JPH02141560A - Ferrous ceramic material and its manufacture - Google Patents

Abstract

PURPOSE:To easily manufacture the title material having dispersed non-oriented cementite crystals and having high strength at low cost by dispersing fine foams in micron order into a molten metal contg. iron and specific amt. of carbon and thereafter cooling it. CONSTITUTION:Fine foams in micron order are formed to disperse into a molten metal contg. iron and, by weight, 3 to 6% C preferably into about <=10 micron distance of foams. The above foams can be formed by rising the temp. of the molten metal to the high one of about >=1600 deg.C with a crucible made of SiO2, bringing C in the molten metal into reaction with SiO2 in the crucible and generating a CO gas. The molten metal having the above dispersed fine foams is cooled. ln this way, the ferrous ceramic material having high strength, excellent wear resistance and toughness which is constituted of 3.0 to 5.5% C, 2.0 to 28.0% Cr and Fe and has dispersed cementite as non-oriented fine crystals of <=100 micron average grain size can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to ceramic materials that can be used as wear-resistant parts and the like.

[Prior Art] As heat-resistant and wear-resistant ceramic materials, materials whose main components include oxides such as alumina, as well as various carbides, borides, and silicides are widely used.

[Problems to be Solved by the Invention] All conventional ceramic materials have excellent heat resistance and wear resistance, but the raw materials are generally expensive and the manufacturing cost is also high.

Furthermore, it has been almost impossible to reuse conventional ceramics once they have been used.

The present invention provides a highly practical ceramic material that has appropriate wear resistance and toughness that can be used as wear-resistant parts, is easy to manufacture, and has low manufacturing costs.

[Means for Solving the Problems] The iron-based ceramic material according to the present invention contains iron, 3.0 to 5.5% carbon and 2.0 to 28.0% chromium by weight, It is characterized in that cementite is dispersed as non-directional fine crystals with an average grain size of 100 microns or less.

In addition, the method for manufacturing the iron-based ceramic material according to the present invention involves generating and dispersing fine bubbles on the order of microns in a molten metal containing iron and 3 to 6% carbon by weight, and then cooling it to form non-oriented cement. This method is characterized by obtaining a ceramic material having crystals.

Conventionally, alloys of iron and carbon that have been used industrially have mainly had a carbon content of 3% or less, and alloys with a higher carbon content have rarely been used. Furthermore, it is difficult to increase the amount of carbon in iron-carbon alloys without precipitating a large amount of graphite, and this has been almost impossible from an industrial perspective.

The present inventor focused on the high carbon range, which has not been used industrially in the past, and conducted various studies, and as a result, it was possible to obtain practical ceramics with excellent wear resistance and strength in these high carbon ranges. The present invention was completed by discovering this. This will be explained in detail below.

First, the problem is how to increase the amount of bonded carbon in iron-carbon systems without precipitating large amounts of graphite.
) was found to be solved by adding.

One possible reason for this is that chromium thermodynamically lowers the activity of carbon (C), so even if the amount of carbon increases, it becomes difficult to precipitate as graphite.

The ceramic material of the present invention has iron and carbon as main components as described above, and has a carbon content in the above range, that is, 3.0
% (weight %, the same applies hereinafter) to 5.5%, the higher the carbon content, the higher the amount of cementite, and conversely, the lower the carbon content, the higher the amount of ledebrite. A more preferable range of carbon content is 4.5 to 5.3%, and in this range a mixed structure of cementite and ledebrite is obtained.

The smaller the amount of graphite crystallized, the better, ideally 0%, but 0.3% or less is practically acceptable and 0%.
．． It is particularly preferable to set it to 0.5% or less.

Note that depending on the application, the amount of graphite may be slightly larger than this.

As additives other than the above chromium, one or more other elements such as molybdenum (MO), vanadium (V), tungsten (W), manganese (Mn), boron (B), etc. may be added as necessary. Can be added. All of these are cementite stabilizing elements and promote the precipitation of carbon as graphite.

