CN109652739B - High-strength cold-rolled steel strip for enamel and preparation method thereof - Google Patents

High-strength cold-rolled steel strip for enamel and preparation method thereof Download PDF

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CN109652739B
CN109652739B CN201910058419.5A CN201910058419A CN109652739B CN 109652739 B CN109652739 B CN 109652739B CN 201910058419 A CN201910058419 A CN 201910058419A CN 109652739 B CN109652739 B CN 109652739B
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steel
temperature
rolling
cooling
billet
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CN109652739A (en
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孙建卫
刘洪银
王伟
亓伟伟
王孝科
王利
郝帅
张章
李玉功
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Shandong Iron and Steel Co Ltd
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/004Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236Cold rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/14Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite

Abstract

The invention discloses a high-strength cold-rolled steel strip for enamel and a preparation method thereof, wherein the steel strip comprises the following chemical components in percentage by weight: 0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, Al: 0.015 to 0.055%, 0.12 to 0.15% of Ti, 0.002 to 0.005% of N, more than or equal to 0.05% of Ti- (4 XC +3.43 XN +1.5 XS) and the balance of Fe and inevitable impurities, wherein the preparation method comprises the following steps: 1) manufacturing a billet; 2) reheating the billet of step 1) at a temperature above 1200 ℃; 3) carrying out rough rolling and finish rolling on the reheated steel billet; 4) after finish rolling, carrying out laminar cooling on a rolled material, and then coiling the hot rolled steel plate, wherein the coiling temperature is 750-800 ℃; 5) cooling the coiled rolling material to room temperature, and then cold rolling the rolling material at a reduction rate of 60-90%; 6) after the cold rolling, a cap annealing is performed. The steel strip has the advantages of good fish scaling resistance, high strength and good formability.

Description

High-strength cold-rolled steel strip for enamel and preparation method thereof
Technical Field
The invention belongs to the technical field of plate and strip steel production, and particularly relates to a high-strength cold-rolled steel strip for enamel and a preparation method thereof.
Background
The production process of the enamel steel comprises the following steps: the steel plate is processed and formed to prepare a base blank, then the surface of the base blank is coated with enamel, the temperature of the enamel treatment of the steel plate reaches over 800 ℃, and the enameled product has the characteristics of beautiful appearance, good corrosion resistance, easy cleaning and the like, so that the application field of the enameled steel is very wide.
The main service properties of the enamel steel include strength, formability and fish scaling resistance, the strength of the steel plate is mainly related to the chemical composition, structure and the quantity of precipitation strengthening particles of the steel plate, the formability of the steel plate is mainly related to the chemical composition and structure of the steel plate, and the fish scaling resistance of the steel plate is mainly related to the type and quantity of hydrogen storage traps in the steel plate.
The scale explosion is the main defect of enamel products, and the mechanism of the scale explosion is mainly that crystal water in porcelain slurry reacts with iron and carbon on the surface of a steel plate to generate atomic hydrogen when an enamel blank is sintered at high temperature. The scale explosion refers to the defect that hydrogen accumulated in the steel is released between the surface of the steel and an enamel layer, and breaks through the surface of the enamel layer to generate scale-shaped fragments. In the cooling process of the enameled steel sheet, hydrogen dissolved in steel is released to the surface of the steel in a cooled state, and the enamel layer on the surface of the steel is hardened and cannot be released to the outside, thereby generating the fish scaling phenomenon. The cause of the scale-off defect is hydrogen. Therefore, in order to prevent the occurrence of such defects, it is necessary to provide a site capable of adsorbing hydrogen inside the steel. Micro-void (micro-void), inclusions, precipitates, dislocations, grain boundaries, and the like may be the hydrogen-absorbing site. In order to ensure the enamel properties, in particular the fishscaling resistance, it is necessary to deliberately disperse many precipitates in the structure.
Some special-purpose enameled steels, such as those used for water heater liners, need to maintain high strength to achieve high pressure resistance.
The patents published at home and abroad at present have good research on ultra-low carbon enamel steel and low carbon enamel steel.
