JPH0770712A - High rigidity composite material and production thereof - Google Patents

Abstract

PURPOSE:To produce a high rigidity composite material high in Young's module by dispersing dispersion particles into a matrix of a ferritic steel containing a specific quantity of Al and Cr and prescribing a integrated degree of (111) plane in the vertical face to a certain direction. CONSTITUTION:A composite powder is prepared by dispersing 0.2-5vol.% dispersion particles (of Y2O3 or the like and having 0.005-0.1mum average particle diameter) into the matrix of the ferritic steel containing >=16wt.%-<=30wt.% Cr and 0-<=4wt.% Al. Next, the composite powder is, after extruded at the extruding ratio of >=3, heat treated and secondarily recrystallized to make the integrated degree of (111) plane in the vertical face to the fixed direction >=30 times of that of an isotropic polycrystalline body in X-ray integrated intensity ratio. As a result, the high rigidity composite material having about 25000kgf/ mm<2> Young's module is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is mainly applied to automobiles, aircraft,
The present invention relates to a high-rigidity material used as a structural member requiring excellent rigidity such as a rocket, an industrial machine, and a robot, and a manufacturing method thereof.

The high-rigidity composite material according to the present invention is used, for example, more specifically in crankshafts, piston pins, connecting rods, various valves as engine parts mainly for automobiles, and ball screws as machine parts. It may be used for parts such as golf clubs and other golf club shafts.

[0003]

2. Description of the Related Art In recent years, for example, as materials for automobiles, there is an increasing need for lightweight materials for improving fuel efficiency and damping materials for improving riding comfort. If a high-rigidity material is used to reduce the weight, the high-rigidity material has an advantage that the amount of strain such as bending can be absorbed and the shape of the component can be reduced. This is because the high-rigidity material has a property of absorbing strain.

On the other hand, even if a high rigidity material is used as the vibration damping material, it is possible to absorb vibration = strain by using a small amount of material. Therefore, as is clear from the future, expectations are growing for a high-rigidity material capable of absorbing a large amount of strain with a small shape in all structural members as well as automobile parts.

By the way, conventionally, the rigidity of a material has been improved by adding an alloying element or dispersing and compounding particles having a high Young's modulus. However, in the former case, in the Fe-based alloy, even if the Re element is added, only a Young's modulus improvement of at most about 21,000 to 22,000 kgf / mm ² can be obtained, and in the latter case, Ti
Even with the combination of (C, N) particles, etc., it will be at most 24,000-25,0
The Young's modulus of 00 kgf / mm ² can only be obtained as a practical material, and since it is necessary to add a large amount of particles, the ductility and toughness are not sufficient.

On the other hand, for steel materials, a method of realizing high rigidity by aligning crystal orientations having a high Young's modulus in a specific direction by thermomechanical processing, that is, by integrating them, is adopted. That is, it is a material design and process design aiming at the integration of the {111} planes of ferritic steel having a body-centered cubic lattice.

However, as disclosed in JP-A-56-23223 and JP-A-59-83721, in the past, after processing at a processing rate of 5 to 10% or more, 720 to 90
Even if the crystal orientation was accumulated in a certain direction by heat treatment such as tempering or winding at a temperature of 0 ℃ or less, the Young's modulus was only 23,000 to 24,000 kgf / mm ² at most.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to more generally propose a high rigidity material having high toughness and a method for producing the same. More specifically, an object of the present invention is to provide a highly rigid material having a Young's modulus of over 25,000 kgf / mm ² and a method for producing the same.

[0009]

The inventors of the present invention have made various investigations in order to achieve such an object. As a result, it is found that in the conventional method, the Young's modulus is slightly improved even by the thermomechanical treatment method. , In ferritic steels {111}
It was found that the degree of surface integration is as small as 15 to 20 times as high as that of the isotropic polycrystal, and this is due to the processing strain introduced in the processing step and its accumulation.

Therefore, as a result of various studies to find out a material system capable of imparting high working strain and an imparting method thereof,
The following points were found and the present invention was completed. Pinning of dislocations by dispersed particles is effective for introducing processing strain, and in a material system containing such dispersed particles, sufficient strain should be imparted by hot extrusion molding with an extrusion ratio of 3 or more, for example.

