JPH05279835A - Production of titanium alloy valve - Google Patents

Abstract

PURPOSE:To manufacture a valve excellent in wear resistance without generating the thermal deformation of the shape at the time of manufacturing a Ti alloy valve, by preliminarily regulating the structure of Ti alloy stock to work it into a valve and thereafter oxidizing or nitriding its surface. CONSTITUTION:Stock constituted of the wire rod or bar stock of an alpha+beta type Ti alloy is preliminarily subjected to heat treatment to regulate its structure into an equi-axed alpha crystalline one, an acicular alpha crystalline one or a mixed one having 6 to 25mum grain size. On one end of the Ti allay wire rod or bar rod of 5 to 8mmphi constituted of equi-axed alpha crystals, acicular alpha crystals or the like, a ball shape heated to the beta transformation point or above is formed, and the part is subjected to die casting and is thereafter water-cooled or air- cooled to form a bevel part. After that, it is annealed under heating to the temp. range of 700 to 900 deg.C, is subjected to machining to improve its dimensional accuracy and is finished into a valve. Next, it is heated agbin at 700 to 900 deg.C to subject the surface to oxidation or nitridation or oxidation and nitridation simultaneously, by which the objective valve made of a Ti alloy excellent in wear resistance and good in dimensional accuracy is manufactured without generating the deformation of the shape caused by heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear resistant treatment of a titanium alloy valve used for an engine of a four-wheeled motor vehicle and other vehicles, and can be widely applied to a titanium alloy part requiring wear resistance. It is a thing.

[0002]

2. Description of the Related Art Oxidation (see Japanese Patent Application Laid-Open No. 62-256956) and nitriding (Japanese Patent Application Laid-Open No. 61-62
81505), ion nitriding (JP-A-61-2)
No. 34210), hard Cr plating, Ni-P plating (see JP-A-1-96407), molybdenum spraying (see JP-A-62-41908), and the like have been tried.

[0003]

Molybdenum thermal spraying has a proven record as a seizure prevention treatment for the shaft surface of titanium alloy valves of competitive automobile engines and competitive motorcycle engines, but the cost is actually high. .. Hard Cr plating and Ni-P plating are oxide films that inevitably exist on the surface of titanium alloys, so it is essentially difficult to secure plating adhesion, but surface roughening by shot blasting is essential. Efforts have been made to improve the plating adhesion by removing the oxide film by fluoric acid pickling and by heat diffusion after plating.

On the other hand, for oxidation and nitriding, a simple method is required in which the titanium alloy is heated in the atmosphere.
Although it has been attracting attention since it has excellent adhesion due to diffusion treatment, there is a problem in that it is not possible to secure the shape and dimension accuracy required for titanium alloy valves due to the need for heating at a high temperature, which causes thermal deformation. It was It is said that ion nitriding can lower the nitriding temperature,
The shape is still insufficient, and there are similar problems.

An object of the present invention is to provide a wear resistant treatment for a titanium alloy valve that solves the above problems.

[0006]

SUMMARY OF THE INVENTION The present inventor has found that in the conventional oxidation or nitriding treatment of titanium alloy,
It has been found that by adjusting the structure of the titanium alloy material in advance before the heating, it is possible to remarkably prevent the thermal deformation that occurs during the oxidation or nitriding treatment, which has been a problem in the past.

The present invention is based on such knowledge. In the wear resistance treatment of a titanium alloy valve, the structure of the titanium alloy, which is the valve material, is set to 6 μm or more and 25 μm or more.
After adjusting to an equiaxed α-crystal structure having a grain size of μm or less or a needle-shaped α-crystal structure or a mixed structure of equiaxed α-crystals and needle-shaped α-crystals,
The gist is a method for manufacturing a titanium alloy valve, which is characterized by processing into a valve shape and performing oxidation or nitridation or oxidation and nitridation by heating at 700 ° C. or higher and 900 ° C. or lower.

[0008]

In the present invention, the material of the titanium alloy valve is
Ti-3Al-2.5V, Ti-6Al-4V, Ti-
It is a wire rod or rod having a diameter of 5 to 30 mm, such as an α + β type titanium alloy such as 6Al-2Sn-4Zr-6Mo.

These wire rods or rods are manufactured for the purpose of obtaining an equiaxed α crystal structure uniformly in order to enhance both strength and ductility. The manufacturing conditions at this time are such that the hot working of these alloys is carried out at a temperature in the α + β range and at a sufficient reduction ratio, so that it is almost inevitable that a fine equiaxed α with a grain size of 3 to 6 μm is used. It has a crystal structure. Here, it is necessary to adjust the structure of the titanium alloy, which is the valve material, to an equiaxed α-crystal structure or a needle-shaped α-crystal structure or a mixed structure of equiaxed α-crystals and needle-shaped α-crystals having a grain size of 6 μm or more and 25 μm or less This is to prevent thermal deformation due to subsequent heating. Equiaxed α crystal is 6μ
If it is less than m, thermal deformation tends to occur remarkably as has been conventionally experienced, and if it exceeds 25 μm, the effect of preventing thermal deformation is the same, but it takes a long time to adjust the grain size, which is not realistic. In the case of a needle-shaped α crystal structure, either a fine needle-shaped α crystal structure (alpha prime) obtained by water cooling from the β region or a needle-shaped α crystal structure (play strike alpha) obtained by furnace cooling from the β region Effective in preventing thermal deformation. The mixed structure of equiaxed α-crystals and needle-shaped α-crystals can be obtained, for example, by using a material having an equiaxed α-crystal structure as T _β (β transformation point)>T> T _β −100.
The tissue may be water-cooled or air-cooled from the temperature T of ℃, or may be aged thereafter. In addition, the wire rod
During hot rolling in the + β area, the center of the wire is
It may be close to the range or beyond the β range.

