JPS603913A - Extrusion method of titanium alloy - Google Patents

Abstract

PURPOSE:To form the surface layer of a billet into a (alpha+beta) structure of regular system and the inner part into a transformed (beta) structure by heating the (alpha+beta) type Ti alloy to the temperature of its (beta) transus or higher before uniformly cooling its surface to the temperature of a (alpha+beta) two-phase region, to perform an extrusion of the billet. CONSTITUTION:A billet of (alpha+beta) type Ti alloy is heated to the temperature of its (beta) transus or higher in a heating furnace, and then is taken out. A glass lubricant is coated on the surface of the billet to uniformly cool it to the temperature of a (alpha+beta) two-phase region. Then the billet is subjected to an extrusion work.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for extruding a titanium alloy, and in particular to a method for extruding an α+β type titanium alloy, which allows a titanium alloy with good properties to be obtained even under processing conditions with a small extrusion force.

Conventionally, extrusion of α+β type titanium alloys has been carried out in a single-phase temperature range of only the β phase or in a two-phase temperature range of the α+β phase. β
In extrusion in the − phase temperature range, that is, β-phase extrusion, the deformability of the billet is good and the deformation resistance is low, but the product has a transformed β structure containing the grain boundary α phase and has low strength.

On the other hand, extrusion in the two-phase temperature region of α + β phase, that is, α + β
Two-phase extrusion produces an equiaxed α+β structure, which improves strength, but requires a large extrusion force due to high deformation resistance.

As a result of many years of research, the present inventors have developed a titanium alloy that combines the advantages of the β-phase extrusion method, in which the extrusion force is small, and the advantages of the α+β two-phase extrusion method, in which an equiaxed α+β structure is formed and the strength is high. We discovered a method for extruding shapes and completed the present invention.

In other words, the gist of the present invention is to heat an α+β type titanium alloy billet to a temperature higher than the β transus, for example, in the air, and then uniformly cool the surface layer of the billet to a temperature range of α+β two phases. This is a method for extruding an α-1β type titanium alloy, in which the surface layer of the product has an equiaxed α+β structure and the inside has a transformed β structure, which consists of extruding the bireno 1.

As described above, according to the present invention, after taking out the extrusion fillet heated to a temperature higher than β(・Ranzas) from the IP,
Before inserting into the container of the extruder, the outer surface is uniformly cooled to lower only the surface layer of the fin to a temperature in the α→−β two-phase region, and then extrusion processing is carried out, thus improving the surface of the product. An α→-β type alloy shape is obtained in which the layers have an equiaxed α+β structure and the inside has a transformed β structure.

Please note that Tj-6AI is an α-ρ type alloy! −4ν,
Examples include Ti68β-6V-2Sn, but the present invention is not particularly limited thereto. Also, the β transus temperature is Ti-6^7! -4V is approximately 980'c, and Ti-6Aβ-6V-2Sn is approximately 950''c, and temperatures below these are in the α+β two-phase temperature range.Also, the α+β two-phase temperature range is from the β transus temperature to the α10β temperature range. Although it is preferable to uniformly cool the billet by using a billet rotating table as described later, it is not necessarily limited to this.

It is sufficient that the surface layer cooled to the α+β two-phase temperature region is only the outermost layer, and this does not limit the present invention, but generally, the thickness is about 100 mL, which is sufficient to impart the required mechanical properties. It is sufficient if it is about 2 to 3 dragons.

In addition, in a physical embodiment of the present invention, the fillet throat is heated at a temperature not much higher than the β transus, and after applying the glass moisturizing agent and the Fk agent, in order to uniformly cool the fillet throat surface. The billet is placed on a table equipped with a rotation mechanism and allowed to cool while rotating at -V, and the surface layer of the fillet is cooled to below the β transus for extrusion. When using a coated billet, the step of applying a glass moisturizing agent may be omitted.

A few benefits of the present invention are as follows.

