RU2395591C1 - Procedure for production of sheets out of corrosion resistant steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to ferrous metallurgy, particularly to production of sheets used in structures of nuclear power plants operating at temperature up to 600°C. The procedure consists in melting steel, in producing a work piece, in heating the work piece to temperature of hot deformation, and in hot deformation with controlled reduction per pass. Also steel is melt out of charge materials with contents, wt %: lead ≤ 0.001, tin ≤ 0.008, antimony ≤ 0.01 and bismuth ≤ 0.005. Defects are removed off surface of the work piece; it is successively heated to temperature 1150-1170°C and conditioned at rate of 0.8-1.2 min/mm of cross section. Further the work piece is subject to hot deformation in the interval of temperature 1120-980°C with single reductions of 8-12% during the first three passes and successive reductions of not less, than 18% per pass at summary reduction of not less, than 65%. An intermediate work piece is sub-cooled to temperature 900°C. Successive deformation is carried out with single reductions of not less, than 8% per pass at summary deformation of not less, than 40% and successive cooling is performed at rate not less, than 40°C/min to temperature not above 200°C, and finally in air.

EFFECT: upgraded plasticity and durability of sheets.

5 cl, 1 ex, 3 tbl

Description

The invention relates to ferrous metallurgy, in particular to the production of sheets of corrosion-resistant steel, intended for use in the construction of nuclear power plants operating in continuous operation at temperatures up to 600 ° C. A significant part of the equipment of power plants is made of sheets up to 300 mm thick.

Known steel grades that are used for the manufacture of power plant designs, for example, corrosion-resistant steel grades 12X18H9, 10X17H13M2T, as well as other analogues mentioned in the scientific and technical patent literature [1 ÷ 7]. However, these steels lose their structural strength due to precipitation of carbides and carbonitrides along the grain boundaries during prolonged operation at temperatures above 400 ° C. Known steel grade for nuclear energy, JP 2005-023343, containing, wt.%:

15 ÷ 30 Cr; 8 ÷ 30 Ni; 0.001-0.1 C; 0.1-1.0 Si; 0.1-2 Mn; P≤0.05; S 0 0.05; N = 0.001-0.15; iron the rest. This grade of steel with a content of Cr = 30% and Ni = 8% contains about 80% ferrite in its composition, which leads to a noticeable decrease in performance at temperatures above 300 ° C. With a maximum content of Ni and Cr, this composition already belongs to the category of alloys.

A known technology for the production of sheets of corrosion-resistant steel, including heating to a temperature of 1200 ° C, deformation without limiting the temperature of the end of rolling and without regulation of single reductions and cooling after rolling in air [1]. In this case, the sheets are made of stainless steel of the following chemical composition, wt.%:

carbon - not more than 0.10

silicon - not more than 0.8

Manganese - no more than 2.0

chrome - 16.0 ÷ 18.0

nickel - 12.0 ÷ 14.0

molybdenum - 2.0 ÷ 3.0

titanium - 0.3 ÷ 0.7

sulfur - not more than 0,020

phosphorus - not more than 0.035

iron the rest [1].

This method provides the production of sheets of stainless steel used for the manufacture of structures operating at temperatures up to 350 ° C. During long-term operation at temperatures above 350 ° C, titanium carbides and carbonitrides are released along grain boundaries, which leads to embrittlement of the metal during operation. In addition, during hot rolling of sheets without regulation of compression, the microstructure of the sheets consists of large grains with thick intergranular layers. Designs made from such sheets have low performance characteristics. When operating at temperatures above 350 ° C, the closest in scope and accepted by us as a prototype is the technology of manufacturing sheets of steel grade 10X18H9, which includes the preparation of steel billets, heating to a temperature of 1180-1200 ° C, rolling in the first 2 ^x passes with reductions of 6 ÷ 14% per passage, in 3 ÷ 6 passes with reductions of 9 ÷ 14%, and the final part of the deformation is performed with reductions of 9 ÷ 18% per passage with subsequent cooling without regulation or cooling rate to 300 ° C [9] . According to this method, the preform is obtained from steel of the following composition, wt.%: Carbon no more than 0.10, silicon no more than 0.8, manganese no more than 2.0, chromium 17.0-19.0, nickel 8.6-10 , 0, titanium is not more than 0.10, sulfur is not more than 0.020, phosphorus is not more than and 0.025, iron is the rest.

Sheets made of this steel using the above technology can be used for the manufacture of structures operating at temperatures not exceeding 400 ° C. In addition, steel has reduced strength and plastic properties at normal temperature and lower technological ductility at 1200-1000 ° C.

The technical result of the invention is to increase technological plasticity at a temperature of 1200-1000 ° C level of strength and plastic properties of the workpieces, which allows to increase the service life of power plants at temperatures up to 600 ° C.

