RU2790333C1 - Method for production of thin microcrystal wide tapes of stainless nickel chromium steel of austenite grade by melt spinning - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular to the production of microcrystal tapes intended for creation of high-temperature superconductors on a tape carrier of stainless nickel chromium steel of an austenite grade by spinning a melt on a single-roll installation. A method for the production of a microcrystal tape of stainless nickel chromium steel of an austenite grade by melt spinning includes obtainment of a melt of stainless nickel chromium steel of an austenite grade and formation of fast-cured steel in the form of a tape by brining the melt into contact with a surface of a rotating cooling roll. Stainless nickel chromium steel of an austenite grade is melted, brought into contact with a surface of a rotating copper water-cooled crystallizer roll, and a tape is formed with a width of 27 mm, thickness of 41 or 44 mcm by extrusion of the melt under pressure of 0.3-0.9 MPa through a nozzle with a rectangular hole vertically upward to the specified copper water-cooled crystallizer roll rotating relatively to the horizontal axis with a linear rotational speed of 20-40 m/s. At the same time, stainless nickel chromium steel is melted, having a carbon content of ≤0.2 wt.%, total silicon and manganese content of 2.5-4.5 wt.%, total phosphorus and sulfur content of ≤0.05 wt.%, wherein the manganese content is ≤2 wt.%, phosphorus content is ≤0.03 wt.%, and the ratio of a chromium content to iron is 0.46-0.48.

EFFECT: resulting continuous integral tapes have high physical and mechanical properties, resistance to high-temperature oxidation, and a linear expansion temperature coefficient in longitudinal and transverse directions of a spinning track within (10-20)·10⁶ K^-1.

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Description

The invention relates to metallurgy, in particular to the production of thin wide microcrystalline tapes, promising for the creation of high-temperature superconductors on a tape carrier, from austenitic stainless chromium-nickel steel by melt spinning on a single-roll installation. A set of requirements is imposed on tape high-temperature superconductors for products with a wide range of applications: variable tape width from 5 to 100 mm without thickening, high tensile strength, high current-carrying capacity, high values of generated magnetic fields, operability in a wide temperature range. Taking into account the specifics of the fabrication of high-temperature tape-type superconductors, most of these requirements can be met by manufacturing a high-quality tape-substrate. The economic efficiency of the implementation of methods for direct production of cast strip and strip directly from the melt is obvious, associated with a sharp reduction in investment costs and significant energy savings, compared with traditional rolling methods.

A known method for producing powder, fiber or tape from the melt (RU 95 102 577 A1, 22.02.1995) heat-resistant and carbon steels, such as chromium-nickel and stainless steels, metals and alloys with a low melting point, such as aluminum, copper. According to the method, which includes applying a layer of slag to the surface of the melt and immersing a rotating cooled disk into the melt, a layer of slag is applied to the surface of the melt, the thickness of which is inversely proportional to its viscosity, which varies within 2°С 10 Pa⋅s, and the disk is immersed with a change in the linear speed in the contact zone of the disk with the melt, which ensures the production of a homogeneous product from the melt of heat-resistant and carbon steels at high process productivity. The disadvantages of the method are the complexity of controlling the geometric parameters of the product (width and thickness of the tape), which is regulated by the system of raising/lowering the mold disk and depends on the melt level, the decrease in the level of which leads to the breakage of the tape, and the absence of the above possibility of forming tapes longer than 10 meters. There is also contamination of the belt surface with slag material.

A known method for producing thin sheets-tapes and devices for its implementation (RU 2002 119 233 A, 07/16/2002), including the supply of liquid metal into the gap formed by a pair of rotating cooled mold rolls with the issuance of solidified metal in the opposite direction from the liquid metal supply side, the end part of which on one or both sides is protected by a fixed heated or unheated plate or plates, characterized in that the formation of sheets-tapes during casting is carried out from a container of liquid metal formed by at least two pairs of rolls, molds with the introduction of liquid metal into the formed container through one or both ends of the block of rolls. The disadvantage of the known method is the complexity of the multi-roll design, the features of which exclude the possibility of forming tapes with a width of more than 15 mm and a length of more than 5 meters from materials with a melting point above 1400°C, as well as controlled creation of a directed microcrystalline structure. The method includes the need to close the metal mirror in the inter-roll space with slag or heat-insulating filling, which leads to contamination of the belt surfaces with the material used for these purposes.

