CN109097705B - 800 MPa-grade cold-rolled hot-galvanized dual-phase steel and production method thereof - Google Patents
800 MPa-grade cold-rolled hot-galvanized dual-phase steel and production method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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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- 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
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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
- C21D8/0247—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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- 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
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
Abstract
The invention discloses 800 MPa-grade cold-rolled hot-galvanized dual-phase steel which comprises the following raw materials in percentage by mass: 0.05 to 0.10 percent of C, 1.60 to 2.30 percent of Mn, 0.010 to 1.0 percent of Als, 0.10 to 0.60 percent of Si, 0.010 to 0.050 percent of Nb, 0.05 to 0.30 percent of Cr, 0.05 to 0.30 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and inevitable impurities, wherein the noble metal elements Cr and Mo satisfy the relation formula: cr + Mo is more than or equal to 0.05 and less than or equal to 0.30, and C + Si/30+ Mn/20 is more than or equal to 0.22. The production method of the hot galvanizing steel for the automobile wheel cover comprises the steps of smelting, continuous casting, heating, hot rolling, cooling, coiling, pickling, cold rolling, annealing and coating. The cold-rolled hot-galvanized dual-phase steel obtained by the method has less noble alloy elements, and the product has good mechanical property, surface quality, forming property and welding property, and can be produced on the conventional production line without additionally adding equipment.
Description
Technical Field
The invention relates to 800 MPa-grade cold-rolled hot-galvanized dual-phase steel and a production method thereof, belonging to the field of manufacturing of ultrahigh-strength steel for cold-rolled hot-galvanized automobiles.
Background
In recent years, with the advance of automobile energy saving and emission reduction technology, the weight reduction of automobiles becomes a development trend. The 780MPa grade and above ultrahigh-strength steel is one of the development directions of automobile lightweight materials, and is widely applied due to good strong plasticity, low yield ratio, high initial work hardening rate and good bake hardenability of ferrite and martensite dual-phase high-strength steel. Compared with the common cold-rolled high-strength dual-phase steel, the galvanized dual-phase steel also has good corrosion resistance, so that the galvanized dual-phase steel is widely applied to automobile structural members such as door anti-collision beams, longitudinal beam reinforcing plates, guide groove reinforcing plates and the like.
In order to ensure the mechanical property, welding property, forming property, surface quality and the like of the galvanized ultrahigh-strength dual-phase steel, the current 800 MPa-grade galvanized dual-phase steel adopts a low-carbon, medium-manganese and low-silicon component system, and is compounded and added with more expensive alloy elements such as Cr, Mo, V and the like. The production process route adopts the process flows of steel making, continuous casting, hot rolling, cold rolling and galvanizing annealing.
In the prior art, the alloy cost is high due to the addition of high alloy elements such as Cr and Mo (the content of Cr + Mo is generally more than 0.3), and the content of Si in steel is generally controlled below 0.05% in order to control the surface quality of products. In order to reduce the alloy cost, more than 0.40 percent of Si is adopted to produce 800MPa grade dual-phase steel in the prior art, but when the high Si content is adopted for production, a production line has the function of pre-oxidation or direct-fire heating so as to solve the problem of plating leakage during galvanizing due to external oxidation, and thus galvanized products with high surface quality are produced, and therefore, the conventional production line without the direct-fire heating function is difficult to produce galvanized products with high surface quality. In addition, the existing product has the problems of forming cracking and the like in the using process of a user.
Reference documents:
1, CN 106399857A: a production method of Si-containing cold-rolled hot-galvanized dual-phase steel with 800 MPa-level tensile strength;
CN 106011631 a: 800 MPa-grade low-carbon hot-galvanized dual-phase steel and a preparation method thereof;
3, CN 102433509A: 780 MPa-grade cold-rolled hot-galvanized dual-phase steel and a preparation method thereof;
CN 105441805A: a galvanized dual-phase steel for 800MPa class cars and a production method;
5, CN 1782116A: a 800MPa grade cold-rolled hot-galvanized dual-phase steel and a manufacturing method thereof.
