RU2582171C1 - Titanium-based alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to titanium alloys, and can be used in making structures operated in aggressive media, such as marine water at high temperatures. Titanium-based alloy contains, wt %: aluminium 3.0-4.2, zirconium 2.0-3.0, silicon 0.02-0.12, iron 0.05-0.25, oxygen 0.03-0.14, nitrogen 0.01-0.04, carbon 0.05-0.10, hydrogen 0.001-0.006, ruthenium 0.05-0.15, niobium 0.7-1.5, vanadium 0.7-1.5, balance is titanium.

EFFECT: alloy is characterised by high strength, resistance to slot, pitting and hot salt corrosion in aggressive selenium-containing media with pH>2 and temperature of up to 250°C.

1 cl, 2 tbl

Description

The invention relates to the field of non-ferrous metallurgy, in particular to the creation of titanium alloys with increased strength, corrosion resistance and used in aircraft, shipbuilding, nuclear energy and other industries related to the operation of structures in an aggressive environment, such as sea water, at elevated temperatures .

Known alloy based on titanium grade PT-7M according to GOST 19807, containing in mass. %: aluminum 1.8-2.5, zirconium 2.0-3.0, silicon no more than 0.12, iron no more than 0.25, oxygen no more than 0.15, hydrogen no more than 0.006, nitrogen no more than 0 , 04, carbon not more than 0.10, titanium - the rest.

The alloy has high ductility, due to which it is able to deform in the cold state, welds well without subsequent heat treatment.

The main disadvantage of this alloy is the low level of strength properties. A disadvantage of pipes made of this alloy is the tendency to pitting, crevice and hot salt corrosion when used as heat transfer elements of water vapor generators with increased salt deposition on carriers.

The closest in technical essence to the proposed is an alloy based on titanium (prototype), containing in mass. %: aluminum 1.8-2.5, zirconium 2.0-3.0, silicon 0.02-0.10, iron 0.05-0.15, oxygen 0.03-0.13, hydrogen 0.001- 0.006, nitrogen 0.01-0.03, carbon 0.01-0.10, ruthenium 0.05-0.12, titanium - the rest (RF patent No. 2426808, IPC C22C 14/00, publ. 08.20.2011 .).

The alloy is highly resistant to crevice and pitting corrosion at temperatures up to 250 ° C.

However, the disadvantage of this alloy is the low level of strength properties at room temperature and reduced resistance to hot salt corrosion at a temperature of 250 ° C.

The technical result of the invention is the creation of a titanium alloy having higher strength at room temperature and resistance to hot salt corrosion at temperatures up to 250 ° C while maintaining high resistance to crevice and pitting corrosion at temperatures up to 250 ° C.

The technical result is achieved due to the fact that the titanium alloy containing aluminum, zirconium, silicon, iron, oxygen, hydrogen, nitrogen, carbon, ruthenium, titanium - the rest, additionally contains vanadium and niobium and a higher aluminum content in the following ratio of components, wt . %:

Aluminum 3.0-4.2 Zirconium 2.0-3.0 Silicon 0.02-0.12 Iron 0.05-0.25 Oxygen 0.03-0.14 Nitrogen 0.01-0.04 Carbon 0.05-0.10 Ruthenium 0.05-0.15 Vanadium 0.7-1.5 Niobium 0.7-1.5 Hydrogen 0.001-0.006 Titanium rest

Vanadium and niobium within the specified limits are introduced to increase the strength characteristics. Vanadium is an isomorphic beta stabilizer and affects both the increase in strength and increase ductility. Niobium is a processing aid for introducing carbon and vanadium into a titanium alloy.

Aluminum in the specified range of 3.0-4.2% is introduced to increase the strength properties. Aluminum is an alpha stabilizer and the main alloying element in titanium alloys; it effectively hardens alloys while maintaining satisfactory ductility. With an aluminum content of less than 3.0%, the strength of the titanium alloy is relatively low, with an aluminum content of more than 4.2%, the alloy may be less resistant to hot salt corrosion. Technological ductility is also reduced, which can lead to a loss of ability to cold deformation in the manufacture of pipes.

The amount of ruthenium increased to 0.15% is introduced to increase the resistance of pipes to hot salt corrosion in chlorine-containing environments at temperatures up to 250 ° C. Ruthenium is a beta stabilizer and provides stable passivity of the titanium alloy by reducing the overvoltage of the hydrogen evolution reaction. As a result, the electrochemical potential shifts to the region of stable passivity of the alloy, which eliminates the risk of pitting, crevice and salt corrosion. With a ruthenium content of less than 0.05%, stable passivity does not occur in titanium alloys and the likelihood of crevice and pitting corrosion increases. When the ruthenium content is more than 0.15%, a stable passive state is stabilized due to overvoltage of hydrogen evolution, which contributes to stabilization in the passive region of the titanium alloy under saline conditions.

To study the properties in a vacuum arc furnace by the double remelting method, ingots from the claimed alloy and prototype alloy were smelted (table 1). The ingots were deformed to produce 52 mm forgings, from which special samples were then made:

- samples with dimensions 4 × 35 × 35 mm for testing crevice and pitting corrosion;

- a sample simulating a pipe with an external diameter of 15 mm, a wall thickness of 2.5 mm and a length of 30 mm for testing for hot salt corrosion.

Mechanical properties were checked using standard mechanical tensile tests according to GOST 1497 and impact bending according to GOST 9454 at room temperature.

Tests for crevice and pitting corrosion were carried out in an autoclave in an aqueous medium of a 20% NaCl solution at a temperature of 250 ° C for 2000 hours.

Hot salt corrosion tests were carried out in an autoclave in a mixture of crystalline NaCl and KBr salts, taken in a ratio of 300: 1 at a temperature of 250 ° C for 500 hours.

The test results are shown in table 2.

The tendency to crevice corrosion was assessed based on the results of measuring the weight loss of the samples (10 ^-4 g / dm ² hours).

The tendency to pitting corrosion was assessed visually by examining the surface of the samples, as well as using an optical microscope at twelve-fold magnification (no lesions were found).

Assessment of the tendency to hot salt corrosion is carried out according to the results of measuring the weight loss and the results of its conversion to the corrosion rate (estimated corrosion rate of the proposed alloy is 0.005 mm / hour, and the prototype is 0.02 mm / hour).

The presented results show that in terms of resistance to crevice and pitting corrosion, the proposed alloy is at the level of the known prototype alloy, but in terms of resistance to hot salt corrosion, the proposed alloy is superior to the known prototype alloy. The strength properties of the proposed alloy is significantly higher than the known prototype alloy.

Technical and economic efficiency from the use of the proposed alloy in comparison with the prototype alloy is expressed in a 10-fold increase in the service life of the pipes of the proposed alloy in saline solutions and in places of scaling at temperatures up to 250 ° C, due to an increase in resistance to hot salt corrosion.

Claims (1)

A titanium-based alloy containing aluminum, zirconium, silicon, iron, oxygen, nitrogen, carbon, ruthenium, hydrogen and titanium, characterized in that it additionally contains vanadium and niobium in the following ratio of components, wt. %:
Aluminum 3.0-4.2 Zirconium 2.0-3.0 Silicon 0.02-0.12 Iron 0.05-0.25 Oxygen 0.03-0.14 Nitrogen 0.01-0.04 Carbon 0.05-0.10 Ruthenium 0.05-0.15 Vanadium 0.7-1.5 Niobium 0.7-1.5 Hydrogen 0.001-0.006 Titanium rest