JPS58147542A - Wear resistant alloy cast iron - Google Patents

Abstract

PURPOSE:To obtain the titled cast iron preventing effectively the gravity segregation of VC and giving a large-sized casting or a centrifugally cast product having a homogeneous structure, by restricting the V content of a wear resistant cast iron alloy contg. a large amount of V and by adding Nb. CONSTITUTION:This wear resistant alloy cast iron consists of, by weight, 2.4- 3.6% C, 0.5-1.5% Si, 0.3-1.0% Mn, 3-8% Cr, <=9% Mo, <=8% W, 2-8% V, 2-8% Nb and the balance Fe with inevitable impurities or further contains <=3% Ni and/or 0.5-3% Co. Since Nb crystallizes as fine lump carbide in the presence of V after casting, Nb is substituted for part of V in crystallized VC with very low specific gravity, so the gravity segregation of high hardness VC can be prevented.

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 is about twice as hard as Umu carbide, and since the amount of vanadium is very large compared to the amount of carbon, it crystallizes in small lumps during casting and solidification, and austenite crystallizes surrounding it. In addition to the wear resistance that vanadium carbide itself has, it also has the effect of improving toughness.

However, while the specific gravity of molten cast iron is generally about 7.0, the specific gravity of crystallized vanadium carbide is about 4.0.
5, which is extremely small. For this reason, alloyed cast iron containing a large amount of vanadium has both excellent wear resistance and toughness, but on the other hand,
In large castings or centrifugal castings, weight segregation of vanadium carbides occurs, making it impossible to obtain sound castings. In other words, in large castings, the crystallized vanadium carbide floats upward, and in the casting area, as seen in the micrograph shown in Fig. On the other hand,
At 1h, as shown in Fig. 1fbl, at 4J, there are many rook-shaped M6C carbides and a cast structure with few vanadium carbides. In addition, in centrifugal casting, the crystallized vanadium carbide is concentrated and distributed on the side of the rotating shaft, which has the disadvantage of causing local unevenness in the wear resistance and toughness of the casting itself. Ta.

The purpose of the present invention is to effectively prevent gravity segregation of vanadium carbides in such high vanadium cast iron alloys, and to create a wear-resistant casting alloy suitable for large castings with a homogeneous structure or centrifugal casting castings. It is about providing.

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. It was completed based on the knowledge that 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 this MC type carbide C, niobium carbide (N b C''), is about 4, while the specific gravity of vanadium carbide is about 4.
．． 5, whereas it is about 7.7, 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 of vanadium carbide is fly2800.
It is low at 1Iv2400 compared to . Also, vanadium has an atomic weight of 50.92, while niobium has an atomic weight of 92.9.
Since the amount of niobium is as large as 1, approximately twice the amount of niobium as vanadium is required to form a MC type carbide with a ratio of 7-1.

The present invention uses a predetermined tungsten (or molybdenum)
Completed by supplementing with other alloying elements.

After casting, the base is generally hardened and tempered to strengthen it before use.

The wear-resistant alloy cast iron of the present invention has a weight a fraction of carbon of 2.4 to 3.6, a s of of 0.5 to 1.5, and a mankan of 0.
3 to 1.0, chromium 3 to 8, molybdenum 9 to F, tungsten 8 to 1, vanadium 2 to B, niobium 2 to 8 and the balance iron and inevitable impurities,
Furthermore, to this, 2. Nokel 3 or more F and cobalt 0.
It contains one or more of 5 to 3.

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 carbide, it is added to form a composite carbide by combining with chromium, tungsten, molybdenum, iron, manganese, etc., 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 fl%. .

In addition, when the amount of [i is increased, the wear resistance is improved by the carbides formed, but if the amount of bonding between added vanadium and niobium is significantly exceeded, each eutectic carbide crystallizes at the austenite grain boundaries, resulting in casting There is a risk that the strength of the material may be decreased unduly, and the limit is 3.6% by weight.