Disclosure of Invention
The invention aims to provide 800 MPa-grade cold-rolled hot-galvanized dual-phase steel and a production method thereof, which solve the problem that the cost is higher due to more noble alloy elements such as Cr, Mo and V in the prior art; when galvanized dual-phase steel with higher Si content is produced on a conventional production line without direct-fire heating, the surface quality problem occurs; and the existing product has lower forming performance in the forming process and has the technical problems of cracking and the like. The cold-rolled hot-galvanized dual-phase steel has less noble alloy elements, and the product has good mechanical property, surface quality, forming property and welding property, and can be produced on the conventional production line without additionally adding equipment.
The invention relates to 800 MPa-grade cold-rolled hot-galvanized dual-phase steel which comprises the following raw materials in percentage by mass: 0.05 to 0.10 percent of C, 1.60 to 2.30 percent of Mn, 0.010 to 1.0 percent of Als, 0.10 to 0.60 percent of Si, 0.010 to 0.050 percent of Nb0.010 percent, 0.05 to 0.30 percent of Cr, 0.05 to 0.30 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and inevitable impurities, wherein the noble metal elements Cr and Mo satisfy the relation formula: cr + Mo is more than or equal to 0.05 and less than or equal to 0.30, and C + Si/30+ Mn/20 is more than or equal to 0.22.
On the other hand, the invention also relates to a production method of 800 MPa-grade cold-rolled hot-galvanized dual-phase steel, which comprises the steps of smelting, continuous casting, heating, hot rolling, cooling, coiling, pickling, cold rolling, annealing and coating, and is characterized in that:
1) in the smelting step, molten steel is refined by adopting refining modes such as RH, LF and the like;
2) in the continuous casting step, the casting superheat degree is 15-30 ℃;
3) in the slab heating step, the slab discharging temperature is 1180-1300 ℃, and the heating time is 150-300 min;
4) in the hot rolling step, the final hot rolling temperature is 850-950 ℃;
5) in the cooling step, when the temperature of the strip steel is more than or equal to 620 ℃, the average cooling rate of the strip steel is more than or equal to 15 ℃/s;
6) in the coiling step, the coiling temperature is 500-620 ℃;
7) in the step of pickling and cold rolling, the cold rolling reduction is controlled to be 40-70%;
8) in the continuous annealing step, the annealing temperature is 760-840 ℃, wherein the heating speed is less than or equal to 5 ℃/s when the temperature is less than or equal to 760 ℃, the heat preservation time is 60-300s when the temperature is 760-840 ℃, the cooling speed is more than or equal to 15 ℃/s, the dew point in the annealing furnace is 0-40 ℃, and H in the furnace is2Content of 1-5%, H2O/H2≤1.0；
9) In the coating step, the temperature of the strip steel in a zinc pot is 440-500 ℃, the temperature of zinc liquid is 450-470 ℃, and the content of zinc liquid and aluminum is 0.15-0.25%.
Description
The invention provides 800 MPa-grade cold-rolled hot-galvanized dual-phase steel which comprises the following raw materials in percentage by mass: 0.05 to 0.10 percent of C, 1.60 to 2.30 percent of Mn, 0.010 to 1.0 percent of Als, 0.10 to 0.60 percent of Si, 0.010 to 0.050 percent of Nb0.010 percent, 0.05 to 0.30 percent of Cr, 0.05 to 0.30 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and inevitable impurities, wherein the noble metal elements Cr and Mo satisfy the relation formula: cr + Mo is more than or equal to 0.05 and less than or equal to 0.30, and C + Si/30+ Mn/20 is more than or equal to 0.22.
The cold-rolled hot-dip galvanized dual-phase steel provided by the invention can further comprise at least one or more elements of Ti, Ca, Ni, Cu and B, and the components in percentage by mass (%) are as follows: 0.005-0.030% Ti, 0.0001-0.10% Ca, 0.03-0.20% Ni, 0.03-0.30% Cu, 0.0005-0.0050% B.
The following are descriptions of the role of the main components involved in the invention and their limitations:
carbon: carbon has a solid solution strengthening effect in steel, or forms fine MC particles with carbide forming elements such as Nb, Ti, Mo and the like in the steel, plays a role in precipitation strengthening and grain refinement, and improves the strength of steel. The carbon content also affects the content and strength of martensite in the steel, and the excessively high carbon content reduces the weldability of the steel, so that the content of the C element in the steel is limited to 0.05% to 0.10% in comprehensive consideration.
