RU2288967C1 - Corrosion-resisting alloy and article made of its - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to iron-chrome-nickel-base compositions of corrosion-resisting alloys and articles made of this alloy with the required complex of anti-corrosion, mechanical and technological properties. Invention proposes corrosion-resisting alloy comprising components taken in the following ratio, wt.-%: carbon, 0.005-0.02; silicon, 0.01-0.2; manganese, 0.5-1.8; chrome, 26.0-29.0; nickel, 29.0-32.0; molybdenum, 2.6-3.5; copper, 0.9-1.5; nitrogen, 0.08-0.2; niobium, 0.05-0.2; titanium, 0.01-0.1; aluminum, 0.01-0.1; boron, 0.0005-0.004; calcium or magnesium, 0.005-0.03; sulfur, 0.001-0.015; phosphorus, 0.002-0.020, and iron and imminent impurities, the balance under condition of the following ratios: (Cr + 1.5 Si + 2 Nb + Mo + 3 Ti + Al + B):(Ni + 1.5 Mn + 0.5 Cu + 30 (C + N) = 0.75-0.9; ΣC + N < 0.21. Articles made of the proposed alloy can be manufactured, for example, as hot-rolled and cold-rolled sheets or rods, or as seamless cold-deformed tubes. Invention provides enhancing structural stability of alloy, the strength level against pitting corrosion and tenacity in the range of temperatures of hot tenacity deformation and with retaining strength and tenacity properties at 20°C and the general corrosion resistance in corrosive media. Articles: sheet, gage, tubes, wire made of the proposed alloy can be used in chemical machine engineering in making welded chemical equipment designated for working in media with high corrosive activity.

EFFECT: enhanced and valuable properties of alloy and articles.

5 cl, 3 tbl

Description

The invention relates to the field of metallurgy, to the compositions of highly alloyed corrosion-resistant alloys on an iron-chromium-nickel basis, as well as to products made from them, and can be used in chemical engineering in the manufacture of welded chemical equipment for use in environments of high oxidative corrosion activity and restorative in nature. In addition, in the form of seamless cold-deformed pipes with various strength levels, including for oil and gas production in gas condensate fields with a high content of hydrogen sulfide, carbon dioxide and chlorine ion at high reservoir temperatures and pressures.

In areas where the material requires a combination of high corrosion resistance and increased strength, corrosion-resistant high-alloy steels of austenitic-ferritic and austenitic classes, as well as iron-based alloys, are used.

Known corrosion-resistant steel of the austenitic-ferritic class, designed for equipping oil wells and equipment used in the chemical industry.

Steel contains the following components, wt.%:

Carbon 0.01-0.03

Chrome 23-26

Nickel 5.5-7.0

Molybdenum 2.5-4.0

Silicon 0.2-0.4

Manganese 1.0-2.0

Nitrogen 0.05-0.25

Cerium 0.05-0.1

Zirconium 0.05-0.1

Boron 0.0005-0.001

Aluminum 0.01-0.06

Titanium 0.01-0.06

Sulfur 0.05-0.15

Calcium 0.08-0.2

Iron is the rest

when performing the following ratios:

Ca / S = 1.0-2.8

Cr _eq / Ni _eq = 2.1-2.9, where

Cr _equiv =% Cr + 1.5% Si +% Mo +% (Ti + Al + Zr + Ce + B) and

Ni _equiv =% Ni +% 0.5% Mn + 30 *% (C + N).

(RF patent 2004612, IPC C 22 C 38/60, publ. 15.12.1993).

Steel is characterized by increased machinability by cutting while maintaining high corrosion resistance, technological ductility and mechanical properties.

However, this steel, having an austenitic-ferritic structure, does not fully satisfy the requirements for the level of sensitivity to hydrogen embrittlement when working in hydrogen sulfide-containing environments.

Known dispersion hardening corrosion-resistant alloy with a guaranteed yield strength of 522 MPa at a temperature of 59 ° C, containing, wt.%:

Nickel 25-35

Chrome 19-24

Molybdenum 1.5-7

Titanium 1.5-3.5

Aluminum <0.4

Carbon 0.002-0.02

Niobium <1.2

Manganese <5

Copper <1

Cobalt <2

Boron 0-0.005

Iron is the rest, as well as incidental impurities and deoxidants.

(International application WO 00/24944, IPC C 22 C 38/44 publ. 10/23/1999).