The technical result is achieved due to the fact that the method of manufacturing sheets of corrosion-resistant steel mainly for the manufacture of structures of nuclear power plants operating at temperatures up to 600 ° C, including steel smelting, preparation of billets, heating of billets to hot deformation temperature, hot deformation with regulated compression for passage, characterized in that the steel is produced from charge materials with a content, wt.%: lead ≤0.001, tin ≤0.008, antimony ≤0.01 and bismuth ≤0.005, on the workpiece surface defects are removed, subsequent heating is carried out to a temperature of 1150-1170 ° C with a shutter speed of 0.8-1.2 min / mm section, hot deformation is carried out in the temperature range 1120-980 ° C with a single reduction of 8-12% in the first three passes with subsequent reductions of at least 18% per pass with a total compression of at least 65%, then intermediate billet is forced to a temperature of 900 ° C, subsequent deformation is performed with single compressions of at least 8% per pass with a total deformation of at least 40%, followed by cooling at a speed of at least 40 ° C / min to a temperature not exceeding 200 ° C, then in air.

According to this invention, the sheets are obtained from steel of the following composition, wt.%:

carbon 0.04 ÷ 0.06 silicon 0.30 ÷ 0.80 manganese 1,0 ÷ 1,7 chromium 16.0 ÷ 18.0 nickel 10.0 ÷ 12.0 molybdenum 2.0 ÷ 2.5 titanium 0.03 ÷ 0.08 niobium 0.04 ÷ 0.06 vanadium 0.03 ÷ 0.05 sulfur ≤0.005 phosphorus ≤0.008 arsenic ≤0.008 lead ≤0.001 tin ≤0.008 antimony ≤0.01 bismuth ≤0.005 iron rest

while the ratio

the attitude

The total content of arsenic, lead, tin, antimony and bismuth should not exceed 0.03%, since with a higher content of fusible impurities, ductility decreases during hot deformation due to the formation of fusible interlayers along grain boundaries.

The total content of sulfur and phosphorus should not exceed 0.012%, which excludes the formation of sulfides in the structure.

Heating before deformation to temperatures of 1150 ÷ 1170 ° C with a shutter speed of 0.8 ÷ 1.2 min / mm significantly reduces the growth of grains and intergranular layers, which leads to an increase in plastic properties during hot deformation. Compression of 8 ÷ 12% in the first three passes allows to crush the cast structure of the workpieces and prepare the structure for more intense deformation to grind the structure.

Subsequent deformation is performed with reductions of at least 18% per passage for the formation of a fine-grained structure.

Tightening to a temperature of 900 ° C is necessary to reduce the rate of collective recrystallization; the final stage of deformation is performed at temperatures no higher than 900 ° C, which helps to obtain a fine-grained structure in the workpieces.

The accelerated cooling of the sheets upon completion of deformation prevents an increase in the thickness of intergranular layers during the cooling process. At temperatures below 200 ° C, the rate of diffusion processes is negligible.

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, полуфабрикаты получаются с крупнозернистой структурой. При крупнозернистой структуре по границам зерен образуются толстые прослойки из карбидов и карбонитридов сульфидов и других примесей, поэтому при сварке возможно образование микротрещин по межзеренным прослойкам.The decrease in the content of harmful and fusible impurities in comparison with the known composition virtually eliminates the appearance of fusible interlayers at the grain boundaries, which contributes to an increase in technological plasticity, welding and technological properties and the life of structures at temperatures up to 600 ° C. 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, insufficient amounts of stable carbides are formed, the number of crystallization centers decreases, and semi-finished products are obtained with a coarse-grained structure. With a coarse-grained structure along the grain boundaries, thick layers of carbides and carbonitrides of sulfides and other impurities are formed, therefore, during welding, microcracks can form along intergranular layers.

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

менее 2,2 наблюдается снижение коррозионной стойкости за счет образования большого количества карбидов хрома и снижения содержания хрома до значений, при которых утрачивается коррозионная стойкость.The 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 2.2, a decrease in corrosion resistance is observed 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.

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 are possible.

более 1,3 содержание ферритной фазы в стали может превышать 10%, что приводит к образованию трещин при горячей обработке.With the ratio

more than 1.3, the content of the ferritic phase in steel can exceed 10%, which leads to the formation of cracks during hot processing.

Concrete example

3 melts of 120 tons of the inventive steel were smelted in an oxygen-purged converter and one melting of a well-known brand in a 50-ton electric arc furnace using charge materials containing wt.%: Lead 0,0008; tin 0.005; antimony 0.006 and bismuth 0.003; the smelting of known steel was carried out from an ordinary charge. Smelted metal is poured into ingots from which slabs 450 mm thick were made. After that, the surfaces of the slabs were cleaned to remove all surface defects.

