JP2000096111A - Production of ferrous alloy for structural material and ferrous structural material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a ferrous alloy capable of obtaining a ferrous structural material maintaining a superfine structure of <1 μm even if a ferrous alloy composed of Fe-Ti-O is subjected to heating treatment in a high temp. region and good in elongation and strength with high efficiency and enabling mass-production. SOLUTION: At the time of blending an Fe material and a Ti material, the blending is executed in such a manner that 3 to 6% Ti and 0.1 to 1.5% O are contained, also, in the range of the Ti content, O is contained so as to control the upper limit to (0.2 ×Ti%+0.3)% and the lower limit to (0.3×Ti%-1.2)%, and the balance Fe, and the blended material is made to be the superfine one of <1 μm average crystal grain size by crushing means and is moreover subjected to alloying. Even if the ferrous alloy produced in this way is subjected to heating treatment at a high temp., the structural material maintaining a superfine structure of <1 μm average crystal grain size can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an iron-based alloy for a structural material and an iron-based structural material.

[0002]

2. Description of the Related Art In manufacturing a steel structural material, it is possible to improve the strength without deteriorating the strength and ductility by reducing the crystal grain size of the steel material. Many studies have been made conventionally. However, in the case of a steel material mass-produced by a conventional process including steps such as melting, casting, and rolling, miniaturization to about 1 μm is the limit. To further improve the strength of the structural material, the finer the crystal grain size of the structure, the better. Under these circumstances, recently, the crystal grain size has become 1 μm
A mechanical milling method has been proposed as a new process capable of achieving ultra-miniaturization to below. A typical mechanical milling method uses a ball mill. In this method, a steel container is filled with metal powder and hard balls made of steel, etc., and by vibrating or planetary motion of the container, a very high plastic strain is applied to the metal powder when the ball collides with the powder. This is a method of reducing the crystal grain size. By this method, for example, Materials Transac
Tion, JIM, Vol. 36, no. 2 (1
995), pages 289 to 296, pure iron powder is subjected to mechanical milling to reduce the average crystal grain size to about 20 to 30 nanometers, and to reduce the Vickers particle size. 95 hardness
It has been reported to reach zero.

[0003]

Since the thus obtained iron material having an ultrafine structure having an average crystal grain size of less than 1 μm is powdery, it is necessary to use this to produce a structural material. The powder having the ultrafine structure must be solidified and formed into a bulk material, that is, a metal mass having a density sufficient to be used as a structural material. Heat treatment such as sintering and HIP processing is required for the solidification molding. However, the powder composed of the ultrafine structure is 800
When producing a structural material by keeping it at a high temperature exceeding ℃, the average crystal grain size is coarsened to several to several tens of microns due to the heating at the high temperature, and as a structural material with extremely low strength, Since there is a very high risk of producing the obtained results, the structural material having good strength and ductility is obtained by solidifying and molding by suppressing coarsening so that the average crystal grain size of the ultrafine structure does not become 1 μm or more by heating. For example, there is little danger that the average crystal grain size of the ultrafine structure is coarsened to 1 μm or more. For example, heat treatment such as sintering at less than 800 ° C. or HIP treatment or vacuum sealing in a steel container is performed. And rolling. However, in such a method, it takes a considerable time to produce a structural material having good strength and ductility, and the productivity is poor and mass production is difficult. Therefore, the average crystal grain size 1
In producing an iron-based structural material using an iron-based powder having an ultrafine structure of less than μm, coarsening of the crystal grain size can be suppressed to an average value of less than 1 μm even when heated at a high temperature, and the obtained iron For producing an iron-based alloy having an ultra-fine structure in which the average crystal grain size of the iron-based structural material is suppressed to less than 1 μm and having high efficiency and an iron-based structural material having excellent strength and ductility, and improving mass productivity The development of is desired.

[0004]

According to the present invention, there is provided a method for producing an iron-based structural material comprising an ultrafine structure having an average crystal grain size of less than 1 μm and having improved strength and ductility even after heat treatment which has solved the above-mentioned problems. It is intended to provide a method of manufacturing an iron-based alloy for a structural material which can improve efficiency and improve mass productivity.
In mixing the material and the O material, Ti: 3 to 6% by weight,
O: 0.1 to 1.5%, and in the range of the Ti content, the O content is the upper limit (0.2 × Ti% +
0.3)%, the lower limit (0.3 × Ti% -1.2)%, and the balance Fe. The mixture is ultrafine-refined to a grain size of less than 1 μm by crushing means. And alloying. Further, the present invention provides an iron-based structural material comprising a superfine structure having ductility and improved strength suitable for practical use, and heat-treating an iron-based alloy for a structural material obtained by the above manufacturing method. It is made by depositing ultrafine titanium oxide. Thus, in the iron-based structural material of the present invention, the average crystal grain size of the parent phase is less than 1 μm,
Vickers hardness is 300 or more and elongation is 3% or more.

