JPH05295574A - High speed pickling method for steel metal - Google Patents

Abstract

PURPOSE:To provide the high speed pickling method not requiring to select a properly applicable acid soln. according to the kinds of steel in the melt- grinding of scales by pickling, i.e., the pickling method by which the performance of melt-grinding is enhanced regardless of the kinds of steel and imparting smooth surface properties after pickling. CONSTITUTION:A steel metal is immersed in an aq. soln. of hydrochloric acid with 100 to 450g/l concn. containing one or >= two kinds among Pt, Pd and Rh in the form of chloride or nitrate and held under heating to 50 to 110 deg.C or is subjected to electrolytic treatment. In particular, at the time of regulating the concn. of NO3<-> ions in the aq. soln. of hydrochloric acid into <=300g/l and the concn. of Pt, Pd and Rh into <=500mg/l, by the improvement of the effect of melt-grinding by pickling and the surface smoothness after the pickling, the pickling rate can extremely be accelerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to ordinary steel, Cr, Ni,
The present invention relates to a method for rapidly removing oxide scale formed on the surface of a steel metal such as an alloy steel containing Nb by pickling.

[0002]

2. Description of the Related Art In the production of thin steel metal sheets by cold rolling, mechanical descale treatment such as shot blasting is performed to remove oxide scale formed on the surface of hot coils after hot rolling. Do a wash. This pickling treatment also has an important role of improving the surface quality of the final thin plate product by dissolving and removing surface flaws of the hot coil generated during hot rolling to form a smooth surface.

As a method of pickling a steel strip for the purpose of smoothing the surface, Japanese Patent Laid-Open No. 59-37883 discloses a first method in which a steel strip is immersed in an aqueous sulfuric acid solution to remove oxide scale on the surface.
A pickling method is disclosed which comprises a step and a second step in which a steel strip is immersed in an aqueous nitric acid solution to passivate it together with smut removal for removing dirt on the surface. In this pickling method, the oxide scale is removed by sulfuric acid pickling, which requires a relatively long time for pickling. Therefore, it takes a lot of time to remove the oxide scale, and the annealing of the hot-rolled steel sheet such as low alloy steel or special steel containing iron, carbon, and Cr is particularly omitted or simplified. The pickling of steel metal having grain boundary Cr deficiency has a drawback that grain boundary corrosion occurs in the step of immersing in a nitric acid aqueous solution.

For low alloy steel and special steel such as ferritic stainless steel, hydrochloric acid or sulfuric acid pickling, and Ni
In austenitic stainless steels containing Cr, cold rolling is performed after immersing in an aqueous solution of nitric acid and hydrofluoric acid to dissolve and remove scale remaining on the surface.

It was necessary to properly use the pickling solution depending on the type of steel because of the difference in the cutting ability of the pickling solution and the surface properties after pickling. That is, in sulfuric acid, the dissolution rate is remarkably reduced as Ni increases, and it takes a long time to obtain the required amount of ablation in austenitic stainless steel containing Ni, but in a mixed aqueous solution of nitric acid and hydrofluoric acid, High fusing ability and good surface quality after pickling can be obtained. With nitric hydrofluoric acid, when pickling low-alloy steels or ferritic stainless steels, the ablation capacity is large, but the dependence of the ablation on the amount of Cr is large and the higher the Cr concentration, the smaller the ablation amount. In a material having grain boundary Cr deficiency in which annealing of a hot rolled steel strip is omitted or annealing is simplified, intergranular corrosion occurs due to a difference in solubility between the grain boundary and the grain. For this reason, sulfuric acid pickling, which has a small scraping ability, is performed, although the scraping has little dependency on the Cr amount.

As described above, conventionally, in order to remove the steel surface scale at high speed, it was necessary to select the pickling solution for each steel type. Moreover, there was a problem that the high speed on the left could not be expected.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-speed pickling method that does not require proper use of pickling solutions depending on steel types in pickling and lapping of scales, that is, the ability of ablation does not depend on steel types. It is to provide a pickling method which is large and has a smooth surface property after pickling.

[0008]

The present invention provides Pt, Pd,
One or more of Rh is added in the form of chloride or nitric oxide at a concentration of 100 to 450 g / l, and 5
It is characterized in that the steel metal is immersed or electrolyzed in a hydrochloric acid aqueous solution heated and kept at 0 to 110 ° C.