A method of processing into a valve shape is, for example, to make a ball-like shape heated at a β transformation point or more at one end of a wire having a diameter of 7 mmφ and a length of 200 mm to obtain sufficient deformability,
The portion is die-forged and water-cooled or air-cooled to form an umbrella portion. After that, it is annealed at 700 to 900 ° C., and finished with dimensional accuracy by cutting. Here, the annealing temperature is
The temperature is higher than the heating temperature for the later abrasion resistance treatment, and cooling is performed at a low cooling rate of air cooling or lower so as to prevent deformation due to stress-induced transformation during processing and deformation during reheating due to introduction of strain.

By adjusting the structure of the present invention, it is possible to prevent the valve shaft from being excessively deformed during the annealing heating. Therefore, since the wire diameter close to the shaft diameter can be specified, the cutting load can be reduced. Note that if the deformation during annealing heating is cold-corrected, it will be deformed due to heating for later abrasion resistance treatment.

Next, oxidation or nitridation or oxidation and nitridation by heating at 700 ° C. or higher and 900 ° C. or lower is performed for abrasion resistance treatment. Wear resistance treatment is applied to the face part, shaft part,
Although required for the shaft end, the required level of wear resistance varies depending on the engine system and the mating material. For example, the face portion may be untreated when the mating material is a copper-based sheet. The shaft end is not necessary if iron is friction-welded. For example, assuming that each part is treated at the same time, the case of performing the abrasion resistance treatment of the valve face (the mating material is an iron-based sheet), which is the case where the most abrasion resistance is required, will be described.
This is because if the temperature is lower than 0 ° C, an extremely long time is required. Also, if the temperature exceeds 900 ° C., thermal deformation becomes apparent and the shape and dimensional accuracy of the valve cannot be secured even if the above-mentioned structure adjustment is performed.

[0013]

【Example】

[Example 1] No. 1 in Table 1 As shown in FIG. 1, 7 made of Ti-6Al-4V titanium alloy having an equiaxed α crystal structure with a grain size of 5 μm.
After heating the wire of mmφ to 900 ℃, cool it down to 15μ
The grain size was adjusted to an equiaxed α crystal structure of m grain size. Next, a valve was produced by the method described above. The annealing heating was performed for 1 hour at the same temperature as the abrasion resistance treatment temperature. Shaft is 6.6 mmφ
Approximately 810 ℃ in order to process the shaft and wear-proof the shaft.
It was heated in the atmosphere for 30 seconds. The heating was carried out by placing a titanium alloy valve on a rotatable table and rotating the shaft while using a propane gas burner. as a result,
The bending was 2 μm or less for a shaft length of 90 mm. Subsequently, when the titanium alloy valve was tested for 200 hours at 6000 RPM using a four-cylinder engine using a valve guide equivalent to F _C 25, no problem such as seizure of the shaft part occurred.

Example 2 The same test as in Example 1 was carried out under some conditions, and the results are shown in Table 1. 2-1
2 shows. It is apparent from Table 1 that the method of the present invention has almost no bending and is excellent in preventing seizure of the shaft portion. In addition, No. The needle-like structure of No. 6 is obtained by heating an air-structure of equiaxed α crystal at 1050 ° C. and air cooling. N
o. The structure of No. 7 was obtained by heating an equiaxed α crystal structure to 950 ° C. and air cooling.

[Example 3] In the same test as in Example 1,
Nos. 13 to 16 in Table 1 show the results of wear resistance treatment of the face portion (the mating member is a Fe-C-Cu based valve seat). As shown in Table 1, there is almost no bending, and as a result, the degree of umbrella runout of the face part is good, and the engine test result shows that the shaft part does not have seizure, and the face wear amount is practically usable. It was In addition, No. 13, 14,
16 needle-like structures are 9 mm in the β temperature range of 1000 to 1050 ° C.
It is a φ wire rod that is air-cooled. The line width of the needle-shaped α crystal was 3 to 4 μm.

[0016]

[Table 1]

[0017]

EFFECTS OF THE INVENTION According to the present invention, the face portion, the shaft portion, and the shaft end portion of the titanium alloy valve have been adopted because of the thermal deformation while being excellent in the ease of treatment and the abrasion resistance treatment. Oxidation and nitriding methods that could not be performed can be put to practical use because they can be performed with sufficient shape and dimension accuracy.

Claims (2)

[Claims] 1. In the wear resistance treatment of a titanium alloy valve, the structure of the titanium alloy, which is a valve material, is preliminarily set to 6
After adjusting to either equiaxed α-crystal structure with a grain size of μm or more and 25 μm or less, needle-shaped α-crystal structure or a mixed structure of equiaxed α-crystal and needle-shaped α-crystal, processed into a valve shape and 700 ° C or more 9
A method for manufacturing a titanium alloy valve, which comprises oxidizing or nitriding or oxidizing and nitriding by heating at a temperature of 00 ° C. or less. 2. The process for forming a valve shape according to the preceding paragraph is 5
-8mmφ titanium alloy wire or rod is made into a ball-shaped shape that is heated above the β transformation point at one end, and that part is die-forged and water-cooled or air-cooled to form an umbrella part and then machined. The method for manufacturing a titanium alloy valve according to claim 1, wherein: