RU2613256C1 - Manufacturing method for welded titanium tubes - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: tube blank (3) is received by bending flat sheet blank (2) and welding longitudinal edges (1). Rotary rolling of a weld (4) of a tube blank (3) mounted on a rotating mandrel (5) by means of pressing elements (6) of the hard tool (7) is performed. Annealing of welded titanium tube (8) is carried out to remove the residual stresses. Therein rolling of the weld (4) is produced with relative deformation of 8%≤ε≤20% along the wall thickness of tube blank (3), wherein ε=(t₀-t)/t₀×100%, where t₀ is the wall thickness of the tube blank (3), t is the wall thickness of the welded titanium tube (8) after rolling the weld (4) and subsequent annealing - at temperature (T_rs-170)°C≤T_ann≤(T_rs-50)°C which is determined from the range, where T_rs is the temperature of recrystallization start of the titanium alloy,°C.

EFFECT: increased strength and cycle life of welded titanium tubes through the optimal selection of thermomechanical processing parameters for tube round billets.

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Description

Technical field

The invention relates to the processing of metals by pressure, and in particular to methods of manufacturing pipes by welding seams with subsequent rotary rolling on mandrels and heat treatment, and can be used in the field of engineering and other industries, in the production of thin-walled pipes, mainly from titanium alloys.

State of the art

A known method of manufacturing especially thin-walled pipes, mainly from titanium alloys and stainless steel (description of the invention to patent 2047966 of the Russian Federation, IPC B21C 37/08 from 02.24.1994, publ. In bulletin No. 31 10.11.1995, authors Egorov V.G., Kovalev R.N., Tafintsev E.A., Shabunin I.N., analogue), including the production of tubular blanks from a sheet, flanging of edges for joints 1.6 to 2.4 thicknesses of blanks, welding of joints with the formation of a weld with a width of 6 -8 thickness of blanks. Despite the high quality of the weld obtained as a result of the implementation of the known method, there are differences in the mechanical characteristics of the material of the weld itself, the heat-affected zone and the base metal. The weld is a stress concentrator when loading the pipeline with internal pressure, which leads to its low resource.

A known method of manufacturing thin-walled axisymmetric vessels (description of the invention to patent 2131787 of the Russian Federation, IPC B21D 51/10, 22/16 from 02/04/1998, published in bulletin No. 1720.06.1999, authors Golub VV, Egorov V.G. , Nevstroyev Yu.A., Zakharchenko ND, analogue), including cutting flat sheet blanks, obtaining the cylindrical part of the prefabricated vessel by convolution of the flat sheet preform and welding longitudinal edges, shaping the bottom of the prefabricated vessel, welding the bottom and cylindrical parts of the prefabricated vessel, rotary hood with Court is rolled with simultaneous circumferential and longitudinal welds. As a result of the implementation of the method, the microstructure of the welds and heat-affected zones becomes identical to the base metal after rolling. At the same time, the welds are no longer stress concentrators when pressure drops of the working medium and the cyclic durability of the products increases. Disadvantages: in the known method, heat treatment of finished tubular products is not provided, which is unacceptable for titanium alloys due to the occurrence of excessive residual stresses that lead to the destruction of the walls of the welded pipe over time. In addition, the relative deformation ε over the wall thickness is not limited by anything, which increases the likelihood of microcracks in the heat affected zone of the weld, which serve as centers for the development of fatigue cracks during subsequent operation of the product.

A known method of manufacturing welded titanium pipes (Production of welded high-resource pipeline / Guiding technical material RTM 1.4.1999-90. - M .: NIAT, 1992. - S.113-117. - prototype), including obtaining a tube stock by convolution of a flat sheet stock and welding of longitudinal edges, rotational rolling of a weld seam of a tubular billet mounted on a rotating mandrel using hard tool pressing elements, annealing of a welded titanium pipe to relieve residual stresses. In a known manner, high-quality welded pipes of deformable titanium alloys VT 1-0 and PT-7M are obtained with a minimum permissible deviation in diameter and minimum non-circularity, with a surface roughness of not higher than Ra 1.6 μm. Disadvantages: the method allows thinning (relative deformation ε along the wall thickness of the pipe billet) up to 50%, which is unacceptable for titanium alloys due to the formation of microcracks in the heat affected zone of the weld. The subsequent heat treatment modes according to the current instructions can lead either to excessive softening of the material, or to insufficient removal of residual stresses. All these factors are the reason for the decrease in strength and cyclic durability of welded titanium pipes.

