JPH06184683A - Titanium alloy wire suitable for producing valve and its production - Google Patents

Abstract

PURPOSE:To realize a titanium alloy material applicable to an automotive engine on the market by forming the microstructure of alpha+beta titanium alloy wire rod into an acicular crystal structure and regulating the width of the crystals and the size of the old beta grains into specified value. CONSTITUTION:The microstructure of alpha+beta type titanium alloy wire rod is formed of an acicular alpha crystal structure, and the width of the alpha crystals is regulated to 1 to 4mum and the size of the old beta grains to <=300mum. The diameter of the wire rod is regulated to 5 to 10mm. Hot rolling is executed in the temp. range of the beta phase. It is heated in the temp. range of the alpha+beta phases and is subjected to hot rolling to generate heat by the working and to regulate the temp. range into a one of the beta phase. Successively, hot rolling is executed. In this way, thermal deformation which has been the problem from the viewpoint of the production of the conventional titanium alloy valve can be prevented, a rough shape material small in grinding margins can be formed, the yield is improved, the grinding cost is reduced and oxidizing and nitriding which are simple treatment for preventing seizure on the shaft part are made practicable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium alloy wire suitable for the production of a titanium alloy valve mainly used in high performance engines for commercial vehicles and a method for producing the same, on the premise of mass production.

[0002]

2. Description of the Related Art Up to now, there has been no report on a titanium alloy wire suitable for manufacturing valves for commercial vehicle engines. The reason for this is that the titanium alloy valve was only applied to the engine of a race car that emphasizes performance. On the other hand, in a conventional engine valve manufacturing method, for example, a heat-resistant steel wire having a wire diameter of 7 mm is hot-die forged by an electric shrinkage method to form a rough valve. The umbrella part is mainly ground on the contact surface with the valve seat, and the shaft part is finished by grinding with a centerless grinder about 0.3 mm in diameter, which is extremely efficient in production. .

For engine valves made of titanium alloy,
Titanium-zirconium magazine, Vol.35, No.2, reports that it is made in the same way, but it is disclosed in Japanese Patent Laid-Open No. 64-283.
Japanese Patent No. 47 describes that the shaft portion needs to be straightened after forging. As a solution to this problem, Japanese Patent Laid-Open No. 64-28
Japanese Patent No. 347 proposes a method of avoiding the bending of the shaft portion and the correction necessary therefor by a method of forming the umbrella portion and the shaft portion separately and then performing diffusion bonding or pressure welding.

Next, the valve that has been subjected to grinding finish is subjected to a surface treatment in order to impart wear resistance. The heat-resistant steel valve is nitrided and has extremely high productivity. On the other hand, the shaft of the titanium alloy valve is Mo-sprayed and then center-lace ground.

Finally, the umbrella portion is required to have creep strength. In Japanese Patent Laid-Open No. 64-28347, after cooling with water from the β-phase temperature range, it is heated again to 950 ° C., and a forging ratio of 2.
A method of processing at 0 and air cooling is proposed. But,
It is difficult to maintain the forging ratio of 2.0 and form the umbrella portion having a complicated shape, and it is unavoidable to cut the forged material into a cylindrical shape.

[0006]

The method of separately forming the umbrella portion and the shaft portion and joining them has low productivity. INDUSTRIAL APPLICABILITY The present invention is a titanium alloy wire suitable for producing a rough valve which is produced by an electric shrinkage method like an ordinary heat-resistant steel engine valve and has no bending of a shaft portion and a small grinding allowance. And the method of performing Mo spraying on the shaft portion are expensive, but effective oxidation and nitriding are performed not only on the shaft portion which has been conventionally studied but also on the face portion and the shaft end portion. Providing a titanium alloy wire that can be put to practical use (Oxidation and nitriding have not been applied so far because thermal deformation occurs.) In addition to the fatigue strength and creep strength of the umbrella part, considering productivity, The purpose is to ensure a level applicable to commercial vehicle engines.

[0007]

Means for Solving the Problems The gist of the present invention is that (1) the microstructure of an α + β type titanium alloy wire is an acicular α crystal structure, and the width of the α crystal is 1 μm or more and 4 μm or less. A titanium alloy wire suitable for valve production, and (2) a microstructure of an α + β type titanium alloy wire rod is an acicular α crystal structure, and an old β grain size is 300 μm or less, which is suitable for valve production. Titanium alloy wire,
(3) The wire rod of the preceding paragraph has a diameter of 5 to 10 mm, and (4) the wire rod of the preceding paragraph is hot-rolled in the β phase temperature range to be manufactured, and (5) α + β phase temperature. It is a method for producing a titanium alloy wire suitable for valve production, which is characterized in that heating is performed in a zone and hot rolling is performed to generate processing heat, a β phase temperature range is obtained, and hot rolling is subsequently performed.

