Low-cost ultra-thin ultra-deep drawing steel strip and production method thereof

Abstract

The invention discloses a low-cost ultra-thin ultra-deep drawing steel strip and a production method thereof, and belongs to the technical field of steelmaking, rolling and heat treatment, and the low-cost ultra-thin ultra-deep drawing steel strip comprises the following chemical components in percentage by mass: 0.015-0.035% of C, less than or equal to 0.03% of Si, 0.15-0.50% of Mn, less than or equal to 0.020% of P, less than or equal to 0.012% of S, less than or equal to 0.003% of T [O], less than or equal to 0.0035% of N, 0.0020-0.0035% of B, more than or equal to 0.004% of Al and the balance of Fe and inevitable impurities. Wherein the mass percentage content of B, N and Al meets the relational expression that B / N is 0.77-1.5, and Al is smaller than or equal to 20 (B-0. 77 N). The ultra-thin ultra-deep-drawing steel strip with the thickness of 0.20-0.30 mm can be produced, and the steel strip is excellent in forming performance, low in punching lug pressing rate, stable in performance and capable of being widely applied to battery shells, electronic elements, tinplate deep-drawing two-piece cans and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, rolling and heat treatment, and relates to a steel strip production method, in particular to a low-cost ultra-thin ultra-deep drawing steel strip and a production method thereof. Background Art

[0002] With the development of lightweight applications in automobiles, electronic products, and food and beverage packaging, the demand for ultra-thin ultra-deep drawing steel materials such as battery cases, electronic components, and tinplate has grown rapidly. The cold rolling continuous annealing (CA) process is more suitable for high-speed stamping than the hood annealing (BA) process due to its uniform annealing temperature and stable performance. The production processes used for continuous annealing ultra-deep drawing steel strips mainly include: (1) ultra-low carbon IF steel production process, and (2) low carbon aluminum killed steel production process.

[0003] The first type: IF steel process, application publication number CN1401807, CN100106449A, CN109136444A, CN113774274A, CN113930664A and other IF steels add Nb, Ti, Al and other elements that fix interstitial atoms such as C and N. The precipitates increase the cold rolling annealing recrystallization temperature. The CA process requires a higher annealing temperature. High temperature annealing is prone to "thermal buckling" defects, and extremely thin specifications The strip is easy to break. These process difficulties limit the production of ultra-thin ultra-deep drawing steel on the continuous annealing unit. The lower limit specification of the conventional continuous annealing unit is 0.30mm. The thin-gauge tin-plated substrate continuous annealing unit generally cannot produce IF steel; the second type: low-carbon aluminum killed steel process, application publication number CN114107833A, when Al≤0.02%, N cannot be fully fixed, resulting in aging hardening, deteriorating stamping performance, increasing Al content, AlN precipitation during continuous annealing inhibits grain growth, making <110> Increased texture, <111> The texture is reduced, the stamping performance is reduced, and the addition of micro Ti or B and other fixed N, Al-Ti and Al-B fixed N requires a higher annealing temperature than 720℃, and the r value is reduced to 0.9%~1.3%, which does not meet the requirement of r value ≥1.6 for ultra-deep drawing DC04 grade. At the same time, the addition of alloying elements such as Nb, Ti, and Al increases the alloy cost, and high-temperature annealing increases the energy consumption of the unit, resulting in the cost of ultra-thin CA material products being much higher than the cost of annealing. Therefore, how to use the CA process to produce ultra-thin ultra-deep drawing steel strips with uniform performance at low cost to replace BA process products is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In order to solve the problems that the annealing temperature is high after adding more precious alloys such as Nb, Ti, Al, etc. in the production of ultra-thin ultra-deep drawing steel strip by continuous annealing process, high temperature annealing is prone to "thermal buckling" defects, and ultra-thin specifications are prone to breakage, high energy consumption and high cost, the present invention provides a low-cost ultra-thin ultra-deep drawing steel strip and a production method thereof.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A low-cost ultra-thin ultra-deep drawing steel strip, whose chemical composition and mass percentage are: C: 0.015-0.035%, Si≤0.03%, Mn: 0.15-0.50%, P≤0.020%, S≤0.012%, oxide inclusions T[O]≤0.003%, N≤0.0035%, B: 0.0020-0.0035%, Al≥0.004%, and the balance is Fe and unavoidable impurities; wherein the mass percentages of B, N and Al elements satisfy the relationship: B / N: 0.77-1.5, Al≤20 (B-0.77N).

