JPS63186841A - Titanium alloy forged parts and its production - Google Patents

Abstract

PURPOSE:To produce a lightened Ti alloy forged parts having high hardness at low cost, by subjecting a material obtd. by preliminarily applying an alloy consisting of specific compsns. of Zr and Ti to wire drawing machining to a specified oxidizing treatment and thereafter subjecting the alloy to a lubrication treatment and cold forging. CONSTITUTION:The Ti alloy composed of 5-22wt.% Zr and the balance consisting of Ti with inevitable impurities is preliminarily applied to the wire drawing machining. Said material is subjected to the oxidizing treatment at 450-600 deg.C for 10-60min to form an oxidized film onto the surface thereof. Said material subjected to the oxidizing treatment is then applied to the lubrication treatment and thereafter is subjected to the main molding by executing the cold forging. In this way, the Ti alloy forged parts having the hardness >=270Hv is obtd. Said forged parts are furthermore subjected to a nitriding treatment at 400-550 deg.C after the main molding, by which the wear resistance can be improved while retaining the internal hardness to >=270Hv.

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention provides a forged titanium alloy that becomes highly hard when processed into a predetermined shape by cold forging, secures the required strength, and is lightweight. Regarding parts and their manufacturing methods.

(Conventional technology and its problems) Valve retainers conventionally used in automobiles, aircraft, etc.
Alternatively, gears and the like were manufactured by carburizing, quenching, and tempering case-hardened steel or structural steel, but recently, as engines are becoming increasingly high-torque and high-speed, it is necessary to reduce the weight of these parts. The use of titanium as the material is being considered.

However, pure Ti material with good cold forgeability (hereinafter abbreviated as "cold forgeability") lacks the hardness after forging for this part that requires wear resistance, and (α+β) type Ti material has
Although it has high hardness, it has poor cold forging properties, so it can only be manufactured by hot forging, resulting in high costs.

With β-type Ti material, work cracking during cold forging, that is, cold forging cracking, does not occur, and the hardness after forging is high, and it is possible to further increase the hardness by aging in the post-process, but the alloy composition There was a problem that the material cost was high and the deformation resistance was too high, resulting in a short tool life.

Therefore, an object of the present invention is to provide a lightweight forged part that has sufficient hardness after cold forging and is made of inexpensive material.

Furthermore, another object of the present invention is to provide a method for manufacturing the above-mentioned forged parts from a titanium alloy, which can easily reduce the weight.

(Means for Solving the Problems) In view of the above-mentioned current situation, the inventors of the present invention started with and studied Zr-based Ti alloys, which have low material costs, and found that a specific alloy composition among them He realized that it exhibited excellent workability during cold forging and maintained a high level of hardness after cold forging, making it ideal for forged parts such as valve retainers and gears. The inventors found that in order to maintain cold forgeability and make the hardness of the part after main forming by cold forging to Hv270 or more, Zr≧1.0% by weight and Zr+25
X [(h]≧5wt% and 3×Zr+ 220X
It has been found that a Ti-Zr alloy containing zirconium in an amount satisfying the condition of [0□]≦66% by weight and oxygen as an impurity or an active additive element is suitable.

In addition, when applying the specific material to the production of forged parts,
Wire drawing is performed in advance to increase the hardness by work hardening so that the hardness after cold forging is Hv270 or higher, and oxidation treatment is performed with limited temperature and time to prevent seizure before the main forming by cold forging. , and learned that subsequent lubrication treatment can prevent softening and ensure the required cold forgeability.

Furthermore, it has been found that after the main forming by cold forging, a low-temperature nitriding treatment of 400 to 550°C is performed to harden the surface but prevent internal softening, thereby further preventing wear.

That is, the gist of this invention is that Zr≧1.
0% by weight, and Zr+25X [0□]≧5% by weight and 3×Zr+ 220X [Oz] 566% by weight
This forged part is made of a titanium alloy and has a hardness of Hv 270 or more, which is made of a titanium alloy having a composition of zirconium and oxygen in amounts that satisfy the following conditions, the balance being titanium and unavoidable impurities.

