RU2519064C1 - Rust-resisting alloyed neutron-absorbing steel for production of hexagonal shell pipes for sealed storage of nuclear fuel in pumped pools and its transportation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed composition contains the following substances, in wt %: carbon - 0.02-0.05, silicon - 0.10-0.80, manganese - 0.10-0.50, chromium - 13.0-16.0, boron - 2.01-3.5, vanadium - 0.15-0.35, cerium - 0.03-0.07, aluminium - 0.15-0.80, titanium - 4.02-8.50, nickel - 0.05-0.50, sulphur - 0.005-0.02, phosphorus - 0.005-0.03, lead - not over 0.005, bismuth - not over 0.005, iron making the rest.

EFFECT: higher process plasticity at hot deformation temperature, decreased disposition to intercrystalline corrosion and cracking at stress.

Description

The invention relates to the field of metallurgy, in particular to the composition of corrosion-resistant alloyed neutron-absorbing steel, which has high mechanical and plastic properties, high ability to absorb neutrons, manufacturability during hot processing, machining - boring and turning and can be used in nuclear power engineering as a material for sheath tubes - neutron absorbers in the means of transportation and compacted storage of spent nuclear fuel and in exposure pools.

In metallurgy, corrosion-resistant steel 0X18H15P (EP 304) is known, containing, wt.%:

Carbon up to 0.07 Silicon up to 0.8 Manganese up to 1.5 Chromium 18-20 Nickel 9.0-11.0 Boron 0.65-1.15 Iron Rest

(ChMTU / TsNIICHM 630-62. Steel 08X18H15R (EP 304).

A disadvantage of the known steel, with a relatively satisfactory ability to absorb neutrons, is the low technological ductility at hot deformation temperatures, as well as the tendency to intergranular corrosion and corrosion cracking in nuclear power plant environments, which does not allow using it as a material for sheath tubes - neutron absorbers in transportation vehicles and storage of spent nuclear fuel of nuclear power plants.

In metallurgy, corrosion-resistant steel 04Kh14T3R1F (ChS 82) is also known for use in the manufacture of hexagonal covers for shelves of compacted storage in the storage and transportation pools of nuclear fuel, containing, wt.%:

Carbon 0.02-0.10 Silicon 0.10-0.80 Manganese 0.10-0.50 Chromium 13.0-16.0 Boron 1.0-2.0 Vanadium 0.05-0.35 Cerium 0.01-0.04 Aluminum 0.15-0.8 Titanium 2.0-4.0 Iron Rest

(Patent RU No. 1122009, CL. C22C 38/32 and TU 14-3-1630-89 "Cold-deformed hexagonal steel pipes").

A disadvantage of the known steel with a satisfactory ability to absorb neutrons, reduce the tendency to intergranular corrosion and stress corrosion cracking is that its use in the storage racks of the pools of spent nuclear fuel (SNF) does not ensure the safety of its storage and transportation when it contains u- 235> 5%, which is explained by the low percentage of boron in its composition.

In metallurgy, neutron-absorbing steel containing, wt.%: Is also known for use in the manufacture of hexagonal jacketed tubes for compacted storage in the storage and transportation pools of nuclear fuel.

Carbon 0.021-0.10 Silicon 0.10-0.80 Manganese 0.10-0.50 Chromium 13.0-16.0 Boron 2.1-3.5 Vanadium 0.05-0.35 Cerium 0.01-0.04 Aluminum 0.15-0.8 Titanium 4.02-10.0 Iron Rest

(Patent RU No. 2399691, CL. C22C 38/32, publ. 09/20/2010).

The disadvantage of this steel is the relatively low technological ductility, which leads to a narrowing of the temperature range during hot deformation of 1150-900 ° C, which leads to the formation of defects in the form of flaws and transverse cracks during unsteady rolling processes on TPU with pilgrim mills (when seeding and rolling in pilgrim heads )

The closest technical solution (prototype) for the manufacture of hexagonal jacketed tubes for compacted storage in pools of exposure and transportation of nuclear fuel is neutron-absorbing steel, containing, wt.%:

Carbon 0.02-0.08 Silicon 0.10-0.80 Manganese 0.10-0.50 Chromium 13.0-16.0 Boron 1,5-3,2 Vanadium 0.05-0.25 Cerium 0.01-0.04 Aluminum 0.15-0.8 Titanium 3.0-6.58 Sulfur ≤0.015 Phosphorus ≤0.020 Hydrogen ≤2ppm Iron Rest

The contents of titanium and boron are related by a relationship of 1.7≤Ti / B≤2.05, and the contents of titanium, chromium and boron by a relationship of Cr-5 (B-Ti / 2) ≥14 (RF Patent No. 2434969, Cl. C22C 38 / 32, publ. 11/27/2011).

The disadvantage of this prototype, as well as the above analogue, is the relatively low technological ductility, leading to a narrowing of the temperature range during hot deformation of 1150-900 ° C, which leads to the formation of defects in the form of flaws and transverse cracks during unsteady rolling processes on TPU with pilgrim mills (when seeding and running in pilgrim heads) and during machining - boring and turning.