NO 300 g / l or less in hydrochloric acid aqueous solution
It is possible to contain ₃ ^- ions, and Pt, P
The d and Rh concentrations are preferably 500 mg / l or less.

When the present invention is applied to electrolytic treatment, a coil is used as an anode and an electric current is passed between the coil and a cathode provided facing the anode, or the surface to be pickled of steel metal is opposed. A normal method can be adopted in which one or more pairs of anode and cathode electrode plates are placed in a hydrochloric acid aqueous solution, and the scale produced on the steel metal surface is dissolved while direct current is applied between them. The current density at this time is not particularly limited, but a range of 5 to 200 A / dm ² is preferable from the viewpoint of efficient and stable long-term ablation.

[0011]

[Function] Hydrochloric acid was selected as the basic component because it has a better ability to dissolve base iron than sulfuric acid and shortens the pickling time of steel metal.
This action of hydrochloric acid cannot be obtained at any concentration, and the dissolving ability becomes insufficient at a thin concentration of less than 100 g / l, and the dissolving ability reaches supersaturation at a concentration of more than 450 g / l.

Addition of Pt, Pd, Rh chloride or nitric oxide increases the ablation ability of the hydrochloric acid solution of this specific concentration, and enables descaling in a short time. In particular, when treating steel that causes grain boundary Cr deficiency, grain boundary corrosion does not occur and a smooth pickled surface can be obtained. The addition amount of 1 mg / l shows a smelting effect even when added in a minute amount, but the expected smelting effect required for high-speed pickling is obtained at 3 mg / l or more. However, excessive addition causes the fusing capacity to reach the supersaturation region and is economically disadvantageous, and the total amount is set to 500 mg / l or less.

The chlorides and nitric oxides of Pt, Pd and Rh are not specified, but PdCl ₂ and [Pd (NH ₃ ) ₂ ] Cl are used because they can be industrially used.
₂ , Pd (NO ₃ ) ₂ , PdO, PdSO ₄ , H ₂ Pt
_{Cl 6, H 2 PtCl 4,} PtCl 4, RhCl 3 · 3
H ₂ O, Rh (NO ₃ ) ₃ and Rh ₂ O ₃ are used.

[0014] NO ₃ ^- for the ion concentration, Pt, P
When a large amount of NO ₃ ⁻ ions are added to nitric acid or NaNO _{3 in} a hydrochloric acid aqueous solution containing chloride or nitric oxide of d and Rh, the machinability is remarkably improved. But 30
An excessive content of NO ₃ ⁻ ions exceeding 0 g / l causes a problem of intergranular corrosion. Therefore, it is necessary to suppress the content of NO ₃ ⁻ ions to 300 g / l or less.

The heating of the hydrochloric acid aqueous solution for pickling is carried out in order to efficiently ablate the scale. At that time, the ablation ability becomes smaller as the temperature becomes lower and becomes larger as the temperature rises. From the point of, it was set to 50 to 110 ° C.

[0016]

【Example】

[Example 1] Low Cr steel containing 7% of Cr, about 1% of Cr
Chromium-based stainless steel containing 7% SUS430, C
High Cr steel containing 19% r, 18% Cr, 8 Ni
% Of austenitic stainless steel SUS30
4. Mechanical descaling of high-carbon steel containing 1.2% carbon and 0.4% Cr, where hot-coil with remarkable sensitization without annealing and hot coil annealed with sand iron particles mixed in high-pressure water and sprayed The present invention was applied to the applied 1 m-wide 10 t coil.

100-450 g / l hydrochloric acid and 30
Contains NO ₃ ⁻ ions of 0 g / l or less, and further contains Pt,
Pd, Rh up to 500 mg / l as Pd, Rh
Chloride and / or nitric oxide of d and Rh, or both of them are mixed and added, and when the pickling is carried out in a hydrochloric acid aqueous solution heated at each temperature, the fusing depth and the fusing capability for 1 minute and the surface grain Table 1 shows the results of the test for evaluating the presence or absence of intergranular corrosion.