The composite material in which the dislocations pinned by the dispersed particles are introduced is then subjected to a heat treatment at a high temperature of, for example, 1300 ° C. to cause a rapid secondary recrystallization and a {111} plane in the processing direction. Remarkably accumulated. Here, the present invention is a composite material in which dispersed particles are dispersed in a matrix of ferritic steel containing Cr: more than 16% by weight and 30% by weight or less, and further, Al: 4% by weight or less, in a fixed direction. It is a high-rigidity composite material characterized in that the degree of integration of {111} planes in X is 30 times or more in X-ray integrated intensity ratio as compared with an isotropic polycrystal.

As described above, there are various means for increasing the degree of integration of {111} planes in a certain direction by 30 times or more in X-ray integrated intensity ratio as compared with an isotropic polycrystalline body. A method can be considered. The "constant direction" means any one direction, and in the present invention, at least that direction may satisfy the above relationship. Generally, the "constant direction" is the extrusion direction.

That is, it is a method of subjecting the composite powder in which the particles are dispersed to a strong forming process with an extrusion ratio of 3 or more and then performing a secondary recrystallization heat treatment. Preferably, such a composite powder used is one produced by a mechanical alloying method.

[0014]

Next, the reason why the steel composition and the like are limited as described above in the present invention will be explained. In the present invention, the matrix of the composite material is constituted by the ferritic steel having the crystal structure of the body-centered cubic lattice, the <111> direction has the highest Young's modulus as confirmed in the iron single crystal, In the case of ferritic iron, the value is almost 29,000 kgf / mm ²
Because it is.

The matrix phase in the present invention comprises Cr: 16
A ferrite phase containing more than 30% by weight and more than 30% by weight, and optionally 4% by weight or less of Al. The reason why the content of Cr exceeds 16% by weight is to improve the corrosion resistance in addition to the purpose of addition as a ferrite forming element.

That is, the addition of Cr in excess of 16% improves the corrosion resistance to various acids such as nitric acid, and exhibits excellent weather resistance even under the environment of sea salt particles, which is a problem for coastal structures. In addition, the reason why it is set to 30 wt% Cr or less is
This is because if Cr exceeds 30% by weight, a decrease in toughness and strength is recognized.

It is effective to add Al for oxidation resistance, if desired. However, addition of more than 4% Al causes a decrease in toughness, and when the dispersed particles are Al ₂ O ₃ , the effect of fine dispersion is lost due to the coarsening of the particles, which may hinder the improvement of rigidity.

When Cr is added in excess of 16% and the amount of Al added exceeds 4%, the problem of 475 ° C. brittleness arises. That is, in high Cr and high Al steel, the material becomes brittle when exposed to the environment in the temperature range near 475 ° C.
If Al is added in excess of%, this problem becomes remarkable. This is a big problem for automobile engines, especially for parts exposed to high-temperature environments such as exhaust valves.
It can be avoided by suppressing the amount of Al or less.

The matrix phase in the present invention is mainly composed of a ferrite phase exhibiting a high Young's modulus, but other phases such as an austenite phase and a martensite phase have a Young's modulus of 25000 kgf / As long as it does not fall below mm ² , of course, it may be a multiphase structure. For other phases, there is no problem if it is within 5%.

The present invention is intended to achieve high rigidity by utilizing the characteristics of ferritic steels and is not particularly limited as long as it has the above composition, but generally has the following steel composition: Is desirable.

Mn: 1.0% or less, Ni: 5.0% or less, Mo:
2.5% or less, W: 5.0% or less, Nb: 3.0% or less, Ti: 2.
0% or less, V: 2.0% or less, Si: 0.5% or less, P: 0.1
% Or less, S: 0.1% or less, oxygen: 0.2% or less excluding oxygen contained in oxide, N: 0.2% or less excluding N contained in nitride, C: C content contained in carbide. Except 0.
Less than 2%, balance iron. (All percentages are% by weight.) These elements do not necessarily need to include all of them, but Ni, Mo, W, Nb, Ti, and
It is desirable to add one or more elements such as V. That is, the addition of a small amount of C and Mn improves the strength,
Addition is effective in improving toughness.

Addition of Mo and W up to 2.5% and 5.0% respectively is effective for improving strength by solid solution strengthening, but if it exceeds this, embrittlement occurs due to intergranular precipitation of intermetallic compounds such as σ phase. Sometimes.

The addition of small amounts of Nb, Ti and V stabilizes C as a carbide, stabilizes the ferrite phase, and has the effect of improving strength by precipitation strengthening. But each
Addition of 3.0%, 2.0%, or more than 2.0% may cause embrittlement due to carbide precipitation on grain boundaries.

