RU2094141C1 - Method of producing hot-rolled titanium-alloy tubes - Google Patents

Abstract

FIELD: metal working. SUBSTANCE: method allowing reduced metal loss when manufacturing large-diameter titanium-alloy pipes includes forging ingot with loss y = (1-1.25)A_in/A_st wherein minimum y value is 2.7, drilling central hole in the stock, heating it to a temperature above polymorphic transformation temperature, piercing on rotary pierce with no rise of diameter and stretching in the range 1.20-1.35, rolling on pilger seamless-tube mill, cooling in water and machining outer and inner surfaces. Value of permissible metal removal in machining process is regulated by a mathematical dependence. Method also reduces crack formation in alpha-treated layer of machined stock. EFFECT: reduced metal loss.

Description

 The invention relates to pipe production, namely to rolling large diameter pipes of titanium alloys.

 A known method for the production of large diameter pipes from titanium alloys, including heating a machined drill ingot, piercing on a Kosovalenny piercing mill with a drawing ratio of 1.470-1.770, rolling on a pilgrim mill with drawing coefficients 2.74-3.61, machining of a hot-rolled pipe with removal outer and inner defective layers of 8-10 mm.

 The disadvantage of this method is the low yield due to the occurrence of surface cracks.

 In the production of large diameter pipes, large mass ingots are used, which require a long heating time, which results in gas saturation of the surface of the ingot (occurrence of an alpha layer). In the process of cross-screw flashing under the action of tensile and compressive stresses, cracks arise in the alfin layer, which, under the influence of water and deformation that have entered them, develop deep into the body of the sleeve. To clean cracks from finished pipes, mechanical removal of defective metal layers is required, the thickness of which in the production of large-diameter pipes reaches 10 mm, which leads to significant losses of expensive alloys.

 The problem to which the invention is directed, is to increase the yield in the production of hot-rolled tubes of large diameter from titanium α- and (α + β) alloys.

 The invention achieves a reduction in crack formation in the alpha layer of the workpiece.

где:
У величина укова;
A_с средняя величина зерна слитка, мм;
A_з средняя величина зерна заготовки, мм;
H величина съема при мехобработке, мм;
D_тр диаметр горячекатаной трубы, мм;
D_з диаметр заготовки, мм;
μ общий коэффициент вытяжки при прокатке;
K= 0,5-1,5 коэффициент, учитывающий глубину газонасыщенного слоя в зависимости от продолжительности нагрева, мм.To solve the above problem, a method has been developed for the production of hot-rolled pipes from titanium α- and (α + β) alloys, comprising forging an ingot with a yoke Y = (1-1.25) A _s / A _s , where Y = 2.7, mechanical processing a workpiece and drilling a central hole, heating to a temperature above the temperature of polymorphic transformation, flashing on a Kosovolkov stitching mill without raising the diameter with a hood in the range of 1.20-1.35, rolling on a pilgrim mill, cooling in water and machining of the external and internal surfaces , while the value of minimum d admissible removal during machining is determined from the expression

Where:
Y is the size of the uk;
A _{with the} average grain size of the ingot, mm;
A _{s the} average grain size of the workpiece, mm;
H the amount of removal during machining, mm;
D _{tr the} diameter of the hot rolled pipe, mm;
D _{s the} diameter of the workpiece, mm;
μ the total coefficient of drawing during rolling;
K = 0.5-1.5 coefficient taking into account the depth of the gas-saturated layer depending on the duration of heating, mm

где:
У величина укова;
A_с средняя величина зерна слитка, мм;
A_з средняя величина зерна заготовки, мм;
H величина съема при мехобработке, мм;
D_тр диаметр горячекатаной трубы, мм;
D_з диаметр заготовки, мм;
μ общий коэффициент вытяжки при прокатке;
K= 0,5 1,5 коэффициент, учитывающий глубину газонасыщенного слоя в зависимости от продолжительности нагрева, мм.Comparative analysis with the prototype shows that the inventive method is characterized in that the workpiece is made by forging with a yoke Y = (1-1.25) A _c / A _s , where Y _min = 2.7, the firmware is produced without lifting with a hood in the interval 1 , 2-1.35, while the value of the minimum allowable removal is determined from the expression:

Where:
Y is the size of the uk;
A _{with the} average grain size of the ingot, mm;
A _{s the} average grain size of the workpiece, mm;
H the amount of removal during machining, mm;
D _{tr the} diameter of the hot rolled pipe, mm;
D _{s the} diameter of the workpiece, mm;
μ the total coefficient of drawing during rolling;
K = 0.5 1.5 coefficient taking into account the depth of the gas-saturated layer depending on the duration of heating, mm

 Thus, the claimed method meets the criterion of "novelty."

