EP3196328B1 - Enamel steel having high-temperature baking hardenability and manufacturing method therefor - Google Patents

Enamel steel having high-temperature baking hardenability and manufacturing method therefor Download PDF

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EP3196328B1
EP3196328B1 EP15841538.0A EP15841538A EP3196328B1 EP 3196328 B1 EP3196328 B1 EP 3196328B1 EP 15841538 A EP15841538 A EP 15841538A EP 3196328 B1 EP3196328 B1 EP 3196328B1
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steel
temperature baking
baking hardenability
enamel steel
enamel
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German (de)
English (en)
French (fr)
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EP3196328A4 (en
EP3196328A1 (en
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Quanshe c/o Baoshan Iron & Steel Co. Ltd. SUN
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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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
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/041—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular fabrication or treatment of ingot or slab
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0442—Flattening; Dressing; Flexing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention relates to an alloy steel and a method for manufacturing the same, in particular an enamel steel and a method for manufacturing the same.
  • a liner is a critical component, which determines the service safety and service life of the water heater.
  • An enamel liner having a steel plate as a base slab has a number of features such as a good corrosion resistance, a high surface hardness, being smooth and easy to clean, and such an enamel liner significantly improves the service life and comprehensive performance of the water heater liner.
  • the steel plate When using a steel plate as a base slab to manufacture an enamel liner of a water heater, the steel plate first needs to undergo blanking, processing and forming and welding, is further subjected to enamelling, and finally fired under conditions of a high temperature of about 830°C.
  • the steel plate in order to satisfy the requirements of producing a high quality enamel liner, and the steel plate must meet performance requirements in various aspects of formability, strength, weldability, fish-scaling resistance, pinhole resistance, high temperature firing resistance, etc.
  • an enamel liner is generally formed by welding three parts, i.e., two end caps and a barrel body, and therefore one enamel liner generally has three welds, including two circumferential welds and one straight weld, wherein the two caps have relatively lower requirements on the formability.
  • a new type of liner appears in the prior art, wherein this new type of liner is formed by welding two parts, i.e., an upper barrel and a lower barrel, and the primary three welds are reduced to one circumferential weld in the middle; therefore, circular rolling, hole expansion and two welds are omitted in the process of processing the new type of liner, the manufacturing process being greatly simplified.
  • the reduction of welds can substantially improve the pressure-resistance of the liner.
  • the new type of liner is stamped relatively deeply, and processes of hole expansion etc. are further performed after the stamping, the requirements for the stamping property and hole expansion property of the steel plate are obviously improved.
  • cold-rolled steel plates are mainly used, where the formability is superior to that in a hot-rolled steel plate.
  • steel plates generally used for liners can meet the stamping requirements, but the hole expansion property is lower, that is to say, cracking easily occurs when hole expansion is made after deep stamping.
  • a mechanism of inhibiting abnormal growth of ferrite grains at a high temperature is lacked in the steel, grains in the welds and heat affected zones after welding severely grow abnormally, and grains after high-temperature enamelling firing also easy grow, the yield strengths of the base steel plate, welds, heat affected zones, etc.
  • the structure in a hot rolled state is ferrite with a grain diameter of 2-20 ⁇ m, and TiC particles with a diameter of not greater than 20 nm are uniformly distributed in the structure.
  • the steel plate for enamel has a higher content of element Ti and a lower content of element S.
  • the enamel steel disclosed in the Chinese patent document has a yield strength after simulated enamelling firing lower than the yield strength before the simulated enamelling firing.
  • WO 00/12773 discloses a steel for manufacturing high adherence enamel coating steel with good formability having 0.004 wt.% or less of carbon.
  • An object of the present invention lies in providing an enamel steel having a high-temperature baking hardenability, which has an excellent formability, a good welding property and a good enamelling property.
  • the enamel steel of the present invention further has an excellent enamelling firing property, and the yield strength after high-temperature enamelling firing will be significantly improved, i.e., having a high-temperature baking hardenability.
  • the alloy addition cost of the enamel steel of the present invention is low.
  • the present invention provides an enamel steel having a high-temperature baking hardenability, the chemical elements thereof, in mass percentage, being:
  • the inevitable impurities mainly refer to elements P and Si.
