CN112553537A - Cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa and manufacturing method thereof - Google Patents

Cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa and manufacturing method thereof Download PDF

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CN112553537A
CN112553537A CN201910909497.1A CN201910909497A CN112553537A CN 112553537 A CN112553537 A CN 112553537A CN 201910909497 A CN201910909497 A CN 201910909497A CN 112553537 A CN112553537 A CN 112553537A
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rolling
cold
hot
dip galvanized
galvanized steel
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王进
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Shanghai Meishan Iron and Steel Co Ltd
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Shanghai Meishan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/58—Roll-force control; Roll-gap control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
    • B21B45/08—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing hydraulically
    • 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
    • C21D1/26—Methods of 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
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/0236—Cold 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
    • C21D8/0247—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
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/02—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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/221—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by cold-rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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
    • C21D2211/009—Pearlite

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  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

The invention discloses a cold-rolled hot-dip galvanized steel sheet with 240 MPa-grade yield strength and a manufacturing method thereof, and mainly solves the technical problems that the 240 MPa-grade cold-rolled hot-dip galvanized steel sheet in the prior art has large yield strength fluctuation and chromatic aberration on the surface. The invention provides a high-surface hot-dip galvanized steel sheet with yield strength of 240MPa, which comprises the following chemical components in percentage by weight: c: 0.025-0.050%, Si is less than or equal to 0.030%, Mn: 0.18-0.28%, P is less than or equal to 0.020%, S is less than or equal to 0.018%, B: 0.0010-0.0020%, Al: 0.025-0.050%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurity elements. The yield strength of a cold-rolled hot-dip galvanized steel plate with the thickness of 0.35-0.65 mm is 240-280 MPa, and the steel plate is mainly used in the household appliance industry in the high surface passivation direction.

Description

Cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa and manufacturing method thereof
Technical Field
The invention relates to a cold-rolled hot-galvanized steel sheet, in particular to a cold-rolled hot-galvanized steel sheet with yield strength of 240MPa and a manufacturing method thereof, and specifically relates to a cold-rolled hot-galvanized low-carbon steel sheet with yield strength of 240-280 MPa and a manufacturing method thereof, belonging to the technical field of iron-based alloys.
Background
In recent years, with the development of industries such as household appliance manufacturing and the like and the fierce competition of the steel industry, the requirement of the domestic household appliance industry on products in the manufacturing process is developed towards the trend of high surface, high performance, high strength and thinning, and the requirement of the hot galvanized plate for manufacturing passivation direction household appliance steel on the performance that the yield strength fluctuation is less than or equal to 60MPa is met, so that the hot galvanized plate has stable deformation resistance; but also has the requirement of high surface quality without obvious color difference on the surface of the galvanized sheet, and improves the appearance aesthetic property of the galvanized sheet.
The application publication number is CN109778069A, and Chinese patent application discloses a one-steel multi-stage cold-rolled low-alloy high-strength steel with yield strength covering 240-270 Mpa and a manufacturing method thereof, wherein the steel comprises the following components in percentage by weight: c: 0.05-0.09% of Mn, 0.30-0.50% of Mn, and noble Nb elements are added: 0.010-0.020%, the hot rolling coiling temperature adopts a design of higher coiling temperature, the scale of the strip steel can be thickened due to the high coiling temperature, and the strip steel is not easy to clean during acid washing of the next process and is easy to generate the problem of surface color difference in the subsequent process.
The Chinese patent application with the application publication number of CN104451377A discloses a low-carbon aluminum killed steel hot-dip galvanized sheet and a production method thereof, and the product is used for a color-coated sheet and mainly solves the problem of bending and chamfering; the hot rolling coiling temperature adopts a design of higher coiling temperature, and the scale of the strip steel can be thickened due to the high coiling temperature, so that the strip steel is not easy to clean during acid washing in the next process and is easy to cause the risk of surface color difference in the subsequent process.
