JP2681125B2 - Iron-based ceramic material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ceramic material that can be used as a refractory material or the like.

[Prior Art] As ceramic materials having heat resistance and wear resistance, materials containing oxides such as alumina as well as various carbides, borides, and silicides as main components are widely used.

[Problems to be Solved by the Invention] Conventional ceramic materials all have excellent heat resistance and abrasion resistance, but generally the raw materials are expensive and the production cost is high. Moreover, it was almost impossible to recycle the conventional ceramics once used.

The present invention provides a highly practical ceramic material that can be used as a furnace material and the like, has heat resistance, appropriate wear resistance, and some drossiness, and is easy to manufacture and has a low manufacturing cost. .

[Means for Solving the Problems] The iron-based ceramic material according to the present invention contains iron as a main component, and 4.3% or more and 6.7% or less carbon by weight ratio, 4.5% or more and 25% or less chromium, and 3% by weight as essential components. % Or more and 10% or less of vanadium, and the crystal structure is cementite, reedbrite (eutectic structure of pearlite and cementite), or a mixed structure thereof.

Conventionally, the iron-oxygen alloy that was industrially used was exclusively for carbon contents of 4.3% or less, and those with more carbon than this were not used.

Further, in an iron-carbon alloy, it is extremely difficult to increase the carbon content to 4% or more without crystallizing a large amount of graphite, and it was almost impossible industrially.

The present inventor paid attention to the high carbon region which has not been industrially used in the past, and as a result of various researches, a practical ceramic excellent in heat resistance and wear resistance in these high carbon regions can be obtained. That is, the present invention has been completed. Hereinafter, this will be described in detail.

First, a method of increasing the amount of bound carbon without crystallizing a large amount of graphite in an iron-carbon system is problematic. This problem is caused by an appropriate cementite stabilizing element such as chromium (C
It was found that the addition of r) solved the problem. The reason is that chromium is thermodynamically carbon (C)
It is conceivable that crystallization of graphite becomes difficult even when the carbon content is large because the activity of the carbon is reduced.

The ceramic material of the present invention is mainly composed of iron and carbon as described above, and the above range, that is, the amount of carbon is 4.3.
% (Weight%, the same applies hereinafter) to 6.7%, the greater the amount of carbon, the greater the amount of cementite. Theoretically carbon amount is 4.3
When it is%, all are redeburite. The more preferable range of the amount of carbon is 4.8 to 5.8%.

The crystallized amount of graphite is preferably as small as possible, ideally 0% is desirable, but if 0.3% or less is practically acceptable,
It is particularly preferably set to 0.05% or less. Note that the amount of graphite may be slightly larger than this depending on the application.

As an additive other than the above carbon, chromium and vanadium, if necessary, other elements such as molybdenum (Mo),
One or more of tungsten (W), manganese (Mn), boron (B) and the like can be added. These are all elements for stabilizing cementite and prevent carbon from crystallizing as graphite.

Of the above-mentioned additional elements, chromium (Cr) is an element that dissolves in cementite up to about 90%, and is an element particularly effective for cementitization. If the amount is small, not only is it difficult to form cementite, but also the stability of the obtained ceramics at high temperatures is deteriorated. Conversely, if the added amount of chromium is too large, the product becomes brittle and the raw material cost increases. The preferable addition amount of chromium is 0.1 to 40%, more preferably 4.5 to 25%, and particularly preferably 7 ± 2%.

Molybdenum (Mo) is an element that forms MoC in advance at high temperatures and is difficult to dissolve in cementite.There is no significant difference between chromium alone and chromium alone. Increases hardness at high temperatures, significantly increasing wear resistance and high temperature strength. Increases high temperature strength, so high temperatures (eg,
It is considered that addition of a large amount of molybdenum is not preferable for plastic working at 1100 ° C). The preferable addition amount of molybdenum is 0 to 10%, more preferably 0 to 5.0%, and further preferably 0.1 to 4%. In the above range, when the amount of molybdenum is small, the abrasion resistance, high-temperature strength and corrosion resistance tend to decrease. When the amount is too large, the raw material cost increases and the ligature tends to deteriorate.