Chinese patent CN 200810013480-discloses a cold rolling water heater enamelPorcelain steel and a production method thereof, the porcelain steel comprises the following components (by weight percent): 0.01-0.08 percent of Si, less than or equal to 0.03 percent of Si, 0.10-0.60 percent of Mn0.02 percent of P, S: 0.003-0.02%, N: 0.001-0.006 percent of AlSThe process is characterized in that the heating temperature of a steel billet is 1160-1300 ℃, the hot rolling finishing temperature is 850-950 ℃, and the coiling temperature of a steel plate is 660-760 ℃, and the enamel steel produced by the process has high carbon content, the surplus titanium is less than or equal to 0, carbon is not completely fixed by titanium, so that the steel contains a certain amount of solid solution carbon atoms, and is finally precipitated in the form of pearlite, and the formability of the steel is poor.
The manufacturing technique of the enamel steel disclosed in Japanese Kokai publication Sho 62-151546 is limited: when the excess titanium content is Ti- (4 xc +3.43 xn +1.5 xs) ≦ 0, carbon is not completely fixed by titanium, a certain number of solid-solution carbon atoms are contained in the steel material, and finally, the carbon is precipitated as pearlite, and the formability of the steel material is not good.
The production technique of enamel steel disclosed in Japanese Kokai publication Sho 61-117246 does not limit the relationship between Ti and C, N, S in the steel composition, and the existence form of C in the rolled steel cannot be determined.
Chinese patent CN200980131505 discloses an enameled steel sheet and a manufacturing method thereof, the invention provides the enameled steel sheet, by weight, with more than 0 and less than 0.005% of C, 0.2-1.0% of Mn, 0.04-0.08% of S, 0.005-0.02% of P, 0.01-0.1% of Al, 0.06-0.1% of Ti, more than 0 and less than 0.003% of N, and the balance of Fe and other inevitable impurities, wherein the size of TiS or (Ti, Mn) S precipitates is 0.01-0.4 μm, and the number of precipitates per square centimeter is 3 × 108More than one. The steel produced by the method has good formability and scale explosion resistance, but the yield strength of the steel plate is low due to low carbon content, and the steel plate is easy to deform during high-temperature enameling and use.
In conclusion, the enamel steel with the carbon content less than 0.005 percent has the defect of low strength; with the increase of the carbon content, the enamel steel has the defect of slightly poor formability; the prior published technology lacks an enamel steel production process which can simultaneously meet the requirements of scale explosion resistance, high strength and good formability
Disclosure of Invention
In order to solve the technical defects, the invention provides the production process of the enamel steel which can simultaneously meet the requirements of good scale explosion resistance, high strength and good formability.
In order to achieve the purpose, the invention adopts the following technical scheme:
a high-strength cold-rolled steel strip for enamel comprises the following chemical components in percentage by weight: 0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, Al: 0.015 to 0.055%, 0.12 to 0.15% of Ti, 0.002 to 0.005% of N, and the balance Fe and inevitable impurities, wherein the content of excess titanium in the steel is Ti- (4 XC +3.43 XN +1.5 XS) ≥ 0.05%.
The invention also provides a manufacturing method of the high-strength cold-rolled steel strip for enamel, which comprises the following steps:
1) the process flow for manufacturing the steel billet comprises the following steps: molten iron pretreatment → combined blowing converter → RH vacuum degassing treatment → slab continuous casting, wherein the chemical components in the steel billet comprise, by weight, 0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, and Al: 0.015 to 0.055 percent, 0.12 to 0.15 percent of Ti, 0.002 to 0.005 percent of N, and the content of the excessive titanium in the steel is more than or equal to 0.05 percent of Ti- (4 XC +3.43 XN +1.5 XS);
2) reheating the billet at a temperature of 1200 ℃ or higher;
3) rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: 1180-1220 ℃, and performing heat preservation and soaking on the intermediate blank by using a hot coil box after rough rolling, so that the head-tail temperature difference of the intermediate blank is reduced, and the temperature of the intermediate blank is as follows: 1050-1080 ℃. Then at Ar3Finish rolling is carried out at the above temperature, and the finish rolling temperature: 910-940 ℃, and the temperature difference of the poker is controlled within 30 ℃;
4) after finish rolling, the rolled material is subjected to laminar cooling, and then the hot-rolled steel sheet is coiled, wherein the coiling temperature is 750-800 ℃, the coiling temperature is not up to the pearlite transformation temperature, carbon in the rolled material cannot be precipitated in the form of pearlite structure, and all carbon in the rolled material is precipitated in the form of TiC.
