JPS61204359A - Manufacture of beta type titanium alloy material - Google Patents

Abstract

PURPOSE:To obtain the titled material having superior mechanical strength and plenty ductility, by applying ingot break down such as forging or bloom rolling to beta Ti alloy ingot at two temp. ranges by specified drafts respectively. CONSTITUTION:beta Ti alloy ingot is forged or rolled by iota10%, favorably >=30% draft at temp. of beta transformation point +>=100 deg.C, favorably beta transformation point +200 deg.C- said point +300 deg.C. Next, said ingot is heated to temp. range of beta transformation point +100 deg.C- said point -150 deg.C, successively forged or loom rolled by >=30% total draft at >=2 heats in said temp. range to carry out ingot break down. Since beta Ti alloy material obtd. by the method has extremely superior ductility, working at the following process is easy and is applied as intermediate material for hot rolling, warm rolling, finish forging, extrusion, cold rolling, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The invention of this application relates to a method for producing a β-type titanium alloy material that has excellent mechanical strength and is highly ductile.

Prior Art and Problems Titanium and titanium alloys have excellent specific strength, corrosion resistance, and heat resistance, so they are used in a wide range of applications such as spacecraft materials, various chemical plants, and seawater desalination equipment. .

Among titanium alloys, Ti-6 is an α+β type titanium alloy.
AI-4V alloy is well known, but this α+β type titanium alloy generally has poor workability and has the drawback of requiring many complicated steps to produce the final product.

On the other hand, β-type titanium alloys, which form a single β phase even at room temperature by rapid cooling from the β region, are said to have excellent workability and age hardenability, but their manufacturing process has not been fully elucidated.

Furthermore, in actual manufacturing, it has been considered difficult to fully bring out the five characteristics mentioned above.

Structure of the Invention The invention of this application was made in view of this point, and β
The type titanium alloy cast ingot is heated to a temperature of β transformation point +100°C or higher, then forged or bloomed at a processing rate of 10% or more in the above temperature range, and then heated to β transformation point +100°C.
It is recommended to perform ingot breakdown by heating to a temperature range of ℃ to β transformation point -150 ℃, and then performing forging or blooming at a total processing rate of 50% or more in the above temperature range at least 2 heat or more. A method for producing a β-type titanium alloy material with a fine β-type titanium alloy material, and a β-type titanium alloy casting ingot is heated to a temperature of β transformation point + 100 ° C. or higher, and then forged or fractionated at a working rate of 10 mm or higher in the above temperature range. Perform block rolling, then β transformation point +100℃ to β transformation point -150℃
After the ingot is broken down by heating to a temperature range of °C and then forging or blooming at a total working rate of 50q6 or more at at least 2 heat in the above temperature range, β transformation point -250 °C to β transformation The present invention provides a method for producing a β-titanium alloy material, characterized in that hot rolling or the like is performed at a point.

Strictly speaking, the β-cracked titanium alloy mentioned above is a metastable β-type alloy, and as such a metastable β-type titanium alloy, Ti-
15V-! 1Cr-3Sn-3AI alloy, Ti-13V
-11Cr-! iA1 alloy, 'l'l-115MO-1
-1l5.5Sn alloy, Tl-8Mo-8V-2Fe-
5A1 alloy, etc., and the present invention is applied to beta-teta y alloys containing such alloys.

Detailed Description of the Invention Generally, ingots that have been melted and cast are subjected to ingot breakdown in order to destroy the casting structure and to create an intermediate material suitable for subsequent processes.
When producing the β-type titanium alloy material of the present invention, first, a β-type titanium alloy cast ingot is heated to a temperature of β transformation point + 100°C or higher, and then forged or bloomed at a processing rate of 10- or higher in the above temperature range. It is characterized by the fact that

Although the cast structure of the ingot is destroyed in this step, a high temperature region with a fast diffusion rate and good workability is desirable. If the processing rate is low, the above-mentioned objective of destroying the cast structure cannot be achieved. Furthermore, if the temperature is too low, cracks are likely to occur, which is dangerous.

More preferably β transformation point +200°C to β transformation point +300
Better results can be obtained if forging or rolling is carried out at a temperature of 30° C. and a processing rate of 30 inches or more.

If only the above steps are used, the β grain size of the material becomes coarse, resulting in poor ductility.

Next, the present invention has a β-transformation point of +100°C to a β-transformation point of −150°C.
It is further characterized in that it is heated to a temperature range of 'C, and then forged or bloomed at a total working rate of 30 heat or more in the above temperature range at least 2 heat or more.

This makes the β grains finer and significantly improves ductility. In the above, temperatures below β-150°C are unsuitable because the deformation resistance is high and surface cracks occur. Further, at temperatures exceeding the β transformation point +100° C., the β grains tend to become coarser, so no improvement in ductility can be expected.

Further, in this step, it is necessary to repeat the process at least twice or more with a total processing rate of 30 inches or more.

