WO2024088378A1 - 一种光伏桩基用耐蚀钢及其制造方法 - Google Patents

一种光伏桩基用耐蚀钢及其制造方法 Download PDF

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WO2024088378A1
WO2024088378A1 PCT/CN2023/127065 CN2023127065W WO2024088378A1 WO 2024088378 A1 WO2024088378 A1 WO 2024088378A1 CN 2023127065 W CN2023127065 W CN 2023127065W WO 2024088378 A1 WO2024088378 A1 WO 2024088378A1
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corrosion
steel
resistant steel
rolling
temperature
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PCT/CN2023/127065
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English (en)
French (fr)
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宋凤明
温东辉
周庆军
陆敏
李育霖
华骏山
徐嘉春
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宝山钢铁股份有限公司
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Publication of WO2024088378A1 publication Critical patent/WO2024088378A1/zh

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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
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present disclosure relates to the field of low alloy steel manufacturing, and in particular to a corrosion-resistant steel that can be used for photovoltaic pile foundations and a manufacturing method thereof.
  • Chinese patent publication number CN101660099B relates to "high-strength low-alloy hot-rolled ferrite bainite weathering steel and its production method".
  • the weathering steel is designed with a higher Mn content and has a yield strength of 450MPa.
  • the corrosion resistance of the weathering steel is only at the level of conventional weathering steel and does not involve soil corrosion resistance.
  • Chinese patent application publication number CN1986864A relates to "a high-strength low-alloy atmospheric corrosion-resistant steel and its production method"
  • Chinese patent announcement number CN102168229B relates to "weathering steel plate and its manufacturing method”
  • Chinese patent application publication number CN107779740A relates to "hot-rolled steel strip with yield strength of 700MPa and its manufacturing method”.
  • the steel plates in these patents/patent applications have a higher strength of more than 450MPa, but they all use a higher Mn content in the composition design, and the cost is higher through the composite addition of strengthening elements such as Mo, Nb, V, and Ti.
  • the weather resistance level of these steel plates is also only equivalent to that of traditional weathering steel, that is, the relative corrosion rate is ⁇ 55%, which does not meet the requirements of soil corrosion resistance.
  • weathering steel in addition to high strength, is also developing towards high corrosion resistance and high toughness, and is required to have good machinability and lower cost.
  • Japanese patent application publication number JP10025550A relates to "corrosion-resistant steel”
  • Japanese patent application publication number JP2002363704A relates to "corrosion-resistant steel with excellent toughness in base material and heat-affected zone”
  • Chinese patent application publication number JP10025550A relates to "corrosion-resistant steel with excellent toughness in base material and heat-affected zone”.
  • Opening number CN102127717A involves "Cr-containing weathering steel with excellent toughness and high corrosion resistance".
  • the steel types involved in these patent applications all have better corrosion resistance and lower relative corrosion rate, but do not involve sulfate and chloride ion corrosion resistance; in addition, the content of Cr, Al, Ni and other elements in these steels is very high, which makes steelmaking difficult and the manufacturing cost high.
  • the sulfate ion concentration in the soil is in the range of 300-30000 mg/kg, and the chloride ion concentration is also in the range of 1500-8000 mg/kg.
  • the corrosion of steel materials is caused by a large amount of chloride and sulfate ions in the soil, which is significantly different from the use environment of conventional weathering steel.
  • Chinese patent application publication number CN102268613A relates to "a hot-rolled steel plate resistant to atmospheric corrosion for railway vehicles and a method for manufacturing the same".
  • the steel contains 0.01-0.04% P and also needs to add appropriate amounts of Ca, Mg, Ce and Sb. Higher P is not good for low-temperature toughness and formability, while the addition of Mg and Ce increases the difficulty of production, and the addition of Sb is not good for the human body and the environment.
  • Chinese patent application publication number CN109023071A relates to "a steel for buried structures resistant to neutral soil corrosion and a method for manufacturing the same".
  • the steel also contains 0.08-0.18% Sb.
  • Sb combined with Cu can form a Cu 2 Sb protective film on the surface of the steel, thereby improving the sulfuric acid dew point corrosion resistance.
  • Sb is obviously detrimental to the environment and the human body.
  • Sb is a typical toxic and harmful heavy metal element that produces chronic toxicity and potential carcinogenicity to humans and animals. With the improvement of environmental awareness in the whole society and the tightening of environmental protection policies, the production and application of Sb-containing steel will inevitably be subject to more restrictions.
  • the purpose of the present disclosure is to provide a corrosion-resistant steel suitable for photovoltaic pile foundations and a manufacturing method thereof.
  • the corrosion-resistant steel can meet the corrosion resistance requirements in various environments, especially has good corrosion resistance in soil corrosion environments with high concentrations of sulfate ions and chloride ions, and also has good atmospheric corrosion resistance.
  • the present disclosure provides a corrosion-resistant steel, which contains the following chemical components by weight percentage:
  • the contents of Cr and Al satisfy: 1.0 ⁇ Cr/Al ⁇ 4.0;
  • the corrosion-resistant steel further contains one or more of Ti, Nb and V, wherein Ti: 0.01-0.06%, Nb: 0.01-0.03% and/or V: 0.01-0.04%.
  • the corrosion-resistant steel further contains Sn and/or RE, wherein Sn: 0.01-0.12% and/or RE: 0.01-0.12%.
  • the content of Mn is 0.5-0.8%.
  • the content of Cu is 0.15-0.35%.
  • the content of Cr is 0.6-1.0%.
  • the corrosion-resistant steel does not contain Sb, Mg or Ce.
  • the microstructure of the corrosion-resistant steel is ferrite+pearlite and a small amount of bainite.
  • the microstructure of the corrosion-resistant steel is ferrite+pearlite and no more than 5% of bainite.
  • the corrosion rate of the corrosion-resistant steel relative to ordinary carbon steel is lower than 16.5%; in an atmospheric environment, the corrosion rate of the corrosion-resistant steel relative to ordinary carbon steel is ⁇ 55%.
  • the yield strength of the corrosion-resistant steel is ⁇ 345MPa, more preferably the yield strength is ⁇ 420MPa; the tensile strength is ⁇ 485MPa, more preferably the tensile strength is ⁇ 630MPa; the elongation A is ⁇ 20%, more preferably the elongation A is ⁇ 32%; the impact energy value at -40°C is ⁇ 160J, more preferably the impact energy value at -40°C is ⁇ 200J.
  • the corrosion-resistant steel disclosed in the present invention adopts a Cu-Cr-Al composition design and has good corrosion resistance in a soil corrosion environment with a sulfate ion concentration of 300 to 30,000 mg/kg and a chloride ion concentration of 1,500 to 8,000 mg/kg.
  • the corrosion-resistant steel disclosed in the present invention selectively adds an appropriate amount of V, Ti, and Nb on the basis of a relatively low content of C-Si-Mn to produce a precipitation strengthening effect, thereby further improving the strength and achieving good low-temperature toughness.
  • the corrosion-resistant steel disclosed in the present invention achieves a combination of corrosion resistance and high strength and high toughness at a low cost.
  • the corrosion-resistant steel disclosed in the present invention does not contain Sb and is more environmentally friendly.
  • the corrosion-resistant steel disclosed in the present invention has one or more of the following advantages:
  • the corrosion-resistant steel disclosed in the present invention has good corrosion resistance in a soil corrosion environment with a sulfate ion concentration of 300 to 30,000 mg/kg and a chloride ion concentration of 1,500 to 8,000 mg/kg (the corrosion resistance in the same corrosion environment is more than 6 times that of ordinary carbon steel, and the relative corrosion rate is lower than 16.5%), and the atmospheric corrosion resistance also reaches the level of conventional weathering steel (the corrosion rate relative to Q345B is lower than 55%), thereby meeting the corrosion resistance requirements in a variety of environments.
  • the corrosion-resistant steel disclosed in the present invention does not contain Sb, thus avoiding harm to the environment and human health, and is an environmentally friendly product.
  • the present disclosure also provides a method for manufacturing the above-mentioned corrosion-resistant steel, which comprises the following steps:
  • the heating of the casting is carried out in a heating furnace with a reducing atmosphere.
  • the casting temperature is above 1230°C and the holding time is 2 to 4 hours.
  • the rough rolling end temperature of the steel billet is above 1000°C, and the cumulative rough rolling reduction rate is ⁇ 80%; the finishing rolling adopts ferrite rolling process, the finishing rolling start temperature is ⁇ 950°C (preferably 920-950°C, more preferably 923-950°C), the finishing rolling final temperature is 820-880°C, and then cooling and coiling are carried out.