Manganese: manganese plays a role in solid solution strengthening, austenite stabilizing and hardenability improvement in steel, and the content is too low, the strengthening effect is too small, and the austenite is unstable. The Mn content is too high, serious segregation is easily formed in the thickness center of the plate strip, the toughness of the product is reduced, cracking is easily caused in the forming process, meanwhile, the Mn content is too high, the alloy cost of the product is obviously increased, and therefore the Mn element content is limited to 1.50-2.30%.
Silicon: silicon plays a remarkable role in solid solution strengthening in steel, effectively inhibits precipitation of carbides, delays pearlite transformation and the like in the phase transformation process, has low Si content and unobvious effects of inhibiting precipitation of carbides and transformation of pearlite, but has high Si content, easily forms iron sheets which are difficult to remove in hot rolling, and finally remains on the surface of a product to seriously affect the surface quality, so that the Si element content is limited to 0.10-0.60%.
Aluminum: aluminum is a strong deoxidizer, can effectively reduce the residual oxygen in steel, reduce the content of inclusions in the steel, and easily causes the problems of difficult casting and the like due to excessive addition of Als. Therefore, the content of Als element in the present invention is limited to 0.01 to 1.0%.
Sulfur: sulfur is an impurity element in steel, is easy to generate segregation in grain boundaries, forms FeS with low melting point with Fe in the steel, reduces the toughness of the steel, and is fully removed during steel making, so that the content of the S element is controlled to be less than 0.010%.
Phosphorus: phosphorus is an impurity element in steel, is easy to segregate in grain boundaries and influences the toughness of products, so that the lower the content of phosphorus, the better the product. According to the actual control level, the content of the S element is controlled to be below 0.015 percent.
Nitrogen: nitrogen is an impurity element in steel, reduces toughness of steel, easily reacts with nitride particles in the form of Al, Nb, Ti, etc. in steel, and is excessively high, and coarse AlN and TiN are easily formed to reduce toughness of steel, so that the content thereof is reduced as much as possible, and the content of N element is controlled to 0.008% or less.
Chromium: the chromium can remarkably improve the hardenability of the steel, has the functions of inhibiting carbide precipitation and pearlite transformation, is beneficial to promoting the formation of martensite in the dual-phase steel, but the content is too high to increase the cost, so the content of the Cr element is limited to 0.05-0.30 percent.
Molybdenum: molybdenum can remarkably improve the hardenability of steel and inhibit pearlite transformation and bainite transformation, and the manufacturing cost of the steel is remarkably increased due to the excessively high content of Mo, so that the content of Mo element is limited to 0.05-0.30 percent in the invention.
Niobium: niobium can significantly refine ferrite grains in steel and improve the strength and toughness of steel, and also forms particles such as NbC, NbN and the like with elements such as C, N and the like in steel, thereby playing a role in significantly strengthening precipitation and improving the strength of steel, but the content of Nb is too high, which increases the manufacturing cost of steel, so the content of Nb is limited to 0.01-0.05% in the invention.
Titanium: titanium plays a role in solid solution strengthening in steel, and Ti combines with C, N in steel to form TiC and TiN, playing a role in precipitation strengthening. However, since the cost increases due to the excessively high Ti content, the Ti element content is limited to 0.005 to 0.030% in the present invention.
Calcium: since a certain amount of calcium improves the state of inclusions in the steel, thereby contributing to the improvement of toughness of the steel, the content of Ca element is limited to 0.0001 to 0.10% in the present invention.
Nickel: nickel is a solid solution strengthening element in steel, and a certain content of Ni can improve the oxidation resistance and the corrosion resistance of the steel, but the Ni is expensive, so the content of the Ni element in the invention is 0.03-0.20%.
Copper: copper plays a role in solid solution strengthening and precipitation strengthening in steel, but the surface quality is adversely affected by the excessive Cu content, and the Cu content is 0.03-0.30% due to the high price.
Boron: boron has an effect of improving austenite hardenability, effectively promotes the formation of martensite in the dual-phase steel, and forms BN by bonding with N in the steel to play a role of precipitation strengthening, but too high content of B deteriorates the toughness of the steel and increases the production cost of the steel, so that the content of B element is limited to 0.0005 to 0.0050% in the present invention.
