JPH0637701B2 - Manufacturing method of β titanium alloy forged products - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a β-titanium alloy forged product suitable for automobile forgings, and produces a lightweight and high-strength β-titanium alloy forged product at low cost. About possible ways.

Conventional technology and its problems Conventionally, forgings for automobiles manufactured by cold forging, especially valve retainers for automobile engines, were manufactured by carburizing, quenching and tempering case-hardening steel or structural steel, but recently engine The demand for higher torque and higher rotational speed has been increasing, and the weight and strength of valve retainers are being increased by using titanium as the material.

However, pure Ti, which has good cold forgeability, lacks hardness after forging in parts such as valve retainers that require wear resistance, and (α + β) type Ti has high hardness but cold forgeability. Since it is bad, it can be manufactured only by hot forging, and the cost is high.

On the other hand, β-type titanium alloy has good cold forgeability and high hardness after forging, and can be further hardened by performing an aging treatment in a post process, and is suitable as a retainer material. However, there is a problem that the deformation resistance is large and seizure easily occurs when oil or the like is used.

Therefore, it is conceivable to form an oxide film on the surface of the material by subjecting it to an oxidation treatment that is generally performed as a lubricating treatment method for titanium, and use the oxide film as a lubricating base film for forging. When high temperature annealing is performed, it absorbs gas and a hard and brittle surface hardened layer (abnormal layer) is easily developed, which causes cracking during cold forging. Further, low temperature annealing causes aging, resulting in excessively high hardness and markedly deteriorated deformability. Further, the cooling rate after annealing is also one of the important conditions for maintaining the deformability. However, in the past, appropriate conditions for them have not been clarified, and the present situation is that they have not been applied to automobile parts such as retainers of β-type titanium alloy.

The present invention has been made in view of the above circumstances, and proposes a method for manufacturing a forged product made of a β titanium alloy which is lightweight and has high strength.

Means for Solving the Problems The present inventor has studied in detail the suitable annealing conditions for β-type titanium alloys, and as a result, forms an oxide film without forming a surface-hardened layer, and appropriately anneals it without softening and aging. By finding the conditions, annealing under these conditions, and then cold forging at a slower processing speed, a high hardness of Hv 320 or higher is obtained, and there is no cracking or seizure, etc. It became possible to manufacture cold forged products, and by performing an appropriate nitriding treatment that combines aging and surface hardening, it was possible to manufacture cold forged products with excellent internal hardness Hv 350 or higher at low cost β It proposes a method for manufacturing a titanium alloy forged product.

That is, the present invention is a β-type titanium alloy slag obtained by descaling after cutting or pre-cold forging 600 ~ 7
Oxidation treatment at a temperature of 50 ° C for 10 to 60 minutes, followed by rapid cooling at a cooling rate of 1 ° C / sec or more to form an oxide film on the surface, and after lubrication treatment, strain rate of 100sec ^-1 or less by cold forging. The internal hardness of Hv 3
The internal hardness is set to 20 or more, and the internal hardness is set to Hv 350 or more by performing descaling after the main forming and nitriding at a temperature of 400 to 550 ° C. .

In the present invention, the temperature condition for the oxidation treatment of the β-type titanium alloy slag is limited to the temperature range of 600 to 750 ° C. The reason is that if the temperature is less than 600 ° C., it is hardened by aging, cold forgeability deteriorates, and cracking occurs during main forming. On the other hand, if the temperature exceeds 750 ° C, the surface hardened layer becomes thick and cracks occur during the main molding. In addition, the holding time in the oxidation treatment is set to 10 to 60 minutes, because if the time is less than 10 minutes, the oxide film is insufficiently formed, seizure occurs during forging, and cold forgeability deteriorates due to insufficient softening. On the other hand, if it exceeds 60 minutes, the surface hardened layer will develop and the layer thickness will increase.
It becomes 0.04 mm or more, which not only causes cracking but is uneconomical. Also, the cooling rate of 1 ° C / sec or more is
This is to prevent age hardening during cooling.

