JPH02298240A - Ti and ti alloy material having superfine structure and its production - Google Patents

Abstract

PURPOSE:To produce Ti or Ti alloy having superfine-grained structure and excellent in characteristics, such as toughness at low temp., ductility, and yield strength, by heating and holding Ti and Ti alloy containing alpha-phase in the structure up to and at a temp. of the transformation point or above while applying specific amounts of plastic working to the above Ti and Ti alloy and then subjecting the above Ti and Ti alloy to cooling. CONSTITUTION:Ti or Ti alloy having an alpha-single structure in which the whole or at least a part of the structure is composed of alpha-phase or a mixed structure composed principally of alpha-phase is subjected to plastic working, such as rolling and swaging, at >=20% amount of strain. Simultaneously, the above Ti or Ti alloy is heated up to a temp. of the transformation point or above, that is, a temp. in the range where the alpha-phase containing working strain is inversely transformed into beta-phase, and then, the Ti or Ti alloy is held at the above temp. for <=100sec to provide sufficient time to carry out transformation. Since the alpha-phase in the structure is inversedly transformed into a fine and uniform beta-phase crystalline structure of <100mum grain size, the Ti and Ti alloy excellent in various physical properties can be produced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a titanium alloy (Ti or Ti alloy) material having an ultrafine structure, and a method for stably manufacturing it on an industrial scale. It is something.

<Conventional technology and its issues> Generally speaking, it refers to the characteristics of metallic materials (e.g. low temperature toughness).

It is well known that ductility, yield strength, corrosion resistance, superplasticity, etc.) improve as the structure becomes finer. Tissue miniaturization techniques have been developed. especially,
In the field of steel materials, in recent years there has been remarkable progress in technology that refines the structure by regulating the rolling conditions during hot rolling (controlled rolling) or even adjusting the subsequent cooling rate (accelerated cooling). This has had a great effect on the stable production and supply of high-quality steel materials. Recently, the concept of controlled rolling technology and accelerated cooling technology has been spreading to non-ferrous materials, and various studies are being conducted to achieve a stable microstructure for titanium or titanium alloy materials. .

By the way, in the past, a method of hot working in a high temperature β phase region where the resistance to change was small was adopted for manufacturing titanium and titanium alloy materials. However, the β phase, which is stable at high temperatures, cannot be easily refined by the above-mentioned hot working, and on the contrary, the β grains tend to become coarser during this hot working (the β grain size becomes 1100a or more). Moreover, it cannot be improved by heat treatment (microstructure refinement) and the ductility and reduction of area deteriorate significantly, so it is currently mainly applied when processing ingots into slabs or billets. It's staying.

Therefore, a technology for processing in the α phase or α+β two-phase region that is stable at low temperatures (processing in the α region for titanium and the α+β region for titanium alloys) was developed and is now being applied to finishing processing. Ta. Although this method has higher deformation resistance than processing in the β phase region, the heat treatment effect is recognized in the resulting material, especially when rolling titanium alloys in the α+β region, an appropriate heat treatment (α recrystallization treatment) is performed after processing. As a result, equiaxed α crystals (α grain size is about 10 degrees) and β transformation products were formed, and the ductility and reduction of area were improved.

However, as long as rolling is carried out in the β region of raw processing, the β layer becomes coarse-grained, and it is difficult to sufficiently refine the structure by subsequent α-filling rolling or semi-+β-layer filling rolling and heat treatment. .

Therefore, an object of the present invention is to provide an industrial means for stably and reliably manufacturing titanium and titanium alloy materials having a uniform ultrafine structure, which has been impossible to achieve using conventional techniques. It was written.

Means for Solving the Problems> In order to achieve the above object, the present inventors have conducted research from various viewpoints and found that [the conventional manufacturing process for titanium and titanium alloy materials is as described above] Rough processing of lumps” and “α
or finishing processing by α+β phase region processing.
The reason why a fine and uniform structure cannot be achieved using conventional technology is ultimately the β phase crystal grains (former β grains) that have become coarse due to the previous β phase region processing. Processing in the sum region (processing in the α or α+β phase region)
They concluded that it is impossible to obtain a sufficiently fine and uniform structure even if

Moreover, the crystal structure of the β phase of titanium and titanium alloys is a body-centered cubic (b, c, c,) structure, and because the stacking fault energy is high, surface roughness is likely to be formed during recovery, and recrystallization is There is a basic fact that recrystallized grains become very large because they are performed by coalescence of crystals. Therefore, it must be considered that it is extremely difficult to uniformly refine the β phase using recrystallization.

