Method for improving corrosion resistance of SPCC cold-rolled cover-annealed steel coil

Abstract

The invention provides a method for improving the corrosion resistance of an SPCC cold-rolled cover-removed steel coil, and relates to the technical field of metal materials. The method comprises the following steps that an SPCC hot-rolled coil is subjected to acid pickling treatment; carrying out cold rolling on the SPCC hot-rolled coil subjected to acid pickling treatment; the cold-rolled steel coil is subjected to cover annealing; and the annealed steel coil is flattened, the roughness of a working roller of a flattening unit is 1.0-2.0 microns, the roughness of the steel coil is controlled to be 0.4-0.8 microns, and the flattening elongation is 0.6-1.3%. By adjusting the composition of the SPCC and optimizing the cover annealing condition and the flattening condition of the steel coil, the prepared SPCC cold-rolled cover-annealed steel coil is high in surface hardness and good in corrosion resistance, and the application range of the SPCC cold-rolled cover-annealed steel coil can be effectively widened.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly relates to a method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils. Background Art

[0002] The alloy composition, microstructure morphology, crystal defect density and surface roughness of steel strips have a significant impact on the corrosion resistance of steel. For SPCC cold-rolled steel strips, since they do not contain alloying elements that are easy to form a dense passivation layer, the formed passivation layer has weak corrosion protection. In terms of microstructure morphology, the heating and cooling rates during batch annealing are low, and in order to achieve the purpose of full recrystallization of the ferrite matrix, a relatively long isothermal annealing time is generally set, resulting in large and uneven sizes of ferrite and cementite in the annealed structure. There may also be chain-like distributed cementite particles due to the influence of hot-rolled banded structure. In a corrosive medium, cementite and the ferrite matrix form an approximate primary battery, and the matrix around the carbide is corroded, causing the cementite to peel off. The continuous pits formed after the corrosion of chain-like cementite will accelerate the corrosion process; and the uneven ferrite grain size has worse corrosion resistance. Due to the poor corrosion resistance of SPCC cold-rolled batch annealing steel strips, their application in some fields is limited. For example, when producing engine oil seal gaskets, a gluing operation is carried out before stamping. Rusting begins to occur in the SPCC cold-rolled batch annealing steel strip about 3 minutes after gluing, leading to material failure. Therefore, how to improve the corrosion resistance of SPCC cold-rolled batch annealing steel strips is crucial.

[0003] Research has found that increasing the dislocation density will enhance the reactivity of the steel surface with the corrosive medium, that is, reduce the activation energy of the corrosion reaction. Moreover, a larger surface roughness corresponds to a higher specific surface area. Both will further increase the corrosion active sites on the steel surface, increase the corrosion rate, and reduce the corrosion resistance. There is less research on the use of SPCC cold-rolled batch annealing steel strips in corrosive medium service environments in the prior art. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: aiming at the deficiencies existing in the prior art, to provide a method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils, which can effectively solve the problem of poor corrosion resistance of SPCC cold-rolled batch annealing steel coils and broaden the application range of SPCC cold-rolled batch annealing steel coils.

[0005] To solve the above technical problem, the technical solution of the present invention is:

[0006] A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils, comprising the following steps:

[0007] Pickle the SPCC hot-rolled coil;

[0008] Cold-roll the pickled SPCC hot-rolled coil;

[0009] The cold-rolled steel coil is subjected to box annealing;

[0010] The annealed steel coil is leveled. The roughness of the work rolls of the leveling mill is 1.0 - 2.0 μm, the roughness of the steel coil is controlled at 0.4 - 0.8 μm, and the leveling elongation is 0.6 - 1.3%.

[0011] Preferably, the SPCC hot-rolled coil, by mass percentage, comprises the following components: C ≤ 0.06%, Si ≤ 0.05%, Mn ≤ 0.4%, Cr 0.25 - 0.5%, P ≤ 0.03%, S ≤ 0.02%, Als ≤ 0.06%, the balance being Fe and unavoidable impurities, and the mass percentage of the unavoidable impurities is not greater than 0.04%.

[0012] Preferably, during pickling, the hydrochloric acid content in the acid solution > 150 g / L, the pickling temperature is 70 - 100 °C, and the pickling time is 0.5 - 1 min.

[0013] Preferably, the cumulative deformation during cold rolling ≥ 80%.

