CN113604728A - High-surface-quality hot-galvanized high-strength steel and manufacturing method thereof - Google Patents
High-surface-quality hot-galvanized high-strength steel and manufacturing method thereof Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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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
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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
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- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C21D2211/00—Microstructure comprising significant phases
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- C21D2211/008—Martensite
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Abstract
The invention belongs to the field of hot-dip galvanized ultrahigh-strength steel manufacturing, and particularly relates to a high-surface-quality hot-dip galvanized high-strength steel and a manufacturing method thereof, wherein the hot-dip galvanized high-strength steel comprises the following chemical components in parts by mass: c: 0.08% -0.15%, Mn: 1.80% -2.70%, Si: 0.50% -1.50%, Als: 0.010-0.05%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.008 percent, Nb: 0.01-0.05%, Cr: 0.30-0.60%, Mo: 0.10-0.30%, and the balance of Fe and inevitable impurities. The invention has the advantages that the comprehensive effect of chemical components ensures that the organization structure and the crystal grain size in steel meet the requirements, the galvanized product has good surface quality and no plating leakage defect, the tensile strength is more than or equal to 780MPa, the elongation A is more than or equal to 20 percent, the hole expansion rate is more than or equal to 25 percent, and the forming performance is good.
Description
Technical Field
The invention belongs to the field of hot-dip galvanized ultrahigh-strength steel manufacturing, and particularly relates to high-surface-quality hot-dip galvanized high-strength steel and a manufacturing method thereof.
Background
With the further development of the current new energy automobile, the energy consumption and CO in the using process of the automobile are reduced2Emission, automobile steels and the like are being developed toward thin gauge and high strength. Compared with common cold-rolled high-strength steel, the galvanized high-strength steel not only has high strength, but also has good corrosion resistance, so the galvanized ultrahigh-strength steel is widely applied. In the process of producing galvanized high-strength steel, in order to make the ultrahigh-strength steel have good formability, a certain amount of alloying elements such as Mn, Si, Cr and the like are usually added, but the addition of the alloying elements deteriorates the surface quality of a steel plate and affects the normal use of the product, so that how to improve the surface quality of the galvanized ultrahigh-strength steel becomes one of the key technical problems which need to be solved urgently.
In the prior art, the main technology for improving the surface quality mainly focuses on the processes of cold rolling and annealing galvanizing, and mainly comprises the steps of improving the surface quality by controlling an acid washing process, the atmosphere in an annealing furnace, the dew point, the components of zinc liquid and the like, and reducing the defects of surface plating leakage and the like.
Patent CN201910726102.4, disclosing a high surface quality 1200MPa galvanized dual-phase steel and a production method thereof, and the related steel plate comprises the following main chemical components: 0.07-0.10%, Mn: 1.00-4.00%, Si: 0.25-0.55%, P: less than or equal to 0.016 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.006 percent, Als: 0.01-0.05%, Nb: 0.015 to 0.055%, Ti: 0.040-0.080%, B: 0.008-0.0010%, Mo: 0.15-0.45%, and the balance of Fe and inevitable impurity elements. The production method comprises the working procedures of continuous casting, rolling and cold rolling galvanization. Wherein the rolling procedure comprises the rolling heating temperature of 1200-1260 ℃, the final rolling temperature of 900-920 ℃, the coiling temperature is controlled by adopting a U-shaped coiling process, the coiling temperature of the head part and the tail part of the steel coil within the range of 30m is 600 +/-20 ℃, the middle coiling temperature is 550 +/-20 ℃, and in the annealing procedure, the atmosphere of the pre-oxidation section in the furnace is controlled to be 2.0 percent of O2+98 percent of N2The pre-oxidation time is 9-11s, the hydrogen content in the furnace is more than or equal to 4.5 percent, the oxygen content is less than or equal to 20ppm, the pre-oxidation technology in the galvanizing furnace and the furnace nose dew point are controlled within the range of-35 to-15 ℃, the aluminum content in the zinc pot is controlled within the range of 0.18 to 0.24 percent, and the surface quality of the zinc pot is improved.
