JPS61227140A - Titanium alloy excelling in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a titanium alloy excelling in corrosion resistance by blending specific amounts of Nb and O with Ti. CONSTITUTION:The titanium alloy has a composition consisting of, by weight, 1-5% Nb, 0.05-0.6% O and the balance Ti with inevitable impurities, or further contains 0.1-5% Mo, or 0.10% Ni, or both of 0.1-5% Mo and 0.1-10% Ni. This titanium alloy excels in corrosion resistance and it shows excellent corrosion resistance particularly in an acidic environment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a titanium alloy with excellent corrosion resistance, particularly titanium alloy I which shows excellent corrosion resistance in an acidic environment:
It is related to

[Conventional technology]

Due to the strong passive oxide film formed on its surface, titanium exhibits excellent corrosion resistance against chloride solutions, etc., and is therefore widely used as a constituent material for chemical industrial equipment. General di-neutral chlorides (e.g. NaC6
) and oxidizing environments, but in acidic environments where non-oxidizing acids such as hydrochloric acid or sulfuric acid are present, the oxide film is destroyed and active dissolution occurs across the entire surface, resulting in a decline. . Therefore, it covers such weaknesses of titanium. As a titanium alloy that exhibits excellent corrosion resistance even in acidic environments, a small amount, approximately 0.2
40) A Ti-0,24Pd alloy containing Pd was developed, and a large amount of Me was added to a nickel-based alloy. Hastelloy B alloy (284Mo-Ni alloy) is known as a hydrochloric acid corrosion-resistant material.

[Problem that the invention seeks to solve]

Although the Ti-0,21Pd alloy that replaced titanium and the Hastelloy B alloy, which is a non-titanium alloy, exhibit better corrosion resistance than titanium in acidic environments, the corrosion resistance of these materials is particularly poor in acidic environments. In view of the increasing demand for corrosion resistance in chemical industrial equipment etc. that are conveniently used in the environment.

However, since these alloys are still relatively expensive, their applications are limited.

[Means for solving problems]

Therefore, from the above-mentioned viewpoint, the present inventors have conducted various studies to find a titanium alloy that has better corrosion resistance than the Ti-0,21Pd alloy and Hastelloy B alloy, especially in a diacid environment. The result.

1) When niobium, which is a complete solid solution with titanium, is added to titanium and alloyed, titanium oxide, which is easily soluble in acidic solutions, dissolves preferentially on the surface, while niobium, which is stable in acidic solutions, dissolves preferentially. As a result of the oxide remaining, an oxide film mainly composed of niobium oxide is formed, which significantly improves the corrosion resistance of the niobium-containing titanium alloy in an acidic environment.2) Adding O (oxygen) to this niobium-containing titanium alloy 3) When MO is added to a titanium alloy containing niobium and oxygen, the formation of a film mainly composed of niobium oxide is promoted, and even more reliable corrosion resistance can be ensured. While the film is reinforced, a portion of the MO becomes molybdate ions and dissolves in the solution, exerting the effect of an inhibitor.

4) When Ni is added to a titanium alloy containing niobium and oxygen, the hydrogen overvoltage decreases, and the reduction reaction of hydrogen ions itself makes the alloy passivated, improving its corrosion resistance. 5) The above MO and Addition of Ni in combination further improves corrosion resistance.

I found out.

This invention was invented based on the above knowledge.

Nb: 1.0~50%, O: 0.05~0.6
% and further required (depending on MO: 0.1-5
．． It is characterized by having a composition containing one or two of Ni: 0.1 to 104, and the remainder consisting of Ti and unavoidable impurities (the above by weight, the same applies below unless otherwise specified). The present invention provides a titanium alloy with excellent corrosion resistance.

Next, in this invention (section 2), the reason why the component composition range is limited as described above will be explained.

(a) As mentioned above, the Nb excitation element has the effect of stabilizing the passive film on the surface of the titanium alloy in an acidic solution, but if its content is less than 1.0, the stabilizing effect is not as desired. However, even if the content exceeds 50%, the effect will be saturated, so the content should be reduced to 1.0 to 50%.
%.

(b) The 00 component has the effect of promoting the formation of niobium oxide, which contributes to improving corrosion resistance, but if its content is less than 0.05%, the desired effect will not appear; .61
If the content exceeds 0.05 to 0, the workability of the obtained titanium alloy will deteriorate significantly.
．． It was designated as Section 6.

(c) M.

The Mo component has the effect of reinforcing the niobium oxide film,
Group in solution; dissolves into molybdate ions and exerts an inhibitory effect, but if the content is less than 0.11, the desired effect cannot be obtained;
% would deteriorate the corrosion resistance of the alloy in an oxidizing acid environment, so the content was set at 0.1 to 5.04.

(d) Ni The Ni component has the effect of lowering the hydrogen overvoltage of the alloy, thereby contributing to its passivation and improving corrosion resistance, but if its content is less than 0.1 factor, the above effect is insufficient. On the other hand, if it exceeds 10, the cold workability of the alloy will deteriorate, so the content should be reduced from 0.1 to 10.
It was decided that there would be 10 sections.