The alloy has a sufficiently high aged strength, satisfactory corrosion resistance when tested under stress in an acidified solution containing 15% NaCl, 0.435 psi H ₂ S, 700 psi CO ₂ at pH 4.0 and a temperature of 194 ° F.

However, to increase the strength of the alloy without losing its corrosion resistance, the use of dispersion hardening, accompanied by the release of intermetallic phases of the type Ni ₃ (Ti, Nb), is less effective than the use of cold deformation for alloys with single-phase γ-solid solution for these purposes.

Known austenitic alloy and a wire from it, containing the following components, wt.%:

Chrome 23-30

Nickel 25-35

Molybdenum 3-6

Manganese 1-6

Nitrogen 0-0.4

Carbon up to 0.05

Silicon up to 1.0

Sulfur up to 0.02

Copper up to 3

Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd - one of the elements or several in the amount of up to 0.2 wt.%

Iron is the rest, and commonly found impurities.

(International application WO 01/90432 A1, IPC C 22 C 38/44, published on November 29, 2001).

Products made from this alloy, in particular cold-deformed wire, have (subject to certain conditions) high structural stability, resistance to hydrogen sulfide corrosion cracking and high strength.

This is achieved with a sufficiently high content of deficient molybdenum (4-6%), increased nitrogen content (preferably 0.35-0.49%) and a high degree of cold plastic deformation (60%).

Known corrosion-resistant alloy and products made from it - seamless and electric-welded pipes for working in inorganic and organic acids and their mixtures, environments containing chlorides, such as sea water.

The alloy contains the following components, wt.%:

Chrome 24.0-30.0

Nickel 26.0-35.0

Molybdenum 2.0-6.0

Manganese> 2.0-6.0

Nitrogen> 0-0.5

Carbon> 0-0.05

Silicon> 0-1.0

Sulfur> 0-0.02

Copper> 0-3.0

Tungsten> 0-6.0

One or more elements from the group Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd in an amount of up to 2.0 wt.%

Iron is the rest, and the usual inclusions and additives used in the manufacture of the alloy.

(International application WO 03/044239, IPC C 22 C 38/44, publ. 05/30/2003).

The alloy composition is balanced in such a way that the alloy and the product made from it, in the quenched state, have high corrosion resistance, good structural stability, as well as improved mechanical properties combined with good suitability for the manufacture of pipes. The preferred alloy composition is, wt.%: Cr 27-29, Ni 30-35, Mo 4-5.5, Mn 3-6.0, C≤03, Si <0.5, S <0.002.

The disadvantages of the alloy include the limitation of the content in the alloy of one or more elements from the group Mg, Ce, Ca, B, La, Pr, Zr, Ti, Nd in an amount of up to 2%. It is known that these elements, with the exception of titanium, have very low solubility (or do not dissolve at all) in the iron-chromium-nickel base and are introduced into the metal in the form of microadditives (less than 0.1; 0.01 or 0.001%, depending on the specific item). The introduction of these elements in large quantities affects the technological properties of the alloy.

Known alloy Nicrofer 3127hMo (alloy 31 - No. 14562 DIN) and products made from it in the form of grades, sheets, pipes, etc.

The alloy contains the following components, wt.%:

Carbon ≤ 0.15

Silicon ≤ 0.3

Manganese ≤ 0.2

Chrome 26-28

Nickel 30-32

Molybdenum 6.0-6.7

Copper 1.0-1.4

Nitrogen ≤ 0.2

Sulfur ≤ 0.015

Phosphorus ≤ 0.010

Iron - the rest

(Review journal "Metallurgy". Consolidated volume, 2001, No. 5 - ref. 15I237 / Alloy 31 (Nikrofer 3127): properties and application in technological processes, p. 25).

The alloy is recommended for use in highly aggressive environments where conventional stainless steels are not suitable. The alloy is well resistant to pitting and crevice corrosion in neutral and acidic aqueous solutions. This is due to the presence in its composition of a high content of molybdenum (6.5%) and nitrogen (up to 0.2%).

A disadvantage of the known products is that they are made of alloys containing an increased amount of scarce and expensive elements.

The prototype of the invention is the alloy and the product made from it, the KhNZOMDB alloy is selected from which rods, hot-rolled and cold-rolled sheets, wire, pipes are made. Metal products are supplied in hardened condition.