Patent CN201810716171.2 discloses a control method for coatability and surface quality of a dual-phase steel cold-rolled high-strength automobile plate, and the related steel plate comprises the following main chemical components: 0.06-0.09%, Mn: 1.40-2.00%, Si: 0.20-0.60%, P: less than or equal to 0.025 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.005 percent, Als: 0.015-0.060% of Fe and inevitable impurity elements as the rest. The production method comprises the working procedures of steel making, continuous casting, rolling, descaling, acid rolling, continuous annealing and leveling, and specifically comprises the following steps: the descaling process adopts a three-stage descaling process, the descaling position comprises descaling after a heating furnace, descaling before rough rolling and descaling before finish rolling, the descaling water pressure of each descaling point is more than or equal to 24MPa, wherein the rough rolling is reciprocating rolling, the rolling is carried out for 5 passes, and high-pressure water descaling is carried out for each pass. The slab discharging temperature is 1120-1230 ℃, the furnace time is 120-300min, and the residual oxygen content of the flue gas in the furnace is less than or equal to 4 percent. The inlet temperature of finish rolling is 1025-2The residual iron amount on one side is less than or equal to 50mg/m2. The hydrogen content in the furnace is 1.9-5.5%, the oxygen content in each section in the furnace is 0-30ppm, the dew point is-75 ℃ to-35DEG C. The surface roughness Ra of the flattened steel is controlled to be 0.6-1.4mm, and the Rpc value is controlled to be more than or equal to 55.
The patent CN201910725364.9 discloses a surface control method for cold rolling production of 800MPa grade dual-phase steel, which solves the problem of zinc layer fluctuation of cold rolling galvanized dual-phase high-strength steel by controlling the dew point condition of a furnace area, the humidifying state of a furnace nose and the atmosphere in the furnace, and mainly comprises the steps of rolling and coiling a steel billet, cold rolling and galvanizing, wherein the dew point in the furnace in the galvanizing process is-25 ℃ to-35 ℃, the furnace nose is humidified and closed before the dual-phase steel is produced, and the volume content of hydrogen in the furnace atmosphere is adjusted to 1-3%. Wherein the rolling coiling temperature is 610-630 ℃, and the main chemical components of the dual-phase steel are C: 0.145-0.175%, Si: 0.45-0.55%, Mn: 1.85-1.95%, P is less than or equal to 0.015%, S is less than or equal to 0.007%, Al: 0.020-0.070%, less than or equal to 0.005% of N, and the balance of Fe and inevitable impurities.
Patent CN 201510968633.6 discloses a galvanized dual-phase steel for 800MPa class cars and a production method thereof, and the main chemical components C are as follows: 0.06-0.10%, Si: less than or equal to 0.01 percent, Mn: 1.50-2.50%, Als: 0.01-0.080%, P: less than or equal to 0.015 percent, S: less than or equal to 0.010 percent, Mo 0.01-0.30 percent or Cr: 0.02 to 0.90%, Nb: 0.01-0.03%, N: less than or equal to 0.005 percent, and the balance of Fe and inevitable impurity elements. The production steps comprise heating a casting blank after smelting, refining and continuous casting, finish rolling, coiling, cold rolling after acid cleaning, hot galvanizing and finishing. The mechanical property index of the obtained product reaches: the yield strength is 480-.
Disclosure of Invention
In view of the above problems, the present invention provides a high surface quality hot dip galvanized high strength steel and a method for manufacturing the same, so as to solve the technical problem that the surface quality of a steel sheet is deteriorated due to the addition of alloy elements in the prior art.
The technical scheme for realizing the purpose is as follows: the high-surface-quality hot-dip galvanized high-strength steel comprises the following chemical components in percentage by mass: c: 0.08% -0.15%, Mn: 1.80% -2.70%, Si: 0.50% -1.50%, Als: 0.010-0.05%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.008 percent, Nb: 0.01-0.05%, Cr: 0.30-0.60%, Mo: 0.10-0.30%, and the balance of Fe and inevitable impurities.
