框形范围；其中，A点为850℃保温190s、B点为850℃保温750s、C点为940℃保温550s、D点为940℃保温150s；
②当镀锌成形热硬化钢板厚度1.4mm＜T≤2.5mm时，钢板保温温度和加热时间限定在EFGH范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围520℃～640℃；EFGH范围如图4所示，为E点、F点、G点和H点围成的方框形范围；其中，E点为870℃保温240s、F点为870℃保温850s、G点为955℃保温600s、H点为955℃保温200s；
③当镀锌成形热硬化钢板厚度2.5mm＜T≤4.0mm时，钢板保温温度和加热时间限定在IJKL范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围540℃～660℃；IJHK范围如图5所示，为I点、J点、K点和L点围成的方框形范围；其中，I点为890℃保温270s、J点为890℃保温880s、K点为960℃保温630s、L点为960℃保温230s。
Ⅱ)当镀锌成形热硬化钢板的基板中3.0wt％＜Mn含量≤10.0wt％时，采用如下加热工艺：
①当镀锌成形热硬化钢板厚度0.7mm≤T≤1.4mm时，钢板保温温度和加热时间限定在A1B1C1D1范围内；室温～T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围500℃～620℃；A1B1C1D1范围如图6所示，为A1点、B1点、C1点和D1点围成的方框形范围；其中，A1点为750℃保温200s、B1点为750℃保温930s、C1点为840℃保温630s、D1点为840℃保温180s；
②当镀锌成形热硬化钢板厚度1.4mm＜T≤2.5mm时，钢板保温温度和加热时间限定在E1F1G1H1范围内；室温至T1温度区间的加热速率Vr控制在3℃～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围520℃～640℃；E1F1G1H1范围如图7所示，为E1点、F1点、G1点和H1点围成的方框形范围；其中，E1点为770℃保温270s、F1点为770℃保温980s、G1点为855℃保温680s、H1点为855℃保温230s；
③当镀锌成形热硬化钢板厚度2.5mm＜T≤4.0mm时，钢板保温温度和加热时间限定在I1J1K1L1范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围540℃～660℃；I1J1K1L1范围如图8所示，为I1点、J1点、K1点和L1点围成的方框形范围；其中，I1点为790℃保温330s、J1点为790℃保温1010s、K1点为870℃保温710s、L1点为870℃保温260s。
d)冷却和去氧化层：热处理后的零件坯料转移到冷却装置进行冷却，然后去除氧化层；冷却过程为：采用水冷或者气冷方式以20℃/s～100℃/s冷却速度将零件坯料冷却，冷却至铁素体(Fs)或贝氏体(Bs)开始析出温度以上的10℃～20℃，即F相或B相中较高的相变点温度以上10℃～20℃，保证热冲压前不析出铁素体或贝氏体相。
该冷却工序的作用机理：锌层热成形钢坯料经过奥氏体化热处理后温度与热成形温度差达到300℃～400℃，若采用传统的热成形工艺，在传送带、热成形阶段空冷降温会降低生产效率，在模具内冷却降温会导致冷却不均匀；本申请在坯料奥氏体化加热后设置了水冷或气冷工序，能够有效缩短后续热冲压保温时间，提高生产效率，提高冷却过程中温度控制的均匀性；此外，通过水冷或气冷工序能够有效去除经过高温加热后坯料锌层表面疏松的Al2O3、MgO、Cr2O3等氧化物。
e)入模：将冷却后的零件坯料转移到模具。
f)整形或低温热成形：对零件形状进行精确整形，或者对形状复杂的零部件进行小变形量的低温热成形，提高零部件成形精度，即可得到最终的零部件成品。低温热成形过程和整形过程均为：当基板中Mn≤3.0wt％，热冲压温度范围450℃～760℃；当基板中3.0wt％＜Mn≤10.0wt％时，热冲压温度范围350℃～660℃；保压时间4s～8s；淬火冷速≥27℃/s，最好为27℃/s～60℃/s。
本方法公开的低温热整形/成形淬火与传统热成形工艺原理对比如图9所示；其中，Ms指代的线条表示传统热成形工艺中马氏体相变开始转变温度曲线，Ms＇指代的线条表示低温热成形工艺中马氏体相变开始转变温度曲线。B表示传统热成形工艺中贝氏体相变转变区域，B＇表示低温热成形工艺中贝氏体相变转变区域。P表示传统热成形工艺中珠光体相变转变区域，P＇表示低温热成形工艺中珠光体相变转变区域。F表示传统热成形工艺中铁素体相变转变区域。临界冷却从传统热成形工艺中的30℃/s，降至15℃/s。本方法整形或低温热成形工艺中，对零件形状进行精确整形，或者对形状复杂的零部件进行小变形量的热成形，能有效地提高零部件成形精度。从图9中可以看出，低温热成形工艺的热成形温度范围明显比传统热成形工艺低50℃～200℃，这主要是由于：其一，本方法中基板的热状态奥氏体的稳定性比较高，具有较低的Ms、及Bs和Fs析出温度右移，在低温热成形过程中不会析出贝氏体、铁素体或马氏体相，不会出现因混晶或多相组织而导致Zn容易渗透进晶界造成的脆性；其二，在较低的温度条件下，变形量限制在≤20％零件总变形量，甚至不发生变形的情况下，热成形不容易导致锌层裂纹的产生。
实施例1-30：本申请高耐蚀镀锌热成形硬化钢及其零部件以及制备方法具体如下所述。
(1)通过炼铁、炼钢、连铸、热轧、酸洗或酸轧、连续退火镀锌工序制备镀锌热成形硬化钢板或钢卷，其基板化学成分如表1所述。
表1：各实施例基板化学成分

