RU2333285C2 - 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. Steel contains carbon, silicon, manganese, chrome, molybdenum, vanadium, niobium, calcium, cerium, nitrogen, tungsten, boron, sulphur, phosphorus and iron, at a following components ratio, mass %: carbon 0.08-0.12, silicon 0.15-0.20, manganese 0.40-0.60, chrome 8.0-9.5, molybdenum 0.4-0.6, tungsten 1.0-2.0, vanadium 0.15-0.30, niobium 0.04-0.09, calcium 0.005-0.05, cerium 0.02-0.05, nitrogen 0.03-0.07, boron 0.001-0.006, sulphur not more than 0.01, phosphorus not more than 0.015, the rest is iron.

EFFECT: improving of steel heat-resistance, long-term strength and plasticity.

2 tbl

Description

The invention relates to the field of metallurgy, in particular to the composition of heat-resistant steel for thermal power plants with a working temperature of steam up to 620 ° C.

Known steel containing 0.10-0.16% carbon; 0.17-0.37% silicon; 0.4-0.7% manganese; 1.10-1.40% of chromium; 0.9-1.1% molybdenum; 0.20-0.35% vanadium (RU, issue 16, “Properties of steels and alloys used in boiler turbine construction”, CKTI, 1966 ”, p. 92).

не обеспечивает возможности повышения параметров пара тепловых энергоблоков свыше 560°С.The specified steel, having 40 years of operating experience in the power system as a material of pipelines and other elements due to low heat resistance

It does not provide the possibility of increasing the parameters of the steam of thermal power units above 560 ° C.

Also known is a steel selected as a prototype containing carbon; silicon; manganese; chromium; molybdenum; vanadium; niobium; cerium; calcium; nitrogen; phosphorus; sulfur and iron (see patent No. 2229532 RU 2229532 C2 7 C22C 38/26). However, this steel also does not have the necessary heat resistance at temperatures up to 620 ° C.

One of the basic problems in creating thermal power units with supercritical parameters of a temperature level of 620 ° C and a pressure of 30-35 MPa is the need to develop more heat-resistant and relatively economical structural materials, including for superheaters and steam pipelines. In this regard, the task was set to develop a new heat-resistant steel that provides the required level of long-term strength σ ₁₀ ^{5 of} at least 98 N / mm ² at a temperature of 620 ° C and a long ductility of at least 10%. The basis of the development was adopted steel with 8-10% chromium and 0.08-0.12% carbon.

As a result of the application of optimized complex alloying of the base composition with molybdenum, tungsten, vanadium, niobium, microalloying with calcium, cerium, nitrogen and boron, while limiting the content of manganese, silicon, phosphorus and sulfur, a new heat-resistant steel was developed that meets the specified requirements.

Proposed steel containing carbon; silicon; manganese; chromium; molybdenum; vanadium; niobium; calcium, cerium, nitrogen; phosphorus; sulfur and iron, characterized in that it further comprises tungsten and boron in the following ratio of components, wt.%: carbon 0.08-0.12%; silicon 0.15-0.20%; manganese 0.4-0.6%; chromium 8.0-9.5%; molybdenum 0.4-0.6%; tungsten 1.0-2.0%; vanadium 0.15-0.30%; niobium 0.04-0.09%; calcium 0.005-0.05%; cerium 0.02-0.05%; nitrogen 0.03-0.07%; boron 0.001-0.006%; phosphorus - not more than 0.015%; sulfur - not more than 0.010%, iron - the rest.

длительная пластичность

при вышеуказанном содержании компонентов.The technical result of the proposed steel is that the required level of heat resistance characteristics (long-term strength

long ductility

with the above content of the components.

The introduction of tungsten in an amount of 1.0-2.0% increases the heat resistance of steel due to the hardening of the solid solution and Me ₂₃ C ₆ carbide present in the steel and the separation of the Laves phase Fe ₂ W.

The introduction of boron in an amount of 0.001-0.006% increases the long-term strength and long-term plasticity due to the dissolution of boron as a surface-active element in the boundary zones, strengthening grain boundaries and slowing the flow of diffusion processes in these areas.

The limitation of the niobium content to 0.04-0.09% contributes to the production of smaller carbides of NbC and, as a result, increase the long-term strength.

Limiting the content of phosphorus to 0.015%, sulfur to 0.010% contributes to higher plasticity characteristics of steel.

The carbon content of 0.08-0.12% provides the required level of desired properties. A carbon content of less than 0.08% does not provide the necessary level of short-term mechanical properties and long-term strength. An increase in carbon content in excess of 0.12% is impractical because degrades weldability of steel.

Silicon in an amount of 0.15-0.20% and manganese in an amount of 0.4-0.6% are used for deoxidation of steel. With a silicon content of less than 0.15%, poorly removable liquid silicates are formed, with a content of 0.15-0.20%, solid, well-removable silica inclusions are formed, with a silicon content of more than 0.20%, the tendency of steel to thermal brittleness increases.

With the introduction of manganese less than 0.4% - low deoxidizing ability of silicon, more than 0.6% - practically does not affect the deoxidizing ability, therefore, it is impractical.

The chromium content of 8.0-9.5% provides a given amount, not more than 10%, of structurally free ferrite, the processability of steel in pipe production, high heat resistance and toughness of steel. When the content is less than 8.0% chromium, the heat resistance of steel decreases, when the content is more than 9.5% chromium, the proportion of structurally free ferrite in the steel structure increases, the toughness and technological properties decrease.

The molybdenum content of 0.4-0.6% provides heat-resistant properties of steel. A molybdenum content of less than 0.4% does not provide the required degree of alloying of the solid solution, carbide phase and heat resistance, more than 0.6% is not economically feasible.