The closest in technical essence to the claimed invention is a method for producing a rapidly hardened alloy for a magnet (RU 2 255 833 C1, 30.06.2003), selected as a prototype. A well-known patent discloses a process for producing a rapidly solidified alloy, comprising obtaining a melt and forming a rapidly solidified alloy with an average crystal grain size of approximately 10 ^{-9 to} 10 ^-6 m. The melt has a composition represented by the general formula (Fe _1-m T _m ) _100-xyz Q _x R _y M _z , where T is Co and/or Ni; Q is B and/or C; R-rare earth element, M is selected from Al, Si, Ti, V, Cr, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au and Pb, with mole fractions x, y, z and m satisfy the following inequalities: 10 at.% ≤ x ≤ 35 at.%; 2 at.% ≤ y ≤ 10 at.%; 0 at.% ≤ z ≤ 10 at.% and 0 ≤ m ≤ 0.5. At the stage of forming a rapidly solidified alloy, the melt is poured onto a guide element, the guide surface of which forms an angle of inclination with respect to the horizontal plane, and the melt flowing down the guide surface is fed through the opening of at least one pouring channel to the contact section of the surface of the chill roll at a rotation speed of 15 m / s, as a result, a rapidly solidified alloy in the form of thin strips with a uniform thickness can be obtained at a constant cooling rate. Significant disadvantages of the known method are:

- the presence of a rare earth element in the melt, which adversely affects the material efficiency;

- to obtain a nanocomposite alloy, it is of great importance how the conditions for rapid cooling and solidification of the molten alloy are set, since these conditions should determine the specific structure (for example, the percentage of amorphous phases) of the resulting rapidly solidified alloy, which significantly reduces the possibility of controlled creation of a directed microcrystalline structure ;

- at the stage of formation of a rapidly solidified alloy, a guide element is installed in such a way as to provide a distance of about 1 to about 50 mm between the end of at least one casting channel and the surface of the cooling roll with a low rotation speed, which introduces additional temperature losses of the melt before it contacts the mold and significantly affects the microcrystalline structure, increasing the grain misorientation angle, which entails an increase in surface roughness above R _z =800 nm.

The disadvantages of the known methods, including the prototype, include the impossibility of obtaining long tapes with a width of more than 20 mm and a thickness of 30 μm or more from austenitic stainless chromium-nickel steel with a high melting point, resistant to high-temperature oxidation with a high temperature coefficient of linear expansion in the longitudinal and transverse to the spinning track, with a controlled microcrystalline structure represented by elongated grains oriented perpendicular to the spinning track.

The technical result of the present invention is the creation of a method for producing thin microcrystalline wide tapes of austenitic stainless chromium-nickel steel by the melt spinning method, more than 5 m long, 27 mm wide, 41 or 44 μm thick in the microcrystalline state, resistant to oxidation up to 900 ° C by the melt spinning method austenitic stainless chromium-nickel steel suitable for the production of second-generation high-temperature superconductors. The spread of grain sizes in the tape is from about 1-2 μm to about 17 μm, there are also individual grains up to 25 μm in size, which ensures the ultimate strength σ _of 550-600 MPa. The roughness parameters of the sides of the tape are in the range R _z =300-500 nm.

The technical result is achieved due to the fact that in the method for producing thin microcrystalline wide tapes from stainless chromium-nickel steel of the austenitic class by melt spinning, including the production of a melt in a crucible by induction melting in an inductor with a power of 60-100 V from steel grade 20X23H18, the melt is extruded under a pressure of 0 ,3-0.9 MPa through a nozzle with a rectangular hole vertically upwards onto a copper mold roll, while the rotation speed relative to the horizontal axis is provided within 20-40 m / s. At the same time, stainless chromium-nickel steel with a carbon content ≤0.2 wt. %, the total content of silicon and manganese 2.5-4.5 wt. %, the total content of phosphorus and sulfur ≤0.05 wt. %, and the content of manganese ≤2 wt. %, phosphorus content ≤0.03 wt. %, and the ratio of chromium to iron is 0.46-0.48.