5) And after cooling the coiled rolling material to room temperature, cold rolling the rolling material at a reduction rate of 60-90%.
6) After the step of manufacturing the cold rolled steel sheet, cap annealing was performed under annealing process parameters as shown in the following table 1;
TABLE 1 annealing Process regime
Process stage Temperature of heating Time of heating
Heating section 1 0~470℃ 1~3h
Heating section 2 470℃~750℃ 6~10h
Thermal insulation section 750℃ 10~14h
Cooling section 1 750~550℃ 6-10 h cooling with cover
Cooling section 2 550~380℃ Air cooling
Cooling section 3 380~80℃ Water cooling
Due to the adoption of a high-temperature coiling measure, the coiling temperature is 750-800 ℃, a pearlite structure cannot be formed at the temperature, so that most of carbon in steel components is precipitated in a TiC form at an austenite stage, C atoms are dissolved in the steel without gaps, the formability of the steel is good, the size of TiC particles precipitated at the temperature of 750-800 ℃ is 5-30 nm, the size of the TiC particles is small, the strength of the steel is greatly improved by the precipitation strengthening effect of the precipitated TiC, and the precipitated TiC can play a hydrogen storage trap effect in a second phase particle form, so that the scale explosion resistance is greatly improved.
The calculation formula of the solubility product of TiC in austenite at different temperatures is shown as the following formula (I), and the expression of the solubility product of TiC is shown as the following formula (II):
lgKTiC=-7000/T+2.75 ①
KTiC=ωTi×ωC
k in formula ①②TiCThe product of TiC solubility, T temperature (K), ω Ti mass percent (%) of Ti solid solution in the steel, and ω C mass percent (%) of C solid solution in the steel.
K was calculated according to formula ① at 750 deg.C, 780 deg.C, 800 deg.CTiCValue, then K will be calculatedTiCThe saturated Ti content (%) when the solid solution carbon content ω C in the steel product obtained by substituting the value into the formula ② was 40ppm was as shown in Table 2 below.
TABLE 2 saturated Ti content (%)
Temperature of 750℃ 780℃ 800℃
Product of solubility 8.13×10-5 1.26×10-4 1.70×10-4
Carbon content (%) 4×10-3 4×10-3 4×10-3
The carbon content corresponds to the saturated Ti content (%) 0.0203 0.0315 0.0425
As is apparent from Table 2, since the saturated Ti contents (%) at 750 ℃, 780 ℃ and 800 ℃ with a solid solution C content of 40ppm were 0.0203%, 0.0315% and 0.0425%, respectively, it was found that keeping the excess titanium content in the steel material at not less than 0.05% was sufficient to control the solid solution C in the steel material to not more than 40ppm, and within this range of the solid solution carbon content, the formability of the steel material was good and the elongation could be about 45%.
The invention has the advantages that:
1. according to the method provided by the invention, more C in the steel is precipitated in the form of TiC, the strength of the precipitated TiC is greatly improved in a precipitation strengthening effect, the yield strength of the steel can be improved to 350MPa, the tensile strength is 450-550 MPa, and a large amount of precipitated TiC can also play a hydrogen storage trap effect in the form of second-phase particles, so that the scale explosion resistance is greatly improved.
2. Since the steel contains an excessive amount of Ti and is kept at a pearlite transformation temperature or higher for a long time after rolling, most of carbon in the steel component precipitates as TiC in the austenite phase, and the amount of solid solution C in the steel is controlled to 40ppm or less, the formability of the steel is excellent within the range of the solid solution carbon component, and the elongation can reach about 45%.
Drawings
FIG. 1: metallographic structure of enamel steel corresponding to example 1;
FIG. 2: metallographic structure of enamel steel corresponding to example 2;
FIG. 3: metallographic structure of enamel steel corresponding to example 3;
FIG. 4: comparative example 4 shows the metallographic structure of the corresponding enamel steel.