[0006] Elements not intentionally added to the steel strip: Cu≤0.06%, Cr≤0.06%, Ni≤0.04%, Mo≤0.02%, Nb≤0.005%, V≤0.005%, Ti≤0.008%, and the content of other residual elements is ≤0.02% and the total amount does not exceed 0.15%.

[0007] Furthermore, the thickness of the ultra-deep drawn steel strip is 0.20-0.30 mm.

[0008] Furthermore, the tensile strength of the ultra-deep drawing steel strip is 320-360 MPa, the yield strength is 220-260 MPa, and the elongation after fracture is A 80 ≥34%, r 90 ≥1.6, |Δr|≤0.3.

[0009] The production method of the above-mentioned low-cost ultra-thin ultra-deep drawing steel strip includes slab continuous casting, hot rolling and cold rolling processes; In the hot rolling process, the steel strip is cooled to 680-720℃ in a laminar cooling section and then coiled into a steel coil; In the cold rolling process, the steel strip is pickled and then cold rolled to 0.2-0.3 mm at a total reduction rate of 85-90%, and the continuous annealing temperature is 680-720°C.

[0010] Furthermore, in the hot rolling process, the steel billet is rolled into a steel strip with a thickness of 1.8 to 3.0 mm at a final rolling temperature of 880 to 920°C.

[0011] Furthermore, the annealed steel strip is flattened and straightened at a total elongation of 1.5 to 3.0%.

[0012] The beneficial effects of the above technical solution are: the present invention can produce ultra-thin ultra-deep drawn steel strips with a thickness of 0.20-0.30 mm, with a tensile strength of 320-360 MPa, a yield strength of 220-260 MPa, and an elongation after fracture of A 80 ≥34%, r 90≥1.6, |Δr|≤0.3. The finished steel is pure, with excellent forming performance, low punching ear rate and stable performance. It can be widely used in battery shells, electronic components and tinplate deep-drawn two-piece cans. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a typical microstructure diagram of the cold-rolled finished steel strip of the present invention. DETAILED DESCRIPTION

[0014] The chemical composition and mass percentage of the low-cost ultra-thin ultra-deep drawing steel strip of the present invention are: C: 0.015-0.035%, Si≤0.03%, Mn: 0.15-0.50%, P≤0.020%, S≤0.012%, oxide inclusions T[O]≤0.003%, N≤0.0035%, B: 0.0020-0.0035%, Al≥0.004%, wherein the mass percentages of B, N and Al elements satisfy the relationship: B / N: 0.77-1.5, Al≤20 (B-0.77N).

[0015] The chemical composition of the ultra-thin ultra-deep drawn steel strip of the present invention is described below.

[0016] When the C content is between 0.0035% and 0.015% and above 0.035%, the aging hardening effect is strong, which deteriorates the deep drawing performance of the steel. When using ≤0.0035% ultra-low carbon production, the RH vacuum degree is high and the processing time is increased, the production cost is increased, and the oxygen level in the molten steel is high after RH decarburization to the end point, and more aluminum needs to be added, and the probability of generating Al2O3 inclusions increases. The C content of 0.015-0.035% has a weak aging hardening effect. RH is lightly treated, C is used for deoxidation, the end point oxygen level is low, the amount of aluminum added for deoxidation is small, the probability of generating Al2O3 inclusions is low, the steel is pure, the RH processing time is short, the temperature is reduced, and the smelting cost is low. Therefore, the C content of the ultra-deep drawing steel strip of the present invention is 0.015-0.035%.

[0017] Si is a ferrite strengthening element. A high Si content is detrimental to deep drawing performance. At the same time, the probability of SiO2 inclusion increases, and the addition of ferrosilicon increases smelting costs. The Si content of the ultra-deep drawing steel strip of the present invention does not exceed 0.03%.

[0018] The positive effect of Mn is within the range of 0.15% to 0.50% by mass fraction, because a small amount of Mn is conducive to improving strength. At the same time, adding a small amount of Mn can combine with S to form MnS, reduce surface hot brittleness, and avoid surface quality problems. However, adding too much is not only unfavorable for stamping, but also the cost of Mn element alloy is relatively high. Therefore, in order to control costs, the mass fraction of Mn element is limited to 0.15% to 0.50%.