SUMMARY OF THE INVENTION

The objective of the invention is to increase the strength and cyclic durability of welded titanium pipes due to the optimal choice of thermomechanical processing parameters of pipe billets.

The problem is achieved due to the fact that in the known method of manufacturing welded titanium pipes, including obtaining a tube billet by convolving a flat sheet billet and welding longitudinal edges, rotational rolling of a weld seam of a tube billet mounted on a rotating mandrel using pressing elements of a rigid tool, annealing the welded titanium pipe to relieve residual stresses, according to the invention, the rolling of the weld is carried out with a relative deformation ε along the wall thickness of the pipe billet and determined by the interval

8% ≤ε≤20%,

(where ε = (t ₀ -t) / t ₀ × 100%, t ₀ is the wall thickness of the pipe billet, t is the wall thickness of the welded titanium pipe after rolling the weld), and subsequent annealing at temperature T _anne , determined from the interval

(T _nr -170) ° C≤T _annele ≤ (T _nr -50) ° C,

where T _nr is the temperature of the onset of recrystallization of the titanium alloy, ° C.

In the process of rolling, the value of the relative deformation ε along the wall thickness of the pipe billet should be selected for reasons of sufficiently complete elimination of the geometric concentrator (undercut) on the fusion line of the weld and at the same time ensuring optimal plastic deformation for hardening the titanium alloy.

At ε <8%, the undercut on the fusion line of the weld is not completely eliminated (smoothed out), and during cyclic loading of the welded titanium pipe with internal pressure, this undercut, acting as a stress concentrator, significantly reduces cyclic durability.

At ε> 20%, cyclic durability begins to decrease due to the accelerated development characteristic of titanium alloys, the development of recrystallization processes, accompanied by softening and, as a consequence, a decrease in fatigue strength. In addition, in the heat affected zone of the weld of the tube billet during rolling, the likelihood of microcracks forming, which are the centers of development of fatigue cracks in the welded titanium pipe, is increased.

When heating a plastically deformed metal, recrystallization processes begin to develop, accompanied by the restoration of plasticity and softening. Annealing temperature T _anne , selected from the interval

(T _nr -170) ° C≤T _annele ≤ (T _nr -50) ° C,

where T _нр - the temperature of the onset of recrystallization of the titanium alloy, ° C, allows you to almost completely remove residual stresses, restore plastic properties without significantly reducing the strength and cyclic durability of the welded titanium metal.

At T _anne <(T _nr -170) ° C, the residual stresses are not completely removed, and the plastic properties cannot be restored sufficiently, which can lead to rejection signs during further processing of the welded titanium pipe using bending and other forming operations.

At Т _annealing > (Т _нр -50) ° C, softening processes begin, leading to a decrease in fatigue strength and cyclic durability during further operation of welded titanium pipes.

The invention is illustrated by the following drawings.

In FIG. 1 shows a convolution of a flat sheet blank;

in FIG. 2 - welding of the longitudinal edges of the pipe billet;

in FIG. 3 - rotational rolling of the weld on the mandrel by deformation by pressing elements of a rigid tool;

in FIG. 4 - obtained welded titanium pipe.

The implementation of the invention

The method is as follows. Weld the longitudinal edges 1 of the rolled flat sheet billet 2, obtaining a tube billet 3 with an outer diameter D _s , wall thickness t ₀ , length L _s with a weld 4 of width b. Set the pipe billet 3 on the mandrel 5 and carry out the rotation rolling of the weld 4 of the rotating pipe billet 3 by deformation by the pressing elements 6 of the rigid tool 7 to obtain the relative deformation ε along the wall thickness of the pipe billet, determined from the interval

8% ≤ε≤20%,

(where ε = (t ₀ -t) / t ₀ × 100%, t ₀ is the wall thickness of the pipe billet 3, t is the wall thickness of the welded titanium pipe 8 after rolling the weld 4). After that, the rotation rolling process is stopped and the rigid tool 7 with the pressure elements 6 is removed. The obtained welded titanium pipe 8 with an outer diameter D, wall thickness t, length L from mandrel 5 is _removed , placed in an oven and annealed at a temperature T _anne , determined from the interval

(T _nr -170) ° C≤T _annele ≤ (T _nr -50) ° C,

where Т _нр is the temperature of the onset of recrystallization of the titanium alloy, ° C.