  • the content of P is higher, segregation easily occurs at the grain boundary in the steel, thereby bubbles and black spots are easily produced when enamelling firing, which thus affects the surface quality of the enamel.
  • the content of Si is higher, not only the enamel properties of the steel will be damaged, but also oxide inclusions having very poor ductility may be formed, thus damaging the plasticity of the steel.
  • elements P and Si are harmful elements, the contents of these two elements in the steel needs to be as low as possible; therefore, the content of element Si can be controlled at ⁇ 0.10wt.%, and the content of element P is controlled at ⁇ 0.035wt.%.
  • the design principle of various chemical elements of the enamel steel having a high-temperature baking hardenability of the present invention is: C and Ti, wherein firstly, the content of carbon in the steel greatly affects the formability and strength of the steel plate, the higher the content of carbon, the lower the plasticity, and the higher the strength, vice versa. Secondly, in addition to being present in the steel in a solid solution, carbon can further form a microstructure such as cementite or pearlite. In addition, after titanium alloy is added, carbon can further form titanium carbide compounds with titanium.
  • carbon will not form a microstructure of pearlite, but is present in a form of dispersed carbides (such as titanium carbide, cementite) or a small amount of a solid solution. Due to the substantial aggregation of cementite in the microstructure of pearlite, on the one hand, a great amount of bubbles will be formed in the process of enamelling, and on the other hand, it is not disadvantageous to improve the strength of the steel in the process of enamelling firing.
  • dispersed carbides such as titanium carbide, cementite
  • the addition amount of titanium alloy is very important. It can be seen according to calculation of the solubility product of the formation of titanium compounds that titanium first reacts with nitrogen, then reacts with sulphur, and finally reacts with carbon; therefore, in such a precipitation order, it shall be certainly ensured that a part of titanium forms titanium carbide by reacting with carbon.
  • the content of element titanium in mass percentage is excessively low, if lower than the content as defined in the relational formula, i.e., when Ti ⁇ 3.43N + 1.5S + 0.02, it will be very difficult to ensure that a certain quantity of titanium carbide and titanium carbonitride particles are present in the steel, such that the purpose of precipitation strengthening cannot be achieved.
  • the strength of the steel cannot be further improved. Consequently, the content of element C in the enamel steel having a high-temperature baking hardenability of the present invention should be controlled at 0.008-0.020 wt.%, and the content of element Ti should meet Ti ⁇ 3.43N + 1.5S + 0.02.
  • the content of element C is controlled in a range between 0.015-0.020 wt.%.
  • Mn Manganese is a deoxidation element in the steel, and adding such an element can control the content of oxygen in the steel. Manganese can react with sulphur to produce manganese sulphide. After adding element titanium in the steel, manganese can further form a composite inclusion with the element, such as manganese titanium sulphide. Such an inclusion is in a spherical shape, and can remarkably reduce the effect of manganese sulphide on the processability. However, when the content of manganese is excessively high, the reaction at the interface of steel and enamel will be affected in the enamelling process, such that the adherence of the enamel is damaged, and defects such as bubbles are easily produced. In view of this, the content of Mn in the enamel steel having a high-temperature baking hardenability of the present invention is set as 0.05-0.50 wt.%.
  • the content of Mn in the enamel steel having a high-temperature baking hardenability of the present invention is further set as 0.1-0.3 wt.%.
  • S generally, sulphur is a harmful element in the steel, this is because sulphur and manganese will form an inclusion of manganese sulphide, which may damage the transverse plasticity of the steel plate.
  • element S is not a harmful element, the content of S in the enamel steel needs to be controlled within a range between 0.021-0.035 wt.%, and it is further ensured that S ⁇ Ti ⁇ 2 ⁇ 10 -3 .
  • the reason why the content of sulphur is controlled within a range between 0.021-0.035 wt.% is that on the basis of adding titanium, sulphur and titanium will form titanium sulphide, a great amount of hydrogen storage traps will be formed around titanium sulphide particles, and as a result, defects of fish-scaling in the enamelling process are less likely produced.
  • element titanium is added in the steel, adverse effect of manganese sulphide formed in the steel on the plasticity of steel can be further reduced.
