CN115478208A - Thin-specification high-formability stamping steel based on CSP production line and preparation method thereof - Google Patents

Thin-specification high-formability stamping steel based on CSP production line and preparation method thereof Download PDF

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CN115478208A
CN115478208A CN202110598574.3A CN202110598574A CN115478208A CN 115478208 A CN115478208 A CN 115478208A CN 202110598574 A CN202110598574 A CN 202110598574A CN 115478208 A CN115478208 A CN 115478208A
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蔡珍
刘永前
王成
陈昊
孙宜强
刘洋
刘昌明
胡俊
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Baoshan 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/068—Decarburising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron

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Abstract

A thin-specification high-formability stamping steel based on a CSP production line and a preparation method thereof are disclosed, wherein the thin-specification high-formability stamping steel comprises the following chemical components in percentage by weight: c0.001-0.006%, si less than or equal to 0.03%, mn 0.15-0.30%, N less than or equal to 0.004%, P less than or equal to 0.015%, S less than or equal to 0.0080, als 0.015-0.040%, and further includes one of Ti, nb, V, cr + B, wherein 4[C ] +3.42[ N ] +3[S ] ≦ Ti ] ≦ 0.065%,7.75[ C ] +6.64 ] ≦ Nb ≦ 0.075%,4.25[ C ] +3.64 ] ≦ N ] ≦ 0.045%, cr 0.1-0.3%, 0.78[ N ] ≦ 0.0035%, and the balance being Fe and unavoidable impurities. The invention realizes no solid solution C, N interstitial atoms in ferrite through the design of ultra-low carbon and microalloy chemical components, combines the two-section deformation process of low-temperature austenite area rolling and ferrite area lubrication rolling, high-temperature coiling and slow cooling, has the product yield strength of 120-180 MPa, the tensile strength of 270-370 MPa, the elongation of 42-55 percent and the r value of more than or equal to 1.3, achieves the performance and thickness precision of the same specification cold rolling product level, and can realize the replacement of cold by heat.

Description

Thin-specification high-formability stamping steel based on CSP production line and preparation method thereof
Technical Field
The invention belongs to the technical field of strip steel production, and particularly relates to thin-specification high-formability stamping steel based on a CSP production line and a preparation method thereof.
Background
The CSP technique is a thin slab continuous casting and rolling technique developed by Germany SMS research and is called compact strip steel production technique. The typical process flow of CSP is as follows: (electric furnace or) converter → ladle refining furnace → thin slab caster → soaking furnace → hot continuous rolling mill → laminar cooling → underground coiling, and the production line layout is shown in fig. 1. The thickness of the blank drawn from the continuous casting blank is less than 70mm, and the blank is rolled into 0.8-12.5 mm strip steel by 6-7 finishing mills.
The thin slab continuous casting and rolling product has the characteristics of high precision and thin specification, so that the production of the thin specification hot rolling product realizes the replacement of cold by hot, and is one of the development trends of the thin slab continuous casting and rolling. In the replaceable cold-rolled products, the market demand of the thin-specification stamping steel is large, the low yield ratio, the high elongation and a certain r value are required, and the thin-specification stamping steel is widely applied to high-end products such as automobile parts, household appliances and the like. The thin hot rolled product is used for realizing replacement, the profitability of the product can be improved, and the simple and efficient manufacturing of the product is realized.
Chinese patent CN200610098394.4 discloses a production process for producing IF steel by thin slab continuous casting and rolling, which comprises a converter smelting process, an LF furnace refining process and a thin slab continuous casting process, wherein the weight percentage of molten steel is as follows: c:0-0.0050%; si:0 to 0.03 percent; mn:0 to 0.60 percent; p:0 to 0.015 percent; s:0 to 0.010 percent; n:0-0.050%, ti = 6-10 times of the mass percentage of C + N, and the balance of iron and inevitable impurities. The heating and rolling process comprises the following steps: soaking in a tunnel furnace at 1130-1150 deg.c, 1050-1100 deg.c, 850-950 deg.c and 650-750 deg.c. The yield strength of the hot-rolled product is 265-285MPa, the tensile strength is 340-355MPa, and the elongation is 35-43%. The disadvantage of this patent is that the hot rolled product performance cannot meet the stamping requirements, and subsequent cold rolling and annealing are required to reduce the yield strength, yield ratio and increase the r value.