The internal microstructure of the cold-rolled hot-dip galvanized dual-phase steel is ferrite and martensite, the grain size is more than or equal to 13 grade, and the microstructure type can ensure that the cold-rolled hot-dip galvanized dual-phase steel has good mechanical property, surface quality, forming property and welding property.
In the application, the low-carbon equivalent design is adopted, proper Si is added, the use of Cr and Mo noble metal alloy elements is reduced, the alloy cost is greatly reduced, the finished steel has good welding performance, and the comprehensive effect of the elements ensures that the mechanical property of the finished steel can reach: the tensile strength is more than or equal to 800MPa, the yield strength is more than or equal to 450MPa, the elongation A80 is more than or equal to 16%, the n 10-20% value is more than or equal to 0.12%, the r value is more than or equal to 0.70, and the hole expansion rate is more than or equal to 30%.
The invention also provides a production method of the 800 MPa-grade cold-rolled hot-galvanized dual-phase steel, which comprises the steps of smelting, continuous casting, heating, hot rolling, cooling, coiling, pickling, cold rolling, annealing and coating, and is characterized in that:
1) in the smelting step, molten steel is refined by adopting refining modes such as RH, LF and the like;
2) in the continuous casting step, the casting superheat degree is 15-30 ℃;
3) in the slab heating step, the slab discharging temperature is 1180-1300 ℃, and the heating time is 150-300 min;
4) in the hot rolling step, the final hot rolling temperature is 850-950 ℃;
5) in the cooling step, when the temperature of the strip steel is more than or equal to 620 ℃, the average cooling rate of the strip steel is more than or equal to 15 ℃/s;
6) in the coiling step, the coiling temperature is 500-620 ℃;
7) in the step of pickling and cold rolling, the cold rolling reduction is controlled to be 40-70%;
8) in the continuous annealing step, the annealing temperature is 760-840 ℃, wherein the heating speed is less than or equal to 5 ℃/s when the temperature is less than or equal to 760 ℃, the heat preservation time is 60-300s when the temperature is 760-840 ℃, the cooling speed is more than or equal to 15 ℃/s, the dew point in the annealing furnace is 0-40 ℃, and H in the furnace is2Content of 1-5%, H2O/H2≤1.0；
9) In the coating step, the temperature of the strip steel in a zinc pot is 440-500 ℃, the temperature of zinc liquid is 450-470 ℃, and the content of zinc liquid and aluminum is 0.15-0.25%.
According to the production method of the cold-rolled hot-galvanized dual-phase steel, the content of the alloy elements involved in the method is high, and the continuous casting in the step 2) is controlled by the superheat degree of 15-30 ℃, so that the alloy segregation can be reduced, the uniformity of the components and the final structure of the plate blank is improved, and the forming performance is improved.
According to the production method of the cold-rolled hot-galvanized dual-phase steel, the heating temperature of the plate blank in the step 3) is 1180-1300 ℃, the temperature of the plate blank is lower than 1180 ℃, the homogenization of alloy elements in the steel is not facilitated, the composition and the structure are segregated, the heating temperature is higher than 1300 ℃, and Fe which is difficult to remove is easily formed on the surface2SiO4The surface quality of the product is deteriorated. The heating time is 150-300min, the heating time is too short, alloy elements in the plate blank are difficult to fully diffuse, composition and structure segregation is caused, the heating time is too long, surface iron scales are easy to thicken, and Fe which is difficult to remove is formed2SiO4And causes decarburization to reduce the strength of the product.
Preferably, in order to ensure sufficient diffusion of the alloying elements, the heating time of the slab above 1200 ℃ should be ensured to be 40-100 min.
More preferably, the heating time of the slab above 1200 ℃ is 50-90 min.
According to the production method of the cold-rolled hot-galvanized dual-phase steel, in the step 4), the final rolling temperature is low in the hot rolling process, uneven structures are easily formed in the steel, coarse grain structures are easily formed at high temperature, and the mechanical properties of the product are not facilitated, so that the hot rolling final rolling temperature is limited to 850-950 ℃.
Preferably, the hot rolling finishing temperature is 860 ℃ and 900 ℃.
According to the production method of the cold-rolled hot-dip galvanized dual-phase steel, in the step 5), the cooling speed of over 620 ℃ is lower than 15 ℃/s, so that a coarse uneven ferrite structure is easily formed in the steel, and the performance of the product, particularly the toughness index such as elongation, is reduced.