[0005]

Next, embodiments of the present invention will be described in detail. In order to produce the iron-based alloy of the present invention, an Fe material, a Ti material, and an O material are prepared as raw materials for the production. As the Fe material as the main material, at least one selected from iron-based materials such as pure iron and carbon steel is prepared. As the Ti material, metallic titanium, Fe-Ti alloy, Fe-Ti intermetallic compound or Ti ₂ O, TiO, Ti ₂ O ₃ , Ti ₃ O ₅ , TiO ₂
Prepare at least one selected from titanium-based oxides, such as titanium-based oxides or Fe-based oxides.
_An O material of at least one selected from iron-based oxides such as ₂ O, Fe ₂ O ₃ and Fe ₃ O _4, or gaseous oxygen or a mixed gas of oxygen and argon or helium is prepared. The above-mentioned Fe material is mainly used, a small amount of a Ti material and a small amount of an O material are blended with the Fe material, and the compounding ratio of the Ti element and the O element is blended within the range shown by the oblique line in FIG. An ultrafine structure having an average crystal grain size of less than 1 μm is obtained by a mechanical milling method or other crushing means, and an iron-based alloy made of a solid solution of Fe—Ti—O having a body-centered cubic structure is manufactured. In such a case, when the iron-based alloy is used as a raw material and solidification molding such as sintering, HIP processing, or heat treatment such as hot extrusion or hot forging or hot rolling is performed, the above ultrafine structure is required. The fine precipitation of the titanium-based oxide in the Fe-Ti-O alloy having the following can suppress the coarsening of the average crystal grain size to less than 1 µm, thereby providing excellent strength and elongation of 3% or more. It was confirmed that an iron-based structural material having good strength and ductility was obtained.

The embodiments of the present invention will be described in more detail with reference to specific examples. Pure iron powder is selected as the Fe material, metal titanium powder is selected as the Ti material, Fe ₂ O ₃ powder is selected as the O material, and these are blended to prepare a blend. In this case,
The composition is such that the Fe element, the Ti element, and the O element are contained in the following contents, respectively. That is, the composition of the three components is as follows: Ti: 3 to 6% by weight, O: 0.1
１．５1.5%, and in the range of the Ti content, the O content is the upper limit (0.2 × Ti% + 0.3)
%, The lower limit (0.3 × Ti% -1.2)%, and the balance F
and e. Next, this compounded powder is treated by a crushing means, for example, by a mechanical milling method, so that crystal grains are refined and alloyed. That is, the compound powder is placed in a steel container filled with an appropriate amount of hard balls such as steel, and the container is vibrated or planetary-moved to ultrafine the average crystal grain size to less than 1 μm and An iron-based alloy powder which is a Fe-Ti-O solid solution having a body-centered cubic structure is manufactured. Thus, the iron-based alloy is, of course, composed of the Fe, Ti, and O components having the specific contents described above.
The ratio of the contents of i and O is obtained within the range shown by the hatched lines in FIG. As will be apparent from the results of a comparative test between the alloy of the present invention and a comparative alloy described later, in particular, Ti and O
If the ratio of the content and the ratio of the content of the two are not in the range shown by the oblique lines in FIG. 1, a practically excellent iron-based structural material having an elongation of 3% or more and a Vickers hardness of 300 or more is obtained. I can't.

In the present invention, the iron-based alloy containing Ti and O in the above specific range is heated at a high temperature range and solidified and formed by sintering or HIP processing in order to produce a structural material. Also, since a very fine titanium-based oxide precipitates during the temperature rise, the titanium-based oxide prevents the ultrafine structure from being coarsened to several μm to several tens of μm, and 1 μm even if the average crystal grain size increases
As a result, an iron-based structural material having excellent elongation and excellent strength, which is composed of an extremely fine structure, can be obtained. On the other hand, as will be described later, when the contents of Ti and O in the iron-based alloy of the present invention are out of the above-specified ranges, a high-temperature range is required in producing a structural material using the same. However, the desired iron-based structural material having the above-mentioned required characteristics could not be obtained.
Here, titanium raises the A ₃ transformation point with respect to iron,
₍₄₎ An element that generates a γ-loop type phase diagram that lowers the transformation point.It has the effect of stabilizing the parent phase into a body-centered cubic iron solid solution in the high-temperature region. It precipitates and brings about the effect of suppressing the coarsening of the ultrafine structure.