[0019] P is an impurity. If the P content exceeds 0.020%, it may become easy to segregate at the grain boundary, deteriorating the formability. Therefore, the P content is 0.020% or less. On the other hand, the P content may be 0%. From the viewpoint of reducing the dephosphorization cost, the P content may exceed 0%. Therefore, the P content of the ultra-deep drawing steel strip of the present invention does not exceed 0.020%.

[0020] S is an impurity. If the S content exceeds 0.012%, coarse MnS may be generated, which may deteriorate the formability. Therefore, the S content is 0.012% or less. On the other hand, the S content may be 0%, and from the perspective of reducing the desulfurization cost, the S content may exceed 0%. Therefore, the S content of the ultra-deep drawing steel strip of the present invention does not exceed 0.012%.

[0021] In order to ensure the deoxidation effect of steel, the Al content in steel should not be less than 0.004%; if Al is higher than 20 (B-0.77N), AlN will precipitate below the A1 temperature during hot rolling and annealing. The pinning effect of AlN during hot rolling will refine the grains and be detrimental to grain growth. As the Al content decreases, the recrystallization temperature of cold rolling decreases, which promotes <111> / / ND component formation, slowing down <110> / / ND component formation is beneficial to improve deep drawing performance, so the Al content is ≤20 (B-0.77N). In addition, reducing the addition of Al can reduce costs.

[0022] The present invention uses 0.0020% to 0.0035% B, which is lower in cost, to replace fine grain strengthening elements such as Nb, Ti, and Al to fix N, thereby reducing the aging hardening effect of N. Since the precipitation temperature of BN is higher than that of AlN, the precipitation of coarse BN and the precipitation of fine AlN are reduced, thereby improving the grain growth performance. In order to ensure that N is fully fixed, the B / N mass percentage should be ≥0.77 (10.8 / 14). If B is higher than 0.0035% or the B / N mass percentage is higher than 1.5, excessive B will form tiny Fe 23 (CB)6 inhibits grain growth and is detrimental to deep drawing performance.

[0023] N is a residual element in steel. If the N content exceeds 0.0035%, B cannot fully fix nitrogen, resulting in an aging hardening effect, which is detrimental to deep drawing performance. Therefore, the N content is ≤0.0035%.

[0024] T[O] is an oxide inclusion. If the T[O] content exceeds 0.003%, the high inclusion content will easily form large-sized inclusions, causing "sand holes" defects and affecting deep drawing performance. Therefore, the O content is ≤0.0030%.

[0025] Residual elements in steel strip: Cu≤0.06%, Cr≤0.06%, Ni≤0.04%, Mo≤0.02%, Nb≤0.005%, V≤0.005%, Ti≤0.008%, other residual elements are ≤0.02% and the total amount does not exceed 0.15%; if the residual elements exceed the above values, the strength of the steel will increase, the annealing temperature will increase, and the energy consumption and cost will increase.

[0026] The production process of the low-cost ultra-thin ultra-deep drawn steel strip of the present invention is as follows: (1) Smelting process The molten steel with the steel strip composition is obtained by adding desulfurized molten iron and scrap steel into a converter / electric furnace for smelting, and then treated in an RH furnace or other refining furnace, and then cast into slabs of 180 to 230 mm by a slab continuous casting machine.

[0027] (2) Hot rolling process The slab is heated to 1210-1260℃. Within this temperature range, the metallographic structure in the ingot can be completely austenitized, and the final rolling temperature of the fine rolling can be guaranteed, while the heating cost is controlled. After high-pressure water dephosphorization, it is rolled into a 32-40mm intermediate billet through one or two reversible roughing mills for multiple passes. After high-pressure water dephosphorization by the flying shear head, the steel strip is controlled to be rolled into a 1.8-3.0mm steel strip at a temperature above the Ar3 line, and the final rolling temperature is 880-920℃. After rolling, the steel strip is cooled to 680-720℃ in the laminar cooling section and coiled into a steel coil at high temperature. High-temperature coiling can make the carbides, nitrogen compounds and carbonitrides larger in size, which is beneficial to grain growth and improves forming performance.

[0028] (3) Cold rolling process After pickling, the steel strip is cold rolled with a total reduction rate (ε%) of 85-90%, and then cold rolled to 0.2-0.3 mm steel strip. The total reduction rate (ε%) of cold rolling of 85-90% is beneficial to control the Δr value ≤ 0.3 and reduce earing.

