RU2333287C2 - Heat-resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy field. Particularly it concerns heat-resistant steel content for heat power plant parts with steam operating temperature till 620°C. Heat-resistant steel contains carbon, silicon, manganese, chrome, nickel, tungsten, molybdenum, vanadium, niobium, nitrogen, boron, tin, antimony, arsenic, sulphur, phosphorus, cerium, calcium, aluminium and iron, at a following components ratio, mass%: carbon 0.10-0.14, silicon ≤0.10, manganese 0.20-0.40, chrome 9.00-10.50, nickel 0.30-0.50, tungsten 0.90-1.10, molybdenum 0.90-1.10, vanadium 0.18-0.30, niobium 0.04-0.06, nitrogen 0.03-0.08, boron 0.003-0.012, aluminium 0.005-0.012, sulphur ≤0.010, phosphorus ≤0.010, tin ≤0.006, antimony ≤0.006, arsenic ≤0.006, cerium 0.005-0.03, calcium 0.005-0.02, the rest is iron. Total content of aluminium, calcium and cerium is 0.015-0.04 mass %.

EFFECT: rising of heat resistance and mechanical properties.

2 cl, 3 tbl

Description

The invention relates to the field of metallurgy, in particular to heat-resistant steels, in particular, to the creation of steels that can be used for forging large-sized rotors and other equipment of thermal and gas turbines of power plants with operating temperatures up to 620 ° C.

The invention can most effectively be used in the manufacture of forgings of large diameter rotors, steam pipes and boilers with high strength, endurance and heat-resistant properties at temperatures up to 620 ° C.

The applied steel 15X12 VNMF (EI802) GOST 5632-72 has proven itself in the production of rotor blanks for a gas turbine operating at temperatures not exceeding 570 ° C. However, when operating at temperatures above 600 ° C, this steel has reduced heat resistance.

Known steel 13X11H2 B2MF (EI961-SH) used for such purposes, consisting of the following components (wt.%):

Carbon 0.10-0.16 Silicon ≤0.60 Manganese ≤0.60 Chromium 10.5-12.0 Nickel 1.50-1.80 Molybdenum 0.35-0.50 Vanadium 0.18-0.30 Tungsten 1,60-2,00 Copper ≤0.30 Iron and impurities the rest (see GOST 5632-72)

The disadvantage of this steel is reduced heat resistance at temperatures above 570 ° C and the scatter of data on mechanical properties due to the large interval in carbon content.

The closest to the proposed steel in technical essence and the achieved result is heat-resistant steel (see RF Patent RU 2272852 C1, Cl. C22C 38/48) of the following composition (wt.%):

Carbon 0.11-0.20 Silicon 0.03-0.20 Manganese 0.1-0.30 Chromium 9.00-12.0 Nickel 0.00-0.7 Tungsten 0.00-2.0 Molybdenum 0.90-1.60 Vanadium 0.15-0.30 Niobium 0.02-0.06 Boron 0.00-0.02 Nitrogen 0.005-0.05 Tin 0.00-0.006 Antimony 0.00-0.006 Arsenic 0.00-0.007 Sulfur ≤0.015 Phosphorus ≤0.020 Iron rest

This steel has significant changes in the characteristics of heat resistance and mechanical properties at temperatures above 600 ° C due to the large variation in the content of carbon, chromium, tungsten, nickel and boron. In addition, when the carbon content is above 0.15%, steel is prone to the formation of hot cracks during the production of billets by the ESR method and requires complex heat treatment with multiple supercoolings to prevent cracking in the forgings during cooling from forging temperatures. With the content of ferrite-forming at the upper limit, the steel structure becomes martensitic-ferritic with a significant amount of ferrite, which significantly reduces the heat-resistant and plastic properties of steel, as well as resistance to brittle fracture.

The proposed steel containing carbon, silicon, manganese, chromium, nickel, tungsten, molybdenum, vanadium, niobium, nitrogen, boron, tin, antimony, arsenic, sulfur, phosphorus and iron, characterized in that it additionally contains cerium, calcium and aluminum at the following ratio of components (wt.%):

Carbon 0.10-0.14 Silicon ≤0.10 Manganese 0.20-0.40 Chromium 9.00-10.5 Nickel 0.30-0.50 Tungsten 0.90-1.10 Molybdenum 0.90-1.10 Vanadium 0.18-0.30 Niobium 0.04-0.06 Nitrogen 0.03-0.08 Boron 0.003-0.012 Aluminum 0.005-0.012 Sulfur ≤0.010 Phosphorus ≤0.010 Tin ≤0.006 Antimony ≤0.006 Arsenic ≤0.006 Cerium 0.005-0.03 Calcium 0.005-0.02 Iron rest

Moreover, the total content of residual aluminum, calcium and cerium is 0.015-0.04 wt.%.