For this reason, the present inventors first found a means to make the Mi texture in the β phase region of titanium and titanium alloys more fine than the conventional technology, and thereby made the subsequent transformed structure uniform and ultra-fine. As a result of further research, we were able to obtain the following findings (al~).

(al) After preparing the desired titanium or titanium alloy, it is first brought to a temperature such that at least a portion of it exhibits an α phase, and then plastic working is applied to the titanium or titanium alloy at a transformation temperature (heated α phase line, heated co-optional line). , heating enfolding line, heating β-ray)
If the α phase is reversely transformed into the β phase by heating to the above temperature range, the 100 m
The following ultrafine β-phase structure can be achieved. Here, “heating α
"phase line", "heating eutectoid point" 1 "heating enclosing point" is the transformation temperature at which the α phase precipitates the β phase for the first time during heating and heating, and
The heating β phase line is the transformation temperature at which the α phase completely transforms into the β phase during heating and heating.

(b) As mentioned above, when the temperature is increased while applying plastic working to the structure containing the α phase, and the α phase is reversely transformed into the β phase by exceeding the transformation temperature, in order to fully complete the reverse transformation, It is preferable to maintain the temperature in a temperature range equal to or higher than the above-mentioned transformation temperature for a certain period of time after the temperature increase process carried out while applying plastic working is completed.

(C1) The hot material with the ultra-fine β-phase structure obtained in this way is then cooled (such as by standing to cool, accelerated cooling, and sloughing while adding processing) to produce a uniform and ultra-fine material that cannot be obtained using conventional techniques. It becomes a titanium or titanium alloy material with a transformed structure.

This invention was made based on the above-mentioned knowledge, etc., and it is based on the following. The present invention provides processed titanium and titanium alloy materials characterized in that they have a plasticity of at least 20% strain. Change M while adding processing
The temperature is raised to a temperature range of A degree or higher, and 100%
Titanium or titanium alloy materials with ultra-fine and uniform structures can be stabilized on an industrial scale by holding for a time not exceeding 2 seconds to reversely transform part or all of the α phase into the β phase, and then cooling. It is also characterized by the fact that it can be manufactured easily.

It should be noted that the titanium alloy may be any other constituents as long as it can exhibit a structure at least partially composed of α phase.

Furthermore, "a structure at least partially composed of an α phase" refers to a "structure entirely composed of an α phase" as well as a "mixture consisting of an α phase and one or more precipitated phases of rare earth elements and rare earth oxides! JIV
"li", "mixed structure consisting of α phase and β phase", "mixed structure consisting of α phase, β phase, and one or more precipitated phases of rare earth elements and rare earth oxides", etc. .

As mentioned above, in the present invention, an α phase is prepared in titanium or a titanium alloy so that desired β crystal grains can be generated by hot working, and the α phase is changed to this α structure at the final stage of processing, for example. By increasing the temperature while applying plastic working to exceed the transformation point, it reversely transforms into a β structure to achieve an ultra-fine β crystal grain structure, and then cools to transform to a low temperature phase, creating a new uniformity that has never existed before. Although the main point is to realize an ultra-fine-structured material, the reason why the crystal grain size of the uniform ultra-fine-structured material according to the present invention and the various conditions for manufacturing it are limited as described above will be explained below. will be explained along with its function.

First, the reason why the β grain size or the old β grain size before cooling of titanium or titanium alloy material is limited to 100 μm or less is because the grain size is 10 μm or less.
If it exceeds 0m, there are various ductility values.

The superiority of properties such as yield strength, low-temperature toughness, corrosion resistance, and superplasticity may not be sufficiently obvious to distinguish them from conventional materials, and the new ultrafine-structured titanium or titanium alloy materials themselves may differ from conventional materials. This is because there is a risk that the differences between the two may become unclear.

In addition, in titanium or titanium alloy materials, “old β before cooling”
It is well known that the grain size can be accurately determined based on the arrangement of the α grains, the state of etching with nitric hydrofluoric acid, etc.