The application publication number CN104651712A discloses a CQ-grade hot-dip galvanized steel strip for a door plate of an anti-theft door and a production process thereof, wherein the yield strength is reduced mainly through high coiling temperature, but the oxide scale of the steel strip is thickened due to the high coiling temperature, and the steel strip is not easy to clean during acid washing of the next process and is easy to generate the problem of surface color difference in the next process.
Disclosure of Invention
The invention aims to provide a cold-rolled hot-dip galvanized steel sheet with a yield strength of 240MPa and a manufacturing method thereof, and mainly solves the technical problems that the yield strength of the 240MPa cold-rolled hot-dip galvanized steel sheet fluctuates greatly and the surface has color difference in the prior art.
The invention adopts the technical idea that under the condition of not adding noble alloy, the design of economic carbon, manganese and a proper amount of boron in the components is reasonably utilized, meanwhile, the contradiction between the structure performance and the surface quality of the strip steel is regulated and controlled by fully utilizing the processes of hot rolling temperature and the like, and the recrystallized ferrite and a small amount of pearlite structures are obtained by utilizing the characteristics of short-time annealing and rapid heating capabilities of a horizontal continuous annealing furnace through a high-temperature rapid annealing process, so that the narrow yield performance range required by products is ensured, and the products with no surface color difference in the passivation direction are also met.
The invention adopts the technical scheme that a cold-rolled hot-dip galvanized steel plate with the yield strength of 240MPa is characterized in that a substrate comprises the following chemical components in percentage by weight: c: 0.025-0.050%, Si is less than or equal to 0.030%, Mn: 0.18-0.28%, P is less than or equal to 0.020%, S is less than or equal to 0.018%, B: 0.0010-0.0020%, Al: 0.025-0.050%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurity elements.
The metallographic structure of the cold-rolled hot-dip galvanized steel plate is ferrite and pearlite, the ferrite grain size grade is I7.5-I9.0 grade, and the yield strength R of the cold-rolled hot-dip galvanized steel plate with the thickness of 0.35-0.65 mmP0.2240 to 280MPa, tensile strength Rm340-380 MPa, elongation after break A80mmNot less than 30 percent, and the surface of the cold-rolled hot-dip galvanized steel plate has no color difference.
The reason why the chemical composition of the substrate of the high-surface hot-dip galvanized steel sheet with a yield strength of 240MPa is limited to the above range is as follows:
carbon: carbon is a solid solution strengthening element that increases the strength of the steel. When the carbon content in the steel is higher, the strength is increased, and more large and thick brittle carbide particles are formed in the steel, so that the forming is not favorable; if the carbon content is too low, the strength of the steel plate is also inevitably reduced, and the carbon content range of the invention needs to be strictly limited, because the strength of the steel plate is sensitive to the carbon content, if the carbon content range is wider, the strength fluctuation of the steel plate is large, and the requirement of a user on the narrower performance range of the product cannot be met; the carbon content range of the invention is set to be 0.025-0.050 percent in comprehensive consideration;
silicon: silicon is taken as a solid solution strengthening element, and has a good strengthening effect when being dissolved in a steel plate matrix; however, the invention must control the silicon content, and when the silicon content is higher, heavier Fe is formed on the surface of the hot rolled plate2O3The steel is difficult to be washed and removed completely in the acid washing process, the surface quality of a zinc coating is affected in the subsequent hot galvanizing process, iron atoms in a steel matrix can be rapidly transferred to zinc liquid on the surface layer of a plated part when the SI content is higher, the zeta-phase growth speed is also accelerated, the steel can penetrate into a thin pure zinc layer and be damaged, and the surface of the coating becomes rough and dull, so that the Si content is controlled to be less than or equal to 0.030 percent.
Manganese: manganese is used as a main element for solid solution strengthening, and proper manganese is added into steel, so that the strength is improved, the desulfurization is facilitated, and the hot brittleness of the steel can be avoided; but the Mn content is high, the strength is higher, and the cost of steel is correspondingly increased; meanwhile, in order to reduce the fluctuation of the strength, the manganese content range needs to be limited. Therefore, the Mn content is limited to be 0.18-0.28 percent in the invention.