The alloy contains the following elements, wt.%:

Carbon ≤ 0.020

Silicon ≤ 0.20

Manganese 0.5-1.8

Chrome 27.0-29.0

Nickel 29.0-31.0

Molybdenum 2.8-3.5

Copper 0.9-1.5

Niobium 0.05-0.2

Sulfur <0.020

Phosphorus <0.020

Iron - the rest

(Shlyamnev A.P., Svistunova T.V., Lapshina O. B. et al. Corrosion-resistant heat-resistant and high-strength steels and alloys. Reference book - M .: Intermet engineering, 2000, p. 111).

The alloy is recommended for the manufacture of welded, chemical equipment operating in aggressive environments for the production of complex mineral fertilizers (in phosphoric and sulfuric acids contaminated with halogens), in the pulp and paper and oil industries. Recommended for the manufacture of parts and components of gas production equipment operating in hydrogen sulfide-containing environments.

The disadvantages of this alloy include the fact that in the case of an unfavorable combination of chromium, molybdenum, niobium in its composition (mainly when they are kept at the upper limit), excessive phases (such as σ) can be present in its structure.

This adversely affects its resistance to pitting corrosion, corrosion in chlorine and fluorine-containing environments. In addition, the alloy is not sufficiently ductile in the temperature range 900-1200 ° C.

The problem to which the invention is directed, is to increase the manufacturability, operability and operational reliability of the alloy and its products, including cold-deformed seamless pipes with a high level of strength and corrosion properties for gas production.

The technical result of the present invention is the creation of a new alloy having a balanced chemical and phase composition and having improved structural stability and an increased level of resistance to pitting corrosion and ductility in the temperature range of hot deformation in comparison with the known analogue while maintaining high strength and plastic properties at 20 ° C and general corrosion resistance.

The specified technical result is achieved in that the corrosion-resistant alloy containing carbon, silicon, manganese, chromium, nickel, molybdenum, copper, niobium, sulfur, phosphorus and iron, according to the invention additionally contains nitrogen, titanium, aluminum, boron and calcium (or magnesium), and also has restrictions on the content of impurity elements - sulfur and phosphorus.

An alloy composition is proposed in the following ratio of components, wt.%:

Carbon 0.005-0.02

Silicon 0.01-0.2

Manganese 0.5-1.8

Chrome 26.0-29.0

Nickel 29.0-32.0

Molybdenum 2.8-3.5

Copper 0.9-1.5

Nitrogen 0.08-0.20

Niobium 0.05-0.2

Titanium 0.02-0.1

Aluminum 0.01-0.1

Boron 0.0005-0.004

Calcium (or Magnesium) 0.005-0.03

Sulfur 0.001-0.015

Phosphorus 0.002-0.020

Iron is the rest

when the following relations are satisfied: (Cr + 1.5Si + 2Nb + Mo + 3Ti + Al + B) / (Ni + 1.5Mn + 0.5Cu + 30 (C + N)) = 0.75-0.9 ( one); ΣC + N <0.21.

The specified technical result is also achieved by the fact that the products are made of a corrosion-resistant alloy of the above composition.

Products can be made in the form of a sheet, or in the form of rods, or in the form of seamless hot-rolled and cold-rolled pipes.

The essence of the invention lies in the fact that in the alloy the ratio of elements stabilizing the γ-solid solution is regulated with respect to the release of excess phases (type σ _f ) during high-temperature heating (> 800 ° C) (1), nitrogen, boron and calcium (or magnesium ), as well as a limited content of titanium, aluminum, sulfur and phosphorus.

The main alloying elements in the alloy are chromium, nickel, molybdenum.

The high nickel content (29-32%), on the one hand, is due to the need to stabilize a γ-solid solution with a high content of chromium (26-29%) and molybdenum (2.8-3.5%), and on the other hand, the need giving the alloy high corrosion resistance in reducing environments and resistance to corrosion cracking, including in hydrogen sulfide-containing environments.

The high content of chromium alloy (26-29%) is due to the need to give it high corrosion resistance in oxidizing and redox environments and resistance to pitting corrosion in chlorine-containing environments.

The high content of nickel and chromium in the alloy is very favorable for ensuring its high corrosion resistance in hydrogen sulfide-containing environments contaminated with chlorine ion.

Molybdenum in an amount of up to 3.5% increases the resistance of the alloy against pitting corrosion. An increase in the molybdenum content above the stated limits at high chromium initiates the release of excess phases (type σ) at temperatures above 800 ° C, i.e. reduces its structural stability.

Nitrogen was introduced as an austenite-forming element that increases the structural stability of the γ-solid solution from the point of view of the allocation of the σ-phase during technological heating. In addition, nitrogen in combination with molybdenum increases the resistance of the alloy to pitting corrosion and inhibits the formation of cross-border emissions, increases strength. The lower limit of 0.08% is determined by the fact that, at a lower content, its effect is not effective. The upper limit (0.20%) is limited in order to avoid difficulties during hot deformation due to the increase in strength properties.

