JP3234180B2 - Method for pickling Fe-Ni based low thermal expansion alloy products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to descaling, rust removal, etc. of Fe-Ni-based low thermal expansion alloy products, for example, sheet materials, pipe materials, wire materials, and various products made from these materials. It relates to a pickling method.

[0002]

2. Description of the Related Art A Fe-Ni alloy containing 30 to 45% by weight of Ni has a remarkably low coefficient of thermal expansion. In particular, 36% Ni-Fe alloys and 42% Ni-Fe alloys have been put into practical use as various component materials called "invar" which dislike thermal expansion due to temperature change. However, in the conventional applications, there are many components of relatively small precision equipment such as a shadow mask of a bimetal or a cathode ray tube.

[0003] The above low thermal expansion alloy is converted to liquefied natural gas (LN).
If applied to piping for transporting low-temperature substances (low-temperature piping) such as G), extremely great benefits can be obtained. Low temperature piping
Usually, it is made of austenitic stainless steel such as SUS304, but since this material has a large coefficient of thermal expansion, the amount of expansion and contraction caused by a change in the temperature of the pipe is large.
Therefore, it is necessary to interpose a loop pipe for absorbing the expansion and contraction in some parts of the pipe. Due to the presence of this loop tube, the number of welded joints increases, and it takes time to keep the loop tube cool, an expensive elbow tube for the loop tube is required, and a large installation space is required for the overhang of the loop tube. In the case of a pipe in a tunnel, there are various problems such as a need to increase the diameter of the tunnel, a change in the flow direction of the fluid due to the loop pipe, and an increase in pressure loss.

[0004] The thermal expansion coefficient of the above Fe-Ni alloy is about 1/10 of that of austenitic stainless steel. If such an alloy is used as a material for low-temperature piping, it is not necessary to provide a loop pipe in the middle of the piping, and the above problem can be solved at once. However, there are various problems to be solved in order to put a pipe made of a low thermal expansion coefficient alloy into practical use. One of them is Fe
-Descaling and rust removal of Ni-based alloys.

[0005] When the Fe-Ni alloy is heated, oxide scale is generated on the surface. In addition, brown-green rust is generated when left in the air for a long time or when it comes into contact with moisture. Since these oxide scales and rust impair the corrosion resistance, surface treatment workability, appearance, etc. of the alloy, when manufacturing a plate or pipe made of an Fe-Ni alloy, the oxide scale or rust may be generated during or in the final manufacturing process. Rust must be removed.

When descaling general stainless steel, a method of dipping in a mixed solution of nitric acid and hydrofluoric acid is widely used. However, since the Fe-Ni-based low thermal expansion alloy does not contain Cr, it does not have a Cr oxide protective film on the surface. Therefore, when treated with an acid solution used for descaling stainless steel, pitting corrosion easily occurs.

Under the circumstances described above, descaling and rust removal of an Fe—Ni-based low thermal expansion alloy are usually performed by grinding or cutting. However, it is not efficient to descaling a plate material or a tube material used for a large structure such as the low-temperature pipe by such a mechanical method. In particular, for a product having a curved surface such as a tube or a product having a complicated shape, a mechanical method such as buffing is difficult to apply.

In some cases, descaling is carried out by using a treatment solution containing ferric chloride as a main component instead of an acid. However, pitting corrosion may also occur, and the descaling efficiency is poor. . Therefore, for example, Japanese Patent Application Laid-Open No. 5-78788 discloses a measure for preventing pit-like or pock-like corrosion when pickling with a treatment solution containing ferric chloride as a main component.
An invention for adjusting the components of the alloy has been proposed. However, it is not practical to change the chemical composition of the alloy used in large quantities merely for the purpose of improving pickling properties.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide Fe-
Plates, pipes, wires (for example, welding wires) made of Ni-based low thermal expansion alloys or equipment made by combining them (in this specification, these materials, semi-finished products, and products are collectively referred to as "Fe-Ni-based low heat An object of the present invention is to provide a method of efficiently pickling an alloy product having an expansion coefficient) without causing the aforementioned pitting corrosion or the like.

[0010]

According to the present invention, there is provided a method for preparing a "5 to 10% by weight"
Nitric acid and 1.5 ~ 3wt% hydrofluoric acid, temperature is 20 ~ 45 ℃
Fe-Ni, characterized by being immersed in an aqueous solution for 2 to 13 minutes
Method of pickling low-thermal-expansion alloy products ".

The above-mentioned Fe—Ni-based low thermal expansion alloy is an alloy containing 30 to 45% by weight of Ni and the balance substantially consisting of Fe, and further contains Co, Ti, Nb, Cr, Mo, and the like. Means an alloy containing a small amount of subcomponents.

The preferred range of the nitric acid concentration is 7 to 10% by weight,
The preferred range of hydrofluoric acid concentration is 2-3% by weight, the preferred temperature of the solution is 25-40 ° C, and the preferred range of treatment time is 3-8 minutes.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The descaling and rust removal of pipes and plates used for structures such as low-temperature pipes and tanks, or welding materials (wires) used for welding them, require a large amount of processing. Due to the variety of shapes, mechanical methods are inefficient. Therefore, a method of dipping in an acid solution (pickling), which is widely used in general stainless steel, is desirable.
However, the conditions for pickling stainless steel cannot be directly applied. As described above, since the Fe-Ni-based low thermal expansion alloy basically does not contain Cr, there is no oxide film that prevents pitting corrosion on the material surface. This is because the base material itself is locally corroded while being removed.

