JPS59189025A - Superplastic forging method - Google Patents

Abstract

PURPOSE:To obtain a superplastically forged product having a desired shape in a short time with one forging stage and a small scale installation by controlling temp. and straining speed over the entire part of the forging stage in accordance with the information obtd. by measuring continuously the temp., straining speed, forging load, etc. CONSTITUTION:A raw material of preferably <=10mu crystal grain size consisting of a Ti alloy, etc. is set in the die in a pressurizing chamber and the inside of the chamber is maintained in a vacuum or inert atmosphere. The raw material in this state is heated up to a prescribed temp. by an external power source and forging is started at said temp. The temp. for starting the forging is preferably about 700-850 deg.C in the case of a Ti alloy. The end temp. is then increased with respect to the temp. for starting the forging. More specifically, the temp. for starting the forging is kept relatively low in order to obtain a superplastic state in an early time and a specified strain is applied on the raw material to form finer crystal grains at said temp. and to obtain the superplastic state and thereafter the temp. is increased gradually or stepwise. The min. amt. of strain and straining speed required for the formation of the finer crystal grains are required to be controlled respectively to about >=0.1 and about 10<-5>-10<-2>sec<-1> in the case of the Ti alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superplastic forging method that utilizes the so-called superplastic phenomenon in which a metal material exhibits abnormal ductility under specific conditions.

Conventionally, forged parts have been used for structural members that require strength, and these forged parts have been made by cutting from forged blocks or forged preforms that are relatively close to the product shape.

However, in recent years, die-forged parts made of difficult-to-work high-grade alloys such as Ti alloys and Ni alloys have been increasingly used for aircraft body parts, engine parts, and other parts that require properties such as heat resistance and high strength. As a result, it has become necessary to improve material yield from an economic standpoint. As a solution to this problem, the superplastic forging method has recently attracted attention and is being put into practical use. Although the strain rate is slow, this method produces low deformation resistance and ultra-high ductility. is carried out, tightened, material flow is facilitated, and "near"
netshape” can be finished forged parts,
This results in significant material savings.

By the way, the superplastic forging method includes a step of subjecting a workpiece to hot working to refine the crystal grains and impart superplasticity (hereinafter referred to as a "pre-process"), and hot forging the workpiece, It consists of a process of finishing the final shape (hereinafter referred to as the main process). One of the known superplastic forging methods uses extrusion at an extrusion ratio of 5 to 10 in the pre-process, but in this case, a high-capacity extruder is required. , which makes the work complicated. In addition, in the conventional method, isothermal forging is usually performed in the main process, but the super g2H state is always in a perfect state such as ultra low deformation resistance and ultra high ductility.
Therefore, it is affected by the expansion of the material area as the material deforms and the increase in frictional resistance between the material and the mold. Furthermore, at the final stage, the forging load M increases rapidly as the end of the process approaches, due to reasons such as large amounts of energy being required for the material to disappear into the narrow part of the mold and to flow into the narrow part of the mold. . Therefore, when a large-sized product is manufactured by super-ijQ forging, it becomes thicker using the conventional method, but becomes smaller due to an increase in temperature. In particular, in superplastic materials, deformation resistance is highly dependent on crystal grain size compared to normal materials. (For normal materials, the deformation resistance is proportional to the first power of the grain size, but for superplastic materials, the deformation resistance is proportional to the first power of the grain size.
Proportional to the power. ) Therefore, if the temperature can be increased while suppressing the growth of crystal grains, and if the strain rate is appropriately controlled in accordance with the temperature, it is possible to significantly reduce the deformation resistance of superplastic materials.

Therefore, the present inventors conducted research to improve the drawbacks of the conventional method based on the above-mentioned idea, and as a result, they came to the following knowledge.

(1) In superplastic materials, in the normal hot forging temperature range (hereinafter referred to as this temperature range) above the recrystallization temperature, there is a significant decrease in deformation resistance with temperature rise that is not observed in general materials. Can be seen. This phenomenon is particularly noticeable in Ti alloys.