Phosphorus: phosphorus is an element with low price and strong solid solution strengthening capability, is easy to segregate in grain boundaries, reduces the bonding force of the grain boundaries, deteriorates the cold workability of steel, and therefore, the content of the phosphorus in the steel is reduced as much as possible; meanwhile, too high phosphorus is segregated in the grain boundary to accelerate the corrosion of the steel plate matrix, and the problem of surface color difference caused by over-pickling is easy to occur, so that the surface quality of subsequent galvanization is influenced. Therefore, the invention limits P to less than or equal to 0.020%.
Sulfur: sulfur is a harmful element in steel; sulphur forms sulphide inclusions in the steel, reducing its ductility and toughness; therefore, the S is controlled to be lower level as much as possible, and the invention limits the S to be less than or equal to 0.018 percent.
Boron: in the invention, trace boron is added to delay the precipitation of ferrite, namely, the nucleation rate of the ferrite can be reduced, and coarse grains can be obtainedThe size not only improves the plasticity of the steel plate, but also can reduce the yield strength to meet the product performance requirement; meanwhile, the N fixation capacity is far greater than that of Ti and Al, so that the occurrence of aging can be prevented and alleviated; and adding B element and optionally reducing Ar3The temperature of the phase transition point. The content of B is limited to be 0.0010-0.0020%.
Nitrogen: nitrogen belongs to harmful elements in the steel, can seriously reduce the plasticity and toughness of the material, is sensitive to time efficiency and is not beneficial to the subsequent processing formability of the steel plate, so the nitrogen content is required to be limited; the invention limits N to be less than or equal to 0.005 percent.
Aluminum: aluminum is a strong oxidizing element and forms Al with oxygen in steel2O3Removing the steel during steel making; and the bonding force with N is strong, and compound AlN is formed, so that the strain timeliness of the steel is changed, and the continuous yield phenomenon is eliminated. However, too high aluminum will form too much Al2O3Inclusion and the continuous casting are easy to block the casting nozzle. The invention limits the Al content to be 0.025-0.050%.
A method for manufacturing a cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa grade comprises the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.025-0.050%, Si is less than or equal to 0.030%, Mn: 0.18-0.28%, P is less than or equal to 0.020%, S is less than or equal to 0.018%, B: 0.0010-0.0020%, Al: 0.025-0.050%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurity elements;
heating the continuous casting plate blank to 1180-1220 ℃ by a heating furnace, and then carrying out hot rolling, wherein the hot rolling is a two-section type rolling process, the rough rolling is 5-pass continuous rolling, the rough rolling is carried out at a temperature above the austenite recrystallization temperature, the rough rolling finishing temperature is 1030-1080 ℃, and the rough rolling descaling water pressure is 18-20 MPa; after rough rolling, controlling the thickness of the intermediate billet to be 38-42 mm; the finish rolling is 7-pass continuous rolling, rolling is carried out in an austenite single-phase region, the finish rolling temperature is 860-900 ℃, the descaling water pressure at the finish rolling inlet is 18-20 MPa, and the descaling water pressure between finishing mill frames is 10-12 MPa; after finish rolling, controlling the thickness of the steel plate to be 2.5-3.5 mm, adopting front-section cooling for laminar cooling, and coiling at 590-650 ℃ to obtain a hot-rolled steel coil;
and (2) uncoiling the hot-rolled steel coil again, then carrying out acid pickling, cold rolling, annealing in a horizontal continuous annealing furnace, hot galvanizing and leveling, and coiling to obtain a finished hot-galvanized steel plate with the thickness of 0.35-0.65 mm, wherein the acid pickling speed of the strip steel is 60-75 m/min, the cold rolling reduction rate is 75-90%, the temperature of the cold-rolled hard strip steel in the annealing soaking section of the horizontal continuous annealing furnace after cold rolling is 770-800 ℃, the annealing time of the strip steel in the soaking section is 30-50 s, and the leveling elongation rate is 0.8-1.2%.
