JPH04154945A - Manufacture of beta type titanium alloy strip - Google Patents

Abstract

PURPOSE:To manufacture the strip of a beta type Ti alloy with a fine grain structure, excellent in strength and ductility, at the time of rolling a beta type Ti alloy slab into a sheet material by properly controlling hot rolling conditions. CONSTITUTION:The slab of a beta type Ti alloy, e.g., having a compsn. constituted of 15% V, 3% Cr, 3% Sn, 3% Al and the balance Ti or having a compsn. constituted of 3% Al, 8% V, 6% Cr, 4% Mo, 4% Zr and the balance Ti is hot-rolled at >=850 deg.C and is thereafter coiled at <=350 deg.C. Or, the coiled Ti alloy hot rolled sheet is subjected to cold rolling, e.g. of about >=10% without executing heat treatment such as soln. treatment. The beta type Ti alloy strip with a fine structure in which working straines are uniformly dispersed and having high strength and high ductility is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides Ti-15%V-3%Cr-3%5n-3%
Aj2 alloy or Ti-3%Al2-8%■-6%Cr-4
By appropriately controlling the hot rolling conditions of titanium alloys containing β-phase stabilizing elements, such as %MO-4%Zr alloys, β-type titanium alloy strips having a fine grain structure with excellent strength and ductility can be produced. This relates to a manufacturing method.

[Conventional technology]

Titanium and titanium alloys have high specific strength and excellent corrosion resistance, so they are used in many material fields including aircraft parts, and their uses are expanding further. Among these, β-type titanium alloys have excellent cold workability and high strength compared to α-type and α+β-type titanium alloys, so they have been actively developed in recent years, and their demand is increasing. be. Strictly speaking, β-type titanium alloy is a metastable β-type alloy, and due to rapid cooling from the β region, β-type titanium alloy can be used even at room temperature.
It has a single phase structure and has age hardening properties.

The conventional manufacturing method for β-type titanium alloy strip is to perform heat treatment such as solution treatment after hot rolling, followed by cold rolling, solution treatment, and then aging treatment. The β grain size of the steel tends to become coarse, making it difficult to obtain a product with sufficient strength and ductility.

In order to refine the β grains in the final product, it is common practice to adjust the heat treatment conditions after hot rolling (for example, Japanese Patent Application Laid-Open No. 64-28348, Japanese Patent Publication No. 1-16910, etc.) ). The heat treatment temperature after hot rolling is 750-1150
It is shown in the above-mentioned patent documents that °C is commonly adopted.

[Problem to be solved by the invention]

However, in order to carry out the heat treatment after hot rolling,
There are problems in that the fuel cost for the heat source required for heating becomes large and expensive equipment is required. Moreover, since these methods do not take into account the state of the material, that is, the structure after hot rolling, it cannot be said that the β grains in the final product are sufficiently refined.

The present invention was completed as a result of various studies in response to the above-mentioned demands, and provides a hot-rolled material with a uniform structure and excellent ductility in the production of β-type titanium alloy strip. The purpose is to provide a material with excellent strength and ductility by using inter-rolled material to refine the structure of the final cold-rolled product without heat treatment after hot rolling.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present inventors focused on hot rolling conditions and conducted various studies on the effects of hot rolling temperature and coiling temperature on the structure and material properties of hot rolled materials. , found the following facts.

(1) When a β-type titanium alloy is hot-rolled and then wound into a coil at a high temperature, the cooling rate of the coil is slow, so that the β grains become coarser and the α phase precipitates during the cooling process after winding. As a result, the structure becomes non-uniform, the material becomes hard and its ductility decreases.

Therefore, the cold rolling properties of the hot rolled material are extremely poor, and the material itself is difficult to handle, so it is essential to perform solution treatment prior to cold rolling. In that case, the structure of the final product tends to become coarse grained.

(2) By hot rolling the β-type titanium alloy in a temperature range of 850° C. or higher and then winding it at a predetermined temperature or lower, coarsening of β grains and precipitation of α phase can be prevented. It also homogenizes the texture throughout the strip. Therefore, it is possible to cold-roll the hot-rolled material by subjecting it to heat treatment such as solution treatment.
In this case, the structure after cold rolling is fine and processing strain is uniformly distributed.

Therefore, since the recrystallization nuclei generated during the final solution treatment are uniformly and finely dispersed, a uniform fine grain structure can be obtained.

The present invention has been made based on the above findings, and its gist is as follows.

(1) A method for producing a β-type titanium alloy strip, which comprises hot rolling a β-type titanium alloy slab at a temperature range of 850°C or higher and then winding it at a temperature of 350°C or lower.

(2) A β-type titanium alloy slab is hot rolled at a temperature range of 850°C or higher, then coiled at a temperature of 350°C or lower, and then cold rolled without heat treatment. A method for producing β-type titanium alloy strip.

The present invention will be explained in detail below.

The β-type titanium alloy targeted by the present invention is Ti-15%V
-3%Cr-3%5n-3%A! , Ti-3%AI! ,
It is an alloy such as -8%V-6%Cr-4%Mo-4%Zr, and the target hot-rolled material is a slab manufactured by forging, blooming, etc., and the manufacturing conditions are not specified. It is not limited.