(2) Crystal grains of metallic materials usually grow rapidly in this temperature range, but in superplastic materials, significant growth of crystal grains does not occur even in this temperature range. Therefore, in this A) J fee,
The rate at which the decrease in deformation resistance due to an increase in temperature is offset by the increase due to coarsening of crystal grains is relatively small.

3) In superplastic materials, not only is the coarsening of crystal grains due to temperature rise in this temperature range suppressed, but also the selection of strain rate makes the crystal grains even finer than the initial state, making superplasticity more pronounced. As a result, viscous fluid-like behavior is recognized.

(4) Superplastic forging, which now exhibits viscous fluid-like behavior, further reduces deformation resistance and can be processed at higher strain rates, avoiding the drawbacks of superplastic forging such as long processing times. .

(5) Appropriate selection of temperature and strain rate (from C, forging can give more superplasticity to the metal material, and therefore the pre-process and main process can be continuous processes using the same die) can.

The present invention was completed based on the above knowledge, and it is possible to obtain the desired IDi by forging gold Bj3 alloy, which becomes a superplastic state at high temperatures, such as T1 alloy, in a high-temperature die. In the method of imparting the shape, the material is first processed to a certain amount of strain to refine the crystal grains of the material to give it superplasticity, and then the crystal grains are coarsened to provide a superplastic forging method. It is. According to the superplastic forging method of the present invention, the size range of workpieces that can be used with the same equipment is expanded compared to conventional methods, and even relatively large parts can be processed with small-scale equipment. Machining is completed in a relatively short time.

Hereinafter, the configuration of the present invention will be explained in more detail.

Since the material used in the present invention undergoes large deformation, a homogeneous material with little segregation is desirable. In this sense, materials made by powder metallurgy using atomized powder etc. are suitable, but
Similar effects can be obtained even when the present invention is applied to melted lumber. The thinner the crystal grains of the material used for processing (hereinafter referred to as raw material), the more refined it will be during processing, resulting in ultra-g-
It is easy to enter the j-like state (and the deformation resistance becomes even lower).

From the ``Konoyo Tsuna'' 4 [1 reason, the crystal grain size of the raw material is:
10μ or less is desirable, but the same effect can be obtained up to about 15μ, but the one with a mechanism that can accurately control the speed is "7":
) IK-ish. Furthermore, a forging mold and a pressure chamber are required between the rams of the press.The material is set in the mold in the pressurizing chamber, the chamber is made into a vacuum or inert atmosphere, and the temperature is raised to a predetermined temperature using an external power source. Then, forging is started at that temperature.The temperature and strain rate are controlled by the controller, but the desired values for the temperature and strain rate are set in advance, and the program?
It is also effective to forge it under the control of LJ.

Control of forging temperature is particularly important. The starting temperature for forging can be selected appropriately depending on the type of material and the initial grain size. However, if the temperature is too low, the deformation resistance of the material will increase, causing problems such as die breakage and wear. Since the deformability is low, problems such as cracking of the material will occur. On the other hand, if the forging temperature starting temperature is too high, the crystal grains become coarse and it becomes impossible to achieve crystal grain refinement, and even if a large amount of strain is reached, a superplastic state cannot be obtained. The deformation resistance in the case of T1 alloy can be significantly lowered, thus suppressing the increase in forging load caused by an increase in the area of the workpiece, etc., and in some cases, increasing the strain rate by 1 to shorten the forging time. It is also possible to do so.

fti of f speed! I am also important. The minimum strain amount and strain rate required for grain refinement vary depending on the forging temperature, material type, initial grain size, etc., but in the case of T1 alloy, the strain amount is approximately 0.1 (height 10 % reduction) or more, preferably about 0.15 to 045, and the strain rate is 10 to 10
It is about sec. The refinement of crystal grains gives the workpiece material a super-grainy property, and the progress of deformation 1 (accompanying this, the crystal grains become finer and the deformation resistance further decreases, but the area of the workpiece increases and the workpiece The total forging load does not necessarily decrease due to an increase in frictional resistance between the clamp and the die.