The technical key for realizing the invention is the control of the surface iron scale of the hot rolled steel plate through the regulation and control of components and the hot rolling process. Calculated by simulation test, the component system Ar of the invention3Point phase transition temperature of 835 ℃ and Ar1The point transition temperature was 698 ℃. The hot rolling process adopted by the invention is based on the component system and the phase transformation point calculated by a simulation test.
The production process adopted by the invention has the following reasons:
1. setting of heating temperature of continuous casting slab
In order to ensure the finish rolling temperature, the hot rolling process is carried out in an austenite region, the temperature of the continuous casting plate blank out of a heating furnace cannot be too low, otherwise, the finish rolling temperature cannot be ensured, and the smooth operation of production is not facilitated; if the heating temperature of the plate blank is too high, thicker iron scale can be generated on the surface of the plate blank, and the plate blank is easy to press into the surface of the strip steel in the subsequent hot rolling rough rolling and finish rolling processes, so that the surface quality of a finished product is influenced. The heating temperature of the plate blank is set to 1180-1220 ℃.
2. Setting of roughing finishing temperature and roughing descaling water pressure
The rough rolling process needs to be controlled above the austenite recrystallization temperature for rolling. The finish temperature of rough rolling is too high, excessive secondary iron scale is easy to form, the finish rolling process is not easy to remove, and the landscape-shaped iron scale defect can be formed on the surface of the steel plate after acid washing, so that the use of the surface of the steel plate and a user is influenced; if the rough rolling finishing temperature is too low, the finish rolling finishing temperature, namely rolling above the austenite recrystallization temperature, cannot be ensured, and the rough rolling finishing temperature is set to be 1030-1080 ℃.
The rough rolling descaling aims to remove iron scales generated on the surface of a slab in the heating process, if the iron scales are not removed effectively in time, the surface of the slab is roughed slightly, and the iron scales generated on the surface of strip steel are pressed into the surface of the strip steel seriously, so that the surface quality is influenced; in order to meet the quality requirement of high-surface products, the descaling pressure is set to be 18-20 MPA.
3. Setting of thickness of intermediate blank
The thickness of the intermediate billet affects the finish rolling temperature of the steel plate, if the thickness of the intermediate billet is too low, the temperature drop of the strip billet is too large, so that the subsequent finish rolling temperature is reduced, particularly the temperature drop of the edge of the steel plate is large, the steel plate can be rolled in an austenite and ferrite two-phase region, and the structure performance of the strip steel can be deteriorated. If the intermediate slab is too thick, the finish rolling load and rolling stability increase. The thickness of the intermediate blank is set to be 38-42 mm.
4. Setting of finish rolling inlet temperature and finish rolling descaling water pressure
The finish rolling inlet temperature affects the finish rolling temperature and surface quality of the steel sheet. The entry temperature of finish rolling is too high, excessive secondary iron scale is easily formed, the finish rolling process is not easy to remove, and a landscape-shaped iron scale defect is formed on the surface of the steel plate after acid washing, so that the use of the surface of the steel plate and a user is influenced; if the finish rolling entry temperature is too low, the finish rolling end temperature, i.e., the rolling temperature above the austenite recrystallization temperature, cannot be ensured. The inlet temperature of the finish rolling is set to be 990-1040 ℃.
The finish rolling descaling is also to remove surface iron scale generated in the rolling process, and in order to obtain high surface quality requirements, the descaling pressure at the finish rolling inlet is 18-20 MPA; the descaling pressure between the racks is 10-12 MPA.
5. Setting of finish Rolling finishing temperature
The finish rolling process of the invention needs to roll in an austenite single-phase region, and if the finish rolling temperature is too low, the finish rolling process can deteriorate the organization performance of the product when rolling in a ferrite and austenite two-phase region; if the finish rolling finishing temperature is set to be too high, not only is the production line difficult to reach, but also the iron scale on the surface of the steel plate is serious and is difficult to remove during acid cleaning, so that the surface quality is influenced; the finish rolling finishing temperature of the invention is set to 860-900 ℃.
