JP3295910B2 - Method for manufacturing Ti alloy member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is a connecting rod, valve, Li
The present invention relates to a method for manufacturing a Ti alloy member such as a tena, and more particularly, to a method for manufacturing a Ti alloy member by directly hot forging a Ti alloy material.

[0002]

BACKGROUND OF THE INVENTION Connecting rods, valves,
Conventionally, iron-based materials have been mainly used for retainers and the like. However, since iron-based materials have a large specific gravity, they cannot always be said to be satisfactory materials for a demand for a lighter engine or a higher engine speed.

[0003] Therefore, recently, in some special vehicles such as racing cars, a Ti alloy having a small specific gravity has begun to be used as a material for connecting rods and the like. The composition of the Ti alloy in this case is 6% Al-4% V
An alloy represented by -Ti is generally used. 6% A
In the case of manufacturing the above-mentioned member using the 1-4% V-Ti alloy, a Ti alloy having the above composition is melted, and then the ingot is subjected to hot forging to obtain a product member having a desired shape. Further, if necessary, the obtained member is subjected to a cutting process for finishing.

[0004] In general, as hot forging is performed at a higher temperature, the deformability of the ingot material is increased, and the forgeability is improved. However, in the case of a Ti alloy having the above composition, hot forging is performed by α
If the temperature is higher than the temperature in the + β region, the crystal grain in the obtained alloy structure is coarsened and the toughness of the alloy is reduced. Therefore, hot forging is usually performed in the α + β region. ing. Accordingly, the impact value is also reduced.

However, in the hot forging in the above α + β temperature range, it is necessary to control the temperature of the surface and the inside of the ingot material as a whole in the α + β range, and in this temperature range. Ti of the above composition
Since the deformability of the alloy is not always high, the forgeability cannot be said to be good. Moreover, the cutting workability of the Ti alloy is not good. For this reason, in the case of supplying a large amount of stable products industrially, in forging, it is necessary to ensure sufficient forging quality. There is also a problem in terms of economics because it is inferior.

It is industrially advantageous to perform hot forging in a temperature range having a high deformability such as the β range, but as described above, such a temperature (β range temperature) is advantageous. Hot forging was not usually performed from the viewpoint of product characteristics because the toughness of the Ti alloy member was reduced.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a slight decrease in toughness is observed even when hot forging is performed directly on the ingot of a smelted Ti alloy in the β region. When it is applied to actual engine parts and it is an important factor to secure the fatigue strength accompanied by the stress concentration caused by the deformed shape, 6% Al-4 hot forged in the α + β region. It is an object of the present invention to provide a method of manufacturing a Ti alloy member having the same level of fatigue strength as that of a 5% V-Ti alloy, and has significantly improved workability as compared with a 6% Al-4% V-Ti alloy. The purpose of the present invention is to provide a method of manufacturing a Ti alloy member, and furthermore, the hot forgeability evaluated in items such as easy forging, easy temperature control, and obtaining a stable forged product. Is better, T
An object of the present invention is to provide a method for manufacturing an i-alloy member.

[0008]

In the present invention, Al: 2 to 4% by weight, V: 1.5 to 2.5% by weight,
A Ti alloy made by melting a Ti alloy substantially consisting of Ti, forming the Ti alloy into a desired shape by wasteland forming and hot forging at a β region temperature , and air cooling as it is. A method for manufacturing a member is provided, wherein Al:
2 to 4% by weight, V: 1.5 to 2.5% by weight, rare earth element (hereinafter referred to as REM): 0.20 to 0.45% by weight,
S: 0.05 to 0.11% by weight, the balance substantially consisting of Ti, and the ratio of the REM content to the S content is 3.
A Ti alloy of 8-4.2 obtained by melting a Ti alloy, shaping the obtained Ti alloy into a desired shape by rough terrain forming and hot forging in a temperature range of β region , and air cooling as it is. A method for manufacturing an alloy member is provided.

The method of the present invention comprises the steps of:
V: 1.5 to 2.5% by weight, with the balance being substantially composed of Ti
i alloy, Al: 2 to 4% by weight, V: 1.5 to 2.
5% by weight, REM: 0.20 to 0.45% by weight, S: 0.05
Applied to two types of Ti alloys consisting of 0.11% by weight and having a ratio of REM content to S content (REM / S) of 3.8 to 4.2. Is done. Among these two types of Ti alloys, the latter alloy is an alloy having improved machinability by containing REM and S.

[0010] In the Ti alloy used in the present invention, Al
Is a stable element of Ti and is a component that contributes to the improvement of the strength of the Ti alloy, and its content is set in the range of 2 to 4% by weight. If the Al content is less than 2% by weight, the above-mentioned effects cannot be obtained, while if it exceeds 4% by weight, the machinability is reduced. Preferably it is 2.5-3.5% by weight, more preferably 2.75-3.25% by weight.