Optionally, the metallographic structure of the hot-dip galvanized high-strength steel comprises, by volume fraction, 10% -40% of martensite, 10% -30% of bainite and 30-80% of ferrite.
Optionally, the ferrite has an average diameter of 0.5-5.0 μm.
Optionally, the average diameter of the grains in the martensite is 0.5-3.0 μm.
Optionally, the properties of the hot-dip galvanized high-strength steel include: the tensile strength is more than or equal to 780MPa, the elongation A is more than or equal to 20 percent, and the hole expansion rate is more than or equal to 25 percent.
A preparation method of high-surface-quality hot-dip galvanized high-strength steel comprises the following steps,
obtaining a casting blank containing the chemical components;
heating, hot rolling, cooling after rolling and coiling the casting blank in sequence to obtain a hot rolled coil;
sequentially carrying out acid washing, continuous annealing and hot galvanizing on the hot-rolled coil to obtain hot-galvanized high-strength steel;
the temperature of the hot galvanizing is 440-500 ℃, and the mass fraction of aluminum in the zinc liquid is 0.15-0.25% in the hot galvanizing.
Optionally, the heating temperature is 1150-1250 ℃, the heating time is less than or equal to 50min, and the mass fraction of oxygen during heating is less than or equal to 3%.
Optionally, the final rolling temperature of the hot rolling is 900-.
Optionally, the cooling rate after rolling is more than or equal to 25 ℃/s, the coiling temperature is less than or equal to 650 ℃, and the roughness Ra of the acid-rolled plate surface is less than or equal to 2.0 mu m.
Optionally, the continuous annealing comprises heating, soaking and cooling, wherein the soaking temperature is 760-; the protective atmosphere of the continuous annealing comprises: the dew point temperature is-30 to-50 ℃, the mass fraction of the hydrogen is 5 to 15 percent, and the volume concentration of the oxygen is less than or equal to 20 ppm.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the carbon provided by the embodiment of the invention has the solid solution strengthening effect in steel, or forms MC fine particles with carbide forming elements such as Nb, Mo and the like in the steel, plays the roles of precipitation strengthening and grain refinement, and improves the strength of steel; si plays roles of improving strength, inhibiting the formation of pearlite and carbide and promoting the transformation of a low-temperature bainite structure in high-strength steel, but Si is easy to form oxides and is enriched on the surface of steel, so that the surface quality of a product is influenced, particularly the hot-dip galvanized high-strength steel is greatly influenced, and the selection of proper Si content is very important; due to the proper Al content, sharp-angled oxides and coarse AlN in the steel are reduced, and the hole expansion performance is improved; nb can obviously refine ferrite grains and martensite grains in the steel, and improve the strength and hole expansion performance of the steel; the proper Si, Mn and Cr alloy content obviously reduces complex oxides of Fe, Si, Mn and Cr, and further ensures good surface quality.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
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Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a flow chart of the preparation of high surface quality hot dip galvanized high strength steel in the practice of the present application;
FIG. 2 micrograph of complex oxide of FeMnSiCr formed by hot rolling of example 1;
FIG. 3 is a graph showing the complex oxide content of FeMnSiCr formed by hot rolling in example 1;
FIG. 4 Hot-dip galvanized high strength steel of example 1 with a defect-free surface;
FIG. 5 is a hot-dip galvanized high-strength steel with surface defects according to comparative example 5;
FIG. 6 is a graph showing Al due to large size in the course of enlarging a hole in comparative example 52O3And cracks caused by AlN inclusions.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
It should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
In order to solve the technical problems, the technical scheme in the embodiment of the invention has the following general idea:
the high-surface-quality hot-dip galvanized high-strength steel comprises the following chemical components in percentage by mass: c: 0.08% -0.15%, Mn: 1.80% -2.70%, Si: 0.50% -1.50%, Als: 0.010-0.05%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.008 percent, Nb: 0.01-0.05%, Cr: 0.30-0.60%, Mo: 0.10-0.30%, and the balance of Fe and inevitable impurities.