The lower limit of carbon content (0.005%) is determined by technical capabilities for smelting in induction furnaces using a clean charge. The upper limit of 0.02% is limited by the fact that at a higher content a tendency to intergranular corrosion may occur, especially in welded joints.

Moreover, the total content of interstitial elements - carbon and nitrogen should not exceed 0.21%.

Niobium is introduced in an amount of 0.05-0.2% to prevent the possibility of precipitation of carbides of the type Cr ₂₃ C ₆ along the grain boundaries during provoking heating.

An increase in the content of niobium as a strong carbide-forming and nitride-forming element above the stated limits can lead to an increase in the heterogeneity of the distribution of carbonitride phases with a simultaneous decrease in physical and mechanical properties.

Failure to comply with the limits specified in the claims, as well as additional conditions to limit the implementation elements (C + N <0.21), leads to an increase in metal contamination with carbonitride inclusions.

Introduction to the claimed composition of microadditives of calcium (or magnesium) (0.005-0.03%) and boron (0.0005-0.004%), together with a limitation of sulfur content (0.001-0.015%), as well as aluminum (0.01-0 , 1%) and titanium (0.02-0.1%) due to the need to regulate the shape, dispersion and distribution of oxides and sulfides.

The introduction of calcium (or magnesium) achieves a higher purity of the metal, since, having high thermodynamic activity and an affinity for sulfur and oxygen, calcium (magnesium) inhibits their diffusion activity.

The influence of microadditives of calcium (or magnesium) and boron is also manifested in the fact that both elements, being surface-active elements, affect the surface tension of a liquid metal and, as a result, the nucleation of crystallization centers and grain growth, as well as the state of grain boundaries, which together contributes to a marked improvement in the most important structurally sensitive characteristics of the metal, which largely determine its structural strength and ductility at high temperatures.

Iron-chromium-nickel-molybdenum-based alloys modified with an optimal amount of boron and calcium (magnesium) are also characterized by an increase in the resistance of the base metal and welded joints against intergranular corrosion and corrosion cracking, which makes the claimed alloy practically immune to local types of corrosion (in including in environments containing H ₂ S and chlorine ion) and increases its operational reliability during prolonged exposure to corrosive environments.

The introduction of the elements in question into the claimed composition outside the limits indicated in the claims reduces the effectiveness of their positive effect on the complex of corrosion and mechanical properties and reduces the operational characteristics of the material.

The resulting higher level of basic corrosion and technological properties of the claimed alloy is ensured by complex alloying of the composition in the specified ratio with other elements. In order to ensure structural stability, the ratio (1) of the total content of ferrite-forming (Cr, Si, Nb, Mo, Ti, Al, B) and austenite-forming elements (Ni, Mn, Cu, C, N) should be within 0.75- 0.90. At a ratio of more than 0.90, the alloy will contain an increased amount of the σ phase.

The following are embodiments of the invention, not excluding others in the scope of the claims.

The metal was smelted in an induction furnace, followed by electroslag remelting of the consumable electrode into an ESR ingot.

The resulting metal was subjected to pressure treatment on industrial forging and rolling equipment with the receipt of either sheet metal or seamless cold-rolled pipe of various sizes with the required set of strength and plastic properties, as well as corrosion resistance.

In the case of using metal products (sheet, grade, pipes) of the alloy for the manufacture of welded chemical equipment, it is supplied in a hardened state, i.e. with a reduced level of strength properties (σ _in = 685-730 MPa, σ _0.2 = 360-395 MPa, δ≥40%).

In the case when the alloy is used to make seamless pipes for oil and gas production, they are delivered after cold plastic deformation, which provides high strength (σ _in ≥793 MPa, σ _0.2 = 758-965 MPa) and ductility (δ≥12% ) along with high resistance to local types of corrosion (hydrogen sulfide corrosion cracking, pitting corrosion). Cold plastic deformation in this case is the only way to achieve the required level of strength of a single-phase γ-solid solution without significantly affecting its corrosion resistance.

The chemical composition of the melts proposed and known alloys are given in table 1.

The ductility of alloys in the temperature range of hot plastic deformation (900-1200 ° C) was determined by the value of impact strength (GOST 9454), mechanical properties at 20 ° C - according to GOST 1497 (Table 2). The object of the study was a hot-rolled sheet (10 mm thick) in a state of quenching (from 1070 ° C into water), as well as subsequent cold deformation (25%).