Furthermore, the gist of this invention is that Zr≧1.0
% by weight, and an amount of zirconium and oxygen that satisfies the conditions of Zr + 25X [Oz] ≧ 5% by weight and 3 x Zr + 220x [0□] ≦ 66% by weight, the balance consisting of titanium and unavoidable impurities, consisting of a titanium alloy. Prior to final forming by cold forging, the wire-drawn material is oxidized for 10 to 60 minutes at a temperature range of 450 to 600°C to form an oxide film on the surface, and then lubricated. This is a method for manufacturing a forged titanium alloy part, which is characterized by subjecting the titanium alloy to a treatment, followed by main forming by cold forging to obtain a hardness of Hv 270 or more.

In addition, when oxygen exists only as an impurity, the above-mentioned alloy composition becomes Zr: 5 to 22% by weight, and the balance is titanium, which is an inevitable impurity.

In another aspect of the invention, the forged part is made of 400
Nitriding treatment in the temperature range of ~550℃ to reduce the internal hardness to Hv
Provided is a method for manufacturing a titanium alloy forged part characterized in that the titanium alloy forged part is maintained at a temperature of 270 or higher.

(Function) Hereinafter, a case in which the present invention is applied to a valve retainer for an automobile will be described in detail with reference to the accompanying drawings.

Figure 1 fat and Cb) are processing material (slag) I
FIG. 2 is a schematic cross-sectional view of the valve retainer 12 and the valve retainer 12. FIG. The slug 10 is manufactured by cutting or cold forging from a wire rod that has been work-hardened by drawing a hot-rolled material. This is formed into a general shape, and then subjected to proper lubrication treatment and finally formed by cold forging to form the valve retainer 12 of a predetermined shape and size.

Note that it will be clear to those skilled in the art that the dimensions, shape, etc. are not limited to specific values. The illustrated example is for illustration only.

FIG. 2 is a process diagram of a method for manufacturing a valve retainer according to the present invention.

As shown in the process diagram of FIG. 2, first, a titanium alloy material having the alloy composition according to the present invention is prepared, and then hot-rolled into a hot-rolled material with approximate dimensions (hereinafter referred to as "hot-rolled material J").
get.

Next, when the Ti alloy hot-rolled material obtained in this way is coated with a fluororesin lubricant for lubrication treatment to produce a cutting slag, it is subjected to wire drawing with an area reduction rate of 20 to 40% and then cold-rolled. In the case of forged slag, it is subjected to wire drawing with an area reduction rate of 5 to 15% and work hardened. Hot-rolled materials have oxide scale, so
Wire drawing is possible only with lubrication treatment (fluororesin, pre-die lubrication). In this invention, wire drawing is performed in order to compensate for work hardening by work-hardening the parts with a low degree of processing in advance during the actual molding, and also to improve roundness and wire diameter accuracy. .

Then, the drawn wire material thus obtained is cut into appropriate lengths, and slags are manufactured by cutting or cold forging, respectively. Cold forged slag is shot blasted after processing.
Descale by fluorofluoric acid pickling, etc.

These slags are formed into forged parts by cold forging, but according to the present invention, prior to cold forging,
The slag is heated in an atmospheric furnace at 450 to 600°C for 10 to 60 minutes, and scale for a lubricating base is attached under conditions that the slag does not soften. After that, after lubrication treatment with fluororesin etc., main forming by cold forging is performed, and the average hardness is H.
v 270 or more.

Such lubrication treatment ensures excellent cold forging properties, reduces deformation resistance during cold forging, and extends tool life.

Next, in order to further prevent wear, a nitriding treatment is preferably performed, but descaling is performed before nitriding. The nitriding method uses 400-55 to prevent softening inside the forged product.
This is carried out at 0° C., and suitable methods include ion nitriding and soft nitriding. In any case, the nitriding method itself is well known, and the present invention is not limited to any particular method as long as it is carried out at a relatively low temperature of 400 to 650°C.

As described above, according to the present invention, titanium alloy forged parts having sufficient hardness for use can be mass-produced at low cost.

Next, the reasons for limiting the alloy composition and processing conditions in this invention are as follows.

First, the reason for limiting the alloy composition as described above will be described. Percentages relating to component compositions are "wt% J" unless otherwise specified.

If zirconium is added alone, it must be added in an amount of 5% or more to ensure hardness after cold forging.
If it exceeds 2%, the cold forging properties required for forged parts cannot be obtained.