By adding one or two of the above predetermined amounts of MO and Ni to the Nb-0-containing titanium alloy I, it can be used not only in non-oxidizing acid solutions but also in oxidizing acids such as nitric acid. Excellent corrosion resistance can be obtained even when 4= in solution.

〔Example〕

Next, the titanium alloy of the present invention will be specifically explained in Example ζ:YT).

A mixture prepared in advance by blending commercially available titanium sponge and powdered Nb in a predetermined ratio was melted using an electrobeam to melt 13 types of ingots each having the component composition shown in Table 1. Then, each ingot was forged, hot-rolled, and cold-rolled, followed by annealing to produce a plate material with a thickness of ]Ow+, according to a process similar to that of commercially available pure titanium. Sa: 4
0 wi The zero content in the ingot was adjusted to various values by changing the manufacturing conditions.

Next, test pieces 1 to 13 of the present invention obtained in this way
, boiling condition ■: 51 GHC6 aqueous solution 1 condition ■: 10 HC1 aqueous solution, and condition ■: 501 H
A corrosion resistance test was conducted by immersing each test piece in 50 Oec of NOx aqueous solution for 72 hours, and the corrosion rate of each test piece was determined from the resulting weight loss to evaluate the corrosion resistance of each test piece. In this test, the same test was repeated twice for each type of test piece, and the average value of the two weight loss values obtained as a result was used to determine the corrosion rate.

Further comparisons were made as described above. Comparative test specimens 1 and 2 obtained from comparative alloys having compositions outside the scope of the present invention (components outside the scope of the present invention are not marked with a pot mark), and were separately prepared. Two similar test pieces C were cut from commercially available industrially pure titanium (JIS Class 2), Ti-0,2-Pd alloy, and No-1 Steroid B alloy. [Effects of the Invention] From the results shown in Table 1 (2), In both conditions (2) and (2), the commercially available pure titanium material exhibits a significant amount of corrosion, and compared to this pure titanium material and a titanium alloy whose composition is outside the scope of the present invention, conventional Ti = 0.
．． Although the corrosion rate of the 21Pd alloy and )/steroid B alloy is quite low, it is still at most 0.1 under condition (2).
0g/fr? hr, whereas the Ti alloy of the present invention has 0.01 to 0.03 g/hr under the same conditions.
It can be seen that the Ti alloy of the present invention, which exhibited a significantly low corrosion amount of m'' hr, exhibited significantly superior corrosion resistance, especially in an acidic environment, compared to the comparative alloys and conventional corrosion resistant materials.

In addition, the Ti alloy of the present invention (test specimens 8 to 13 of the present invention) to which one or two of Mo and Ni were added had excellent corrosion resistance in boiling 501 HNO and aqueous solutions under one condition. It can be seen that the Ti alloy of the present invention exhibiting corrosion resistance and containing O and O: The Ti alloy of the present invention to which MO or Ni or both have been added exhibits excellent corrosion resistance even against an oxidizing acid aqueous solution.

In addition, in the above examples, it was shown that the Ti alloy of the present invention exhibits excellent corrosion resistance against corrosion by HCl and HNO, but it also shows similar corrosion resistance against other acids such as sulfuric acid. Furthermore, even in a neutral chloride solution environment, the Ti alloy of the present invention was compared to the conventional Ti-0,21Pd
Needless to say, it exhibits corrosion resistance comparable to alloys.

As mentioned above, the Nb-containing Ti alloy of the present invention exhibits much better zero corrosion resistance than the conventional Ti-0.2%Pd alloy or Hastelloy B alloy in an acidic environment. For example, dew point corrosion such as hydrochloric acid or sulfuric acid or corrosion caused by oxidizing acids such as nitric acid is a problem (-
When used as a structural material for equipment that handles various acids or acidic solutions, it is possible to provide a Ti alloy that exhibits particularly excellent corrosion resistance.

Claims (4)

[Claims] (1) Contains Nb: 1.0 to 5.0%, O: 0.05 to 0.6%, and the remainder is Ti and unavoidable impurities (weight %). , titanium alloy with excellent corrosion resistance. (2) A composition containing Nb: 1.0-50%, O: 0.05-0.6%, Mo: 0.1-5.0%, with the remainder consisting of Ti and unavoidable impurities (by weight) %), a titanium alloy with excellent corrosion resistance. (3) A composition containing Nb: 1.0 to 50%, 0: 0.05 to 0.6%, Ni: 0.1 to 10%, and the remainder consisting of Ti and unavoidable impurities (weight %). A titanium alloy with excellent corrosion resistance. (4) Contains Nb: 1.0-50%, O: 0.05-0.6%, Mo: 0.1-5.0%, Ni: 0.1-10%, and the rest is Ti. A titanium alloy with excellent corrosion resistance, characterized by having a composition (the above weight %) consisting of unavoidable impurities.