A method of manufacturing a sheet of semi-finished products of technical titanium

 

The invention relates to the field of metallurgy, mainly to processing of metals by pressure, in particular to the technology of production of high strength thin sheets, strip and foil of technical titanium, and can be used in instrumentation, aerospace, and medicine. A method of manufacturing a sheet of semi-finished products of technical titanium, involving pre-treatment of the workpiece, cold rolling and annealing, in this pre-processing is done on the structure with submicron grain size, are rolling in several passes to obtain a semi-product of a specified thickness or hardness, and the annealing is carried out before rolling and/or between passes at a temperature below the recrystallization temperature of the beginning of tHPwith the decrease in the hardness on the amount compensated during the subsequent rolling. Homogeneous structure with submicron grain size in the billet for rolling form through the various options of intensive plastic deformation. The technical result - getting submicrocrystalline sheets of semi-finished products of technical titanium with high strength and fatigue properties, characterized by one is eenie relates to the field of metallurgy, mainly to processing of metals by pressure, namely the technology of manufacturing high-strength thin sheets, strip and foil of technical titanium, and can be used in instrumentation, aerospace, and medical.

A known method of manufacturing thin sheets, strip and foil of technical titanium [1] , which includes hot rolling of the slab on the strip, etching to remove the oxide layer and the cold rolling with intermediate annealing at 650-700oAnd the maximum permissible total deformation between the intermediate annealing is not more than 50%.

The disadvantages of this method, limiting the use of sheet semifinished products of technical titanium, include low level of their strength. This is due to the inheritance in the semi-coarse-grained structure subjected to cold rolling the workpiece. In addition, the obtained sheet semi-finished products can be inhomogeneous microstructure and texture, causing the anisotropy and heterogeneity of mechanical properties.

For the prototype of the present invention is adopted a method of obtaining rods and strips of technical titanium with regulated-structure [2]. The way predu on 40-180oC below the temperature of polymorphic transformation, rolling in-the field for several stages with one-time reductions for stage 20-30% to the total degree of deformation, regulated the required grain size in the finished product, annealing at 600-680oWith cooling after annealing and subsequent cold deformation with the degree of 1-1,5%, and the total degree of deformation-the field is determined from the relation:=323,12 d-0,405%, where d is the desired grain size in the finished product microns.

The disadvantage of this method is that it does not significantly grind the grain structure in the finished product and, thereby, to obtain a high level of strength and fatigue properties. So based on the above ratio, the total degree of deformation-the area around 96% in the finished product is achieved grain size of approximately 20 microns.

The objective of the invention is to provide a method of manufacturing a sheet of semi-finished products (thin sheets, strips and foil) of technical titanium with high strength and fatigue properties, characterized by homogeneity and small size of the in-plane anisotropy.

For the preliminary processing of the workpiece, cold rolling and annealing, in this pre-processing is done on the structure with submicron grain size, are rolling in several passes to obtain a semi-product of a specified thickness or hardness, and the annealing is carried out before rolling and/or between passes at a temperature below the recrystallization temperature of the beginning of tHPwith the decrease in the hardness on the amount compensated during the subsequent rolling.

The problem is solved, if: - pre-processing of the workpiece on the structure with submicron grain size exercise deformation at temperatures below the temperature of polymorphic transformation tPP400750oWith; - rolling exercise with strain rates in the range of 10-4100with-1; - rolling are several passes with private reductions of 1030%; - annealing between the passages is carried out at achieving total degree of deformation 6075%; - temperature tHPdetermined from the temperature dependence of hardness of the workpiece, the last pre-treatment on the structure with submicron grain size, as the temperature began resmd>50oC.

The invention consists in the following. Increased strength and fatigue resistance at a sufficiently high level of plasticity of the sheet of semi-finished products of technical titanium is provided by creating in them sverkhelastichnosti microstructure with grain size in tenths of a micrometer, called submicrocrystalline (QMS). In titanium technical purity depending on the impurity content, the formation of this microstructure occurs at temperatures of deformation below the temperature of polymorphic transformation (tPP) 400750oC. For uniform development of recrystallization at such low temperatures and homogeneous QMS structure section sheet semi-finished product of the required high degree of deformation. Providing an intense and homogeneous plastic deformation of the material directly rolling is not possible. However, the use as the source for rolling blanks with QMS structure obtained by other means, enables the manufacture of sheet material with homogeneous substructures. Moreover, the level of strength and hardness of the sheet semi-finished product will be higher than in the rolling deformation hardening, and even more crushing of the microstructure of titanium with a combination of cold rolling and annealing.