[0008]

Here, the reason why the microstructure of the α + β type titanium alloy wire is the needle-shaped α crystal structure and the width of the α crystal is 1 μm or more and 4 μm or less is that the equiaxed α crystal structure is formed by the electric stretching method. This is because the shaft portion near the umbrella portion is greatly bent when the valve is manufactured by. This is because after the die forging is completed, the valve is conveyed while rolling it in a random manner, but at this time, the main reason is that the shaft portion, which has a high temperature of about 700 ° C. or higher, is deformed by its own weight. Similar to the above, strain relief annealing after forging and oxidation and nitriding as surface treatment are also performed at about 700 ° C or higher, but at this time, it is inserted into the furnace randomly or inserted into a rope-like object. It was proved that it is heated by and it is thermally deformed by its own weight. To further suppress such thermal deformation, a coarse acicular α-crystal structure of more than 4 μm is suitable, but considering the decrease in the fatigue strength of the shaft part, the width of the α-crystal is 1 μm or more and 4 μm or less. The ones are suitable. Those having a thickness of less than 1 μm can be obtained by quenching from the β-phase temperature range after hot rolling, but there is no elongation and it becomes difficult to straighten the wire. The old β particle size is set to 300 μm or less because if it exceeds this value, the elongation becomes 10% or less, and similarly, it becomes difficult to straighten the wire. Further, when the old β particle size is so small that it cannot be confirmed, the problem of thermal deformation does not occur as long as it has a needle-like structure.

In the present invention, the diameter of the wire is preferably 5 mm or more and 10 mm or less. The reason is that α + β type titanium alloys generally have low cold drawing efficiency, so that they are as close to the valve shaft diameter as possible in manufacturing. This is because the diameter having a necessary grinding allowance is directly obtained. Further, since the cooling rate can be increased because of the thin wire, it is possible to prevent the fatigue strength from being lowered due to the increase in the β grain size and the width of the α crystal during the cooling from the β phase temperature range after the rolling. Further, it is also advantageous in the case of forming needles due to heat generated during processing during rolling.

In the β-phase temperature range, a wire rod having a needle-like structure is manufactured by hot rolling. When a α + β titanium alloy wire rod having a wire diameter of 5 mm or more and 10 mm or less is produced by hot rolling, α +
If it is carried out in the β-phase temperature range, it is rolled at a sufficient reduction ratio, and unlike thick plates and the like, cooling is fast, so the diameter of the α crystal is necessarily 2
This is because a fine equiaxed α-crystal of about 4 μm is obtained. Those having this structure are apt to cause a creep phenomenon and are extremely disadvantageous to thermal deformation. Further, in order to avoid this, it is possible to obtain equiaxed α-crystals having a large α-crystal diameter, acicular crystals, and bimodal structure by heat treatment to prevent creep from occurring. It is not realistic because it is greatly deformed and difficult to correct. Incidentally, for example, Ti-6Al-4V wire rods have bolts and the like as a conventional main application, but since fatigue strength and elongation are important, they are all fine equiaxed α crystals.

On the other hand, when hot rolling in the β phase temperature range,
Normally, it is heated in the β-phase temperature range, but since surface defects due to oxidation are likely to occur, it is heated in the α + β-phase temperature range and hot-rolled to generate working heat, and then placed in the β-phase temperature range, followed by hot rolling. The method of doing is advantageous.

For the above reasons, heating in the β-phase temperature range or α
In either case of heating in the + β phase temperature range, a method of obtaining a needle-like structure by hot rolling substantially in the β phase temperature range is suitable. Since the wire diameter is small, it is easily cooled, so it is necessary to perform hot rolling at a high speed of, for example, about 50 m / sec. Regarding the creep strength of the umbrella portion, it was found that by using the wire rod of the present invention and forging at the umbrella portion forging temperature in the β range, a needle-like structure was obtained, and the creep strength had no practical problem. did.

