RU2522252C1 - Thin sheet manufacturing method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: manufacturing method of thin sheets from pseudo-alpha titanium alloys involves deformation of an ingot into a slab, mechanical processing of a slab, multipass rolling of a slab for a semi-finished rolled stock, cutting of the semi-finished rolled stock into sheet workpieces, their assembly into a pack and its rolling and finishing operations. Multipass slab rolling is performed at several stages. After the semi-finished rolled stock is cut into sheet workpieces, their finishing operations are performed. Assembly of sheet workpieces into a pack is performed by laying so that direction of sheets of the previous rolling is perpendicular to direction of sheets of the next rolling. Rolling of the pack is performed till a final size, and then, obtained sheets are removed from it and finishing operations are performed.

EFFECT: obtaining a microstructure of sheets, which provides high and uniform level of strength and plastic properties.

1 dwg, 2 tbl

Description

The invention relates to the processing of metals by pressure, and in particular to methods of manufacturing thin sheets of pseudo-alpha titanium alloys intended for the manufacture of parts of aircraft.

A known method of manufacturing parts from pseudo-alpha titanium alloys, including heating in the beta region above the temperature of the polymorphic transformation (hereinafter - TPP), cooling, reheating in the two-phase region, re-deformation in this region during cooling, re-cooling, final heating in two-phase region, exposure and cooling (AS USSR No. 1740487, publ. 06/15/1992). The known method is intended for the manufacture of forged and stamped products and is not optimized for the production of sheet semi-finished products.

A known method of manufacturing sheets of low-alloyed titanium alloys, including heating a flat ingot, hot rolling it on a tackle, cutting a rolled product into billets, heating the billet in a two-phase region, rolling them into sheets, heat treatment, etching, dressing, cutting the sheets to a finished size (RF patent No. 2198237, publ. 02/10/2003). The known method does not take into account the technological features of pseudo-alpha titanium alloys.

A known method of manufacturing particularly thin sheets of high-strength titanium alloys, including obtaining the original sheet billet, assembling a package of sheet billets with a coating using a case, hot rolling and heat treatment of the package, separation and decoration of the obtained sheets (RF Patent No. 2381297, publ. 10.02. 2010) - a prototype. However, in the known method are not regulated modes of thermomechanical processing, which does not allow to provide a given level of mechanical properties and structure.

The problem to which the invention is directed is the development of a method for manufacturing thin sheets of pseudo-alpha titanium alloys with a homogeneous structure and mechanical properties, as well as high surface quality and geometric parameters.

The technical result achieved by the implementation of the invention is to obtain a microstructure of the sheets, providing a high and uniform level of strength and plastic properties.

The problem is achieved in that in a method for manufacturing thin sheets of pseudo-alpha titanium alloys, including the deformation of an ingot into a slab, machining a slab, rolling a slab into a tack, cutting a rolled tack into billets, rolling the billets into sheets and jointing operations, according to the invention for manufacturing sheets use a slab obtained from a deformed ingot after heating to a temperature of 150 ÷ 250 ° C above the CCI with a total degree of deformation of 30 ÷ 60% and after heating 100 ÷ 200 ° C above the CCI with a total degree of deformation of 40 ÷ 70%, o there is multi-pass rolling of a slab to a tackle by heating to a temperature 90 ÷ 150 ° above the CCI with a degree of deformation of 10 ÷ 20% per pass and additional heating after reaching a degree of deformation of 25 ÷ 35% with a total deformation of 50 ÷ 80% at this temperature, heating to temperatures 30-60 ° C below the CCI with a degree of deformation per pass 5 ÷ 10%, with a total deformation at this temperature of 15 ÷ 25%, heating to a temperature 80 ÷ 120 ° C above the CCI with a degree of deformation per pass 10 ÷ 20% and additional heatings after reaching a degree of deformation of 25 ÷ 35% at a total deformation at this temperature of 50–80%, heating to a temperature of 50–70 ° C below the CCI with a degree of deformation of 5–10% per pass and additional heatings after reaching a degree of deformation of 15–25% at a total deformation of 40 ÷ 65%, then they cut the rolled products into sheet blanks and jointing operations, assemble the sheet blanks into a bag in such a way that the direction of the sheets of the previous rolling was perpendicular to the direction of the sheets of the subsequent rolling, rolling the bag to the finished size with heating to perature at 70 ÷ 100 ° C below the strain with CCI packet per passage 10 ÷ 20%, and further heating the stack after the degree of deformation of 25 ÷ 35% when the total packet strain 55 ÷ 70%.