  • sulphur can form titanium sulphide with titanium or can form composite manganese titanium sulphide with titanium and manganese. By controlling the content of sulphur and ensuring S ⁇ Ti ⁇ 2 ⁇ 10 -3 , titanium sulphide may be formed in advance of manganese sulphide.
  • manganese may also form a composite inclusion of manganese titanium sulphide, the particles shape of the composite inclusion is also a spherical shape; to this end, the formation of pure plastic manganese sulphide inclusion can be avoided in the steel, thus improving the processability of the steel.
  • controlling the content of S in the enamel steel at 0.021-0.03 wt.% is a more preferred technical solution.
  • Alt or Als Aluminium is also a strong deoxidization element.
  • the content of aluminium When the content of aluminium is higher, the content of oxygen in the steel will be reduced; on the contrary, when the content of aluminium is excessively low, the content of oxygen in the steel will be improved.
  • the oxygen remaining in the steel is mainly present in a form of an oxide inclusion, which will severely damage the plasticity of the steel.
  • An appropriate amount of aluminium can reduce the content of oxygen in the steel, and thus aluminium is one of elements to be necessarily added in the steel.
  • N Nitrogen is one of inevitable residual elements in the steel. Generally, nitrogen is a solid solution element, wherein after the addition of titanium into the steel, since nitrogen is extremely easy to form a metal compound with titanium, in the steel to which titanium is added, nitrogen will be more preferential to form titanium nitride with respect to sulphur and carbon.
  • titanium nitride particles tiny holes will be formed around the particles so as to beneficial for hydrogen storage in the steel plate during the enamelling process; however, titanium nitride particles can further seriously damage the plasticity, hole expansion property and other mechanical properties of the steel plate. In addition, the titanium nitride particles also cannot improve the strength of the steel and the strength of the steel after enamelling firing.
  • the nitrogen in the steel should be as low as possible, and the content of nitrogen is controlled at 0 ⁇ N ⁇ 0.003 wt.% and meeting N ⁇ Ti ⁇ 3 ⁇ 10 -4 .
  • O Since the process of smelting of liquid steel mainly relies on reactions of carbon and oxygen, oxygen is inevitable in the steel. However, when the content of oxygen in the steel is excessively high, an oxide inclusion may be formed to affect the processability of the steel. On this basis, O in the enamel steel having a high-temperature baking hardenability of the present invention has to be controlled as 0 ⁇ O ⁇ 0.010 wt.%.
  • the definition of the content of titanium in mass percentage is defined by the following three constraint formulae: 1) N ⁇ Ti ⁇ 3 ⁇ 10 -4 , 2) S ⁇ Ti ⁇ 2 ⁇ 10 -3 , and 3) Ti ⁇ 3.43N + 1.5S + 0.02. That is to say, the addition of element Ti is restricted and limited by the contents of elements N and S in mass percentage.
  • the element C in the enamel steel having a high-temperature baking hardenability of the present invention is present in a dispersed carbide form.
  • said carbide is cementite and finely granulated titanium carbide and titanium carbonitride.
  • the grain diameter of said titanium carbide and titanium carbonitride particles are 10-30 ⁇ m.
  • the enamel steel having a high-temperature baking hardenability of the present invention further comprises at least one of 0 ⁇ Cu ⁇ 0.10%, 0 ⁇ Cr ⁇ 0.10%, 0 ⁇ Ni ⁇ 0.10%, 0 ⁇ Mo ⁇ 0.10%, 0 ⁇ Nb ⁇ 0.010%, 0 ⁇ V ⁇ 0.020%, and 0 ⁇ B ⁇ 0.0005%, with 0.05% ⁇ 5 ⁇ Nb + Cu + V + Ni + Cr + Mo + 10 ⁇ B ⁇ 0.20%.
  • the addition of the elements is controlled as 0 ⁇ Cu ⁇ 0.10wt.%, 0 ⁇ Cr ⁇ 0.10 wt.%, 0 ⁇ Ni ⁇ 0.10 wt.%, 0 ⁇ Mo ⁇ 0.10 wt.%.
  • niobium, vanadium and boron can improve the recrystallization temperature of the steel plate.
  • the hot rolling temperature for the steel plate also needs to be accordingly improved.
  • thin steel plates for example, steel plates having a finished product thickness of not greater than 2.5 mm, it is very difficult to achieve an excessively high final rolling temperature, and a problem of non-uniform temperatures at different parts of a strip steel will be caused, finally leading to defects of mixed grains and structure abnormality of the steel plate.
