JPH0724759B2 - Metal chloride reduction and purification container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for the reduction / purification of metals such as high melting point and high toughness metals such as titanium and zirconium produced by reduction / purification of chlorides. Regarding the container.

[Conventional technology]

The high melting point and high toughness metal is manufactured as a metal sponge by exclusively reducing its chloride with an active metal such as magnesium. The metal sponge produced is typically further purified by vacuum separation.

The reaction vessel used for such reduction / purification of chloride is generally made of carbon steel or stainless steel in order to prevent corrosion by active metals such as magnesium. Also has the following problems.

[Problems to be solved by the invention]

Since the carbon steel container lacks high temperature strength, it easily deforms and has a short life. Further, since there is a problem in durability, it is inevitably necessary to make the thickness large, which causes an increase in weight and makes handling difficult.

On the other hand, stainless steel containers have excellent high-temperature strength, but alloy components such as Ni and Cr contained in steel elute into active metals such as magnesium during the reduction process, which contaminates metal sponges. Therefore, there is a problem that the concentration of impurities such as Ni and Cr is increased.

[Means for solving problems]

By the way, as one means to solve these problems,
The use of clad steel is considered. That is, the inside of the container is made of carbon steel and the outside is made of stainless steel to prevent contamination of the metal sponge, ensure high temperature strength, and suppress scale generation. However, when such a clad steel container is used for the reduction / refining of metal chlorides, the present inventor may cause the following serious problems due to the peculiarities of the use environment. It became clear from their experience.

First, the reduction / purification of metal chlorides will be briefly described by taking a titanium production process as an example. In the reduction process,
The magnesium charged in the reaction vessel is melted by a heating device, and titanium tetrachloride is dropped into the reaction vessel while continuing heating. As a result, titanium sponge is gradually refined on the grate of the reaction vessel.

When the reduction reaction is completed, the inside of the reaction vessel is degassed while continuing heating. As a result, the unreacted magnesium taken into the sponge generated in the reaction container and the by-product magnesium chloride are separated and scattered outside the container. This is the purification process.

In the production process of titanium as described above, the present inventors used SS4, which is typical as carbon steel, as the inside of the reaction vessel.
1.When a clad steel container made of SUS304L, which is one of the stainless steels on the outside, is used, remarkable intergranular corrosion cracking occurs on the stainless steel on the outside, and the original durability of stainless steel is not exhibited and it cannot be used practically. I experienced that I could not get a good container.

FIG. 1 shows the heating temperature pattern in the above-mentioned titanium manufacturing process by the temperature change of the reaction vessel.
As can be seen from this figure, the reaction vessel is subjected to a thermal history of normal temperature → about 850 to 1000 ° C. → normal temperature in one manufacturing cycle, and chromium carbides that cause intergranular corrosion cracking in each process of heating and cooling. The precipitation temperature range (about 600 to 800 ° C). In other words, it is exposed twice in an environment where intergranular corrosion cracking is likely to occur in one use. On the other hand, however, when a container made of stainless steel alone is used under the same conditions, intergranular corrosion cracking does not become a serious problem. From this, the problem of intergranular corrosion cracking in the clad steel container of SS41 and SUS304L is
It is considered that this is because the carbon contained in 41 permeates into SUS304L and increases the amount of carbon in SUS304L, making it easier to form chromium carbide. By the way, the carbon content of SS41 is about 0.15%, and the carbon content of SUS304L is about 0.01%.

The present invention is based on the above, is lightweight, and is a metal sponge N
(EN) A metal chloride reduction and refining vessel made of clad steel, which is provided with practically sufficient durability by preventing the above-mentioned intergranular corrosion cracking while preventing contamination by i and Cr. Is that the outer side of the container is made of stainless steel and the inner side is made of clad steel made of low carbon steel having a lower C content than the stainless steel.

In the present invention, low carbon steel refers to carbon steel such as rolled steel for general structure (SS, SM type), carbon steel for boilers and pressure vessels (SB type) specified in JIS, and the C content in the steel. It has been lowered. The components other than C are appropriately selected from the range of the various component systems of the above carbon steel according to the properties to be obtained.

The C content of the low carbon steel inside the container is further required to be equal to or lower than the C content of the stainless steel outside the container, but from the viewpoint of obtaining a more reliable effect, the C content in the low carbon steel is It is desirable to keep the amount of C to less than 1/2 of the amount of C in stainless steel.

Stainless steel is also appropriately and selectively used according to the properties to be obtained, but a smaller amount of C (0.03% or less) is preferable because a reliable effect on intergranular corrosion prevention can be obtained.

Further, this stainless steel is preferably an austenitic stainless steel rather than a ferritic stainless steel in terms of high temperature strength and the like.

[Action]

In the container of the present invention, the inside is low carbon steel, since the content of the alloy components such as NI and Cr is small, there is no risk of contaminating the metal sponge generated in the container with Ni, Cr and the like, Since the C content of the low carbon steel on the inside is made smaller than the C content of the stainless steel on the outside, there is no risk of C in the low carbon steel penetrating into the stainless steel, and the C content in the stainless steel is It is kept low to prevent the precipitation of chromium carbide and effectively prevent intergranular corrosion cracking of the outer stainless steel. As a result, the original strength and durability of stainless steel is exhibited,
Since the life of the container is extended and deformation is less likely to occur, the material thickness can be reduced and the weight of the container can be reduced.

Further, the combination of the inner low carbon steel and the outer stainless steel in the container of the present invention is also effective from the following points.