The Fe material may contain trace amounts of unavoidable impurities such as Si, Mn, P and S. Further, the Fe material may contain carbon, but if the iron solid solution having a body-centered cubic structure is stable in a high-temperature region and the content is within a range that does not hinder the precipitation of the above-mentioned titanium-based oxide, the content may be reduced. You can include anything. Considering these points, Fe
The amount of carbon in the material is 0.3 wt. % Is preferable. When a gaseous oxygen or a mixed gas of oxygen and argon or helium is used instead of a solid O material as the O material, the compound is put in a closed container, and these gases are injected.
When the Fe material or the Ti material is subjected to the mechanical milling treatment, the Fe material and the Ti material are combined with each other to contain a predetermined amount thereof.

According to the present invention, the above-mentioned composition is kept in a solid state by means of crushing means such as the above-mentioned mechanical milling method.
After obtaining an alloy that is ultrafine to less than μm, this alloy is solidified and formed by conventional sintering, HIP processing, etc., and when manufacturing structural materials, an ultrafine titanium-based oxide is used in the initial stage of heating. Since the material can be precipitated, the coarsening of the ultrafine structure of the base material can be suppressed to less than 1 μm during the heat treatment, and an iron-based structural material having excellent strength and ductility can be obtained. Any crushing means capable of achieving this object is not limited to the mechanical milling method, but may employ any crushing means capable of achieving ultrafine grain size and alloying. Thus, the obtained iron-based alloy having an ultrafine structure is not limited to a powdery one, but may be any one such as a foil or a lump. Then, to use this to produce an iron-based structural material,
If the iron-based alloy is obtained in powder form, sintering or HIP
It is necessary to perform treatment or forging thereafter, and when the iron-based alloy is obtained in the form of a foil or a lump, it is necessary to impart a final shape by rolling or forging. Alternatively, in some cases, it is necessary to devise heat treatment conditions in addition to the hot working to obtain a final product. What is important here is that the ultra-fine structure of the iron-based alloy does not cause grain growth of 1 μm or more due to the hot working or the working heat treatment. Since the alloy contains the Ti element and the O element in a predetermined mixing ratio in advance, when the iron-based alloy is heat-treated in order to produce the structural material having the predetermined shape, the average particle diameter is 0%. Since a titanium-based oxide composed of ultrafine particles of about 0.03 μm precipitates, it is possible to suppress the crystal coarsening of the iron alloy which is the parent phase, to suppress the average crystal grain size to less than 1 μm, and According to experiments, 700 ° C to 850 ° C
In the heating in various high-temperature regions from 850 ° C. to 1150 ° C., which is usually performed in the production of structural materials, it is possible to suppress the coarsening of the crystal grains of less than 1 μm, which is the main phase. An iron-based structural material having a fine structure and good strength and ductility is obtained.

Next, specific embodiments of the present invention will be described in detail. Manufacture of the iron-based alloy of the present invention: Pure iron powder (Fine Atmel 300NH manufactured by Kobe Steel Co., Ltd.) as Fe material, pure Ti powder (TILOP manufactured by Sumitomo Citix Co., Ltd.) as Ti material
150), Fe ₂ O ₃ was selected as the O material, and these were blended such that the addition amounts (blending amounts) of the Ti component and the O component as shown in Table 1 below were the blending ratios shown by the black dots in FIG. ,
The balance of Fe was added to each of them, and the target 1 shown in the table was set.
Powdery compounds A, B,... L each having the chemical composition of the two iron-based alloys are prepared, and the respective compounds A, B,.
Are placed together with the same ball in a container made of steel, for example, SUS304 so that the weight ratio of the compound powder and the ball is 1:10, and each of these mixtures is mixed with a planetary ball mill in an argon atmosphere. 10 mechanical milling for ultra-fine grain size and alloying
Performed for 0 hours to produce each of the iron-based alloys A, B,... L of the present invention. When the constituent phases of the 12 kinds of iron-based alloys thus obtained were evaluated by an X-ray diffraction method, they were all iron solid solutions having a homogeneous body-centered cubic structure. It is composed of the same chemical composition as the composition,
It was confirmed that each of the iron-based alloys of the present invention indicated by black spots in the range surrounded by the oblique lines was obtained. When the structure was observed by a scanning electron microscope (SEM), the average crystal grain size was less than 0.1 μm in all cases.