The rate of general corrosion of the base metal and welded samples of alloys in the quenched state was determined in a solution of extraction phosphoric acid (EPA) of the following composition: 54.8% P ₂ O ₅ + 2.65% SO ₃ + 9.4% F at a temperature of 120 ° C for 500 hours (Table 3, Wednesday 1).

Testing alloy samples for sulfide corrosion cracking (SCR) was carried out according to the method MSKR-01-85 (medium: aqueous solution containing 5 wt.% NaCl + 0.5 wt.% CH ₃ COOH, saturated with H ₂ S at a pressure of 0.1 MPa) at a temperature of 23 ° C, pH 3.0. Samples under constant load were subjected to unilateral tension σ = 758 MPa, (σ = 0.9σ _0.2 ), the test duration was 720 hours (Table 3, medium 2). Tests for the general and pitting corrosion of the samples were carried out in a solution of 5% NaCl + 0.5% CH ₃ COOH + H ₂ S (pH ₂ s = 15 atm) + CO ₂ (PcO ₂ ) at a total pressure of 50 atm (CH ₄ ), at a temperature of 115 ° C for 1440 h (Table 3, Wednesday 3). In media 2 and 3, the samples were tested in a cold-deformed state.

The phase composition of the alloys was studied by the method of X-ray diffraction analysis of anodically insulated precipitates, isolated by electrochemical method from samples in a quenched state (Table 3.).

Analysis of the materials presented shows that the proposed alloy surpasses the prototype in structural stability (Table 3), resistance to local types of corrosion and technological plasticity at the same level of general corrosion resistance in aggressive environments, strength and plastic properties at 20 ° C.

The expected technical and economic effect of using a new brand of alloy and products from it will be expressed in increasing operational reliability and safety, as well as the overall service life, including in the form of welded chemical equipment for highly aggressive environments, as well as underground well equipment operating in gas condensate fields with high content of hydrogen sulfide and chlorine ion.

 Table 1 Alloy Conventional heat number The content of components, wt.% FROM Si Mn Cr Ni Mo Cu Nb Ti Al N AT S R C + N Ca (Mg) Ratio (1) Proposed one 0,020 0.20 0.6 26.5 31.5 3.2 0.9 0.15 0,07 0.09 0.10 0.001 0.003 0.004 0.12 0.009 0.83 2 0.005 0.10 1,2 28.0 32,0 2.9 1,5 0.05 0.02 0.02 0.08 0.002 0.002 0.006 0,085 0.006 0.84 3 0.015 0.05 0.9 27.0 31,0 3,1 1.3 0.08 0.06 0,07 0.18 0,0008 0.005 0.005 0.195 0.010 0.79 Famous four 0.015 0.15 0.8 28.0 30,0 3.2 1.3 0.08 - - - - 0.007 0.009 - - -

Claims (5)

1. Corrosion-resistant alloy containing carbon, silicon, manganese, chromium, nickel, molybdenum, copper, niobium, sulfur, phosphorus and iron, characterized in that it additionally contains nitrogen, titanium, aluminum, calcium or magnesium and boron in the following the ratio of components, wt.%: Carbon 0.005-0.02 Silicon 0.01-0.2 Manganese 0.5-1.8 Chromium 26.0-29.0 Nickel 29.0-32.0 Molybdenum 2.8-3.5 Copper 0.9-1.5 Nitrogen 0.08-0.20 Niobium 0.05-0.20 Titanium 0.02-0.1 Aluminum 0.01-0.1 Boron 0.0005-0.004 Calcium or Magnesium 0.005-0.03 Sulfur 0.001-0.015 Phosphorus 0.002-0.020 Iron and inevitable impurities Rest when performing the following ratios: (Cr + 1.5 Si + 2Nb + Mo + 3Ti + A1 + B) / (Ni + 1.5 Mn + 0.5 Cu + 30 (C + N)) = 0.75-0.9; ΣC + N <0.21. 2. The product is made of a corrosion-resistant alloy, characterized in that it is made of an alloy according to claim 1. 3. The product according to claim 2, characterized in that it is made in the form of a hot-rolled and cold-rolled sheet. 4. The product according to claim 2, characterized in that it is made in the form of a bar. 5. The product according to claim 2, characterized in that it is made in the form of a seamless cold-deformed pipe, including for gas wells operating in an environment with a high content of hydrogen sulfide.