Further, Si, P, and S are acceptable as long as the impurities are 0.5% or less, 0.1% or less, and 0.1% or less, respectively. If it exceeds this value, the toughness is lowered due to precipitation at grain boundaries and the like. When oxygen and nitrogen are contained in a small amount of 0.2% or less, the strength is improved, but if the contents are exceeded, the toughness may decrease.

As described above, according to the present invention, in order to increase the rigidity of the material, it is important to highly integrate the {111} plane in the plane perpendicular to one direction in the ferritic steel. is there. {11 in ferritic steel
It is easier to integrate the 1} plane as the amount of processing strain = dislocation accumulation increases. Therefore, the strain = dislocation given in the processing step is pinned by the dispersed particles to increase the accumulated amount. .

Here, as the dispersed particles, an oxide,
There are dispersed particles of carbides, nitrides, borides, and further intermetallic compounds, and the average particle size thereof is not particularly limited, but preferably 0.005 to 0.1 μm.
, Its compounding ratio is 0.2 to 5% (volume%).

That is, the type, shape, size, and amount of the dispersed particles are not particularly limited, but preferably they are of a size that is thermally stable and that dislocations are effectively pinned. Also, in order to secure ductility and toughness as a practical material, it is preferable to limit the amount to a small amount. Average grain size that does not re-dissolve in ferritic steel as a base component even at high temperatures of 1200 ° C or higher.
Borides of 1 μm or less and 3% by volume or less, oxide particles of easily oxidizable metal elements (eg, Al, Ti, Y, etc.), and nitride particles are preferable.

The ferritic steel containing such dispersed particles is
Strain is accumulated by performing hot extrusion molding at about 1000 to 1200 ° C. Of course, it is needless to say that the strain imparted by warm and cold working is also good. The processing ratio in the strong work forming is set to an extrusion ratio of 3 or more, but if it is smaller than this, sufficient dislocations may not be introduced.

Further, even if HIP, CIP, rolling and forging are performed before the extrusion, if the extrusion is finally performed at an extrusion ratio of 3 or more, a sufficient processing strain is imparted. Furthermore, after extrusion processing,
Even if HIP, rolling, forging, etc. are performed, there is no problem as long as the processing strain due to extrusion is sufficiently imparted.

More preferably, in the step of dispersing the particles, a mechanical alloying method capable of uniformly finely dispersing the material while cold-working is used. Here, the mechanical alloying method (MA) is a method of using a ball mill or the like to forcefully mix the powders in a cold manner and repeatedly perform rolling, forging, and pressure bonding.

The composite material thus hard-worked and molded is then subjected to a secondary recrystallization heat treatment at a high temperature. The heat treatment conditions at that time are the type of matrix and dispersed particles,
It depends on the number, amount, size, etc., but preferably from 1100
A secondary recrystallization heat treatment is performed at 1400 ° C for 0.5 to 2 hours.

Here, the secondary recrystallization heat treatment is a heat treatment performed to align the {111} planes with the planes perpendicular to the specific direction. In other words, as long as such an object can be achieved, the heat treatment is not limited to the specific condition.

In the composite material thus obtained, the degree of integration of the {111} planes in the plane perpendicular to the fixed direction is 30 times or more that of the isotropic polycrystalline body in terms of the X-ray integrated intensity ratio. If less than twice, the Young's modulus targeted by the present invention is 25,000 kg.
It is not possible to obtain high-rigidity materials exceeding f / mm ² . As one of the criteria for determining that the X-ray integrated intensity ratio is 30 times or more, the ratio between the X-ray integrated intensity of the {222} plane and the X-ray integrated intensity of the {110} plane in the plane perpendicular to the certain direction is 0.
It may be 10 or more.

Here, these points will be further described. In general, a material having a fine structure in which lattice strain is introduced by strong processing such as extrusion and rolling is subjected to heat treatment to start primary recrystallization with the lattice strain energy as a driving force and to be embedded in crystal grains with extremely few lattice defects. To be done. The material that has undergone the primary recrystallization is further heat-treated for a long time or at a high temperature, and then the coarsening of the primary recrystallized grains is started by using the grain boundary energy as a driving force, resulting in an extremely coarse secondary recrystallized grain structure. To form.

