RU2399448C2 - Method for drawing of pipes - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method includes deformation of stock with ceramic tool, material of which is selected depending on its adhesion properties. Elimination of adhesive damage of surface metal layer is provided by the fact that adhesive properties of tool material are identified by value of tool material electrons yield, which should not be less than 4.0 eV.

EFFECT: invention is intended to improve quality of pipes surface, to produce pipes with submicron purity of surface.

2 dwg, 2 tbl

Description

The invention relates to the field of metal forming and can be used for drawing pipes with submicron surface cleanliness.

For metal forming processes, in particular pipe drawing, the adhesive interaction of the metal with the tool is characteristic. This interaction leads to the transfer of the deformed metal from the product to the tool, the consequences of which are the destruction of the surface layer of the metal (seizures, risks, transverse microcracks) and the violation of the purity of its surface (increased roughness). As for corrosion-resistant steel, the problem is compounded by the fact that due to the welding of metal on the tool it is impossible to carry out mandrel drawing of pipes by known methods.

It is known to use ceramic materials based on refractory compounds, for example, tungsten carbide, titanium carbide as a tool material [Berin I.Sh., Dniester N.Z. Drawing tool. M.: Metallurgy, 1971. S27-28].

Ceramic material (ceramic) is a material based on refractory compounds, i.e. compounds of non-metals of III-VI groups of the periodic system of elements with each other and (or) with any metals. Such compounds are borides, carbides, nitrides and metal oxides or complex compounds based on them. The term ceramics refers to bulk bodies, films, coatings. A special case of ceramics are composite materials (cermets or hard alloys), consisting of one or more ceramic and metal phases. Borides, carbides, nitrides, and metal oxides are usually used as ceramic phases, and metals, for example, Co, Ni, Mo, etc., are used as metal phases [P.82-85, Dictionary-reference for new ceramics / Shvedkov EL, Kovensky I.I., Denisenko E.T., Zyrin A.V .; Repl. ed. Trefilov V.I .; USSR Academy of Sciences. Inst. Materials Science I.N. Frantsevich. - Kiev: Science. Dumka, 1991. - 280 p.].

As for the practical application of ceramic materials, their use is based on high hardness, which in practice is considered equivalent to “high wear and abrasion resistance”. As practice shows, various refractory compounds with similar hardness characteristics exhibit different activity with respect to the same metal (and vice versa) in terms of adhesive interaction. There are currently no criteria that would allow a choice between different materials with similar hardness characteristics.

A known method of controlling the adhesive strength of adhesive joints [A.S. USSR No. 1000863, G01N 19/04, publ. 02/28/1983]. In this method, before gluing the elements, the magnitude of the work function of the electrons from the surfaces to be bonded is measured. The electron work function depends on surface quality. The magnitude of the work function of the electrons is used to judge the quality of surface preparation, which allows predicting the adhesion strength: the greater the work function of the electrons corresponds to a greater adhesive strength of the adhesive joint.

A known method for determining the adhesion ability of a coating to an inorganic substrate [A.S. USSR No. 1390542 A1, G01N 21/17, publ. 04/23/1988]. In this method, the photoemissive current of the substrate is measured before coating and the substrate with the coating portions after it is removed. The presence of organic substances with an electron work function different from the substrate on the surface of the substrate leads to a change in the photoemissive current. The relative change in the photoemission current determines the presence of organic substances on the surface of the substrate, which allows us to judge the adhesive ability of the coating to the substrate.

A known method of drawing pipes, including the deformation of the workpiece with a tool made of a material that prevents aluminum from sticking to it [RF Patent No. 2296635 C1, publ. 04/10/2007 - prototype].

A sign similar to the distinguishing feature of the proposed method is the implementation of the tool from a material that prevents metal from sticking to it, namely, from an alloy based on nickel, the nickel content of which exceeds 74 wt.%. An essential feature in the claimed method is the implementation of the instrument from a material with certain physical properties, namely, from a material whose electron work function is not less than 4.0 eV.

The known method has the following disadvantages. The use of a tool made of nickel-based alloy is limited to drawing aluminum blanks.

The technical problem to which the claimed invention is directed, is to improve the quality of the surface of the pipes by eliminating the adhesive destruction of the surface layer of the metal and ensuring the roughness of its surface by the parameter R _a not more than 1.0 μm.