In the embodiment of the present application, C: carbon has a solid solution strengthening effect in steel, or forms fine MC particles with carbide forming elements such as Nb, Mo and the like in steel, plays a role in precipitation strengthening and grain refinement, and improves the strength of steel. Too high a carbon content lowers the weldability and formability of the steel, so that the C content in the steel is selected to be 0.08% -0.15% in consideration of the balance.
Mn: mn plays a role in solid solution strengthening, austenite stabilization and hardenability improvement in steel, and the content is too low, the strengthening effect is too small, and the austenite is unstable. The excessive Mn content is easy to form serious segregation in the thickness center of the plate strip, reduces the toughness of the product and causes forming cracking, and the excessive Mn content is easy to form complex oxides together with Si and Cr in steel and is not beneficial to controlling the surface quality of the product, so the Mn content of the invention is 1.80-2.70%.
Si: si plays a role in improving the strength, inhibiting the formation of pearlite and carbide and promoting the transformation of low-temperature structure in the high-strength steel, but Si is easy to oxidize, is easy to form complex oxides together with Fe, Mn and Cr, is enriched on the surface of steel, and affects the surface quality of products, and particularly for hot-dip galvanized high-strength steel, the content of Si is reduced as much as possible. Therefore, the Si content in the present invention is 0.50 to 1.50%.
Al: al is easily bonded with oxygen in steel to form a sharp oxide, adversely affecting the hole-expanding property, and easily bonded with N to form a coarse AlN precipitate, lowering the toughness of the steel, so that the a. content in the present invention is 0.010 to 0.05%.
P: p is an impurity element in steel, so the lower the content of P, the better, according to the actual control level, should be controlled below 0.015%.
S: s is an impurity element in steel, is easy to generate segregation at a crystal boundary, and is fully removed during steel making and is controlled to be 0.008%.
N: n is an impurity element in steel, and reduces the toughness of steel, so the content of N is reduced as much as possible and is controlled to be less than 0.008%.
Nb: nb can obviously refine ferrite grains in the steel, improve the strength and toughness of the steel, play a role in precipitation strengthening and steel strength improvement, but the manufacturing cost of the steel is increased due to the excessively high Nb content, so the Nb content is 0.010-0.050%.
Cr: cr can significantly improve hardenability of steel, and has an effect of inhibiting carbide precipitation and pearlite transformation, which is advantageous for promoting the formation of bainite and martensite in steel, but Cr is also liable to form complex oxides with Fe, Si, Mn, etc. in steel, thereby adversely affecting the surface, and therefore, the Cr content is 0.30 to 0.60% in the present invention.
Mo: mo can remarkably improve the hardenability of steel and promote the transformation of bainite and martensite of a low-temperature structure of the steel, and the manufacturing cost of the steel is remarkably increased due to the excessively high Mo content, so that the Mo content is 0.10-0.30 percent in the invention.
As an alternative embodiment, the metallographic structure of the hot-dip galvanized high-strength steel comprises 10% -40% of martensite, 10% -30% of bainite and 30-80% of ferrite in volume fraction.
In the examples of the present application, the hole expansion ratio was adjusted by changing the microstructure of the steel. In the embodiment of the application, the hole expansion rate indicates the flanging capacity. The specific calculation method is to subtract the pre-reaming aperture from the post-reaming aperture and divide the pre-reaming aperture by the pre-reaming aperture, which is the percentage of the aperture that can be enlarged, also called the reaming ratio.
In an alternative embodiment, the ferrite has an average diameter of 0.5 to 5.0 μm,
as an alternative embodiment, the average diameter of the grains in the martensite is 0.5 to 3.0 μm.
The ratio of the metallographic structure and the average diameter of the crystal grains directly influence the mechanical properties of the high-strength steel, and simultaneously can influence the hole expansion rate in the later period in the later processing process.
As an optional embodiment, the mechanical properties of the microstructure of the hot-dip galvanized high-strength steel are that the tensile strength is greater than or equal to 780MPa, the elongation A is greater than or equal to 20 percent, and the hole expansion rate is greater than or equal to 25 percent.
In the embodiment of the application, the hole expansion rate is more than or equal to 25 percent, the hole expansion rate of the steel can be between 10 percent and 120 percent in general, and the higher the strength is, the lower the hole expansion rate is.