Vanadium (V) is an element that dissolves well in cementite. There is almost no difference from chromium alone when used alone, and in some cases, it tends to crystallize a small amount of graphite. When graphite is crystallized in a product, the wear resistance and strength are reduced, and the corrosion resistance is reduced because the interface between graphite and iron is easily eroded. Together with chromium, it improves the shape of cementite and promotes acicularization of crystals. The preferred range of vanadium is 3 to
It is 10%, more preferably 7 ± 2%. If the amount of vanadium in this range is small, the wear resistance, corrosion resistance and high temperature strength tend to decrease, and if it increases, the raw material cost rises. In addition, the ligature tends to be improved when the amount of vanadium is large.

Tungsten (W) alone shows almost the same effect as chromium, and together with chromium shows the same tendency as that of molybdenum. The preferable range of tungsten is 0 to 10%, more preferably 0 to 3.0%, further preferably about 2 ± 0.5%. The smaller the amount, the lower the abrasion resistance, corrosion resistance and high temperature strength. The cost becomes high, and the tendency to deteriorate the durability is shown.

Manganese (Mn) is an element that dissolves in cementite by about 60%, and when added alone, it shows almost the same tendency as chromium,
Corrosion resistance seems to be inferior to chromium. In cooperation with chromium, it shows the same tendency as molybdenum, vanadium, tungsten, etc., but it is not so remarkable. The preferred amount of manganese added is 0 to 10%, more preferably 0 to 5.0.
%, And more preferably 0 to 1.5%. When the manganese content is low within this range, the tendency is almost similar to that of chromium, but the tendency is not so remarkable as that of chromium. Also,
The more manganese, the more brittle and the corrosion resistance and oxidation resistance tend to deteriorate.

Boron (B) cannot be expected to be effective when added alone, and on the contrary, the product may be too hard.
Together with chrome, it has the effect of refining the cementite crystals and improving the durability. The same applies to the case where not only chromium but also chromium and molybdenum and chromium and vanadium are added together. The preferred addition amount of boron is 0
~ 1.0%, more preferably 0-0.5%, even more preferably
It is 0.1 ± 0.05%, and if it is too small, the grain refining effect is insufficient, and if it is too large, it becomes extremely brittle.

In addition, as an element for miniaturization or graphite crystallization prevention, 0.1
% Or less of Te or Bi can be used. Further, in addition to these additional elements, other elements that do not inhibit the stabilization of cementite, such as rhenium (Re), niobium (Nb), tantalum (Ta), and technetium (Tc) may be added.
Further, other elements may be contained as long as they do not hinder practical use, and impurities that are unavoidably mixed and small amounts of graphite as described above may be present.

This iron-based ceramic material is preferably used as a refractory, a mechanical part, a structural material, etc., which is used at a temperature of 1000 ° C. or lower. Further, since it has high hardness at room temperature or high temperature, it can be used as a material for parts and structures having wear resistance.

This iron-based ceramic material is produced by using, for example, casting, sintering, or
It can be manufactured relatively easily by a thermal spraying method or the like.
Since the main raw materials are iron and carbon, the raw materials are easily available and the raw material cost is low. Further, since it is structurally composed of a compound of iron and carbon, iron can be easily recovered from the used one by a method such as blowing oxygen at a high temperature and can be recycled. There is little risk of pollution in the manufacturing process and recovery process.

[Example] Next, an example of the present invention will be described.

Using the raw materials shown in Table 1, test pieces of various compositions were produced by casting method, sintering method and thermal spraying method. FIG. 1 shows an example of the centrifugal casting apparatus used. This casting apparatus 1 has a crucible 4 on one supporting member 3 which is provided on a rotary shaft 2 so as to project horizontally.
And the mold 5 are supported, and the fireproof ring 6 is interposed between the two.
Is interposed. A coil 7 for high frequency induction heating is wound around the outer periphery of the crucible 4, and the upper opening of the crucible 4 is covered with a quartz dome 8. Argon gas from the outside is supplied into the crucible 4 through the core of the rotary shaft 2. A counterweight 10 is attached to the other support member 9 protruding from the rotating shaft 2. The rotating shaft 2 is driven to rotate by a motor 11, and the raw material melted in the crucible 4 is centrifugally cast.