Cold rolling pre-treated billet structure with submicron grain size perform several passes, to a predetermined thickness or hardness of the semi-finished product. This annealing is carried out before rolling and/or between passes to achieve an adequate technological plasticity rolled blank. In contrast to known methods [1, 2] , in which the annealing is carried out at temperatures, providing course of recrystallization and removal work hardening, created by rolling, in the present invention, the annealing is carried out at a temperature below the recrystallization temperature of the beginning. In rolled the workpiece remains submicron grain size, however, is provided by the development processes of return, leading to the redistribution and reduction of the dislocation density, the reduction of internal stresses. As a result of this annealing is a slight decrease in strength and hardness, but achieved the necessary technological plasticity of the material for the rolling. Moreover, the decrease in the hardness after annealing occurs only on the value to the rollers and annealing between the passages under these conditions provides an additional refinement of the structure of the material and thus increase the strength. Despite the highly technical strength of titanium with the QMS structure it is sufficient for cold rolling plasticity is caused by the specifics of the deformation of the QMS titanium at room temperature, contribute to maintaining during rolling of ravnovesnost grains and essential blurry textures, resulting in the isotropy of the mechanical properties of the finished cake mix.

The invention additionally developed and updated using the following methods.

Getting up in the billet for rolling patterns with submicron grain size shall be implemented by deformation processing, which is implemented intensive plastic deformation of titanium, is provided by the development of dynamic recrystallization and the formation of homogeneous in the volume of the billet microstructure with a grain size less than 1 μm (0.1 to0.5 µm). The temperature interval of intensive plastic deformation is determined from experimentally constructed of the temperature dependence of the size of dynamically recrystallized grains of the processed material. For titanium of various degrees of purity, this interval corresponds to the temperature of deformation below the pace is key microstructure of cross section of the workpiece and homogeneous QMS patterns use different methods of intensive deformation processing: - multilateral deformation, comprising a set of operations precipitation and pulling with the change of the axis of the workpiece; - equal-channel angular pressing; - combined loading, combining draft or tension with torsion.

Rolling blanks, pre-processed on the QMS structure, carried out with the strain rates in the range of 10-4100with-1that is optimal for achieving the objectives. The use of strain rate is less than the lower limit is impractical because of the increased duration of rolling to the desired thickness or hardness of the semi-finished product, and at strain rates above the upper limit decreases significantly technological plasticity of rolled material.

Depending on the strain rate are rolling with private reductions of 1030% per pass, and, as a rule, higher rolling speed corresponds to a smaller amount of compression for the passage.

To obtain the necessary technological plasticity rolled blank when reaching the aisles of the total degree of deformation 6075%, which limited technological PLA is s the beginning of recrystallization tHP. Implementation of rolling with a total value of compression 6075% between annealing allows better use of the plastic properties of metal and power capabilities of rental equipment. Rolling with a total degree of deformation less than 60% impractical due to the reduction process performance. At total level more than 75% is a decrease in the deformability of the material during rolling, which leads to cracking of the edges of the sheet of semi-finished and reduction of yield.

The temperature at which recrystallization tHPthe processed material is determined from the experimental dependence of the changes of hardness pretreated on QMS structure of the workpiece from the annealing temperature. Typical graphical dependence of the hardness of the deformed material from the annealing temperature has a characteristic sigmoidal appearance shown in Fig.1. The curve consists of three sections. The first segment of the curve corresponds to the temperature range of annealing, in which the material of the developing processes of return, and its hardness with increasing temperature weak or practically does not change. With further increase of the annealing temperature hardness Reschensee hardness. Typically, the temperature at which recrystallization tHPdetermine from the specified graphics according to the temperature at which a sharp decrease in hardness.

The best result is achieved when the annealing temperature is chosen below the recrystallization temperature of the beginning of tHP1050oC. the duration of the annealing is selected experimentally from a condition of maintenance at the chosen temperature development in the structure of the deformed billet processes return. Decrease annealing temperature below the specified limit significantly increases the annealing time required to achieve the necessary technological plasticity of the material in the implementation of the subsequent cold rolling.

It should be noted that annealing at relatively low temperatures (200400oBelow the annealing temperature known methods) does not lead to the formation of gas-saturated surface layer, requiring subsequent removal, thereby improving the utilization rate of material and reduces the complexity of the technological process of manufacturing of sheet cake mix of technical titanium.

