RU2539799C2 - Production of thin-wall pipes of higher precision from alloyed copper-based strain-hardened alloys - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metal forming and can be used for production of said pipes of alloyed strain-hardened alloys containing 0.4-3% of beryllium and up to 2% of nickel or cobalt. Pipe billet is reduced by cold radial forging in steps at fixed mandrel with conical working surface. Mandrel working surface is located in reduction zone. Reduction is carried out with reduction factor at every step not exceeding 1.3. Billet as-forged at previous step is subjected to homogenising tempering to solid solution by heating to above the eutectoid conversion and abrupt cooling point.

EFFECT: higher coefficient of material use.

3 cl, 1 dwg, 2 tbl, 1 ex

Description

The invention relates to the field of metal forming and can be used in the manufacture of precision tube billets from difficult to deform beryllium-containing alloys on a copper matrix (beryllium bronzes with a beryllium content of from 0.4 to 3%, nickel or cobalt - up to 2%), widely used for manufacture of sliding supports of increased elasticity, for corrosion-resistant pipes for the oil and chemical industries, which are subject to increased requirements for mechanical properties.

A known method of pressing pipes on a rigid mandrel, which includes the deformation of the workpieces through the point of the matrix on a rigid mandrel. The mandrel is removed from the pressed part of the preform when it leaves the matrix, and then the remaining part of the preform is pressed through the matrix. A device for pressing pipes on a rigid mandrel contains a container with a conical matrix installed at its output. The workpiece is pushed by the plunger through the matrix. The axial movement of the mandrel, coaxial with the matrix, container and rod, introduces the mandrel through the matrix point. The plunger is equipped with a tip with an axial cavity centering the upper end of the mandrel relative to the die during pressing (patent RU 2123900 C1, B21J 5/04, publ. 12/27/1998). A disadvantage of the known technical solution is the possibility of obtaining only a thick-walled relatively short pipe, since the extrusion of hardly deformed material, prone to strain hardening, is possible only with small hoods in a narrow range of forging temperatures, and the known method involves obtaining the product in one transition. In addition, the lack of heating of the product in the container, which leads to the pre-cooling of the preheated to forging temperature workpiece with slow hydraulic extrusion, and, therefore, to change the rheological properties and the appearance of defects in the form of a network of cracks.

A technical solution is known for manufacturing tube blanks from a hardly deformable material — hot hydrodynamic extrusion (GGDV) —which consists in implementing a scheme of comprehensive uneven compression of an extruded billet in a heated stamp in a quasi-hydraulic medium formed by a graphite jacket obtained by breaking a graphite washer placed between the heated blank punch (Severdenko A.P. Hot hydrodynamic extrusion of a cutting tool [Text:] / V.P. Severdenko, BC Muras, .Sh.Suhodrev - Minsk. Science and technology, 1974. - 274 c). The punch is equipped with a mandrel, which passes through a central hole made in a graphite washer, through a hole in the original workpiece, and then through the point of the conical matrix. During the movement of the punch, the workpiece is compressed on the mandrel by extruding the workpiece through the conical point of the matrix, and the compressed workpiece is removed from the mandrel when it leaves the matrix by the volume of graphite filling the matrix point at the final stage of extrusion. The use of a quasi-hydraulic medium and heating of the container make it possible to obtain tube blanks in 1 transition with a higher compression compared to the conventional extrusion scheme.

A disadvantage of the known solution is the possibility of obtaining a tube billet with a limited maximum drawing coefficient λ = 4 (for the indicated material). In addition, the extruded tubular billet has a conical hole, since the mandrel is tapered in order to facilitate easier billet descent, otherwise the internal cavity of the extruded billet contacts along the entire length of the mandrel, which leads to setting along the contact surfaces and the formation of a network of transverse cracks. These known technical solutions have a common drawback - the inability to obtain long thin-walled products due to limitations on the ductility of the wrought material subjected to large hoods.

A well-known technical solution are methods for the manufacture of hollow billets on mandrels, the local periodic application of radial compressive forces along the perimeter along the generatrix. Such methods are characterized by a small shift in the volume of the deformable material beyond a single compression step, which does not lead to a loss of plasticity in the process of deformation.