It has been determined that the ratio of chromium to iron content in the original steel is an important parameter: for example, with its value from 0.46 to 0.48, the spinning process makes it possible to obtain continuous integral tapes with a length of more than 5 meters. When the ratio changes to a smaller side, a longitudinal stratification of the tape into strips 4-8 mm wide occurs, while maintaining a thickness of about 30 microns at lengths up to 50 cm. When the ratio changes to a larger side, deformation and a transverse through violation of the integrity of the tape occur, most likely caused by an increase in fragility and a significant difference in the thermal conductivity of the materials of the copper mold and the spinning tape. Also samples of tapes with a ratio of chromium to iron content of 0.47 have a higher resistance to high temperature oxidation.

If the ratio of the components of the composition of steel grade 20X23H18 deviates from the declared ones (carbon ≤0.2 wt.%, the total content of silicon and manganese 2.5-4.5 wt.%, the total content of phosphorus and sulfur ≤0.05 wt.%, the content manganese ≤2 wt.%, phosphorus content ≤0.03 wt.%) to a greater extent leads to a decrease in the resistance of the resulting tapes to high-temperature oxidation, and to a smaller one leads to steel embrittlement and the impossibility of obtaining single tapes longer than 5 meters.

The melt is extruded at a pressure of 0.3-0.9 MPa through a nozzle with a rectangular hole vertically upwards onto a copper mold roll, at a pressure below 0.3 MPa it is impossible to continuously supply the melt into the contact zone with the mold, resulting in frequent breaks and single tapes 40-50 cm long are formed, at a pressure above 0.9 MPa, the meniscus shape is perturbed, which leads to the formation of a tape with torn edges and makes it unsuitable for use as a substrate tape for the production of high-temperature superconductors on a tape carrier.

Rotation speeds relative to the horizontal axis should be in the range of 20-40 m/s, at a speed of less than 20 m/s, directional grain growth from the surface of the mold to the outer surface of the tapes is not achieved, but an equiaxed microcrystalline structure of the tape is formed, which entails an increase in roughness surface above R _z =600 nm, at speeds above 40 m/s, a partial amorphization of the tape layer occurs from the side in contact with the mold, which significantly reduces the ultimate strength σ _in .

The practical implementation of the proposed technical solution was carried out according to the following developed scheme:

- obtaining in an induction furnace with a stuffed lining of a steel ingot of a precision composition,

- loading a portion of the original steel in a crystalline state into the melting crucible of the pouring machine and secondary melting, heating to the temperature required for pouring and pouring;

- the melt is fed from bottom to top through a metal wire, which is a quartz tube;

- extrusion of the melt from the melting crucible by inert gas pressure along the metal pipeline upwards to the pouring unit (in order to compensate for the cooling of the melt in the metal pipeline, induction heating is carried out in the upper part of the metal pipeline);

- spinning of the melt on the surface of a copper water-cooled roll-mould rotating about a horizontal axis.

The essence of the invention is illustrated by the following figures:

in fig. 1 - scheme of spinning with bottom melt supply;

in fig. 2 - SEM image of the surface of the tape obtained by melt spinning a) glossy side, b) matte side;

in fig. 3 - a typical map of the distribution of crystallographic orientations of the material of the tapes, compiled for cross sections

In FIG. 1 shows a diagram of the spinning method with the lower melt supply: 1 - mold roll; 2 - heated crucible with melt; 3 - the resulting tape; 4 - filling nozzle; 5 - metal wire; 6 - inductor.