The method is implemented as follows.

The smelted and machined cylindrical ingot is heated to a temperature of 150 ÷ 250 ° C above the TPP and is forged with a total degree of deformation of 30 ÷ 60%, which destroys the cast structure, averages the chemical composition of the alloy, compacts the workpiece, eliminating casting defects such as voids, sinks and others. Heating temperature below the specified limit leads to a decrease in plastic characteristics, difficulty in deformation and the appearance of surface cracking, the heating temperature above the specified limit causes a significant velichenie gas-saturated layer, resulting in a straining surface upon deformation, deterioration of the quality of the metal surface and accordingly to increased metal removal from workpieces. The following deformation of the workpiece with a total degree of 40–70% after heating 100–200 ° C above the CCI allows you to slightly grind the grain size in relation to the initial state. To completely remove surface defects, the resulting slab is machined from all sides. Further multi-pass rolling of the slab into a tackle with a total degree of deformation of 50 ÷ 80% after heating to a temperature of 90 ÷ 150 ° C above the TPP increases the ductility of the metal and limits the formation of defects during subsequent deformation in the (α + β) region. The slab is rolled with a degree of deformation per pass of 10 ÷ 20%, and after reaching a degree of deformation of 25 ÷ 35%, additional heating is performed, which allows to improve the ductility of the metal, to maintain a satisfactory surface quality during rolling and to prevent the formation of cracks. After deformation in the β-region, it is heated to a temperature 30–60 ° C below the TPP and multi-pass rolling is carried out with a total deformation of 15–25% to break the high-angle grain boundaries and increase the dislocation density, i.e. carry out deformation hardening. The degree of deformation per passage of 5 ÷ 10% is determined by the technological properties of the alloys at a given deformation temperature. The resulting metal has increased internal energy and subsequent heating to a temperature of 80 ÷ 120 ° C above the CCI with a total strain of 50 ÷ 80% is accompanied by recrystallization with grain refinement, which makes it possible to obtain equiaxed macrograin in the workpiece. Then, further rolling is carried out with a degree of 40 ÷ 65% after heating 50 ÷ 70 ° C below the CCI in order to prepare a given microstructure to obtain mechanical properties in the transverse direction, so that during further batch rolling, the microstructure is prepared to obtain mechanical properties mainly in the longitudinal direction. The degree of deformation per pass 5 ÷ 10% is determined by the technological properties and conditions for achieving the minimum thickness difference of the sheet stock before batch rolling. At this stage, after reaching a degree of deformation of 15 ÷ 25%, additional heating of the rolled product is performed, which allows to maintain a satisfactory surface quality.

In the absence of the possibility of using cold rolling to obtain thin sheets due to the low ductility of alloys and high loads on the mill due to the high deformation resistance, the final deformation of the sheets to the finished size is carried out in a batch manner, for which the tack is cut into dimensional sheet blanks, while sheet blanks are laid in a package with a change in rolling direction so that the direction of the subsequent rolling is perpendicular to the direction of the previous rolling. Changing the rolling direction of the package allows you to get the optimal crystallographic texture in the sheets and reduce the anisotropy of the mechanical properties. The temperature range of heating (heating at 70 ÷ 100 ° C above the CCI) and the degree of deformation at this stage of 55 ÷ 70% allows to increase the level of grinding and coagulation of the primary α-phase, which contributes to the production of equiaxed fine micrograins that provide uniform mechanical properties in all directions . After batch rolling, the obtained sheets are removed from the package and carry-out processing, testing of sheets and their packaging.