  • step 1) LF refining is used for smelting.
  • the soaking time is not less than 40 minutes.
  • the cooling rate is above 10°C/s, and the coiling temperature is 520-580°C.
  • LF refining is used in smelting, which reduces the RH link and further reduces the cost.
  • Controlled rolling and controlled cooling have a wider process window and simple process steps.
  • the rolled product does not require heat treatment, has a short production cycle, low cost, and can be implemented using existing steel rolling equipment.
  • the ferrite rolling process is adopted to avoid the rolling force fluctuation and plate shape difference problems of two-phase rolling.
  • the strip steel can obtain bainite structure at a cooling rate above 10°C, and with the coiling temperature, a matrix structure of ferrite + pearlite and a small amount of bainite can be obtained.
  • the yield strength of the steel produced by the method disclosed in the present invention meets the high strength requirement of more than 345 MPa, the tensile strength is ⁇ 485 MPa, the elongation A is ⁇ 20%, and the low-temperature impact energy value of -40°C is more than 160 J. At the same time, it also has good processing properties such as welding and cold bending, and has excellent elongation. It is particularly suitable for various cold forming processes in the pile foundation production process, and can be used in high-concentration sulfate ion and chloride ion corrosion environments such as soil, seawater, gas pipelines, etc.
  • FIG. 1 is a CCT phase transformation temperature curve of the steel according to the embodiment of the present disclosure.
  • FIG. 2 is a TTT phase transformation temperature curve of the steel according to the embodiment of the present disclosure.
  • FIG3 shows the microstructure of Example 8, in which the bainite content is about 2%.
  • plain carbon steel refers to Q345B steel, the composition of which is shown in the following table:
  • the corrosion rate in a soil corrosion environment is determined by a full immersion test.
  • the full immersion test is carried out according to GB 10124-1988 "Method for full immersion test of uniform corrosion of metal materials in laboratory", the test solution is 10.0% H2SO4 + 3.5 %NaCl, the test time is 24h, and the test temperature is 23 ⁇ 2°C.
  • the corrosion rate in the atmospheric environment is measured according to TB/T2375 "Cyclic Immersion Corrosion Test Method for Weathering Steel for railway Use", such as the method described in the Examples.
  • the yield strength, tensile strength and elongation A are measured according to GB/T 228.1
  • the -40°C impact energy value is measured according to GB/T 229
  • the transverse cold bending 2a and 180° cold bending are measured according to GB/T 232.
  • ferrite rolling process refers to a steel rolling process in which the strip steel is in the ferrite phase transformation zone during the finishing rolling stage, which is different from the conventional austenite zone rolling.
  • Conventional hot rolling and finishing rolling are all carried out in the austenite phase transformation zone at a higher temperature.
  • the strip steel is prone to enter the austenite-ferrite two-phase zone due to the decrease in temperature, which leads to drastic fluctuations in rolling force, which on the one hand damages the equipment and on the other hand causes poor plate shape.
  • Ferrite zone rolling can achieve better deformation because the temperature is lower and it is in the single-phase zone; in addition, since the rolling temperature of ferrite is low, the corresponding heating temperature is also low, thereby reducing energy consumption and reducing production costs.
  • the chemical composition design principle of the corrosion-resistant steel disclosed in the present invention is as follows:
  • Carbon (C) is an effective strengthening element in steel. When dissolved in the matrix, it has a solid solution strengthening effect. At the same time, C exists in the form of carbides in steel. When combined with alloying elements, it can play a role in precipitation strengthening and grain refinement. Therefore, the amount of C added should not be less than 0.03%. However, excessive C will form more carbides in the steel, which will act as a galvanic cell, promote corrosion, reduce the corrosion resistance of the steel, and be unfavorable for welding. Therefore, the C content should not be higher than 0.12%.
  • Si is generally added to deoxidize steel. It is also a corrosion-resistant element and has a solid solution strengthening effect. Therefore, the lower limit of Si content is controlled to 0.20%. However, a higher Si content will lead to deterioration of weldability and toughness of the heat-affected zone. Therefore, the upper limit of Si content is controlled to 0.50%.
  • Mn is an important strengthening element, which plays a role in solid solution strengthening and can improve the strength and toughness of steel.
  • Mn can also expand austenite, reduce the transformation temperature of supercooled austenite, promote the transformation of medium and low temperature strengthening structure in steel, and is beneficial to improve the strength of steel.
  • too much Mn content will increase the hardenability, thereby causing the weldability and toughness of the welding heat affected zone to deteriorate.
  • higher Mn also increases the cost. Therefore, the present disclosure limits the Mn content range to 0.4-0.9%, preferably 0.5-0.8%.
  • Phosphorus (P) is the main corrosion-resistant element in traditional atmospheric corrosion-resistant steel. It can promote the formation of a protective rust layer on the surface and effectively improve the atmospheric corrosion resistance of steel. However, P is prone to segregation at the grain boundaries, reducing the grain boundary binding energy and the toughness and plasticity of the steel. Moreover, the coexistence of P and Mn will aggravate the temper brittleness of the steel. The segregated P makes the steel plate prone to intergranular fracture and reduces the impact toughness of the steel plate. Moreover, P is not good for welding performance. Since the steel type disclosed in the present invention requires high toughness, P is controlled as an impurity element to minimize the P content in the steel. However, if the P content is controlled too low, it will increase the difficulty of steelmaking and manufacturing costs. Therefore, the P content is controlled to not exceed 0.018%.
  • S in steel is controlled as a harmful impurity element. S not only reduces the low temperature toughness of steel, but also promotes the anisotropy of the steel plate, which is detrimental to the cold forming performance. In addition, sulfide inclusions will significantly reduce the weather resistance of steel. Therefore, the steel grade of the present disclosure is designed to use an extremely low S content, which is controlled to be below 0.006%.
  • Aluminum (Al) Al is usually added to steel as a deoxidizer during the steelmaking process. Trace amounts of Al are also beneficial for grain refinement and improving the strength and toughness of steel. Adding appropriate amounts of Al increases the corrosion potential of steel, which is beneficial for inhibiting corrosion. At the same time, the formation and aggregation of nanoscale complex oxides containing Al and Si in the inner rust layer can increase the charge transfer resistance, thereby inhibiting the corrosion process.
  • Al will reduce the stability of austenite, reduce the supercooling of austenite, and cause the new phase nucleus to grow rapidly, thereby reducing hardenability and increasing the critical quenching rate.
  • Al is a ferrite-forming element. More Al will not only reduce the strength of the steel plate, but also increase the brittleness of ferrite in the steel, resulting in a decrease in the toughness of the steel. Therefore, the present disclosure controls the Al content to 0.2-0.8%.
  • Chromium (Cr) is a precious alloy element and an effective element for improving the corrosion resistance of steel plates. Cr forms a continuous solid solution with Fe in steel, which has a solid solution strengthening effect, and forms various types of carbides with C, such as M 3 C, M 7 C 3 and M 23 C 6 , which produce a secondary strengthening effect. Cr has a significant effect on improving the passivation ability of steel and can promote the formation of a dense passivation film or protective rust layer on the steel surface. Its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media. At the same time, the addition of Cr can effectively increase the self-corrosion potential of steel and improve the steel's resistance to corrosion. Atmospheric corrosion performance. However, the addition of too much Cr will increase the manufacturing cost. Therefore, in order to reduce the cost, the present disclosure controls the Cr content to 0.30-1.2%, preferably 0.6-1.0%.
  • Cu plays a major role in solid solution and precipitation strengthening in steel.
  • the electrochemical potential of Cu is higher than that of Fe, which can promote the formation of a dense rust layer on the steel surface, which is beneficial to the improvement of corrosion resistance.
  • an appropriate amount of Cu will combine with the residual S in the steel to form a Cu2S protective film, which can alleviate corrosion in a high sulfate corrosion environment.
  • too high Cu will not only damage the toughness of the welding heat affected zone, but also easily cause cracking during hot rolling, deteriorate the surface properties of the steel plate, and increase costs. Therefore, the present disclosure controls the Cu content to 0.10-0.50%, preferably 0.15-0.35%.
  • Ni is an element that expands austenite. Ni can improve low-temperature impact toughness by refining grains and reducing stacking fault energy; at the same time, grain refinement also has a fine grain strengthening effect. In addition, Ni is also an important element for improving the corrosion resistance of steel, which can promote the stability of the rust layer and improve the hot working brittleness problem caused by Cu. However, Ni is a precious element and can be added selectively (i.e., added or not added), and the content is controlled to be below 0.2%.