6. Setting of laminar cooling mode after finish rolling
After finishing rolling, if the steel plate is cooled at the rear section, the strip steel is exposed in the air and contacts with oxygen for a long time to generate thick iron scales; therefore, the invention adopts front-stage cooling, and mainly reduces the thickness of the iron scale as much as possible, thereby being beneficial to the surface quality of subsequent pickling. Therefore, the invention sets the laminar cooling mode after finish rolling to adopt front-stage cooling.
7. Setting of coiling temperature in Hot Rolling
If the hot rolling coiling temperature of the strip steel produced by the invention is too high, not only recrystallized grains are easy to grow up and the yield strength is too low, but also the scale is too thick, and the scale on the surface is easy to acid and cannot be completely washed in the subsequent acid washing process, particularly in the push-pull acid washing process, so that the friction effect between the steel plate and a roller is changed, the non-uniform deformation degree in cold rolling is increased, and the problem of surface color difference caused by cold rolling and galvanization is solved; if the hot rolling coiling temperature is too low, the performance is improved, and the stability of the whole coiling performance of the steel coil is influenced; in order to ensure the surface quality and narrow performance range, the coiling temperature range set by the invention is 590-650 ℃.
8. Acid cleaning process parameter setting
The acid washing process is a simple push-pull type acid washing process, wherein the temperature of an acid washing tank is 70-80 ℃, and the acid liquor concentration of a main tank is 18-20%; in order to ensure the pickling effect and avoid the surface quality problems of over-pickling and under-pickling, thereby causing the defects of surface color difference and the like of the subsequent process, the pickling production speed is set as follows: 60 to 75 m/min.
9. Cold rolling reduction setting
Due to the increase of the cold rolling deformation, the recrystallization of the subsequent annealing can be promoted, and a fine grain structure is obtained, so that the strength of the steel plate is improved; if the deformation is too high, the load of the rolling mill is too large, and the shape and the production stability of the strip steel are influenced; the cold rolling reduction rate is set to be 75-90%;
10. setting of annealing temperature and annealing time
In order to ensure that the galvanized product of the invention obtains proper and stable yield strength, the grain size of recrystallization is controlled, the annealing temperature of continuous annealing is not too high, and the annealing time can ensure that the recrystallization is finished. The annealing temperature of the strip steel in the soaking section of the horizontal continuous annealing furnace is set to 770-800 ℃, and the annealing time of the strip steel in the soaking section of the horizontal continuous annealing furnace is set to 30-50 s
11. Setting of the Flat elongation
The flattening can not only ensure the good plate shape of the strip steel, but also be beneficial to the surface quality through proper flattening rate, and the flattening elongation rate of the invention is 0.8-1.2%.
The metallographic structure of the cold-rolled hot-dip galvanized steel sheet produced by the method is ferrite and pearlite, the ferrite grain size level is I7.5-I9.0, and the yield strength R of the cold-rolled hot-dip galvanized steel sheetP0.2240 to 280MPa, tensile strength Rm340-380 MPa, elongation after break A80mmNot less than 30 percent, and the surface of the cold-rolled hot-dip galvanized steel plate has no color difference.
Compared with the prior art, the invention has the following positive effects: 1. the invention adopts the design of the composition of the low-carbon steel containing micro boron, and the matching design of hot rolling, pickling, cold rolling, annealing and flattening processes, thereby obtaining the high-surface galvanized product meeting the passivation direction, and the surface quality and the product performance, particularly the yield strength of the high-surface galvanized product meet the processing requirements of high-end household appliance users. 2. By adopting the reasonable design of proper boron content and low coiling temperature, the invention not only can reduce the yield strength of the product to proper performance requirements, but also can obviously reduce the thickness of the oxide scale on the surface of the hot rolled steel, and can effectively improve the surface effect of the post-process acid washing process, particularly push-pull acid washing, and obtain the hot galvanized plate with high surface quality, thereby meeting the product requirements in the passivation direction. 3. The overall design of the invention not only ensures that the surface quality and the performance of the product meet the product requirements in the passivation direction, but also can improve the pickling efficiency of the pickling process to a certain extent and reduce the production process cost.