Industrial applicability is confirmed by a specific embodiment of the invention.

To obtain sheets with a thickness of 2 mm, ingots of pseudo-alpha titanium alloy with a diameter of 540 mm and a weight of 740 kg were smelted.

The chemical composition of the alloy is given in table 1. The temperature of the polymorphic transformation of the alloy is 1008 ° C.

Table 1 Sampling Place Mass fraction of elements,% Al Mo Zr Sn Fe Si Nb Gd ABOUT FROM N H Top 6.40 0.51 3.96 2.12 0,034 0.15 1.39 0.25 0.116 0.012 0.001 0.002 Bottom 6.69 0.56 3.48 2.24 0,035 0.15 1.35 0.19 0.119 0.004 0.002 <0.002

The ingot was forged by flattening along a generatrix to a thickness of 250 mm after heating to 1200 ° C (190 ° C above the CCI) with a degree of deformation of 53%. After that, the preform was heated to a temperature of 1150 ° С (140 ° С higher than the CCI) and forging was carried out on a rectangular preform with dimensions 130 × 680 × 1700 mm with a total degree of deformation of 55%. Further, the forged slab was planed to dimensions 117 × 680 × 1100 mm. The slab was heated to a setting temperature of 1130 ° C (120 ° C above the CCI) and rolled in 2 passes with a degree of deformation in each pass of 16.3% and 10.6% mm, respectively, after which, when the total deformation due to heating reached 30%, the tackle heated at the same installation temperature. Further rolling was carried out according to the above scheme to a thickness of 30 mm. The total degree of deformation for the stage was 74.4%. To improve the quality of the surface, the tackle was machined (continuous abrasive cleaning) with removal of 0.30 mm per side. Next, the tackle was heated to a temperature of 970 ° C (40 ° C below the CCI) and rolled in 2 passes to a thickness of 25 mm with degrees of deformation in each pass, respectively, 10% and 7.5% with a total deformation of 15%. Further rolling was carried out at a temperature of 1100 ° C (80 ° C above the CCI) to a thickness of 12 mm. Rolling was carried out in 2 passes with degrees of deformation in each pass, respectively 10 and 20%, and after reaching the accumulated strain of 30%, heating was carried out at the same temperature. The total degree of deformation was 58%. Further rolling was carried out at a temperature of 950 ° C (60 ° C below the CCI), rolled in 2 passes to a thickness of 10 mm with a degree of deformation of 5 ÷ 10% in each pass with a total degree of deformation of 15%. Then rolling was carried out at a temperature of 950 ° C (60 ° C below the CCI), rolled in 2 passes to a thickness of 8.5 mm with a degree of deformation of 5 ÷ 10% in each pass with a total degree of deformation of 15%. Then rolling was carried out at a temperature of 950 ° C (60 ° C below the CCI), rolled in 2 passes to a thickness of 7.3 mm with a degree of deformation of 5 ÷ 10% in each pass with a total degree of deformation of 15%. Then rolling was carried out at a temperature of 950 ° C (60 ° C below the CCI), rolled in 2 passes to a thickness of 6.2 mm with a degree of deformation of 5 ÷ 10% in each pass. The total degree of deformation at a temperature of 950 ° C was 49%. Then, the tackle was cut into dimensional sheet blanks, a pairing operation was carried out, and the bags were collected, while the sheet blanks were stacked in such a way that the direction of the subsequent rolling was perpendicular to the direction of the previous rolling. Three sheet blanks were placed in a bag, taking into account the upper and lower steel plates, the thickness of the bag was 50.9 mm. Next, the final stage of rolling was carried out in a batch method, for which the packages were heated to a temperature of 920 ° C (90 ° C below the CCI) and rolled in 2 passes to a thickness of 38.5 mm (degree of deformation of 16% and 10% of the passes). Then, heating and rolling was carried out in 2 passes for a package thickness of 29 mm (the degree of deformation along the passages 16% and 10%, the total degree of deformation was 24.7%), after which the package was heated and rolled in 2 passes for a thickness of 22 mm (degree deformations along the passages 16% and 10%), the total degree of deformation 24.0%), then heating and rolling were carried out in 2 passes to the thickness of the package 16 mm (the degree of deformation along the passages 16% and 13%, the total deformation 27.2%) . The total degree of deformation of the package was 61%. Then the packages were disassembled, as a result of which sheets with sizes of 2.3 ÷ 2.4 × 900 ÷ 910 × 2900 ÷ 2950 mm were obtained.