  • N Nitrogen
  • AlN can form nitrides with Al and Ti in steel. Fine nitride precipitates have the effect of pinning grain boundaries and thus can refine austenite grains. Higher N is easy to form AlN when combined with Al in steel, which significantly increases the number of nitrides in the steel.
  • AlN exists independently in steel as a non-metallic inclusion, it will destroy the continuity of the steel matrix.
  • the Al content is high, the amount of AlN formed is large and distributed in an aggregated manner, the degree of harm is even greater, and at the same time, oxides with poor plasticity are formed.
  • higher N is easy to enrich in defects and deteriorate low-temperature impact toughness. Therefore, the present disclosure requires that the N content be controlled below 0.0060%.
  • the steel disclosed in the present invention may further selectively add one or more of Nb, V, Ti, Sn and RE.
  • Titanium (Ti) is a strong ferrite-forming element and carbonitride-forming element, and is easy to form compounds with C, N, O, S, etc. Ti exists in steel mainly in the form of TiC or Ti(C, N).
  • the purpose of adding Ti in the present disclosure is mainly to utilize TiN to inhibit the growth of austenite grains and play a role in refining the structure; at the same time, it produces a precipitation strengthening effect during the cooling process.
  • Ti has the effect of preventing the recrystallization of deformed austenite and promoting the formation of granular bainite.
  • the precipitated Ti carbonitride particles can prevent the grain coarsening of the welding heat-affected zone and improve the welding performance.
  • the present disclosure controls the Ti content to be 0.01-0.06%.
  • Nb is a strong nitrogen carbide forming element. During the cooling process after rolling, it can combine with carbon and nitrogen in steel to form intermediate phases such as NbC, Nb (CN) and NbN. The fine carbide particles formed can refine the structure, produce fine grain strengthening and precipitation strengthening, and significantly improve the strength of the steel plate. At the same time, the refinement of the structure is conducive to improving the toughness of the steel plate. In addition, Nb can inhibit the expansion of the austenite interface and increase the recrystallization temperature of the steel, which can be used in a more Rolling in the non-recrystallization zone is achieved at high temperature. Therefore, adding an appropriate amount of Nb to the steel is beneficial to improving the strength.
  • Nb content is high, coarse carbonitride particles will be formed at the grain boundary, which will deteriorate the impact toughness.
  • Nb is a precious alloying element. Therefore, when adding Nb, the Nb content is controlled to 0.01-0.03%.
  • V Vanadium (V): V is a strong carbonitride-forming element, which can precipitate during phase transformation, has solid solution strengthening and carbonitride precipitation strengthening effects in steel, and increases tempering stability, thereby improving strength. Therefore, when adding V, the V content is controlled to 0.01-0.04%.
  • Tin (Sn) Sn has a good corrosion inhibition effect in steel. At the same time, Sn ions can dissolve in the anode to inhibit the anode reaction and reduce the formation of ⁇ -FeOOH that is unfavorable to corrosion resistance. Therefore, when adding Sn, the Sn content is controlled to 0.01-0.12%.
  • RE Rare earth
  • RE/Fe intermetallic compounds and solid-solution rare earth formed by RE in steel are hydrolyzed in the thin corrosion film and precipitated at the cathode with a higher pH value, thereby playing a corrosion inhibition role. Therefore, when adding RE, the RE content is controlled to 0.01-0.12%.
  • the corrosion-resistant steel disclosed in the present invention has good corrosion resistance in a soil corrosion environment with a sulfate ion concentration of 300 to 30,000 mg/kg and a chloride ion concentration of 1,500 to 8,000 mg/kg, and at the same time, the atmospheric corrosion resistance is equivalent to that of conventional weathering steel, especially meeting the corrosion requirements of photovoltaic pile foundations in soil corrosion environments with high concentrations of sulfate ions and chloride ions, and can also be used in equipment such as seawater and gas pipelines that are corroded by chloride ions and sulfate ions, as well as conventional steel structure production that requires atmospheric corrosion resistance.
  • the corrosion-resistant steel disclosed in the present invention also has good forming performance and low-temperature impact toughness, meets the use and processing requirements of photovoltaic pile foundation steel, and is also suitable for seawater environments with high chloride ion content and gas pipelines with high sulfate ions.
  • the corrosion-resistant steel disclosed in the present invention adopts a Cu-Cr-Al component system design, and achieves a significant improvement in corrosion resistance in a soil corrosion environment with high concentrations of sulfate and chloride ions through the synergistic effect of multiple corrosion-resistant elements.
  • Cu is an effective element for improving sulfate ion corrosion.
  • Cr is a commonly used corrosion-resistant element. In addition to solid solution strengthening and improving hardenability, the addition of Cr also increases the corrosion potential.
  • the addition of Cu and Cr alone cannot achieve the improvement of corrosion resistance in soil corrosion environments with high concentrations of sulfate ions and chloride ions.
  • Cu is a must-add element in acid-resistant steel at present, but at the same time, about 0.1% Sb must be added to obtain the expected corrosion resistance.
  • the present disclosure abandons the addition of Sb from the perspective of environment and human health.
  • relying solely on Cr and Cu cannot obtain excellent corrosion resistance in soil environments with high concentrations of sulfate ions and chloride ions.
  • Al itself is relatively active and easily reacts with oxygen in the air.
  • Al has a passivation effect in the natural environment and can form a layer of Al 2 O 3 film on the surface of steel, thereby achieving corrosion resistance. Therefore, Al is usually added to steel as a deoxidizing element.
  • the inventors have found that Cr and Al have a synergistic effect in steel, which can significantly improve the corrosion resistance of steel in high-concentration sulfate and chloride ion environments.
  • the mechanism is: on the one hand, the combined addition of Cr and Al significantly increases the corrosion potential of steel, with an increase of about 200 mA, while 1% Cr only increases the corrosion potential of steel by 40 mA; on the other hand, Cr and Al form intermetallic compounds Fe2CrAl and Cr8Al5 in steel. In a high sulfate and chloride ion environment, these two compounds gather on the surface of steel, improving the corrosion resistance of steel. The increase in corrosion potential reduces the corrosion current and reduces the occurrence of corrosion.
  • the Cr and Al intermetallic compounds protect the surface layer and hinder the penetration of corrosion, playing an isolating role. It is under this synergistic effect of Cr and Al that the corrosion resistance in a high sulfate and chloride ion environment is obtained.
  • Cu and Cr are combined with an appropriate amount of Al to obtain excellent corrosion resistance in a soil corrosion environment with a sulfate ion concentration of 300 to 30,000 mg/kg and a chloride ion concentration of 1,500 to 8,000 mg/kg.
  • the inventors found that when the contents of Cu, Cr and Al satisfy the relationship: 1.0 ⁇ Cr/Al ⁇ 4.0 and Cu+1.22Cr+35.3Al ⁇ 9.2, the corrosion resistance in the above environment is more than 6 times that of ordinary carbon steel (relative corrosion rate is less than 16.5%); and it has atmospheric corrosion resistance equivalent to that of conventional weathering steel, and the corrosion rate relative to ordinary carbon steel is ⁇ 55%, thereby meeting the corrosion resistance requirements in a variety of environments.
  • the new corrosion-resistant component system disclosed in the present invention avoids the toxic pollution of Sb in conventional sulfate ion corrosion-resistant steel to the environment and human body, and at the same time, the corrosion resistance is greatly improved, and it is an environmentally friendly product.
  • the corrosion-resistant steel disclosed in the present invention utilizes the solid solution strengthening of C and Mn and the precipitation strengthening and fine grain strengthening effects of V, Nb and Ti to obtain a yield strength of more than 345 MPa, and at the same time has good low-temperature impact toughness (the low-temperature impact energy value at -40°C exceeds 160J), an elongation of more than 20%, achieving a match between high corrosion resistance and high toughness, and has good forming properties, meeting the use requirements of pile foundation steel.
  • the matrix structure of the corrosion-resistant steel of the present application is mainly ferrite + pearlite, and there is a small amount (no more than 5%) of bainite.
  • the method for manufacturing corrosion-resistant steel disclosed in the present invention comprises the following steps:
  • the heating of the casting is carried out in a heating furnace with a reducing atmosphere.
  • the casting temperature is above 1230°C and the holding time is 2 to 4 hours.
  • the rough rolling finishing temperature of the steel billet is above 1000°C, and the cumulative rough rolling reduction rate is ⁇ 80%; the finishing rolling adopts ferrite rolling process, the finishing rolling start temperature is ⁇ 950°C (preferably 920-950°C, more preferably 923-950°C), the final rolling temperature is 820-880°C, and then cooling and coiling are carried out.