The application provides a preparation method of high-surface quality hot-dip galvanized high-strength steel, as shown in figure 1, the method comprises the following steps,
s1, obtaining a casting blank containing the chemical components;
s2, heating, hot rolling, cooling after rolling and coiling the casting blank in sequence to obtain a hot rolled coil;
s3, sequentially carrying out acid washing, continuous annealing and hot galvanizing on the hot-rolled coil to obtain hot-galvanized high-strength steel;
the temperature of the hot galvanizing is 440-500 ℃, and the mass fraction of aluminum in the zinc liquid is 0.15-0.25% in the hot galvanizing.
In the embodiment of the application, the mechanical property and the corrosion resistance of the steel are improved by cooling, finishing, heating, hot rolling, cooling after rolling, coiling, pickling and continuous annealing of a casting blank; improve the evaporation of the zinc coating in the processing process.
In the embodiment of the application, the casting blank is cooled by stacking, the cooling rate is controlled, and when the cooling rate is less than or equal to 100 ℃/min, microcracks on the surface of the slab can be reduced, so that a surface sample in the heating process is prevented from entering a slab matrix, and the surface quality of the slab is prevented from being deteriorated.
In the embodiment of the application, the iron oxide skin is removed by finishing, so that the surface quality of the plate blank can be further improved, impurities on the surface of the continuous casting plate blank are effectively removed, and the high-strength steel is more favorable for removing surface microcracks and defects thereof, thereby being favorable for improving the surface quality.
In the embodiment of the application, the temperature of the steel strip entering a zinc pot is controlled to be 440-500 ℃, the temperature of the steel strip is 440-480 ℃, zinc liquid is favorably coated, the adhesion of zinc slag and the like on the surface is reduced, the surface quality is improved, and when the aluminum content of the zinc liquid is 0.15-0.25%, the zinc liquid is favorably subjected to reduction reaction with SiMn-containing oxide in iron scale on the surface of steel, the iron scale structure on the surface is damaged, a continuous inhibition layer is favorably formed, and the surface quality is improved.
As an optional implementation mode, the heating temperature is 1150-1250 ℃, the heating time is less than or equal to 50min, and the mass fraction of oxygen during heating is less than or equal to 3%.
In the embodiment of the application, the heating temperature is 1150-1250 ℃, the temperature of the plate blank is lower than 1150 ℃ which is not beneficial to uniformizing alloy elements in steel, so that composition and structure segregation is caused, the heating temperature is higher than 1250 ℃, and composite oxides such as Fe2SiO4, Fe2CrO4, SiO2, Cr2O3 and the like which are difficult to remove are easily formed on the surface, so that the surface quality of a product is deteriorated. Preferably, the heating temperature is 1200-1250 ℃, the heating time is less than or equal to 50min, the oxidation of the grain boundary on the surface of the slab is favorably reduced, the oxygen content in the furnace is less than or equal to 3%, the oxidation of the surface is favorably reduced, and oxides such as FeSiO3 and the like which seriously affect the surface quality are formed.
As an optional implementation mode, the final rolling temperature of the hot rolling is 900-.
In the embodiment of the application, in the hot rolling step, the surface iron scale can be removed favorably by adopting high-pressure descaling for more than or equal to 5 times, particularly for steel grades with high alloy content, the composite oxide containing Si, Cr and Mn can be effectively removed, and the surface quality is improved.
In the embodiment of the application, the finish rolling temperature is 900-.
As an optional implementation mode, the cooling rate after rolling is more than or equal to 25 ℃/s, the coiling temperature is less than or equal to 650 ℃, and the surface roughness Ra after acid rolling is less than or equal to 2.0 mu m.
In the embodiment of the application, the cooling after rolling adopts front-section rapid cooling, and the cooling rate after rolling is more than or equal to 25 ℃/s, so that the growth speed of oxides such as Fe2SiO4, Fe2CrO4, SiO2 and Cr2O3 is reduced, the thickness of an iron scale is reduced, the surface is kept smooth after pickling, and the roughness is reduced. The fast cooling speed is beneficial to refining the tissue and obtaining high strength, elongation and hole expansion rate.
