RU2350674C1 - Heat-resistant alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy of heat-resistant alloys with cast structure on the basis of iron-chrome-nickel with carbide strengthening and can be used while creating of units for high-temperature pyrolysis for petrochemical industries. Alloy contains carbon, nitrogen, chrome, nickel, niobium, tungsten, molybdenum, titanium, silicium, manganese, aluminium, copper, magnesium, zirconium, yttrium, boron, cerium, lanthanum, neodymium, praseodymium and iron, at following ratio of components, wt %: carbon 0.35 - 0.55, nitrogen 0.02 - 0.05, chrome 22 - 27, nickel from 25 till less than 40, niobium 1 - 2, tungsten 0.5 - 5, molybdenum 0.2 - 0.6, titanium 0.05 - 0.6, silicon 0.8 - 2.0, manganese 0.8 - 1.5, aluminium 0.1 - 1.0, copper 0.1 - 1.0, magnesium 0.01 - 0.1, zirconium 0.005 - 0.15, yttrium 0.008 - 0.1, boron 0.007 - 0.01, cerium 0.022 - 0.063, lanthanum 0.006 - 0.027, neodymium 0.002 - 0.005, praseodymium 0.005 - 0.008, iron - the rest. At that there are kept correlations %C+%N-((%Nb+2×%Ti)/10)=0.24÷0.28 and (%La+%Ce+%Nd+%Pr)/%B=5÷10.

EFFECT: durability increasing in air medium against stress corrosion fracture in conditions of continuous static loading at temperatures of degree 1100°C, and also increasing of plasticity without impairment of long-term strength at specified temperatures.

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Description

The invention relates to the metallurgy of heat-resistant alloys with a cast structure on an iron-chromium-nickel basis with carbide hardening and can be used to create high-temperature pyrolysis plants for the petrochemical industries, in particular in the manufacture of reaction coils.

The temperature range of the materials of these structures is in the range of 900-1100 ° C. Contact of the outer surface of the reaction coils with air at a temperature of 1000-1100 ° C causes oxidation of the heat-resistant heat-resistant steels and alloys used for their manufacture.

The most noticeable development of this type of damage is observed in materials with a cast structure along the boundaries of the crystals. The greatest danger to the survivability of the designs of the pipe system of the coils, as shown by many years of experience in their operation, are those areas where the effect of local structural corrosion at the crystal boundary is amplified by static stresses.

Materials characterized by low long-term ductility, as a rule, have a low resistance to corrosion and mechanical stress. Under these conditions, the growth of the length of the cracks occurs at high speeds, which reduces to a critical level the living section of the wall of the molded product.

The tendency of heat-resistant heat-resistant materials to local structural oxidation is usually revealed by the depth of oxidizability of the boundaries having access to the surface of cast products.

Known alloy [1] having a composition having ultra-high resistance to uniform oxidation. However, its ductility both in the initial state and after isothermal holdings is low — less than 5–7%, and the tendency to form the σ phase at operating temperatures is the most serious drawback. As a prototype [2] selected alloy containing, wt.%:

Carbon 0.35-0.55 Nitrogen 0.02-0.05 Chromium 22-27 Nickel 25-40 Niobium 1-2 Tungsten 0.5-5 Molybdenum 0.2-0.6 Titanium 0.05-0.6 Silicon 0.8-2 Manganese 0.8-1.5 Boron 0.0005-0.005 Aluminum 0.1-1.0 Copper 0.1-1 Magnesium 0.01-0.1 Zirconium 0.005-0.15 Yttrium 0.008-0.1

Iron the rest,

under the condition

The microalloying of the heat-resistant alloy of the indicated composition by such elements as yttrium, zirconium and boron, contributed to a significant improvement in the heat-resistant properties. The disadvantages of the alloy include the following:

- low ductility (less than 5%) under static stress at a temperature of 1000 ° C;

- low resistance of the alloy to mechanical corrosion at 1100 ° C.

These shortcomings in operating conditions lead to the failure of the reaction tube system of pyrolysis coils operating at high temperatures of 1000-1100 ° C, which significantly reduces the period of "overhaul run".

The technical result of the invention is the creation of a heat-resistant alloy with increased resistance in air to corrosion-mechanical effects under long-term static loading at maximum operating temperatures of 1100 ° C, and increasing its ductility without compromising long-term strength at temperatures of 1000 ° C and 1100 ° C That provides an increase in operational reliability and an increase in the period of "overhaul mileage" of high-temperature coils.