[0014] Preferably, the conditions for box annealing are: the annealing temperature is 560 - 600 °C, and the annealing time is 3 - 5 h.

[0015] Preferably, during leveling, the roughness of the work rolls of the leveling mill is 1.5 - 1.8 μm, and the roughness of the steel coil is controlled at 0.5 - 0.7 μm.

[0016] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0017] The present invention discloses a method for improving the corrosion resistance of SPCC cold-rolled box annealed steel coils. By adding an appropriate amount of Cr element to the SPCC steel alloy, combined with incomplete recrystallization annealing, adjusting the surface roughness of the annealed steel coil through leveling, and controlling the leveling deformation amount, the surface hardness of the SPCC cold-rolled box annealed steel strip is improved, thereby obtaining excellent corrosion resistance. During subsequent use, the corrosion resistance is good. For example, when manufacturing engine oil seal gaskets, the SPCC cold-rolled steel strip after coating with glue does not rust before reaching the stamping process, meeting the requirements for the corrosion resistance of the material.

[0018] The present invention appropriately increases the surface roughness of the SPCC cold-rolled batch annealing steel coil, increases the surface active sites of the SPCC cold-rolled batch annealing steel coil, promotes the rapid formation of the passivation layer, is conducive to the densification of the passivation layer and the improvement of the bonding force with the substrate, effectively hinders the penetration of corrosive media. At the same time, appropriate surface roughness is conducive to the dispersion of corrosion current and reduces the tendency of local corrosion. Appropriately increasing the surface hardness of the SPCC cold-rolled steel strip can promote the increase of dislocation density and grain refinement, further improve the formation and growth rate of the passivation layer, increase the densification of the passivation layer, reduce the local potential difference, and inhibit galvanic corrosion.

[0019] The chromium element added in the present invention combines with oxygen on the surface of the steel strip to form a dense Cr2O3 protective film, which can effectively block the contact between the corrosive medium and the substrate, prevent further oxidation reaction, and improve the corrosion resistance of the material. Moreover, the solid solution of Cr in ferrite can refine grains, improve the uniformity of the matrix structure, and reduce the corrosion sensitivity at microdefects. Moreover, during the subsequent incomplete recrystallization annealing, the Cr element diffuses sufficiently at high temperature, promoting the uniformity of the surface oxide film. At the same time, the incomplete recrystallization annealing can eliminate the cold rolling stress, reduce the risk of stress corrosion cracking induced by residual stress, enhance the bonding force between the passivation layer and the substrate, and improve the long-term protection effect.

[0020] The present invention provides a method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils. By optimizing the alloy composition and process parameters for coordinated control, the problem that traditional SPCC materials are prone to rust in humid environments is successfully solved. Specifically, the present invention introduces an appropriate amount of chromium element into the alloy system of conventional SPCC steel, combines with a unique incomplete recrystallization annealing process, and precisely controls the surface roughness and leveling deformation amount, so that the surface hardness and corrosion resistance of the material are significantly improved.

[0021] The present invention enables the Cr element to diffuse sufficiently at high temperature through incomplete recrystallization annealing, promoting the uniformity of the surface oxide film. At the same time, annealing can eliminate the cold rolling stress, reduce the risk of stress corrosion cracking induced by residual stress, enhance the bonding force between the passivation layer and the substrate, and improve the long-term protection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0023] Figure 1 FIG. is the Nyquist diagram obtained by EIS (electrochemical impedance spectroscopy) test for the SPCC cold-rolled batch annealing steel coils prepared in the examples and the comparative examples;

[0024] Figure 2 Polarization curves of the cold-rolled batch-annealed SPCC steel coils for the examples and comparative examples. Specific embodiments

[0025] In order to better understand the above objects, features and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0026] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0027] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with the examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0028] The conditions of the pickling treatment described in the following examples and comparative examples are as follows: a hydrochloric acid solution with a concentration of 180 g / L is used for pickling at 80 °C for 1 min.

[0029] Example 1

[0030] A method for improving the corrosion resistance of cold-rolled batch-annealed SPCC steel coils includes the following steps:

[0031] (1) Using an SPCC hot-rolled coil with a thickness of 0.35 mm, the composition of which is C 0.058%, Si 0.03%, Mn 0.38%, P 0.028%, S 0.015%, Als 0.055%, Cr 0.4%, and the rest is Fe and inevitable impurities, and the mass percentage of the inevitable impurities is not more than 0.04%;

[0032] (2) Subjecting the above-mentioned SPCC hot-rolled coil to pickling treatment;

[0033] (3) Cold-rolling the pickled SPCC hot-rolled coil, and the cumulative cold-rolling deformation is 87.3%;

[0034] (4) Subjecting the cold-rolled steel coil to batch annealing, and the annealing temperature and time are 560 °C and 5 h respectively;

[0035] (5) Leveling the annealed steel coil, the roughness of the work roll of the leveling mill is 1.6 μm, the surface roughness of the steel coil is controlled at 0.6 μm, and the leveling elongation is 1.1%. The steel coil after the above treatment is denoted as No. 1.

[0036] Example 2

[0037] A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils, comprising the following steps:

[0038] (1) Using an SPCC hot-rolled coil with a thickness of 0.5 mm as the raw material, with the composition of C 0.055%, Si 0.035%, Mn 0.37%, P 0.027%, S 0.018%, Als 0.055%, Cr 0.5%, and the rest being Fe and unavoidable impurities, and the mass percentage of unavoidable impurities not exceeding 0.04%;

[0039] (2) Pickling the above-mentioned SPCC hot-rolled coil;

[0040] (3) Cold-rolling the pickled SPCC hot-rolled coil, with the cumulative cold-rolling deformation amount being 83.3%;

[0041] (4) Batch annealing the cold-rolled steel coil, with the annealing temperature and time being 560 °C and 3 h respectively;

[0042] (5) Temper rolling the annealed steel coil, with the roughness of the work roll of the temper rolling mill being 1.6 μm, the surface roughness of the steel coil being controlled at 0.6 μm, and the temper rolling elongation being 1.0%. The steel strip after the above treatment is denoted as 4#.

[0043] Example 3

[0044] A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils, comprising the following steps:

[0045] (1) Using an SPCC hot-rolled coil with a thickness of 0.25 mm as the raw material, with the composition of C 0.056%, Si 0.035%, Mn 0.38%, P 0.025%, S 0.012%, Als 0.045%, Cr 0.3%, and the rest being Fe and unavoidable impurities, and the mass percentage of unavoidable impurities not exceeding 0.04%;

[0046] (2) Pickling the above-mentioned SPCC hot-rolled coil;

[0047] (3) Cold-rolling the pickled SPCC hot-rolled coil, with the cumulative cold-rolling deformation amount being 90.9%;

[0048] (4) Batch annealing the cold-rolled steel coil, with the annealing temperature and time being 600 °C and 4 h respectively;

[0049] (5) Temper rolling the annealed steel coil, with the roughness of the work roll of the temper rolling mill being 1.4 μm, the surface roughness of the steel coil being controlled at 0.5 μm, and the temper rolling elongation being 1.2%. The steel coil after the above treatment is denoted as 5#.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the SPCC hot-rolled coil does not contain Cr, and other process conditions are the same as those in Example 1. The steel coil after the above treatment is denoted as 2#.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that the annealing temperature is 650 °C and the annealing time is 6 h, and other process conditions are the same as those in Example 1. The steel coil after the above treatment is denoted as 3#.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that the surface roughness of the batch annealing steel coil is controlled at 0.06 μm, and other process conditions are the same as those in Example 1. The steel coil after the above treatment is denoted as 6#.

[0056] Next, performance tests were carried out on the SPCC cold-rolled batch annealing steel coils in the above examples and comparative examples, and the test methods and results are as follows.

[0057] 1. Vickers hardness

[0058] The test was carried out according to the standard of GB / T 4340.1-2024.

[0059] The test results are shown in Table 1.

[0060] Table 1

[0061] Surface topography Vickers hardness / HV 1# Fine linen surface 150 4# Fine linen surface 165 5# Fine linen surface 140 2# Fine linen surface 145 3# Fine linen surface 105 6# Bright surface 143

[0062] 2. Electrochemical test:

[0063] 2-1: EIS (electrochemical impedance spectroscopy) test:

[0064] The electrochemical corrosion test was carried out using a three-electrode system. The SPCC cold-rolled batch annealing steel sample was used as the working electrode, the saturated calomel electrode was used as the reference electrode, and the graphite rod was used as the counter electrode. After the SPCC cold-rolled batch annealing steel sample was immersed in a solution of "10 g / L sodium bicarbonate + 2.5 g / L sodium chloride" for 1800 s for open-circuit potential test, the electrochemical impedance spectroscopy test was carried out under the open-circuit potential condition. The AC bias voltage was 10 mV, and the test frequency was 105-0.1 Hz. The corrosion resistance of the SPCC cold-rolled batch annealing steel was evaluated by comprehensive equivalent circuit fitting and Nyquist diagram. As Figure 1 shown, the horizontal and vertical coordinates are the real part and the imaginary part of the impedance, (Zr 2 +Zi 2 ) 1 / 2 That is, the distance from the zero point to the highest point on the Y-axis in the figure can characterize the corrosion resistance. The larger this value is, the better the corrosion resistance. From Figure 1It can be seen that for the corrosion resistance, 5# > 1# > 4# > 2# > 3# > 6#.

[0065] 2-2: Polarization curve:

[0066] The three-electrode system was used for the electrochemical corrosion test. The SPCC cold-rolled pickled and annealed steel sample was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the graphite rod was used as the counter electrode. After the SPCC cold-rolled pickled and annealed steel sample was immersed in the solution of "10 g / L sodium bicarbonate + 2.5 g / L sodium chloride" for 1800 seconds for the open-circuit potential test, the anodic polarization curve test was carried out. The potential of the polarization curve test was scanned from the open-circuit potential to 1.0 V vs. SCE, and the potential scanning rate was 1 mV / s. The corrosion resistance of the SPCC cold-rolled pickled and annealed steel was comprehensively evaluated through the passivation interval range and passivation current density of the polarization curve. As Figure 2 shown, Figure 2 in which, the horizontal and vertical coordinates are the corrosion current and potential respectively. From Figure 2 it can be seen that taking 5# as an example, the corrosion / passivation current is smaller and the potential passivation interval is larger, both indicating that the passivation performance of the 5# steel coil is relatively excellent, that is, the corrosion resistance of 1#, 4# and 5# is better than that of 2#, 3# and 6#.

[0067] To sum up, from Figure 1 and Figure 2 the comprehensive results can be seen that the comparison between 1#, 4#, 5# and 2# shows that adding an appropriate amount of Cr element can make the SPCC cold-rolled pickled and annealed steel coil obtain better corrosion resistance; the comparison between 1#, 4#, 5# and 3# shows that by incomplete annealing to improve the hardness of the SPCC cold-rolled pickled and annealed steel coil, the corrosion resistance is improved, while the comparison between 1#, 4#, 5# and 6# shows that by increasing the surface roughness of the temper mill roll, the SPCC cold-rolled pickled and annealed steel coil obtains a fine matte surface topography, that is, a larger roughness, and the corrosion resistance is also improved.

[0068] In this article, specific examples are used to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that have no substantial difference from the literal expression of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils, characterized in that, It includes the following steps: Pickle the SPCC hot-rolled coil; Cold-roll the pickled SPCC hot-rolled coil; Anneal the cold-rolled coil in a bell-type furnace; Level the annealed coil. The roughness of the work rolls of the leveling mill is 1.0 - 2.0 μm, the roughness of the coil is controlled at 0.4 - 0.8 μm, and the leveling elongation is 0.6 - 1.3%.

2. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils according to claim 1, characterized in that, The SPCC hot-rolled coil, by mass percentage, includes the following components: C ≤ 0.06%, Si ≤ 0.05%, Mn ≤ 0.4%, Cr 0.25 - 0.5%, P ≤ 0.03%, S ≤ 0.02%, Als ≤ 0.06%, and the balance is Fe and unavoidable impurities, and the mass percentage of the unavoidable impurities is not greater than 0.04%.

3. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing coils according to claim 1, characterized in that, When pickling, the hydrochloric acid content in the acid solution is > 150 g / L, the pickling temperature is 70 - 100 °C, and the pickling time is 0.5 - 1 min.

4. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils according to claim 1, characterized in that, The cumulative deformation amount during cold rolling is ≥ 80%.

5. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing coils according to claim 1, characterized in that, The conditions for bell-type annealing are: the annealing temperature is 560 - 600 °C, and the annealing time is 3 - 5 h.

6. A method for improving the corrosion resistance of SPCC cold-rolled batch annealing steel coils according to claim 1, characterized in that, When leveling, the roughness of the work rolls of the leveling mill is 1.5 - 1.8 μm, and the roughness of the coil is controlled at 0.5 - 0.7 μm.

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