When analyzing the level of tech is Beketov of technical titanium with fine-grained structure, found no solution, characterized by signs, identical to all the essential features of the claimed invention. Therefore, the claimed invention meets the condition of "novelty."

In the analysis of the distinctive features found that the claimed invention is not obvious from the prior art. First proposed a method of manufacturing a sheet of semi-finished products (thin sheets, strips and foil) of technical titanium with submicrocrystalline structure with high strength and fatigue properties while maintaining sufficient ductility, characterized by their homogeneity and small size of the in-plane anisotropy. The basic signs are new and non-obvious. Thus, the claimed invention meets the condition of "inventive step".

The invention is illustrated by the following materials.

Fig. 1 shows a typical dependence of the hardness of the deformed material on the temperature.

Fig. 2 - dependence of the grain size of titanium VT1-0 temperature deformation.

Fig. 3 - microstructure of billet for rolling of titanium VT1-0 with QMS structure.

Fig.4 - temperature dependence of hardness of the QMS titanium VT1-0.

measures given to the manufacture of sheet semi-finished products with grain size 0.10.2 μm. Processing was subjected to a rod with a diameter of 50 mm technical titanium VT1-0 (impurity content of not more than 0.5 mass%, PL.1) with the temperature of polymorphic transformation tPP910oC and the value of the original grains 30 μm. The examples do not exhaust the possibilities of the method for making a sheet of semi-finished products of different thickness with a larger or smaller size grains of technical titanium this purity, as well as titanium with a different content of impurities.

Example 1.

You want to get a tape with a thickness of 0.8 mm with QMS structure. Used a billet with a diameter of 50 mm and a length of 100 mm Pre-processing to obtain the billet for rolling homogeneous QMS structure was carried out by multilateral deformation, including the sequence of operations precipitation and pulling with the change of the axis of the workpiece. At the end of deformation of the workpiece is acquired approximate original shape. This allowed to repeat the cycles of multilateral deformation to achieve volume with a piece of large plastic deformations. For strain used hide. Deformation was performed in conditions that are close to isothermal, for the four stages at temperatures of stages equal to 650, 500, 450, 380oC. the Choice of temperature of the last stage was determined from the experimental dependence of the size of recrystallized grains on the temperature of deformation (Fig. 2). The heat distortion temperature of 380oFor titanium VT1-0 below tPP530oAnd it matches the size of recrystallized grains of 0.15 μm (Fig.3). After deformation and subsequent mechanical processing received billet sizes 405095 (mm) and with homogeneous QMS structure.

To determine the temperature of the beginning of recrystallization tHPand, accordingly, the annealing temperature used is obtained by experiment, the dependence of the hardness of titanium VT1-0 with QMS structure from the annealing temperature (Fig.4). TemperatureHPwas determined 440oC. the annealing Temperature was chosen on the 20oWith the below tHPthat corresponded 420oC. the Microhardness Hvthe original piece with the QMS structure before annealing was equal 2470 MPa. After performing annealing at 420oWith over 5 hours microhardness decreased to 2320 MPa, and the grain size was 0.2 μm.

From 4 mm. Cold rolling plate to a thickness of 0.8 mm was performed for three passes with private reductions of 30% and a total deflection of about 67% without carrying out annealing between passes. As rolling equipment used sentially rolling mill. The strain-rate corresponded to the interval 10-3-10-4c-1. The resulting tape sizes of 0.820260 mm3. The microstructure of the ribbon with the size of equiaxial grains of about 0.2 μm is shown in Fig.5. The microhardness of the tape was 2730 MPa, i.e., the decrease of hardness of the workpiece (to 2320 2470 MPa) as a result of annealing before rolling was compensated by its increase during subsequent rolling.

For the comparative analysis of the impact of the formation of the QMS structure and cold rolling on the mechanical properties of titanium from the original rod with a grain size of 30 μm were cut plate and rolled it into the tape with a thickness of 0.8 mm according to the same modes as for QMS tape. Evaluation of mechanical properties (of 0.2,B,,,) tensile carried out along the direction of rolling. Evaluation of the fatigue limit (

The results of the mechanical tests of titanium VT1-0, are presented in table. 2, indicate increased in 1,5-2 times strength characteristics, and 25% of the endurance limit of titanium, the last pre-treatment on the structure with submicron grain size (row 3 of table.2) in comparison with the original coarse-grained state (line 1 table.2). In QMS tape marked an even higher level of strength while preserving the ductility, while in coarse-grained titanium after rolling elongation decreases.