Next, as mentioned above, the reason why the pre-structure of titanium or titanium alloy to be subjected to the treatment according to the present invention is "α-phase single structure or mixed structure mainly composed of α-phase" is because the present invention applies to titanium or titanium alloy. This is because the main requirement is to cause the reverse transformation from α phase to β phase without adding plastic working, and as a result, an unprecedented fine β phase structure is generated, and then by cooling, this fine β phase structure is formed. This is because a uniform and ultra-fine transformed &11 weave is generated from the phase structure. by the way,
"A single α-phase structure or a mixed structure centered on the α-phase" is naturally achieved in cold materials, but once the material undergoes a thermal or processing history such as in normal hot working, , it is practical to realize this by controlling the temperature so that at least a part of the structure exhibits the α phase. In the latter case, as the final step of the subsequent working, the temperature may be raised again to exceed the transformation temperature while plastic working is applied, and the α phase may be reversely transformed into the β phase.

Plastic working methods for applying a predetermined strain to titanium or titanium alloys include various rolling methods, as well as hammers, swaggers, and stretch reducers.

Any method can be used as long as it can be processed to the required degree of processing in the required temperature range, such as processing using a stretcher, twisting machine, etc., or shot blasting.
There are no particular restrictions.

The amount of strain in plastic working is important in that it causes the following three effects. In other words, the first is the process-induced formation of very fine β-phase crystal grains from the work-hardened α-phase by processing the α-phase, and the second is the transformation of the α-phase into the β-phase. The third effect is to work-harden the fine β-phase crystals that have been generated, and to further fine them during subsequent α-phase generation. This is the effect of forming alpha grains through deformation-induced transformation.

However, when the amount of strain during processing is less than 20%, even if the α phase is transformed into the β phase, the processing-induced generation of fine β phases is insufficient, and the resulting β phase crystal grains cannot be adjusted to the desired level. It becomes difficult to make uniform fine particles.

In other words, the desired uniform and fine β-phase structure can be relatively easily achieved only when the strain amount is 20% or more, so the strain amount due to plastic working is set to be 20% or more. However, even if this range is met, if the amount of strain is relatively low, the heat generated by machining will be small, so some kind of auxiliary heat means will be required to raise the temperature of the workpiece during machining. . On the other hand, if the amount of strain is 50% or more, depending on the machining shape and machining speed, the predetermined temperature increase can be achieved just by machining without using auxiliary heating means. It is desirable that the amount of strain imparted by processing is 50% or more if possible.

Raising the temperature while applying plastic working when transforming from α phase to β phase is because, as explained earlier, “α grains become fine due to processing in the α region,” “fine β grains from work hardened α grains This is for the purpose of "work-induced generation of grains" and "refining by addition of β grains", as well as "promotion of strain-induced transformation of fine α grains from work-hardened β grains during cooling", and the present invention In terms of methods, these poetic actions and their effects are continuously condensed and manifested in the technique of ``raising the temperature while adding plastic working.''

The heating temperature of the workpiece should be higher than the transformation temperature, that is, the temperature range where α phase reversely transforms into β phase (temperature higher than heating α phase line, heating α
Temperature above phase line, heating α temperature above phase line, or heating β
It is essential that the temperature rises to a temperature above the line.

However, in a temperature range that simply exceeds the heating α phase line, heating co-fraction line, or heating envelopment line, a two-phase mixed structure of α phase and β phase will result, but in the method according to the present invention, processing is performed while increasing the temperature. Therefore, even in this temperature range, the crystal grains are sufficiently refined by processing and recrystallization. However, in order to fully ensure the effect that "very fine β-phase crystal grains are induced and generated from the work-hardened α-phase by processing the α-phase", it is necessary to increase the temperature. It is desirable to carry out the process to a temperature range equal to or higher than the β phase line.

Now, in order to obtain a uniform and fine β phase structure, it is important to raise the temperature to a temperature range above the transformation temperature while applying plastic working to the material to be treated, and then hold it in that temperature range for a period not exceeding 100 seconds. This is an important element.

In other words, when the material to be treated is subjected to plastic working according to the method of the present invention while being heated and reversely transformed into the β phase, in actual work, the temperature often increases rapidly at a high processing speed, and the reverse transformation to the β phase occurs. There is no time to proceed.