  • step 1) LF refining is used for smelting.
  • the soaking time is not less than 40 minutes.
  • step 3 the cooling rate is above 10°C/s, and the coiling temperature is 520-580°C.
  • the heating of the ingot requires a reducing atmosphere in the heating furnace and the ingot outlet temperature should be controlled above 1230°C.
  • the heating temperature is selected to be above 1230°C
  • the holding time is 2 to 4 hours
  • the soaking holding time is preferably not less than 40 minutes.
  • the ingot can be hot-charged into the furnace after the casting is completed, that is, after confirming that there is no quality problem on the surface of the ingot, it is directly transported from the casting area to the heating furnace through the roller for heating and heat preservation, thereby reducing energy consumption.
  • the rolling adopts hot rolling.
  • the method disclosed in the present invention requires that the end temperature of rough rolling is not less than 1000°C, the cumulative reduction rate of rough rolling is ⁇ 80%, and the finishing rolling adopts ferrite rolling process.
  • the starting temperature of finishing rolling is controlled to be ⁇ 950°C (preferably 920-950°C, more preferably 923-950°C), and the ending temperature of finishing rolling is 820-880°C.
  • the corrosion-resistant steel disclosed in the present invention adds more Cr and Al elements, both of which are ferrite-forming elements, which reduce the stability of low austenite and reduce the supercooling of austenite, thereby improving the stability of ferrite formation.
  • the starting temperature of ferrite formation under continuous cooling conditions is about 945°C; in order to avoid sudden changes in rolling force caused by rolling in the two-phase region, the present invention requires the use of a ferrite rolling process in the finishing stage. According to the ferrite formation temperature requirement, the finishing rolling start temperature is controlled not to be higher than 950°C.
  • the finishing rolling end temperature is controlled to be 820-880°C.
  • the method disclosed in the present invention requires the coiling temperature to be controlled at 520-580°C. If the coiling temperature is too high, the steel will enter the pearlite phase transformation zone, while if it is too low, it will not be conducive to the formation of more bainite structure. From the phase diagram, the steel type disclosed in the present invention forms ferrite structure in a large range; pearlite begins to form after the temperature drops to 740°C. As the temperature decreases, regardless of the cooling rate, bainite phase transformation will occur, forming a small amount of bainite structure.
  • Figure 3 is the microstructure morphology of Example 8, where The bainite content is about 2%.
  • the matrix structure of the steel disclosed in the present invention is mainly ferrite + pearlite, supplemented by no more than 5% of bainite structure.
  • water cooling can be performed immediately after rolling to refine the structure as much as possible to form a fine ferrite + pearlite structure.
  • Pearlite in the matrix is a high C component, which is easy to form a galvanic cell in the matrix and promote the occurrence of corrosion.
  • the formation of pearlite in the matrix should be minimized.
  • the post-rolling cooling rate is required to control more than 10°C/s to reduce the formation of pearlite during the cooling process; but at the same time, it is required to control the coiling temperature not to exceed 600°C to avoid the formation of pearlite in the steel coil during the subsequent slow cooling process, which is not conducive to corrosion resistance.
  • Table 2 shows the composition of the steel of Examples 1-12 and Comparative Examples 1-4.
  • Table 3 shows the production process parameters of the steel of Examples 1-12 and Comparative Examples 1-4.
  • Table 4 shows the performance parameters of the steel of Examples 1-12 and Comparative Examples 1-4.
  • the steels of Comparative Examples 1 and 2 are highly corrosion-resistant and weathering steels, wherein the steel of Comparative Example 1 is disclosed in Chinese Patent Application Publication No. CN102127717A, and the steel of Comparative Example 2 is disclosed in Chinese Patent Application Publication No. CN102268613A.
  • the steels of Comparative Examples 3 and 4 are 450MPa grade conventional weathering steels, wherein the steel of Comparative Example 3 is disclosed in Chinese Patent Application Publication No. CN109023071A.
  • the microstructures of the steel plates of Comparative Examples 1-4 are mainly ferrite + pearlite structures.
  • Comparative Example 1 is designed with a high Cr-Ni component, in which the Cr content is 2.5-7.0% and the Ni content is 0.2-1.2%, which is much higher than the steel types of Examples 1-12.
  • Comparative Example 2 not only contains Sb, but also contains a relatively high P, and requires the addition of Mg and Ce at the same time.
  • the low-temperature toughness and forming properties of Comparative Example 2 are not good, and the addition of Mg and Ce increases the difficulty of production.
  • Sb is a typical toxic and harmful heavy metal element, which produces chronic toxicity and potential carcinogenicity to humans and animals.
  • the content of Cr and Mo in Comparative Example 3 is also very high.
  • the corrosion rate in the atmospheric environment is tested according to TB/T2375 "Test method for periodic immersion corrosion of weathering steel for railway use”; the simulated soil environment is a high sulfate ion + chloride ion corrosion environment (sulfate ion concentration is 300-30000 mg/kg, chloride ion concentration is 1500-8000 mg/kg), the full immersion test is carried out according to GB 10124-1988 "Metallic Materials Laboratory Uniform Corrosion Full Immersion Test Method", the test solution is 10.0% H2SO4 +3.5%NaCl, the test time is 24h, and the test temperature is 23 ⁇ 2°C.
  • the corrosion resistance of Examples 1-12 is more than 6 times that of ordinary carbon steel (Q345B), and the corrosion rate relative to ordinary carbon steel is less than 16.5%; the atmospheric corrosion resistance also reaches the level of conventional weathering steel, and the corrosion rate relative to ordinary carbon steel is less than 55%. It has good corrosion resistance in the soil corrosion environment (simulated soil environment) with a sulfate ion concentration of 300-30000 mg/kg and a chloride ion concentration of 1500-8000 mg/kg and in the atmospheric environment, thereby meeting the corrosion resistance requirements in various environments.
  • Comparative Examples 1 and 2 also have corrosion resistance that exceeds that of ordinary weathering steel in the atmospheric environment, the relative corrosion rate in the simulated soil environment of high sulfate ion + chloride ion is much higher than that of the steel of Examples 1-12, indicating that its corrosion resistance does not meet the requirements of the present disclosure, and the low-temperature impact toughness of Comparative Examples 1 and 2 is poor; Comparative Examples 3 and 4 are similar.
  • the steels of Examples 1-12 have a yield strength of more than 345 MPa, an elongation of more than 20%, and an impact energy value of more than 160 J at -40°C, and have high strength and toughness.
  • Example 1 In addition, the process of Examples 1-12 adopts a hot rolling process, and the ferrite rolling process is adopted in the finishing rolling stage.
  • the post-rolling layer cooling process it is only required to control the cooling rate above 10°C/s, which has a wider process window, reduces the production difficulty, and is convenient for on-site production.
  • Comparative Example 1 requires controlling the post-rolling cooling rate to 5-20°C/s, and has a clear limit on the cooling rate range, which obviously increases the difficulty of controlling water cooling;
  • Comparative Example 2 requires air cooling for 1-35 seconds after final rolling at 880-950°C, and then cooling to 550-690°C at a cooling rate of more than 10°C/s for coiling.
  • the cooling process of air cooling and water cooling after rolling obviously increases the production difficulty, especially air cooling leads to an extension of production time, affecting the production rhythm.

