Layer-modified stainless steel produced by additive growth

Abstract

FIELD: powder metallurgy; additive technologies.SUBSTANCE: invention relates to layered austenitic stainless steel obtained by additive growth. The steel comprises an alternating layer of steel and a layer of steel modified with nanosized particles of titanium and titanium carbide ranging in size from 50 to 100 nm in an amount of 0.1 to 0.4 wt.%.EFFECT: production of steel with high tensile strength and relative elongation.2 cl, 1 dwg, 1 tbl

Description

[0001] The invention relates to the production of stainless steels, particularly high-quality steels containing chromium and chromium-nickel, in a melting device having at least two metal receivers for supplying a steel casting plant. Stainless steels encompass a large group of chromium, chromium-nickel, and chromium-manganese-nickel steels containing over 12% Cr that retain a bright metallic luster when exposed to the atmosphere, i.e., stainless properties. Chromium increases the corrosion resistance of stainless steels.

[0002] Typically, when producing stainless steels (IPC patents C21C552, C21C7 / 58) containing chromium-nickel, an electric furnace of conventional design, implemented as a DC or AC furnace, is used in which scrap and / or other iron-containing metallic source material, such as cast iron or DRI (Direct Reduced Iron), are melted together with an adequate amount of alloying carriers. The melted semi-finished product, at a temperature of 1670 to 1700°C, is poured into a ladle. This ladle is then emptied into a container, and the resulting melt, containing approximately 2.5% carbon and approximately 1% silicon, is subjected to frying, first with oxygen and, at a reduced carbon content, with oxygen / nitrogen mixtures and later with oxygen / argon mixtures.Depending on the application of various process technologies, decarburization is carried out down to a final carbon content of less than 0.1%, and the resulting losses of chromium in the scrap must then be restored again by reaction with ferrosilicon or secondary aluminum (Povolotsky D.Ya., Gudim B.A. Stainless steel production. Chelyabinsk: Publishing house of SUSU, 1998. - 236 p.).

[0003] Patents are known for the production of austenitic and martensitic-austenitic stainless steels (for example, RU 2270269 "Steel, steel product and method of manufacturing it", IPC C22C38 / 58, C22C38 / 54, C21D8 / 06, published on 20.02.2006), as well as patents for the composition and structure of stainless steels (RU 2169205, "Stainless steel", IPC C22C38 / 38, published on 20.06.2001; US ​​5096664 "Alloys having excellent erosion resistance and stress corrosion cracking resistance", IPC C22C38 / 00, C22C38 / 38, published on 17.03.92).

[0004] Stainless steels are widely used in various industries. However, despite their excellent performance properties, they require further development to enhance their functional capabilities.

[0005] Additive manufacturing technologies for various materials, particularly metals, have recently gained widespread popularity. In this regard, well-known technologies include powder laser cladding (SLM technology) and wide-arc additive manufacturing (WAAM technology), among others.

[0006] SLM technology is an additive manufacturing process for manufacturing parts using an electronic geometric model by laser-assisted cladding of metal raw materials. Both powder and wire can be used as metal raw materials. SLM technology enables the creation of high-precision blanks.

[0007] WAAM technology uses metal wire (including powder-based wire) as the starting material. It is easy to produce, store, and transport. This technology allows for the rapid production of necessary parts and structural elements. Additive arc welding is the most productive (up to 15 kg / h) and the most common method for domestic manufacturing, as arc cladding and welding are used in virtually every enterprise that processes metals.

[0008] The most common method of 3D printing today is the method of selective laser sintering (fusion), patents US 4863538 (“Method and apparatus for producing parts by selective sintering”, IPC B05C19 / 00, B22F3 / 00, B22F3 / 105, B22F7 / 02, B23K26 / 08, B23K26 / 34, B29C41 / 12, B29C41 / 46, B29C67 / 00, C23C24 / 08, C23C24 / 10, C23C26 / 02, G05B19 / 41, published 05.09.1989) and US 5182170 (“Method of producing parts by selective beam interaction of powder with gas phase” reactant", IPC B22F3 / 00, B22F3 / 105, B23K26 / 34, B29C67 / 00, C04B35 / 622, C04B35 / 64, published 26.01.1993). This method of manufacturing metal and products requires finely dispersed powder as a raw material, or wire produced by rolling or from powders, which has good viscosity and rapid hardening.

[0009] The essence of the selective laser sintering method (US patent 4863538) is as follows. A digital 3D model of the object being formed is divided into layers in a computer, which then generates the print control program. The powder used to construct the object is placed in a sealed chamber and preheated to a temperature below its melting point. It is then laid in layers on a substrate. The powder is then smoothed with a roller, after which laser radiation scans the layer surface along the XY axes and sinters the desired contour. In the next step, the substrate is lowered by the depth of the layer, and the layer formation process is repeated. After completing the process of creating the object, it is removed from the chamber and cleaned of unsintered powder with compressed air, a brush, or a spatula. Excess (unsintered) powder can be reused; gradual cooling of the powder prevents significant deformation of the product's shape.During the printing process, the powder level is monitored as each new layer is laid down. Metal forming of parts can be performed in a protective gas environment such as nitrogen or argon to minimize oxidation processes during powder heating.

[0010] This metal fabrication technology offers several advantages: a high level of detail, satisfactory roughness of approximately Ra 12.5, and the ability to create complex generative design structures and honeycomb structures for the internal structure of the product. However, it also has a number of disadvantages: high levels of internal stress, lack of fusion of layers, anisotropy of properties, limited build size, strict requirements for powder quality (size, geometry, chemical composition, storage conditions), high cost of the technology, requirements for personnel protection from powder, and a low build speed of approximately 90 cm. 3 / h.

[0011] Also known is a method for manufacturing metal products according to patent US 6143378 ("Energetic additive manufacturing process with feed wire", IPC B29C67 / 00, C23C26 / 02, published 07.11.2000), which consists of layer-by-layer laser cladding of wire. The process of additive manufacturing of a three-dimensional object includes the following stages: directing an energy beam onto the surface of a layer, forming an area with a liquid melt on it; and moving the energy beam, and with it the melting pool, along the surface. In this case, the initial wire is fed into the central area of ​​the melting pool in such a way that the initial wire melts and enters the area with the liquid melt as needed for the manufacture of the object.

[0012] However, the strength properties of metal products after additive manufacturing by laser cladding, in particular stainless steels, are insufficient due to structural defects (porosity, etc.).

[0013] To improve the performance properties of metal obtained using known additive manufacturing methods, layered materials (bimetals) have been developed.

[0014] A layered bimetal of stainless steel and copper is known (Griroryants A.G., Shiganov I.N., Misyurov A.I., Tretyakov R.S. Laser Additive Technologies in Mechanical Engineering: A Tutorial, Bauman Moscow State Technical University, 2018, p. 278), produced by additive growth. This bimetal allows for expanded functional properties of stainless steel. A drawback is that the improvement in mechanical properties is insignificant. This limits the use of this layered metal in production.

[0015] The closest approximation to the stated structure of stainless steel produced by additive manufacturing is a layered bimetal (Trushnikov D.N., Hybrid Additive Manufacturing of Large-Size Workpieces and Finished Parts by Plasma (Arc) Surfacing of Wire Materials. Presentation, Perm National Research University), where 10Kh18N10T stainless steel is grown with 06Kh15N60M15 steel. However, during the production of this layered metal, a transition layer of reduced strength is formed at the interface. Therefore, the operational properties of such a layered metal are insufficient.

[0016] The purpose of the invention is to develop a structure of layered stainless steel with additive growth of a product that has high mechanical properties.

[0017] The technical result is achieved by the developed structure of layered austenitic stainless steel, obtained through additive manufacturing, which, like the prototype, contains alternating layers of steel. What's new is that the alternating layers consist of a successive layer of steel and a layer of steel modified with nanoscale titanium and titanium carbide particles ranging in size from 50 to 100 nm in proportions of 0.1 to 0.4% by weight.

[0018] In this particular case, the steel layers are 12X18N10T steel.

[0019] The invention is explained by a figure, which shows a diagram of the arrangement of layers in the claimed workpiece.

[0020] The proposed structure of austenitic stainless steel contains alternating layers modified and unmodified with titanium and titanium carbide particles.

[0021] The essence of additive manufacturing is the layer-by-layer deposition of metal into a product based on a 3D model. Therefore, by introducing nanoscale titanium and titanium carbide particles layer by layer into the molten metal of the product in a specific sequence, the product is strengthened. As a result, the mechanical properties of this layered stainless steel are significantly improved.

[0022] Unlike the structure of the prototype (bimetal - layered stainless steel from 10X18N10T, grown with steel 06X15N60M15), the proposed structure of layered stainless steel with alternating layers containing particles of titanium and titanium carbides does not have brittle transition layers and is more durable.

[0023] Modification of molten metal with Ti, TiC nanoparticles during layer-by-layer growth of the product was carried out using for this purpose the setup described in the work “Methods of modifying deposited metal with nanosized powders to increase the mechanical properties of welded joints” (Zernin E.A., Kuznetsov M.A. / / Modern problems of science and education. - 2014. - No. 5.).

[0024] For testing, walls were manufactured from the claimed 10Kh18N10T layered stainless steel and walls with the structure described in the prototype. The percentage of the feedstock (10Kh18N10T stainless steel) introduced into the liquid phase during additive growth of the wall with nanosized Ti and TiC particles ranging in size from 50 to 100 nm ranged from 0.1 to 0.4% by weight. Samples were then cut from the wall for tensile testing.

[0025] The study, which focused on the process of 3D printing using electric arc cladding to produce tensile test specimens, was conducted using a specially designed and built experimental setup. The experimental setup is described in "Ensuring the Performance of Additively Grown Parts in Autonomous Vehicles Used in Arctic and Far North Conditions" (Yu. G. Kabaldin, V. V. Belyakov, M. S. Anosov, D. A. Shatagin, M. V. Zhelonkin, ed. Yu. G. Kabaldin. - Nizhny Novgorod: R. E. Alekseev State Technical University). The device for 3D printing on CNC machines is protected by patent RU 2696121 (“Method of 3D printing on CNC equipment with intelligent optimization of modes”, IPC B33Y10 / 00, B22F3 / 00, published July 31, 2019).

[0026] 3D printing of a layered stainless steel wall was performed at print speeds of 350 mm / min and 400 mm / min under a protective CO2 atmosphere. The process energy input varied from 150 J / mm to 1200 J / mm. Longitudinal (along the layers) and transverse (across the layers) samples were cut from the resulting blanks.

[0027] As follows from Table 1, samples of layered stainless austenitic steel 10X18N10T, manufactured according to the stated scheme by the WAAM method, have higher values ​​of tensile strength and relative elongation than bimetal 10X18N10T - 06X15N60M15.

[0028] Table 1 - Mechanical properties of laminated stainless steel

[0029] Material Yield strength, σт Tensile strength, σв Relative elongation, δ (%) MPa 10Х18Н10Т, obtained by 3D printing with 06Х15Н60М15 steel 310 555 36 3D printing of 10X18H10T according to the stated structure (modified with Ti, TiC particles) - 0.1% by weight 318 560 36 3D printing 10X18N10T - modified with Ti (TiC) particles - 0.2% by weight 355 590 38 3D printing 10X18N10T - modified with Ti, TiC) particles - 0.3% by weight 368 634 40 3D printing 10X18N10T - modified with Ti (TiC) particles - 0.4% by weight 362 595 36

[0030] Thus, the developed samples of layered stainless austenitic steel 10X18N10T, manufactured according to the above-described scheme by the WAAM method, have higher values ​​of tensile strength and relative elongation than bimetal 10X18N10T-06X15N60M15, which has a positive effect on the properties of this material required for industry.

Claims

1. A layered stainless austenitic steel obtained by additive growth, containing alternating layers of steel, characterized in that it contains an alternating layer of steel and a layer of steel modified with nanosized particles of titanium and titanium carbide of size from 50 to 100 nm in an amount of from 0.1 to 0.4 wt.%.

2. Layered stainless austenitic steel according to claim 1, characterized in that the steel layers are 12X18H10T steel.

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