In FIG. Figure 2 shows the SEM image of the tape surfaces, the difference of which is due to the difference in the conditions of melt crystallization upon contact with the mold. The glossy side (2a) of the tape faces the mold, the matte side (2b) was formed in air. The results of the study of the elemental composition indicate a greater degree of influence of the technological parameters of the process on the distribution of elements over the thickness of the tape than segregation of elements in the thickness of the crystallizing melt. The roughness parameters of the sides are respectively equal to R _zgl =300 nm and R _zsh =500 nm.

Qualitative analysis of crystallographic orientation maps (Fig. 3) indicates directed grain growth from the mold surface to the outer surface of the ribbons. An estimate of the average grain length in the sample gives a value of about 10 µm. The scatter of grain sizes ranges from about 1–2 µm to about 17 µm; there are also individual grains up to 25 µm in size.

Experimental studies were carried out on the equipment of the Center for the Collective Use of Scientific Equipment "Composition, Structure and Properties of Structural and Functional Materials" of the National Research Center "Kurchatov Institute" - Central Research Institute of KM "Prometey" with the financial support of the Ministry of Science and Higher Education - agreement No. 13.TsKP.21.0014 (075 -11-2021-068). The unique identification number is RF-2296.61321X0014.

Example 1

Steel smelting was carried out in an induction furnace PPI-0.06, with a capacity of 60 kg for iron, with a rammed lining. Pouring was carried out through a casting ladle into cast iron molds, with the production of 40 kg of ingot from each heat. The goal was to obtain the required chemical composition of steel grade 20Kh23N18 with a carbon content of ≤0.2 wt. %, the total content of silicon and manganese 2.5-4.5 wt. %, the total content of phosphorus and sulfur ≤0.05 wt. %, and the content of manganese ≤2 wt. %, phosphorus content ≤0.03 wt. % and maintain the ratio of chromium content to iron content close to 0.47. The teapot-type casting ladle was warmed up at the ladle heating stand to a temperature of 650-750°C for 90-120 minutes. The following materials were used as a charge: armco iron type 1 -TS 00187895; ferrochrome low-carbon grade FKh015A - GOST 4757-91; nickel grade N-1-GOST 849-2008; electrolytic manganese Mn998 - GOST 6008-90; ferrosilicon brand FS75 - GOST 1415-93; aluminum brand A7 - GOST 11069-2001; ligature nickel-magnesium-cerium - TU 14-2R-338-2000. The temperature of the melt at the outlet from the furnace was in the range of 1570-1590°C. With the help of an overhead crane, the casting ladle was removed from the ladle heating stand, brought under the spout of the rising furnace, and the melt was discharged. The melt was then merged through a mounted funnel on a profitable mold extension to obtain a 40 kg ingot. As a result of melting, the content of elements in the ingot was achieved that met the requirements for the chemical composition and the ratio Cr/Fe=0.47; .

After the secondary melting of steel in the melting tank of the pouring machine and heating to the required temperature of 1570-1590 ° C, an inert gas was supplied to the melting tank at a pressure of 0.9 MPa, which squeezed the melt from the melting volume to the surface of the hardening roll, the mold rotation speed was 40 m/s . Wetting the surface of the roll, the melt moved along with it, forming a ribbon on the surface, the cooling rates in this case being 10 ⁵ ... 10 ⁶ K/s. The tape was separated from the surface of the roll by a stream of air supplied to the tape stripper. The width of the resulting tape was 27 mm, the average measured thickness was 44 microns, the length of individual tapes was more than 5 meters. The tensile strength (σ _in ), investigated by the tensile method according to GOST 1497-84 on the equipment Zwick/RoellZ 250 was 550 MPa, the roughness of the sides was R _z =300-400 nm. The average grain size is 2-4 microns. The temperature coefficient of linear expansion in the longitudinal and transverse directions of the tape spinning track was 16-17*10 ⁶ K ^-1 . Tape samples are resistant to oxidation up to heating up to 1000°C.