The choice of the value of the parameter R _a not more than 1.0 μm is justified by the requirements of technical conditions (TU 14-ZR-760-2006, TU 14-159-295-2004, TU 14-161-216-2003), according to which the roughness of the inner surface of the pipes according to the parameter R _a should be no more than 1.0 microns.

This problem is solved by the fact that in the method of drawing steel pipes, including selecting a tool material and deforming a workpiece with a tool made of ceramic material, according to the invention, the tool material is selected from the condition of the electron work function of the material of at least 4.0 eV.

The essence of the invention lies in the fact that the metal is deformed by a tool made of a ceramic material with certain physical properties, namely, from a material whose electron work function is not less than 4.0 eV.

The stated value of the work function of the electrons of the material of the tool provides a qualitative change in the mechanism of adhesive interaction of the tool with the metal. This change consists in the fact that the destruction of the adhesive bonds (welding bridges) between the tool and the metal does not occur in the surface layer (volume) of the metal, but along the boundary (surface) of the contact of the tool with the metal and is not a process of cohesive fracture of the metal, but a break in the adhesive ties along the tool-metal boundary. As a result, the destruction of the surface layer of the metal is excluded, which ensures a qualitative change in the surface roughness of the pipes in the inventive drawing method compared to the known one.

The choice of the value of the work function of the material of not less than 4.0 eV is justified by the fact that this value, as established experimentally, ensures the elimination of the destruction of the surface layer of the metal and the achievement of its surface roughness in the parameter R _a not more than 1.0 μm.

The upper value of the electron work function of the material is not specified, since it is not practical to limit it: the greater the work function of the material’s electrons, the lower the intensity of electron emission from its surface and the lower the intensity of adhesive interaction.

The essence of the adhesive interaction of the tool with the metal is as follows. When two solids come closer to a distance commensurate with the lattice parameters, valence electrons combine and a common electron cloud forms, interacting with atoms of both surfaces. The formation of such a metal bond is an adhesive interaction (adhesion, adhesion) of two solids [Sakhatsky G.P. Technology of welding metals in the cold state [Text] / GP Sakhatsky. - Kiev: Naukova Dumka, 1979. - 296 p.].

In the process of friction, the tool material is subject to energy: mechanical and thermal activation. Elastic deformation and heating of the material increase the energy of its atoms. Weakly bound electrons in excited atoms are thrown to higher energy levels, which leads to an increase in the lattice energy and, as a consequence, to a decrease in the electron work function. The same processes occur in a deformable metal. The effect of the energy effect on the material is reduced, in essence, to the activation of exoelectronic emission from its surface and, thereby, to ensure intense electronic exchange between the friction surfaces [A.S. USSR No. 938094, G01N 3/56, publ. 06/23/1982, Deryagin P.V., Krotova N.A., Smilga V.P. Adhesion of solids. M .: Nauka, 1973. P. 57-56].

Refractory compounds: carbides, nitrides and metal oxides have different types of bonds, more precisely, different ratios of metal, covalent, ionic interactions. These differences manifest themselves in different values of the electron work function, which determines the energy threshold of excitation of the material. The higher this threshold, the greater the energy cost for exciting the material and the release of electrons from its surface.

Table 1 shows the electron work function of a number of ceramic materials based on refractory compounds: carbides (WC, SiC, ZrC, B ₄ C), nitrides (TiN, AlN, Si ₃ N ₄ , BN), oxides (Al ₂ O ₃ , ZrO ₂ ) metals and combined compounds (TiCN, (TiCN) _m O _n ). The emission properties of these materials were investigated using the method of photostimulated exoelectronic emission. Samples were made in the form of tablets with a diameter of 10 mm and a thickness of 1 mm. The surface of the samples is treated with a diamond wheel and polished with a diamond paste to a roughness of R _a = 0.32 μm. The studies were performed on an automated scanning flaw detector [Kortov BC Exoemission computer topography: hardware implementation and practical applications / V. S. Kortov [et al.] // Defectoscopy. - 1996. - No. 1. - S.50-60].

As can be seen from table 1, the claimed value of the electron work function is satisfied by materials based on the following refractory compounds: SiC, B ₄ C, ZrC, BN, Si ₃ N ₄ , TIN, AlN, TiCN, (TiCN) _m O _n , ZrO ₂ . Moreover, the choice of materials based on oxides and combined compounds, as follows from table 1, is preferable in comparison with carbides and nitrides.

