JP3828832B2 - Cu-containing plain steel pickled steel sheet having excellent color tone and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plain steel pickled steel sheet containing 0.03% by mass or more of Cu in a steel material and a method for producing the same. Specifically, the present invention relates to a pickled steel sheet that improves the color tone of the steel sheet surface after pickling and descaling of a plain steel hot-rolled steel sheet in which the mass% of Cu in the steel material is 0.03% or more, and a method for manufacturing the same.
[0002]
[Prior art]
Hot-rolled steel sheets are generally pickled with hydrochloric acid or an aqueous sulfuric acid solution after hot rolling, mainly for the purpose of removing scale generated on the steel sheet surface during hot rolling, that is, descaling.
However, in steel making methods (electric furnace steel making method, cold iron source melting method, Cupla hot metal / converter steel making method, blast furnace / converter steel making method, etc.) with a scrap mixing ratio of 5% or more in the main raw material, In some cases, the mass% of Cu in the steel may be 0.03% or more, and the phenomenon that Cu in steel is concentrated at the interface between the scale and the ground iron during the heating process in a hot rolling furnace has been recognized. When this Cu concentration phenomenon occurs, it becomes a starting point for cracking of the steel sheet, and so hot rolling conditions for taking Cu into the scale were selected.
[0003]
Thus, Cu concentrated at the scale on the steel sheet surface and the iron interface is not dissolved in the hydrochloric acid or sulfuric acid aqueous solution used as a general pickling bath, and only the iron is preferentially etched. For this reason, the steel plate surface after pickling is etched unevenly, and as a result, the color tone of the steel plate surface becomes blackish and the gloss is inferior.
In FIG. 1, the change of the color tone of the steel plate surface when changing the mass% of Cu in a steel plate is shown.
L * value as a measure of whiteness after pickling four types of hot-rolled steel sheets with a thickness of 2.3mm and Cu mass% of steel in 0.016%, 0.035%, 0.10%, 0.17% with hydrochloric acid aqueous solution Was measured. As shown in FIG. 1, the L * value decreased with an increase in Cu mass% in the steel material.
Here, the L * value is an index indicating the lightness of the color adopted in CIE (International Commission on Illumination) -1976 and JIS Z8729, adopting the L * a * b * color system and made by MINOLTA. Measured with a total of CR-300.
[0004]
Conventionally, in order to improve productivity by efficiently removing the scale of the hot-rolled steel sheet, for example, (1) the hot-rolled steel sheet after pickling is first roughly cleaned in a rough rinsing tank and then ultrasonically rinsed. A pickling method (JP-A-5-125573) has been proposed in which cleaning is performed while applying ultrasonic energy in a tank.
Further, as a method for improving the color tone of the surface of the pickled steel sheet, (2) a pickling method for etching a hot-rolled steel sheet after pickling with a ferric salt aqueous solution (JP 11-131264 A) Proposed.
The method (1) above is to physically remove so-called smuts adhering to and remaining on the steel sheet by non-uniform pickling, and the method (2) is a technique for excessively etching ordinary steel sheets. However, there is a problem that the amount of chemicals consumed increases due to this excessive etching. In addition, a method of using a pickling inhibitor (organic inhibitor) in a pickling bath in order to suppress peracid washing is also disclosed, and usually 0.1 to 10 g / l is added.
[0005]
It is also disclosed that the pickling inhibitor is preferably an organic inhibitor, for example, an amine derivative, a mercapton, a sulfide, thiourea or a derivative thereof is desirable.
However, none of the above-mentioned methods has led to measures focused on removing Cu remaining on the surface of the steel sheet, and pickling of a normal steel hot-rolled steel sheet in which the mass% of Cu in the steel material is 0.03% or more. Later color tone improvement was not realized.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art and improves the color tone after pickling of a plain steel hot-rolled steel sheet in which the mass% of Cu in the steel material is 0.03% or more, and a method for producing the same It is an issue to provide.
[0007]
[Means for Solving the Problems]
The present invention provides a pickling inhibitor, a surfactant, preferably after pickling of a plain steel hot-rolled steel sheet in which the mass% of Cu is 0.03% or more by pickling under specific conditions in a pickling solution containing nitric acid. The pickling steel plate which improves the color tone of this, and its manufacturing method are provided, and the summary is as follows.
[0008]
(1) An area of a portion of a normal steel pickled steel sheet containing 0.03% by mass or more and 0.17 % by mass or less of Cu in the steel material, where the Cu concentration measured by EPMA on the steel sheet surface after pickling is 5% or more A Cu-containing plain steel pickled steel sheet excellent in color tone, characterized in that the rate is 10% or less.