Here, the α + β type titanium alloy wire occupies most of the titanium alloy, and as a representative of Ti-6Al-4V, which is economically recovered by scrapping, the other is Ti-6Al-.
2Sn-4Zr-2Mo, Ti-6Al-2Fe-0.
1Si, Ti-3Al-2.5V, Ti-5Al-1F
e, Ti-5Al-2Cr-1Fe, Ti-6Al-2
Sn-4Zr-6Mo and the like can also be applied.

[0014]

EXAMPLE A 100 mm square Ti-6Al-4V billet was rolled from the β phase temperature range of 1050 ° C. to obtain a wire rod of about 7.5 mmφ. The microstructure of the L section is a needle-shaped α crystal structure,
The width of the α crystal was about 2 μm. The old β particle size is 30 ~
It was 60 μm. After shaving, the wire rod was straightened and centerless ground to obtain a 7.0 mmφ linear wire rod. Further, using this wire, as shown in FIG. 1, the umbrella portion was forged in the β-phase temperature range (about 1050 ° C.) by the electric shrinkage method, annealed at 810 ° C. for 1 minute and then air-cooled, and the umbrella diameter 36 m.
A valve having m, a shaft diameter of 6.7 mmφ, and a valve length of 110 mm was manufactured by cutting and grinding.

No. 1 in Table 1 As shown in Fig. 1, the runout of the umbrella after the forging was 0 to 50 µm, which was a marked improvement over the conventional method (Comparative Examples A and B in Table 1). Also, with the valve laid horizontally as shown in FIG.
The bending upon partial oxidation was 0 to 5 μm, showing a marked improvement over the conventional method. Furthermore, the estimated fatigue strength of the valve shaft was 50 kgf / mm ² , which was equivalent to that of the conventional method. The estimated creep strength of the valve head portion reaches a creep strain of 0.1% at 10 kg / mm ² under the condition of 500 ° C. for 100 hours, and it can be seen that there is no problem in practical use as an intake valve.

The umbrella run-out was measured by a dial gauge while supporting two points within 80 mm of the shaft and rotating the valve. The bend supports two points within 80mm of the shaft,
When the valve was rotated, the axial runout at the center between the supports was measured with a dial gauge. The estimated fatigue strength of the valve shaft portion was measured by the Ono-type rotary bending test with a shaft diameter of 8 mmφ by treating the same material as the valve shaft portion. The estimated creep strength of the valve umbrella is the same as that of the same material as the valve umbrella.
Performed by ISZ2271 test.

Another embodiment of the present invention (N
o. 2 to 11) are shown in Table 1 together with Comparative Examples. According to this, all of the present invention gave good results. The creep strength of the umbrella portion did not differ from those of the examples and comparative examples. In addition,
The titanium alloy wire of Example 2 was 100 mm square Ti-6Al.
A -4V billet is heated in the α + β phase temperature range of 950 ° C to generate processing heat during rolling, is placed in the β phase temperature range, and is continuously rolled to obtain a wire rod of about 7.5 mmφ. The microstructure of the L section was a needle-shaped α crystal structure, and the width of the α crystal was about 3 μm. The old β particle size was 30 to 60 μm.

[0018]

[Table 1]

[0019]

According to the present invention, thermal deformation, which has been a problem in the production of conventional titanium alloy valves, can be prevented, resulting in a rough material with a small grinding allowance, improving yield, reducing grinding cost, and simplifying. A great effect can be expected in mass production that oxidation and nitriding, which are treatments to prevent seizure of the shaft portion, can be put to practical use.

[Brief description of drawings]

FIG. 1 is a side view of a valve.

FIG. 2 is a view in which the valve is placed horizontally.

[Explanation of symbols]

 1 Umbrella part 2 Shaft part

Claims (5)

[Claims] 1. A titanium alloy wire suitable for valve production, wherein the microstructure of the α + β type titanium alloy wire is an acicular α crystal structure, and the width of the α crystal is 1 μm or more and 4 μm or less. 2. A titanium alloy wire suitable for valve production, wherein the microstructure of the α + β type titanium alloy wire is an acicular α crystal structure and the old β grain size is 300 μm or less. 3. A titanium alloy wire suitable for manufacturing a valve according to claim 1 or 2, wherein the wire has a diameter of 5 mm or more and 10 mm or less. 4. The method for producing a titanium alloy wire suitable for producing a valve according to claim 3, wherein hot rolling is performed in a β phase temperature range. 5. A valve manufacturing method according to claim 3, wherein heating is performed in the α + β phase temperature range and hot rolling is performed to generate processing heat, and the β phase temperature range is obtained, followed by hot rolling. Method for manufacturing titanium alloy wire.