Among the above additive elements, chromium (Cr) is an element that dissolves in cementite up to about 90%, and is an element that is particularly effective in forming cementite. When this amount is small, not only is it difficult to form cementite, but also the stability of the obtained ceramics at high temperatures becomes poor.

On the other hand, if too much chromium is added, the product becomes brittle and raw material costs increase. The preferred amount of chromium added is 2.0 to 28%, particularly preferably 4 to 10%.

Molybdenum (Mo) becomes M in advance at high temperature. It is an element that is difficult to dissolve in cementite because it forms C. When added alone, there is not much difference from adding chromium alone, but when added together with chromium, it increases the hardness at room temperature and high temperatures below 1000℃, and increases the resistance. Significantly increases abrasion resistance and high temperature strength. High temperature (
For example, it is considered that addition of a large amount of molybdenum is not preferable for plastic working at 1100°C. The preferred amount of molybdenum added is 0 to IO%, and 0.3 to 5.0%.
%, and even more preferably 0.5 to 2%. Within the above range, if the amount of molybdenum added decreases, wear resistance, high temperature strength, and corrosion resistance tend to decrease, and if it increases too much, the raw material cost increases,
It tends to deteriorate toughness.

Vanadium (V) is an element that dissolves well in cementite.
When used alone, there is almost no difference from chromium alone, and in some cases there is a tendency to precipitate a small amount of graphite. If graphite precipitates in products, it will reduce wear resistance and strength, and
Corrosion resistance decreases because the interface between graphite and iron is easily attacked. In collaboration with chromium, it improves the shape of cementite and promotes the formation of needle-like crystals. The preferred range of vanadium is 0-10%
A more preferable range is 0 to 9.0%, and even more preferably 0 to 7.0%, and if the amount of vanadium is small within this range, wear resistance, corrosion resistance, and high temperature strength tend to decrease. If the amount increases, the raw material cost will increase. Note that the toughness tends to improve as the amount of vanadium increases.

Tungsten (W) alone shows almost the same effect as chromium, and together with chromium shows the same tendency as molybdenum. The preferred range of tungsten is 0-10%,
More preferably 0 to 160%, still more preferably 2±
It is around 0.5%, and the smaller the content, the lower the abrasion resistance, corrosion resistance, and high-temperature strength, and the higher the content, the higher the raw material cost and the tendency to deteriorate the toughness.

Boron (B) cannot be expected to have much effect when added alone, and there is a risk that the product will become too hard, but when combined with chromium, it has the effect of making cementite crystals finer and improving toughness. The same applies when adding not only chromium but also chromium and molybdenum, chromium and vanadium, etc. The preferred amount of boron added is 0 to 1.
The content is 0%, more preferably 0 to 0.5%, and even more preferably 0.1±0.05%. If it is too small, the crystal refining effect will not be sufficient, and if it is too large, it will become extremely brittle.

Nickel (Ni) is an additional element other than those mentioned above. Nickel is added to improve heat resistance, and it is particularly preferable to add nickel to prevent a decrease in heat resistance when vanadium is added. The amount of nickel added is preferably 0 to 9%, more preferably 0 to 7%. In addition, 0.3±0.2 phosphorus (P) is added to prevent casting and hot cracking.
It is preferable to add %.

In addition, as an element for refining or preventing graphite crystallization, 0.1
% or less of Te or Bi can be used. Also,
In addition to these additive elements, other elements that do not inhibit the stabilization of cementite, such as rhenium (Re) and niobium (Nb), may be added.
), tantalum (Ta), technetium (Tc), etc. may be added. Furthermore, other elements may be contained as long as they do not pose a practical problem, and furthermore, impurities that are unavoidably mixed in or a small amount of graphite as described above may be present.

Next, regarding graphite spheroidizing agents, in order to spheroidize the graphite precipitated with this ceramic material, cerium (nie), Mitsushi metal (Misha + etal),
Calcium (Ca) and calcium silicon (Cas
It was effective to add one or more of i) to the molten metal. Mitshu metal is a relatively inexpensive alloy of naturally occurring cerium and lanthanum (La), and the cerium content is approximately 40 to 90%. Further, calcium silicon has a calcium content of about 30 to 35%, and the remainder is almost silicon.

The amount of these graphite nodularizing agents added is preferably 0.005 to 1.0% in the case of cerium, and 0.005 to 1.0%.
More preferably, the content was 4 to 0.8%. The preferable addition amount of Mitsushi metal is also the same as that of cerium. This is thought to be because lanthanum (La), which is the same rare element as cerium, has the same effect as cerium. Cerium stores hydrogen (H2), and when it is added to the molten metal, it releases this hydrogen gas in the form of bubbles, so it is thought that graphite is precipitated in spherical shapes within these bubbles. In addition, the amount of calcium silicon added was 0.
The content was preferably 1i to 1.2%. When calcium is added alone, it may be added in an amount corresponding to the calcium content in the calcium silicon. However, it was more preferable to add calcium in the form of silicon than to add calcium alone. Calcium, which has a high melting point and is difficult to dissolve in molten iron, is more effective in generating bubbles in molten metal.

As mentioned above, these graphite spheroidizing agents can be added alone or in combination of two or more. Among these, it is more preferable to add a combination of cerium-containing and calcium-containing substances, and among them, the combination of Mitsushi metal and calcium silicon was the most effective.

These graphite spheroidizing agents are, for example, wrapped in granular paper and inserted into a molten metal at 1700° C. or higher, and then quickly added to the molten metal using a phosphorizer. At this time, since the added spheroidizing agent evaporates, it is preferable to cast quickly. A small amount of spheroidized graphite precipitates in the obtained iron-based ceramic material, but a thin Fe layer is formed around this spheroidal softened graphite, which prevents crack propagation and improves strength. It is assumed that this will improve.

This iron-based ceramic material is obtained by casting a molten metal having a desired composition into a mold. In this case, the conditions should be such that decarburization occurs by 0.8% or more, preferably 1% or more. When such relatively large decarburization occurred, a desired structure (referred to as A structure) in which fine non-oriented cementite was dispersed was obtained.

The reason for this is that when decarburization occurs, carbon monoxide (CO), which is a compound of carbon and oxygen, is generated, but a large energy drop occurs at the interface between the liquid (molten metal) and the gas at the outer periphery of the bubble. This is thought to be because cementite tends to crystallize at the interface. In other words, cementite tends to stretch in one direction, and if it is a large bubble, it will likely grow through it, but since the interfacial energy of a bubble is inversely proportional to the square of the radius, If the bubbles are small (e.g. ondastrom units)
It is considered that primary crystals of cementite precipitate at the interface, grow centripetally toward the inside of the bubble, and become stuck inside the bubble. Since this crystal grows as a nucleus, it is thought that nearly spherical cementite crystals with almost no directionality can be obtained. In this sense, the smaller the bubbles, the better, and it is preferable that the fine bubbles are dispersed in the molten metal at a high density. For example, the preferred size of the bubbles is 5 microns or less, more preferably 1 micron or less, and the spacing between the bubbles is preferably 10 microns or less.

In order to generate such bubbles, it is necessary to supply oxygen that combines with carbon in the molten metal to generate CO gas. For example, there is a method in which a material that reacts with carbon to generate CO at high temperatures is brought into contact with the molten metal. Specifically, silica 5
If melted in a crucible made of i02 and maintained at a high temperature of 1600°C or higher, preferably 1700°C or higher, the 5i of the crucible
n2 and carbon in the molten metal react to generate nascent CO. Other possible methods include blowing oxygen into the molten metal and reacting the molten metal with other oxygen compounds. When generating CO bubbles by reacting oxidized compounds with molten metal,
It is necessary to temporarily maintain the temperature at a temperature sufficient for the reaction, for example, 1700° C. or higher.

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

Materials with various amounts of added carbon were melted and cast in a Si02 crucible. An example of the centrifugal casting apparatus used is shown in Fig. 1. In this casting apparatus 1, a crucible 4 and a mold 5 are supported by one support member 3 that projects horizontally from a rotating shaft 2, and a refractory ring 6 is interposed between the two. 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 rotating shaft 2 .

A counterweight IO is attached to the other support member 9 protruding from the rotating shaft 2. Rotating shaft 2 is motor 1
1, and the raw material melted in the crucible 4 is centrifugally cast. The amount of charge per time is 30g, and 1
After holding the temperature at 600° C. or higher for 100 seconds or more, it was cast within 200 seconds.

Figures 2 and 3 show examples of the molds used. Figure 2 is a pure copper mold for atmospheric melting, and Figure 3 is a copper mold.
Each is a centrifugal casting mold made of chromium alloy. In Figure 2, T is 12 mm.

W is 52mm, L is 200mm, A is 160mm
, B is 40m+e.

C was 20 mm. Also, in Figure 3, A is 44
mm, B is 24mm, C is 10mm, D is 54m
m, E is 20m+a.

F is 70mm and G is 53mm. In addition to metal molds, sand molds were also used as molds. In addition, F indicated by the chain line in the figure
is a ceramic home filter (made by Zirconia Z "02")
Since the molten metal is cast through this filter, impurities such as oxides are removed.

The microstructure of the obtained test piece is shown in Figures 4 and 5.
As shown in the figure. FIG. 4 shows the structure of the product of the present invention (Tissue A), and FIG. 5 shows the structure of the comparative example (Tissue C). In these photographs, the white part is cementite (Fe3G), and the gray part is ledebrite. In structure C in Figure 5, cementite is elongated and extends in one direction, but
In the C structure shown in the figure, the cementite is fine and almost spherical, and it can be seen that there is no directionality as in the C structure.

Cementite without such directionality has not been recognized at all in the past, and is the first to be obtained by the present invention. It is easily inferred that high strength can be obtained from this non-directional and fine cementite. Further, ledebrite has higher toughness than cementite, and its strength is improved by making cementite finer. In addition, those with approximately 0.1% boron (B) added have fine particle sizes and improve strength and toughness, but this particle size is also greatly affected by the cooling rate after casting, so it is difficult to achieve the desired high performance. In order to obtain this, it is also important to control the cooling rate.

Table 1 shows the characteristics of the ceramic materials thus obtained, and it can be seen that the transverse rupture strength of the ceramic materials having a hemi-textured structure is significantly improved. Such high toughness has never been achieved with conventional ceramics. It can be seen that this hemistructure is obtained when significant decarburization occurs.

Also, Figure 6 shows that of the He tissue and CIII! It can be seen that the hardness (Rockwell C scale) of the grain is high even if the carbon content is small. Furthermore, FIG. 7 shows the relationship between the initial addition amount of carbon and the amount of decarburization, and it can be seen that the amount of decarburization in the hemi-grain structure is greater than that in the C-structure. This is due to C in the molten metal.
This is thought to mean that O gas was generated.

Table 1 [Effects of the Invention] As is clear from the above explanation, according to the present invention, by creating a non-directional and fine cementite structure that could not be obtained in the past, iron-based It became possible to obtain ceramic materials. Since this material uses iron and carbon as its main raw materials, it is cheap and easy to manufacture. Moreover, by heating it to high temperatures and blowing oxygen into it, the iron can be easily recovered and reused. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the casting apparatus, and FIG. 2(a). (b) and (e) are a plan view, a front view and a side view with the field and some parts omitted, and Figures 3 (a) and (
b) and (c) are a plan view, front view, and side view of the centrifugal casting mold, Fig. 4 (a), (b), (e), and Fig. 5 (a).
, (b) and (c) are micrographs showing the crystal structure, Figure 6 is a graph showing the relationship between hardness and carbon content, and Figure 7 is a graph showing the relationship between carbon addition amount and decarburization amount. It is.

Claims (2)

[Claims] (1) Iron and 3.0 to 5.5% carbon by weight; 2.
An iron-based ceramic material containing 0 to 28.0% chromium and having high strength, characterized in that cementite is dispersed as non-oriented fine crystals with an average grain size of 100 microns or less. (2) A ceramic material having non-oriented cementite crystals is obtained by generating and dispersing micron-order fine bubbles in a molten metal containing iron and 3 to 6% carbon by weight, and then cooling the metal. A manufacturing method for iron-based ceramic materials.