[0011]

[Table 1]

Production of Iron-Based Structural Material of the Present Invention: Next, each powdery iron-based alloy A, B,... That is, each of the alloys of the present invention was filled in a prism made of graphite, housed in a vacuum vessel in a state of being pressed from above and below, and fired in a vacuum of 1 × 10 ⁻⁵ Torr, as shown in Table 2 below. It was processed. That is, first, the aging temperature 850
After heating at 30 ° C. for 30 minutes to precipitate ultrafine titanium-based oxides, the temperature was further increased, and annealing was performed at 1000 ° C. and 11 ° C.
Heated at 00 ° C. for 30 minutes, the structural materials A, B,.
Was manufactured. It was confirmed that the iron-based structural material of the present invention obtained in this manner had the composition of each alloy shown in Table 2. FIG. 2 shows the iron-based alloy composition Fe-3Ti-0.5O among the iron-based alloys of the present invention.
FIG. 1 shows an organization diagram of a structural material B composed of SEM photographs.
Precipitation of an ultrafine titanium oxide having a crystal grain size of about 0.03 μm was observed in the structure of the alloy base material of less than 1 μm. All of the above iron-based structural materials A, B,.
As shown in Table 2, the average particle size of the matrix structure was 0.22 μm, which is much smaller than 1 μm even after the above heat treatment.
It was in the range of 0.86 μm. Further, as is apparent from the iron-based structural material K, even when heated to a high temperature of 1100 ° C.
The average crystal grain size is 0.75 μm, which is much smaller than 1 μm, and it can be seen that a product having excellent strength and elongation can be obtained.

[0013]

[Table 2]

In order to confirm the precipitates of the structural materials A, B,...
The precipitate was coarsened to about 1 μm by heating to 200 ° C., and the constituent phases were evaluated by X-ray diffraction. As a result, a diffraction peak of Ti ₂ O ₃ was recognized. From this, it was confirmed that these precipitates were titanium-based oxides, but 0.1 μm observed when heated to 1100 ° C.
For ultrafine precipitates less than m, titanium-based oxides other than Ti ₂ O ₃ , that is, Ti ₂ O, TiO, Ti ₃ O ₅ ,
It may be TiO ₂ or a Ti—Fe—O composite oxide containing Fe. In addition, these ultrafine precipitates are expected to have a specific crystal orientation relationship with a Ti—Fe—O solid solution having a body-centered cubic structure as a parent phase. Strict identification of ultrafine titanium-based oxides and crystal orientation relationship with the parent phase require further study in the future.

Measurement of Vickers hardness for structural materials A, B,... L, processing of a tensile test specimen having a parallel part diameter of 4 mm and a gauge length of 16 mm, and a crosshead displacement of 0.5 mm / mi
At room temperature, tensile tests were performed at room temperature to measure elongation values. The results were as shown in Table 2, respectively. That is, each of these structural materials has a Vickers hardness far exceeding 300 suitable for practical use as a structural material, and its elongation has excellent strength far exceeding 3% and good ductility. It was found that an iron-based structural material could be obtained.

Comparative Example Manufacture of a comparative iron-based alloy: the same Fe material and Ti
Material and O material, as shown in Table 3 below, Ti component and O material
The added amounts (blended amounts) of the components were blended so as to have a blending ratio shown by a white point outside the chemical composition range of the blend of the present invention in FIG. Ultrafine refining and alloying were carried out under the same mechanical milling conditions as in the example, except that powdery compounds M, N,... U having the respective chemical compositions of the nine target iron-based alloys were prepared. ,
The nine types of comparative iron-based alloys M, N,... U shown in Table 3 below were produced.