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Abstract

本公开涉及一种耐蚀钢及其制造方法，该耐蚀钢以重量百分比计含有如下化学成分：C 0.03～0.12％，Si 0.20～0.50％，Mn 0.4～0.9％，P≤0.018％，S≤0.006％，Al 0.2～0.8％，Cu 0.10～0.50％，Cr 0.3～1.2％，Ni≤0.20％，N≤0.006％，余量为Fe和其它不可避免的杂质元素，且，Cr和Al的含量满足1.0≤Cr/Al≤4.0，Cu、Cr和Al的含量满足Cu+1.22Cr+35.3Al≥9.2。本公开的耐蚀钢在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中的耐腐蚀性能达到普碳钢的6倍以上(相对普碳钢的腐蚀率低于16.5％)，同时在大气环境中相对普碳钢的腐蚀率≤55％，满足多种环境中的耐腐蚀性能要求。

Description

一种光伏桩基用耐蚀钢及其制造方法 技术领域
本公开涉及低合金钢制造领域，具体涉及一种可用于光伏桩基的耐蚀钢及其制造方法。
背景技术
钢的腐蚀是一个普遍而严重的问题。在土壤中，由于微生物、水、氧气及各种矿物的存在，对钢结构也存在一定的腐蚀。特别是一些地区由于在古生代为海洋环境，土壤中含有大量的硫酸盐和氯离子，威胁钢结构的使用安全。
为有效延长设备使用寿命、降低使用成本，耐蚀钢应运而生。在美国Corten钢的基础上，各国根据资源和使用要求开发了一系列的耐蚀钢产品。在强度和性能上从早期的235MPa级别发展到450MPa级别的高强度耐候钢及耐蚀性能更好的高耐蚀钢，同时也产生了许多相关的钢种专利。
中国专利公告号CN101660099B涉及“高强度低合金热轧铁素体贝氏体耐候钢及其生产方法”。该耐候钢采用较高的Mn含量设计，屈服强度达到450MPa级别。然而，该耐候钢的耐腐蚀性能仅为常规耐候钢水平，不涉及耐土壤腐蚀。
中国专利申请公开号CN1986864A涉及“一种高强度低合金耐大气腐蚀钢及其生产方法”，中国专利公告号CN102168229B涉及“耐候钢板及其制造方法”，中国专利申请公开号CN107779740A涉及“屈服强度700MPa级耐大气腐蚀热轧钢带及制造方法”。这些专利/专利申请中的钢板具有450MPa以上的更高强度，但在成分设计上均采用了较高的Mn含量，并通过Mo、Nb、V、Ti等强化元素的复合添加，成本更高。这些钢板的耐候水平同样仅与传统的耐候钢相当，即相对腐蚀率≤55％，不满足耐土壤腐蚀性能要求。
为满足更多工况条件下的应用要求，耐候钢除了高强度外，还朝着高耐蚀、高韧性方向发展，并要求具有良好的可加工性能和更低的成本。
日本专利申请公开号JP10025550A涉及“耐腐蚀钢”、日本专利申请公开号JP2002363704A涉及“母材和热影响区具有优异韧性的耐腐蚀钢”，中国专利申请公 开号CN102127717A涉及“韧性优良的高耐蚀性含Cr耐候钢”。这几个专利申请涉及的钢种均具有更好的耐腐蚀性能，相对腐蚀率更低，但不涉及耐硫酸根、氯离子腐蚀性能；并且，这些钢中的Cr、Al、Ni等元素含量很高，炼钢难度大、制造成本高。
在高硫酸根、高氯离子的土壤腐蚀环境中，土壤中的硫酸根离子浓度在300～30000mg/kg范围内，氯离子浓度也达到1500～8000mg/kg范围。钢材料的腐蚀是土壤中大量氯离子和硫酸根离子导致的，与常规的耐候钢的使用环境显著不同。
中国专利申请公开号CN102268613A涉及“一种铁路车辆用耐大气腐蚀热轧钢板及其制造方法”。虽然该专利申请关注到了硫酸根和氯离子腐蚀，但所述钢中除了含有0.01～0.04％的P外，还需要添加适量的Ca、Mg、Ce和Sb。较高的P对低温韧性和成形性能不利，而Mg和Ce的添加则增加了生产难度，同时Sb的添加对人体和环境不利。
中国专利申请公开号CN109023071A涉及“一种耐中性土壤腐蚀埋地结构用钢及其制造方法”，该钢中除了含有较高Cr(2.0～3.5％)、Ni(0.2～0.4％)和Mo(0.3～0.5％)外，还含有0.08～0.18％的Sb。Sb与Cu结合能够在钢材表面形成Cu2Sb保护膜，从而改善硫酸露点腐蚀性能。但Sb的加入显然对环境和人体不利。Sb属于一种典型的有毒有害重金属元素，对人体和动物体产生慢性毒性及潜在致癌性。随着全社会环保意识的提高及环保政策的加严，含Sb钢的生产及应用必然受到更多的限制。
从与现有专利的对比可发现，当前的耐候钢，无论是常规水平的耐候钢还是高耐蚀的耐候钢，其耐腐蚀性能主要针对的是大气腐蚀环境，不适用于高硫酸根、高氯离子的土壤腐蚀环境。虽然现有一些针对类似土壤腐蚀环境的耐候钢，但其中往往添加了对环境和人体健康不利的Sb元素。
发明内容
本公开的目的在于提供一种适用于光伏桩基的耐蚀钢及其制造方法。所述耐蚀钢可满足多种环境下的耐腐蚀性能要求，特别是在高浓度硫酸根离子和氯离子的土壤腐蚀环境中具有良好的耐腐蚀性，同时还具有良好的耐大气腐蚀性。
为达到上述目的，本公开提供一种耐蚀钢，其以重量百分比计含有如下化学成分：
C：0.03～0.12％，Si：0.20～0.50％，Mn：0.4～0.9％，P≤0.018％，S≤0.006％，Al：0.2～0.8％，Cu：0.10～0.50％，Cr：0.3～1.2％，Ni≤0.20％，N≤0.006％，余量为Fe和其它不可避免的杂质元素；
其中，Cr和Al的含量满足：1.0≤Cr/Al≤4.0；
Cu、Cr和Al的含量满足：Cu+1.22Cr+35.3Al≥9.2。
优选地，耐蚀钢还包含Ti、Nb和V中的一种以上，其中，Ti：0.01～0.06％、Nb：0.01～0.03％和/或V：0.01～0.04％。
优选地，耐蚀钢还包含Sn和/或RE，其中，Sn：0.01～0.12％和/或RE：0.01～0.12％。
优选地，Mn的含量为0.5～0.8％。
优选地，Cu的含量为0.15～0.35％。
优选地，Cr的含量为0.6～1.0％。
优选地，耐蚀钢不含Sb、Mg或Ce。
优选地，耐蚀钢的显微组织为铁素体+珠光体及少量的贝氏体。
优选地，耐蚀钢的显微组织为铁素体+珠光体及不超过5％的贝氏体。
优选地，在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中，所述耐蚀钢相对普碳钢的腐蚀率低于16.5％；在大气环境中，所述耐蚀钢相对普碳钢的腐蚀率≤55％。
优选地，耐蚀钢的屈服强度≥345MPa，更优选屈服强度≥420MPa；抗拉强度≥485MPa，更优选抗拉强度≥630MPa；延伸率A≥20％，更优选延伸率A≥32％；-40℃冲击功值≥160J，更优选-40℃冲击功值≥200J。
本公开的耐蚀钢采用了Cu-Cr-Al成分设计，在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中具有良好的耐腐蚀性能。优选地，本公开的耐蚀钢在较低含量的C-Si-Mn的基础上通过选择性添加适量的V、Ti、Nb以产生析出强化作用，由此进一步提高了强度并实现了良好的低温韧性。本公开的耐蚀钢在低成本的基础上实现了耐蚀和高强、高韧的结合。另外，本公开的耐蚀钢不含Sb，对环境更为友好。
因此，本公开的耐蚀钢具有如下优点中的一种以上：
1.本公开的耐蚀钢在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中具有良好的耐腐蚀性能(同样腐蚀环境中的耐腐蚀性能达到普碳钢的6倍以上，相对腐蚀率低于16.5％)，耐大气腐蚀性能也达到常规耐候钢水平(相对Q345B的腐蚀率低于55％)，从而满足多种环境中的耐腐蚀性能要求。
2.本公开的耐蚀钢力学性能优良，屈服强度≥345MPa，抗拉强度≥485MPa，延 伸率A≥20％，-40℃低温冲击功值≥160J；同时，本公开的耐蚀钢的冷弯性能优良，满足D＝2a、180°的冷弯要求。