Detailed Description
Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. Unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features. The description is only for the purpose of facilitating understanding of the present invention and should not be construed as specifically limiting the present invention.
The invention is described in further detail below with reference to the figures and the detailed description.
The enamel steel provided by the invention comprises the following chemical components in percentage by weight:
0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, Al: 0.015 to 0.055%, 0.12 to 0.15% of Ti, 0.002 to 0.005% of N, and the content of excess titanium in steel: ti- (4 + C +3.43 + N +1.5S) is not less than 0.05%.
Influence of chemical components on the performance of the steel plate:
c: the lower the carbon content, the better the formability of the steel plate, but the lower the yield strength of the steel plate, especially the strength during or after high-temperature enameling firing, and is easy to deform, in order to solve the contradiction, the carbon in the invention is controlled to be 0.008-0.02%, but most of the carbon is precipitated in the form of TiC in the austenite stage, and the yield strength of the steel is greatly improved by precipitating TiC particles. At the temperature at which austenite is transformed into pearlite, the amount of solid-dissolved carbon in the steel material is controlled to be less than 40ppm, and the formability of the steel material is good within the range of the content of the solid-dissolved carbon.
N: nitrogen is an impurity element in conventional steel, and the higher nitrogen, the poorer formability of steel. However, nitrogen reacts with titanium to produce titanium nitride, and the titanium nitride particles contribute to improvement of the fishscale resistance and prevention of growth of austenite grains, and have an effect of refining the grains. Since the formability of steel is impaired if the size of TiN produced is too coarse due to too high nitrogen content, the nitrogen control range in the present invention is: 0.002-0.005%.
Si: the content of Si is controlled to be less than or equal to 0.02% because the content of Si is higher than 0.03% and impairs enamel properties, particularly, causes poor adhesion.
S: sulfur is an impurity element and is mainly present as manganese sulfide inclusions in conventional steels, which are in the form of long strips after rolling, seriously reducing the formability of the steel sheet, particularly the transverse plasticity of the steel sheet. In the enamel steel, by adding titanium, a simple manganese sulfide inclusion can be avoided, but a compound inclusion is formed by sulfur, titanium, manganese and the like, and the inclusion is more spherical, so that the damage to plasticity can be reduced, and the scale-explosion resistance of the steel can be improved. The range of sulfur content is: less than or equal to 0.010 percent.
Ti: titanium is a forming element of titanium carbide, titanium nitride and titanium sulfide. The titanium is added in a suitable excess to completely fix the carbon, nitrogen and sulfur elements in the steel. The second phase particles generated by the reaction of titanium, carbon, nitrogen and sulfur can play a role in hydrogen storage traps, the scale explosion resistance of the steel is greatly improved, and the yield strength of the steel can be greatly improved by TiC. The effective titanium is calculated as: ti ═ 4C +3.42N +1.5S, titanium was added in total: ti is Ti + delta Ti, wherein the excessive titanium delta Ti is more than or equal to 0.05 percent, and under the condition that the excessive titanium with the content of more than or equal to 0.05 percent exists, most of carbon in the steel can be fixed in an austenite stage (about 800 ℃), so that the residual solid solution C in the steel is controlled below 40ppm, and the forming performance of the steel is favorably improved.
Al: in aluminum killed steel, aluminum is a strong deoxidizing element. In addition, aluminum reacts with nitrogen to generate aluminum nitride, and the aluminum nitride plays a certain role in improving the fish scaling resistance of the steel. The Al content in the invention is 0.015-0.055%.
P: phosphorus is a harmful element. The phosphorus content is too high, and the partial polymerization is easy to occur on the crystal boundary, so that the enamel quality is influenced. Phosphorus is less than or equal to 0.015 percent. Mn has a strengthening effect on steel in a low content range, and can improve the strength, hardness and wear resistance of steel, wherein the Mn content is 0.08-0.18%.