  • the increase of the recrystallization temperature has a certain effect on improving the strength of the enamel before the firing, it has not too much effect on the improvement of the strength of the enamel after the firing.
  • the above-mentioned elements when added, further need to meet 0.05 wt.% ⁇ 5 ⁇ Nb + Cu + V + Ni + Cr + Mo + 10 ⁇ B ⁇ 0.20 wt.%.
  • the present invention further provides a manufacturing method for producing the enamel steel having a high-temperature baking hardenability as described hereinabove, comprising the steps of: a liquid iron pretreatment ⁇ smelting with a converter ⁇ refining ⁇ continuous casting ⁇ hot rolling.
  • the method for manufacturing the enamel steel having a high-temperature baking hardenability of the present invention further comprises steps of: acid pickling ⁇ cold rolling ⁇ annealing ⁇ temper rolling, after the hot rolling step.
  • the overall reduction ratio is controlled at greater than 70%. Further preferably, the overall reduction ratio of the cold rolling is controlled at ⁇ 75%.
  • the roughness of the steel plate surface can also be controlled within a range of 0.4-2.0 ⁇ m by changing the roughness of the roll surface of the roller.
  • the annealing temperature is 650-800°C.
  • the heating temperature is 1100-1250°C
  • the heating time is ⁇ plate thickness ⁇ 1 min/mm, wherein the unit of plate thickness is mm, and the plate thickness refers to the plate thickness of a continuous casting slab.
  • the heating temperature for the continuous casting slab is set as 1100-1250°C.
  • the particular heating time within the range can be adjusted according to the thickness of the steel slab, and in general, the thinner the steel slab, the shorter the heating time, the heating time being required to meet t ⁇ plate thickness ⁇ 1 min/mm.
  • the final rolling temperature for the hot rolling is 850-930°C
  • the coiling temperature for the hot rolling is 630-780°C.
  • the final rolling temperature in the hot rolling step needs to be reasonably controlled such that the carbide is distributed in a form of a fine dispersed state in the ferrite matrix.
  • the final rolling for the hot rolling of the enamel steel of the present invention is controlled to be complete within a temperature range of 850-930°C to ensure that the hot rolling is completed at not less than the recrystallization temperature, which avoids rolling in a dual phase area of austenite + ferrite, and prevents causing the defects of mixed grains and structure abnormality in the steel plate.
  • the cementite and titanium carbide are present in a state of fine particles by controlling the process parameters of the hot rolling process so as to achieve the purpose of matrix strengthening.
  • the heating temperature in the continuous casting step and the final rolling temperature and the coiling temperature in the hot rolling temperature the shape and size of titanium sulphide in the steel is further improved.
  • the yield strength of the enamel steel having a high-temperature baking hardenability of the present invention after high-temperature enamelling firing will be significantly improved, thus improving the pressure-resistance of an enamel steel article and prolonging the service life.
  • the enamel steel having a high-temperature baking hardenability of the present invention has a better formability, an elongation of ⁇ 39%, and a hole expansion rate of ⁇ 60%, and is particularly suitable for manufacturing various complex shapes of water heater liners.
  • the enamel steel having a high-temperature baking hardenability of the present invention has a good weldability.
  • the enamel steel having a high-temperature baking hardenability of the present invention has an excellent enamelling property, and a long hydrogen permeation time ( ⁇ 10 min) which is higher than that of a steel for double-side enamel in the prior art ( ⁇ 8 min).
  • the alloy cost of the enamel steel having a high-temperature baking hardenability of the present invention is low, and the manufacturing cost is also relatively economic.
  • the production process of the enamel steel having a high-temperature baking hardenability of the present invention is simple and practicable.
  • the enamel steel having a high-temperature baking hardenability and method for manufacturing the same of the present invention will be further described below according to particular embodiments, but the particular embodiments and related description do not form an inappropriate definition of the technical solution of the present invention.
  • the enamel steels in Examples A1-A5 and Comparative Example B1 are manufactured according to the following steps (1)-(5), and the enamel steel in Example A6 is manufactured according to the following steps (1)-(9):
  • Table 1 lists the mass percentages of various chemical elements in the enamel steels in Examples A1-A6 and Comparative Example B1 of the present case.