[0017]

[Table 3]

Production of Comparative Structural Materials: All nine iron-based alloys M, N,... U obtained by the above-mentioned production method were subjected to aging treatment and subsequent annealing treatment under the same conditions as in the above-mentioned embodiment.
000 ° C. to produce comparative iron-based structural materials M, N,... U. The component analysis was similarly performed for each of them, and the component compositions shown in Table 4 below were confirmed. The structure was observed by SEM. Further, Vickers hardness and elongation were measured in the same manner as above. However, with respect to the iron-based structural material M, the average crystal grain size of the parent phase was 35 μm, and the Vickers hardness was 66, which was out of the question. Therefore, the elongation was not measured. Table 4 shows the results.

[0019]

[Table 4]

As is apparent from Table 4 above, both the Vickers hardness and the elongation do not reach the required values like the comparative iron-based structural materials N and O, or the structural materials P, Q, R, S, and
Like T and U, even if the Vickers hardness is 300 or more, a product whose elongation is 3% or less or which does not satisfy at least one of the properties is obtained.

The present inventor has found that as a result of various test studies, Fe
When preparing a three-component blend by blending Ti and oxygen (O) with the material as a main component, the ratio of the content of the Ti component and the oxygen component to be contained in the blend is shown by the oblique line in FIG. And the remaining Fe component,
That is, Ti: 3 to 6 wt. %, O: 0.1 to 1.5 w
t. % And a Ti content of 3 to 6 wt. %, The content of O is the upper limit (0.2 × Tiw
t. % + 0.3)%, lower limit (0.3 × Tiwt.% −
1.2) As long as a composition is prepared so as to maintain the relationship of% and to be the balance of Fe, alloying of the composition and ultra-fine grain size are performed. About 1150 ℃ over 800 ℃ for conventional sintering
When the iron-based structural material is produced by heat treatment at a high temperature range up to 1 μm, an ultrafine titanium oxide of about 0.01 μm to 0.3 μm is formed and precipitated in the base material composition, so that 1 μm is formed.
It has been found that a structural material having excellent strength and ductility in which an ultrafine structure of less than m is maintained can be reliably obtained. Further, it was found that when the heating temperature exceeded 1200 ° C., the particle size of the titanium oxide exceeded 0.3 μm, and it was found that there was a dislike that the effect of suppressing the growth of the grains of the base metal structure could not be obtained. On the other hand, when the composition contains Ti and O outside the specific ranges shown in FIG. 1, a structural material having the required strength and toughness can be obtained even when the composition is heated to a high temperature range. The lack thereof has not been sufficiently elucidated yet, but it is considered to be the result that the amount of the titanium-based oxide to be deposited is small and that an intermetallic compound of Ti and Fe is easily formed.

[0022]

As described above, by heating to a high temperature range by the production method according to claim 1, an ultrafine titanium oxide having an effect of suppressing the growth of the grain size of the base material structure to less than 1 μm. An iron-based alloy that can be precipitated is obtained. Thus, in producing a structural material by subjecting the iron-based alloy of the present invention to a conventional heat treatment, a Vickers microstructure having an ultrafine structure in which the growth of the average grain size is suppressed to less than 1 μm even when heated in a high temperature range. Since the iron-based structural material having a hardness of 300 or more and a hardness and elongation of 3% or more can be obtained, the production time can be reduced as compared with the conventional case of performing heat treatment in a low temperature range, and mass production of the iron-based structural material can be achieved. Highly efficient.

[Brief description of the drawings]

FIG. 1 is a graph showing the range of the contents of Ti and oxygen suitable for producing an alloy comprising three components of Fe—Ti—O according to the present invention.

FIG. 2 is an SEM micrograph of an example of an iron-based structural material obtained by heating the iron-based alloy of the present invention at a high temperature.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) E04C 3/04 E04C 3/04

Claims (3)

[Claims] 1. When compounding an Fe material, a Ti material, and an O material, the steel contains Ti: 3 to 6%, O: 0.1 to 1.5% by weight, and the content of Ti is within the above range. The content of O is upper limit (0.2 × Ti% + 0.3)%, lower limit (0.3
× Ti% -1.2)%, with the balance being Fe.
A method for producing an iron-based alloy for a structural material, characterized in that the alloy is formed into an ultrafine grain of less than μm and alloyed. 2. An iron-based structural material obtained by subjecting an iron-based alloy for a structural material obtained by the production method according to claim 1 to heat treatment to precipitate an ultrafine titanium-based oxide. 3. The iron-based structural material according to claim 2, wherein the average crystal grain size of the mother phase is less than 1 μm, the Vickers hardness is 300 or more, and the elongation is 3% or more.