The invention provides a method for manufacturing an enameled pressed steel, which comprises the following steps:
1) the process flow for manufacturing the steel billet comprises the following steps: molten iron pretreatment → combined blowing converter → RH vacuum degassing treatment → slab continuous casting, wherein the chemical components in the steel billet comprise, by weight, 0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, and Al: 0.015 to 0.055 percent, 0.12 to 0.15 percent of Ti, 0.002 to 0.005 percent of N, and the content of the excessive Ti in the steel is more than or equal to 0.05 percent of Ti- (4 x C +3.43 x N + 1.5S).
The converter smelting end point control target is as follows: c, 0.035-0.05%, temperature is: 1690 and 1700 ℃, and the manganese is mixed to about 0.14 percent by using low-carbon ferromanganese or metal manganese in the tapping process. And after tapping, uniformly adding an aluminum deoxidizer of 200-300 kg/furnace into the slag surface, wherein the aluminum deoxidizer contains 30% of aluminum, and adding partial aluminum particles into the slag surface if tapping and slagging are carried out by the converter. The sliding plate is adopted to block slag and stop slag, so that the thickness of a slag layer of the top slag of the steel ladle after tapping is ensured to be less than or equal to 100 mm.
After converter tapping, deep decarburization is carried out on the molten steel by adopting an RH refining furnace until the content of C in the molten steel is as follows: 0.008-0.02%, adding Al for deoxidation after the carbon content reaches the target component, then adding ferrotitanium for titanium alloying, continuously stirring molten steel in an RH refining furnace for 7-10min in a circulating manner after the titanium alloying, then turning off a vacuum system, and stirring the molten steel for 13-15 min by soft argon blowing. And after the RH smelting is finished, adding a carbon-free heat preservation agent at the position of the steel ladle inserted into the dip pipe to preserve heat of the molten steel, wherein the adding amount of the carbon-free heat preservation agent is 5-10 kg per ton of steel.
The casting is protected in the whole process of the continuous casting operation, the section of a crystallizer is 175mm multiplied by (950-1350) mm, carbon-free casting powder is added into the crystallizer, the casting blank pulling speed is 1.2-1.3 m/min, the stable pulling speed is kept, and a forced cooling mode is adopted for secondary cooling.
2) The steel billet is reheated at a temperature of 1200 ℃ or higher, and the specific requirements of the heating system of the slab fed into the furnace are shown in Table 3.
TABLE 3 heating System of slabs
3) Rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: 1180-1220 ℃, and performing heat preservation and soaking on the intermediate blank by using a hot coil box after rough rolling, so that the head-tail temperature difference of the intermediate blank is reduced, and the temperature of the intermediate blank is as follows: 1050-1080 ℃. Then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: 910-940 ℃, and the temperature difference of the poker is controlled within 30 ℃.
4) Descaling: the rough rolling and the finish rolling are all put into use, the pressure of a nozzle is ensured to be more than or equal to 18MPa, the nozzle is complete and is not blocked, and the scale is fully removed.
5) After finish rolling, the rolled material is subjected to laminar cooling, and then the hot-rolled steel sheet is coiled, wherein the coiling temperature is 750-800 ℃, the coiling temperature is not up to the pearlite transformation temperature, carbon in the rolled material cannot be precipitated in the form of pearlite structure, and all carbon in the rolled material is precipitated in the form of TiC.
6) And after cooling the coiled rolling material to room temperature, cold rolling the rolling material at a reduction rate of 60-90%.
7) After the step of manufacturing the cold rolled steel sheet, the cap annealing was performed under annealing process parameters as shown in the following table 4.
TABLE 4 annealing Process regime
Process stage Temperature of heating Time of heating
Heating section 1 0~470℃ 1~3h
Heating section 2 470℃~750℃ 6~10h
Thermal insulation section 750℃ 10~14h
Cooling section 1 750~550℃ 6-10 h cooling with cover
Cooling section 2 550~380℃ Air cooling
Cooling section 3 380~80℃ Water cooling
In the following examples, examples 1, 2 and 3 are provided for the production of high strength enamelled steel using the technique according to the invention, example 4 is a prior art production of enamelled steel using a steel mill, example 4 is a comparative example.