Therefore, if the material to be treated is immediately cooled after plastic working, the processed α grains will be cooled before they are transformed into the β phase, and the α phase will remain as it is without undergoing reverse transformation. Become. In this case, the above-mentioned functions and effects aimed at by the present invention cannot be sufficiently obtained, and the purpose of the present invention cannot be fully achieved. Therefore, in order to eliminate such problems, after completing the temperature raising process under the required conditions, the transformation temperature should be adjusted to allow enough time for the α phase, which has built-in processing strain, to reverse transform into the β phase. It is extremely effective to maintain the temperature in the above temperature range.

Note that when the holding temperature is lower than the transformation temperature, the α phase can no longer thermodynamically transform into the β phase, so it goes without saying that the lower limit of the holding temperature is necessarily the transformation temperature.

Further, the required holding time in the temperature range above the transformation temperature varies significantly depending on the processing conditions and the type of workpiece material, and some alloys require a long time of several tens of minutes. Therefore, the upper limit of the holding time was set to 100 seconds, which could sufficiently cover these times and would not cause coarsening of the β phase. Note that there are some alloys that complete transformation sufficiently even after holding for several seconds, so a lower limit value for the holding time was not set in particular.

As mentioned above, the cooling method after the reverse transformation process is not particularly specified, but when reverse transformation is performed to a single β phase temperature range, if the subsequent cooling rate is extremely slow, the β phase will regenerate. Since there is a risk of coarsening, it is preferable to cool at a cooling rate higher than natural cooling.

Here, some preferred embodiments for carrying out the present invention will be illustrated.

When manufacturing soil-like titanium or titanium alloy materials, heating α-phase lines, heating tool fold lines, and heating encapsulated cotton are applied while applying plastic deformation that causes a strain of 20% or more to the α-phase structure of titanium or titanium alloy. , Preferably, the temperature is raised to a temperature range above the heating β phase line, and held in the temperature range for a time not exceeding 100 seconds to reversely transform all or part of the α phase into the β phase. After that, cool it down.

When manufacturing plate-like titanium or titanium alloy materials, while applying plastic deformation that causes a strain of 20% or more to the mixed structure consisting of the alpha phase of titanium or titanium alloy and one or more rare earth elements and rare earth oxides. The heating α phase line, the heating tool fold line, the heating enveloping line, preferably the temperature is raised to a temperature range above the heating β phase line, and held in the temperature range for a time not exceeding 100 seconds to form the α phase. After all or part of the β-phase is reversely transformed into the β phase, it is cooled.

When manufacturing the Shimaki-Yu titanium alloy material, α + β of the titanium alloy
The α phase line and the heating tool fold line are heated while applying plastic deformation that causes a strain of 20% or more to the structure consisting of the phases.

Preferably, the temperature is raised to a temperature range above the heating β phase line, and held in the temperature range for a time not exceeding 100 seconds to reversely transform all of the α phase into the β phase. Cooling.

Asahi - ↓ When manufacturing titanium alloy materials, α + β of titanium alloy
Heating the α phase line while applying plastic deformation that causes a strain of 20% or more to a mixed structure consisting of a phase and one or more of an intermetallic compound, a rare earth element, and a rare earth oxide.

The temperature was increased while heating to a temperature range above the heating valve fold line, preferably the heating β phase line, and held in the temperature range for a time not exceeding 100 seconds to reversely transform all of the α phase into the β phase. After that, cool it down.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> First, vacuum ゛? After obtaining the pure titanium and titanium alloy ingots shown in Table 1 by melting, they were hot forged (150
Heated at 0°C, finished at 1300°C) to a cross section of 60 dragons x 4
A bar with a diameter of 0 am was prepared, and after annealing, a rolled experimental material with a cross section of 50 am x 30 mm was cut out.

Table 1 Using the rolling experimental materials of pure titanium and titanium alloys A-E shown in Table 1, they were heated in an induction heating furnace to the temperatures shown in Table 2, and then heated in a planetary mill or a regular plate. It was rolled to a thickness of 7.5 fl using a rolling mill. Note that the rolling in the normal mill was 3-pass rolling.