Oxygen is usually contained as an impurity, but if oxygen is actively added, oxygen will improve the hardness after cold forging, so zirconium may be less than 5%, but oxygen Zr is also an element that inhibits cold forging properties, so it cannot be added in large amounts, and it is necessary to add 1.0% or more of Zr. Furthermore, zirconium is an alloying element that is completely dissolved in titanium, and by adding 1.0% or more, it is possible to reduce the degree of softening caused by temperature rise during oxidation treatment. Therefore, the lower limit of the zirconium content was set to 1.0%.

On the other hand, main forming by cold forging (normal processing rate is about 60%)
As a result of research, Zr + 25 × [
It has been found that an amount satisfying 0□□≧5% by weight is required.

By the way, if zirconium or oxygen is added to titanium in an unnecessarily large amount, cold forging properties will be inhibited and cracks will occur during main forming.As a result of the research conducted by the inventors, it has been found that such cracks do not occur during cold forging. The upper limit for prevention is 3 x Zr+
220X [0! ]≦66% by weight. Therefore, the upper limit of Zr, 0 is 3 × Zr + 22
(IX [(hl ≦66 IOA.

Note that oxygen is normally contained as an impurity in an amount of 0.04 to 0.06%.

FIG. 3 is a graph showing the relationship between the amount of oxygen and the amount of zirconium in this invention. The titanium alloy according to the present invention, including the case where oxygen is contained as an impurity, falls within the shaded area in FIG.

The temperature conditions for oxidation treatment of slag are 450 to 6
The reason why the temperature range is limited to 00°C is that below 450°C, the oxide film is too thin and the lubricant retention effect is small, causing seizure during main molding. On the other hand, if the temperature exceeds 600°C, the slag becomes too soft and does not have a hardness of Iv270 or higher (after main molding). This oxidation treatment is performed in the above temperature range.
The slag is held in the atmosphere for 0 to 60 minutes, but if it is less than 10 minutes, the formation of an oxide film is insufficient, and if it is more than 60 minutes, the slag may become soft or economically disadvantageous.

Furthermore, in order to prevent surface wear, the forged molded product is nitrided at a temperature range of 400 to 550°C after descaling.
If the temperature is less than 400℃, a sufficiently thick nitrided layer cannot be formed, and if the temperature is lower than 550℃.
This is because the inside of the forged product becomes softer and Hv cannot exceed 270. The reason why the hardness of the forged part is set to Hv270 or higher is that if the hardness is lower than this, insufficient strength and wear will occur.

Next, the present invention will be explained in more detail in conjunction with an embodiment in which an automobile valve retainer is manufactured.

[Example 1] A 30 kg ingot of various titanium alloys whose alloy compositions are shown in Table 1 was melted, heated to 1100°C for β forging, then heated to 850°C to perform α+β forging to obtain a diameter of 2Q mm.
It was made into a wire rod.

The obtained wire rod was lubricated with fluororesin, 7% wire drawn and 25%
% wire drawing, and the former was cold forged to form a slag in the shape shown in Fig. 1. After processing, descaling was performed by shot blasting. The latter was made into slag by cutting.

The two types of slag thus obtained were oxidized at 500° C. for 20 minutes in the atmosphere, then lubricated with molybdenum disulfide and cold forged at 60% to form valve retainers.

The cold forgeability and hardness of the valve retainer thus obtained were evaluated, and the results are summarized in Table 1.

As is clear from the results in Table 1, the average hardness of valve retainers manufactured from either slag is almost the same.
The invention example exhibits Hv270 or more without forging cracks, but Comparative Examples 8 and 9 have good cold forgeability, but the hardness is Hv
If it is less than 270, it is unsuitable.

[Example 2] Among the wire rods of Example 1, the material of Invention Example No. 7 was used, and the wire was drawn to 25% using Ca stearate as a lubricant, and then cut into slag.

The obtained slag was oxidized at different temperatures, lubricated with fluororesin, and then formed into a valve retainer by 60% cold forging.

The results of hardness measurements are summarized in Table 2.

When the oxidation treatment temperature is less than 450°C, the hardness is ) Iv 27
Although it is 0 or more, burn-in has occurred. An oxidation temperature of over 600° C. will not cause seizure, but the hardness will be insufficient. According to this example, it was found that an appropriate oxidation temperature is 450 to 600°C. Note that the oxidation time was 20 minutes in all cases.

