RU2426808C1 - Alloy on base of titanium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: here is disclosed alloy on base of titanium containing wt %: aluminium 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 at maintaining following ratio: (Al+Zr)/(Fe+Si+C) ≥ 15.

EFFECT: high resistance of alloy to slit and pitting corrosion in high temperature, oxidising mediums and mediums with high contents of salts.

2 dwg, 2 tbl, 3 ex

Description

The invention relates to non-ferrous metallurgy, in particular to the creation of titanium-based alloys intended for the manufacture of pipelines and pipe systems of a wide range of products, operating at high temperatures up to 250 ° C and oxidizing environments with pH = 2.0-7.0 with high salinity .

The alloy is highly resistant to crevice and pitting corrosion. Known alloys based on titanium for the manufacture of pipelines specified in the patent [1] and US state standard - (Grade 13, 14, 15, 26, 28) [2]. These alloys have good corrosion resistance, but have certain disadvantages that limit their use for these conditions.

The alloy containing the components, wt.%: Aluminum 2.5-4.0, vanadium 2.5-4.0, molybdenum 2.0-3.5, zirconium 0.4-1.5, iron 0.25, oxygen 0.15, ruthenium or palladium 0.03-0.3 [1]. This alloy is limited weldable.

(Grade 13, 14, 15, 26) [2] - alloys based on technical titanium with ruthenium have low strength properties.

(Grade 28 ELI) [2] - an alloy based on titanium containing components, wt.%: Aluminum 2.5-3.5, vanadium 2.0-3.0, ruthenium 0.08-0.14, inclined to hydrogenation during prolonged use in an environment with atomic hydrogen.

The closest in composition of the ingredients and technical essence is an alloy based on titanium (prototype), containing wt.%: Aluminum 1.8-2.5; zirconium 2.0-3.0; silicon 0.12; iron 0.25; oxygen 0.15; hydrogen 0.006; nitrogen 0.04; carbon 0.10; titanium - the rest [3]. Known alloy is characterized by a good combination of strength, plastic characteristics and weldability.

The disadvantage of this alloy is an increased tendency to pitting and crevice corrosion.

The technical result of the invention is the creation of an alloy with higher resistance against crevice and pitting corrosion for pipelines operating at elevated temperatures (up to 250 ° C) and at high salinity (pH = 2.0-7.0).

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

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 rest,

the following condition must be fulfilled:

(Al + Zr) / (Fe + Si + C) ≥15

Ruthenium is introduced into the alloy in the optimum amount necessary for passivation at elevated temperatures (up to 250 ° C) and at high salinity (pH = 2.0-7.0). When the ruthenium content is less than 0.05% under these conditions, passivation does not occur, complete passivation occurs when the ruthenium content is up to 0.12%, a further increase in the ruthenium content is impractical and inefficient.

In addition, the introduction of the inventive alloy of ruthenium improves its structural stability and ensures stable passivity of the alloy. The electrochemical potential of the alloy shifts to a region of stable passivity due to a decrease in the overvoltage of the hydrogen evolution reaction, which indicates the absence of pitting conditions.

Alloying elements (aluminum, zirconium) and impurities (silicon, iron, carbon) are in such a ratio as to reduce the structural heterogeneity of the alloy and increase resistance to crevice and pitting corrosion. Failure to comply with the ratio specified in the formula makes it difficult to evenly distribute impurities over the grain volume, which reduces corrosion resistance

Ingots from the inventive alloy and prototype alloy were smelted (table 1).

The ingots were forged onto plates and rolled into 4.0 mm thick sheets, from which samples 4 × 35 × 35 mm in size were then made for corrosion testing for crevice and pitting corrosion. In order to accelerate, corrosion tests were carried out in an autoclave in a 20% NaCl solution at a temperature of 250 ° C for 2000 hours. The test results are shown in table 2.

The tendency to crevice corrosion was assessed based on the results of a study of the weight loss of samples in a dimension of 10-4 g / dm ² · hour.

An assessment of the propensity for pitting was performed visually when examining the surface of the samples using an optical microscope at a magnification of × 12. Pitting with a diameter of at least 0.1 mm was detected.

Numerous pitting lesions of the surface in the form of ulcers up to 4.0 mm in size were found on a prototype alloy sample. On the sample of the inventive alloy, no surface lesions were found, the surface of the samples remained shiny.

The surface view of the samples after testing for crevice and pitting corrosion is shown in the photo: (figure 1) - from the prototype alloy, (figure 2) - from the inventive alloy.

The presented results show that the inventive alloy in terms of resistance to crevice and pitting corrosion exceeds the similar characteristics of the known alloy. A batch of pipelines was manufactured from the inventive alloy under production conditions, which successfully passed all operational tests.

Sources

[1] Patent RU No. 2203974, Cl. С22С 14/00, 05/07/2001, "Alloy based on titanium."

[2] Standard for seamless and welded pipes of titanium and titanium alloys for condensers and heat exchangers. ASTM B338-98.

[3] Titanium and wrought titanium alloys. GOST GOST 19807-91.

Table 1 The chemical composition of the proposed and known alloy Alloy Composition number Al Ru FROM Zr Fe Si O ₂ H ₂ N Al + Zr / Fe + Si + C≥15 Ti Proposed one 1.8 0.05 0.01 2.0 0.05 0.02 0,03 0.001 0.01 47.5 rest 2 2.0 0.12 0.05 2.5 0.10 0.05 0,07 0.006 0.02 28.5 rest 3 2.5 0.08 0.10 3.0 0.15 0.10 0.13 0.003 0,03 15.7 rest Famous 2.5 0.08 2.5 0.20 0.10 0.10 0.008 0.04 13 rest

table 2 Corrosion Test Results Alloy Composition number Environmental characteristic 2,000 hours corrosion test results Crevice corrosion Pitting corrosion Degree of damage to test samples Sample surface view Degree of damage to samples Detection of pitting samples on the surface The claimed one Aerated (saturated) - 20% NaCl solution, pH = 2.5, temperature 250 ° С No defeat The surface of the samples is shiny. Weight loss of the sample 1 × 10 ^-4 g / DM ² · hour No defeat The surface of the samples is shiny. No pitting ulcers detected 2 No defeat The surface of the samples is shiny. Weight loss of the sample 1 × 10 ^-4 g / DM ² · hour No defeat The surface of the samples is shiny. No pitting ulcers detected 3 No defeat The surface of the samples is shiny. Weight loss of the sample 1 × 10 ^-4 g / DM ² · hour No defeat The surface of the samples is shiny. No pitting ulcers detected Famous Intensive destruction of the alloy in the cracks A loose gray film with visible through damage of up to 4 mm was detected on the surface. The loss of mass of the sample is more than 8 × 10 ^-4 g / DM ² · hour Surface lesions On the surface of the samples revealed pitting ulcers with a diameter of more than 2.0 mm

Claims (1)

A titanium-based alloy containing aluminum, zirconium, silicon, iron, oxygen, hydrogen, nitrogen, carbon and titanium is the rest, characterized in that it additionally contains ruthenium in the following ratio, wt.%:
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 Rest
when performing the following ratio:
(Al + Zr) / (Fe + Si + C) ≥15.

Images