Chinese patent CN201210051479.2 discloses a processing method for producing low-cost high-formability IF steel, and the weight percentage of molten steel is as follows: less than or equal to 0.007 percent of C, 0.1 to 0.3 percent of Mn, less than or equal to 0.03 percent of Si, less than or equal to 0.008 percent of P, 0.020 to 0.050 percent of Als, and the balance of Fe. The technical scheme is as follows: comprises the working procedures of steel making, continuous casting, heating, rolling, cooling and coiling, a thin slab caster is adopted, the thickness of the continuous casting slab is less than or equal to 100mm, and the charging temperature is more than or equal to 880 ℃. During hot rolling, the rough rolling mill and the finishing mill keep continuous rolling relation and keep micro-tension control, water cooling equipment is used between the rough rolling mill and the finishing mill, the temperature of an intermediate billet with the thickness of 12-25 mm is uniformly cooled to the range of 750-850 ℃ from the temperature of more than or equal to 950 ℃ at the outlet of the rough rolling mill, finish rolling is carried out in a ferrite area, and a lubrication rolling technology is adopted; the coiling temperature is higher and is 680-760 ℃, and the annealing process is finished by slow cooling after coiling. The product performance is as follows: rm is less than or equal to 320MPa, rel is less than or equal to 280MPa, the elongation is more than or equal to 48 percent, and the r value is more than or equal to 1.2. The patent has the defects that the thickness of the product is more than or equal to 3.5mm, and the process is not suitable for the production of thin products.
Chinese patent CN200610047097.7 discloses a method for producing ultra-low carbon steel for car outer plates, which comprises the following molten steel in percentage by weight: less than or equal to 0.006 percent of C, less than or equal to 0.5 percent of Mn, less than or equal to 0.15 percent of Si, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, less than or equal to 0.10 percent of Ti, less than or equal to 0.06 percent of Als, less than or equal to 0.003 percent of N, and the balance of iron and inevitable impurities, and the process has the following key points: continuously casting the molten steel into a plate blank at a casting speed of 1.5-4 m/min, wherein the thickness of the plate blank is 100-170 mm, the casting machine adopts a dynamic soft reduction and crystallizer electromagnetic braking technology, and the superheat degree of a tundish is 20-45 ℃; the slab is directly hot-charged, the charging temperature is more than or equal to 800 ℃, the slab is heated to 1150-1250 ℃ in a heating furnace, and the slab is subjected to rough rolling and cogging after heat preservation for 30-90 min. The rolling temperature of the finish rolling is 1000-1100 ℃, the outlet temperature is 890-950 ℃, the coiling temperature is 700-750 ℃ after laminar cooling, and the r value of the product is more than or equal to 1.8 after cold rolling and annealing. The patent has the defects that the product can obtain good stamping performance only by cold rolling and annealing, and the thickness of the hot rolled product is more than or equal to 2.0-6.0.
Chinese patent CN201710960187.3 patent "method and apparatus for rolling ultra-low carbon steel coil ferrite for endless continuous casting and rolling ultra-deep drawing", the molten steel comprises the following weight percentages: less than or equal to 0.007 percent of C, less than or equal to 0.05 percent of Si, less than or equal to 0.25 percent of Mn, less than or equal to 0.050 percent of Nb, less than or equal to 0.070 percent of Ti, als: 0.010-0.060 percent, 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 0.005 percent of N and less than or equal to 0.0035 percent of O, the patent adopts a headless continuous casting and rolling technology, the casting blank drawing speed is 4-8m/min, the thickness of the plate blank is 70-130mm, the rough rolling temperature is 1050-1150 ℃, the thickness of the intermediate blank is 6-25mm, the intermediate blank is cooled by a water cooling or gas mist cooling mode, the cooling speed is 7-40 ℃/S, the finish rolling temperature is 730-880 ℃, the coiling temperature is 600-730 ℃, the thickness of a finished product is 0.6mm-4mm, the product performance is 270-380MPa of tensile strength, the elongation is more than or equal to 40 percent, the N value is 0.20-0.25, and the r value is 2.0-2.3. The defect of the patent is that no buffer exists between continuous casting and steel rolling, the casting must be stopped when the roll is changed, and in addition, the horizontal performance uniformity of the strip steel is poor because a production line is not provided with a soaking pit.