3.本公开的耐蚀钢不含有Sb，避免了对环境和人体健康的危害，属于环境友好型产品。
本公开还提供一种制造上述耐蚀钢的方法，其包括如下步骤：
1)冶炼、铸造
2)铸坯加热
铸坯加热在还原性气氛的加热炉中进行，铸坯出炉温度为1230℃以上，保温时间为2～4h；
3)轧制
采用热连轧，钢坯的粗轧结束温度为1000℃以上，粗轧累计压下率≥80％；精轧采用铁素体轧制工艺，精轧开始温度≤950℃(优选920-950℃，更优选为923-950℃)，精轧终轧温度为820～880℃，然后进行冷却和卷取。
优选地，在步骤1)中，冶炼采用LF精炼。
优选地，在步骤2)中，均热保温时间不小于40min。
优选地，在步骤3)中，冷速为10℃/s以上，卷取温度为520～580℃。
本公开的方法具有如下优点中的一种以上：
1.冶炼采用LF精炼，减少了RH环节，进一步降低了成本。
2.控轧控冷，具有更宽的工艺窗口，工艺步骤简单。
3.轧态交货无需热处理，生产周期短、成本较低，利用现有轧钢设备即可实施。
4.采用铁素体轧制工艺，避免了两相区轧制的轧制力波动及板形差问题。带钢在10℃以上的冷速下均可获得贝氏体组织，配合卷取温度，可以获得铁素体+珠光体及少量贝氏体的基体组织。
5.由本公开的方法生产的钢的屈服强度满足345MPa以上的高强度要求，抗拉强度≥485MPa，延伸率A≥20％，-40℃低温冲击功值在160J以上，同时还具有良好的焊接、冷弯等加工性能，延伸率优良，特别适用于桩基生产过程中的各种冷成形加工，可以应用于高浓度硫酸根离子、氯离子腐蚀环境如土壤、海水、煤气管道等。
附图说明
图1为本公开实施例钢的CCT相变温度曲线。
图2为本公开实施例钢的TTT相变温度曲线。
图3为实施例8的微观组织形貌，其中贝氏体含量约为2％。
具体实施方式
在本公开中，普碳钢是指Q345B钢，其成分如下表所示：
表1.普碳钢Q345B的化学成分(重量百分比/％)
在本公开中，土壤腐蚀环境(硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg)中的腐蚀率通过全浸试验测定。全浸试验根据GB 10124-1988“金属材料实验室均匀腐蚀全浸试验方法”进行，试验溶液为10.0％H2SO4+3.5％NaCl，试验时间为24h，试验温度23±2℃。
在本公开中，大气环境下的腐蚀率根据TB/T2375“铁路用耐候钢周期浸润腐蚀试验方法”测定，例如实施例中记载的方法。
在本公开中，屈服强度、抗拉强度、延伸率A依据GB/T228.1测定，-40℃冲击功值依据GB/T 229测定，横向冷弯2a、180°冷弯依据GB/T 232测定。
在本公开中，“铁素体轧制工艺”是指精轧阶段带钢均处于铁素体相变区间的一种轧钢工艺，不同于常规的奥氏体区轧制。常规的热轧精轧，都是在奥氏体相变区进行，温度更高。但在精轧末端带钢由于温度的降低易进入奥氏体-铁素体两相区，从而导致轧制力的剧烈波动，一方面损伤设备，同时导致板形不佳。而铁素体区轧制由于温度更低，并处于单相区轧制，所以能够获得更好的变形；另外由于铁素体的轧制温度低，所以相应的加热温度也低，从而减少了能耗，降低生产成本。
本公开的耐蚀钢的化学成分设计原理如下：
碳(C)：C是钢中有效的强化元素，溶入基体时具有固溶强化的作用。同时，C在钢中以碳化物的形式存在，与合金元素结合可以发挥析出强化和细化晶粒的作用。因此，C的添加量不应低于0.03％。然而，过量的C会在钢中形成较多的碳化物起到原电池的作用，会促进腐蚀的进行从而降低钢的耐腐蚀性能，且不利于焊接。因此，C的含量不应高于0.12％。
硅(Si)：Si一般是为了对钢进行脱氧而添加的元素，同时也是耐蚀元素，并具有固溶强化作用。因此，控制Si含量的下限为0.20％。然而，较高的Si含量会导致可焊性和焊接热影响区韧性恶化。因此，控制Si含量的上限为0.50％。
锰(Mn)：Mn是重要的强韧化元素，起到固溶强化的作用，可以提高钢的强度和韧性。同时，Mn还可以扩大奥氏体，能降低过冷奥氏体的转变温度，促进钢中中低温强化组织的转变，有利于钢强度的提高。但是，Mn含量过多会使淬透性增大，从而导致可焊性和焊接热影响区韧性恶化，同时较高的Mn也增加成本。因此，本公开将Mn含量范围限定为0.4～0.9％，优选0.5～0.8％。
磷(P)：P是传统耐大气腐蚀钢中主要的耐蚀元素，能够促进表面保护性锈层的形成，有效提高钢的耐大气腐蚀性能。但是，P易在晶界处产生偏析，降低晶界结合能及钢的韧性及塑性。而且，P与Mn共存将加剧钢的回火脆性，偏聚的P使得钢板易发生沿晶断裂，降低钢板的冲击韧性。而且，P对焊接性能不利。由于本公开的钢种要求高韧性，所以将P作为杂质元素控制，尽量降低钢中P的含量。然而，如果控制P的含量过低会增加炼钢难度和制造成本。因此，将P含量控制为不超过0.018％。
硫(S)：在本公开中，将钢中的S作为有害杂质元素控制。S不仅会降低钢的低温韧性，而且会促进钢板的各向异性，对冷成形性能不利。并且，硫化物夹杂会使钢的耐候性能也明显降低。因此，本公开钢种设计采用极低的S含量，将其控制在0.006％以下。
铝(Al)：在炼钢过程中Al通常作为脱氧剂在钢中添加，微量的Al同时有利于细化晶粒，改善钢材的强韧性能。添加适当的Al使钢的腐蚀电位提高，有利于抑制腐蚀。同时，含Al和Si的纳米尺度的复杂氧化物在内锈层中的形成和聚集可增加电荷传质电阻，从而抑制腐蚀进程。但是，Al会降低奥氏体稳定性、减少奥氏体过冷度，使新相晶核快速长大，从而降低淬透性，提高临界淬火速度。并且，Al是铁素体形成元素，较多的Al不仅会降低钢板强度，还使钢中铁素体脆性增加而导致钢的韧性降低。因此，本公开将Al含量控制为0.2～0.8％。
铬(Cr)：Cr为贵重合金元素，也是提高钢板耐腐蚀性能的有效元素。Cr在钢中与Fe形成连续固溶体，具有固溶强化效果，并与C形成多种类型的碳化物如M3C、M7C3和M23C6等，产生二次强化效应。Cr对改善钢的钝化能力具有显著的效果，可促进钢表面形成致密的钝化膜或保护性锈层，其在锈层内的富集能有效提高锈层对腐蚀性介质的选择性透过特性。同时，Cr的加入能有效提高钢的自腐蚀电位，提高钢的耐 大气腐蚀性能。但是，过多Cr的加入将提高制造成本。因此，从降低成本考虑，本公开将Cr含量控制为0.30～1.2％，优选为0.6～1.0％。
铜(Cu)：Cu在钢中主要起固溶和沉淀强化作用。同时，Cu的电化学电位高于Fe，能促进钢表面致密性锈层的形成，有利于耐腐蚀性能的改善。同时，适量的Cu会与钢中残留的S结合，形成Cu2S保护膜，可缓解高硫酸根腐蚀环境下的腐蚀。但是，过高的Cu不仅会损害焊接热影响区韧性，而且热轧时易发生网裂，恶化钢板的表面性能，且增加成本。因此，本公开将Cu含量控制为0.10～0.50％，优选为0.15～0.35％。
镍(Ni)：Ni为扩大奥氏体形成元素。Ni可以通过细化晶粒及降低层错能提高低温冲击韧性；同时晶粒细化也具有细晶强化作用。此外，Ni也是提高钢耐腐蚀性能的重要元素，能够促进锈层的稳定并改善Cu引起的热加工脆性问题。但是，Ni为贵重元素，可以选择性添加(即，添加或不添加)，并控制含量在0.2％以下。
氮(N)：N在钢中可以与Al和Ti形成氮化物。细小的氮化物析出物具有钉轧晶界的作用从而可以细化奥氏体晶粒。较高的N在钢中与Al结合易形成AlN，从而使钢中的氮化物数量显著增多。AlN作为一种非金属夹杂物独立存在于钢中时，会破坏钢基体的连续性。尤其是Al含量较高时，所形成的AlN数量较多且呈聚集分布，危害程度更甚，并同时形成塑性较差的氧化物。而且，较高的N易于在缺陷处富集，恶化低温冲击韧性。因此，本公开要求控制N含量在0.0060％以下。
除了上述元素外，为了进一步改善性能，本公开的钢种还可以进一步选择性添加Nb、V、Ti、Sn和RE中的一种以上。