V is a β-stable element of Ti;
Contributes to improving the strength of the alloy. If the content is less than 1.5% by weight, the above effects cannot be obtained, and if it exceeds 2.5% by weight, the machinability is reduced.
It is set within the range of 2.5% by weight. Preferably 1.75-
The content is preferably 2.25% by weight, more preferably 2.0 to 2.2% by weight.

[0012] REM and S are chemically bonded to form a stable compound when the alloy is melted. The inclusions in the structure are granulated to contribute to the improvement of the toughness of the Ti alloy and the improvement of the machinability. It is a contributing component. As the REM to be used, Y, Ce and other lanthanide-based REMs are preferable. These may be used alone or in combination.
More than one species may be combined as appropriate.

In this case, the content of REM is 0.20 to 0.4.
5% by weight, S is set to 0.05 to 0.11% by weight, and the ratio of the REM content to the S content (hereinafter referred to as REM /
S) is set to be 3.8 to 4.2. RE
The content of M and S is 0.20% by weight and 0.05% by weight, respectively.
If the amount is less than the above, the machinability and the like described above are not improved, and if the amount is more than 0.45% by weight and 0.11% by weight, respectively, the corrosion resistance and strength of the obtained Ti alloy are reduced. .

The preferred content of REM is 0.25 to 0.40.
%, More preferably 0.30 to 0.42% by weight. The preferable content of S is 0.06 to 0.10% by weight, and more preferably 0.07 to 0.09% by weight. When REM / S is out of the above range, cracks occur frequently during hot forging in the β region of the smelted Ti alloy, and in addition to the stable compound of REM and S, an independent REM or The presence of S in the alloy structure lowers the machinability of the alloy.

The preferred value of SEM / S is 3.9 to 4.1, more preferably 4.0 to 4.1. The Ti alloy used in the present invention may contain N, C, H, O, Fe, and the like as impurities. In that case, N, C, H, O,
The content of Fe was 0.02% by weight or less and 0.02% by weight, respectively.
% By weight, 0.005% by weight or less, 0.3% by weight or less,
It is necessary to regulate it to 4% by weight or less.

[0016] The Ti alloy of the present invention is produced as follows. That is, first, a predetermined amount of each component is introduced into a plasma progressive casting furnace (hereinafter, referred to as a PPC furnace) so as to have the above-described composition, and the whole is melted. In this case, the reason why the PPC furnace is used is that a higher temperature can be obtained as compared with other furnaces. At this time, when the Ti alloy containing REM and S is melted, REM, S
Then, spherical or angularly adjusted granules having a particle size of 0.3 to 2.5 mm are put into a furnace.

If the particle size is smaller than 0.3 mm, the P
In the process of melting in a PC furnace, most of REM and S are gasified and dissipated outside the furnace, and the content in the obtained Ti alloy is reduced, so that the above-mentioned effects are not exhibited. When the particles of the above are used, a part thereof remains in an undissolved state without completely dissolving in the PPC furnace, and finally obtained Ti
This is because ultrasonic defects occur in the structure of the alloy.

In the melt obtained in the PPC furnace, not all the components are dissolved uniformly, but only partially dissolved at the boundary between the components. Therefore, PP
The melt obtained in the furnace C is further transferred to a vacuum melting furnace, where the whole is completely melted and the components are homogenized.
The Ti alloy having the desired composition produced in this manner is then cast into a round bar or an ingot having a shape similar thereto.

After that, the ingot is rough-formed into a shape approximate to a desired shape, and then hot-forged into a predetermined member at a stretch. In any case, the rough land forming and the hot forging are performed at the β region temperature of the target Ti alloy. The boundary temperature between the β region and the α + β region varies depending on the composition of the Ti alloy, but in the case of the Ti alloy of the present invention, it is usually 920 to 930 ° C. (6% Al).
(-4% V-Ti alloy is located at 980 ° C.). Therefore, in the present invention, rough land forming and hot forging may be performed at any temperature within a temperature range higher than this temperature. Needless to say, the temperature is lower than the temperature at which the Ti alloy melts.

Therefore, temperature control during forging is as follows:
It becomes significantly easier than in the case of hot forging in the α + β region. Any method, such as forging or rolling, may be used as the rough land forming. At the time of hot forging, a conventional in-mold stretching method, a swaging method, a roll forging method, or the like may be applied to the material obtained by the rough land forming. In addition, although the working ratio at the time of hot forging is not particularly limited, it is usually preferably 40 to 80%.

[0021] In this way, the connecting rod, valve, Retail
The material hot forged into the desired member shape, such as a tool, is air-cooled as it is, and does not require any heat treatment, is subjected to surface finishing such as deburring, and is incorporated as a component into an automobile engine, for example. be able to.

[0022]

EXAMPLE After each component such as Al and V was put into a PPC furnace and melted, the obtained melt was transferred to a vacuum melting furnace where it was completely melted. The melt was cooled to obtain two types of ingot round bars having the compositions shown in Table 1. In addition, REM,
The average particle size of S was 1.5 mm and 2.0 mm, respectively.