Preferably, the average cooling rate of the strip steel is more than or equal to 20 ℃/s.
According to the production method of the cold-rolled hot-galvanized dual-phase steel, in the step 6), the coiling temperature is too high, so that coarse ferrite and pearlite structures are easily formed, the toughness index of the product is not favorably improved, and the coiling temperature is too low, so that the edge of the product is easily cracked, the rolling load is easily increased and the like in the cold rolling process, so that the coiling temperature is 500-620 ℃.
Preferably, the coiling temperature is 540-600 ℃.
According to the production method of the cold-rolled hot-dip galvanized dual-phase steel, in the step 7), the cold-rolling reduction rate of more than 40% is adopted to fully crush the hot-rolled structure, so that the structure after continuous annealing is fine and uniform, and the cold-rolling reduction rate is too large, so that the rolling load is easily too large, and the quality control of the plate shape and the edge part is not facilitated, therefore, the cold-rolling reduction rate is controlled to be 40% -70%.
According to the production method of the cold-rolled hot-dip galvanized dual-phase steel, in the step 8), the annealing temperature is too low, the cold-rolled structure cannot be fully recovered and recrystallized, an uneven structure is formed, the product is unfavorable for the extension and forming performance, the temperature is too high, a coarse uneven structure is easy to form, the surface external oxidation is easy to promote, and the final coating performance is unfavorable, so that the annealing temperature is 760-840 ℃, in the heating process, if the heating speed of the temperature not more than 760 ℃ is too high, a martensite annular structure is not easy to form in the steel, the forming performance is lower, and therefore the heating speed of the annealing temperature not more than 760 ℃ is not more than 5 ℃/s.
Preferably, the heating speed of the annealing temperature is less than or equal to 760 ℃ and is 1-4.5 ℃/s.
The heat preservation time during annealing is too short, the cold rolled structure can not be fully recovered and recrystallized, uneven structures are easily formed, the toughness indexes such as elongation and the like are obviously influenced, the forming performance is reduced, the soaking time is too long, coarse structures are easily formed, and the surface quality is reduced due to the fact that peroxidation is easily formed on the surface, so that the heat preservation time is 60-300s when the annealing temperature is 760 + 840 ℃.
Preferably, when the annealing temperature is 760 and 820 ℃, the heat preservation time is 60-250s, and the cooling speed is more than or equal to 15 ℃/s.
The cooling speed after annealing is lower than 15 ℃/s, and the steel is easy to have excessive ferrite and pearlite, so that the strength of the steel is reduced, and therefore, the cooling speed of the invention is more than or equal to 15 ℃/s.
According to the production method of the cold-rolled hot-galvanized dual-phase steel, in the step 8), the dew point in an annealing furnace is controlled to be 0-40 ℃, and the hydrogen content in the furnace is controlled to be H2H is more than or equal to 0.1 and is 1-5 percent2O/H2Less than or equal to 1.0, the dew point is too high, special equipment is required, the dew point is too high, the external oxidation and decarburization are easy to cause serious, the galvanized product has surface defects such as plating leakage and the like, the strength of the product is reduced, the dew point is too low to be easily realized, the dew point is too low, the external oxidation is easy to form, the product with higher Si content has defects such as plating leakage and the like, 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 invention21-5%; h2O/H2Too low and too high ratio are both liable to cause external oxidation, so that 0.1. ltoreq. H in the present invention2O/H2≤1.0。
Preferably, the dew point in the annealing furnace is-5 to-35 ℃, and the temperature in the furnace H is2Content of 1-4%, H2O/H20.2 to 1.0.
