RU2318913C1 - METHOD FOR PRODUCING SHEETS OF β-TITANIUM ALLOYS - Google Patents

Abstract

FIELD: non-ferrous metallurgy, namely thermal-mechanical working of hard-to-form high-strength β-titanium alloys, possibly manufacture of thin sheets by rolling.

SUBSTANCE: method comprises steps of mechanically working surface of slab; subjecting it to hot, warm and cold rolling; annealing and aging it. After mechanical working, slab is subjected to scooping and to hot rolling during two stages. At first stage rolling is realized at polymorphous conversion temperature Tpc + (380 - 400)°C and at total deformation degree 85.0 - 95.0% and then blank is subjected to further annealing at temperature Tpc + (145 - 165)°C. At second stage rolling is realized at temperature Tpc + (100 - 120)°C with total deformation degree 45.0 - 55.0% and to further annealing in temperature range Tpc + (50 - 165)°C. Warm rolling is realized at temperature Tpc + (10 - 30)°C with total deformation degree 40 - 60 % for further annealing in temperature range Tpc + (70 - 100)°C. Cold rolling is performed at total deformation degree 50.0 - 55.0%.

EFFECT: improved stable strength and ductile properties of material.

Description

The invention relates to non-ferrous metallurgy, in particular to thermomechanical processing of hardly deformable, high-strength β-titanium alloys, can be used in the manufacture of thin sheets by rolling.

A known method of manufacturing sheets of titanium β-alloys, including hot rolling with intermediate mechanical surface treatment and etching, warm rolling in two stages, cold rolling between the first and second stages of warm rolling, intermediate etching and vacuum annealing (patent RU No. 2052534 C22F 1 / 18) is a prototype.

The above method is quite time-consuming due to the intermediate machining (gouging) of the tackle, etching (leading to hydrogen embrittlement and, consequently, embrittlement of the material in the cold state), as well as vacuum annealing, a very long operation with slow, unregulated cooling with the furnace (up to 4 -5 hours), which results in a decrease in the plastic characteristics of the material due to the ongoing aging processes.

In addition, the intensity of hydrogen disturbance of the material, after vacuum annealing, during operation increases several times.

The aim of the invention is to increase and stabilize the level of strength and plastic properties of thin sheets of high-strength titanium β-alloy, intended for the manufacture of Belleville springs, and reduce the complexity of their manufacture.

The proposed method allows to increase and stabilize the strength and plastic properties of the material due to the deep study of the microstructure and grain grinding by: reducing the temperature of the second hot rolling to 850 ° C and increasing the degree of deformation of 53.3-54.0%, reducing the temperature of warm rolling to 750 ° C and increase the degree of deformation during cold rolling to 55.0-56.0%.

In addition, the exclusion from the technology of the etching operation allows you to automatically exclude such a time-consuming operation, such as vacuum annealing, and replace it with annealing in a continuous electric furnace with a regulated cooling rate of 100 ° C per minute to 200 ° C.

The technical result achieved by the implementation of the invention is: increase and stabilization of the strength and plastic properties of the material.

The specified technical result is achieved by the fact that in the proposed method of manufacturing sheets of β-titanium alloys, including machining the surface of the slab, hot, warm, cold rolling, annealing and aging, the peculiarity is that after machining the slab is made, hot rolling is carried out in two stages, while in the first stage, rolling is carried out at a temperature of T _PP + (380-400 ° C) with a total degree of deformation of 85.0-95.0%, followed by annealing at a temperature of T _PP + (145-165 ° C) , and in the second stage, rolling about lead at a temperature of T _PP ⁺ (100-120 ° C) with a total degree of deformation of 45-55.0% followed by annealing in the temperature range T _PP + (50-165 ° C), warm rolling is carried out at a temperature of T _PP + (10 -30 ° C) with a total degree of deformation of 40.0-60.0%, followed by annealing, in the temperature range T _PP + (70-100 ° C), cold rolling is carried out with a total degree of deformation of 50.0-55.0% .

Hot rolling at a heating temperature below T _pp + 380 ° C, low ductility leads to destruction of the material, at a heating temperature above T _pp + 400 ° C, a significant increase in grain size occurs, which in turn leads to a decrease in ductility. A decrease in the degree of deformation of less than 85.0% leads to insufficient elaboration of the structure along the cross-section of the slab and heterogeneity, while deformation of more than 95.0%, the resource of plasticity of the material is exhausted. Annealing at a lower temperature does not allow recrystallization processes to occur, heterogeneity appears, at a higher temperature there is a significant increase in grain size and a decrease in ductility.

At the second stage of hot rolling, the heating temperature is below T _pp + 100 ° C, low ductility leads to the destruction of the material, at a heating temperature above T _pp + 120 ° C, a significant increase in grain size occurs. A decrease in the degree of deformation of less than 45% leads to insufficient elaboration of the structure along the cross section of the sheet and heterogeneity, with a deformation of more than 55%, the resource of plasticity of the material is exhausted.