Example. It is necessary to obtain a thin-walled welded titanium pipe 8 with a diameter of D = 100 mm, a length of L = 550 mm from VT1-0 alloy (GOST 19807-91) with a wall thickness of t = 0.5 mm from sheet.

First, the wall thickness t _{0 of the} tube billet 3 is determined (which is equal to the thickness of the flat sheet billet 2) so that during subsequent processing the relative deformation ε along the wall thickness of the tube billet 3 is from 8 to 20%.

If ε = (t ₀ -t) / t ₀ × 100%, then at t = 0.5 mm the following inequality must be fulfilled:

0.543≤t ₀ ≤0.625 mm.

Take the sheet thickness closest in accordance with GOST, that is, t ₀ = 0.6 mm.

Flat sheet billet 2 with dimensions 313.1 × 505 × 0.6 mm from VT 1-0 titanium alloy is rolled up on an LGME-0.6 bending machine and longitudinal edges 1 are welded by automatic argon-arc welding with a nonconsumable electrode without an additive on an assembly-welding unit, equipped with a power source VSVU-160 and a welding head ASGV-4. The resulting tube billet 3 has an outer diameter D _z = 100.2 mm, a length L _z = 505 mm, a width of the weld 4b = 5 mm; undercut of the front side of the weld 4 - not more than 0.1 mm

Set the pipe billet 3 on the mandrel 5 of steel HVG (GOST 5950-2000). Rotate rolling is carried out on a lathe 16K20 of a weld 4 of a rotating pipe billet 3 by deformation by pressing elements 6 of a diameter of 10 mm of a rigid tool 7 to obtain a relative deformation of ε = 16.7% of the wall thickness of the pipe billet 3, which corresponds to a wall thickness of t = 0.5 mm welded titanium pipe 8.

After that, the rotation rolling process is stopped and the rigid tool 7 with the pressure elements 6 is removed. The obtained welded titanium pipe 8 is removed from the mandrel 5, placed in the PVT-1.2-1000 furnace and annealed for 1 hour at a temperature T _anf = 550 ° C determined from the interval

(T _nr -170) ° C≤T _annex ≤ (T _nr -50) ° C,

where Т _нр = 600 ° С is the temperature of the onset of recrystallization of VT1-0 titanium alloy.

On the resulting welded titanium pipe 8, the undercut on the fusion line of the weld 4 is completely smoothed by rotational rolling and is not a stress concentrator. Metallographic studies showed the complete absence of 4 microcracks in the heat affected zone of the weld, which indicates the increased strength of the welded titanium pipe 8. As shown by pulsating internal pressure tests, the cyclic durability of the welded titanium pipes was increased by 30-40% due to the optimal selection of thermomechanical parameters for processing tube blanks.

Claims (2)

A method of manufacturing a welded titanium pipe, including obtaining a tube stock by convolution of a flat sheet blank and welding longitudinal edges, rotational rolling of a weld seam of a tube stock mounted on a rotating mandrel using hard tool pressing elements, annealing a welded titanium tube to relieve residual stresses, characterized in that rolling the weld is carried out with a relative deformation of 8% ≤ε≤20% of the wall thickness of the pipe billet, while ε = (t ₀ -t) / t ₀ × 100%, where t ₀ is the wall thickness of the pipe billet, t is the wall thickness of the welded titanium pipe after rolling the weld, and subsequent annealing is carried out at annealing temperature (T _nr -170) ° С≤T _otzh ≤ (T _нр -50) ° С, where Т _нр - temperature of the beginning of recrystallization of a titanium alloy, ° С.

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