The resulting sheets were used for adjustage processing, cutting to the finished size, sampling and testing of mechanical properties and structural analysis. The test results of the mechanical properties of the sheets are given in table 2, images of the microstructure of the sheets are presented in figure 1. The surface quality of the sheets met all the requirements of regulatory documentation, cracks and delaminations were not fixed.

table 2 The condition of the test samples Mechanical properties Yield Strength, σ _0.2 , MPa Temporary resistance, σ _in , MPa Elongation, δ,% Longitudinal direction Cross direction Longitudinal direction Cross direction Longitudinal direction Cross direction After heat treatment according to the mode: 930 ° С - holding for 60 minutes - air cooling 927 903 1001 983 15.8 14.8 After heat treatment according to the mode: 950 ° С - holding for 60 minutes - air cooling 922 908 991 989 15,2 14.3 Level required - ≥950 ≥14

Thus, the present invention, in comparison with known methods, allows to obtain thin sheets from pseudo-alpha titanium alloys with a high level of mechanical properties with minimal anisotropy and a homogeneous structure, as well as a satisfactory surface quality.

Claims (1)

A method of manufacturing thin sheets of pseudo-alpha titanium alloys, including the deformation of the ingot into a slab, machining a slab, multi-pass rolling of a slab into a tack, cutting the tack into sheet blanks, assembling them into a bag and rolling and rolling operations, characterized in that the deformation of the ingot the slab is carried out by heating it to a temperature of 150 ÷ 250 ° C above the temperature of polymorphic transformation (TPP) and deformation with a total degree of deformation of 30 ÷ 60%, subsequent heating to a temperature of 100 ÷ 200 ° C above the TPP and deformation with the total degree of deformation of 40 ÷ 70%, multi-pass rolling of the slab is carried out in several stages, in which the slab is heated to a temperature of 90 ÷ 150 ° C above the TPP and rolled with a total degree of deformation at this temperature of 50 ÷ 80%, the degree of deformation per pass 10 ÷ 20% and with additional heatings after reaching a degree of deformation of 25 ÷ 35%, the tackle is heated to a temperature of 30 ÷ 60 ° C below the CCI and rolled with a total degree of deformation at this temperature of 15 ÷ 25% and a degree of deformation per pass of 5 ÷ 10%, tackle heated to a temperature of 80 ÷ 120 ° C higher TPP and rolled with a total degree of deformation at this temperature of 50 ÷ 80%, a degree of deformation per pass of 10 ÷ 20% and additional heatings after reaching a degree of deformation of 25 ÷ 35%, the tackle is heated to a temperature of 50 ÷ 70 ° C below the TPP and rolled with the total deformation at this temperature of 40 ÷ 65%, the degree of deformation per passage of 5 ÷ 10% and additional heatings after reaching the degree of deformation of 15 ÷ 25%, after cutting the tackle into sheet blanks, they perform jointing operations, the assembly of sheet blanks in a bag is carried out with laying so so that the direction of the sheets of the previous rolling was perpendicular to the direction of the sheets of the subsequent rolling, the package is rolled to the finished size by heating to a temperature of 70 ÷ 100 ° C below the CCI and rolling with a total degree of deformation of 55 ÷ 70%, the degree of deformation per pass 10 ÷ 20% and additional heatings of the bag after reaching the degree of deformation of 25 ÷ 35%, then the resulting sheets are removed from the bag and carry out jointing operations.

Images