[Example 3] An oxide film was formed on the cutting slag produced in Example 2 at an oxidation temperature of 500° C. by varying the oxidation time, and then, after the same lubrication treatment, cold forging with a workability of 60% was performed. It was molded into a retainer. The cold forgeability and hardness measurement results at this time are shown in Table 3. If it takes less than 10 minutes, it will seize, and if it takes more than 60 minutes, the hardness will decrease, causing problems. From this, it was found that the appropriate oxidation time was 10 to 60 minutes.

[Example 4] Regarding the valve retainer obtained by performing the oxidation treatment at 500° C. in Example 2, ion nitriding was performed for 15 hours at each temperature shown in Table 4. The conditions for ion nitriding are a gas pressure of 5 Torr, an atmosphere of Nl/H1-3/7,
The discharge voltage was 300V.

The results at this time are also summarized in Table 4.

At temperatures below 400°C, a sufficiently thick nitrided layer cannot be formed;
If the temperature exceeds .degree. C., a good hardened layer will be formed, but the inside of the retainer will soften and the Hv will be less than 270, which is not suitable.

As is clear from the above description, it has been found that by the method of the present invention, forged parts made of titanium alloy can be manufactured at low cost, and there are no problems in terms of quality. The above explanation has been explained using an example of a valve retainer, but it is not limited to this and can be applied to forged parts such as gears, shafts, and bolts, which were conventionally manufactured by carburizing case hardened steel or structural steel. Of course, extremely useful effects can be obtained in either case.

Table 1 (Note) Table 2 based on the presence or absence of cracks during Honfutaki molding. Table 3 O: Baked, no cracks Table 4

[Brief explanation of the drawing]

Fig. 1 (al and Cb) is a schematic sectional view of the processing material (slag) and the valve retainer; Fig. 2 is a process diagram of the manufacturing method of a forged part according to the present invention; and Fig. 3 is a schematic sectional view of the processing material (slag) and a valve retainer. It is a graph showing the quantitative relationship between oxygen and zirconium in the invention.

Claims (6)

[Claims] (1) Hv composed of a titanium alloy having a composition of Zr: 5 to 22% by weight, the balance consisting of titanium and unavoidable impurities.
Titanium alloy forged parts with hardness of 270 or higher. (2) Zr: 5 to 22% by weight, the balance being titanium and unavoidable impurities. Prior to main forming by cold forging, a pre-drawn material made of a titanium alloy has a composition consisting of titanium and unavoidable impurities. 10-6 in the temperature range of 450-600℃
After oxidation treatment for 0 minutes to form an oxide film on the surface, lubrication treatment was performed, and then cold forging was performed to form the final product to Hv27.
A method for manufacturing a titanium alloy forged part, characterized by having a hardness of 0 or more. (3) After the forged parts are formed by cold forging,
3. The method for producing a forged titanium alloy part according to claim 2, which comprises performing a nitriding treatment in a temperature range of 0 to 550[deg.] C. and maintaining an internal hardness of Hv270 or higher. (4) Zr≧1.0% by weight, and Zr+25×[O_
2]≧5% by weight and 3×Zr+220×[O_2]≦
A forged part made of a titanium alloy and having a hardness of Hv270 or more, which is made of a titanium alloy having a composition of zirconium and oxygen in an amount satisfying the condition of 66% by weight, and the balance being titanium and unavoidable impurities. (5) Zr≧1.0% by weight, and Zr+25×[O_
2]≧5% by weight and 3×Zr+220×[O_2]≦
Prior to main forming by cold forging, a material for processing is made of a titanium alloy having a composition of zirconium and oxygen in an amount satisfying the condition of 66% by weight, and the balance is titanium and unavoidable impurities. 450-60
Titanium, characterized in that it is oxidized in a temperature range of 0°C for 10 to 60 minutes to form an oxide film on the surface, then subjected to lubrication treatment, and then main-formed by cold forging to have a hardness of Hv270 or more. Manufacturing method for alloy forged parts. (6) After the forged parts are formed by cold forging, 40
6. The method for producing a forged titanium alloy part according to claim 5, wherein the titanium alloy forged part is nitrided in a temperature range of 0 to 550°C and its internal hardness is maintained at Hv270 or higher.