Example 1: the chemical composition of the steel slab is shown in Table 5 below
Table 5 chemical composition of example 1
1) The content of C at the smelting end point of the converter is 0.035%, and the temperature is as follows: 1690 deg.C, adding low-carbon ferromanganese or manganese metal to 0.14% during tapping. After tapping, 300kg of aluminum deoxidizer is uniformly added into the slag surface, the aluminum deoxidizer contains 30% of aluminum, and if tapping and slagging are carried out by the converter, partial aluminum particles are added into the slag surface. The sliding plate is adopted to block slag and stop slag, so that the thickness of a slag layer of the top slag of the steel ladle after tapping is ensured to be less than or equal to 100 mm.
After converter tapping, deep decarburization is carried out on the molten steel by adopting an RH refining furnace until the content of C in the molten steel is as follows: 0.008, adding Al for deoxidation after the carbon content reaches the target component, then adding ferrotitanium for titanium alloying, continuously circulating and stirring the molten steel in an RH refining furnace for 7min after the titanium alloying, then turning off a vacuum system, and stirring the molten steel for 13min by soft argon blowing. After RH smelting is finished, adding a carbon-free heat preservation agent into the position of the steel ladle inserted into the dip pipe to preserve heat of molten steel, wherein the adding amount of the carbon-free heat preservation agent is 5 kg/ton of steel
The whole process of the continuous casting operation process is protected and cast, the section of a crystallizer is 175mm multiplied by 950mm, carbon-free protective slag is added into the crystallizer, the casting blank drawing speed is 1.3m/min, the stable drawing speed is kept, and the secondary cooling adopts a forced cooling mode.
2) The steel slab is reheated at a temperature of 1200 ℃ or higher, and the specific requirements of the slab heating system in the furnace are shown in Table 6.
TABLE 6 slab heating System
3) Rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: 1180 ℃, after rough rolling, using a hot coil box to keep and soak the intermediate billet, reducing the head-to-tail temperature difference of the intermediate billet, and the temperature of the intermediate billet: 1050 ℃. Then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: controlling the temperature difference of the poker at 910 ℃ and within 30 ℃;
4) descaling: the rough rolling and the finish rolling are all put into use, the pressure of a nozzle is ensured to be more than or equal to 18MPa, the water nozzle is complete and is not blocked, and the scale is fully removed.
5) After the finish rolling, the rolled material is subjected to laminar cooling, and then the hot-rolled steel sheet is coiled at a coiling temperature of 750 ℃, which is not yet at the pearlite transformation temperature, so that carbon in the rolled material cannot be precipitated in the form of pearlite structure, and all carbon in the rolled material is precipitated in the form of TiC.
6) After the rolled material thus coiled was cooled to room temperature, the rolled material was cold-rolled at a reduction ratio of 90%.
7) After the step of manufacturing the cold rolled steel sheet, the cap annealing was performed under annealing process parameters as shown in the following table 7.
TABLE 7 annealing Process regime
The mechanical properties and metallographic structure of the cold-rolled enamel steel are detected after annealing, the mechanical properties are shown in the following table 8, and the photograph of the metallographic structure is shown in figure 1
TABLE 8 mechanical Properties
The elongation percentage of the enamel steel produced by the process is equivalent to that produced by other plants, but the strength of the enamel steel is about 100MPa higher than that of the enamel steel produced by other plants, and the TiC particles serving as hydrogen storage traps in the steel are numerous, so that the enamel steel has good fish scale cracking resistance after being coated on the enamel.
Example 2:
the embodiment 2 differs from the embodiment 1 in the following points:
the chemical composition of the steel slab of example 2 is shown in table 9 below;
table 9 chemical composition of example 2
The content of C at the smelting end point of the converter is 0.055%, and the temperature is as follows: at 1700 ℃, after tapping, 200kg of aluminum deoxidizer is uniformly added into the slag surface per furnace.
Rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: 1220 ℃, using a coil box to preserve heat and uniformly heat the intermediate billet after rough rolling, reducing the head-to-tail temperature difference of the intermediate billet, and ensuring the temperature of the intermediate billet to be as follows: 1080 ℃. Then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: 940 ℃, the temperature difference of the poker is controlled within 30 ℃, and the coiling temperature is 800 ℃.
After the coiling step, cold rolling was performed at a reduction of 60%.