Annealing at a lower temperature does not allow recrystallization processes to occur, heterogeneity appears, at a higher temperature there is a significant increase in grain size and a decrease in plasticity, instability of the level of mechanical properties.

Warm rolling at a heating temperature below T _pp + 10 ° C, the ductility decreases, which leads to destruction of the material, at a heating temperature above T _pp + 30 ° C, a significant increase in grain occurs, the ductility and manufacturability of the metal decreases. A decrease in the degree of deformation of less than 40.0% leads to insufficient elaboration of the structure along the cross section of the sheet and structural heterogeneity, with deformation of more than 60%, hardening and a decrease in the plastic characteristics of the material occur.

Annealing at temperatures below the polymorphic transformation temperature T _pp + (70-100 ° C) does not allow recrystallization processes to occur, different grain size and insufficient ductility of the metal for subsequent cold deformation, a higher temperature, a significant increase in grain size and a decrease in ductility.

Reducing the degree of deformation during cold rolling, less than 50% leads to the study of only the surface layers of the sheet and the heterogeneity of the structure over the cross section of the sheet, with deformation of more than 55%, the resource of plasticity of the material is exhausted, the sheets are destroyed.

The proposed method was tested in the manufacture of sheets of TC 6 titanium β-alloy. Under the production conditions of the sheet rolling workshop, a batch of sheets of TC 6 alloy was manufactured using the following technology.

The sheets were made of β-forged slab with dimensions of 240x870x1600 mm, with machined main and side faces. The slab is subjected to the shooping of the main and side faces.

The slab was heated in an electric furnace at a temperature of 1130 ° C for 5.4 hours, with a heating rate of 1.3 mm / min. Hot rolling was carried out in the roughing stand of the quarto 2000 hot rolling mill with a total degree of deformation of 88.0%, to a thickness of 30 ^{+ -2} mm. Next, the plates were annealed in an electric furnace in the temperature range of 900 ° C for 60 min. After annealing, a continuous abrasive cleaning of the surface of the plates was performed to remove scale, gas-saturated layer, and surface defects. The size of the removed layer is 0.3 mm per side. Ultrasonic inspection - to detect internal defects formed during the ingot melting process.

The plates were heated before the second hot rolling, in an electric furnace, at a temperature of 850 ° C, for 40 minutes. Heating rate 0.7 mm / min.

The second hot rolling was carried out in the roughing stand of the quarto 2000 mill with a total degree of deformation of 53.0%, to a thickness of 14.0 ^{+ -2} mm. The plates were annealed in an electric furnace at a temperature of 850 ° С; the annealing time was 60 min. After annealing, the surfaces of the plates were cleaned, the size of the removed layer was 0.15 mm per side.

The hot-rolled billet was heated before warm rolling in an electric furnace at a temperature of 750 ° C for 23 minutes. Warm rolling of the billet was carried out in a mill stand of a quarto 1700 warm rolling mill, with a total degree of deformation of 58.0%, to a thickness of 6.0 ^{+ -0.1} mm.

Cold rolling of sheets is carried out in a mill stand of a quarto 1700 warm rolling mill, with a total degree of deformation of 55.0%, to a thickness of 2.7 ^{+ -0.05} mm. Annealing of the sheets is carried out in an electric furnace at a temperature of 795 ° C, annealing time of 30 minutes, cooling in air.

Pilot batch:

TC6 alloy sheets with dimensions 2.5 × 800 × 2000 mm

Mechanical properties.

On Delivery:

Temporary tear resistance - 98.6 ... 100.4 kg / mm ² ;

Relative lengthening - 18.4 ... 21.6%;

Bending angle - 125 ... 143 °;

After heat treatment: Quenching - 800 ° C, holding for 10 minutes, cooling - water, aging - 480 ° C, holding for 25 hours

Temporary tear resistance - 138 ... 145 kg / mm ² ;

Relative lengthening - 6.8 ... 8.3%.

Claims (1)

A method of manufacturing sheets of β-titanium alloys, including machining the surface of the slab, hot, warm, cold rolling, annealing and aging, characterized in that after the machining the slab is punctured, hot rolling is carried out in two stages, while the first stage is rolling at a temperature of T _PP + (380-400 ° C) with a total degree of deformation of 85.0-95.0%, followed by annealing at a temperature of T _PP + (145-165 ° C), and at the second stage, rolling is carried out at a temperature of T _PP + (100-120 ° C) with a total degree of deformation of 45.0-55.0%, followed by conductive annealing in the temperature range _BTT + (50-165 ° C), warm rolling was conducted at a temperature _BTT + (10-30 ° C) with the total degree of deformation 40,0-60,0%, followed by annealing in the temperature range T _pp + (70-100 ° C), cold rolling is carried out with a total degree of deformation of 50.0-55.0%.