  • Table 1. (wt.%, the balance being Fe and other inevitable impurities other than P and S)
  • Serial number A1 A2 A3 A4 A5 A6 B1 C 0.013 0.018 0.02 0.008 0.01 0.013 0.031 Mn 0.25 0.2 0.1 0.3 0.25 0.15 0.22
  • Al 0.041 0.035 0.035 0.028 0.005 0.02 0.031 N 0.0018 0.002 0.0025 0.0015 0.002 0.002 0.0026
  • Si 0.008 0.02 0.05 0.03 0.1 0.008 0.006 Ti 0.09 0.08 0.09 0.085 0.
  • Table 2 lists the process parameters of the method for manufacturing the enamel steels in Examples A1-A6 and Comparative Example B1 of the present case.
  • Table 2. Serial number Thickness of continuous-casting slab (mm) Hot rolling step Cold rolling and annealing Thickness of finished steel plate (mm) Heating temperature (°C) Heating time (min) Final rolling temperature (°C) Coiling temperature (°C) Reduction ratio (%) Annealing tempe rature (°C) Hot rolling Cold rolling A1 200 1100 215 860 630 1.8 - A2 200 1100 220 865 660 2.0 - A3 200 1150 235 860 660 2.0 - A4 200 1250 240 920 730 5.0 - A5 230 1150 235 880 680 2.5 - A6 230 1150 260 880 680 75 760 4.0 1.0 B1 200 1150 210 860 660 1.8 -
  • Table 3 lists the mechanic property parameters of the enamel steels in Examples A1-A6 and Comparative Example B1 of the present case respectively at room temperature and under the condition of heat preservation at 830°C.
  • Table 3. Serial number Mechanical property at room temperature Mechanical property after heat preservation at 830°C for 10 min R eL /MPa R m /MPa A 80 /% Hole expansion rate/% Hydrogen permeation time/min R eL /MPa R m /MPa A 80 /% A1 259 344 40 71 15 361 426 41 A2 241 335 42 80 14 371 429 43 A3 265 360 39 70 16 390 448 44.5 A4 197 315 43.5 72 12 315 420 43 A5 220 321 42 75 22 335 412 40 A6 235 330 44 75 20 375 430 41 B1 194 322 38 48 7 180 301 42
  • the yield strengths in Examples A1-A6 are all ⁇ 197 MPa, the tensile strengths are all ⁇ 315 MPa, the elongations A 80 are ⁇ 39%, the hole expansion rates are ⁇ 70%, and the hydrogen permeation times are ⁇ 12 min; and, under the condition of heat preservation at 830°C, the yield strengths in Examples A1-A6 are improved to ⁇ 315 MPa, the tensile strengths are all ⁇ 412 MPa, and the elongations A 80 are ⁇ 40%; it can be indicated therefrom that, not only the enamel steel of the present invention has a higher elongation, a longer hydrogen permeation time, and a higher hole expansion rate, but also both the yield strengths and tensile strengths in all the examples after heat preservation at 830°C for 10 min are substantially improved, which indicates that the enamel steel involved in this technical solution has a good high-temperature baking hardenability, which is beneficial for significantly improving the pressure-resistance and service
  • the hydrogen penetration time of the enamel steel of the present invention is ⁇ 12 min.
  • the steel plate can meet the requirements of fish-scaling resistance for double-side enamel, that is to say, whatever type of glaze is used in actual productions, and this type of steel plate can meet the requirements of fish-scaling resistance. Since the requirements of fish-scaling resistance for double-side enamel are more rigorous than those for single-side enamel, the enamel steel of the present invention can fully meet the requirements for single-side enamel.
  • Figure 1 shows tendency graph of yield strength of an enamel steel having a high-temperature baking hardenability of Example A1 in a condition of heat preservation at 830°C over time.
  • Figure 2 shows the microstructure of the enamel steel in Example Al
  • figure 3 shows the picture of the morphology of the precipitated phase in the enamel steel.
  • the microstructure of the enamel steel in Example A1 is a uniform ferrite structure, wherein no pearlite structure and larger size cementite particles can be seen, the precipitated phase is in a fine dispersed distribution, mainly having titanium carbide or titanium carbonitride.

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