Compared with the prior art, the cold-rolled hot-galvanized dual-phase steel prepared by the method has the following advantages:
(1) according to the invention, proper Si is added, the use of Cr and Mo precious metal alloy elements is reduced, the alloy cost is greatly reduced, and technological parameters of each section such as hot rolling heating, cooling, coiling, cold rolling heating and cooling are controlled, so that the tensile strength of the product reaches above 800MPa, and meanwhile, the product has high elongation, n, r and hole expansion rate, and the forming performance of the product is greatly improved;
(2) in order to solve the surface problem caused by the increase of Si, the product of the invention has good coating performance and surface quality by adopting lower coiling temperature, reducing the content of H2 and dew point in the existing annealing production line and controlling the proportion of H2O/H2 in an annealing furnace, wherein in the process, the use amount of H2 is further reduced compared with the existing production line, and the production cost is further reduced;
(3) the invention adopts the design of low carbon equivalent, and the product has good welding performance;
(4) the production process can be realized on the existing production line without additionally increasing equipment, investment and the like;
(5) the mechanical property of the product of the invention can reach: the tensile strength is more than or equal to 800MPa, the yield strength is more than or equal to 450MPa, the elongation A80 is more than or equal to 16%, the n 10-20% value is more than or equal to 0.12%, the r value is more than or equal to 0.70, and the hole expansion rate is more than or equal to 30%.
Drawings
FIG. 1 is a metallographic microstructure photograph of the cold-rolled hot-dip galvanized dual-phase steel of the present invention.
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.
The following is an example illustration of a cold rolled hot dip galvanized dual phase steel produced by the present invention:
examples 1 to 6：
The production of the embodiments of the invention is carried out according to the following steps (smelting, continuous casting → heating or soaking → rolling → laminar cooling → coiling → acid washing → cold rolling → continuous annealing → galvanizing → finished product)
1) Smelting and continuous casting: the plate blank drawing speed is 0.1-10.0m/min, the superheat degree is 15-30 ℃, and the specific molten steel chemical components are shown in the following table 1 (wt%);
2) heating the plate blank, wherein the plate blank is taken out of the furnace at the temperature of 1180-;
3) hot rolling: the final rolling temperature of hot rolling is 850-950 ℃, preferably 860-900 ℃;
4) and (3) cooling: when the temperature of the strip steel is more than or equal to 620 ℃, the average cooling rate of the strip steel is more than or equal to 15 ℃/s;
5) coiling: the coiling temperature is 500-620 ℃, and preferably 540-600 ℃;
6) acid washing;
7) cold rolling: the cold rolling reduction rate is controlled to be 40-70 percent;
the main rolling process parameters of hot rolling, cold rolling and the like are shown in the following table 2;
8) and (3) continuous annealing: the annealing temperature is 760-2H is more than or equal to 0.10 and is 1-5 percent2O/H2Less than or equal to 1.0, and the annealing process parameters are shown in the following table 3;
9) hot galvanizing: the temperature of the strip steel when the strip steel enters the zinc pot is 440-500 ℃, the temperature of the zinc liquid is 450-470 ℃, and the content of the zinc liquid and the aluminum is 0.15-0.25%.
The mechanical properties of the cold-rolled hot-galvanized dual-phase steel products produced in examples 1 to 6 of the invention are shown in Table 4.
TABLE 1 chemical composition of molten steel in examples 1 to 6, Wt%
TABLE 2 Main Rolling Process parameters for Hot and Cold Rolling in examples 1-6
Table 3 annealing process parameters in examples 1-6
Table 4 examples 1-6 mechanical properties of cold-rolled hot-galvanized dual-phase steel finished product
As can be seen from Table 4, the tensile strength of the products of examples 1-6 of the present invention is as high as 815MPa or more; the elongation A80 is more than 18%, in example 6 is 30%, n10～20％The hole expansion rate reaches more than 0.12, the r value reaches more than 0.75 in the embodiment 6, the r value reaches more than 1.0 in the embodiment 6, the hole expansion rate reaches more than 34%, and the hole expansion rate reaches 50% in the embodiment 2; the surface quality and the weldability of the examples were good, but the Cr + Mo content of the noble alloy of examples 1 to 6 according to the invention was below 0.30. The heating time of the comparative examples 1 to 3 is less than 40min at the temperature of more than 1200 ℃, which causes the segregation in the steel to be aggravated and is unfavorable for the forming performances of elongation, hole expanding rate and the like of the steel, the cooling speed of the comparative example 1 after final rolling is less than 15 ℃/s, the