The present inventors have paid attention to this point, and
The concentration, temperature, and immersion time were examined in detail, and conditions for pickling without causing pitting corrosion were found even for Fe—Ni-based low thermal expansion alloys. That is, in order to completely remove oxide scale and rust and prevent pitting corrosion, the concentration of the nitric acid in the pickling solution is 5 to 10% by weight and the concentration of hydrofluoric acid is 1.5.
To 3% by weight, and the treatment temperature (temperature of the pickling solution) is 20 to 45 ° C.
It was confirmed that the treatment time (immersion time) needed to be controlled to 2 to 13 minutes . Hereinafter, the reasons for each limitation will be described. (1) Type and concentration of acid As the acid to be used, nitric acid and hydrofluoric acid commonly used for pickling stainless steel were selected. This is because the processing of the Fe—Ni-based low coefficient of thermal expansion alloy is often performed in a factory that handles stainless steel, and therefore it is desirable to divert materials used for processing stainless steel. Then, it was confirmed that even with this mixed aqueous solution of nitric acid and hydrofluoric acid, the pickling of the Fe—Ni-based low thermal expansion alloy can be effectively carried out if the concentration and the use conditions are properly determined.

When the concentration of nitric acid exceeds 10% by weight, and when the concentration of hydrofluoric acid exceeds 3% by weight, pitting corrosion easily occurs in the material to be treated. On the other hand, the nitric acid concentration is 5% by weight.
If the concentration is less than 1.5%, or if the concentration of hydrofluoric acid is less than 1.5% by weight, the pickling ability is reduced, resulting in inefficiency. The most effective case is when the concentration ratio between nitric acid and hydrofluoric acid is about 10: 3.

(2) Treatment temperature If the treatment temperature (the temperature of the pickling solution) is lower than 20 ° C., the pickling ability will be reduced, and the treatment will take a long time and the working efficiency will be reduced. On the other hand, if the processing temperature is higher than 45 ° C., pitting corrosion is likely to occur in the product to be processed, and it becomes difficult to prevent pitting corrosion only by adjusting the processing time.

(3) Treatment time Under the above conditions (1) and (2), no pitting occurs with a treatment time of 2 minutes to 13 minutes (immersion time in pickling solution). Complete descaling or rust removal can be performed. Within this time, an appropriate processing time may be selected according to the scale, rust thickness, and the like. In principle, the treatment time is shortened when the concentration and temperature of the acid in the pickling solution are high, and longer when the concentration is opposite. Considering the dispersion of the concentration of the treatment liquid and the dispersion of the components of the alloy to be treated, the immersion time is
It is desirable to manage in 3 to 8 minutes.

[0018]

【Example】

[Example 1] Pickling was performed under various conditions shown in Table 2 by using a hot-rolled plate of sample 1 shown in Table 1 as a test piece, and the surface of the treated test piece was visually observed. The presence of scale and the presence of pitting were examined. The results are also shown in Table 2.

[0019]

[Table 1]

[0020]

[Table 2]

As shown in Table 2, in the processing time of 2 minutes to 13 minutes, an acceptable level of descaling effect was obtained in any of the processing times of 25 ° C. and 40 ° C. In particular, descaling was completed without any pitting corrosion between 3 minutes and 8 minutes.

In this embodiment, a scale residue may be generated in a processing time of 1 minute.
By increasing the scale, this scale residue could be eliminated. On the other hand, the pitting that occurred in the treatment time of 15 minutes and 20 minutes could be prevented by lowering the pickling temperature to 20 ° C.

Example 2 A pipe (welded pipe) having an outer diameter of 508 mm and a thickness of 9.5 mm was manufactured from the alloy of Test Material 2 shown in Table 1 above, and was pickled under the following conditions to remove scale and rust. The existence of pits and the presence of pits were investigated. It was confirmed that no scale or rust remained in any of the alloy tubes, and that no pitting occurred.

Pickling conditions: Pickling solution: 9% nitric acid, 3% hydrofluoric acid aqueous solution.

Treatment temperature (temperature of pickling solution) 25 ° C Treatment time (immersion time in pickling solution) 5 minutes

[0026]

According to the method of the present invention, the pickling solution containing nitric acid and hydrofluoric acid, which is used for descaling of general stainless steel, has a low thermal expansion coefficient of Fe-Ni system without causing pitting corrosion. Pickling of the alloy can be performed. This method
Since it can be applied regardless of the shape of the product to be processed and is efficient, it greatly contributes to putting Fe-Ni-based low thermal expansion alloys into practical use as materials for pipes and tanks.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masao Shirai Osaka Gas Co., Ltd. 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka (72) Inventor Naoshige Kubo 4, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. 1-2 (72) Inventor Taku Iwahashi Inside Osaka Gas Co., Ltd. 4-1-2 Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture (72) Taketo Yamakawa Niijima, Harima-cho, Kako-gun, Hyogo Prefecture No. 8 Inside the Harima Plant of Kawasaki Heavy Industries, Ltd. (72) Inventor Hiroaki Masatomo 1st place of Nishinocho, Higashimukaijima, Amagasaki City, Hyogo Special Sumitomo Metal Industries Co., Ltd.Kansai Works Special Pipe Works (56) References -139888 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23G 1/08

Claims (1)

(57) [Claims] 1. An Fe-Ni type low thermal expansion characterized by being immersed in an aqueous solution containing 5 to 10% by weight of nitric acid and 1.5 to 3% by weight of hydrofluoric acid and having a temperature of 20 to 45 ° C. for 2 to 13 minutes. Pickling method for high alloy products.