[0029] Since no more Nb, Ti, Al grain refining elements are added, the annealing temperature of the cold-rolled steel strip is controlled at 680-720℃ to meet the requirements of r 90 Ultra-deep drawing steel requirements of ≥1.6. In order to control the aging hardening of the steel strip, R-OA over-aging treatment is carried out on the continuous annealing line, with a treatment temperature of 300-400℃ and an aging time of 300-400s.

[0030] In order to eliminate the yield platform, the steel strip is leveled and straightened at a total elongation (E%) of 1.5-3.0% after annealing to improve the plate shape.

[0031] The chemical composition and mass content of the ultra-deep drawn steel strips of various embodiments are shown in Tables 1 and 2, the production process parameter control is shown in Table 3, and the thickness and mechanical properties of the ultra-deep drawn steel strips are shown in Table 4.

[0032] Table 1 Chemical composition and mass content of ultra-deep drawing steel strips in various embodiments

[0033] Table 2 Chemical composition and mass content of ultra-deep drawing steel strips in various embodiments

[0034] Table 3. Production process parameter control of ultra-deep drawing steel strip in various embodiments

[0035] Table 4. Thickness and mechanical properties of ultra-deep drawn steel strips in various embodiments

[0036] according to Figure 1 It can be seen that the microstructure of the ultra-deep drawing steel strip of the present invention is equiaxed ferrite and dispersed free cementite, the ferrite grain size is about 8 levels, and the structure is uniform.

[0037] The present invention uses B element to replace Al (usually 0.02-0.07% in deep drawing steel) and nitrogen-fixing elements such as Nb, V, and Ti, thereby reducing the alloy cost. The continuous annealing temperature is controlled at 680-720°C to meet the requirements of r 90 The ultra-deep drawing steel (DC04) grade requirement of ≥1.6 significantly reduces the annealing temperature compared to the conventional continuous annealing temperature of 760-850℃. The higher the annealing temperature of thin steel, the more likely it is to cause thermal warping. The present invention reduces the annealing temperature to the conventional DC01 grade annealing temperature, reduces the heating energy consumption, effectively avoids the risk of thermal warping and high-temperature belt breakage, and ensures smoother production.

Claims

1. A low-cost ultra-thin ultra-deep drawn steel strip, characterized in that: Its chemical composition and mass percentage are: C: 0.015~0.035%, Si≤0.03%, Mn: 0.15~0.50%, P≤0.020%, S≤0.012%, T[O]≤0.003%, N≤0.0035%, B: 0.0020~0.0035%, Al≥0.004%, and the remainder is Fe and unavoidable impurities; among them, the mass percentage of B, N, and Al elements satisfies the relationship: B / N: 0.77~1.5, Al≤20 (B-0.77N).

2. The low-cost ultra-thin ultra-deep drawn steel strip according to claim 1, characterized in that: Elements not intentionally added to the steel strip: Cu≤0.06%, Cr≤0.06%, Ni≤0.04%, Mo≤0.02%, Nb≤0.005%, V≤0.005%, Ti≤0.008%, and the content of other residual elements is ≤0.02% and the total amount does not exceed 0.15%.

3. The low-cost ultra-thin ultra-deep drawn steel strip according to claim 2, characterized in that: Its thickness is 0.20~0.30mm.

4. The low-cost ultra-thin ultra-deep drawn steel strip according to claim 3, characterized in that: Its tensile strength is 320-360MPa, yield strength is 220-260MPa, elongation after fracture is A 80 ≥34%, r 90 ≥1.6, |Δr|≤0.

3.

5. The method for producing a low-cost ultra-thin ultra-deep drawing steel strip according to any one of claims 1 to 4, characterized in that: It includes slab continuous casting, hot rolling and cold rolling processes; In the hot rolling process, the steel strip is cooled to 680-720℃ in a laminar cooling section and then coiled into a steel coil; In the cold rolling process, the steel strip is pickled and then cold rolled to 0.2-0.3 mm at a total reduction rate of 85-90%, and the continuous annealing temperature is 680-720°C.

6. The method for producing low-cost ultra-thin ultra-deep drawn steel strip according to claim 5, characterized in that: In the hot rolling process, the steel billet is rolled into a steel strip with a thickness of 1.8 to 3.0 mm at a final rolling temperature of 880 to 920°C.

7. The method for producing low-cost ultra-thin ultra-deep drawn steel strip according to claim 6, characterized in that: After annealing, the steel strip is leveled and straightened at a total elongation of 1.5 to 3.0%.

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