In conclusion, the research results on the production of ultra-low carbon steel/IF steel in the thin slab continuous casting and rolling line are mainly limited to the following two types:
(1) Adopting thin slab continuous casting and rolling to produce cold-rolled base stock with thick specification, and obtaining required thickness and mechanical property in the subsequent cold-rolling and annealing processes;
(2) The endless rolling is adopted to produce thin-specification products and replace cold-rolled products. The ultra-low carbon steel or IF steel produced by the first technology has the disadvantages of complicated manufacturing process, long flow and high cost, and the thin-specification ultra-low carbon steel/IF steel produced by the second technology by endless rolling has poor structural property uniformity in the width direction.
Disclosure of Invention
The invention aims to provide thin-specification high-formability stamping steel based on a CSP production line and a preparation method thereof, wherein the stamping steel has the thickness of 0.8-2.0 mm, the thickness tolerance is controlled within the range of +/-30 microns, the yield strength is 120-180 MPa, the tensile strength is 270-370 MPa, the elongation is 48-53%, the r value is more than or equal to 1.3, the performance fluctuation is controlled within 30MPa, the performance and the thickness precision reach the level of cold-rolled products of the same specification, and the 'hot cooling instead of cold' can be realized.
In order to achieve the purpose, the invention provides the technical scheme that:
a thin-specification high-formability stamping steel based on a CSP production line comprises the following chemical components in percentage by weight: c: 0.001-0.006%, si less than or equal to 0.03%, mn: 0.15-0.30%, N is less than or equal to 0.004%, P is less than or equal to 0.015%, S is less than or equal to 0.0080%, als:0.015 to 0.040 percent and also comprises one of Ti, nb, V and Cr + B, wherein 4[C +3.42[ N ] +3[S ] ≦ Ti ≦ 0.065 percent, 7.75[ C ] +6.64[ N ] ≦ Nb ≦ 0.075 percent, 4.25[ C ] +3.64[ N ] ≦ 0.045 percent, and Cr:0.1 to 0.3 percent, 0.78[ 2 ] or more, 0.0035 percent of B, and the balance of Fe and inevitable impurities.
The thickness of the stamping steel is 0.8-2.0 mm.
The structure of the stamping steel is ferrite crystal grains with uniform {111} plane texture, and the grain size does not exceed grade 7.
The thin high-formability punching steel based on the CSP production line has the yield strength of 120-180 MPa, the tensile strength of 270-370 MPa, the elongation of 48-53 percent and the r value of more than or equal to 1.3.
In the composition design of the stamping steel of the invention:
c: the yield strength and tensile strength of the steel are improved by the solid solution C, but the plasticity is reduced, and the formation of {111} texture is not facilitated by the solid solution C. For high formability stamping steel, low yield strength, high elongation, and high {111} texture strength are required, and therefore, the smaller the solid solution C, the better, but the lower the C content, the higher the refining cost required for reducing the C content, and the longer the refining time, and the C content is controlled to be 0.001-0.006% for balancing mechanical properties and production cost.
Si: si is solid-dissolved in ferrite and austenite to improve strength, but significantly reduces plasticity of steel, and Si is combined with O to generate SiO during heating of steel 2 Then the iron olivine Fe and FeO are subjected to a series of complex solid-phase reactions to generate the iron olivine Fe 2 SiO 4 The invention controls the Si content to be less than or equal to 0.03 percent by comprehensively considering the influence on the surface quality.
Mn: mn is dissolved in ferrite and austenite in a solid solution mode, so that the strength can be improved, the plasticity is reduced, feS is separated out due to the fact that the content of the Mn is too low, and the thermoplasticity of the steel is reduced, and comprehensively considered, the Mn content is controlled to be 0.15-0.3%.