In the conventional method, when the forging load suddenly reaches the late stage of forging, it is not possible to maintain the first state, but of course the processing must be completed below the phase transformation temperature. Therefore, in the case of a Ti alloy, the final forging temperature is preferably 800-+000°C, and for example, in the case of a T1-6%Al-4%■ alloy, the same temperature is preferably 850-950°C.

In the present invention, temperature, strain amount, strain rate, forging load, etc. are continuously measured, and based on this information, temperature and strain rate are controlled to keep the forging load below a certain value throughout the forging process. This makes it possible to obtain a product in a desired shape in a short time using a single forging process and using small-scale equipment.

Hereinafter, specific examples and effects of the present invention will be explained with reference to Examples.

Example 1 A stainless steel container was filled with Tl-6%Al-4%V alloy powder having an average particle size of 100μ, and the inside was evacuated and sealed. Next, 8 between the rams of a 200 ton hydraulic pump
Upsetting was carried out at a constant strain rate of 5 × 1 Osec until the height reached 50 mm with the application of pJ (L) to 00°C. Powdered glass was used as the lubricant.
While increasing the temperature to 00'G, the strain rate was increased to 10 sec, and upsetting was continued under constant strain rate control until the height reached 15 mm. At this time, the total forging load was approximately 251 tons from beginning to end.
oin, and the forging surface pressure at the start and end of forging (the value obtained by dividing the forging load by the forging area) is IOK9A+4, respectively.
It was 9/- for 2 and 2.

In addition, the entire forging process is carried out at a temperature of 800°C, 5XIOs8cm
When carried out at a strain rate of ', the final forging load was 9Q wax. The entire forging process is carried out at a temperature of 900℃, 5×゛↓Os
, e c, the final forging load was 5 Q i
It was OA.

In addition, forging was performed at a temperature of 900 T, a strain rate of l x 1 Osec, and a height of 50 τtmi, and then 5 x 1 O without changing the temperature.
When forged to 15 mm at sec, the final forging load decreased by 45 /ln+, and when the temperature was further raised to 900°C, the forging load decreased further. Therefore, the strain rate was increased to 5 x l0 = sec-', but the forging load only increased slightly and the final value was 201Dn. The initial and final forging surface pressures are 8 to 9/- and 4 KI7/mrl, respectively.
Met.

Example 3 A can body was filled with powder of the same material as in Example 1, and heated to 800°C.
Pressure sintering was performed in the same manner as in Example 1 under the conditions of 2000 atm and 1 hour. At this time, the tissue became a needle-like structure with an average length of Tt]1μ and 7μ. Next, this can body was removed and a billet of Gloo X 20 I-1 was made.
A model of a jet engine combination servo disc with a wall thickness of 5 to 15 m in parts was forged.

Forging was performed in the same manner as in Example 1 using the following steps.

This billet was placed in a constant temperature forging press equipped with a furnace that heats both the mold and the billet in a vacuum, and the shape of the billet was approximately 15 mm.
The deformation resistance of this material is 2 because it has become equiaxed fine grains of μ.
Kg/mTAi decreased.

On the other hand, at this time, the increase in cross-sectional area was 30%, and the increase in 1-kilometer restraint due to friction was 10%, so the total load (・1″44%)
- At this time, the strain rate is deformation resistance 4 Kg/m++! can be increased to a value that indicates . In this case this value is 10 seconds
Therefore, the strain rate was increased sequentially during this process.

As forging progresses further, the contact area eventually increases by 23 times, and the constraint coefficient (an index indicating the difficulty of machining depending on the shape of the workpiece at a certain moment) increases by 16 times. In order to keep the total load constant at this time, the allowable deformation resistance must ultimately be 1.6 kg/1llIll. However, at this time, even after 10 seconds, the temperature was 90
Since the deformation resistance shows the expected value at 0℃, it is possible to avoid increasing the forging load by raising the temperature to 900℃, and it is possible to forge almost the entire forging process with an extremely low constant load of 50℃. was completed.

Claims (1)

[Claims] In the forging method, which utilizes the superplasticity of a metal material to give it a desired shape, there is a process of refining the crystal grains of the metal material to give it superplasticity, and a process of maintaining the superplasticity while controlling the strain rate. Prevents grain growth′-:;