The objective of the proposed corrosion-resistant alloyed neutron-absorbing steel is to use it for the manufacture of hexagonal tubes for compacted storage in fuel storage and transportation pools (FAs) with enrichment of up to 8.0% or more to ensure nuclear safety in normal operation and in emergency situations and, consequently, increasing the environmental and emergency safety of nuclear facilities, increasing technological plasticity at hot deformation temperatures, and reducing STI to intergranular corrosion and stress corrosion cracking.

The technical result is achieved by the fact that corrosion-resistant alloyed neutron-absorbing steel for the manufacture of hexagonal jacketed tubes for compacted storage in the storage and transportation pools of nuclear fuel contains carbon, silicon, manganese, chromium, boron, vanadium, cerium, aluminum, titanium, sulfur , phosphorus, vanadium, cerium, aluminum, titanium, sulfur, phosphorus and iron, characterized in that it additionally contains nickel, a limited amount of lead and bismuth in the following ratio, wt.%:

carbon 0.02-0.05 silicon 0.10-0.80 manganese 0.10-0.50 chromium 13.0-16.0 boron 2.01-3.5 vanadium 0.15-035, cerium 0.03-0.07 aluminum 0.15-0.80 titanium 4.02-8.5 nickel 0.05-0.50 sulfur 0.005-0.02 phosphorus 0.005-0.03 lead no more than 0,005 bismuth no more than 0,005 iron rest

The essence of the proposed technical solution lies in the fact that in the presence of a high boron content in steel, the ability to absorb neutrons increases while drastically lowering the technological plasticity of steel, strength properties increase, and toughness decreases. The decrease in ductility during hot deformation is associated with the formation of boride eutectics located in interdendritic spaces. The melting point of some boride eutectics falls on the heating region under hot metal pressure treatment. During hot deformation of a metal having a boride eutectic in the structure, cracks form. To prevent this phenomenon, it is necessary to bind boron to boride, the melting point of which would be higher than the temperature of hot plastic deformation. Such an element is titanium, which forms titanium boride TiB ₂ with boron, whose melting point is 2800 ° C. In addition, titanium, forming borides, as well as carbides and nitrides, contributes to the preservation of chromium in the metal matrix and thereby contributes to a high level of corrosion characteristics of steel.

The introduction of titanium into a boron-containing corrosion-resistant composition allows one to obtain good technological ductility during metal forming, increases resistance to intergranular corrosion and stress corrosion cracking in environments containing chlorides.

When titanium is introduced into steel in mass fractions equal to mass fractions of boron, it does not ensure complete conversion of boron to titanium boride TiB, nor does it ensure complete replacement of chromium in nonmetallic phases (borides, carbides, nitrides), which leads to instability of technological and corrosion properties of steel. The upper limit of the titanium content in the inventive steel is set for technological reasons: when the content of titanium in the steel is more than 8.5%, with a boron content of 2.1 to 3.5% and chromium from 13.0 to 16.0%, it is significantly difficult to conduct the final stage of steel melting and casting in the manufacture of electrodes for subsequent electroslag remelting them into ESR commodity ingots, since the metal is contaminated with films and contains an excessive amount of oxides and titanium nitrides. Therefore, when smelting this steel, it is necessary to observe the ratio of titanium to boron from 2.0 to 2.5, large values of which apply to steels with a high content of boron and titanium.

To increase technological ductility at hot deformation temperatures, it is necessary to introduce cerium into the steel, the mass ratio of which is given in the claims, and to reduce the tendency to intergranular corrosion and stress corrosion cracking, to limit the content of lead and bismuth to 0.005% and the introduction of nickel to not more than 0.5 %

Since the conversion blanks of 290 × 12 mm in size are subjected to high machinability - boring and turning to a size of 284 × 6 mm, it is proposed to introduce lead and corrosion-resistant alloyed neutron-absorbing steel in order to improve the cleanliness of the machined surfaces of the round conversion blanks: bismuth in amounts of not more than 0.005%.

The proposed steel has good technological ductility in the temperature range from 800 to 1150 ° C, which makes it possible to produce a tube billet of 470 ± x1700 ± 50 mm size from it using the ESR method for conversion to 8-16 "TPU with pilgrim mills into 290 × 12 size conversion tubes × 22000-23000 mm and their further conversion into turnkey hexagonal pipes measuring 257 × 6 × 4300 + 80 / -30 mm and other products. Corrosion tests have shown that there is no tendency to intergranular corrosion and stress corrosion cracking. steel as a material for the manufacture of hexagonal tubular cover pipes with a turnkey size of 255 mm with a wall thickness of 5.0 + 1.5 / -1.0 mm instead of the existing 257 with a wall thickness of 6 + 2.0 / -1.0 mm for storage in the storage and transportation basins of enriched nuclear fuel with 235 uranium more than 8.0%, as well as a sheet for internal protective shields in nuclear power plant reactors.