N: the steel plate is a strong solid solution strengthening element, is not beneficial to the formation of {111} texture, can generate aging to influence the stamping quality of the steel plate, but the production cost is increased due to the excessively low N content, and the N content is controlled not to exceed 0.004% by comprehensive consideration.
P, S is a harmful impurity element in steel, P in the steel is easy to form segregation in the steel, the toughness and the welding performance of the steel are reduced, S is easy to form plastic sulfide, a steel plate is layered, and the performance of the steel plate is deteriorated, so the lower the content of P, S is, the better the steel plate is, the P content is controlled to be less than or equal to 0.015% and the S content is controlled to be less than or equal to 0.008% in comprehensive consideration.
And Als: al is a strong deoxidizer, oxide inclusions in steel are reduced, the steel quality is pure, but the Al content is too high, the effect of refining grains is easily generated, the yield strength and the yield ratio are improved, and the content of Als is controlled to be 0.015-0.040% by comprehensive consideration.
Ti: ti has strong affinity with C, N in steel, and by generating TiC and TiN to fix C, N interstitial atoms, the content of C, N dissolved in steel is reduced, the formation of {111} texture is facilitated, and the r value is improved, and in addition, the Ti has strong affinity with C, N in steelSince the binding capacity of Ti and S is greater than that of Ti and C, in order to ensure that Ti can remove solid-dissolved C atoms, tiC, tiN and Ti are generated 4 C 2 S 2 Should ensure 4[C]+3.42[N]+3[S]≤[Ti]≤0.065％。
Nb: nb has a similar action to Ti and promotes the formation of {111} texture by making NbC and NbN fix C, N interstitial atoms to thereby increase the r value, and in addition, nb has a function of refining grains, and the grain size thereof does not change significantly with an increase in annealing temperature, and is determined to be 7.75[ C ] +6.64[ N ] ≦ Nb ≦ 0.075% in terms of the mass% of NbC and NbN to be produced in terms of C content and N content in the steel.
V: v functions similarly to Nb, ti, and according to the C content and N content in the steel, 4.25[ C ] +3.64[ N ] ≦ [ V ] ≦ 0.045% in terms of mass% for producing VC, VN.
Cr + B: cr is also a carbide-forming element and can fix C atoms in the steel and promote the formation of {111} texture, and the addition amount of Cr in the steel is determined to be 0.1-0.3% according to the bonding property of Cr and C, and B is used for fixing N atoms in the steel, and B is more than or equal to 0.78[ N ] < B < 0.0035%.
By the chemical composition design of ultra-low carbon and microalloy (adding one of Ti, nb, V and Cr + B), C, N interstitial atoms without solid solution in ferrite are realized, ferrite grains which are thick, uniform in size and have {111} plane texture are obtained by combining a low-temperature austenite zone rolling, ferrite zone lubrication rolling two-stage deformation process, high-temperature coiling and slow cooling, and the yield strength of a product is 120-180 MPa, the tensile strength is 270-370 MPa, the elongation is 42-55%, and the r value is more than or equal to 1.3.
The invention relates to a CSP production line-based production method of thin-specification high-formability stamping steel, which comprises the following steps:
1) Smelting and refining
Smelting according to the chemical components and refining by adopting an LF-RH duplex process; the LF refining process is used for carrying out aluminum wire deep deoxidation, and CaO-Al serving as a main component is added 2 O 3 -modifying agent of Al for the first time; in the RH refining process, oxygen blowing decarburization, aluminum grain deoxidation and ferrotitanium alloying are sequentially carried out in a vacuum state; RH refiningAfter the vacuum treatment is finished, caO-Al as a main component is added into the molten steel 2 O 3 -a second modification with a modifier for Al followed by calcium treatment with pure calcium wire;
2) Continuous casting blank
3) Soaking heat
The charging temperature of the casting blank is 850-940 ℃, the discharging temperature is 980-1020 ℃, and the in-furnace time is 25-40 min;
4) Rolling of
Rolling by adopting a 6-frame or 7-frame, wherein the reduction rate of F1 and F2 is 55-65%, the total reduction rate of F3-F6 or F3-F7 is more than or equal to 65%, the temperature of the third rolling is less than or equal to 840 ℃, and the finishing temperature is 750-800 ℃; the descaling pressure at the inlet and the outlet is more than or equal to 300bar; the water amount of cooling water between the frames F1-F2 and F2-F3 is 90-100%; adding lubricating emulsion into an F3-F6 or F3-F7 rolling mill, wherein the oil-water ratio of the lubricating emulsion is 1-5%;
5) Coiling
The coiling temperature is 700-760 ℃;
6) Slow cooling
And slowly cooling the steel plate after coiling.