Also, the strain rate during cold forging was set to 100 sec ^-1 or less because the upsetting limit compressibility was 50 at processing speeds above this value.
%, And cracks occur during the main molding.

The internal hardness is set to Hv 320 or more because it is considered that if the hardness is less than this value, for example, the hardness as a valve retainer will be insufficient and that abrasion will easily occur.

Further, in the present invention, the temperature condition of the nitriding treatment of the molded product is limited to 400 to 550 ° C, because a nitrided layer having a necessary and sufficient layer thickness cannot be obtained below 400 ° C, and when it exceeds 550 ° C. This is because the material part is over-aged and a hardness of Hv 350 or higher cannot be obtained. In this case, the reason why the internal hardness is Hv 350 or higher is that a retainer of high quality and high strength is required to have such hardness.

Disclosure Based on Drawings of the Invention FIG. 1 is a block diagram showing a manufacturing process of the present invention.

That is, Fig. 1 (a) shows a β-type titanium alloy material having excellent cold forgeability and having a hardness of Hv 320 or more in this molded product, for example,
Cutting from Ti -15V-3Cr-3Al-3Sn, Ti-3Al-8V-6Cr-4Mo-4Zr or pre-cold forging and descaling to form slag. Here, the slag means a material for die forging. Figure 2 shows an example of a valve retainer and its slug. Figure (a) shows the slag and Figure (b) shows the valve retainer. Cold forged slag is lubricated with MoS ₂ , oil, etc., and after being formed by simple upsetting and punching,
Descale by shock blasting, pickling, etc.

Next, in the oxidation treatment step, for example, in an atmospheric furnace, 600
Heating and holding in the temperature range of ~ 750 ℃ for 10 ~ 60 minutes, cooling rate 1
Cool rapidly at ℃ / sec or more. An oxide film is formed on the surface of the slag by this treatment. After that, lubrication is performed with a fluororesin, etc., and in the cold forging step, when the main forming is performed at a processing speed of 100 sec ^-1 or less, a cold forged product (valve retainer) with an average hardness of Hv 320 or more is manufactured. . In addition, pay attention to the mold design and slag shape so that the surface on which the valve spring contacts will have even higher hardness.

Further, in the present invention, in order to further prevent abrasion, the molded article is descaled and then subjected to nitriding treatment in a temperature range of 400 to 550 ° C. Ion nitriding and soft nitriding are suitable for the nitriding treatment. Due to this nitriding treatment, the internal hardness is Hv
Improve to over 350.

It is also possible to maintain the temperature within the above range (400 to 550 ° C.) so that both the inner and outer surfaces have a Hv of 350 or higher, and use without nitriding.

Example 1 A β-titanium alloy ingot having the alloy composition shown in Table 1 was melted, heated to a temperature of 1050 ° C., and rolled at a temperature of 940 ° C. to manufacture a 20φ wire rod. Through the cutting process, or cutting-fluorine resin lubrication-cold forging-fluorine nitric acid descaling process, the cutting slag and cold forging slag shown in Fig. 2 (a) are obtained, and these slags are oxidized at the temperatures shown in Table 2. Treated (oxidization time is 20 minutes), air-cooled at a cooling rate of 1.5 ° C / sec, then lubricated with fluororesin, strain rate 10 sec ^-1
Table 2 also shows the cold forgeability and hardness measurement results of the valve retainer shown in Fig. 2 (b) obtained by the main forming at the processing speed of. Both slags showed the same hardness and cold forgeability after forging.

As is clear from Table 2, large cracks were generated at an oxidation treatment temperature outside the temperature range of the present invention (600 to 750 ° C) of 500 ° C, while small cracks were observed at 800 ° C. On the other hand, in all of the examples of the present invention, neither cracking nor cracking occurred and good cold forgeability was exhibited. Further, the hardness is Hv 320 or higher in all cases.

