JPS6051548B2 - Wear-resistant alloy cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wear-resistant cast alloy, particularly a cast iron alloy for use in wear-resistant members, which has excellent wear resistance and less unevenness in casting structure.

Conventionally, wear-resistant cast iron alloys containing a large amount of vanadium are known.

Vanadium is added to combine with carbon to form vanadium carbide (VC). Vanadium carbide has about twice the hardness of chromium carbide, and since the amount of vanadium is very large compared to the amount of carbon, it rises directly from the molten metal in the form of small lumps during casting and solidification, and the austenite surrounding it forms a high pressure. Therefore, it has the effect of improving toughness as well as the wear resistance that vanadium carbide itself has. However, while the specific gravity of molten cast iron is generally about 7.0, the specific gravity of vanadium carbide that is subjected to high pressure is extremely small, about 4.5.

For this reason, alloyed cast iron containing a large amount of vanadium has excellent wear resistance and toughness, but at the same time
Centrifugal casting has the drawback that gravitational segregation of vanadium carbides occurs, making it impossible to obtain sound castings. In other words, in large castings, vanadium carbide under high pressure floats upward, and as seen in the micrograph in Figure 1a, the white lumpy vanadium carbide is distributed over the entire surface of the upper part of the casting. At the bottom, as seen in Figure 1, there is a flaky M. The cast structure has many C carbides and few vanadium carbides. In addition, in centrifugal casting, this highly pressurized vanadium carbide is concentrated and distributed on the core side of the rotating shaft, which has the disadvantage of causing local unevenness in the wear resistance and toughness of the casting itself. . An object of the present invention is to provide a wear-resistant casting alloy that effectively prevents gravity segregation of vanadium carbides in such a high vanadium cast iron alloy and has a homogeneous structure and is suitable for large castings or centrifugal castings. It is in.

That is, the present invention prevents the occurrence of gravitational segregation of vanadium carbide by substituting a part of the vanadium in the vanadium carbide with niobium, and thereby the vanadium carbide is uniformly spread over the entire surface of the casting. This was completed based on the knowledge that large-scale castings and centrifugal castings can be obtained.

In this case, niobium is an element that forms MC type carbide like vanadium.

The specific gravity of niobium carbide (X°C), which is this MC type carbide, is about 7.5, while that of vanadium carbide is about 4.5.
7, which is close to the specific gravity of iron, so it is less likely to float and cause segregation during casting and solidification. However, the hardness is lower at HV24OO compared to vanadium carbide's HV28OO. Also, the atomic weight of vanadium is 50.92, while niobium has a large atomic weight of 92.91, so M with the same molecular weight
In order to form C-type carbide, niobium is required in an amount several times that of vanadium. The present invention has been completed by supplementing this with the combination of predetermined tungsten (or molybdenum) and other alloying elements, and generally after casting, quenching and tempering are performed to strengthen the base before use.

The wear-resistant alloy cast iron of the present invention has a carbon content of 2.0% by weight.
4-3.6, silicon 0.5-1.5, manganese 0.3-
1.01 consisting of 3 to 8 chromium, 9 or less molybdenum, 8 or less tungsten, 2 to 8 vanadium, 2 to 8 niobium, and the balance iron and unavoidable impurities, and vanadium weight %
It is characterized by having the following relationship: +0.5×niobium weight %>6 weight %.

The wear-resistant alloy of the present invention may further contain nickel of 3 or less and cobalt of 0.5 to 3 in weight percent, if necessary.
A desired effect can be expected by adding more than one species. The technical significance of each alloying element constituting the wear-resistant cast iron alloy of the present invention and the basis for limiting the amount added are as follows.

Carbon: Carbon is combined with added vanadium and niobium, M
In addition to forming C-type carbides, chromium, tan. It is added to combine with gsten, molybdenum, iron, manganese, etc. to form a composite carbide, and to form a solid solution in the base to give strength to the base.

If the carbon content is low, the amount of carbides will be insufficient and the wear resistance will deteriorate, and the castability will also deteriorate, making it impossible to produce sound castings, and the lower limit is 2.4% by weight. be. Also,
When the amount of carbon is increased, the wear resistance is improved by the carbides formed, but when the amount of bonding between added vanadium and niobium is greatly exceeded, each eutectic carbide crystallizes at the austenite grain boundaries, resulting in the formation of carbides. There is a risk that the strength will be significantly reduced, and the upper limit is H3. The weight is %. Silicon: Added to prevent oxidation of the molten metal and to impart castability. For this purpose, silicon must be contained in an amount of 0.5 to 1.5% by weight.
(To prevent oxidation of alloying elements in the molten metal like manganese silicon, and to fix sulfur mixed in as impurities from ore raw materials, fuel, etc. as MnS) 0.3 to 1. Add % of slag.

Chromium dichrome is added in the presence of tungsten, molybdenum, etc. to provide hardenability to the base and also to maintain high temperature strength. For this purpose, it is necessary to add 3% by weight, and if it exceeds 8% by weight, it will become saturated. MolybdenumMolybdenum is added to provide the same effect as tungsten, which will be described later.