In the case of the present invention, the <110> extruded texture is changed to the <111> secondary recrystallized texture in the course of this series of recrystallization phenomena, and accordingly, the Young's modulus is about 22,000 kgf / mm.
^{From 2} to about 29,000 kgf / mm ² .

In the present invention, for example, 0.2% by volume Y ₂ O ₃
In the as-extruded material, a very fine crystal grain structure with lattice strain introduced was formed in the as-extruded state.
When a heat treatment of 1200 ° C. × 1 hr is applied, coarsening of crystal grains and formation of <111> texture occur as a result of the secondary recrystallization phenomenon, and the Young's modulus in the extrusion direction is improved to 28,000 kgf / mm ² .

The heat treatment conditions for the secondary recrystallization differ depending on the amount of dispersed particles and processing conditions, and therefore cannot be determined unconditionally. For example, the extrusion conditions 1050 ° C., when the extrusion ratio of 10, but the secondary recrystallization temperature of 1200 ° C. at 0.2 vol% Y ₂ O ₃ added, the secondary re is 1300 ° C. at 0.5 vol% Y ₂ O ₃ added The crystal temperature is reached. This is because the dispersed particles act as an inhibitor that prevents grain boundary migration in the recrystallization process, and the more dispersed particles, the greater the effect.

When the amount of dispersed particles is fixed to 0.5% by volume of Y ₂ O ₃ , the lower the extrusion temperature and the higher the extrusion ratio, the lower the crystallization temperature. This is because recrystallization starts at a lower temperature when the introduced lattice strain energy is higher.

Here, in the present invention, the degree of integration of the {111} planes or {110} planes in a certain direction of the high-rigidity material, that is, in the extrusion direction, is the isotropic (random) polycrystal (for example, the packing ratio). The reduced iron powder sample of 65% and the density of 5.1 g / cm ³ is used as a standard sample).

To obtain the X-ray integrated intensity ratio, for example, the X-ray integrated intensities of the peaks of the {110} plane and the {222} plane in the extrusion direction of ferritic steel are measured and designated as I ₁₁₀ and I ₂₂₂ , respectively. A standard sample is also measured and designated as I ⁰ ₁₁₀ and I ⁰ ₂₂₂ , respectively. At this time, the integrated intensity ratio of the {110} plane is I ₁₁₀ / I ⁰ ₁₁₀ , and the integrated intensity ratio of the {222} plane is I _222.
/ I ⁰ ₂₂₂ .

Thus, according to the present invention, Young's modulus is 25.
000kgf / mm ² greater, many, high rigidity material having 28000kgf / mm ² or more is provided.

[0042]

EXAMPLES The effects of the present invention will be described in detail below with reference to examples. Y ₂ O ₃ particles having an average crystal grain size of about 0.02 μm,
And 0.02, 0.06, 0.10 μm Al ₂ O ₃ particles, and 0.02 μm TiC, AlN, TiB ₂ , BN particles and electrolytic iron powder (average particle size about 100 μm), C (graphite) powder (about 3 μm) ,
Mn powder (about 10 μm), Ni powder (about 100 μm), Cr powder (about 40 μm)
μm), Al powder (about 60 μm), Mo powder (about 3 μm), W powder
(About 2 μm), Nb powder (about 50 μm), Ti powder (about 10 μm), V
Powder (about 20 μm) and Fe-22Cr-3Al alloy powder (gas atomized powder, about 30 μm) were used for mechanical alloying (MA) with an attrition type ball mill to produce a composite powder. The mixing ratio of each powder was set to be the composition of ferritic steel as a whole.

Then, using these composite powders, after strong forming under various conditions such as extrusion, HIP + extrusion, HIP + forging + extrusion, CIP + forging + extrusion, extrusion + forging, extrusion + rolling, 1100- After heating at 1450 ° C. for 1 hour, air-cooled heat treatment was performed.

In Tables 1 and 2, the matrix is 22% Cr-3%
This is the case of Al steel, and Table 3 shows the case of containing 16 to 35% Cr-0 to 3% Al steel and other additive elements. Where N
In Nos. 8, 9, 10, and 11, Fe-22Cr-3Al alloy gas atomized powder was used as the matrix raw material powder, and other than that, the compounded powder of elemental powder was used as the raw material powder.