钛(Ti)：Ti是强铁素体形成元素及碳氮化物形成元素，易与C、N、O、S等形成化合物。Ti在钢中主要以TiC或Ti(C，N)的形式存在。本公开中添加Ti的目的主要是利用TiN抑制奥氏体晶粒长大，起到细化组织的作用；同时在冷却过程中产生析出强化作用。此外，Ti有阻止形变奥氏体再结晶和促进粒状贝氏体形成的作用，析出的Ti的碳氮化物颗粒能阻止焊接热影响区的晶粒粗化，改善焊接性能。然而，Ti含量过高时，在高温下氮化钛颗粒容易长大并团聚，会损害钢的塑性及韧性。因此，在添加Ti时，本公开控制Ti的含量为0.01～0.06％。
铌(Nb)：Nb是强的氮碳化物形成元素，在轧后冷却过程中能够与钢中的碳、氮结合形成NbC、Nb(CN)和NbN等中间相。所形成的微细碳化物颗粒能细化组织，产生细晶强化和析出强化作用，显著提高钢板的强度。同时，组织的细化有利于钢板韧性的提高。另外，Nb能够抑制奥氏体界面的扩展，提高钢的再结晶温度，可以在更 高温度下实现非再结晶区轧制。因此，钢中加入适量的Nb有利于强度的提高。然而，Nb含量较高时在晶界处会形成粗大的碳氮化物颗粒，恶化冲击韧性。同时，Nb为贵重合金元素。因此，在添加Nb时，将Nb含量控制为0.01～0.03％。
钒(V)：V是强的碳氮化合物形成元素，可在相变过程中析出，在钢中具有固溶强化及碳氮化物析出强化作用，并增加回火稳定性，从而提高强度。因此，在添加V时，将V含量控制为0.01～0.04％。
锡(Sn)：Sn在钢中具有较好的缓蚀作用。同时，Sn离子能溶解在阳极从而抑制阳极反应，减少了对耐蚀性能不利的β-FeOOH的形成。因此，在添加Sn时，将Sn含量控制为0.01～0.12％。
稀土(RE)：RE在钢中形成的RE化合物、RE/Fe金属间化合物和固溶稀土等在腐蚀薄液膜中水解，并在pH值较高的阴极沉淀，从而起到缓蚀作用。因此，在添加RE时，将RE含量控制为0.01～0.12％。
通过上述成分设计，本公开的耐蚀钢在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中具有良好的耐腐蚀性能，同时耐大气腐蚀性能与常规耐候钢相当，特别是满足光伏桩基在高浓度硫酸根离子、氯离子的土壤腐蚀环境中的腐蚀要求，也可应用于海水、煤气管道等存在氯离子、硫酸根离子腐蚀的设备中以及常规的要求大气腐蚀性能的钢结构制作。并且，本公开的耐蚀钢还具有良好的成形性能和低温冲击韧性，满足光伏桩基用钢的使用加工要求，也适用于具有高氯离子含量的海水环境及高硫酸根离子的煤气管道等。
本公开的耐蚀钢采用了Cu-Cr-Al成分体系设计，通过多种耐蚀元素的协同作用实现了在高浓度硫酸根、氯离子的土壤腐蚀环境中耐腐蚀性能的显著提高。
Cu是改善硫酸根离子腐蚀的有效元素。Cr是常用的耐蚀元素。Cr的加入除了固溶强化以及提高淬透性外，同时还提高了腐蚀电位。但是，仅加入Cu和Cr并不能实现在高浓度硫酸根离子、氯离子的土壤腐蚀环境中耐腐蚀性能的改善。研究表明，钢中添加1％左右的Cr可以使自腐蚀电位提高约40毫安，腐蚀评价显示电位差低于70毫安时不会引起明显的电偶腐蚀，所以40毫安的腐蚀电位差异不会明显改变腐蚀电流，改变腐蚀倾向，对耐腐蚀性能的改善作用不大。Cu是目前耐酸钢中的必加元素，但同时还必须加入约0.1％的Sb才有望获得预期的耐腐蚀性能。本公开从环境和人体健康的角度考虑，摒弃了Sb的添加。然而，仅依赖Cr和Cu无法获得在高浓度硫酸根离子、氯离子的土壤环境中的优异耐腐蚀性能。
Al本身比较活泼，易与空气中的氧发生反应。Al在自然环境下具有钝化效应，能够在钢材表层形成一层Al2O3薄膜，从而实现耐腐蚀性能。因此，Al在钢中通常作为脱氧元素加入。
本发明人发现，Cr和Al在钢中具有协同效应，能够显著改善钢在高浓度硫酸根和氯离子环境下的耐腐蚀性能。其机理在于：一方面，Cr与Al的配合加入显著提高了钢的腐蚀电位，提高幅度约为200毫安，而1％Cr仅使得钢腐蚀电位提高40毫安；另一方面，Cr与Al在钢中形成了金属间化合物Fe2CrAl和Cr8Al5。在高硫酸根、氯离子环境中，这两种化合物在钢的表面聚集，提高了钢的耐腐蚀性能。腐蚀电位的提高降低了腐蚀电流，减少了腐蚀的发生。并且，Cr、Al金属间化合物对表层保护同时阻碍了腐蚀的深入，起到了隔绝的作用。正是在Cr和Al的这种协同作用下，才获得了在高硫酸根、氯离子环境中的耐腐蚀性能。
因此，在本公开的耐蚀钢中，Cu和Cr与适量的Al配合，从而获得在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中的优异耐腐蚀性能。经大量研究，本发明人发现当Cu、Cr和Al的含量满足关系式：1.0≤Cr/Al≤4.0以及Cu+1.22Cr+35.3Al≥9.2时，在上述环境中的耐腐蚀性能达到普碳钢的6倍以上(相对腐蚀率低于16.5％)；并具有与常规耐候钢相当的耐大气腐蚀性能，相对普碳钢的腐蚀率≤55％，从而满足多种环境下的耐腐蚀性能要求。本公开的新的耐蚀成分体系避免了常规耐硫酸根离子腐蚀钢中Sb对环境和人体的毒性污染，同时耐腐蚀性能得到极大改善，属于环境友好型产品。
本公开的耐蚀钢利用C、Mn的固溶强化及V、Nb和Ti等的析出强化和细晶强化效果获得了345MPa以上的屈服强度，同时具有良好的低温冲击韧性(-40℃下的低温冲击功值超过160J)，延伸率超过20％，实现了高耐腐蚀性能和高韧性的匹配，并具有良好的成形性能，满足桩基用钢的使用要求。
此外，本申请的耐蚀钢的基体组织主要是铁素体+珠光体，并存在少量(不超过5％)的贝氏体。
本公开的耐蚀钢的制造方法包括如下步骤：
1)冶炼、铸造
2)铸坯加热
铸坯加热在还原性气氛的加热炉中进行，铸坯出炉温度为1230℃以上，保温时间为2～4h；
3)轧制
采用热连轧，钢坯的粗轧结束温度为1000℃以上，粗轧累计压下率≥80％；精轧采用铁素体轧制工艺，精轧开轧温度≤950℃(优选920-950℃，更优选为923-950℃)，终轧温度820～880℃，然后进行冷却和卷取。
在一个优选的实施方式中，在步骤1)中，冶炼采用LF精炼。
在一个优选的实施方式中，在步骤2)中，均热保温时间不小于40min。
在一个优选的实施方式中，在步骤3)中，冷速为10℃/s以上，卷取温度为520～580℃。
在本公开的耐蚀钢的制造方法中：
铸坯加热要求加热炉为还原性气氛，控制铸坯出炉温度1230℃以上。
考虑到本公开的钢种中加入了微量的Ti，为保证Ti的碳氮化物充分固溶，选择加热温度为1230℃以上，保温时间2～4h，优选均热保温时间不小于40min。此外，铸坯可以在浇铸完成后热装入炉，即确认铸坯表面无质量问题后从浇铸区通过辊道直接运到加热炉进行加热保温，从而能够降低能源消耗。
轧制采用热连轧，本公开的方法要求粗轧结束温度不低于1000℃，粗轧累计压下率≥80％，精轧采用铁素体轧制工艺，控制精轧开始温度≤950℃(优选920-950℃，更优选为923-950℃)，精轧结束温度为820-880℃。
本公开的耐蚀钢中添加了较多的Cr、Al元素，这两种元素均为铁素体形成元素，使得低奥氏体稳定性降低并减少奥氏体过冷度，提高了铁素体形成稳定性。从图1看，连续冷却条件下铁素体开始形成温度约为945℃；为避免两相区轧制导致轧制力的突变，本公开要求在精轧阶段采用铁素体轧制工艺。根据铁素体形成温度要求控制精轧开始温度不高于950℃，过高则进入铁素体、奥氏体两相区，导致轧制力波动及板形变差，并增加设备载荷，影响厚度控制精度；过低则进入珠光体相变区，同时带钢变形抗力提高，增加设备载荷和能耗，对板形及耐腐蚀性能不利，并损伤设备。所以控制精轧结束温度为820～880℃。