[0018]

[Table 1] FIG. 1 shows a comparison of the shaving ability of SUS430 in the above test when the SUS430 was immersed in an aqueous solution of 300 g / l concentration of hydrochloric acid held at 80 ° C. for 60 seconds, depending on the amounts of Pt, Pd, and Rh added. is there. When the added amount is 3 mg / l or more, all show remarkable fusing effect.

The pickled steel strip thus obtained is subjected to tandem cold rolling by means of a rolling mill train having a large diameter roll (work roll having a diameter of 200 to 600 mm) and cold rolling by means of a Sendzimir mill having a work roll having a small diameter of 100 mm or less. After performing the cold rolling step by combination and the cold rolling (3t to 0.4t) only by the Sendzimir mill, bright annealing was performed. The product plate thus obtained was tested for gold dust (generated if there was intergranular corrosion of the pickled plate). As a result, no gold dust was generated and the surface gloss was good.

Example 2 Table 2 shows low Cr steel containing 7% Cr, SUS430 of chromium-based stainless steel containing about 16.5% Cr, high Cr steel containing 19% Cr and Cr. An example of applying SUS304 of austenitic stainless steel containing 18% and Ni of 8% to a hot coil with remarkable sensitization without annealing and a 12 t coil of 1.25 m width annealed is shown. At the time of pickling, after mechanical descaling in which sand iron particles are mixed in high-pressure water and sprayed on this hot coil, 100-450 g / l hydrochloric acid and 5-300 g / l N are added.
O ₃ ⁻ ion, and further Pt, Pd, Rh amount of 500
Chloride or nitric oxide of Pt, Pd, Rh up to mg / l or both are mixed and added, and immersed in an aqueous hydrochloric acid solution heated at each temperature.
A direct current of / dm ² was applied. When the anodic dissolution pickling is performed by passing an electric current between the coil as an anode and the cathode provided facing the anode, and when facing the pickled metal surface of the steel metal in the liquid, the cathode , 2 pairs of anodes on each side of the steel strip for a total of 8 electrode plates (width 1400 mm, length 400 mm),
Installed with their polarities vertically symmetrical, distance between poles is 30 to 1
In the case of the indirect energization method in which the steel strip is made to be 00 mm and the steel strip is passed from the entrance side of the pickling tank to-++-,-+-+, +-+, +-+-, and the current is passed between the poles. The results of a test for evaluating the fusing depth, the fusing capability for 1 minute, and the presence or absence of intergranular corrosion on the surface are shown.

[0021]

[Table 2] According to the method of the present invention, all steel types exhibited a high fusing rate, and it was possible to improve the descaling pickling efficiency and smooth the pickling surface. The pickled steel strip thus obtained is tandem cold-rolled by a row of rolling mills having large-diameter rolls (work rolls with a diameter of 200 to 600 mm) and cold with a Sendzimir mill having small-diameter work rolls (work rolls with a diameter of 100 mm or less). After performing a cold rolling step by a combination of rolling and a cold rolling (3t → 0.4t) only by a Sendzimir mill, bright annealing was performed. As a result of testing the gold dust of the product plate thus obtained, no gold dust was generated and the surface gloss was good.

[0022]

The present invention has the following effects.

(1) Significantly improved pickling and shaving effect, and smoothing the surface after pickling enables extremely high pickling speed.

(2) In particular, it is not necessary to change the liquid in stainless steel, and the pickling efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of addition of Pt, Pd, and Rh on pickling of steel materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kosai, Inventor Hiroyuki Kozai 1-1, Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka Shin-Nippon Steel Corporation Yawata Works (72) Kazunori Nagai, Inaba, Tobata-ku, Kitakyushu, Fukuoka No. 1 town No. 1 Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. 50 to 11 wherein one or more of Pt, Pd and Rh are added in the form of chloride or nitric oxide.
A high-speed pickling method for a steel metal, wherein the steel metal is immersed in an aqueous hydrochloric acid solution having a concentration of 100 to 450 g / l heated and kept at 0 ° C. 2. The method according to claim 1, wherein the concentration of NO ₃ ⁻ ions in the aqueous hydrochloric acid solution is 300 g / l or less, and
A high-speed pickling method for steely metal having a Pt, Pd, Rh concentration of 500 mg / l or less. 3. A high-speed pickling method for steel metal according to claim 1, wherein the immersion treatment of the steel metal in the hydrochloric acid aqueous solution is dipping or electrolytic treatment.