Method of making thin sheets from difficult-to-form titanium alloys

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to plastic deformation of metals, namely, to production of thin sheets from (α-β)-, pseudo-β, β-titanium alloys. Proposed method comprises preparing stack consisting of the main and clad layers for rolling, assembling said stack, welding, degassing, hot rolling of clad sheet, subsequent rolling and thermal treatment, and surface finishing. Said stack is assembled of the main layer composed of large-size blank from difficult-to-deform titanium alloy and two clad layers from unalloyed titanium used as temporary layers. Clad sheet is rolled in several passes at temperature above and below that of polymorphic transformation Tpt. Note here that after rolling said clad layers are removed in surface finishing.

EFFECT: production of thin high-surface-finish sheets from ((α-β)-)-, pseudo-β, β-titanium alloys.

2 dwg, 4 tbl, 1 ex

 

The invention relates to the field of plastic deformation of metals, in particular, to methods for producing thin sheets of (α-β)-pseudo-β-, β-titanium alloys.

Semi-finished products in the form of sheets are widely used in aircraft and rocket engineering, chemical and naphthene engineering, shipbuilding, metallurgy and other industries.

It is known that the most economical method of producing a sheet of semi-finished products is hot rolling, this is especially true for high-strength (α-β)-pseudo-β-, β-titanium alloys, which have good and satisfactory technological plasticity in the hot condition, which makes it possible to obtain sheets of minimum thickness up to 2.5 mm

In the manufacture of hot rolling of thinner sheets, the effect produced surface defects, while reducing the overall thickness of the sheet becomes critical and eliminates the required quality of the product.

The main reason for this is the high chemical activity of titanium alloys with respect to gases when it is heated. Thus, at temperatures of 350°C and above titanium actively absorbs oxygen with the formation of structures introduction having high strength, hardness (can be 2 times higher than that of titanium) and low plasticity. When heated to a temperature of 550°C and above titanium vigorously dissolves nitrogen, chemically in aimogasta with him, the result is often also formed maloplastichnye the implementation phase (nitrides). The nitrogen in the titanium in the form of nitrides and elements of implementation, increases hardness and reduces its ductility. The surface layer of titanium absorbs an increased amount of nitrogen and oxygen (alteromonas layer). Phase composition and properties of the surface layer differ significantly from the composition and properties of the base metal. In particular, the temperature of polymorphic transformation of this layer is much higher volumetric effect becoming smaller, and the coefficient of linear expansion greater than that of the base metal. As a result, when cooling the inner part of the workpiece undergo less thermal shrinkage force and stretch the surface layer. The resulting tensile stresses in combination with the reduced plasticity of gas-saturated layer lead to the formation of cracks that extend to the surface.

No less unpleasant factor affecting the quality of the surface of titanium semi-finished products, is the process of hydrogen absorption, which occurs when etching in acid solutions. Hydrogen even at low content of the most dramatically affects the properties of titanium. Although the hydrogen content with increasing temperature falls, the hydrogen in supersaturated solid solution is secreted and forms from the preliminary phase the hydrides of titanium, which is heavily abruptive titanium and promotes the formation of cold cracks. In addition, hydrogen promotes the formation of pores. In this context, an acceptable concentration of hydrogen in the metal is limited to 0.01%, and everything is being done to minimize this process.

Note that for a highly responsible sheets aerospace impose very high requirements on the surface quality and mechanical properties. Mechanical properties of thin sheets to a large extent determine the state of the surface and near-surface zones. The manufacturing process sheets must ensure complete removal of the strain-hardened surface layers, surface defects, traces of surface treatment, to ensure a high level of stanoevska.

A known method of protecting the surface layer of the base metal, containing a method of manufacturing packages for the production of large-clad sheets, including sanding and degreasing the contact surfaces of the metal core and cladding layers prior to Assembly, the Assembly of the package and its compression to reduce the size of the gap between the layers, arc welding package, the vacuum at the end of the welding and tempering of the weld, combined with heating for rolling. The way pozvolyaet reliable protection of the surface layer of the base metal material, reducing the harmful effects of the environment. (Patent polar division №2274528, IPC B23K 20/04).

A method of producing sheets of thickness 0.5 mm from commercially pure titanium, including mnogovershinnoe rolling titanium slab, followed by placement of a titanium sheet between two sheets of other material to protect the titanium from cooling and intensive oxidation. Between the outer sheets may be placed one or more of titanium sheets. The outer shell material has a lower thermal conductivity. Temperature rolling is 1300°F (704°C). [US patent N 2651099].

For the production of sheets of commercially pure titanium known method unproductive, has high complexity and cost of products that exceeds the index for processes exploded and rolled rolling of the specified material.

A method of producing thin sheets and foils of commercially pure titanium, comprising hot rolling the strip with a thickness of 3-6 mm, annealing in air atmosphere, surface cleaning from descaling, acid pickling, grinding, cold rolling, finishing surface [Titanium, 1995, t, N 4, C-246].

