JPS58100663A - Production of rolled material of titanium alloy having good texture - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy having good texture with less surface flaws in continuous rolling of the Ti alloy by combining heating in a beta region and sufficient rough processing and intermediate and finish processing in a beta region and alpha + beta region. CONSTITUTION:After an alpha + beta type Ti alloy is bloomed, the bloom is heated to a beta region of <=1,150 deg.C and is subjected to working at >=3 forging ratio in the beta region with continuous rolling mill, and further to working at >=10 forging ratio continuously in the alpha + beta region. If necessary, the same is subjected to a treatment for formation of equi-axed crystals. If the alloy is roughly processed in the beta region where processability is good in the above-mentioned manner, the generation of surface flaws not only in the rough processing but also in the succeeding processing in the alpha + beta region is prevented. Here if the heating temp. in the beta region is too high, the processability is degraded and the control of the temp. during rolling is difficult. Particularly there is the possibility of infeasibility in taking sufficient reduction rate in the alpha + beta region. As the forging ratio is higher, the effect is higher, but there is a limit in the size of blank materials. The forging ratio higher than 3 is sufficient in practicability. If the forging ratio is made >=10 in the alpha + beta region, the rolled material of the alloy having improved texture is obtained efficiently by heating at one time.

Description

[Detailed Description of the Invention] The present invention provides a method for producing a rolled titanium alloy material with a good structure,
In particular, the present invention relates to a method for manufacturing a rolled titanium alloy material with a good h-structure by continuous rolling on a multi-stage stand.

Titanium alloy has a high specific strength k (strength to weight ratio), so it is used in fields such as aircraft and development equipment that require light weight and high stiffness. Used in applications that require high reliability. However, for these uses,
Merely having high strength is not enough; especially when supplied in the form of a wire or rod, a forming process is always required during the manufacturing process to produce the final product as a bolt or structural part. Gender is essential. In order to improve the lint-like appearance, it is essential to have a uniform and fine structure.

By the way, titanium alloy material is one of the difficult-to-process materials, and there are almost no reports on its manufacturing method.For example, forged materials are disclosed in JP-A No. 51-77886;
Regarding rolled materials, there are no reports on the manufacturing conditions known to the Ministry of the Invention and others.

Incidentally, in manufacturing the above-mentioned forged material, after β forging, processing of 10% or more is continuously performed in the α+β region.

Next, after heating to the β region, the fibers are cooled to the α to β region or the α region at a cooling rate of 20° C./min or more, thereby making the braided fibers finer.

However, when a round or small titanium alloy bar is produced by forging, there are fundamental problems associated with forging methods, such as variation in the structure in the longitudinal direction of the forging. Now. In addition, in terms of production efficiency, because heat forging is repeated several times, the efficiency is incomparably inferior to the rolling method.

In addition, even if rolling is carried out, titanium alloy is a difficult-to-process material, so IIEIET flaws are likely to occur, and even if heated at a high temperature within the α+β range, surface flaws will not occur in rough or intermediate rolling rows. I can't. Therefore, it is necessary to perform full-surface peeling in the post-processing process, resulting in a decrease in yield and an increase in man-hours.

A decrease in efficiency is inevitable.

Thus, an object of the present invention is to provide a method for producing a rolled titanium alloy material with a good structure and few surface defects.

By the way, in order to make the structure smooth, it is necessary to lower the rolling temperature, and on the other hand, the higher the processing temperature, the lower the S degree of occurrence of surface flaws. Therefore, the requirement to improve the structure and the requirement to reduce surface flaws are mutually contradictory.

Therefore, as a result of intensive research into the continuous rolling of titanium alloys, the present inventors have found a method that simultaneously satisfies the contradictory requirements described above by controlling the heating temperature during rolling and controlling the material temperature during rolling. T with good texture and no surface flaws
1 alloy rolled material was successfully obtained. In particular, the present invention has discovered the criticality of the combination of heating in the β region to eliminate surface flaws, sufficient working degree in the rough row, and sufficient working degree in the α (β region) in the intermediate and finishing rows. It is based on

Herein, the present invention provides that after rolling α+β Maro Chikuchitough alloy ingot, 1
It is heated to a β range of 160°C or less, processed using a continuous rolling mill to a working ratio of 8 or more in the β range, and then continuously processed to a working ratio of 10 or more in the α+β range.

This is a method for producing a titanium alloy rolled material having a good structure by subjecting the obtained hot rolled material to equiaxed crystal formation treatment (if necessary) to reduce mold.

As shown in ζO1, the present invention uses β region hot rolling as one 411 value, but by performing rough processing in the β region where workability is favorable, it not only prevents the occurrence of surface flaws during @ processing, but also This has the effect of suppressing the occurrence of surface flaws during subsequent processing in the α+l area.

The heating temperature in the β region was set to 1150°C or less.