In this case, in the case of a material rolled by a planetary mill, the temperature of the material to be rolled at the mill exit increases due to the heat generated by the process due to the large reduction rolling in the planetary mill, and the temperature reached can be changed and controlled by changing the rolling speed. However, in the case of this test example, the temperature was raised to a temperature higher than the transformation temperature of the material.

Subsequently, after rolling, the rolled material is left as it is or
After being maintained at the rolling end temperature for various times up to 30 minutes, the specimens were cooled with water and the microstructure was observed.

These results are shown in Table 2 together with specific manufacturing conditions.

Note that the grain size of the β grains before cooling was determined by observing the microstructure of the material for rolling experiments.

As is clear from the results shown in Table 2, titanium or titanium alloy materials that meet the manufacturing conditions specified in the present invention have an extremely fine structure no matter which material is used as the starting material. On the other hand, it can be seen that a uniform microstructure cannot be obtained if the manufacturing conditions deviate from the specifications of the present invention.

Example ↓ Using the experimental rolling material of titanium alloy C shown in Table 1, reverse transformation rolling was performed with various reduction amounts (strain amounts) in a planetary mill, and then held at the rolling end temperature for 10 seconds. The microstructure of the titanium alloy material obtained by immediately cooling it with water was then observed.

Note that the reduction amount (strain amount) in planetary mill rolling is 0.
%, 10%, 20%, 30%, 40%, and 50%, but under these rolling reductions, the temperature of the rolled material does not rise sufficiently above the transformation temperature due to processing heat alone. An induction coil was installed at the exit of the mill, and the induction heating was rapidly heated to a temperature above the transformation temperature: 1050°C.

Table 3 shows the microstructure observation results of each titanium alloy material obtained.

From the results shown in Table 3, the reduction amount (strain amount) is 20%.
In the above case, it can be confirmed that the β grain size before cooling becomes 100 μm or less, and that the desired uniform ultrafine structure can be obtained by subsequent cooling.

Using experimental rolling materials of titanium alloys C and E shown in Table 1, in the present invention, they were first heated in an induction heating furnace to the predetermined temperature shown in Table 4, and then heated in a planetary mill. The material was rolled to a thickness of 7.5mm (reverse transformation rolling) and then held at the rolling end temperature for j seconds to cause sufficient reverse transformation, and then water-cooled.

On the other hand, in the comparative example (conventional example), the titanium alloys C and E
The material for rolling experiments was heated in an induction heating furnace to the predetermined temperature shown in Table 4, then rolled to a fin thickness of 7.5 (β phase rolling) in an ordinary plate rolling mill, and then cooled in air.

Next, the reverse transformation rolled material according to the above-mentioned inventive example and the conventionally rolled material according to the comparative example were heated to 900°C for those made from titanium alloy C, and to 600°C for those made from titanium alloy E. Both were heated to 5.5% each using a normal plate rolling mill. (After rolling to a thickness of hn (Titanium Alloy C is α phase rolling, Titanium Alloy E is α+β phase rolling) and air-cooled, the material made from Titanium Alloy C is 900
℃, while those made from titanium alloy sulfur are heated to 600℃ and kept at this temperature for 1 hour (α
(recrystallization) and then air-cooled.

The microstructure of each titanium alloy material thus obtained was observed, and the results are also shown in Table 4.

As is clear from the results shown in Table 4, β-grain refinement by reverse transformation as specified in the present invention can be obtained even if rolling and heat treatment are performed afterwards. It can be seen that the structure is much finer grained than the conventional one.

Summary of Effects> As explained above, according to the present invention, it is possible to stably mass-produce titanium and titanium alloy materials that have a uniform and ultra-fine structure and exhibit excellent mechanical properties. Industrially, extremely useful effects are brought about.

Claims (2)

[Claims] (1) Processed titanium and titanium alloy materials characterized by having a microstructure in which the β grain size or the prior β grain size before cooling is 100 μm or less. (2) Titanium or a titanium alloy having a structure at least partially composed of the α phase is heated to a temperature range equal to or higher than the transformation temperature while applying plastic working to a strain amount of 20% or more, and then
1. A method for producing an ultrafine-structured titanium or titanium alloy material, which comprises holding for a time not exceeding 0.00 seconds to reversely transform part or all of the α phase into the β phase, and then cooling.