2 and 3 show examples of molds that can be used. FIG. 2 shows a pure copper air melting mold, and FIG. 3 shows a copper-chromium alloy centrifugal casting mold. Each represents. In this embodiment, the mold shown in FIG. 2 was not used. In Fig. 3, A is 44 mm, B is 24 mm, C is 10 mm, and D is 54 m.
m, E was 20 mm, F was 70 mm, and G was 53 mm. A sand mold was used as the mold in addition to the mold.

The microstructure of the obtained test piece is shown in FIGS. 4, 5 and 6. FIG. 4 shows a test piece produced by the casting method, and the composition is shown at the bottom of each photograph.
The magnifications are the same. In these photographs, white is cementite (Fe ₃ C), and gray is redebrite. In the photograph (a), coarse needle-shaped or plate-shaped crystals of cementite are observed, but in the photograph (b), these are needle-shaped (what looks granular is a cross-section of the needle-shaped crystals), and (c) , (D), it is understood that the needle-shaped crystals are miniaturized. The needle crystals have a diameter of preferably 50 μm or less, more preferably 20 μm or less. It is easily inferred that high strength can be obtained by making the crystallizing directions of such needle crystals uniform. Also,
Rhedebrite has higher weatherability than cementite, and strength is improved by refining cementite. The addition of boron (B) at a concentration of about 0.1% has a fine particle size and improves the strength and whiskability. However, since the particle size is greatly affected by the cooling rate after casting, the desired high performance is obtained. In order to obtain it, it is important to control the cooling rate.

FIG. 5 is a microstructure of a test piece manufactured by the sintering method, in which the compositions of (a) and (b) and the compositions of (c) and (d) are the same, and (b) is (a). ) Is enlarged, and (d) is enlarged (c). (A) and (b) and (b) and (d) have the same magnification. Also, (a), (b)
The sintering condition of the test piece is 1100 ℃ × 12hr,
That of (c) and (d) was 1200 ° C. × 4 hr. Although pores (black spheres) are found in places in the test piece produced by the sintering method, it is considered that these pores can be eliminated by, for example, HIPing.

FIG. 6 is a photomicrograph of a test piece manufactured by a thermal spraying method using a powder raw material, which has the same composition, and (a) and (b) show the iron powder as a raw material having a particle size of −.
80mesh, (c) and (d) are -250mesh. Also,
(B) is an enlarged photograph of (a), and (d) is an enlarged photograph of (c). It can be seen that the materials shown in FIGS. 7C and 7D are excellent in strength because the cementite has a small particle size and the dispersed state is good. Since the particle size of the used powder corresponds to the particle size of cementite, the particle size of the raw material powder is preferably −100 mesh, and more preferably −500 mesh. The cementite grain size is preferably 100 μm or less, and most preferably 5 μm or less. Also, from the viewpoint of this structure, the obtained ceramic material is considered to have a considerable degree of drossiness,
The result of actual measurement showed some dullness. It should be noted that the presence of some pores was also confirmed in the test piece produced by thermal spraying.
It is considered that it can be eliminated by performing appropriate processing such as.

Fig. 7 shows the relationship between chemical composition and hardness (H _V ). The hardness of cementite without addition of chromium is
The hardness of 1256 and lederite was 836. When chromium alone is added, the hardness does not seem to change much depending on the amount of chromium. In the case of adding 5% of chromium and molybdenum, it seems that the hardness increases from 1% to 3% of molybdenum, and does not change much beyond that. The hardness of cementite in the case of adding 5% of chromium, 3% of molybdenum and 0.5% of boron is as low as about 1200, which is considered to be due to crystallization of spherical graphite. The addition of 5% chromium and tungsten shows a tendency that the hardness of ledeburite increases with the amount of tungsten. Generally, in the composite additive sample, the average hardness of the cementite part and the redeburite part is 1200 HV, which is comparable to the hardness of the new ceramic ZrO ₂ .