Preferably, in the step 1), caO-Al is added to each ton of molten steel for the first modification 2 O 3 The amount of the-Al modifier is 1.1-1.8 kg; caO-Al is added to each ton of molten steel for second modification 2 O 3 The amount of the-Al modifier is 0.5-0.9 kg.
Preferably, in the step 2), the casting blank pulling speed is 3.5-5 m/min, the thickness of the casting blank discharged out of the crystallizer is 50-70 mm, and the fluctuation of the liquid level of the crystallizer is controlled within 5 mm; the argon blowing seal long water gap and the immersion type water gap are adopted for protection.
Preferably, in the step 1), soft blowing is performed for 5-8 min after the calcium treatment.
Preferably, in the step 1), the flow rate of oxygen in the oxygen blowing decarburization process is 1400-1600 m 3 /h。
Preferably, in the step 4), the descaling pressure at the inlet and the outlet of the rolling mill is more than or equal to 300bar.
Preferably, in the step 5), the coiling temperature is 730 to 760 ℃.
Preferably, in the step 6), the slow cooling is stack slow cooling or heat preservation cover slow cooling, and hot coils are stacked around the stack slow cooling.
In the production method of the thin-gauge high-formability stamping steel based on the CSP production line, the production method comprises the following steps:
the invention adopts an LF-RH duplex process, the top slag needs to be modified and reduced into white slag in the LF refining process, the oxidability of the primary slag in the ladle is very strong, if the top slag is not modified, the secondary oxidation of the molten steel is easy to occur in the casting process, the generated oxides pollute the molten steel, and the tundish nozzle is easy to block. The reduced 'white slag' has stronger adsorbability, and the oxide formed after the aluminum wire is added for deep deoxidation can be absorbed by the white slag, so the oxygen content in the steel can be effectively reduced.
The RH vacuum pumping treatment can realize deep decarburization and deep denitrification, and aluminum particles are added under the vacuum condition to remove the excessive oxygen in the steel. After the RH vacuum treatment is finished, the oxidability of the slag rises, and the slag needs to be modified again, and the secondary modification treatment can avoid secondary oxidation in the subsequent casting process to cause impurity aggregation and water gap blockage. Pure calcium line is fed after RH vacuum treatment is finished to modify the inclusion into 12CaO 7Al of liquid phase 2 O 3 And then soft blowing is carried out for 5-8 min, so that the impurities can fully float upwards and are adsorbed by the top slag. The process can realize smelting of ultra-low C, ultra-low O, ultra-low S and ultra-low N clean steel, realizes the O content of less than or equal to 20ppm, the S content of less than or equal to 30ppm and the N content of less than or equal to 40ppm under the condition that the C content is 0.001-0.006 percent, combines protective casting, ensures that the castability of molten steel is better controlled, and can ensure continuous casting of more than 6 furnaces of a casting machine.
In order to avoid the flowing disorder of molten steel in the crystallizer, the casting blank pulling speed is controlled to be 3.5-5 m/min, the fluctuation of the liquid level of the crystallizer is controlled within 5mm, so that the defects of slag entrapment on the surface caused by slag entrapment of the molten steel are avoided, and the secondary oxidation of the molten steel can be avoided by adopting an argon blowing sealing protection measure for a long water gap and a submerged water gap.
The charging temperature of the casting blank is controlled to be 850-940 ℃ in the soaking process, the discharging temperature is controlled to be 980-1020 ℃, the time in the furnace is 25-40 min, the temperature distribution in the length direction and the width direction of the casting blank can be uniform, and the high-precision control of thickness tolerance and the uniform structure performance can be realized.
Dephosphorization is carried out before rolling, and the inlet and outlet descaling pressure is controlled to be more than or equal to 300bar, so that the defect of scale pressing in of hot-rolled products caused by incomplete dephosphorization on the surface of a casting blank is avoided.