Example 2

Steel smelting was carried out in an induction furnace PPI-0.06, with a capacity of 60 kg for iron, with a rammed lining. Pouring was carried out through a casting ladle into cast iron molds, with the production of 40 kg of ingot from each heat. The goal was to obtain the required chemical composition of steel grade 20Kh23N18 with a carbon content of ≤0.2 wt. %, the total content of silicon and manganese 2.5-4.5 wt. %, the total content of phosphorus and sulfur ≤0.05 wt. %, and the content of manganese ≤2 wt. %, phosphorus content ≤0.03 wt. % and maintain the ratio of chromium content to iron content close to 0.47. The teapot-type casting ladle was warmed up on the stand for warming up the ladles to a temperature of 650-750°C for 90-120 minutes. The following materials were used as the charge: armco iron type 1-TC 00187895; ferrochrome low-carbon grade FKh015A - GOST 4757-91; nickel grade N-1-GOST 849-2008; electrolytic manganese Mn998 - GOST 6008-90; ferrosilicon brand FS75 - GOST 1415-93; aluminum brand A7 - GOST 11069-2001; ligature nickel-magnesium-cerium - TU 14-2R-338-2000. The steel temperature at the outlet from the furnace was in the range of 1570-1590°C. With the help of an overhead crane, the casting ladle was removed from the ladle heating stand, brought under the spout of the rising furnace, and the melt was discharged. The melt was then merged through a mounted funnel on a profitable mold extension to obtain a 40 kg ingot. As a result of melting, the content of elements in the ingot was achieved that met the requirements for the chemical composition and the ratio Cr / Fe = 0.48, after crystallization, the ingot was taken out of the mold and sent to the cutting and stripping area to prepare for further processing to obtain a tape by melt spinning .

After the secondary melting of steel in the melting tank of the pouring machine and heating to the required temperature of 1570-1590 ° C, an inert gas was supplied to the melting tank at a pressure of 0.3 MPa, which squeezed the melt from the melting volume to the surface of the hardening roll, the mold rotation speed was 20 m/s . Wetting the surface of the roll, the melt moved along with it, forming a ribbon on the surface, the cooling rates in this case being 10 ⁵ ... 10 ⁶ K/s. The tape was separated from the surface of the roll by a stream of air supplied to the tape stripper. The width of the tape obtained was 27 mm, the average measured thickness was 41 microns, the length of individual tapes was more than 5 meters. The tensile strength (σ _in ), investigated by the tensile method according to GOST 1497-84 on the equipment Zwick/RoellZ 250 was 600 MPa, the roughness of the sides was R _z =500-600 nm. The average grain size is 4-6 microns. The temperature coefficient of linear expansion in the longitudinal and transverse directions of the tape spinning track was 16-17*106K ^-1 . Tape samples are resistant to oxidation up to heating up to 900°C.

The use of a method for producing thin microcrystalline wide tapes from austenitic stainless chromium-nickel steel by the method of melt spinning is promising for the manufacture of substrate tapes with desired characteristics, which will ensure the production of high-temperature superconductors and the corresponding implementation at enterprises representing the real sector of the Russian economy.

Claims (1)

A method for producing a microcrystalline strip of stainless chromium-nickel steel of austenitic class by melt spinning, including obtaining a melt of stainless chromium-nickel steel of austenitic class and forming a fast-hardening steel in the form of a ribbon by bringing the melt into contact with the surface of a rotating chill roll, characterized in that the stainless chromium-nickel steel of austenitic class is melted containing carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel and the rest - iron, bring it into contact with the surface of a rotating copper water-cooled mold roll and form a tape 27 mm wide, 41 or 44 microns thick by extruding the melt under pressure 0 3-0.9 MPa through a nozzle with a rectangular hole vertically upwards onto the specified copper water-cooled mold roll rotating about the horizontal axis with a linear rotation speed of 20-40 m/s, while stainless chromium-nickel steel is melted with a content carbon content ≤0.2 wt. %, the total content of silicon and manganese 2.5-4.5 wt. %, the total content of phosphorus and sulfur ≤0.05 wt. %, and the content of manganese ≤2 wt. %, phosphorus content ≤0.03 wt. %, and the ratio of chromium to iron is 0.46-0.48.

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