RU2359064C2 - Austenitic corrosion-resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy field, particularly to development of compositions of alloyed austenitic corrosion-resistant steels for atomic electric power installation with liquid-metal coolant. Steel contains components at following ratio, in wt %: carbon 0.05÷0.1, silicon 0.4÷0.8, manganese 1.0÷1.8, chrome 17.5÷19, nickel 8÷9, niobium 0.03-0.06, vanadium 0.02-0.07, titanium 0.05-0.15, sulphur ≤0.002, tin ≤0.015, lead ≤0.004, iron is the rest. Relation of total content of titanium, niobium and vanadium to carbon is not less than 1.6, and relation of chrome content to total content of nickel and manganese must be in the range 1.7÷2.0.

EFFECT: it is increased technological plasticity at hot working and welding-processing characteristics, that leads to receiving of hot-deformed semi-finished products with close-grained structure, allowing increased operating characteristics.

2 tbl, 1 ex

Description

The invention relates to the metallurgy of alloyed austenitic steels used in nuclear power plants. Known currently used brands of corrosion-resistant steel, given in the technical literature: Babakov A.A., Pridantsev M.V. Corrosion-resistant steels and alloys. M., Metallurgy, pp. 137-143, 215-230, GOST 5632-72. The main disadvantage of these steels is a reduced technological ductility, a coarse-grained structure of semi-finished products.

The closest in composition of the ingredients and the purpose of the proposed steel is steel grade 08X18H10 GOST 5632-72, page 16, containing, wt.%:

carbon no more than 0.08 silicon no more than 0.8 manganese no more than 2.0 chromium 17 ÷ 19 nickel 9.0 ÷ 11.0

The sulfur content is not more than 0.02. The content of lead and tin is not standardized.

Known steel has high mechanical properties, but it does not have a sufficiently high technological ductility during hot deformation, a coarse-grained structure and, as a result, reduced welding and technological properties. This is due to the fact that the sulfur content in steel is at a level of ≥0.020%, the content of tin and lead is not standardized. Sulfur compounds are usually located along grain boundaries. Sulfur compounds (sulfides) are, in most cases, fusible and sharply reduce plastic properties during hot deformation.

With a low content of carbide-forming elements, which are the centers of nucleation of new grains during hot deformation, the grain sizes in semi-finished products increase.

With increasing grain sizes, the thickness of the intergranular layers also increases and the plastic characteristics of the metal and the welding and technological properties decrease.

The technical result of the invention is to increase technological ductility during hot deformation and welding and technological properties. The technical result is achieved due to the fact that in the steel containing carbon, silicon, manganese, chromium, nickel and iron, titanium, niobium and vanadium are additionally introduced in the following ratio of components, wt.%:

carbon 0.05 ÷ 0.1 silicon 0.4 ÷ 0.8 manganese 1,0 ÷ 1,8 chromium 17.5 ÷ 19 nickel 8.0 ÷ 9.0 niobium 0.03 ÷ 0.06 vanadium 0.02 ÷ 0.07 titanium 0.05 ÷ 0.15 iron and impurities rest,

, отношение содержания хрома к суммарному содержанию никеля и марганца должно быть в пределах 1,7-2,0, а содержание серы, олова и свинца составляет, мас.%: S≤0,002, Sn≤0,015, Pb≤0,004. Снижение содержания легкоплавких элементов по сравнению с известным составом практически исключает появление на границах зерен легкоплавких прослоек, что способствует повышению технологической пластичности, сварочно-технологических свойств и пластических свойств полуфабрикатов. Введение титана, ниобия и ванадия в соотношении

способствует получению полуфабрикатов с мелкозернистой структурой за счет выделений устойчивых карбидов титана, ниобия и ванадия, которые служат центрами кристаллизации. При более высоких содержаниях титана и ниобия в стали возможно выделение интерметаллидов, которые снижают пластичность металла. При более низких содержаниях титана, ниобия и ванадия образуется недостаточное количество устойчивых карбидов, снижается количество центров кристаллизации и полуфабрикаты получаются с крупнозернистой структурой. При крупнозернистой структуре по границам зерен образуются толстые прослойки из интерметаллидов, сульфидов и других примесей, и поэтому при сварке возможно образование микротрещин по межзеренным прослойкам.while the ratio

, the ratio of the chromium content to the total content of nickel and manganese should be in the range of 1.7-2.0, and the content of sulfur, tin and lead is, wt.%: S≤0.002, Sn≤0.015, Pb≤0.004. The decrease in the content of fusible elements in comparison with the known composition almost eliminates the appearance of fusible interlayers at the grain boundaries, which contributes to an increase in technological plasticity, welding and technological properties and plastic properties of semi-finished products. The introduction of titanium, niobium and vanadium in the ratio

promotes the preparation of semi-finished products with a fine-grained structure due to the precipitation of stable carbides of titanium, niobium and vanadium, which serve as crystallization centers. At higher contents of titanium and niobium in steel, precipitation of intermetallic compounds is possible, which reduce the ductility of the metal. At lower contents of titanium, niobium and vanadium, an insufficient amount of stable carbides is formed, the number of crystallization centers decreases and semi-finished products are obtained with a coarse-grained structure. With a coarse-grained structure, thick interlayers of intermetallic compounds, sulfides, and other impurities are formed along the grain boundaries, and therefore, during welding, microcracks can form along intergrain interlayers.