[0023]

[Table 1]

Each of these samples was subjected to a tensile test at each temperature, and the reduction rate of the cross-sectional area when the sample was broken was measured. For comparison, 6% Al-4% VT
The same test was performed on the i-alloy as Comparative Material 1. The result is shown in FIG. In the figure, the symbol △ indicates sample 1,
○ indicates Sample 2 and ● indicates Comparative Material 1. As is clear from FIG. 1, when the temperature is in the β region (samples 1 and 2 have a temperature of 930 ° C. or higher, comparative material 1 has a temperature of 980 ° C. or higher), sample 1, sample 2 and comparative material 1 all exhibit high deformability. That is, at the β region temperature, the above-described Ti alloy shows good forgeability.

Then, hot forging was performed on Sample 1, Sample 2, and Comparative Material 1 at the temperatures shown in Table 2 at a working ratio of 70%, and the tensile strength of each of the obtained forged products was measured.
In addition, the Ono-type rotary bending fatigue test showed that
The notch material fatigue limit was measured. Table 2 summarizes the results.
It was shown to.

[0026]

[Table 2]

As is clear from the results shown in Table 2, the forged product obtained by the method of the present invention has tensile strength and fatigue limit comparable to those of the forged product in the α + β region, Although the fatigue limit of the smoothed material is lower than that of the forged product of the% Al-4% V-Ti alloy, the fatigue limit of the notch is almost the same, and the notch sensitivity is judged to be at the same level. it can.

Next, the same amount of REM and S
Was melted to form a 6% Al-4% V-Ti alloy, and the ingot was subjected to hot forging at a working ratio of 70% in the β region to obtain a comparative material 2. The cutability of the β region forged product of Sample 1, the β region forged product of Sample 2, the comparative material 1 and the comparative material 2 was examined according to the following specifications.

Cutting tool: Carbide K10, feed: 0.15 mm
/ rev, depth of cut: 1.5mm, cutting speed: 60m / min, cutting oil: none. The result is shown in FIG. In the figure, the mark ○ represents a β-region forged product of sample 1, the mark Δ represents a β-region forged product of sample 2, the mark ● represents a β-region forged product of comparative material 2, and the symbol Δ represents a β-region forged product of comparative material 1. .

As can be seen from FIG. 2, the Ti alloy member of the present invention has a 6% Al-added free-cutting element even when the free-cutting element REM or S is not added (sample 2).
The machinability is superior to the 4% V-Ti alloy member (Comparative Material 2). Sample 2 to which the free-cutting element is added has extremely excellent cutting properties.

[0031]

Taken together, according to the present invention, after the manufacturing process of the Ti alloy member of the present invention, an ingot of Ti alloy which is forged between the following Ide heat the wasteland molded in β region, it is air-cooled
It is manufactured simply by applying simple surface finishing such as deburring.
The temperature control becomes easier as compared with the conventional hot forging in the α + β region. And
Despite hot forging in the β range, the fatigue limit, especially the notch material fatigue limit, is 6% Al-4% VT
Notch sensitivity comparable to that of i-alloy members and notch sensitivity is at the same level. Furthermore, have excellent cutting properties, large industrial value, the automobile engine connecting rods, valves, retail
It can be used for other purposes .

[Brief description of the drawings]

FIG. 1 is a graph showing a reduction in area when a molten Ti alloy ingot is broken in a tensile test at each temperature.

FIG. 2 is a graph showing the machinability of a β-region forged product of a Ti alloy.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-257445 (JP, A) JP-A-58-145323 (JP, A) JP-A-62-109956 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22F 1/00-3/02 C22C 1/00-49/14 B21J 5/06

Claims (4)

(57) [Claims] 1. Al: 2 to 4% by weight, V: 1.5 to 2.
5 wt%, a Ti alloy substantially consisting of Ti is melted, and the Ti alloy is sequentially subjected to rough land forming and hot forging at a β-region temperature to obtain a desired shape , and air-cooled as it is. > A method for producing a Ti alloy member. 2. The method for producing a Ti alloy member according to claim 1, wherein said hot forging is performed by any of an in-mold stretching method, a swaging method and a roll forging method. 3. Al: 2-4% by weight, V: 1.5-2.
5% by weight, rare earth element: 0.20 to 0.45% by weight,
S: 0.05 to 0.11% by weight, the balance being substantially made of Ti, and the ratio of the content of rare earth element to the content of S is 3.8 to 4.2. A method for producing a Ti alloy member, wherein the Ti alloy is subjected to rough land forming and hot forging sequentially in a β-region temperature to obtain a desired shape , and air-cooled as it is. 4. The method for producing a Ti alloy member according to claim 3, wherein said hot forging is performed by any of an in-mold stretching method, a swaging method and a roll forging method.