Sheets of durable and high-strength alloys of a thickness of less than 3 mm on the proposed technology does not produce. High specific pressure, low plasticity, prone to cracking, megachi the certain limits, heat treatment, surface treatment does not provide the required quality of products.

The closest in technical essence and the achieved result of the claimed invention is a way to batch rolling thin sheets (0,076-1.0 mm) made of durable and high-strength metals such as titanium, zirconium and their alloys [U.S. patent N 2985945, publ. 30.05.61] - prototype. The method includes training card blanks with a thickness of 5-10 mm, drawing on both side of the barrier coating, the Assembly package in steel case, heating of the package to 727-759°C, hot rolling package, annealing, cleaning the surface of the case from descaling, cold rolling with a degree of deformation of 10-60%, heat treatment, cutting package, the separation of the sheets, cold sheet rolling with the degree of compression of 3-8%, the finish surface finish, heat treatment, straightening.

The method does not preclude intensive education alteromonas layer in the process of hot thermomechanical processing. In addition, the processing of high-strength alloys in the suggested temperature range is difficult, leads to the formation of micro-cracks and breaks in the processed material. The cold rolling process of the package with the degree of deformation of 10-60% possible to manufacture sheets only alloys with high plasticity.

The challenge which aims this izobreteny is, is to improve the manufacturability and quality of thin sheets of trudnozapominaemyj titanium alloys by reducing the complexity and cost of the process.

Technical result achieved in the implementation of the invention is the production of high performance thin sheets of (α-β)-pseudo-β-, β-titanium alloys hot rolling thickness up to 2.5 mm or less with a quality surface.

This technical result is achieved in that in the method of manufacturing thin sheets of hard titanium alloys, including preparation for rolling package, consisting of a core and a cladding layer, Assembly, welding, vacuum, forming hot rolling of clad sheet, subsequent rolling and heat treatment of sheet and finish of its surfaces, the package consists of a Central layer formed of large slabs of hard-titanium alloy, and two cladding layers, which are used as process and are made from sheets of unalloyed titanium, rolling the sheet is made for multiple transitions at temperatures above and below the temperature of polymorphic transformation TPPafter rolling cladding layers are removed in the process of finishing surfaces.

The essence of the invention. izvestno, the presence of gas-saturated layer on the surface of leaves affects the ductility of the metal, especially when bending tests. The dynamics of increasing the thickness of the gas-saturated layer of α-alloys and alloys high alloyed β-stabilizers and especially β-alloys is significantly different. α-alloys are characterized by frontal nature of gas saturation. Dissolved in the α-phase oxygen is maintained at some relatively small distance from the surface. The formation of gas-saturated layer of this type is explained by the high solubility and low diffusion of gases in α-titanium. High alloyed β-stabilizers titanium alloys selective oxidation occurs to a greater depth at the grain boundaries and subgrains with the formation of precipitates of α-phase. The depth of diffusion of gases in β-titanium much more than in α-titanium. Due to the fact that high-alloy β-stabilizers titanium alloys β-phase is a significant amount, the thickness of the gas layer development in these alloys can be an order of magnitude greater than in α-alloys, and will actually apply to the basic thickness of the thin sheet.

The presence on the surface of the base layer treandatreanda titanium alloy technology of plating layers of technical pure titanium (non-alloy) alloy (α-titanium is afloat) substantially blocks the formation of gas-saturated (alteromonas) layer. Technological layers of commercially pure titanium is then removed without problems at the stage of finishing operations when processing surfaces of mechanical and/or chemical methods.

The invention is illustrated by drawings on which is shown: figure 1 - diagram of connections of plating layer and the basic workpiece, the figure 2 - microstructure of the base metal (alloy Ti-6Al-4V) sheets with a thickness of 2 mm.

An example of a specific implementation.

Were the sheets 2×1000×2000 mm (α-β)-titanium 6Al4V alloy grades, chemical composition presented in table 1.

Table 1
Chem. AlVN2FeH2O2+N2Other
EachOnly
AIMS03-18-001; ABS51255,5
6,75
3,5
4,5
Max
0.08
Max
0.03
Max
0.0
Max
0.0125
Max
0.25
Max
0.10
Max
0.40
Top6.163.830.0200.0060.180.0020.212<0.100.094
Bottom6.193.920.0200.0070.180.0020.234<0.100.095

CCI - 997°C.

For rolling was formed three-layer package (figure 1), including:

- main layer 1 (titanium alloy 6Al4V, forged slab, size 67×1450×1200 mm);

- 2 plating layer 2 (alloy sheet Gr1, the dimensions of 10×1110×1210 mm).

Welding plating layer along the contour of the sheet was conducted in accordance with figure 1. After welding plating layers (weld 3) was produced by pumping air through the channel for pumping air 4 and creating a vacuum of 10-2PA.

Then roll was formed clad sheet (rolling - Test=108010 °C, the thickness H=25±0,5mm).