The vanadium content in the amount of 0.15-0.30% helps to increase long-term strength. When the content of vanadium is less than 0.15%, the required heat resistance is not provided, when the content is more than 0.30%, its effect is negative, because Vanadium, being in solid solution, reduces the strength of interatomic bonds.

The calcium content of 0.005-0.05% increases the isotropy of properties, reducing the secondary oxidation of steel and contributing to a uniform distribution of sulfide and oxide inclusions. The calcium content in an amount of less than 0.005% is impractical due to the lack of influence of low concentrations of this element on the nature of non-metallic inclusions and isotropic properties of steel. The introduction of calcium in an amount of more than 0.05% causes technological difficulties. In the case of the use of metallic calcium, these difficulties are expressed in a strong pyroelectric effect and emissions of liquid steel. In the case of silicocalcium, the silicon content in the steel unacceptably increases.

The content of cerium in an amount of 0.02-0.05% contributes to the globularization of non-metallic inclusions, reduces the amount of oxide inclusions such as alumina and spinel, cleans grain boundaries and increases toughness. When the cerium content is less than 0.02%, this effect is not achieved. A cerium content of more than 0.05% can lead to increased pollution become complex inclusions.

Nitrogen in an amount of 0.03-0.07% is introduced into steel in order to increase heat resistance due to the formation of refractory and finely dispersed compounds such as carbonitrides V (C, N). At a content of less than 0.03% nitrogen, the formation of carbonitrides is not observed. The introduction of nitrogen more than 0.07% can contribute to the formation of shells and blisters in the ingot.

The application of the principle of multicomponent alloying with the combined influence of the above elements made it possible to obtain steel with a high level of service and economic characteristics, such as heat resistance, ductility, toughness, stability during long isothermal holdings, manufacturability and economy in metallurgical production.

Tested production of the proposed steel pipe products. OJSC “Zlatoust Metallurgical Plant” smelted industrial smelting weighing 20 tons by electric smelting followed by electroslag remelting. Chelyabinsk Tube-Rolling Plant OJSC manufactured pipes of 377 × 50 mm and 465 × 75 mm in size. The manufactured products met the specified requirements and were declared fit.

The chemical composition of the proposed steel are shown in table 1, and the mechanical properties in table 2.

The tests were carried out on materials smelted in electric arc furnaces followed by electroslag remelting. Tensile tests were carried out on samples with a working part diameter of 6 mm according to GOST 1497 and GOST 9651, heat resistance tests were carried out on samples with a working part diameter of 10 mm according to OST 108.901.102-78.

то предлагаемой стали -

а

From table 2 it can be seen that the heat resistance of the proposed steel compared with the known increases significantly. If the tensile strength of known steel is

then the proposed steel -

but

Steel is recommended for the manufacture of pipelines and superheaters of boilers with supercritical parameters. The use of steel in the power industry will increase the resource of manufactured equipment to 200,000 hours and increase the design parameters of the boiler to T = 620 ° C and P = 300 ata.

Table 1 The chemical composition of the studied swimming trunks Melting Content Elements FROM Si Mn Cr Mo W V Nb Xie Sa S R N AT Fe one 0.08 0.15 0.40 8.05 0.41 1.05 0.15 0.04 0,022 0.006 0.008 0.009 0,03 0.0015 Rest 2 0,097 0.17 0.54 8.75 0.51 1,50 0.23 0,07 0,025 0.003 0.004 0.007 0.04 0.0030 Rest 3 0.12 0.20 0.59 9.50 0.60 1.98 0.30 0.09 0,048 0,045 0.009 0.010 0,07 0.0057 Rest four 0,097 0.17 0.54 8.75 0.51 1,60 0.23 0,07 0,025 0,037 0.004 0.007 0.04 0.0030 Rest 5 0.10 0.36 0.56 9.50 1.10 - 0.25 0.17 0,035 0.003 0.010 0,021 0,07 - Rest Swimming trunks 1-3 - suggested laboratory swimming trunks Smelting 4 - proposed industrial smelting production of JSC "Zlatoust Metallurgical Plant" Melting 5 - famous

table 2 Steel properties Melting Short-term mechanical properties Long-term strength, N / mm ² , during 10 ⁵ hours at temperatures Test temperature 20 ° C Test temperature 600 ° C 600 ° C 620 ° C σ _In , N / mm ² σ _0.2 , N / mm ² δ,% ψ,% σ _In , N / mm ² σ _0.2 , N / mm ² δ,% ψ,% one 760 590 22.8 75.1 430 350 23,2 74.6 115 90 2 807 617 20.6 75.0 445 370 21.7 76.5 120 96 3 817 630 20.5 72.3 480 385 20.5 75.0 125 one hundred four 810 635 20,0 70.5 437 380 24.1 75.8 135 110 5 790 603 20.5 75.0 350 330 27.0 76,2 98 - Swimming trunks 1-3 - suggested laboratory swimming trunks Melting 4 - proposed industrial melting, metal pipes 377 × 50 mm in size manufactured by Chelyabinsk Tube Rolling Plant OJSC Melting 5 - famous

Claims (1)

Steel containing carbon, silicon, manganese, chromium, molybdenum, vanadium, niobium, calcium, cerium, nitrogen, sulfur, phosphorus and iron, characterized in that it additionally contains tungsten and boron in the following ratio, wt.%: carbon 0.08-0.12 silicon 0.15-0.20 manganese 0.40-0.60 chromium 8.0-9.5 molybdenum 0.4-0.6 tungsten 1.0-2.0 vanadium 0.15-0.30 niobium 0.04-0.09 calcium 0.005-0.05 cerium 0.02-0.05 nitrogen 0.03-0.07 boron 0.001-0.006 phosphorus no more than 0.015 sulfur no more than 0,01 iron rest