(2) A method for producing the pickled steel sheet according to (1), wherein the pickling inhibitor is 0.001 to 0.1 g / l and the surfactant is 0.001 to 0.01 in a pickling bath made of hydrochloric acid or a sulfuric acid aqueous solution. A method for producing a Cu-containing plain steel pickled steel sheet excellent in color tone, characterized by pickling treatment in a pickling bath containing g / l .
[0009]
(3) The pickling steel containing Cu having excellent color tone according to (2), wherein the pickling bath is further pickled in a pickling bath containing 0.1 to 1.0% nitric acid. Production method.
(4) Cu-containing ordinary steel acid excellent in color tone as described in (2) or (3), wherein Cu substitution precipitation reaction on the surface of the steel sheet during pickling is suppressed by an ultrasonic vibration device or a jet device A method for producing washed steel sheets.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
First, as a result of investigating the direct cause that the color tone of the pickled steel sheet becomes black, the present inventors have found countless fine irregularities (hereinafter referred to as cotton-like residues) that look cotton-like on the steel sheet surface of black color tone. It was found that the unevenness of the color caused the light to diffusely reflect on the surface of the steel sheet, resulting in a black color tone.
Furthermore, as a result of performing a line analysis of the steel plate surface after pickling by EPMA, if the area ratio of the portion where the Cu concentration on the steel plate surface is 5% or more is 10% or less, the L * value indicating the lightness of the steel plate surface is It was found to be 55 or more.
[0011]
Here, EPMA is an abbreviation for electronic probe microanalyzer, and the area ratio of the composition existing on the surface of the steel sheet can be measured. The measurement conditions were as follows.
Equipment: EPMA-1400 manufactured by Shimadzu Corporation
Accelerating voltage: 15KV, irradiation current: 30mA,
Analysis range: 51.2 × 51.2μm (measured from the steel plate surface)
Analysis time: 5 ms / pixel Number of pixels: 256 x 256
Preparation of sample: Washed steel plate with water, dried with warm air, put in desiccator,
Within the test apparatus, the steel sheet surface was quickly measured.
The Cu concentration was calculated using analysis software attached to this apparatus.
[0012]
Next, it was found that the flocculent residue was generated by non-uniform etching of Cu and Fe, and a method for suppressing the precipitation of Cu was studied.
First, the amount of dissolution is increased by adding, for example, 0.001 to 0.1 g / l (usually about 1/10) of a pickling inhibitor in the pickling bath, and further, FeC generated on the steel sheet surface by pickling. In order to facilitate removal of so-called pickling smut, such as FeCl2, a surfactant such as ethylene glycol was added.
[0013]
If the amount of the pickling inhibitor is less than 0.001 g / l, the inhibitory effect is completely lost and the iron is excessively consumed, resulting in an increase in cost. Moreover, since the suppression effect is large at 0.1 g / l or more, the surface layer containing Cu cannot be removed.
The surfactant is preferably ethylene glycol, glycerin or the like, and the addition amount is required to be 0.001 g / l or more. Although there is no particular upper limit, the effect is not substantially changed even if 0.01 g / l or more is added.
[0014]
Secondly, 0.1 to 1.0% nitric acid was added to remove Cu during the pickling bath.
If nitric acid is less than 0.1%, the effect of improving the L * value is not sufficient.
Third, in order to suppress Cu precipitation during pickling, ultrasonic waves are generated in the pickling solution to cause liquid vibration, or the flow rate of the pickling solution on the steel sheet surface is increased by a jet device. It was.
As described above, the L * value indicating the color tone of the steel sheet surface after pickling can be increased to 55 or more, which leads to a significant improvement over the conventional L * value of 50.
[0015]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to FIG. This will be described in detail with reference to the embodiments of FIGS. 2, 3, and 4.
In FIG. 1, the change of the color tone of the steel plate surface when changing the mass% of Cu in a steel plate is shown.
Commercial pickling inhibitors containing amine derivatives of four types of hot-rolled steel sheets with Cu mass% of 0.016%, 0.035%, 0.10%, 0.17% in a steel plate with a thickness of 2.3 mm (made by Sugimura Chemical: trade name AS20C) Was pickled in an aqueous hydrochloric acid solution (85 ° C., 8.5% HCL) added so that the weight of the inhibitor component was 0.3 g / l, and then L * value was measured as an index of whiteness. As shown in FIG. 1, the L * value decreased with an increase in Cu mass% in the steel material.
[0016]
FIG. 2 is a diagram showing the relationship between the Cu concentration / area ratio on the steel sheet surface after pickling and the L * value.