For example, there is a known method of manufacturing hollow forgings, which includes heating a hollow billet (cast, obtained by rolling from rolling or otherwise), installing a mandrel in its cavity and then forging the billet simultaneously with four bumps on a radial crimping machine (POM) in one or more passes with feeds and tilting (Rostovshchikov VA Technology and equipment for shaping hollow long forgings with hot radial compression [Text:] / B.A. Rostovshchikov // Forging and stamping. - 1987, No. 6. - S.10-13) . This method is characterized by high productivity, however, it is not possible to obtain thin-walled tube blanks of the required thickness. Wrought hot alloy has high thermal conductivity and a narrow range of forging temperatures to provide the required technological ductility (in the range of 0.6-0.7 Tm), Tm is the melting temperature. During hot forging of a thin-walled workpiece on a mandrel due to the high heat transfer through the contact surface of the mandrel, the tube blank is rapidly quenched, which leads to the appearance of cracks on the surface due to anisotropy of the plastic properties over the cross section of the workpiece. In addition, the mandrel mounted on the holder “floats” during hot forging in the deformation zone relative to the theoretical axis of the forging, which is the reason for the increased difference in the forging of the pipe that is deformed in the hot state.

The closest technical solution to the proposed (prototype) is a method of forming long pipes on a short mandrel, fixedly installed in the area of action of the strikers (patent RU 2248260 C1, B21 / K21 from 08/07/2003). The hot-rolled tube billet or machined concentric tube billet according to the same scheme, that is, on a fixed mandrel, is deformed and cold in one or several transitions, while the wall thickness of the desired size is achieved, the quality of the pipe improves, its difference does not exceed the permissible quantities.

The disadvantage of this method in relation to hard-deformed alloys on a copper matrix containing 0.4 - 3% beryllium, up to 2% nickel or cobalt, does not allow to obtain the final product by forging in the cold state with a degree of deformation of more than 25% due to the strong deformation hardening caused by hardening.

The objective of the method development is to obtain, with a high material utilization coefficient (CMM), long, thin, thin-walled tubes of dispersion hardening alloys on a copper matrix containing 0.4 to 3% beryllium, up to 2% nickel or cobalt from a thick-walled initial tube billet.

This result is achieved by the fact that the proposed method, in contrast to the prototype, according to which, between the forging transitions on the mandrel in the cold state, the tube stock forged at the previous transition is subjected to additional homogenizing quenching on an α-solid solution by heating above the eutectoid transformation point and quenching. Quenching provides obtaining the structure of the material of the tube billet in a non-riveted state with maximum ductility. Each cold transition is carried out with a hood (woven) no more than λ = 1.3. In order to reduce the number of transitions (and therefore, to reduce the diameter of the hole in the initial billet and increase the CMM), the pipe billet is forged in the hot state on the mandrel in the specified manner with a draw ratio of no more than λ = 3.5 to a wall thickness of more than 7 mm.

The method is illustrated in the drawing, where figure 1 shows a diagram of cold radial forging of a cylindrical tube billet.

A tool for manufacturing a precision long cylindrical tubular product by cold radial forging method contains a conical forging mandrel 2 with a minimum cone, ensuring the quality of the inner surface and high accuracy of the channel of the tubular product both in diameter and in length, fixed to the holder 7 and having an additional calibrating girdle 6 taken out of the compression zone and finally forming the inner surface 5 of the tubular product. Forging mandrel 1 is installed motionless in the area of action of the strikers 3 of the radial crimping machine (POM).

The initial tube billet 1, fixed in the grippers 4 of the manipulator, is moved translationally in the deformation zone and forged by the strikers 3 on the stationary mandrel 2, mounted on the holder 7. The grips of the manipulator provide translational and rotational movement of the workpiece relative to the strikers and the mandrel, due to which the local focus of plastic deformation, covering the pipe billet 1 around the perimeter, sequentially moves along a helical line along the axis of the workpiece. Before each cold transition, the tube billet is removed from mandrel 2 and subjected to homogenizing hardening with an α - solid solution by heating above the eutectoid conversion point and rapid cooling (into water), and the subsequent cold forging is carried out to the degree of deformation (20-30%, uk 1.2-1.3), corresponding to the minimum allowable technological plasticity.

Example

Radial forging of pipe billets from beryllium-containing alloys based on copper, consisting of:

1 alloy - beryllium - 1.8%, nickel - 0.5%, impurities - in total no more than 0.5%, copper - the rest;

2 alloy - beryllium - 2.0%, nickel - 0.4%, impurities - in total no more than 0.5%, copper - the rest.

Radial forging of pipe billets with dimensions of ⌀60 × ⌀46 (outer diameter X inner diameter) was carried out on a stationary mandrel on a POM GFM SX16 manufactured by (Gesellschaft fiir Fertigungstechnik und Maschinenbau) (AT).

The initial billets were cast cylinders with a diameter of ⌀125 mm and a length of 500 mm, obtained by the method of semi-continuous casting, with a central axial through hole drilled mechanically in them.