The proposed steel differs from the known also in that the total content of aluminum, calcium and cerium is 0.015-0.04 wt.%.

The introduction of a limited content of active elements of calcium and cerium into the composition of the steel, combined with a balanced content of residual aluminum, favorably changes the shape of non-metallic inclusions, increases heat resistance, ductility and toughness, cleans and strengthens grain boundaries, which leads to a general increase in the service and technological properties of the material. When the content of Ca and Ce is below the lower limit, their effect on the heat-resistant properties has become ineffective, and when they are above the upper limit, it causes excessive enrichment of grain boundaries with non-metallic inclusions, which negatively affects the properties of steel.

Cerium in the presence of calcium improves oxidation resistance and hot deformability. When the total content of cerium and calcium in the specified range increases the long-term strength of the proposed steel.

When the content of calcium and cerium is below the lower limit of the given content, their effect on the heat-resistant properties and resistance to brittle fracture is ineffective.

The residual aluminum content in the steel is 0.005-0.012 wt.%. When the content of residual aluminum is below the lower limit under conditions of restriction on the silicon content, effective deoxidation of steel is not ensured, which leads to an increase in the number of oxide inclusions and a decrease in the strength properties of the metal. With an increase in the residual aluminum content above the upper limit, the characteristics of heat resistance and toughness of the metal decrease, which is caused by the additional release of aluminum nitrides at the grain boundary.

The proposed steel differs from the known one by limiting the content of impurities of phosphorus and sulfur to 0.010% each, which contributes to obtaining higher values of ductility and toughness.

The proposed steel contains boron (0.003-0.012 wt.%), Which contributes to an increase in hardenability, since all boron, being in solid solution, is concentrated in thin layers of austenite grains and reduces the rate of nucleation of crystallization centers, in addition, this boron content provides a good combination of heat resistance and scale resistance, as well as reduced sensitivity to cracking during welding and electroslag remelting.

The boron content below the lower limit is ineffective, and the boron content above the upper limit leads to exceeding the saturation limit at the austenite boundaries, as a result of which excessive boron phases (borides) appear, which act as crystallization centers, which reduces the scale resistance and heat resistance of steel due to the appearance of excess phases.

The proposed steel has a lower carbon content of 0.10-0.14 wt.% Against 0.11-0.20 wt.% In the known steel, which is optimal to ensure high processability in remelting processes, forging and welding. However, this carbon content for the proposed composition provides high heat resistance.

When the carbon content is below the lower limit, its effect on technological and service properties is ineffective, and when the carbon content is above the upper limit, carbide coalescence and depletion of the Mo, W, and V solid solutions are accelerated, which reduces the strength and heat resistance of steel.

Smelting was carried out in a 150 kg induction furnace with metal casting on cast electrodes to obtain ESR ingots. The resulting ESR ingots were forged in the range of 1230–850 ° С onto billets for determining mechanical and heat-resistant properties.

Table 1 shows the chemical composition of the salts.

Table 2 shows the mechanical properties obtained after optimal heat treatment, taking into account the real conditions of technological heating in the manufacture of forgings for the equipment of steam and gas turbines.

Tensile tests were carried out on cylindrical samples of five times the length with a diameter of the working part of 6 mm in accordance with GOST 1497-84.

Determination of impact strength at normal temperature was carried out on samples of type 11 according to GOST 9454-78.

Heat resistant tests were carried out according to GOST 3248-81 for creep and according to GOST 10145-81 for long-term strength (table 3).

As can be seen from tables 2 and 3, the proposed steel has higher mechanical properties and heat resistance.

Using the proposed steel as a material for forgings of large-sized rotors for gas and thermal turbines, as well as piping elements of steam pipelines and boilers with the achievement of supercritical steam parameters at a pressure of 300-350 MPa, makes it possible to increase the operating temperature of the turbines to 620 ° C.