表1中，余量为Fe和不可避免的杂质；对比例的钢种为22MnB5，其中数字22表示碳含量，即0.22wt％碳。
(2)用于热浸镀的镀液成分如表2所述，热浸镀工艺如表3所示，热浸镀后锌层结构如表4所示，热浸镀后热镀锌板力学性能如表5所示；其中实施例4热浸镀钢板镀层组织形貌如图2所示。
表2：各实施例的镀液成分/wt％

表2中，余量为Zn及不可避免的杂质。
表3：各实施例的热浸镀工艺

表4：各实施例所得热浸镀镀层结构

表4中镀层平均含量的余量为Zn及不可避免的杂质。
表5：各实施例所得镀锌热成形硬化钢板的力学性能

(3)各实施例的冷冲压、奥氏体化热处理及预冷却工艺如表6所示，冷却和热成形工艺如表7所示，零件镀层结构如表8所示，零件力学性能如表9所示。
表6：各实施例冷成形和奥氏体化热处理

表6中，第一次加热速率为室温～T1温度区间的加热速率，第二次加热速率为T1温度～保温温度的加热速率。
表6中，实施例1、2、10、11、12对应图3；实施例3、4、13、14、15对应图4；实施例5、16、17、18、19对应图5；实施例8、9、20、21、22对应图6；实施例23、24、25、26、27对应图7；实施例6、7、28、29、30对应图8。
表7：冷却和热成形工艺

表8：零件镀层结构

表9：零件机械性能、电极电位及镀层状态

Claims (7)