It further promotes hardenability than tungsten, and although the addition of molybdenum improves hardenability, hot wear resistance, etc., it is an expensive element and, like tungsten, it Since it promotes the formation of crystalline carbides, the upper limit is set at 9% by weight. Tungsten carbide created by the combination of tungsten and carbon replaces a part of vanadium carbide, increases its specific gravity, and has the effect of preventing its gravitational segregation.
It forms a solid solution in the matrix and increases the wear resistance of the alloy and the high temperature softening resistance of the matrix. However, increasing the amount of tungsten added increases the amount of eutectic carbides formed and reduces the toughness of the casting, so the upper limit is set at 8% by weight in relation to the maximum amount of vanadium added. Further, tungsten has almost the same effect as molybdenum, and can be mutually substituted with molybdenum. Added to form a highly hard carbide by combining with vanadium dicarbon.

This is based on the knowledge that in order to obtain a casting in which crystallized carbides are uniformly distributed without impairing the strength of the casting, the content must be within the range of 2 to 8% by weight. After casting niobium, it coexists with vanadium and has the effect of crystallizing as small-sized carbides (MC).

If this amount is insufficient, niobium will be insufficient in the crystallized carbide (MC), the specific gravity will be small, and there will be no effect of preventing gravitational segregation, and the lower limit is 2% by weight. Furthermore, since niobium has a high melting point, adding a large amount of niobium makes it necessary to increase the melting temperature, so the upper limit is 8% by weight. In addition, within the carbon content range of the present invention, the amounts of vanadium and niobium necessary to directly crystallize the MC carbide from the molten metal are as follows: vanadium weight % + 0.5 × niobium weight %> 6 weight % need to be added.

Depending on the purpose of the alloy of the present invention, it is also effective to further add one or more of 3% by weight or less of nickel and 0.5 to 3% by weight of cobalt in addition to the above-mentioned elements.

That is, nickel is an element that significantly improves hardenability.

In addition, in the presence of tungsten (or molybdenum) and chromium contained within the above-mentioned range, the addition of 3% by weight of nickel does not reduce the high temperature softening resistance of the base. Further, depending on the shape and size of the casting, hardness can be obtained at a low quenching rate by adding an appropriate amount of 3% or less during normal quenching. In addition, cobalt is added in an amount of 0.5 to 3% by weight, and 500%
When subjected to alternating contact with high temperatures above ℃ and suitable water vapor *3, the surface of the base tends to have a high abrasion resistance called so-called black scale, and scale that is firmly attached to the base is likely to occur. It is advantageous for sex. When the alloy of the present invention is used for such purposes, the addition of cobalt becomes effective. Based on the above knowledge, experiments were conducted to examine the characteristics of the alloy of the present invention, and the contents and results of the experiments will be shown below.

An example of the casting structure of the alloy of the present invention (X2OO) is shown in FIGS. 2A and b, and an example of the structure of a conventional high vanadium alloy (X2OO) is shown in FIGS. 1A and b.

These structures are examples of rolling rolls used as wear-resistant members, and were cast in a CO2 mold with an outer diameter of 37 mm, an inner diameter of 250 TWLφ, and a length of 50 mm.
40 from the bottom surface of the casting annealed at 800-850℃
``Tissues at three positions from the outer diameter surface in the upper section are a
Also, the cross section of 5h above the casting bottom surface is 30mm from the outer diameter surface.
The internal organization of TWL is shown in b. The chemical composition of the cast material is shown in Table 1.

In conventional castings of high-vanadium alloys that do not contain niobium, the upper structure is shown in Figure 1a, in which white small-sized vanadium carbides are densely distributed, whereas the superstructure is shown in Figure 1b. There is almost no distribution of vanadium carbide in the underlying structure. On the other hand, there is almost no difference in the distribution state of vanadium carbide in any of the structures shown in FIG. You can know what has been prevented. As described above, it is clear that the alloy of the present invention has less uneven structure of the MC carbide due to gravity segregation of the MC type carbide, and is suitable for manufacturing wear-resistant castings such as large castings and centrifugal castings.

[Brief explanation of the drawing]

The attached micrograph (X2OO) shows the casting structure, and the first
Figures a and b show the upper and lower microstructures of a conventional cast iron casting, and Figures 2a and b show the upper and lower microstructures, respectively, corresponding to Fig. 1 of a casting made of the alloy cast iron of the present invention.

Claims (1)

[Claims] 1% by weight, carbon 2.4-3.6, silicon 0.5-1
．． 5, manganese 0.3-1.0, chromium 3-8, molybdenum 9 or less, tungsten 8 or less, vanadium 2-8,
A wear-resistant cast iron alloy consisting of 2 to 8 niobium, the balance iron and unavoidable impurities, and having the following relationship: vanadium weight % + 0.5 x niobium weight % > 6 weight %.