Example 2.

You want to get a foil thickness of 0.1 mm with QMS structure. The formation of the QMS structure in the billet for rolling and cold rolling two plates cut from the workpiece, on the tape with a thickness of 0.8 mm is produced analogously to example 1. Next, annealing is carried out at 420oWith 5 hours, then cold rolling for 6 passes with private reductions of 15-25% to a thickness of 0.2 mm with a total degree of deformation of 75%.

The obtained tape was cut into pieces with a length of 100 mm, folded set of 4 cut pieces in a package without shell, welding recorded the ends of the package and perform the annealing at 420oC for 5 hours. Cold rolling of the package held for 3 passes at 15-25% for projoy respectively 30 and 300 mm. Structural studies have shown that in the manufacture of the foil, the grain size is reduced to 0.1 μm, while their ravnovesnost saved, raznozernistoy missing. Microhardness foil was 3100 MPa.

In table. 3 shows the mechanical properties obtained QMS foil in three different directions relative to the direction of rolling.

From the data table. 3 shows that the QMS foil, a slight amount of in-plane anisotropy, the level of strength characteristics increases to values typical for titanium alloys.

Thus, the sheet semifinished products of technical titanium produced by the proposed method have uniform submicrocrystalline structure, the isotropy properties, high strength, reaching the level of alloyed titanium alloys, in combination with increased fatigue resistance and satisfactory ductility.

Example 3.

Similar to example 1 except that the pre-processing to obtain the billet for rolling patterns with submicron grain size was carried out by equal-channel angular pressing. For this purpose the workpiece in the form of a parallelepiped section 20

Example 4.

Similar to example 2 except that the pre-processing to obtain the billet for rolling QMS structure was implemented through the combined loading, combining the precipitate with torsion. The workpiece is deformed in isothermal conditions at two stages at temperatures of 500 and 380oWith specialized Rosatom mill DDS-800. After forming a homogeneous QMS structure with a grain size of 0.15 μm, the workpiece has two systems for press forming to a thickness of 10 mm, was cut out of plates, rolled them first in ribbon with a thickness of 0.8 mm, then the batch produced by rolling the foil thickness of 0.1 μm.

Sources of information
1. Semi-finished products from titanium alloys /Aleksandrov, C. K., Anoshkin N. F., Bochvar, A. and others - M.: metallurgy, 1979 (Titanium alloys), 512 S.

2. RF patent 2175994, IPC C 22 F 1/18, 12.01.2000. Publ. 20.11.2001.


Claims

1. A method of manufacturing a sheet of semi-finished products of technical titanium, vkljuchajuwih the processing lead to a structure with submicron grain size, rolling carry several passes to obtain a semi-product of a specified thickness or hardness, and the annealing is carried out before rolling and/or between passes at a temperature below the recrystallization temperature of the beginning of tHPwith the decrease in the hardness on the amount compensated during the subsequent rolling.

2. The method according to p. 1, wherein pre-processing the workpiece on the structure with submicron grain size exercise deformation at temperatures below the temperature of polymorphic transformation tPP400750C.

3. The method according to p. 1 or 2, characterized in that the rolling carried out with strain rates in the range of 10-4100with-1.

4. The method according to any of paragraphs.1-3, characterized in that the rolling is conducted with private reductions of 1030% per pass.

5. The method according to any of paragraphs.1-4, characterized in that the annealing between the passages is carried out at achieving total degree of deformation 6075%.

6. The method according to any of paragraphs.1-5, characterized in that the temperature tHPdetermined from the temperature dependence of hardness of the workpiece held predvaritel.

7. The method according to any of paragraphs.1-6, characterized in that the annealing temperature is chosen below the temperature tHP1050C.

 

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FIELD: plastic working of metals, possibly manufacture of thin high-strength foil of titanium.

SUBSTANCE: method comprises steps of multi-pass reversing cold rolling and vacuum annealing; repeating cycle; using as initial blank titanium blank with ultra-fine grain structure provided due to intensified plastic deformation by equal-duct angular pressing process; rolling at pitch 15 - 8% for achieving total deformation 70 - 86 % per one cycle; setting number N of cycles necessary for making foil with thickness h according to mathematical expression; realizing vacuum annealing, preferably at temperature 350 -360 C for 0.5 - 1 h. Invention provides possibilities for making titanium foil with thickness up to 10 micrometers.

EFFECT: enhanced strength characteristics of titanium foil of lowered thickness with the same technological platicity7777.

2 cl, 2 tbl

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