позволяет получать полуфабрикаты с мелкозернистой структурой, что значительно повышает технологическую пластичность и сварочно-технологические свойства. При отношении

менее 1,6 наблюдается снижение коррозионной стойкости за счет образования большого количества карбидов хрома и снижения содержания хрома до значений, при которых утрачивается коррозионная стойкость.Microalloying of corrosion-resistant steel with titanium, niobium and vanadium in the ratio

allows you to get semi-finished products with a fine-grained structure, which significantly increases the technological ductility and welding and technological properties. With respect

less than 1.6, there is a decrease in corrosion resistance due to the formation of a large number of chromium carbides and a decrease in the chromium content to values at which corrosion resistance is lost.

The sulfur content should not exceed 0.002, tin 0.015, lead 0.0004, since at a higher content the ductility decreases during hot deformation due to the formation of fusible interlayers along grain boundaries.

.To ensure high welding and technological properties, the ratio

.

So, at lower values of this ratio, the content of the ferritic phase in steel decreases and cracks in welded joints may appear.

более 2,0 содержание ферритной фазы в стали может достигать 10%, что приводит к образованию трещин при горячей обработке.With respect

more than 2.0, the content of the ferritic phase in steel can reach 10%, which leads to the formation of cracks during hot processing.

An example of a specific implementation.

3 melts of 120 tons of the inventive steel were smelted in an oxygen-blown converter and one melting of a well-known brand in a 50-ton electric arc furnace and rolled into sheets with a thickness of 20-50 mm from a heating temperature of 1000 and 1200 ° C.

The sheets of the claimed and known steel were austenitized at a temperature of 1030 ÷ 1050 ° C, followed by cooling in air.

After cooling, a visual inspection of the sheets and sampling for mechanical and metallographic tests and determination of welding and technological properties were performed. The chemical composition of the claimed and known brands are shown in table 1, the test results in table 2.

As can be seen from table 2, the inventive steel has a higher ductility during hot deformation, has a finer-grained structure and has improved welding and technological properties.

The expected technical and economic effect from the use of the inventive steel will be expressed in increasing the yield of metal during hot deformation, a significant reduction in the cost of eliminating defects on the surface of sheets and welded joints, as well as in increasing the service life and reliability of the products.

Table 1
The chemical composition of the claimed and known steel grades Steel Conventional No. of swimming trunks The content of elements, wt.% FROM Si Mn Cr Ni Nb V Ti S Sn Pb

Declare Steel one 0.05 0.40 1.8 17.5 8.0 0.04 0,07 0.1 0.001 0.008 0.004 4.2 1.78 2 0.08 0.6 1,0 19.0 8.5 0,03 0.05 0.05 0.0015 0.012 0.003 1,6 2.0 3 0.10 0.8 1,5 17.9 9.0 0.06 0.02 0.15 0.002 0.015 0.002 2,3 1.70 Famous four 0,07 0,07 1.9 17,2 10.0 - - - 0.018 0.002 0.05 - 1,445 Note. The chemical composition was determined on 5 heats of the inventive steel with a total mass of 621 tons and 8 heats of known steel with a total weight of 456 tons

table 2
Properties of the claimed and well-known steel grades Steel Conventional No. of swimming trunks Mechanical properties Technological plasticity,% Grain number Welding and technological
hard sample properties σ _in σ _0.2 δ ₅ ψ 1200 ° C 1000 ° C n / mm ² n / mm ² % % Declared one 620 250 58 65 58 60 6 No cracks 2 630 258 56 640 52 70 four - "- 3 640 265 54 62 60 55 7 - "- Famous four 580 220 51 35 35 40 2 Microcracks Note. 1. The average values of mechanical properties are given according to the test results of 4 samples from each sheet.
2. Technological plasticity was evaluated visually by the appearance of small cracks on the surface of the sheets during hot deformation.

Claims (1)

Austenitic corrosion-resistant steel containing carbon, silicon, manganese, chromium, nickel and iron, characterized in that it additionally contains titanium, niobium, vanadium, sulfur, tin and lead in the following ratio, wt.%:
carbon 0.05 ÷ 0.1 silicon 0.4 ÷ 0.8 manganese 1,0 ÷ 1,8 chromium 17.5 ÷ 19 nickel 8.0 ÷ 9.0 titanium 0.05 ÷ 0.15 niobium 0.03 ÷ 0.06 vanadium 0.02 ÷ 0.07 sulfur ≤0.002 tin ≤0.015 lead ≤0.004 iron rest
the following conditions are met:
the ratio of the total content of titanium, niobium and vanadium to carbon is not less than 1.6

,
a ratio of chromium to total nickel and manganese is in the range 1.7 ÷ 2.0

.