In the embodiment of the application, the coiling temperature is too high, and the iron scale which is thick and difficult to acid wash and is composed of Fe2SiO4, Fe2CrO4, SiO2 and Cr2O3 is easily formed, so the coiling temperature is less than or equal to 650 ℃. The high coiling temperature is unfavorable for grain refinement, and has adverse effects on the strength and the hole expansion rate of the product.
In the embodiment, the hot-rolled coil is formed by taking a continuous casting plate blank or a primary rolling plate blank as a raw material, heating the raw material by a stepping heating furnace, descaling by high-pressure water, then feeding the raw material into a roughing mill, cutting the head and the tail of the rough rolling material, then feeding the rough rolling material into a finishing mill, and performing computer-controlled hot rolling, wherein after the finish rolling, the rough rolling material is subjected to laminar cooling (the cooling rate is controlled by a computer) and coiling by a coiling machine to form a straight coil.
In the present invention, the surface roughness Ra after acid rolling is not more than 2.0. mu.m, preferably not more than 1.0. mu.m. The roughness control after acid rolling is beneficial to reducing residual gas on the surface of the strip steel before galvanization, and according to research, the smooth surface is beneficial to increasing the binding force between zinc liquid and the surface, so that the plating leakage defect is reduced.
As an optional embodiment, the continuous annealing comprises heating, soaking and cooling, wherein the soaking temperature is 760-; the protective atmosphere of the continuous annealing comprises: the dew point temperature is-30 to-50 ℃, the mass fraction of the hydrogen is 5 to 15 percent, and the volume concentration of the oxygen is less than or equal to 20 ppm.
In the embodiment of the application, in the continuous annealing process, the soaking temperature is higher than 760 ℃ so as to be beneficial to the structure recovery and recrystallization of steel, and the temperature is too high so as to cause coarse grains and be unfavorable for performance control, so that the soaking temperature is 760 ℃ and 850 ℃ in the invention. The control of the soaking time is also beneficial to the control of the structure proportion and the grain size, and excellent mechanical properties can be obtained, so the soaking time is controlled to be 100-300 s. In the embodiment of the application, all the steps in the continuous annealing act together, so that microcracks can be effectively reduced, and the mechanical property and the coating quality of the formed part are improved.
In the embodiment of the application, the invention controls the dew point in the annealing furnace to be-30 to-50 ℃, and the hydrogen content in the furnace is H2At 5-15%, the dew point is too high, which easily causes severe external oxidation and decarburization, thus the galvanized product has surface defects such as plating leakage and the like, and the product strength is reduced, while the dew point is too low, which has too high requirement on the equipment capability, and is difficult to realize in the conventional production line. H2Too low a content also tends to cause external oxidation of the surface of the strip, while too high a content increases the cost, so that the annealing furnace H of the present invention2In the range of 5-15%. The residual oxygen content is too high, which easily causes surface oxidation, so that the surface quality after coating has obvious influence, and for the invention, the residual oxygen content in the annealing furnace is less than or equal to 20ppm due to the high alloy content.
In the embodiment of the application, the dew point temperature is the temperature when the air is cooled to be saturated with water vapor under the condition that the water vapor content and the air pressure are not changed. It is said that the temperature at which water vapor in the air turns into dew is the dew point temperature.
The hot-dip galvanized high-strength steel with high surface quality and the manufacturing method thereof provided by the embodiment of the invention will be described in detail below by combining the embodiment and experimental data.
The present example was produced according to the following procedure (smelting, continuous casting → cooling of a cast slab → slab cleaning → heating of a slab → hot rolling of a slab → cooling after rolling → coiling → cold rolling by pickling → continuous annealing → galvanization → finishing → finished product).
Table 1 lists the main ingredients of each example and comparative example.
Table 2 control list of main parameters of hot rolling in examples and comparative examples.
Table 3 table of control of main parameters of cold rolling and continuous annealing in this example and comparative example.
Table 4 list of effects of each example and comparative example.