, дополнительно содержит лантан, церий, празеодим и неодим при следующем соотношении ингредиентов, мас.%:The technical result of the invention is achieved in that a heat-resistant alloy based on iron-chromium-nickel base containing carbon, nitrogen, chromium, nickel, niobium, tungsten, molybdenum, titanium, silicon, manganese, aluminum, copper, magnesium, zirconium, yttrium, boron and iron, when performing conditions

, additionally contains lanthanum, cerium, praseodymium and neodymium in the following ratio of ingredients, wt.%:

Carbon 0.35-0.55 Nitrogen 0.02-0.05 Chromium 22-27 Nickel 25 - less than 40 Niobium 1-2 Tungsten 0.5-5 Molybdenum 0.2-0.6 Titanium 0.05-0.6 Silicon 0.8-2.0 Manganese 0.8-1.5 Aluminum 0.1-1.0 Copper 0.1-1.0 Magnesium 0.01-0.1 Zirconium 0.005-0.15 Yttrium 0.008-0.1 Boron 0.007-0.01 Cerium 0.022-0.063 Lanthanum 0.006-0.027 Neodymium 0.002-0.005 Praseodymium 0.005-0.008 Iron rest,

while the condition

High concentrations of chromium (22-27%) and nickel (25 - up to 40%) provide the best combination of characteristics of long-term strength, resistance to oxidation and carburization.

The introduction of carbon, nitrogen, niobium and titanium provides an increase in heat resistance by increasing the volume content of stable excess phases in the alloy structure.

Tungsten and molybdenum increase the stability of the structural states of the alloy at high temperatures, and also improve the technological characteristics of the alloy, in particular, weldability in the cast state.

Silicon and aluminum, along with chromium, increase the resistance of the alloy to oxidation, increasing the stability of the oxide film under carbonization conditions.

The introduction of copper in these amounts reduces the tendency of the alloy to carburize by stabilizing the oxide film, preventing its destruction.

Magnesium, zirconium and yttrium, in addition to purifying the metal from oxygen and sulfur, increase the adhesion strength of massive precipitates of excess eutectic phases, preventing the development of intergranular displacement.

The introduction of cerium, lanthanum, neodymium and praseodymium microadditives into the composition of the heat-resistant alloy, which are characterized by high affinity for oxygen and low solubility in the austenitic γ-solid solution, ensures their distribution mainly along the crystal boundaries and in the interdendritic space, which contributes to the formation of stable high-temperature oxides, preventing the penetration of oxygen along the boundaries of the crystals.

In order to increase the adhesion strength of the intergranular boundaries with oxide layers under static loads, boron is introduced into the alloy, which, like carbon, is an intercalation element and is characterized by a small atomic radius and extremely low solubility in the austenitic matrix.

определяет их оптимальную концентрацию на межкристаллитных границах, что обеспечивает прочность межфазового сцепления и отсутствие выделения вредных боридных фаз.The ratio of the total amount of rare earth elements and boron

determines their optimal concentration at the intergranular boundaries, which ensures the strength of interfacial adhesion and the absence of release of harmful boride phases.

The selected limits of microalloying with the surface-active elements La, Ce, Nd, Pr, and B, while maintaining the crystalline structure and phase composition of the alloy almost unchanged, significantly improve the state of the intergranular boundaries, which at high temperatures increases the resistance to corrosion and mechanical stress, increases the level of ductility and strength in conditions of prolonged static loading.

The Central Research Institute of CM "Prometheus" was smelted and investigated the properties of the inventive alloy, an alloy containing ingredients that go beyond the declared concentrations, as well as an alloy that coincides in composition with the prototype.

Alloys were obtained in an open induction furnace using high-quality charge materials and special ligatures containing rare-earth elements and boron introduced. The molten metal, which was under the protection of argon in the process of conducting the heat, cast iron molds were cast. The weight of the ingots was 23-25 kg.

To conduct corrosion-mechanical tests and tests for long-term strength, discontinuous samples with a diameter of the working part of 6 mm and a length of 30 mm were cut from the central part of the ingot to a distance of 10 mm from the edge.

Table 1 shows the chemical composition of the studied alloys. Table 2 presents the results of tests of corrosion-mechanical strength and the results of tests for long-term strength.

Corrosion-mechanical tests of alloy samples were carried out in air for 500 hours at a temperature of 1100 ° C and a voltage of 5 MPa. After testing, using the metallographic method, the maximum depth of damage to the alloy was determined at the boundaries with access to the surface of the sample.

From table 2 it follows that the inventive alloy swimming trunks 2, 3, 4 and 5 compared with the compositions of the alloy of the prototype 6 and melting 1, under the conditions of simultaneous exposure to static load and high temperature is characterized by high resistance of the boundaries of the crystals to oxidation.

The improvement of the boundaries achieved as a result of complex microalloying with optimal concentrations of surface-active elements is also manifested in an increase in ductility at a temperature of 1000 ° C, which when assessed by the relative elongation of the metal composition of melts 2, 3, and 4 after tests lasting ~ 3000 hours amounted to a minimum level of 11-16%, which is 3 times higher than the minimum plasticity level of the prototype alloy after testing on the basis of ~ 2500 hours.