Hot rolling of sheet thickness of the base layer of 2 mm was carried out in several stages by known techniques. After determining the thickness of the cladding layers, they were removed by mechanical and chemical methods.

One of the sheets was subjected to periodic tests (in accordance with the requirements of AMS4911) stretching and angle bending test data is given in table 2.

Table 2
No. sampleThe direction of the cut sampleYield strength, MPaTensile strength, MPaElongation, %The bend angle, deg Pot 10tThe bend angle, deg Pot 9t
1L9681105the 11.6105/180105/180
2L972111110,9105/180105/180
3 L962110410,5105/180105/180
4L969111111,1105/180105/180
5L967110810,0105/180105/180
6L9891142to 12.0105/180105/180
7L965109310,4105/180105/180
8L975111212,8105/180105/180
9L969110111,5/td> 105/180105/180
10L9681100the 10.1105/180105/180
11L981112110,6105/180105/180
12L988113111,0105/180105/180
1LT1035110311,8105/180105/180
2LT1027109710,5105/180105/180
3LT1039111011,7105/180105/180
4LT1037110710,5105/180105/180
5LT1039110912,2105/180105/180
6LT1071115211,8105/180105/180
7LT10321096the 11.6105/180105/180
8LT10421109the 13.4105/180105/180
9LT1043111011,1105/180105/180
10LT1040 111111,2105/180105/180
11LT1043111310,7105/180105/180
12LT1057113111,4105/180105/180
AMS491186692010105105

Was also the control of hydrogen content and content uniformity of hydrogen on the sheet, test data respectively provided in table 3 and 4.

Table 3
The hydrogen content in the leaves (the method of determining the ONH-2000)
No. sampleThe hydrogen content, %
10,0062
20,0062
30,0060
40,0064
50,0062
60,0055
70,0069
80,0062
90,0088
100,0080
110,0070
120,0060

Table 4
Control of the uniformity of the hydrogen content of the leaf
No. sampleThe hydrogen content, %
10,0072
20,0062
30,0062
40,0054
50,0058
60,0055
70,0054
80,0058
90,0056
100,0053
110,0057
120,0056
130,0052
140,0054
150,0053

The runway was 0.002% (field sheet).

Figure 2 photographs of the microstructure, the longitudinal direction and the transverse direction (b), of base metal (titanium 6Al4V alloy grades, sheet thickness 2 mm). The grain size of the base metal in the transverse direction is 1.3 μm is 0.7 to 2.8 μm).

Using the proposed method provides the following advantages in comparison with prototype:

- allows you to get from hard-titanium alloys hot rolling the sheet thickness of 2.5 mm or less;

- reduces the complexity and cost of the process;

- prevents the penetration alteromonas layer in the thickness of the base metal;

- prevents the absorption of the parent metal during etching in sour the solutions;

- prevents cooling down, of base metal;

- when rolling cladding layer protects the base metal from defects, which may be a result of the impact tool;

the angle of bending of the sheet meets the requirements of international standards, has a margin of plasticity;

- removal of the cladding layer is produced with a significantly lower cost than the base metal when the final processing of the sheets (in unalloyed titanium, gasanalysis occurs at a much shallower depth than in high-alloy β-stabilizers titanium alloys, in addition undoped alloys are much better mechanically processed).

A method of manufacturing thin sheets of hard titanium alloys, including preparation for rolling package, consisting of a core and a cladding layer, Assembly, welding, vacuum, forming hot rolling of clad sheet, subsequent rolling and heat treatment of sheet and finish of its surfaces, characterized in that assembles the packet of the base layer formed of large slabs of hard-titanium alloy, and two cladding layers, which are used in the process, from sheets of unalloyed titanium, clad rolling l is a hundred make a few transitions at temperatures above and below the temperature of polymorphic transformation T PPand after rolling cladding layers are removed in the process of finishing surfaces.



 

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The invention relates to ferrous metallurgy, in particular to the production of layered corrosion-resistant steel rolling
The invention relates to metallurgy and mechanical engineering, may be used for the manufacture of metallic materials (sheets, strips and tapes) aluminum plating other metals and alloys: copper, titanium, corosion-resistant steel, zinc, silumin, etc
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SUBSTANCE: method comprises steps of heating billets before first rolling stage until temperature exceeding by 50 - 150 C temperature of polymorphous conversion; seasoning for 15 - 50 min and quenching by cooling in water; hot rolling of pack in case heated up to 650-750 C initially lengthwise or crosswise relative to direction of rolling initial billet at total deformation degree 61 - 70 %; hot rolling of pack in case in direction normal relative to direction of first rolling of pack at the same temperature-deformation parameters; subjecting case to annealing. Invention allows to make sheets with ultra-fine grain structure suitable for super-plastic deformation at temperature lower than 800 C.

EFFECT: enhanced strength of material during super-plastic forming process, lowered power consumption.

2 dwg, 1 tbl, 2 ex

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