The offered steel has passed extensive laboratory tests at NPO TsNIITMASH OJSC and industrial tests at OM3-Special Steel OJSC and is recommended for industrial testing under the conditions of OJSC Leningrad Metal Plant.

Table 1 The chemical composition of steel Steel composition The content of components (wt.%) FROM Si Mn Cr Ni Mo W V Nb AT Al S R Sa Xie N As Sb Sn Fe one. 0.10 0.05 0.2 9.0 0.3 0.9 0.9 0.18 0.04 0.003 0.005 0.005 0.005 0.005 0.005 0,03 0.001 0.005 0.005 rest 2. 0.12 0,07 0.3 9.5 0.4 1,0 1,0 0.20 0.05 0.004 0.009 0.01 0.01 0.006 0.009 0.05 0.002 0.003 0.003 rest 3. 0.14 0.10 0.4 10.5 0.5 1,1 1,1 0.30 0.06 0.012 0.012 0.01 0.01 0.02 0.02 0.08 0.006 0.006 0.006 rest four. 0.09 0,03 0.1 8.0 0.2 0.8 0.8 0.15 0.02 0.002 0.003 0.01 0.01 0.003 0.003 0.02 0.001 0.004 0.004 rest 5. 0.16 0.15 0.5 12.0 0.7 1,2 1,2 0.35 0,07 0.013 0.015 0.01 0.01 0.009 0.009 0.09 0.007 0.007 0.007 rest 6. 0.11 0,03 0.1 9.0 0,0 0.9 0,0 0.15 0.02 0,0 - 0.015 0.02 - - 0.008 0.00 0,0 0,0 rest 7. 0.20 0.10 0.3 12.0 0.7 1,6 2.0 0.30 0.06 0.02 - 0.015 0.02 - - 0.05 0.007 0.006 0.006 rest Compounds 1-3 - proposed steel Compositions 4-5 - steel, the content of the components of which is beyond the stated limits Compositions 6-7 - a steel variant of the prototype

table 2 Mechanical properties of steel Steel composition T _isp. ° C σ _0.2 σ _in δ, ψ, Kcv N / mm ² % J / cm ² one. twenty 750 890 15.0 55.0 90.0 620 400 450 20,0 70.0 - 2. twenty 760 910 15.0 52.0 80.0 620 410 470 20,0 65.0 - 3. twenty 810 920 14.0 53.0 75.0 620 435 490 22.0 72.0 - four. twenty 680 810 18.0 60.0 100.0 620 390 440 20,0 70.0 - 5. twenty 650 800 14.0 58.0 70.0 620 360 440 20,0 70.0 - 6. twenty 630 780 15.0 65.0 100.0 620 350 420 20,0 72.0 - 7. twenty 700 880 20,0 59.0 40,0 620 410 460 20,0 72.0 - Compounds 1-3 - proposed steel Compositions 4-5 - steel, the content of the components of which is beyond the stated limits Compositions 6-7 - a steel variant of the prototype

Table 3 Durable steel Steel composition Long-term strength, N / mm ² , during 10 ⁵ hours at temperatures 600 ° 620 ° C one. 115 98 2. 125 105 3. 127 110 four. 124 108 5. 118 one hundred 6. 109 90 7. 110 95 Compounds 1-3 - proposed steel Compositions 4-5 - steel, the content of the components of which is beyond the stated limits Compositions 6-7- prototype steel variant

Claims (2)

1. Heat-resistant steel containing carbon, silicon, manganese, chromium, nickel, tungsten, molybdenum, vanadium, niobium, nitrogen, boron, tin, antimony, arsenic, sulfur, phosphorus and iron, characterized in that it additionally contains cerium, calcium and aluminum, in the following ratio of components, wt.%: carbon 0.10-0.14 silicon ≤0.10 manganese 0.20-0.40 chromium 9.00-10.50 nickel 0.30-0.50 tungsten 0.90-1.10 molybdenum 0.90-1.10 vanadium 0.18-0.30 niobium 0.04-0.06 nitrogen 0.03-0.08 boron 0.003-0.012 aluminum 0.005-0.012 sulfur ≤0.010 phosphorus ≤0.010 tin ≤0.006 antimony ≤0.006 arsenic ≤0.006 cerium 0.005-0.03 calcium 0.005-0.02 iron rest 2. Steel according to claim 1, characterized in that the total content of aluminum, calcium and cerium is 0.015-0.04 wt.%.