  1. 一种高耐蚀镀锌热成形硬化钢，其特征在于：包括基板和镀层；
    所述基板的成分及其质量百分含量为：C 0.12％～0.35％，Si 0.08％～2.12％，Mn 0.42％～10.00％，Al 0.03％～0.12％，Cr 0.02％～0.65％，Mo≤1.12％，Nb+V+Ti 0.02％～0.25％，B 0.0003％～0.005％，S≤0.012％，P≤0.08％，余量为Fe和不可避免的杂质；
    所述镀层的成分及其质量百分含量为：Al 0.15％～0.45％，Fe 0.05％～2.50％，La 0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，余量为Zn及不可避免的杂质；
    所述镀层包括镀锌层和扩散层，所述扩散层中含有抑制层；所述镀锌层的厚度为6μm～20μm，所述镀锌层主要由η相组成，所述镀锌层的成分含有：固溶Fe 0.08％～2.20％，Al 0.08％～0.45％，La 0.08％～1.4％和/或Ce 0.12％～2.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，Si/Mn≥1.1，Mg/Cr≥0.8；
    所述扩散层的厚度为2μm～4μm，占所述镀锌层的厚度≤40％，主要由αFe、Г相组成，所述扩散层中αFe≥80％，主要固溶元素的平均含量为：Al 0.34％～1.45％，La 0.1％～2.5％和/或Ce 0.2％～3.1％，Si+Mn≤15.0％，Mg+Cr≤2.4％；
    所述抑制层的厚度为100nm～200nm，所述抑制层的厚度占所述扩散层的厚度的5％～10％，所述抑制层的主要成分为Fe2Al5。
  2. 权利要求1所述高耐蚀镀锌热成形硬化钢的制备方法，其特征在于：
    将硬化钢板进行热浸镀；镀液成分及其质量百分含量为：Al0.12％～0.35％，Fe0.005％～0.06％，La0.08％～3.2％和/或Ce 0.12％～5.0％，Si+Mn≤3.0％，Mg+Cr≤3.5％，Si/Mn≥1.1、Mg/Cr≥0.8，其余为Zn及不可避免的杂质；
    所述热浸镀工艺为：硬化钢板入锌锅温度Ts 410℃～475℃，镀液温度Tz 420℃～475℃，热浸镀时间3s～10s；Ts、Tz的温度满足条件∣Ts-Tz∣≤40℃。
  3. 一种高耐蚀镀锌热成形硬化钢零部件，采用权利要求1所述的高耐蚀镀锌热成形硬化钢制备而成，其特征在于：包括基板和镀层；所述镀层由外表面到所述基板依次为表面氧化层、Zn-Fe合金基体层和扩散层；
    所述表面氧化层主要由Al2O3、MgO、MnO、SiO2、ZnO、CeO、La2O3中的一种或多种氧化物构成，厚度1.0μm～2.0μm，颗粒尺寸小于3μm；
    所述Zn-Fe合金基体层由αFe、Г相以及中间合金相组成，所述中间合金相包括ZnxSiyFez、ZnxMnyFez、ZnMg2；所述Zn-Fe合金基体层中Fe含量40wt％～70wt％、Zn含量20wt％～50wt％，厚度10μm～35μm。
  4. 权利要求3所述高耐蚀镀锌热成形硬化钢零部件的制备方法，其特征在于：镀锌热成形硬化钢经冷冲压预成形、修整、奥氏体化热处理；将奥氏体化热处理后的零件坯料转移到冷却装置，进行冷却和去氧化层；将冷却和去氧化层后的零件坯料再转移到模具，进行整形或低温热成形。
  5. 根据权利要求4所述的高耐蚀镀锌热成形硬化钢零部件的制备方法，其特征在于，所述冷却和去氧化层工艺为：采用水冷或者气冷方式将零件坯料温度降至铁素体或贝氏体的析出温度以上10℃～20℃。
  6. 根据权利要求4所述的高耐蚀镀锌热成形硬化钢零部件的制备方法，其特征在于，所述整形或低温热成形工艺为：保压时间4s～8s，淬火冷速≥27℃/s；当基板中Mn≤3.0wt％，热冲压温度范围450℃～760℃；当基板中3.0wt％＜Mn≤10.0wt％时，热冲压温度范围350℃～660℃。
  7. 根据权利要求4、5或6所述的高耐蚀镀锌热成形硬化钢零部件的制备方法，其特征在于，所述奥氏体化热处理工艺为：
    Ⅰ)当镀锌成形热硬化钢板的基板中0.42wt％≤Mn含量≤3.0wt％时，采用如下加热工艺：
    ①当镀锌成形热硬化钢板厚度0.7mm≤T≤1.4mm时，钢板保温温度和加热时间限定在ABCD范围内；室温～T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围500℃～620℃；其中，A点为850℃保温190s、B点为850℃保温750s、C点为940℃保温550s、D点为940℃保温150s；
    ②当镀锌成形热硬化钢板厚度1.4mm＜T≤2.5mm时，钢板保温温度和加热时间限定在EFGH范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围520℃～640℃；其中，E点为870℃保温240s、F点为870℃保温850s、G点为955℃保温600s、H点为955℃保温200s；
    ③当镀锌成形热硬化钢板厚度2.5mm＜T≤4.0mm时，钢板保温温度和加热时间限定在IJKL范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围540℃～660℃；其中，I点为890℃保温270s、J点为890℃保温880s、K点为960℃保温630s、L点为960℃保温230s；
    Ⅱ)当镀锌成形热硬化钢板的基板中3.0wt％＜Mn含量≤10.0wt％时，采用如下加热工艺：
    ①当镀锌成形热硬化钢板厚度0.7mm≤T≤1.4mm时，钢板保温温度和加热时间限定在A1B1C1D1范围内；室温～T1温度加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围500℃～620℃；其中，A1 点为750℃保温200s、B1点为750℃保温930s、C1点为840℃保温630s、D1点为840℃保温180s；
    ②当镀锌成形热硬化钢板厚度1.4mm＜T≤2.5mm时，钢板保温温度和加热时间限定在E1F1G1H1范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围520℃～640℃；其中，E1点为770℃保温270s、F1点为770℃保温980s、G1点为855℃保温680s、H1点为855℃保温230s；
    ③当镀锌成形热硬化钢板厚度2.5mm＜T≤4.0mm时，钢板保温温度和加热时间限定在I1J1K1L1范围内；室温至T1温度区间的加热速率Vr控制在3℃/s～7℃/s，T1温度～保温温度区间的加热速率Vr控制在6℃/s～18℃/s；其中T1温度范围540℃～660℃；其中，I1点为790℃保温330s、J1点为790℃保温1010s、K1点为870℃保温710s、L1点为870℃保温260s。
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