The degree of integration of {111} planes, Young's modulus, and Charpy impact value of the thus obtained material in the processing direction were measured. Further, in order to investigate the influence of 475 ° C. brittleness, these materials were heat-treated for 475 × 24 hours (atmosphere atmosphere), and then the Charpy impact value was measured again at room temperature. The results are shown in Tables 1 to 3 together with the comparative examples.

The influence of the amount of dispersed particles is No. 2, which is an example of the present invention,
3, 4 and No. 1 which is a comparative example. When there are no dispersed particles, secondary recrystallization hardly occurs, the {111} planes are not integrated, and the Young's modulus does not increase. It can be seen that dispersed particles are essential. Optimal 2 when the amount of dispersed particles increases
Although the secondary recrystallization temperature increases, the {111} planes are integrated and a high Young's modulus is exhibited.

The influence of heat treatment conditions was investigated by changing the temperature from 1100 ° C to 1450 ° C. As already mentioned, generally 11
00 to 1400 × 0.5 to 2 hours is sufficient, but in the case of this example, as shown in the invention sample No. 5 and the comparative samples No. 23 and 24, the heat treatment temperature may be low or high. It can be seen that secondary recrystallization does not occur and the optimum temperature exists at about 1200 to 1400 ° C. Of course, this optimum secondary recrystallization temperature differs depending on the composition component, dispersed particle type, diameter, and amount.

Comparative Example No. 1, Inventive Example Nos. 3, 5, 8, 9
As is clear from 10 and 11, the presence of fine dispersed particles is essential for achieving high rigidity. When finely dispersed particles are present, they are all secondarily recrystallized by heat treatment and the degree of accumulation of {111} faces is 30 times or more. However, when there are no dispersed particles, secondary recrystallization is performed under any heat treatment condition. It did not crystallize and therefore little integration of {111} faces occurred.

The influence of the processing conditions is shown in Example Nos. 5, 12, 1 of the present invention.
3, 15, 16, 17, 18, 19, 20, 21 and Comparative Example No. 14 are shown. As will be clear from now on, an extrusion process is required,
The lower the temperature and the higher the extrusion ratio, the more likely secondary recrystallization will occur. Moreover, unless the extrusion ratio is 3 or more,
The integration of {111} faces by secondary recrystallization is insufficient and Young's modulus is not sufficient.

Finally, regarding the influence of the components, as shown in Table 3, if the matrix is essentially a ferrite phase, a high Young's modulus can be obtained, of course. Even in a matrix having a mixed phase structure of ferrite and austenite as shown in No. 43, a Young's modulus of 25000 kgf / mm ² or more may be obtained.

For components above 16 Cr, the increase in Al is 475 ° C.
Causes brittleness. This 475 brittleness was not seen in the composition of 4% Al or less, but was remarkable in the composition of more than 4% Al. (Comparative Examples No. 29, 50, 51)

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

According to the present invention, a large amount of processing strain can be imparted, and the degree of integration of {111} planes can be remarkably improved. As a result, it becomes possible to manufacture high-rigidity materials with a Young's modulus of over 25,000 kgf / mm ^2, and it is possible to apply them to various spring materials, various shaft materials, and various structural members such as automobiles that require vibration absorption. It was

Claims (4)

[Claims] 1. Cr: more than 16% by weight and 30% by weight or less and Al: 0
A composite material in which dispersed particles are dispersed in a matrix of ferritic steel containing up to 4% by weight, and the degree of accumulation of {111} planes in a plane perpendicular to a certain direction is X.
A high-rigidity composite material having a linear integrated intensity ratio of 30 times or more that of an isotropic polycrystal. 2. Cr: more than 16% by weight and 30% by weight or less and Al: 0
A composite material in which dispersed particles are dispersed in a matrix of ferritic steel containing up to 4% by weight, and the X-ray integrated intensity of {222} and the X-ray integration of {110} plane in a plane perpendicular to a certain direction. A high-rigidity composite material characterized by a ratio to strength of 0.10 or more. 3. A method for producing a high-rigidity composite material, which comprises subjecting a composite powder in which particles are dispersed to a heat treatment and then subjecting the composite powder to heat treatment, wherein the working includes extrusion molding with an extrusion ratio of 3 or more, wherein the heat treatment is a secondary recrystallization. The method for producing a high-rigidity composite material according to claim 1 or 2, which is heat treatment. 4. The method for producing a high-rigidity composite material according to claim 3, wherein the composite powder is obtained by dispersing the particles by a mechanical alloying method.