When the area ratio of the portion where the Cu concentration measured by EPMA on the steel plate surface after pickling was 5% or more was 10% or less, the L * value was 55 or more.
The graph on the right-hand side of Fig. 3 shows the L for the steel plate with 0.17% Cu in the steel when 0.03g / l of pickling inhibitor and 0.01g / l of surfactant (ethylene glycol) are added to the pickling solution. * Indicates value.
As a result, the L * value on the steel sheet surface after pickling in the inventive example was 55 or more, which was significantly improved as compared with 52 in the comparative example.
[0017]
FIG. 4 is a diagram showing L * values when nitric acid is further added to the pickling solution.
When pickling is performed by adding 0.1 to 1.0% nitric acid into a pickling solution containing 0.03 g / l of a pickling inhibitor and 0.01 g / l of a surfactant, the L * value on the steel sheet surface after pickling is 60 or more. It became.
[0018]
As shown in FIG. 5, when pickling is performed while generating ultrasonic waves in a pickling solution containing a pickling inhibitor 0.03 g / l and a surfactant 0.01 g / l, L * of the steel plate surface after pickling The value was 65 or more.
Furthermore, when pickling was performed by adding 0.03 g / l of a pickling inhibitor, 0.01 g / l of a surfactant, and 0.1 to 1.0% nitric acid, the L * value on the steel sheet surface after pickling became 70 or more.
As described above, the L * value on the steel sheet surface is improved by pickling under the pickling conditions of the present invention, thereby reducing the amount of cotton-like residue forming the irregularities on the steel sheet surface. Because.
In addition, the L * value is improved by using an ultrasonic vibration device or a jet device. The ultrasonic vibration device or jet device increases the flow rate of the pickling solution that comes into contact with the steel plate surface. This is because the precipitation of is suppressed.
[0019]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the pickling steel plate which improves the color tone after the pickling of the normal steel hot-rolled steel plate whose mass% of Cu in steel materials is 0.03% or more, and its manufacturing method can be provided.
As for the accumulation of steel products in Japan, it is assumed that a large amount of iron scrap will be generated and accumulated when consumer materials such as building structures, automobiles and home appliances are scrapped down in the future.
[0020]
On the other hand, high-function and high-value-added building structures, automobiles and home appliances, etc. that have been promoted so far have complicated the material composition, and in scrap, non-ferrous metals such as copper and aluminum as well as iron and It is no longer possible to avoid contamination with organic and inorganic substances.
Therefore, when steel companies recycle these scraps and manufacture hot-rolled steel sheets, Cu detoxification technology inevitably mixed in the steel sheets is essential. INDUSTRIAL APPLICABILITY The present invention is an effective means for solving the previous problems that steel companies that manufacture hot-rolled steel sheets encounter in the future, and has a remarkable effect that is industrially useful.
[Brief description of the drawings]
FIG. 1 is a diagram showing changes in the color tone of a steel sheet surface when the Cu mass% in the steel sheet is changed.
FIG. 2 is a diagram showing the relationship between the Cu concentration / area ratio on the steel sheet surface after pickling and the L * value.
FIG. 3 is a diagram showing L * values when a pickling inhibitor and a surfactant are added to the pickling solution.
FIG. 4 is a diagram showing L * values when nitric acid is further added to the pickling solution.
FIG. 5 is a diagram showing L * values when ultrasonic waves are performed during pickling.

Claims (4)

An ordinary steel pickled steel sheet containing 0.03% by mass or more and 0.17 % by mass or less of Cu in the steel material, and the area ratio of the portion where the Cu concentration measured by EPMA on the steel sheet surface after pickling is 5% or more is 10%. A Cu-containing plain steel pickled steel sheet excellent in color tone, characterized by being: A method for producing a pickled steel sheet according to claim 1, wherein the pickling inhibitor is 0.001 to 0.1 g / l and the surfactant is 0.001 to 0.01 g / l in a pickling bath made of hydrochloric acid or sulfuric acid aqueous solution. A method for producing a Cu-containing plain steel pickled steel sheet having excellent color tone, wherein the pickling treatment is performed in a pickling bath containing the pickling bath. The method for producing a Cu-containing plain steel pickled steel sheet with excellent color tone according to claim 2, wherein the pickling treatment is further performed in a pickling bath containing 0.1 to 1.0% nitric acid in the pickling bath. The Cu-containing plain steel pickled steel sheet having excellent color tone according to claim 2 or 3, wherein Cu substitution precipitation reaction on the steel sheet surface during pickling is suppressed by an ultrasonic vibration device or a jet device. Production method.

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