After removal of defects, the slabs were planted in a heating furnace, heated to a temperature of 1160 ° С and maintained at this temperature for complete heating over the entire cross section for 450 min. After that, the slabs were rolled on sheets with a thickness of 130 mm. Slabs of known steel were heated to 1190 ° C with a holding time of 485 minutes, after which they were rolled onto sheets with a thickness of 130 mm. The rolling modes are given in table.3.

The results of chemical analysis and testing of the mechanical properties of sheets made by the known and proposed method are shown in tables 1 and 2.

Samples for testing were selected in accordance with GOST 7564-73.

Table 3 The parameters of the proposed and known methods Preparation method Option No. Heating temperature Exposure at a given temperature Compression in the first 3 passes Compression in 4 and subsequent passes Total reduction Tempering Compression after 900 ° C Total reduction after 900 ° C Cooling rate The end pa accelerated cooling ° C min / mm % % % ° C mm % ° C / min ° C Proposed one 1150 0.8 8 twenty 65 900 10 48 40 180 2 1160 1,0 10 twenty 70 900 12 56 45 190 3 1170 1,2 12 25 68 900 fifteen fifty 42 190 Famous four 1190 - in 2 passes 10 fifteen - - - - - - Note. The table shows the parameters of the manufacturing processes of sheets of compositions 2 and 4 of table 1.

Literature

1. Corrosion-resistant, heat-resistant and high-strength steels and alloys. Handbook "Intermet Engineering". Moscow, 2000

2. Technical specifications TU 5.961.11255-84 "Workpieces from corrosion-resistant steel grades 08X16H11M3, 08X16H11M3-VD and 08X16H11M3-Sh."

3. M.I. Goldstein, S.V. Grachev, Yu.G. Veksler. "Special steels and alloys", M., publishing house "Metallurgy", 1985.

4. Yu.F. Balandin, I.V. Gorynin, Yu.I. Zvezdin and others. "Construction materials of nuclear power plants", Moscow: Energoatomizdat, 1984.

5. V.P. Goltsev, A.Ya. Kamenev. "Construction materials of nuclear power plants", Moscow: Energoatomizdat, 1984.

6. A.M. Sukhotin. "Passivity and Corrosion of Metals," L., GIPH, 1975.

7. A.M. Parshin. "Structure, Strength, and Radiation Damage of Corrosion Resistant Steels and Alloys," Chelyabinsk, Metallurgy, 1988.

8. M.Ya. Dzugutov. "Plastic deformation of high alloy steels and alloys", Moscow, Metallurgy, 1977.

9. Proceedings of the 7th Congress of distributors. Volume 2, Moscow, October 15-18. 2007, pp. 212-224.

Claims (5)

1. A method of manufacturing sheets of corrosion-resistant steel, mainly for the manufacture of structures of nuclear power plants operating at temperatures up to 600 ° C, including steel smelting, preparation of billets, heating of the billet to the temperature of hot deformation, hot deformation with regulated compression for the passage, characterized in that steel is smelted from charge materials with a content, wt.%: lead ≤0.001, tin ≤0.008, antimony ≤0.01 and bismuth ≤0.005, surface defects are removed from the workpiece, heating is carried out to t temperatures 1150-1170 ° C with a shutter speed of 0.8-1.2 min / mm section, hot deformation is carried out in the temperature range 1120-980 ° C with single compressions of 8-12% in the first three passes with subsequent compressions of at least 18% per a passage with a total reduction of at least 65%, then the intermediate billet is cooled up to a temperature of 900 ° C, subsequent deformation is carried out with a single reduction of at least 8% per passage with a total deformation of at least 40%, followed by cooling at a speed of at least 40 ° C / min to a temperature not exceeding 200 ° C, and then in air. 2. The method according to claim 1, characterized in that the smelting of steel containing the following chemical composition, wt.%:
carbon 0.04-0.06 silicon 0.30-0.80 manganese 1.0-1.7 chromium 16-18 nickel 10-12 molybdenum 2-2.5 titanium 0.03-0.08 niobium 0.04-0.06 vanadium 0.03-0.05 sulfur ≤0.005 phosphorus ≤0.008 arsenic ≤0.008 lead ≤0.001 tin ≤0.008 antimony ≤0.01 bismuth ≤0.005 iron rest,
while the total content of sulfur and phosphorus does not exceed 0.012, the total content of arsenic, lead, tin, antimony and bismuth does not exceed 0.03. 3. The method according to claim 2, characterized in that the steel is melted when the ratio of the total content of titanium, niobium and vanadium to the carbon content is fulfilled:

. 4. The method according to claim 2, characterized in that the steel is melted when the ratio of the chromium content to the total content of nickel, manganese and molybdenum is fulfilled:

5. The method according to claim 2, characterized in that the total content of arsenic, lead, tin, antimony and bismuth should not exceed 0.03%.