Table 5 performance effects of examples and comparative examples.
The components and parameters listed in the invention 1-4-1 are controlled to obtain a product with good performance and surface quality, while the comparative example 4-2 adopts high heating temperature, long heating time and high coiling temperature, so that the surface roughness of the product is larger after acid rolling, the surface of the product is defective after galvanizing, and ferrite grains and martensite grains are larger due to the high coiling temperature, and the strength and the hole expansion rate are adversely affected. Comparative examples 4-3 employed a long heating time and a low finish rolling temperature and a slow cooling rate, resulting in a large surface roughness after acid rolling thereof, resulting in surface defects after galvanization, and a large ferrite grain and martensite grain, both of which had adverse effects on strength and hole expansibility, due to a low cooling rate. Comparative example 5 employs a lower C content and Si content in the composition design, resulting in a low final strength and hole expansibility, and a long time in annealing and a high dew point, resulting in surface defects. Comparative example 6 uses higher C and Si in the composition design, has a rough surface after acid rolling, and uses higher annealing temperature and high dew point in the annealing, resulting in poor surface quality to the finished product.
Claims (10)
1. The high-surface-quality hot-dip galvanized high-strength steel is characterized by comprising the following chemical components in percentage by mass: c: 0.08% -0.15%, Mn: 1.80% -2.70%, Si: 0.50% -1.50%, Als: 0.010-0.05%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent, N: less than or equal to 0.008 percent, Nb: 0.01-0.05%, Cr: 0.30-0.60%, Mo: 0.10-0.30%, and the balance of Fe and inevitable impurities.
2. The hot-dip galvanized high-strength steel according to claim 1, characterized in that the metallographic structure of the hot-dip galvanized high-strength steel contains, in terms of volume fraction, 10% to 40% of martensite, 10% to 30% of bainite, and 30% to 80% of ferrite.
3. A hot-dip galvanized high-strength steel according to claim 1, characterized in that the average diameter of crystal grains in the ferrite is 0.5 to 5.0 μm.
4. A hot-dip galvanized high-strength steel according to claim 1, characterized in that the average diameter of crystal grains in the martensite is 0.5 to 3.0 μm.
5. The hot-dip galvanized high-strength steel according to claim 1, characterized in that the properties of the hot-dip galvanized high-strength steel include: the tensile strength is more than or equal to 780MPa, the elongation A is more than or equal to 20 percent, and the hole expansion rate is more than or equal to 25 percent.
6. A preparation method of high-surface-quality hot-dip galvanized high-strength steel is characterized by comprising the following steps of,
obtaining a casting blank containing the chemical components;
heating, hot rolling, cooling after rolling and coiling the casting blank in sequence to obtain a hot rolled coil;
sequentially carrying out acid washing, continuous annealing and hot galvanizing on the hot-rolled coil to obtain hot-galvanized high-strength steel;
the temperature of the hot galvanizing is 440-500 ℃, and the mass fraction of aluminum in the zinc liquid is 0.15-0.25% in the hot galvanizing.
7. The method as claimed in claim 6, wherein the heating temperature is 1150-1250 ℃, the heating time is less than or equal to 50min, and the mass fraction of oxygen during heating is less than or equal to 3%.
8. The method as claimed in claim 6, wherein the final rolling temperature of the hot rolling is 900-960 ℃, and the hot rolling adopts high-pressure descaling with the pass descaling pressure being more than or equal to 5 passes, and the pass descaling pressure being more than or equal to 10 MPa.
9. The method as claimed in claim 6, wherein the cooling rate after rolling is more than or equal to 25 ℃/s, the coiling temperature is less than or equal to 650 ℃, and the surface roughness Ra after acid rolling is less than or equal to 2.0 μm.
10. The method as claimed in claim 6, wherein the continuous annealing comprises heating, soaking and cooling, the soaking temperature is 760-; the protective atmosphere of the continuous annealing comprises: the dew point temperature is-30 to-50 ℃, the mass fraction of the hydrogen is 5 to 15 percent, and the volume concentration of the oxygen is less than or equal to 20 ppm.
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Application publication date: 20211105 |