Drawings
FIG. 1 is a photograph showing a metallographic structure of a cold-rolled hot-dip galvanized steel sheet according to example 1 of the present invention.
Detailed Description
The present invention is further described with reference to examples 1 to 4, and as shown in tables 1 to 4, Table 1 shows the chemical compositions (in weight%) of the substrates of the hot-dip galvanized steel sheets according to examples of the present invention, and the balance Fe and inevitable impurities.
Table 1 chemical composition of substrate of hot dip galvanized steel sheet according to example of the present invention, unit: and (4) weight percentage.
Element(s) C Si Mn P S B Al N
The invention 0.025-0.050 ≤0.030 0.18-0.28 ≤0.020 ≤0.018 0.001-0.002 0.025-0.050 ≤0.0050
Example 1 0.0317 0.0021 0.182 0.0107 0.0112 0.0016 0.0428 0.00144
Example 2 0.0405 0.0024 0.195 0.0146 0.008 0.0018 0.0318 0.00177
Example 3 0.0437 0.0024 0.189 0.0137 0.005 0.0014 0.0376 0.00156
Example 4 0.0452 0.0026 0.207 0.0103 0.0084 0.0015 0.038 0.00199
The method comprises the steps of smelting in a converter to obtain molten steel meeting the requirements of chemical components, carrying out vacuum decarburization and degassing treatment on the molten steel in an RH furnace, and carrying out continuous casting on the molten steel under the protection of Ar blowing in the whole process to obtain a continuous casting slab, wherein the thickness of the continuous casting slab is 210-230 mm, the width of the continuous casting slab is 900-1600 mm, and the length of the continuous casting slab is 8500-11000 mm.
And (3) sending the fixed-length plate blank produced in the steel-making process to a heating furnace for reheating, taking out the plate blank from the furnace for descaling, and sending the plate blank to a hot continuous rolling mill for rolling. Descaling and controlled rolling by a rough rolling and finish rolling continuous rolling unit, coiling after laminar cooling, cooling the front section of the laminar flow to produce a qualified hot rolled steel coil, wherein the thickness of the hot rolled steel coil is 2.5-3.5 mm. The hot rolling process control parameters are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
Figure BDA0002214288480000061
And uncoiling the hot-rolled steel coil again, then carrying out acid pickling, cold rolling, degreasing, annealing by a horizontal continuous annealing furnace, hot galvanizing and leveling, and coiling to obtain the hot-galvanized steel coil with the thickness of 0.35-0.65 mm. The degreasing adopts the conventional process, and the annealing process comprises the following steps: the temperature of the rolled hard strip steel after cold rolling in the annealing soaking section of the horizontal continuous annealing furnace is 770-800 ℃, the annealing time of the strip steel in the soaking section is 30-50 s, and the flat elongation is 0.8-1.2%. The control parameters of the cold rolling, annealing and flattening processes are shown in Table 3.
TABLE 3 control parameters of the cold rolling, annealing and leveling processes of the examples of the present invention
Figure BDA0002214288480000062
Figure BDA0002214288480000071
Referring to fig. 1, the metallographic structure of the cold-rolled hot-dip galvanized steel sheet is ferrite + pearlite, the ferrite grain size is in the grade of I7.5 to I9.0, and the yield strength R of the cold-rolled hot-dip galvanized steel sheet isP0.2240 to 280MPa, tensile strength Rm340-380 MPa, elongation after break A80mmNot less than 30 percent, and the surface of the cold-rolled hot-dip galvanized steel plate has no color difference.
The hot dip galvanized steel sheet obtained by the invention is subjected to a tensile test on a GB/T228.1-2010 metal material part 1: the mechanical properties of the hot-dip galvanized steel sheets are shown in Table 4.