Ingot breakdown is completed through the above steps, but since the β-ya titanium alloy material obtained by this method has extremely excellent ductility, it is easy to process in the next step, and it is suitable for hot rolling, warm rolling, etc. It is applied as an intermediate material for rolling, finish forging, extrusion, cold rolled materials, etc.

In the present invention, the material which has undergone the above ingot breakdown is further heated to a temperature range of -250°C to the β transformation point, and then subjected to processing such as hot rolling, thereby achieving even better ductility and strength. can be granted.

This processing such as hot rolling is performed by repeatedly holding the β-transformation point at −250° C. several times, and usually turning the material around 2 to 20 times. The above-mentioned excellent properties can be obtained by repeating this heating and processing such as rolling 5 to 15 times.

The α phase and the like are precipitated by heating from the β transformation point of −450° C. to the β transformation point after processing such as hot rolling.

This precipitation is shifted to the short time side due to the processing strain in the previous process, and the precipitation is well impacted. Furthermore, since the strain or dislocation accumulated during processing such as rolling becomes a precipitation site, the precipitation does not concentrate on the grain boundaries, so the ductility of the material is not lost. During processing such as hot rolling, some precipitation of α phase may be observed during processing, but this does not impede the effects of the present invention in any way.

In addition to the hot rolling process, similar effects can be obtained by performing processes such as hot forging and extrusion drawing, and the present invention includes all of these processes.

Effects of the Present Invention The present invention can provide a titanium alloy material with extremely excellent ductility compared to the conventional method of simply performing ingot breakdown at a high temperature higher than the β transformation point.

Further, by hot rolling in the temperature range shown above after the ingot breakdown of the present invention, it has a remarkable effect of maintaining excellent ductility and imparting strength.

Next, an example will be described.

Tables 1 and 2 show the ingot breakdown conditions and hot rolling conditions as well as the resulting properties when applied to the Ti-15V-5Cr-3Sn-5AI alloy of Example. The same table also shows comparative examples different from the articles of the present invention.

Note that the β transformation point of the titanium alloy is 760°C, and 71
Ingot breakdown was performed by forging using a 0φ ingot.

Table 1 shows the materials that have gone through various ingot breakdown conditions, in solution treatment (ST) state at 788°C x 20 m1nAC.
The tensile properties of the specimen were evaluated in the state of surface cracking. A 1- JIS No. 13 B test piece was used as the tensile test piece. In addition, the surface crack condition is determined by the depth α in a surface area of 100 cm.
Evaluation was made based on the total length of surface cracks of 5 fi or more.

In addition, process ■ and process ■ in the table are performed after step I.
It is carried out. As is clear from Examples 1 to 4 of the present invention shown in Table 1 above, it can be seen that by applying a processing rate of 10% or more in Step I, remarkable ductility can be obtained compared to the comparative example. Moreover, as the processing rate gradually increases, the elongation value further improves.

Examples 3.5 to 8 are different in the number of heats in step (2) and the total processing rate, but it can be seen that when the number of heats is 5 or more, the elongation value further improves. It can be seen that when the number of times of heating is two or more, superior ductility is obtained compared to the comparative example.

In addition, Examples 3, 10, and 11 show examples in which the processing temperature range in step (2) was different, and all of them show superior ductility compared to the comparative example. It can be seen that among these, the heating temperature of 800° C. is the most superior.

Comparative Examples 12 to 17 were all conducted under conditions that did not satisfy the present invention, but the ductility (elongation value)
It is also inferior in terms of surface cracks, etc.

Table 2 shows evaluations of materials obtained by hot rolling according to the present invention after ingot breakdown according to the present invention, and comparative examples under different implementation conditions from the present invention. The evaluation method is the same as in Table 1, but the heat treatment is solution aging treatment (STA) 78 s”CX20m1nAC+5
Conducting 10°C x 8 hrAc.

As is clear from Table 2, the samples satisfying the present invention are good in all aspects of strength, ductility, and surface condition, but the comparative examples are inferior to the present invention in these respects.

Claims (2)

[Claims] (1) β-type titanium alloy casting ingot with β transformation point +10
Heating to a temperature of 0℃ or higher, then 10% in the above temperature range
Forging or blooming at the above processing rate is performed, then heated to a temperature range of β transformation point +100°C to β transformation point -150°C, and then the total processing rate is 30% or more with at least 2 heat or more in the above temperature range 1. A method for producing a β-type titanium alloy material, which comprises performing ingot breakdown by forging or blooming. (2) β-type titanium alloy casting ingot with β transformation point +10
Heating to a temperature of 0°C or higher, and then heating in the above temperature range for 10
Forging or blooming with a working rate of % or more, then heating to a temperature range of β transformation point +100°C to β transformation point -150°C, and then continuing at least 2 heat in the above temperature range to 30% total working rate. After performing ingot breakdown by performing the above forging or blooming rolling, β transformation point -2
A method for producing a β-type titanium alloy material, which comprises performing processing such as hot rolling at a temperature of 50° C. to a β transformation point.