本公开的方法要求控制卷取温度520～580℃。卷取温度过高将进入珠光体相变区，过低则不利于形成较多的贝氏体组织。从相图看，本公开所述钢种在很大范围内均形成铁素体组织；在温度降低到740℃后珠光体开始形成。随着温度降低，不论冷速高低，都会发生贝氏体相变，形成少量的贝氏体组织。图3为实施例8的微观组织形貌，其中 贝氏体含量约为2％。所以本公开钢种的基体组织为铁素体+珠光体为主，并辅以不超过5％的贝氏体组织。为获得更好的强韧性，可以轧后立即水冷以尽可能细化组织，形成细小的铁素体+珠光体组织。基体中珠光体为高C组分，易于在基体中形成原电池，促进腐蚀的发生。为改善钢的耐腐蚀性，应尽量减少基体中珠光体的形成。从图1的CCT曲线看，要求控制轧后冷速10℃/s以上即可降低冷却过程中珠光体的形成；但同时要求控制卷取温度不得超过600℃，以避免钢卷在随后的缓冷过程中有珠光体生成，对耐腐蚀性能不利。
从图2的TTT温度曲线看，538℃左右是贝氏体形成最快的温度，为让基体中尽量形成更多的贝氏体以获得更高的强度，最优选在此温度卷取。本公开的钢种不需要轧后热处理，缩短生产周期、降低生产成本。
实施例
下面结合实施例和附图对本公开的耐蚀钢及其制造方法做进一步说明。
表2示出了实施例1-12和对比例1-4的钢的成分。表3示出了实施例1-12和对比例1-4的钢的生产工艺参数。表4示出了实施例1-12和对比例1-4的钢的性能参数。
对比例1和2的钢为高耐蚀耐候钢，其中对比例1的钢公开于中国专利申请公开号CN102127717A，对比例2的钢公开于中国专利申请公开号CN102268613A。对比例3和4的钢为450MPa级常规耐候钢，其中对比例3的钢公开于中国专利申请公开号CN109023071A。对比例1-4的钢板的显微组织主要为铁素体+珠光体组织。


从表2至表4可以看出，实施例1-12的钢种与对比例1-3的钢种的化学成分有明显不同。实施例1-12的钢种采用Cu-Cr-Al成分体系。对比例1为高Cr-Ni成分设计，其中Cr含量为2.5-7.0％、Ni含量为0.2～1.2％，远高于实施例1-12的钢种。对比例2不仅含Sb，还含有较高P，还需要同时添加Mg和Ce。对比例2的低温韧性和成形性能不佳，且Mg和Ce的添加增加了生产难度。特别是，Sb属于一种典型的有毒有害重金属元素，对人体和动物体产生慢性毒性及潜在致癌性。对比例3除了Sb外，Cr、Mo的含量也很高。
大气环境下的腐蚀率根据TB/T2375“铁路用耐候钢周期浸润腐蚀试验方法”检测；模拟土壤环境为高硫酸根离子+氯离子腐蚀环境(硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg)，全浸试验根据GB 10124-1988“金属材料实验室均匀腐蚀全浸试验方法”进行，试验溶液为10.0％H2SO4+3.5％NaCl，试验时间为24h，试验温度23±2℃。
结果表明，在高硫酸根离子+氯离子的模拟土壤环境中，实施例1-12的耐腐蚀性能达到普碳钢(Q345B)的6倍以上，相对普碳钢的腐蚀率低于16.5％；耐大气腐蚀性能也达到常规耐候钢水平，相对普碳钢的腐蚀率低于55％，在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境(模拟土壤环境)中和大气环境中均具有良好的耐腐蚀性能，从而满足多种环境下的耐腐蚀性能要求。与此相对，虽然对比例1和2在大气环境中也具有超过普通耐候钢的耐腐蚀性能，但在高硫酸根离子+氯离子的模拟土壤环境中的相对腐蚀率远高于实施例1-12的钢，说明其耐腐蚀性能达不到本公开的要求，且对比例1和2的低温冲击韧性较差；对比例3、4也是类似。
此外，由表4可以看出，实施例1-12的钢种的力学性能也明显优于对比例1-4。实施例1-12的钢种的屈服强度在345MPa以上，延伸率超过20％，-40℃冲击功值在160J以上，具有高强高韧性。
此外，实施例1-12的工艺采用热连轧工艺，精轧阶段采用铁素体轧工艺，在轧后层冷过程中仅要求控制冷速在10℃/s以上，工艺窗口更宽，降低了生产难度，便于现场生产。而对比例1要求控制轧后冷速5～20℃/s，对冷速范围有明确限定，这显然增加了水冷的控制难度；对比例2则要求在880～950℃终轧后经1～35秒空冷再以10℃/s以上冷速冷却到550～690℃卷取，轧后空冷再水冷的冷却工艺显然增加了生产难度，特别是空冷导致生产时间的延长，影响生产节奏。
本公开中提及的所有出版物、专利申请、专利以及其他参考文献均通过引用全文的方式并入本文。
虽然通过参照本公开的某些优选实施方式，已经对本公开进行了图示和描述，但本领域的普通技术人员应该明白，以上内容是结合具体的实施方式对本公开所作的进一步详细说明，不能认定本公开的具体实施只局限于这些说明。本领域技术人员可以在形式上和细节上对其作各种改变，包括做出若干简单推演或替换，而不偏离本公开的精神和范围。

Claims (13)

  1. 一种耐蚀钢，其以重量百分比计含有如下化学成分：
    C：0.03～0.12％，Si：0.20～0.50％，Mn：0.4～0.9％，P≤0.018％，S≤0.006％，Al：0.2～0.8％，Cu：0.10～0.50％，Cr：0.3～1.2％，Ni≤0.20％，N≤0.006％，余量为Fe和其它不可避免的杂质元素，
    其中，Cr和Al的含量满足：1.0≤Cr/Al≤4.0；
    Cu、Cr和Al的含量满足：Cu+1.22Cr+35.3Al≥9.2。
  2. 如权利要求1所述的耐蚀钢，其特征在于，所述耐蚀钢还包含Ti、Nb和V中的一种以上，其中，Ti：0.01～0.06％、Nb：0.01～0.03％和/或V：0.01～0.04％。
  3. 如权利要求1或2所述的耐蚀钢，其特征在于，所述耐蚀钢还包含Sn和/或RE，其中，Sn：0.01～0.12％和/或RE：0.01～0.12％。
  4. 如权利要求1～3中任一项所述的耐蚀钢，其特征在于，所述耐蚀钢满足如下中的一个以上：Mn的含量为0.5～0.8％，Cu的含量为0.15～0.35％和Cr的含量为0.6～1.0％。
  5. 如权利要求1～4中任一项所述的耐蚀钢，其特征在于，所述耐蚀钢不含Sb、Mg或Ce。
  6. 如权利要求1～5中任一项所述的耐蚀钢，其特征在于，所述耐蚀钢的显微组织为铁素体+珠光体及少量的贝氏体。
  7. 如权利要求1～6中任一项所述的耐蚀钢，其特征在于，所述少量的贝氏体为不超过5％的贝氏体。
  8. 如权利要求1～7中任一项所述的耐蚀钢，其特征在于，在硫酸根离子浓度为300～30000mg/kg、氯离子浓度为1500～8000mg/kg的土壤腐蚀环境中，所述耐蚀钢相对普碳钢的腐蚀率低于16.5％；在大气环境中，所述耐蚀钢相对普碳钢的腐蚀率≤55％。
  9. 如权利要求1～8中任一项所述的耐蚀钢，其特征在于，所述耐蚀钢的屈服强度≥345MPa，抗拉强度≥485MPa，延伸率A≥20％，-40℃冲击功值≥160J。
  10. 一种制造权利要求1～9中任一项所述的耐蚀钢的方法，其特征在于，包括如下步骤：
    1)冶炼、铸造
    按权利要求1～9中任一项所述成分进行冶炼、铸造成坯；
    2)铸坯加热
    铸坯加热在还原性气氛的加热炉中进行，铸坯出炉温度为1230℃以上，保温时间为2～4h；
    3)轧制
    采用热连轧，钢坯的粗轧结束温度为1000℃以上，粗轧累计压下率≥80％；精轧采用铁素体轧制工艺，精轧开始温度≤950℃，精轧终轧温度为820～880℃，然后进行冷却和卷取。
  11. 如权利要求10所述的方法，其特征在于，在步骤1)中，冶炼采用LF精炼。
  12. 如权利要求10或11所述的方法，其特征在于，在步骤2)中，均热保温时间不小于40min。
  13. 如权利要求10至12中任一项所述的方法，其特征在于，在步骤3)中，冷速为10℃/s以上，卷取温度为520～580℃。
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