The use of this corrosion-resistant alloyed neutron-absorbing steel will allow rolling of conversion pipes with a size of 288 × 11 mm without the formation of defects in the form of flaws during the steady rolling process and longitudinal cracks during seeding and rolling of the pilgrim heads for subsequent redistribution by machining, turning, boring and profiling into commodity hexagonal jacketed tubes measuring 255 × 5 + 1.5 / -1.0 × 4300 + 80 / -0 mm for transportation and compacted storage in spent nuclear fuel storage pools. The hexagonal pipes made of the proposed steel provide reliable protection during the transportation of enriched nuclear fuel with 235 uranium of more than 8.0%, make it possible to increase environmental and emergency safety, reduce the material consumption of racks at newly commissioned and reconstructed nuclear energy facilities, and maintain and increase the position of Russia's nuclear energy industry on the world the market.

The production of the proposed steel was tested at TPU 8-16 "with pilgrim mills of conversion tubes of 290 × 12 mm in size for subsequent machining - boring, turning and profiling of turnkey hexagonal tubes of 257 + 2.0 / -1 in size, 0 × 6 + 2.0 / -1.0 × 4300 + 80 / -30 mm. Three industrial melts of steel 04Kh14T5R2F-Sh with a boron content of 2.54 or more were smelted at the Zlatoust Metallurgical Plant by electroslag remelting (ESR). up to 2.97, titanium from 4.80 to 6.00, cerium from 0.01 to 0.02% in accordance with RF patent No. 2434969 and three swimming trunks containing boron from 2.61 to 2.87, titanium from 6.00 to 6.65 and cerium from 0.05 to 0.06% in accordance with the proposed composition (six ingots 470 × 1700 mm in size with a total weight of 13, 26 tons). On melts cast in accordance with patent No. 2434969, the ratio of titanium to boron was from 1.89 to 2.09, and in experimental melts, from 2.28 to 2.38. At Chelyabinsk Tube Rolling Plant OJSC through ingots, through holes with a diameter of 100 ± 5 mm were drilled. The ingots were heated to the ductility temperature (1150 ° C), stitched in a cross-helical rolling mill into sleeves 470hvn in size. 295 × 2620 mm, which were rolled at 8-16 "TPU with pilgrim mills into 290 × 12 × 22400-22800 mm conversion lash pipes. The lash pipes were cut into four grooves, bored, turned into 284 × 6 mm and When rolling steel tubes from steel ingots of the brand according to RF patent No. 2434969 on one pipe with a ratio Ti / B = 1.89 there were flaws on the seed end, and on the pipe with a ratio Ti / B = 2.09 there were through flaws under the pilgrim head, which led to the marriage of 3 krats. 21 times were sent for machining. During machining - turning and boring due to rolled defects, two more edges were rejected: one time for the outer film and the second for the inner film. 19 hexagonal workpieces with a total weight of 3,515 tons Consumption coefficient of metal (the ratio of the mass of a given metal in production to the mass of hexagonal workpieces) for this batch of hexagonal workpieces amounted to 3,772. At the same time, three melts of steel grade 04X14T5R2F-Sh (6 ingots of ESR) cast at OAO ZMZ in accordance with the claims were set into production. The ingots were heated to the ductility temperature (1150 ° C), stitched in a cross-helical rolling mill into sleeves 470hvn in size. 295 × 2620 mm and rolled at 8-16 "TPU with pilgrim mills into conversion pipes measuring 290 × 12 × 22300-22800 mm, cut into four edges, turned and bored to a size of 284 × 6 mm and profiled into hexagonal tube blanks. There were no defects during rolling of the conversion pipes from ingots of this steel grade. 24 cents were sent for machining. During the machining process, boring and turning due to rolled defects on the outer film, which displays the wall thickness outside the negative tolerance field, was rejected one time. From this batch Fractional pipes were set to be profiled into 23-krath hexagonal billet pipes, 23 of which were obtained hexagonal billet pipes with a total weight of 4.255 tons. The metal consumption coefficient for this batch of hexagonal billet pipes was 3.116. The strength and corrosion properties of the proposed and existing steels are on one level, while plastic is significantly higher than δ by 15%, and ψ by 20%.

Thus, the proposed steel 04X14T5R2F-Sh (ChS 82 M2) is recommended for the manufacture of hexagonal workpieces and for the manufacture of racks for compacted storage of spent nuclear fuel in the storage pools at nuclear power plants and the manufacture of covers for its transportation.

Claims (1)

Corrosion-resistant alloyed neutron-absorbing steel for the manufacture of hexagonal jacketed tubes for compacted storage in the storage and transportation pools of nuclear fuel containing carbon, silicon, manganese, chromium, boron, vanadium, cerium, aluminum, titanium, sulfur, phosphorus and iron, characterized the fact that it additionally contains nickel, a limited amount of lead and bismuth in the following ratio of components, wt.%:
carbon 0.02-0.05 silicon 0.10-0.80 manganese 0.10-0.50 chromium 13.0-16.0 boron 2.01-3.5 vanadium 0.15-0.35 cerium 0.03-0.07 aluminum 0.15-0.80 titanium 4.02-8.50 nickel 0.05-0.50 sulfur 0.005-0.02 phosphorus 0.005-0.03 lead no more than 0,005 bismuth no more than 0,005 iron rest