After annealing, the mechanical property and the metallographic structure of the cold-rolled enamel steel are detected, the detection result of the mechanical property is shown in the following table 10, and the photograph of the metallographic structure is shown in fig. 2;
TABLE 10 mechanical Properties
The elongation percentage of the enamel steel produced by the process is equivalent to that produced by other plants, but the strength of the enamel steel is about 120MPa higher than that of the enamel steel produced by other plants, and the TiC particles serving as hydrogen storage traps in the steel are numerous, so that the enamel steel has good fish scale cracking resistance after being coated on the enamel.
Example 3
The embodiment 3 differs from the embodiment 1 in the following points:
the chemical composition of the steel slab of example 3 is shown in table 11 below;
table 11 chemical composition of example 3
The content of C at the smelting end point of the converter is 0.04 percent, and the temperature is as follows: 1695 deg.C, after tapping, 250 kg/furnace of aluminum deoxidizer is added on the slag surface.
Rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: and 1200 ℃, after rough rolling, using a coil box to preserve heat and uniformly heat the intermediate billet, reducing the head-to-tail temperature difference of the intermediate billet, and ensuring the temperature of the intermediate billet to be as follows: 1060 ℃. Then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: 920 ℃, the temperature difference of the whole noodles is controlled within 30 ℃, and the coiling temperature is 790 ℃. (ii) a
After the coiling step, cold rolling was performed at a reduction of 80%.
After annealing and leveling, detecting the mechanical property and the metallographic structure of the cold-rolled enamel steel, wherein the mechanical property is shown in the following table 12, and a photograph of the metallographic structure is shown in fig. 3;
TABLE 12 mechanical Properties
The elongation percentage of the enamel steel produced by the process is equivalent to that produced by other plants, but the strength of the enamel steel is about 50MPa higher than that of the enamel steel produced by other plants, and the TiC particles serving as hydrogen storage traps in the steel are numerous, so that the enamel steel has good fish scale explosion resistance after being coated on the enamel.
Comparative example 4
The embodiment 4 differs from the embodiment 1 in the following points:
the chemical composition of example 4 is shown in table 13;
table 13 chemical composition of example 4
The content of C at the smelting end point of the converter is 0.04 percent, and the temperature is as follows: 1690 deg.C, after tapping, 300 kg/furnace of aluminum deoxidizer is added uniformly on the slag surface.
Rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: and 1200 ℃, after rough rolling, using a coil box to preserve heat and uniformly heat the intermediate billet, reducing the head-to-tail temperature difference of the intermediate billet, and ensuring the temperature of the intermediate billet to be as follows: 1050 ℃. Then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: 900 ℃, the temperature difference of the poker is controlled within 30 ℃, and the coiling temperature is 610 ℃. (ii) a
After the coiling step, cold rolling was performed at a reduction of 70%.
The mechanical properties of the steel plate are detected after the steel plate is annealed and flattened, the result is shown in the following table 14, and the metallographic structure picture is shown in fig. 4;
TABLE 14 mechanical Properties
Example comparison:
the mechanical properties are compared in table 15 below:
TABLE 15 comparison of mechanical properties
Comparing the strength and the elongation of the rolled stock provided by the embodiments 1, 2 and 3 of the invention with the elongation of the rolled stock provided by the comparative embodiment 4, the strength of the rolled stock produced by the technology provided by the invention is higher than about 50MPa, and the elongation is higher than about 4 percent, because the process route of high titanium and high temperature coiling is adopted, most of C in the rolled stock is precipitated in a TiC form, the TiC particles greatly improve the strength of the rolled stock in a precipitation strengthening form, and the scale and explosion resistance of the rolled stock is improved by a large amount of TiC particles; because most of C in the rolled stock is precipitated in the form of TiC, the C content remained in the steel in solid solution is less than 40ppm, basically no pearlite is generated in the low C content range, and the rolled stock is ferrite in structure, so that the elongation of the rolled stock is also high.
Comparison of examples 1, 2 and 3 of the present invention with comparative example 4 provides metallographic photographs of rolled materials, and rolled materials produced by the technique of the present invention have a high elongation because they have a high ferrite content and a low pearlite content.