When heated to a temperature above *a, a gas absorption layer (so-called α-(:a
This is because s@) is generated, deteriorating workability, and difficulty in controlling temperature during thread rolling, and there is a risk that a sufficient degree of O workability cannot be obtained, especially in the α+β region.

A larger training ratio is advantageous for preventing surface flaws in the α+β region, but it cannot be increased in practice due to restrictions on material dimensions. By setting the forging ratio to at least @, it is possible to obtain a practically sufficient surface quality.

Furthermore, according to 1-shot@, the degree of processing in the α+β region is regulated, but as mentioned in Wt, the forging ratio is 1 in the α+β region continuously.
Another feature of the present invention is that zero or more processing is added. In other words, in one heat, the amphibious part is forged in the β region, and the second half is given as α+βtILIIIiill[Kj:O, so that a T1 alloy rolled material with a good structure is produced extremely efficiently and without any surface scratches. It was.

The training ratio in the α+β region plays a very important role in organizational improvementvR)
Microstructure-wise, the larger the training ratio in the α+β region, the finer the equiaxed grains will be formed, but practical soils also have restrictions on material dimensions (To4), which are set empirically from a practical standpoint. If the permissible limit of the organization is considered as the standard, the training ratio is set to 10.
The above is sufficient.

Although the processing temperature in the α+β region is not limited to 41 by ζζ,
If the temperature is just below the β temperature, the number of metamorphosed β structures increases within one tissue, which is undesirable. Processing temperature is approximately 700℃
If the value is lower than , the movement of grain boundaries, recrystallization, etc. during processing becomes extremely slow.

It is preferable to carry out tube-axis crystallization by using an equiaxed crystal formation process which will be described later. Therefore, the machining temperature in the α+β region is as follows:
Although not necessarily limited thereto, preferably ttsoo-
soo℃teal.

In this case, the axial crystal formation treatment refers to the process of cooling at 1100°C in a 1700"C trench immediately following the pressure reduction, or by cooling in a furnace or in a furnace.
/hr or less, and then allowed to cool to room temperature, or after hot rolling, open at a predetermined time at a temperature of 800 to 960°C.
In general, it is held for 80 minutes or more, preferably for 1 hour or more, and in some cases, after hot rolling, it is first allowed to cool down to 100°C or less, and then reheated in a furnace maintained at 850 to 96 G'CK to 800 to 1160°C. It is a treatment in which the temperature is opened at a predetermined time, generally held for 80 minutes or more, preferably 1 hour or more, and then allowed to cool to 700° C. or less. Such treatment promotes the formation of equiaxed crystals.

The reason for slowly cooling the hot-rolled material immediately after rolling is that it is effective in releasing the crystal strain accumulated during rolling in the α (β region) and achieving uniaxial crystallization. Therefore, K is It is necessary to allow sufficient holding time at temperatures above 700°C, where grain boundary movement is likely to occur, and for this purpose gradual cooling is performed. Slow cooling is required.

The same effect can be obtained by maintaining the temperature at 800 to 950°C after hot rolling.

Before rounding, the hot-rolled material is left to cool and then reheated at the primary φ to refine the crystal grains.
Heating is effective. When it exceeds 950℃! The number of phases increases and the acicular structure increases in the cold region, which is unfavorable.
On the other hand, when the temperature is lower than 800'C, it is possible to refine the crystal grains by heating for a long time to around 100°C, but it is not economical because it takes a long time.

The equiaxed crystal thus obtained is a crystal whose crystal grain morphology is isotropic, and ideally consists of crystal grains that do not extend in any particular direction in an arbitrary cross section.

When carrying out the present invention, continuous rolling on a multi-stage stand is generally carried out using a spinning machine, and rolling is started after heating to the β range, so that the temperature decreases to the α to β range during rolling. It is necessary to control the rolling temperature. It was. To prevent heat generation from the rolled material during processing, cooling by water cooling, etc. is necessary at an appropriate part of the slow rolling rolling row, so water cooling between p10 and 10, water cooling immediately after rolling, or a combination of both can be considered. However, it is not necessarily limited to these. If water cooling is used, the temperature may be adjusted by adjusting the flow rate.
.

α÷/! to which the present invention is applied! Typical titanium alloys are T1-・At-4V, Tl-4mut-4Mn, and other examples include Ti-8Mn and T1-BAA-
476Cr-IJIF@, Tl-4ATl-4At-4
, Tl-4ATl-4AA-I and the like. However, it will be understood that the invention is not limited thereto.

The invention will now be further described in connection with examples.

Example Tl-6At-4V was melted in a vacuum arc to produce a 1) ingot, which was then subjected to blooming and peeling to remove surface defects. As shown in No. 1 IIK, billets F with diameters of 180 mm and 58 square squares were produced, and rolled into round bars with a diameter of 9 mm using a continuous hole type abrasive at the finishing rolling speed also shown in No. 111. Since rolling was carried out at a high speed and the temperature increased due to rolling, we carried out cooling by water spraying between the rolls and immediately after rolling. For each rolling mill obtained.