Hot forging blanks were heated in the high-frequency inductor to a temperature of 790 ± 10 ° С with temperature control using a photopyrometer.

Before each cold forging transition, the tube billet was quenched with an α - solid solution by heating in an inductor to a temperature of 810 ± 10 ° С, isothermal holding for 15 minutes and fixation of a metastable solid solution by rapid cooling in water (T _water <30 ° С).

Technological approbation of radial forging of pipe blanks ⌀60 × 46 was carried out according to 2 technological forging schemes. The first scheme - according to the proposed method for 6 transitions with the recommended maximum degree of deformation (drawing value λ <1.3). 2nd circuit (for 4 transitions) - with a hood exceeding the recommended one. After each transition, the pipe forging was checked visually for cracks. In the case of obtaining a defect-free pipe forging, the macrostructure was studied along cross sections that were selected in the forging sections, where forging conditions were the least favorable due to the workpiece being stiffened. The parameters and results of radial forging according to the first recommended scheme are given in table 1. Parameters and results for the 2nd different from the recommended scheme - in table.2.

Table 1 Parameters of radial forging of a tube billet ⌀60 × 46 from alloy No. 1 and No. 2 for 6 transitions by the proposed method (lot of 10 pieces for each alloy) Transition Outer diameter d mm Int. diameter, d _int , mm

Ukov (hood), $$\lambda =\frac{d_{\mathrm{one}}^2-d_{\mathrm{at}n\mathrm{one}}^2}{d_2^2-d_{\mathrm{at}n2}^2}$$

Compression, $${\lambda }_0=\frac{d_{\mathrm{one}}}{d_2}$$

d ₁ → d ₂ Initial sizes 125 62 2,100 1,316 125 → 95 "hot" 95 58 2,000 1,250 95 → 76 "hot" 76 54 1,250 1,070 76 → 71 “cold” 71 52 1,200 1,060 71 → 67 “cold” 67 fifty 1,200 1,063 67 → 63 “cold” 63 48 1,160 1,050 63 → 60 “cold” Final dimensions 60 46 Note: No defects detected during forging

table 2 Parameters of radial forging of a tube billet ⌀60 × 46 from alloy No. 1 and No. 2 for 4 transitions with differences in hood from the proposed method Transition Outer diameter d mm Int. diameter, d _int , mm

Ukov (hood), $$\lambda =\frac{d_{\mathrm{one}}^2-d_{\mathrm{at}n\mathrm{one}}^2}{d_2^2-d_{\mathrm{at}n2}^2}$$

Compression, $${\lambda }_0=\frac{d_{\mathrm{one}}}{d_2}$$

d ₁ → d ₂ Initial sizes 125 58 2.2 1.359 125 → 92 "hot" 92 54 2.2 1,296 92 → 71 "hot" 71 fifty 1.35 1,092 71 → 65 “cold” 65 48 1.33 1,083 65 → 60 “cold” Final dimensions 60 46 Note: Cracks were detected at the 3rd cold transition 71 → 65. The development of cracks subsequently led to the destruction of the workpiece.

d ₁ , d ₂ - the outer diameters of the tube stock before and after crimping for the transition;

d _VN1 , d _VN2 - inner diameters of the pipe billet before and after crimping for the transition.

The parameters of the “hot transitions” were preliminarily selected. It was found that radial forging with a draft λ≥4 per transition leads to the destruction of samples due to intense deformation. In radial forging with a yoke of γ≥3 per transition due to the considerable time required for forging, it is possible to reinforce the ends of the workpiece due to heat transfer through the grips of the manipulator, loss of ductility and the formation of end cracks.

Claims (3)

1. A method for the production of thin-walled pipes of high accuracy from alloyed strain-hardened copper-based alloys containing 0.4-3% beryllium and up to 2% nickel or cobalt, characterized in that it involves crimping the pipe billet by cold radial forging on transitions to a stationary mandrel with a conical surface located in the compression zone, which is carried out with a drawing coefficient at each transition not exceeding 1.3, while between the radial forging transitions the pipe forged at the previous transition the preparation is subjected to homogenizing hardening in an α-solid solution by heating above the eutectoid transformation point and quenching. 2. The method according to claim 1, characterized in that they preliminarily carry out hot radial forging of the tube billet heated to the forging temperature on a mandrel with a draw ratio per transition not exceeding 3.5. 3. The method according to claim 1 or 2, characterized in that they carry out hot radial forging of the tube stock with a thickness of more than 7 mm.