Example 2 The cutting slag manufactured from the test material B of Example 1 was air-cooled at a cooling rate of 1.5 ° C./sec (constant) at an oxidizing temperature of 650 ° C. and various oxidation times, and then the same as in Example 1. Table 3 shows the cold forgeability and hardness measurement results of the retainer obtained by subjecting the retainer to lubrication and main forming at a strain rate of 10 sec ^-1 .

As is clear from Table 3, seizure occurs when the oxidation time is out of the range of the present invention (10 to 60 minutes), and seizure occurs.
Minute streaks were observed at 00 minutes. On the other hand, all the examples of the present invention showed good cold forgeability.

Example 3 The cutting slag produced from the test material B of Example 1 was subjected to an oxidation treatment at an oxidation temperature of 650 ° C. for 20 minutes, then cooled at various cooling rates, and subjected to the same lubrication treatment and main forming as those of Example 1. Table 4 shows the cold forgeability and hardness measurement results of the obtained valve retainer.

From Table 4, it can be seen that cracking occurs when the cooling rate is less than 1 ° C / sec.

Example 4 The cutting slag produced from the test material B of Example 1 was oxidized at an oxidation temperature of 650 ° C. for 20 minutes, cooled at a cooling rate of 1.5 ° C./sec, and subjected to the same lubricating treatment as in Example 1. Table 5 shows the cold forgeability and hardness measurement results of the valve retainer obtained by performing main forming with various strain rates thereafter.

From Table 5, it can be seen that cracks occur at processing speeds where the strain rate exceeds 100 sec ^-1 .

Example 5 The cutting slag produced from the test material B of Example 1 was oxidized at a temperature of 650 ° C. for 20 minutes and then cooled at 1.5 ° C./sec.
After descaling the valve retainer obtained by the same lubrication treatment and main molding as in Example 1, the nitriding depth of the product subjected to ion nitriding treatment at the temperature shown in Table 6 and the hardness measurement result after nitriding are shown in Table 6. Shown in the table.

From Table 6, a nitrided layer with a sufficient layer thickness cannot be obtained at temperatures below 400 ° C, and inside the retainer softens due to overaging at temperatures above 550 ° C, and internal hardness above Hv350 cannot be obtained. I understand.

Effects of the Invention As described above, according to the method of the present invention, since a β titanium alloy forged product having an internal hardness of Hv 320 or more and excellent cold forgeability than the β type titanium alloy slag can be manufactured at low cost, It is now possible to apply β-type titanium alloy not only to valve retainers where β-titanium alloy could not be applied as a material, but also to various forged products such as gears, shafts, bolts, etc., only automotive parts In addition, the present invention has a great effect that its application is expanded to parts such as aircraft.

[Brief description of drawings]

FIG. 1 is a block diagram showing the manufacturing process of the present invention, and FIG. 2 is a longitudinal sectional view showing the shapes of the slag of the valve retainer and the valve retainer.

Claims (2)

[Claims] 1. A β-type titanium alloy slag obtained by cutting or pre-cold forging followed by descaling is 600 to 750.
Oxidation treatment at a temperature of ℃ for 10 to 60 minutes, followed by 1 ℃ / s
An oxide film is formed on the surface by quenching at a cooling rate of ec or more, and after the lubrication treatment, a strain rate of 100 is obtained by cold forging.
A method for producing a β-titanium alloy forged product, wherein the internal hardness is set to Hv320 or more by main forming at a processing speed of sec ^-1 or less. 2. A β-type titanium alloy slag obtained by cutting or pre-cold forging and then descaling is 600 to 750.
Oxidation treatment at a temperature of ℃ for 10 to 60 minutes, followed by 1 ℃ / s
An oxide film is formed on the surface by quenching at a cooling rate of ec or more, and after the lubrication treatment, a strain rate of 100 is obtained by cold forging.
A β-titanium alloy forged product characterized by having an internal hardness of Hv350 or more by main forming at a processing speed of sec ⁻¹ or less, descaling of the formed product, and nitriding at a temperature of 400 to 550 ° C. Manufacturing method.