TABLE 4 mechanical properties of hot-dip galvanized steel sheets according to examples of the present invention
Figure BDA0002214288480000072
From the performances of table 4, the hot-dip galvanized sheet of the invention has a proper strength range, particularly the indexes such as yield strength and the like meet the requirements, and the hot-dip galvanized sheet has excellent surface quality and no color difference on the surface, and completely meets the processing requirements of household electrical appliances users in the passivation direction for manufacturing the household electrical appliance sheet.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.

Claims (4)

1. A cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa grade comprises the following chemical components in percentage by weight: c: 0.025-0.050%, Si is less than or equal to 0.030%, Mn: 0.18-0.28%, P is less than or equal to 0.020%, S is less than or equal to 0.018%, B: 0.0010-0.0020%, Al: 0.025-0.050%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurity elements; metallographic structure of cold-rolled hot-dip galvanized steel sheetIs ferrite and pearlite, the ferrite grain size grade is I7.5-I9.0 grade, and the yield strength R of a cold-rolled hot-dip galvanized steel plate with the thickness of 0.35-0.65 mmP0.2240 to 280MPa, tensile strength Rm340-380 MPa, elongation after break A80mmNot less than 30 percent, and the surface of the cold-rolled hot-dip galvanized steel plate has no color difference.
2. A manufacturing method of a cold-rolled hot-dip galvanized steel plate with yield strength of 240MPa is characterized by comprising the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.025-0.050%, Si is less than or equal to 0.030%, Mn: 0.18-0.28%, P is less than or equal to 0.020%, S is less than or equal to 0.018%, B: 0.0010-0.0020%, Al: 0.025-0.050%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurity elements;
heating the continuous casting plate blank to 1180-1220 ℃ by a heating furnace, and then carrying out hot rolling, wherein the hot rolling is a two-section type rolling process, the rough rolling is 5-pass continuous rolling, the rough rolling is carried out at a temperature above the austenite recrystallization temperature, the rough rolling finishing temperature is 1030-1080 ℃, and the rough rolling descaling water pressure is 18-20 MPa; after rough rolling, controlling the thickness of the intermediate billet to be 38-42 mm; the finish rolling is 7-pass continuous rolling, rolling is carried out in an austenite single-phase region, the finish rolling temperature is 860-900 ℃, the descaling water pressure at the finish rolling inlet is 18-20 MPa, and the descaling water pressure between finishing mill frames is 10-12 MPa; adopting front-section cooling for laminar cooling, and coiling at 590-650 ℃ to obtain a hot-rolled steel coil;
and (2) uncoiling the hot-rolled steel coil again, then carrying out acid pickling, cold rolling, annealing in a horizontal continuous annealing furnace, hot galvanizing and leveling, and coiling to obtain a finished hot-galvanized steel plate with the thickness of 0.35-0.65 mm, wherein the acid pickling speed of the strip steel is 60-75 m/min, the cold rolling reduction rate is 75-90%, the temperature of the cold-rolled hard strip steel in the annealing soaking section of the horizontal continuous annealing furnace after cold rolling is 770-800 ℃, the annealing time of the strip steel in the soaking section is 30-50 s, and the leveling elongation rate is 0.8-1.2%.
3. The method for manufacturing a cold-rolled hot-dip galvanized steel sheet with a yield strength of 240MPa according to claim 2, wherein the thickness of the steel sheet is controlled to be 2.5 to 3.5mm after the hot-rolling and finish-rolling.
4. The method for manufacturing a cold-rolled hot-dip galvanized steel sheet with a yield strength of 240MPa according to claim 2, wherein the metallographic structure of the cold-rolled hot-dip galvanized steel sheet is ferrite + pearlite, the ferrite grain size is I7.5-I9.0 grade, and the yield strength R of the cold-rolled hot-dip galvanized steel sheetP0.2240 to 280MPa, tensile strength Rm340-380 MPa, elongation after break A80mmNot less than 30 percent, and the surface of the cold-rolled hot-dip galvanized steel plate has no color difference.
CN201910909497.1A 2019-09-25 2019-09-25 Cold-rolled hot-dip galvanized steel sheet with yield strength of 240MPa and manufacturing method thereof Pending CN112553537A (en)

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