The rolling reduction of the F1 and F2 frames is 55-65%, austenite grains are refined through rolling in a low-temperature austenite region under high pressure, more grain boundaries are formed, more nucleation points are provided for the subsequent transformation of austenite into ferrite, and the phase transformation of austenite to ferrite is promoted. The water quantity of cooling water between the frames F1-F2 and F2-F3 is controlled to be 90-100 percent so as to realize rapid cooling of the intermediate blank, avoid the reduction of rolling speed and the incapability of ensuring the required coiling temperature, and more than 90 percent of austenite is converted into ferrite in the cooling process. The total reduction rate of F3-F6 (F7) is controlled to be more than or equal to 65%, the lubrication rolling and the finishing rolling temperature are combined to be 750-800 ℃, so that ferrite phase is accumulated with a certain reduction rate, and the {111} surface texture which is beneficial to punch forming is generated. During lubrication rolling, the oil-water ratio of the emulsion lubricating emulsion is controlled to be 1-5%, if the oil-water ratio is less than 1%, the friction coefficient between a steel plate and a roller is large, a shear texture which is not beneficial to forming is easily formed, and if the oil-water ratio is more than 5%, the rolling process is easy to slip, and the rolling stability is poor.
The coiling temperature is controlled to be 700-760 ℃, and the steel coil is slowly cooled, so that ferrite extending along the rolling direction is fully recovered after the rolling is finished, and coarse and equiaxial ferrite grains are formed, and the required mechanical property is obtained. In addition, the steel coil is slowly cooled, and the uniformity of the structure performance of the product can also be improved.
The invention utilizes the chemical composition design of the non-solid-solution C, N interstitial atoms to obtain coarse ferrite grains with {111} plane texture based on the ferrite rolling technology, thereby obtaining the hot rolled product with low strength, high elongation and high r value, and the hot rolled product can replace cold rolled DC01 and DC03 steel plates to be used for manufacturing and forming more complex automobile and household appliance parts.
Because the cold-rolled DC01 and DC03 steel plates are generally thinner, the defects of mixed crystal, drift, strip breakage and the like are easily generated when the conventional hot continuous rolling production line is adopted for production, and the thin hot-rolled product with the thickness of 0.8-2.0 mm is produced by utilizing the advantages of the thin product produced by the CSP. However, when the CSP is used for casting the ultra-low carbon steel, secondary oxidation is easy to occur in molten steel, the generated oxides are easy to block a nozzle, the castability of the molten steel is poor, and casting break can be caused in serious cases. Aiming at the problem, the invention provides a smelting and casting process of ultra-low carbon steel, so that the castability of molten steel is better controlled, and continuous casting of more than 6 furnaces of a casting machine can be ensured. In addition, in order to realize the process window of ferrite rolling, the corresponding soaking and rolling process is designed by combining the production line arrangement form and the equipment characteristics of the CSP production line, and it is worth noting that lubricating emulsion must be added during ferrite phase zone rolling to avoid forming a shear texture which is not beneficial to forming. When the finish rolling is finished, the structure is deformed ferrite extending along the rolling direction, the structure has high strength and poor plasticity, and the cracking is easy to occur during the forming. Therefore, the coiling temperature of 700-760 ℃ is selected, slow cooling is carried out after rolling, ferrite is promoted to be fully recovered, and in the recovery process, the strength is reduced, the plasticity is improved, and the r value is increased.
The invention has the beneficial effects that:
1. the invention realizes no solid solution C, N interstitial atoms in ferrite by the chemical composition design of ultra-low carbon and microalloy (adding one of Ti, nb, V and Cr + B), so that the structure of the punching steel obtains coarse ferrite grains with uniform size and {111} plane texture, the yield strength of the punching steel is 120-180 MPa, the tensile strength is 270-370 MPa, the elongation is 42-55%, and the r value is more than or equal to 1.3.