coiling temperature of the comparative examples 2 and 3 is more than 620 ℃, uneven and coarse microstructures are easy to form and the toughness and the forming performance of the steel are reduced, the average heating speed of the comparative examples 1 to 3 is more than 5 ℃/s during continuous annealing, the soaking time of the comparative examples 1 and 2 is short, the soaking time of the comparative example 3 is too long, which is not favorable for the recovery and recrystallization of the microstructures and the diffusion of the metal elements such as C, Mn, Cr, Si and the like, and can cause the nonuniform structure and obvious banded structure in the steel and reduce the toughness and the forming performance of. The comparative examples 1 and 3, in which the cooling rate after the soaking for continuous annealing was less than 15 ℃/s, were disadvantageous in the formation of martensite in the steel, and therefore the tensile strength of the steel was low. Dew point, H of comparative examples 1-32Content and H2O/H2Is outside the scope of the present invention, and thus the final surface quality of the product is poor. In addition, the comparative examples 1 to 3 each had a Cr + Mo content of 0.50 or more, the comparative example 1 had a high Si content, and the comparative example 3 had a poor weldability due to a high carbon content and carbon equivalent.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (8)
1. A production method of 800 MPa-grade cold-rolled hot-galvanized dual-phase steel comprises the steps of smelting, continuous casting, heating, hot rolling, cooling, coiling, pickling, cold rolling, annealing and coating, and is characterized in that:
1) in the smelting step, molten steel is refined in an RH and LF refining mode, and the molten steel comprises the following chemical components in percentage by mass: 0.05 to 0.10 percent of C, 1.60 to 2.30 percent of Mn, 0.50 to 1.0 percent of Als, 0.10 to 0.50 percent of Si, 0.010 to 0.050 percent of Nb0.010 percent, 0.05 to 0.30 percent of Cr, 0.05 to 0.30 percent of Mo, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and inevitable impurities, wherein the noble metal elements Cr and Mo satisfy the relation formula: cr + Mo is more than or equal to 0.05 and less than or equal to 0.30, and C + Si/30+ Mn/20 is more than or equal to 0.22; the alloy also comprises at least one element of Ti, Ca, Ni, Cu and B, and the mass percent (%) of the components is as follows: 0.005-0.030% of Ti, 0.0001-0.10% of Ca, 0.03-0.20% of Ni, 0.03-0.30% of Cu and 0.0005-0.0050% of B;
2) in the continuous casting step, the casting superheat degree is 15-30 ℃;
3) in the heating step, the plate blank discharging temperature is 1180-1300 ℃, and the heating time is 150-300 min;
4) in the hot rolling step, the final hot rolling temperature is 850-950 ℃;
5) in the cooling step, when the temperature of the strip steel is more than or equal to 620 ℃, the average cooling rate of the strip steel is more than or equal to 15 ℃/s;
6) in the coiling step, the coiling temperature is 500-620 ℃;
7) in the step of pickling and cold rolling, the cold rolling reduction is controlled to be 40-70%;
8) in the step of annealing, the annealing step is carried out,the annealing temperature is 760-2Content of 1-5%, H2O/H2≤1.0；
9) In the coating step, the temperature of the strip steel in a zinc pot is 440-500 ℃, the temperature of the zinc liquid is 450-470 ℃, and the content of the zinc liquid and the aluminum is 0.15-0.25%.
2. The method for producing cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that the slab is heated at 1200 ℃ or higher for 40-100min in step 3).
3. The method for producing cold-rolled hot-dip galvanized dual-phase steel according to claim 2, characterized in that the slab is heated at 1200 ℃ or higher for 50-90 min.
4. The production method of cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that the hot-rolled finish rolling temperature in step 4) is 860 ℃ and 900 ℃.
5. The production method of cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that the average cooling rate of the strip steel in the step 5) is not less than 20 ℃/s.
6. The production method of cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that the coiling temperature in step 6) is 540-600 ℃.
7. The production method of cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that the heating rate of the annealing temperature of 760 ℃ or less in step 8) is 1-4.5 ℃/s; when the annealing temperature is 760 and 820 ℃, the heat preservation time is 60-250s, and the cooling speed is more than or equal to 15 ℃/s; the dew point in the annealing furnace is-5 to-35 ℃, and the temperature in the furnace is H2Content of 1-4%, H2O/H20.2 to 1.0.
8. The cold-rolled hot-dip galvanized dual-phase steel obtained by the production method of the cold-rolled hot-dip galvanized dual-phase steel according to any one of claims 1 to 7, wherein the internal microstructure of the cold-rolled hot-dip galvanized dual-phase steel is ferrite + martensite, and the grain size of ferrite is more than or equal to 13 grade.
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