Table 1 Alloy Condition melting number The content of elements, wt.% % C +% N - (% Nb + 2% Ti): 10 (% La +% Ce +% Nd +% Pr):% B FROM N Cr Ni Nb Mo W Ti Si Mn Al Cu Mg Zr Y AT La Xie Nd Pr Fe 2 3 four 5 6 7 8 9 10 eleven 12 13 fourteen fifteen 16 17 eighteen 19 twenty 21 22 23 24 25 one 0.35 0.04 23.0 33.5 1,1 0.25 1.8 0.06 1.55 1,0 0.3 0.25 0.08 0.06 0.009 0.005 0.003 0.006 0.001 0.001 OCT. 0.27 2.2 The claimed 2 0.35 0.05 22.0 25.0 1,0 0.2 2.1 0.3 0.8 0.8 0.1 1,0 0.1 0.15 0.1 0.007 0.006 0,022 0.005 0.005 // - // 0.24 5,4 3 0.55 0.02 27.0 33.0 1.8 0.45 0.5 0.6 2.0 1,2 1,0 0.5 0.01 0.005 0.008 0.008 0.015 0,030 0.003 0.006 // - // 0.27 6.75 four 0.45 0.04 24.3 39.9 2.0 0.6 5,0 0.5 1,5 1,5 0.52 0.1 0.05 0,077 0,054 0.010 0,027 0,063 0.002 0.008 // - // 0.28 10.0 5 0.55 0.05 27.0 35.0 2.0 0.26 0.8 0.4 1.86 1,2 0.82 0.84 0.05 0.04 0.08 0.015 0,065 0.147 0.014 0,025 // - // 0.32 16.7 According to the prototype 6 0.45 0,03 24.5 39.7 1,5 0.5 4.9 0.32 1.45 1,5 0.5 0.1 0.05 0,07 0,053 0.005 - - - - - - - table 2 Conventional heat number The maximum depth of damage to the alloy along the boundaries of the crystals after Plasticity of the alloy depending on the duration of tests for long-term accuracy (T = 1000 ° C, σ = 20 MPa) Characteristics of the heat resistance of the alloy at a temperature of 1100 ° C and a voltage of 20 MPa Test duration, hour The minimum level of elongation at failure,% Time to destruction, hour Relative extension, % one 0,080 2000 6 130 16 2 0.015 3000 eleven 181 28 3 0.005 3000 fifteen 212 25 four 0.010 3000 16 203 31 5 0.012 1000 32 85 62 6 0,120 2500 four one hundred 10 1. Test results are averaged over 3 samples per point. 2. Tests of samples for long-term strength were carried out in accordance with the requirements of GOST 10145-81

Thus, the compositions of the bottoms 2, 3 and 4 compared with the composition of the alloy of the prototype 6 are characterized by the highest set of characteristics of heat resistance at a temperature of 1000 ° C.

The composition of the melt 1 does not provide an improvement in the complex of characteristics of heat resistance compared with the complex of characteristics of the prototype alloy. The same can be said of melting alloy 5, which, with a significant deterioration in long-term strength, shows a high deformation ability (δ = 30-35%).

An analysis of the data in Table 2 indicates that the nature of the change in the heat resistance characteristics of the investigated alloy compositions at a temperature of 1100 ° C is almost the same as the change in the corresponding characteristics of these materials compositions at a temperature of 1000 ° C.

Thus, we can conclude that the set of characteristics of the heat resistance of the alloy of the compositions of heats 2, 3 and 4 at a temperature of 1100 ° C has a higher level of long-term strength and ductility.

From the obtained research results it follows that the claimed alloy is superior to the alloy, which coincides in composition with the prototype both in resistance to airborne corrosion and mechanical stress at a temperature of 1100 ° C, and in terms of ductility and heat resistance at temperatures of 1000 ° C and 1100 ° C .

The manufacture of critical cast products for high-temperature chemical and oil refineries from the claimed alloy due to an increase in its resistance to corrosion and mechanical stress and an increase in the level of remarks on the characteristics of heat resistance will make it possible to increase the terms of “overhaul runs” of reaction coils by 2–2.5 times.

Information sources

1. RF patent No. 215110, C22C 19/05.

2. RF patent No. 2026401, C22C 19/05 - prototype.

Claims (1)

A heat-resistant alloy based on iron-chromium-nickel base containing carbon, nitrogen, chromium, nickel, niobium, tungsten, molybdenum, titanium, silicon, manganese, aluminum, copper, magnesium, zirconium, yttrium, boron and iron, subject to the conditions:

characterized in that it additionally contains cerium, lanthanum, neodymium and praseodymium in the following ratio of ingredients, wt.%:
carbon 0.35-0.55 nitrogen 0.02-0.05 chromium 22-27 nickel 25 - to less than 40 niobium 1-2 tungsten 0.5-5 molybdenum 0.2-0.6 titanium 0.05-0.6 silicon 0.8-2.0 manganese 0.8-1.5 aluminum 0.1-1.0 copper 0.1-1.0 magnesium 0.01-0.1 zirconium 0.005-0.15 yttrium 0.008-0.1 boron 0.007-0.01 cerium 0.022-0.063 lanthanum 0.006-0.027 neodymium 0.002-0.005 praseodymium 0.005-0.008 iron rest,
under the condition