The method can be realized by upper and lower limit values and interval values of intervals of process parameters (such as temperature, time and the like), and embodiments are not listed.
Conventional technical knowledge in the art can be used for the details which are not described in the present invention.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (4)

1. A preparation method of a high-strength cold-rolled steel strip for enamel is characterized in that the steel strip comprises the following chemical components in percentage by weight:
0.008-0.02% of C, less than or equal to 0.020% of Si, 0.08-0.18% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, Al: 0.015 to 0.055%, 0.12 to 0.15% of Ti, 0.002 to 0.005% of N, the content of excess titanium in the steel = Ti- (4 XC +3.43 XN +1.5 XS) > 0.05% or more, and the balance of Fe and inevitable impurities;
the preparation method comprises the following steps:
1) manufacture of billets
The process flow comprises the following steps: molten iron pretreatment → combined blown converter → RH vacuum degassing treatment → continuous casting of plate blank;
2) reheating the billet in the step 1);
3) rough rolling is carried out on the reheated steel billet, and the rough rolling initial rolling temperature is as follows: 1180-1220 ℃, performing heat preservation and soaking on the intermediate billet after rough rolling, reducing the head-to-tail temperature difference of the intermediate billet, and ensuring the temperature of the intermediate billet to be as follows: 1050-1080 ℃; then, finish rolling is performed at a temperature of Ar3 or higher, and the finish rolling temperature: 910-940 ℃, and the temperature difference of the poker is controlled within 30 ℃;
4) after finish rolling, carrying out laminar cooling on a rolled material, and then coiling the hot rolled steel plate, wherein the coiling temperature is 750-800 ℃;
5) after cooling the coiled rolling material to room temperature, cold rolling the rolling material at a reduction rate of 60-90%;
6) after cold rolling, performing cover annealing;
in the step 2), the billet reheating system is as follows:
the tapping temperature is 1180-1220 ℃; the temperature of the soaking section is controlled to be 1200-1260 ℃, the temperature of the heating section is controlled to be 1210-1280 ℃, and the temperature of the preheating section is controlled to be 1000-1150 ℃; the heating time of the cold blank is more than or equal to 130 min, and the heating time of the hot blank is more than or equal to 100 min;
the cover annealing process system comprises:
heating section 1: 0-470 ℃ for 1-3 h; and (3) heating section 2: 470-750 ℃ for 6-10 h; a heat preservation section: the temperature is 750 ℃, and the time is 10-14 h; cooling section 1: cooling with a cover at 750-550 ℃ for 6-10 h; a cooling section 2: air cooling at 550-380 ℃; a cooling section 3: and cooling at 380-80 ℃ by water.
2. The method according to claim 1, wherein, in step 1),
the converter smelting end point control target is as follows: c, 0.035-0.05%, temperature is: 1690) and 1700 ℃, and the manganese is mixed to about 0.14 percent by using low-carbon ferromanganese or metal manganese in the tapping process; after tapping, uniformly adding an aluminum deoxidizer of 200-300 kg/furnace into the slag surface, wherein the aluminum deoxidizer contains 30% of aluminum, and adding partial aluminum particles into the slag surface if tapping and slagging of the converter are finished; the sliding plate is adopted to block slag and stop slag, so that the thickness of a slag layer of the top slag of the steel ladle after tapping is ensured to be less than or equal to 100 mm.
3. The method according to claim 1, wherein, in step 1),
after converter tapping, deep decarburization is carried out on the molten steel by adopting an RH refining furnace until the content of C in the molten steel is as follows: 0.008-0.02%, adding Al for deoxidation after the carbon content reaches the target component, then adding ferrotitanium for titanium alloying, continuously stirring molten steel in an RH refining furnace for 7-10min in a circulating manner after the titanium alloying, then turning off the vacuum, and stirring the molten steel for 13-15 min by soft argon blowing.
4. The method according to claim 1, wherein, in step 1),
the casting is protected in the whole process of the continuous casting operation, the section of a crystallizer is 175mm multiplied by (950-1350) mm, carbon-free casting powder is added into the crystallizer, the casting blank pulling speed is 1.2-1.3 m/min, the stable pulling speed is kept, and a forced cooling mode is adopted for secondary cooling.
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