As described above, the heating temperature pattern shown in FIG. 2 is adopted in the production of titanium by reduction purification. During the temperature rising period up to the reduction step, the container is heated from the outside, the outside temperature is high and the inside temperature is low, and the temperature gradient in the thickness direction is not so large. However, during the temperature decreasing period after the refining process until the temperature reaches room temperature, it is cooled from the outside and exhibits a temperature form in which the outside is low temperature and the inside is high temperature, and the temperature gradient in the thickness direction rises to the reduction process. Big compared to the period.

Under such circumstances, when a container made of stainless steel alone is used, the inner part of the container shows a greater elongation than the outer part, and the container may be deformed, causing strain cracking. However, in the container of the present invention, the inner low-carbon steel has a smaller coefficient of thermal expansion than the outer stainless steel, so that the elongation of the inner and outer materials in the above-described temperature form is offset, and the durability of the container is also improved from this direction. Be done.

Conventionally, as a reduction / purification vessel in which different materials are combined, an austenitic stainless steel vessel with a weld bead of carbon steel or ferritic stainless steel lined (JP-A-60-110823) is also used. Stamped lining (JP-A-60-110824)
No.) is well known, but all of them are not only difficult to withstand repeated use of the container because the lining is troublesome and the durability of the lining material is low, and even the lining material itself has sufficient durability. Even if
Since the consideration of the C content is lacking, intergranular corrosion is caused in the inner stainless steel, and the life of the container is limited in this direction. As a result, the container of the present invention is economical, durable and practical. There is no such thing.

〔Example〕

Using a carbon steel or low carbon steel with a thickness of 20 mm on the inside, a small container for testing made of clad steel using various stainless steel with a thickness of 5 mm on the outside, Ar atmosphere inside, air atmosphere outside, A thermal cycle of normal temperature −850 ° C. × 7 Hr−1000 ° C. × 7 Hr−normal temperature was applied.

The inner material is specifically SS41 with a C content of 0.1%, SS41
The other components are fixed in the material, and only C content is 0.03%, 0.00
Those used were those in which the C content of the SB42 material was reduced to 5%, the C content of the SB42 material was reduced to 0.005%, and the C content of the SM41 material was reduced to 0.005%. The outer stainless steel is SUS304.
304L, 316, 310, and 305B materials were used, respectively.

Table 1 shows the results of repeating the thermal history for each container. In the table, the life represents the number of thermal cycles until intergranular corrosion occurs in the outer stainless steel.

The outside is SUS304 material and the inside is normal SS41 material (C content 0.1%) N
In the case of o.1, the maximum number of allowable heat cycles was 5 due to intergranular corrosion, and it could not be put to practical use. In contrast, the C content of the inner material is 0.03
In the No. 2 container within the scope of the present invention, which has been reduced to%, the allowable number of heat cycles is at least 30 and is evaluated as ◯.

In the case of No.3 container, the stainless steel on the outside of No.2 container was changed to low C type SUS304L, and it should have been hard to generate chromium carbide, but the inner material is better. Since the C content is high, intergranular corrosion cracking occurs in about 30 thermal cycles, and the evaluation is Δ.

Nos. 4 to 9 are all within the scope of the present invention.
Intergranular corrosion does not occur even when subjected to more than one thermal cycle, and its life is limited by the oxidation loss of the outer stainless steel, and the evaluation is ⊚.

In consideration of cost, weldability, etc. to the above test results, the No. 4 material combination was used for the actual machine container (outer thickness 25 mm, inner thickness
7mm) was manufactured and is used for actual operation in a thermal cycle of normal temperature −850 ° C. × 75 Hr −1000 ° C. × 70 Hr−normal temperature, but even after it has been used 40 times, it is still in a state that can withstand considerable use. . In addition, in this actual operation, the Ni and Cr contents of the titanium sponge produced were 30 ppm or less. By the way, S
In a container made of US304L alone, the above content exceeds 100 ppm. Furthermore, no strain cracking occurred in the container in this actual operation.

〔The invention's effect〕

As is clear from the above description, the metal chloride reduction purification container of the present invention is a clad steel (inside: low carbon steel, outside:
The use of (stainless steel) reduces the contamination of the metal sponge with alloy components, improves the product quality, and solves the problem of scale. The improved strength makes it possible to reduce the thickness, makes it easier to handle, and makes it easier to handle, and is more advantageous in cost than a container made of stainless steel alone. Not only that, intergranular corrosion cracking and strain cracking that specifically occur in the clad steel during the use process can be effectively prevented by means of subtle material selection, and this will result in practically sufficient durability.

The container of the present invention can be used not only in a reduction / purification integrated device but also in a conventional general device for separately carrying out a reaction step and a separation step.

[Brief description of drawings]

FIG. 1 is a time chart exemplifying a thermal cycle in a titanium production process by reduction purification of chloride.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shohei Okamoto 1 Higashihama-cho, Amagasaki City, Hyogo Prefecture Titanium Manufacturing Co., Ltd. (72) Inventor Shigeo Suzuki 1 Higashihama-cho, Amagasaki City Hyogo Osaka Titanium Manufacturing Co., Ltd. ( 72) Inventor Takashi Sumida 1850 Minato Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Works

Claims (1)

[Claims] 1. A clad steel, wherein the inner surface side is low carbon steel and the outer surface side is stainless steel, and the low carbon steel on the inner surface side has a lower C content than the stainless steel on the outer surface side. A container for reduction and purification of metal chlorides.