2. According to the invention, an LF-RH duplex process is adopted, and two-time modification is carried out, so that the smelting of ultra-low C, ultra-low O, ultra-low S and ultra-low N clean steel is realized, the O content is less than or equal to 20ppm, the S content is less than or equal to 30ppm and the N content is less than or equal to 40ppm under the condition that the C content is 0.001-0.006 percent, the castability of molten steel is better controlled by combining protective casting, and the continuous casting of more than 6 furnaces of a casting machine can be ensured.
3. On the basis of component design, rolling adopts a two-stage deformation process, the reduction ratios of F1 and F2 are controlled to be 55-65%, austenite grains are refined to form more grain boundaries through rolling in a low-temperature austenite region under high pressure, more nucleation points are provided for the subsequent transformation of austenite into ferrite, and the phase transformation of austenite to ferrite is promoted; lubrication rolling is adopted at F3-F6 (F7), the oil-water ratio of emulsion lubrication emulsion is controlled to be 1-5%, the formation of a shear texture which is not beneficial to forming is avoided, ferrite phase accumulates a certain reduction rate, a {111} surface texture which is beneficial to punch forming is generated, and thick and equiaxial ferrite grains are formed by combining subsequent high-temperature coiling and slow cooling, so that the required mechanical property is obtained.
4. The invention utilizes the advantages of CSP to produce thin-specification products, produces thin-specification hot rolled products with the thickness of 0.8-2.0 mm, designs corresponding soaking and rolling processes by combining the layout form and the equipment characteristics of a production line of the CSP production line, controls the temperature fluctuation of a casting blank within +/-10 ℃, the thickness tolerance within +/-30 mu m and the performance fluctuation within 30MPa, achieves the level of cold rolled products with the same specification, and can realize 'replacing cold by heat'.
Drawings
FIG. 1 is a photograph of a metallographic structure of a stamped steel according to example 1 of the present invention.
FIG. 2 shows the ODF orientation of the stamped steel of example 1 of the present invention.
FIG. 3 is a graph showing the longitudinal property distribution of the steel punched in example 1 of the present invention.
FIG. 4 is a widthwise property distribution diagram of the steel punched in example 1 of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples.
The production process flow of the high-strength steel comprises the following steps: refining → continuous casting → soaking → rolling → coiling → slow cooling.
The specific components of the examples of the invention are shown in table 1, the preparation process parameters of the invention are shown in tables 2 and 3, and the steel performance of each example is shown in table 4.
FIG. 1 is a photograph showing a metallographic structure of a stamped steel according to example 1 of the present invention, and FIG. 2 is an ODF orientation of a stamped steel according to example 1 of the present invention, and it can be seen from FIGS. 1 and 2 that the metallographic structure of the finished steel sheet is coarse ferrite grains having a {111} plane texture and uniform size. Fig. 3 and 4 are graphs showing the property distribution in the length direction and the width direction of the punching steel of example 1 according to the present invention, respectively, and it can be seen from the figures that the properties obtained in the length direction and the width direction of the punching steel obtained according to the present invention are relatively uniform.
The invention adopts the chemical composition design of ultra-low carbon and microalloy (adding one of Ti, nb, V and Cr + B), combines two-stage deformation process, subsequent high-temperature coiling and slow cooling in the rolling process to form coarse and equiaxial ferrite grains, ensures that the structure of the stamping steel obtains coarse and uniform-sized ferrite grains with {111} plane texture, ensures that the yield strength is 120-180 MPa, the tensile strength is 270-370 MPa, the elongation is 42-55 percent, the r value is more than or equal to 1.3, the performance and the thickness precision reach the level of cold rolling products with the same specification, and can realize 'cooling by heat'.
Figure BDA0003092087330000101
Figure BDA0003092087330000111
Figure BDA0003092087330000121
Figure BDA0003092087330000131

Claims (12)

1. A thin-specification high-formability stamping steel based on a CSP production line comprises the following chemical components in percentage by weight: c: 0.001-0.006%, si is less than or equal to 0.03%, mn: 0.15-0.30%, N is less than or equal to 0.004%, P is less than or equal to 0.015%, S is less than or equal to 0.0080%, als:0.015 to 0.040 percent and also comprises one of Ti, nb, V and Cr + B, wherein 4[C +3.42[ N ] +3[S ] ≦ Ti ≦ 0.065 percent, 7.75[ C ] +6.64[ N ] ≦ Nb ≦ 0.075 percent, 4.25[ C ] +3.64[ N ] ≦ 0.045 percent, cr:0.1 to 0.3 percent, 0.78[ 2 ] or more, 0.0035 percent of B, and the balance of Fe and other inevitable impurities.