Next, regarding the hot rolling conditions, if the rolling temperature is less than 850°C, recrystallization or recovery of the β phase will not be sufficient, and if the coiling temperature exceeds 350°C, the α phase will precipitate. Therefore, the structure of the material after hot rolling becomes non-uniform, hardens and the ductility decreases. Therefore, the hot rolling end temperature was set to 850°C or higher, and the coiling temperature was set to 350°C or lower. Note that the rolling reduction rate in hot rolling is not particularly limited, but a higher one is desirable in order to make the crystal grains finer. Further, the cooling rate from the end temperature of hot rolling to the coiling temperature is desirably fast, and is preferably 20° C./second or more.

As described above, according to the method of the present invention, a hot rolled strip having a uniform β single phase structure and excellent ductility can be manufactured, but this is a hot rolled product as well as a cold rolled product. Also applied as an excellent intermediate material for manufacturing. In the present invention, the above hot rolled material is further cold rolled without being subjected to heat treatment such as solution treatment. In that case,
As mentioned above, the heat treatment after hot rolling that allows a uniform fine grain structure to be obtained after the final solution treatment means all commonly performed heat treatments such as solution treatment and softening annealing.

This is omitted and cold rolling is performed as it is, and the rolling reduction ratio is not particularly limited, but is preferably 10% or more. In addition, in the present invention, since no heat treatment is performed after hot rolling, the surface scale of the material is rough and thin, so descaling before cold rolling can be easily carried out, and there is little yield loss. As described above, the present invention is also excellent in terms of productivity and economy.

〔Example〕

Example 1 Typical β-type titanium alloy Ti-15%■-3%C
Slab of r-3%5n-3%AI2 alloy (thickness: 120
mm), and the hot rolling temperature and coiling temperature were varied to a plate thickness of 5III11. The structure and material evaluation results of the hot rolled material are shown in Table 1 and Figure 1, respectively. As shown in Table 1, the microstructures of hot-rolled materials Nos. 1 to 3 of the present invention are uniform β single-phase structures, whereas those of comparative material Nos.
No. 4 has a low rolling finish temperature and has a non-uniform structure with residual rolling strain, while Comparative material No. 5 has a high coiling temperature and has a non-uniform structure with precipitated α phase.

In Figure 1, the heating temperature is 1100℃, and the rolling end temperature is 95℃.
The temperature was kept constant at 0°C. As is clear from FIG. 1, when the coiling temperature exceeds 350° C., the ductility of the hot rolled material decreases extremely.

As an example of the microstructure of a hot-rolled plate produced by the method of the present invention,
Figure 2 shows a microstructure photograph of No. 1 material in Table 1, in which the heating temperature was 1100°C, the rolling end temperature was 950°C, and the coiling temperature was 300''C. Figure 3 shows a photograph of the microstructure of the material at a finishing temperature of 800°C.As described above, according to the present invention, the hot-rolled material has excellent ductility and has a uniform and fine β single phase. In addition, these hot-rolled materials were also cold-rolled, but since materials with a coiling temperature of 400°C or higher have poor ductility, edge cracks occur even at a rolling reduction of about 20%. Cold rolling with a high reduction ratio was not possible.

Example 2 Typical β alloy Ti-15%V-3%Cr-3%
A slab of 5n-3%An alloy (thickness = 120 mm) was hot-rolled to a thickness of 5+nm at a heating temperature of 950'C, finishing temperature of 900'C, winding temperature of 100'C, and then solution treatment. (Materials that were air-cooled after being held at 800″C for 100 minutes (comparative example) and materials that were not air-cooled (invention),
The results of investigating cold rolling-recrystallization behavior will be explained. Note that the solution treatment after cold rolling was performed by holding at so o "c for 5 minutes and then cooling in air.

The results are shown in Figure 4. The material subjected to solution treatment after hot rolling had a relatively coarse grain structure and was difficult to recrystallize. As a representative example of the structure, FIG. 5 shows a microstructure photograph of a hot-rolled material that was subjected to solution treatment after being cold rolled at a rolling reduction of 75% without being subjected to solution treatment.

As described above, it can be seen that according to the present invention, a uniform microstructure can be obtained.

〔Effect of the invention〕

As described above, the method of the present invention makes it possible to efficiently produce β-type titanium alloy strips having a uniform fine grain structure, which is difficult to achieve using conventional methods. is extremely large.

[Brief explanation of the drawing]

Figures 1 and 4 show Ti-15%V-3%Cr-3% respectively.
5n-3%A! FIG. 2 is a diagram showing the relationship between the coiling temperature during hot rolling of an alloy and the elongation at break of the hot rolled material, and a diagram showing the relationship between the cold rolling reduction ratio and the grain size after solution treatment. Further, Fig. 2 and Fig. 5 are both metallographic micrographs showing the cross-sectional metal structure of the Ti-15%V-3%Cr-3%5n-3% Affi alloy manufactured by the method of the present invention, and Fig. 3 is Ti-15%l-3%Cr-3%5n produced by comparative method
- It is a metal micrograph showing the cross-sectional metal structure of Affi alloy. (-utY) ”'f;) H tube color (%) make#γ

Claims (2)

[Claims] (1) A method for producing a β-type titanium alloy strip, which comprises hot rolling a β-type titanium alloy slab at a temperature range of 850°C or higher and then winding it at a temperature of 350°C or lower. (2) A β-type titanium alloy slab is hot rolled at a temperature range of 850°C or higher, then coiled at a temperature of 350°C or lower, and then cold rolled without heat treatment. A method for producing β-type titanium alloy strip.