JPS619543A - Titanium alloy having superior crevice corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy having superior crevice corrosion resistance in a halide soln., especially seawater by adding a prescribed amount of Ru to Ti. CONSTITUTION:This Ti alloy consists of 0.005-<0.5wt% Ru and the balance Ti. The alloy has much superior crevice corrosion resistance as compared with conventional Ti-Pd and Ti-Ni alloys which are considered to be alloys having superior crevice corrosion resistance. It is important that the Ti-Ru alloy has much superior crevice corrosion resistance as compared with the Ti-Pd alloy in spite of the very low Ru content. Since Pd is much more expensive than Ru, the effect of this invention is very remarkable. In case of the Ti-Ni alloy, a large amount of Ni provides crevice corrosion resistance, but only about 0.3wt% Ni added to Ti deteriorates the workability.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention of this application relates to a titanium alloy having excellent crevice corrosion resistance in halide solutions, particularly seawater.

In general, metals such as iron and steel are severely corroded by halide solutions such as seawater, but pure titanium or titanium alloys have high corrosion resistance against seawater, so they are widely used in industrial equipment that uses seawater, etc. . However, even pure titanium and titanium alloys, which are generally said to have extremely high corrosion resistance, have a serious material problem of being susceptible to crevice corrosion in seawater. Crevice corrosion is a type of corrosion that occurs particularly between two metal surfaces or non-metallic surfaces such as Teflon gaskets, and at joints in equipment such as containers and pipes used in seawater. This crevice corrosion is related to concentration batteries that create a potential difference between adjacent parts of titanium.

A γ node region and a peripheral cathode region are formed, which are subject to corrosion, and as the area ratio of these regions increases, corrosion is further accelerated.

When using pure titanium in containers, pipes, or plates that are subjected to isopressure processing in areas that come into contact with seawater, take measures to prevent crevice corrosion from occurring in the structure used, such as by welding the joints instead of bolting them. I needed it. However, it is difficult to completely prevent crevice corrosion from occurring in seawater-resistant equipment, and this cannot be considered a fundamental solution. In addition, titanium alloys have improved general corrosion resistance in acidic solutions such as HOI and SO4.

For example, Oo, Ou, HftMo, N'b, Ta, V, Z
We considered using alloys with a few percent of r added, but these alloys have the same resistance to crevice corrosion as pure titanium, and their corrosion resistance to acidic aqueous solutions (versus general corrosion) is not effective for immediate crevice corrosion resistance. I couldn't say that there was. Among these, Tt is one of the few alloys with excellent crevice corrosion resistance.
-pb (palladium) and Ti-Ni alloys are known (Japanese Patent Publication No. 46-21086).

However, in the former alloy, the added element P(l
It is very expensive, and the crevice corrosion resistance is not effective unless approximately α15 is added, so even though it has excellent crevice corrosion resistance, it is still a problem as an industrial material.

In addition, the latter alloy has extremely poor workability such as press formability and drawability, and also has manufacturing problems because the recrystallization temperature increases, so it is not suitable as a material for use in seawater equipment. Good and difficult.

In view of the problem of crevice corrosion, the inventors of the present application have developed a titanium alloy with excellent crevice corrosion resistance, which is composed of ruthenium (Ru) with less than αo o s wt-~α5 wt1, the balance being titanium, and unavoidable impurities. developed. Since the addition of ruthenium for crevice corrosion resistance is significantly effective even in small amounts, titanium alloys can be manufactured at low cost and have good workability.

The reason why the lower limit of the amount of ruthenium added in the titanium alloy of the present invention is set to αo o s vt- is that if the amount added is less than , the effect on preventing the occurrence of crevice corrosion is very small and is not practical. Preferably α0
1 wt fight or higher is required. The reason why the upper limit of the amount of ruthenium added is set to less than 15wt16 is because if the amount added is more than this, the workability deteriorates and the added ruthenium is undesirably expensive.

In comparison, a crevice corrosion resistance test was conducted to explain the effectiveness of the alloy of the present invention.

All the alloys used in the above corrosion tests have excellent resistance to crevice corrosion, so it is not possible to simply tighten titanium alloy plates/titanium alloy plates or titanium alloy plates/Teflon plates with bolts and conduct corrosion tests, which is normally done. Corrosion is very unlikely to occur. Therefore, Ti-Ni alloy, Ti-I'd, was created by dissolving Styrofoam in trichlorethylene.
It was applied to the surfaces of the alloy and the Ti-Ru alloy, which is the alloy of the present invention, and these were opposed to each other and tightened with bolts, and subjected to a crevice corrosion test.

The test was conducted in a boiling corrosive environment with a Mail concentration of 1% and a pH of 6.1. The results are shown in Table 1.

These samples are subjected to harsh conditions where crevice corrosion is likely to occur; therefore, even materials that are normally excellent at crevice corrosion may show crevice corrosion after a day.

As shown in Table 1, conventional α has excellent crevice corrosion resistance.
The 15 wtl Pd large Schiff alloy (sample number 41) shows a 1E3 crevice corrosion resistance effect, but crevice corrosion occurs after the second day.

Similarly, in the conventional a6wtllNi alloy (sample number 42), crevice corrosion occurs already on the first day.

α8 wt again! ! The Mi-containing T1 alloy (sample number 43) has crevice corrosion resistance on the first day, but crevice corrosion occurs on the second day. On the other hand, in the alloy of the present invention, aOO5w
Although there is discoloration on the first day in the T1 alloy (sample number 4), no complete crevice corrosion is observed. In addition, crevice corrosion does not occur completely on the first day in the aOj wtlRu pTi alloy (sample number 5). And this is P (19 T1 alloy (A1) and α8 wtll N, which are conventionally considered to have excellent crevice corrosion resistance.
It has crevice corrosion resistance equivalent to that of i-filled fiTi alloy (n5)'. Furthermore, □・Ru is o,, o2. α0
3. α04. As α05wt16 increases, the crevice corrosion resistance becomes K, which is higher than that of the conventional alloy.

What is even more important is that even with a very small amount of Ru added, the T1 alloy with Pil has excellent crevice corrosion resistance. For example, α15vt-M? ) The T1 alloy and the α01 wtl Ru Jll Ti alloy of the present invention have equivalent resistance 1! Although it is corrosive, the amount added in the 9 Ti alloy is 15 times that of the alloy of the present invention. Considering that Pb is a much more expensive surface material than Ru, the effects of the present invention are extremely remarkable.

In addition, unless a large amount of N1 is contained in the r1 alloy, the crevice corrosion resistance effect shown in Table 1 will not occur. However, in practice, when Ti contains about α5 wt% of N1, processing becomes difficult, but when Ni reaches a8wts, processability deteriorates significantly. Therefore, compared to the alloy of the present invention, it is inferior not only in crevice corrosion resistance but also in workability.

In the alloy of the present invention, a very small amount of 05wtLs
With the addition of Ru, it is already effective as it has an effect similar to that of PfL T1 alloy.

As the Ru content increases, the crevice corrosion resistance increases, but as the Ru content exceeds υα5 wtlG, the workability becomes poor and the price also increases.

From this point of view, it should be less than α5 wt-.

The above-mentioned two alloys of the present invention are excellent titanium alloys that have strong resistance to crevice corrosion in halide solutions, especially seawater, have good workability, and can be manufactured at low cost.

Claims (1)

[Claims] A titanium-based alloy with excellent crevice corrosion resistance, consisting of 0.005 wt% to less than 0.5 wt% of ruthenium, the balance being titanium, and unavoidable impurities.