 Based on the analysis of the depth of the alpha layer arising from the heating of large-sized billets, and the size of the initial grain in the billets, the relationship between the minimum possible removal of metal from a hot-rolled pipe (depth of the defective layer) and the grain size of the billet, the total rolling elongation, the diameter of the initial billet and the diameter is revealed hot rolled pipe.

Since the depth of the gas-saturated (H ₂ , O ₂ , N ₂ ) layer is related to the grain size, and the grain size on turned ingots and workpieces during etching is clearly visible to the naked eye, the minimum yield limit V = 2.7 is determined based on the conditions for obtaining a defective layer on the pipe with a depth of not more than 3 mm for certain hoods on the piercing and pilgrim mills, and the maximum limit, based on the feasibility of the cost of billets.

 The range of the hood on the piercing mill is selected from the specifics of the transverse screw firmware process.

 In order to reduce tensile stresses, the flashing process is carried out for landing or, as they say, size in size with the minimum possible deformations, providing the size of the sleeves, allowing them to be worn on the mandrel and to obtain a given pipe size from titanium a- and (α + β alloys.

 In the production of large titanium pipes, the hood on the piercing mill is maintained in the range of 1.20 -1.35.

 The coefficient K takes into account the depth of gas saturation of the metal depending on the duration of heating the workpiece and is determined empirically from 0.5 mm to 1.5 mm.

 Thus, the claimed technical solution meets the criterion of "inventive step".

 This method was tested on TPA 8-16 ChTP3 in the production of pipes 273x30 mm in size from titanium alloy "Grade 9M" and "Grade 23M".

A mechanically machined drilled workpiece with a yield of U 3.2 (A _s = 5 mm) was assigned to production.

Previously, the removal depth H was calculated using the formula, the grain size A _{s was} determined, and the hood in the pilgrim mill m.

The pipe was manufactured using the following technology:
heating a workpiece with a size of 450x100 vn x1750 mm in a methodical furnace to a temperature of 1110 ^o C;
firmware blanks in a sleeve 450x275 vn x2280 mm with a hood 1.307;
rolling in a pilgrim mill to a tube measuring 279x36x9200 mm with an extract of 4.2 (m5.5);
editing
machining to a size of 273x30x9150 mm.

 Thus, the removal of the defective layer from the outer and inner surfaces was 3 mm each.

 According to the existing technology for the production of titanium pipes to produce pipes of the same clean size of 273x30 mm, a hot-rolled pipe of 293x50 mm in size was made.

Claims (1)

A method for the production of hot-rolled pipes from titanium α- and (α + β) alloys, including obtaining a machined billet, drilling a central hole in the billet, heating it to a temperature above T _pn , flashing it on a Kosovolova piercing mill, rolling it on a pilgrim mill, cooling in water and machining, characterized in that the workpiece is forged with a yoke U (1 1.25) A _c / A _s , where U _{m i n} 2.7, the firmware is produced without raising the diameter with a hood in the range 1.2 1, 35, while the value of the minimum allowable removal with mechanical processing is determined from the expression

where U is the magnitude of ukova;
And _{with the} grain size of the ingot, mm;
And _{s the} grain size of the workpiece, mm;
N the amount of removal during the machining of pipes, mm;
D _{tr the} diameter of the hot rolled pipe, mm;
D _{s the} diameter of the workpiece, mm;
μ is the drawing coefficient during rolling;
K 0.5 1.5 coefficient taking into account the depth of gas saturation of the metal depending on the duration of heating the workpiece.