2. The thin gauge high formability punching steel based on CSP production line as claimed in claim 1 wherein the thickness of said punching steel is 0.8-2.0 mm.
3. The CSP-based thin gauge high formability punching steel according to claim 1 or 2, wherein the structure of the punching steel is ferrite grains having {111} plane texture uniformly and the grain size is not more than 7 grade.
4. The thin gauge high formability punching steel based on CSP production line according to claim 1, 2 or 3, wherein the punching steel has a yield strength of 120 to 180MPa, a tensile strength of 270 to 370MPa, an elongation of 48 to 53%, and an r value of 1.3 or more.
5. The CSP production line-based production method of thin gauge high formability stamping steel according to any of claims 1 to 4, characterized by comprising the steps of:
1) Smelting and refining
Smelting according to the chemical components and refining by adopting an LF-RH duplex process; the LF refining process is used for carrying out aluminum wire deep deoxidation, and CaO-Al serving as a main component is added 2 O 3 -modifying agent of Al for the first time; in the RH refining process, oxygen blowing decarburization, aluminum grain deoxidation and ferrotitanium alloying are sequentially carried out in a vacuum state; after the RH refining vacuum treatment is finished, caO-Al which is the main component is added into the molten steel 2 O 3 -a second modification with a modifier for Al followed by calcium treatment with pure calcium wire;
2) Continuously casting into a blank;
3) Soaking heat
The charging temperature of the casting blank is 850-940 ℃, the discharging temperature is 980-1020 ℃, and the in-furnace time is 25-40 min;
4) Rolling of
Rolling by adopting a 6-frame or 7-frame, wherein the reduction rate of F1 and F2 is 55-65%, the total reduction rate of F3-F6 or F3-F7 is more than or equal to 65%, the temperature of the third rolling is less than or equal to 840 ℃, and the finishing temperature is 750-800 ℃; the water amount of cooling water between the frames F1-F2 and F2-F3 is 90-100%; adding lubricating emulsion into an F3-F6 or F3-F7 rolling mill, wherein the oil-water ratio of the lubricating emulsion is 1-5%;
5) Coiling
The coiling temperature is 700-760 ℃;
6) Slow cooling
And slowly cooling the steel plate after coiling.
6. The CSP production line-based production method of thin gauge high formability stamping steel according to claim 5, wherein in the step 1), caO-Al is added to each ton of molten steel for the first modification 2 O 3 The amount of the-Al modifier is 1.1-1.8 kg; caO-Al is added to each ton of molten steel for second modification 2 O 3 The amount of the-Al modifier is 0.5-0.9 kg.
7. The CSP production line-based production method of thin gauge high formability stamping steel according to claim 5, wherein in the step 2), the casting blank casting speed is 3.5-5 m/min, the casting blank thickness out of the crystallizer is 50-70 mm, and the fluctuation of the crystallizer liquid level is controlled within 5 mm; the argon blowing seal long water gap and the immersion type water gap are adopted for protection.
8. The CSP production line-based production method of thin gauge high formability stamping steel according to claim 5, wherein in step 1), the soft blowing is performed for 5-8 min after the calcium treatment.
9. The CSP production line-based production method of thin gauge high formability stamping steel according to claim 5 or 8, wherein in step 1), the oxygen flow rate during the oxygen decarburization process is 1400-1600 m 3 /h。
10. The CSP production line-based production method of thin gauge high formability stamping steel according to claim 5, wherein in step 4), the mill inlet and outlet descaling pressure is equal to or more than 300bar.
11. The method for producing a thin gauge high formability punching steel according to claim 5, wherein the coiling temperature in the step 5) is 730 to 760 ℃.
12. The CSP production line based production method of thin gauge high formability stamping steel according to claim 5, wherein in step 6), the slow cooling is stack slow cooling or heat preservation cover slow cooling, and hot coils are stacked around the stack slow cooling.
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Application publication date: 20221216