Figure 8 is a graph showing the relationship between additives and high temperature hardness. In both cases, hardness decreases with increasing temperature.
It can be seen that it has sufficient strength up to about 00 ° C. Of these, 5% chrome alone has a hardness of 700 ° C.
Since the temperature drops to about 250 ° C (H _v ) at high temperature, the possibility of plastic working at high temperature can be seen. In addition, chromium 5% and 13
% And 3% molybdenum add up to about 360 at 800 ℃
(HV) and comparable to tempered martensite. Also, Cr5
% And Mo3% samples were gradually heated from room temperature to 1000 ° C over 333 minutes, and then gradually cooled to room temperature over 333 minutes, and the microscopic structure was observed. It was found that it has excellent heat resistance.

Fig. 9 is a graph showing the relationship between the added amount of chromium and the corrosion resistance (acid resistance). It shows the weight loss (mg / cm ² ) when immersed in 1: 1 hydrochloric acid at 20 ° C. As can be seen from the figure, the amount of chromium added at 5% is about 1/40 of the amount of chromium added at 1%, which is almost equal to that of 18-8 stainless steel. Judging from this fact, 5% chromium and 3% molybdenum were added, 13% chromium was added, 25% chromium was added, 13% chromium and 3% molybdenum were added, and 25% chromium was added. It is expected that those with 3% molybdenum added will have better acid resistance than stainless steel.

Figure 10 shows the results of line analysis by EPMA to examine the solubility of each additive element. The tabular part is cementite, and the part with minute irregularities is reedebrite. Figure 10 (a) shows the solubility of molybdenum in the product with 5% chromium and 3% molybdenum (test piece No. 14).
(B) Tungsten solubility of the product with 5% chromium and 3% tungsten (test piece No. 17), (c) Manganese with 5% chromium, 3% molybdenum and 5% manganese (test piece No. 27) Represents each solubility. Further, (d) and (e) both represent the solubilities of chromium and vanadium in the product containing 5% chromium and 3% vanadium (test piece No. 18). The same figure (d), (e)
It can be seen from the results that chromium and vanadium dissolve well in cementite.

[Effects of the Invention] As is clear from the above description, the iron-based ceramic material according to the present invention has fire resistance, high hardness, and corrosion resistance sufficient to withstand use at a temperature of 1000 ° C or less. It can be used in a wide range of fields such as objects and wear resistant parts. Moreover, since this ceramic material is mainly composed of iron, the raw material cost is low and the raw material is easily available. In addition, since both cementite and redeburite that compose this ceramic material are compounds of iron and carbon, it is possible to re-use those that have been used once. It has a high industrial utility value in various respects, such as exhibiting some dullness that has not been achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a casting apparatus, and FIGS. 2 (a), (b),
(C) is a plan view of the air-melting die used, and a front view and a side view with a part omitted, FIGS. 3 (a), (b),
(C) is a plan view, front view, side view, FIG. 4 (a), (b), (c), (d), FIG. 5 (a) of the centrifugal casting mold.
(B), (c), (d) and FIGS. 6 (a), (b),
(C) and (d) are micrographs showing the crystal structure, No. 7.
Fig. 8 is a graph showing the relationship between hardness and chemical composition, Fig. 8 is a graph showing the effect of additives on high temperature hardness, and Fig. 9 is a graph showing the effect of chromium on acid resistance.
FIGS. 10 (a), (b), (c), (d) and (e) are micrographs showing the solubility and crystal structure of each additive element. 1 ... Centrifugal casting device, 2 ... Rotating shaft 4 ... Crucible, 5 ... Mold

Claims (2)

(57) [Claims] Claims: 1. 3% to 6.7% carbon by weight, 4.5% to 25% chromium, 3% to 10% by weight as essential components
A heat-resistant iron-based ceramic material containing the following vanadium, the balance being substantially iron, and the crystal structure being cementite, ledeburite, or a mixed structure thereof. 2. In addition to the above essential components, one or more of molybdenum of 10% or less by weight, tungsten of 10% or less, manganese of 10% or less and boron of 1% or less are added. The iron-based ceramic material according to claim 1.