The following rolling conditions and results were subjected to microstructure determination and flaw determination as described below, along with those of the comparative example. K are shown together.

Note that various companies have devised various methods for determining the set of fII& based on past experience and results. ζ
For ζ, as shown in the attached drawing, α÷β equiaxed grains are classified as 1st grade (see figure (~)). The figure shows that the condition is evaluated as grade 4 (see Φ).

The intermediate stage is divided into 02 stages, with a high degree of processed structure remaining (see Figure (e)), and a low stage, that is, those with insufficient equiaxed crystallization (see Figure (6)).
There were a total of 4 classes. Grades 1 to 2 are structures that can withstand practical use, and grades 8 to 4 are structures that require improvement.

For the determination in Table 11i11, the surface of the product is visually inspected to detect surface flaws, and at 9:00, the part is ground with a grinder and the depth of the flaw is measured. Depending on the depth of the flaw, it is classified from grade 1 to grade 4 as shown in the breath table.

Grades 1 to 1 are p, which can withstand practical use, and grades 8 to 4 are 11 degrees, which require further care.

Number 1! In the table, Examples 1 to 1 indicate examples of the present invention, 1 Example 1 to O indicate comparative examples, 0 Examples 2 and 1 are round hot-rolled materials (respectively C materials) obtained by Examples C and D, respectively. This example shows an example in which the K equiaxed insect formation process (denoted as DI and DI) was applied.

In the example of the present invention, the above-mentioned tissue JPL density and surface flaw judgment were both 1t or 8, which was 6, which was satisfactory.

However, as Example J shows, the training ratio in the α+β region is l
When it is less than -1, the structure is not refined sufficiently, and as shown in the -1 example and L, rolling is performed only in the α+β region, and in the case of 9, the occurrence of m-plane perpendicularity is inevitable.

In the case of tight rolling, hot rolling in the α+β region is generally considered to improve the structure, but in that case, the temperature of the entire material is low and some corners are lower due to the shape. Ninth, during rolling, that part is subjected to elongation, and it is thought that surface defects occur because the deformation is originally poor in the 8-phase heterogeneous region. Before, as examples M and N show, α+
When rolling is started in the β range and the temperature is raised during rolling, raising the temperature to the / range as in Example M reduces the occurrence of 1 surface flaws, but prevents the deterioration of 4 sets at any stage. I can't do it 0
Example O shows a case where the heating temperature is higher than the temperature specified by the present invention.

As described above, in the present invention, prior to hot rolling, surface flaws can be prevented from occurring during rough rolling or intermediate rolling by heating the material in the β region to raise the material temperature and form a single-phase structure. Prevent 1
Next, after increasing the training ratio.

Controlled cooling is performed so that intermediate rolling to finish rolling can be performed in the α+β region. As a result, as shown in Table 1, even when heated and rolled to very high temperatures in the β range, by combining it with controlled cooling, both the AI and surface defects are good.
We succeeded in obtaining a jointly rolled material. As shown in the comparative examples, even if these conditions are varied, it is difficult to simultaneously satisfy both the tissue and the nature at a level that is acceptable for practical use, even if these conditions are outside the scope of the present invention.

[Brief explanation of the drawing]

The attached drawings are schematic diagrams of crystal structures showing criteria for determining equiaxed crystal structures.
d) #'i corresponds to the structures of 1st class, 2nd class, 8th class and 4th class, respectively. Applicant's representative Patent attorney Akira Hirose ((2) tb+ tc+
td) Continued from page 1 0 Author Tomio Yamakawa 1-3 Nishinagasu Hondori, Amagasaki City, Sumitomo Metal Industries, Ltd. Central Technology Laboratory 0 Author Takashi Okuyama Sumitomo 1-3-2 Marunouchi, Chiyoda-ku, Tokyo Metal Industry Co., Ltd. 9

Claims (2)

[Claims] (1) Heat the material to the Oβ region of α + β 2 degrees or less and process it using a continuous rolling mill at a working ratio of 8 or more in the β region. Further, the training ratio is continuously increased to 1 in the α+β region.
1. A method for producing a rolled titanium alloy material having a good one-structure structure, the method comprising adding 0 or more processing steps. (2) After rolling α÷β Chikuchitough alloy ingot. It is heated to a β range of 1150℃ or less, and then passed through a continuous rolling mill to a forging ratio of 8 in the β range.
In addition to the above processing, the forging ratio is 10 in the α and β regions continuously.
After the above processing, the resulting hot-rolled material is subjected to equiaxed crystal formation treatment! A method for producing a rolled titanium alloy material having a good structure of Vt mold.