Example. Pipes were made from corrosion-resistant steel grade 08X18H10T.

Pipes 12 × 1.2 mm in size were made by drawing on a mandrel. Pipes were drawn along the route 16 × 1.5 → 12 × 1.2 mm with a draw ratio of 1.68. As a process lubricant, chlorinated paraffin brand HP-600 was used. The surface of the mandrel is treated with a diamond wheel and polished with a diamond paste to a roughness of R _a = 0.32 μm.

When drawing according to the described method, as the ceramic material of the mandrel selected materials based on refractory compounds:

- titanium carbonitride (Material composition: 78% TiCN - Mo, Ni. The electron work function of the material is 5.2 eV (see Table 1));

- titanium oxycarbonitride (Material composition: at least 70% (TiCN) _m O _n - Zr, Ta, Nb. The electron work function of the material is 5.5 eV (see Table 1));

- zirconium dioxide (Material composition: ZrO ₂ - 20% Al ₂ O ₃ - 4% Y ₂ O _3. The electron work function of the material is 5.8 eV (see Table 1)).

To obtain comparative data, pipe drawing was carried out in a known manner. When drawing according to the known method, a material based on tungsten carbide was used as the ceramic mandrel material. Material Composition: WC - 15% Co. The electron work function of the material is 3.8 eV (see Table 1).

The adhesive interaction of the tool with the metal was evaluated by the state of the inner surface of the pipes before and after drawing. The surface condition was assessed by determining the roughness parameter R _a according to GOST 2789-73. The parameter R _{a was} measured in accordance with GOST 2789-73 and was carried out on a model 296 profilometer (type II). According to the measurement results, the minimum and maximum values were determined, and the sample average value of the parameter R _{a was} calculated. The data are presented in table 2 and are illustrated in figure 1, 2.

As can be seen from table 2, in comparison with the known, the proposed method of drawing ensures the achievement of surface roughness of the pipe by the parameter R _a not more than 1.0 μm.

The figure 1 shows the dependence of the roughness of the pipe surface on the work function of the electrons of the tool material.

In figure 2 - the roughness of the surface of the pipe and a diagram of the electron work function of ceramic materials.

In figure 1 it can be seen, the greater the work function φ, the lower the average roughness parameter R _a . This dependence is described by a linear equation with an approximation confidence coefficient of R ² = 0.9987. The scattering field of the parameter R _a , limited by thin lines in FIG. 1, also depends on the work function: the larger the work function, the smaller the scattering field of the roughness parameter R _a . These results show that the adhesive interaction is associated with the work function of the electrons: the greater the work function of the electrons, the less the adhesive interaction of the tool with the metal.

From figure 1 it also follows: to achieve submicron cleanliness of the surface of the pipes with a roughness parameter R _{a of} not more than 1.0 μm, the electron work function must be at least 4.0 eV.

As can be seen from figure 2, the claimed value of the electron work function is satisfied by materials based on the following refractory compounds: SiC, B ₄ C, ZrC, BN, Si ₃ N ₄ , TIN, AlN, TiCN, (TiCN) _m O _n , ZrO ₂ . Moreover, the choice of materials based on oxides and combined compounds, as follows from figure 2, is preferable in comparison with carbides and nitrides.

Table 1 Work function of electrons of ceramic material Ceramic material Work function, φ, eV Connection type Main cast Carbides WC 3.8 SiC 4.0 At _{4 s} 4.3 Zrc 4.6 Nitrides Bn 4.4 Si ₃ N ₄ 4.7 TiN 4.9 A1N 4.9 Combined TiCN 5.2 (TiCN) _m O _n 5.5 Oxides ZrO ₂ 5.8

table 2 The composition and the work function of the electrons of the tool material, the surface roughness of the pipes in the manufacture of known and proposed methods Drawing method Tool Material Composition Work function, eV The surface roughness of the pipes, R _a , microns before drawing after drawing famous WC - 15% Co 3.8

proposed 78% TiCN - Mo, Ni 5.2

not less than 70% (TiCN) _m O _n - Zr, Ta, Nb 5.5

ZrO ₂ - 20% Al ₂ O ₃ - 4% Y ₂ O ₃ 5.8

Claims (1)

A method of drawing steel pipes, including selecting a tool material and deforming a workpiece with a tool made of ceramic material, characterized in that the tool material is selected from the condition of the electron work function of the material of at least 4.0 eV.

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