First, titanium and titanium alloys have almost the same specific heat as iron, but their specific gravity is smaller (iron is about 7.9, titanium is about 4.5 > s conductivity (iron is about 0. 1
5 cal/cm/sec/'C, titanium is 0.041 cal/cm/sec/'C).Therefore, the surface of the material A'4 has a small heat capacity, so it is easy to cool down, and its thermal conductivity is small, so it is easy to cool down. It is a material that receives little heat from within, which means that it is easy for there to be temperature differences between the inside and outside.7 However, it is better to create a temperature difference between the inside and outside than to maintain a uniform temperature. It is a natural direction of effort, and its implementation is simple and easy.

In addition, the strength of products processed in the α + β two-phase temperature range to form an equiaxed α-deca β structure is superior to that processed in the β-phase temperature range to form a transformed β structure. . Profiles with irregular cross-sections are used as structural materials and therefore during use bending stresses are the predominant loaded stress state, in which case the highest stresses (i.e. tensile stresses)
is generated on the surface of the material, so the surface layer of the product is more N than the inside.
In other words, the inside is less important than the surface. Therefore, the products according to the invention can also be used satisfactorily as such structural materials.

Furthermore, in the method of the present invention, the extrusion force is smaller than when extruding an equiaxed α+β structure that is homogeneous throughout the cross section. It becomes possible to fear.

Next, the present invention will be further explained by examples.

α of Tt-6Ax-4■ having the alloy composition shown in Table 1
Using +β two-phase alloy (β transus temperature 980℃),'
l゛U-shaped carved shape moon (head: 60III x 12ml,
Legs: 28 dragons x 7III1. ) was extruded.

Figure 1 shows the glass 'a'irk after heating to 995°C.
This is a microstructure photograph of a monthly charge that was extruded after being cooled for 2 minutes after applying the agent. Figure 1 (bl shows the center part, and it can be seen that the center part is a transformed β structure. On the other hand, Figure 1 fal shows the surface layer, and the surface layer is a fine equiaxed structure) It can be seen that it has an α-1-β structure.

Figure 2 shows the glass/r! after heating to a temperature of l020°C. This is a microstructure photograph of a material that was extruded after being cooled for 1 minute after applying a disinfectant. Figure 2 tbl shows the central part, and it can be seen that the central part is a transformed "β structure. Figure 2 fal shows the surface layer, and the surface layer is also a fine transformed β structure. This is because the cooling time was short and the temperature was not cooled to the α+β two-phase temperature region.

In addition, the size of the β grains in the center structure in Figure 2 1b) is
The reason why it is larger than that in FIG. 1 fbl is due to the difference in heating temperature between the two.

Table 1 (% by weight) As described above, according to the present invention, relatively large shapes can be easily extruded and manufactured, and the resulting shapes have excellent resistance to bending stress. zu<41. I can see that it is.

[Brief explanation of drawings]

Figures 1 (+) and 1 (bl are partial cross-sectional micrographs of extruded moons extruded according to the method according to the present invention; This is a partial cross-sectional micrograph of the microscopic structure of the extruded material.Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose - Figure 1 Figure 2

Claims (3)

[Claims] (1) After heating a billet of α''-β type titanium alloy to a temperature above the β transus, the surface layer of the billet is
A method for extruding an α+β type titanium alloy in which the surface layer of the product has an equiaxed α+β structure and the inside has a transformed β structure, which comprises uniformly cooling the billet to a temperature in the two-phase region and then extruding the billet. . (2) The extrusion method according to claim 11, wherein the billet is coated with copper and then heated when the billet is heated to a temperature equal to or higher than the β transus. (3) The extrusion method according to claim 11'1, wherein when cooling the billet heated to a temperature equal to or higher than the β transus, a glass lubricant is applied to the surface of the billet. (a) A patent claim in which, when uniformly cooling the surface layer of the billet heated to a temperature higher than βl/Ranzas, the billet is kept on standby and rotated on a stand equipped with a rotating mechanism for billets and g. The extrusion method according to any one of items 111 to (3).