Silicon: Added to prevent oxidation of molten metal and give castability (7) ? ,, Me4. :,t! , 0.5-1.5
11(@o/6)RL) element is required.

Manganese: Like silicon, it is used to prevent the oxidation of alloying elements in the melt, and to fix sulfur that comes in as impurities from mineral raw materials, bonito flakes, etc. as MnS.
．． 3~t, oii setting% is added.

Chromium dichrome is added in the presence of tungsten, molybdenum, etc. to provide hardenability to the matrix and also to maintain wet strength. For this purpose, it is necessary to add 3% by weight, and if it exceeds 8111%, it will become saturated.

Molybdenum: Molybdenum is added to provide the same effect as tungsten, which will be described later. It further improves hardenability than tungsten, and the addition of molybdenum improves hardenability, V% wear resistance, etc., but it is an expensive element and is similar to tungsten. Since it promotes the formation of Kuro carbide, the upper limit is 91! ! m1%
shall be.

Tungsten: Tungsten carbide created by the combination of added tungsten and carbon replaces a part of vanadium carbide, increases its specific gravity, and has the effect of preventing its gravitational segregation, as well as solid solution in eutectic carbide and matrix. This increases the wear resistance of the alloy and the high temperature softening resistance of the matrix. but,
An increase in the amount of tungsten added increases the amount of eutectic carbide 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. Also,
Tungsten has almost the same effects as molybdenum, and can be substituted with molybdenum.

Vanadium: Added to form a hard carbide by combining with carbon. Without compromising the strength of the casting,
In order to obtain a casting with uniformly distributed crystallized carbides,
Based on the knowledge that IIIWB should be within 2-8% by weight.

Niobium: After casting, Niobium remains with vanadium and crystallizes as small block-like carbide (MC) at °C, which has an effect. If this amount is insufficient, there will be a lack of -ob 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 21! It is I setting%. Furthermore, since niobium has a high melting point, adding a large amount does not require an increase in the melting temperature, so the upper limit is 8% by weight.

In addition, within the carbon content range of the present invention, the niobium required to directly crystallize the MC carbide from the molten metal needs to be added in the relationship of 6% by weight and % vanadium weight → 0.5 x niobium% by weight. .

Depending on the purpose of the present invention, it is also effective to use elements other than the above-mentioned elements such as nickel and cobal. That is, in addition to the elements mentioned above, nickel is added at 3fI%, cobalt is added at 0.5 to 3% by weight, and at least one of the following is added. The content of these elements was determined for the following reasons.

Nickel is an element that significantly improves hardenability. In the presence of tungsten (or molybdenum) and chromium contained within the above-mentioned range, the high temperature softening resistance of the matrix does not decrease until 3% by weight of nickel is added. 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, when cobalt is added at 0.5 to 3% by weight, 50%
When subjected to alternating contact with high temperatures of 0°C or higher and appropriate water vapor, the surface of the base has 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 When the alloy of the present invention is used for such purposes, the addition of cobalt becomes effective.

Based on the above knowledge, an experiment was conducted to investigate the properties of the alloy of the present invention at °C, and the contents and results of the experiment will be shown below.

FIG. 2(a) shows an example of the casting structure (X200) of the alloy of the present invention.

('b) also shows an example of the structure of a conventional high vanadium alloy (X
200) are shown in Figure 1 (al and bl). These structures are examples of rolling rolls used as wear-resistant members, and have an outer diameter of 370 mφ and an inner diameter of 250 mφ.
Cast in a CO2 mold with mφ and length of 500 ts, 800 ~
The structure at 300 positions from the outer diameter surface in a cross section 400 days above the bottom surface of the casting annealed at 850°C was ialized.
Also, from the bottom surface of the casting, the cross section of 1 part of 50 cranes is 3 mm from the outer diameter surface.
The internal organization of Ofi is shown in fb).゛The chemical composition of the cast castings is shown in Table 1. 4゜Table 1: Conventional vanadium alloy castings that do not contain niobium have the upper structure as shown in Figure 1 (a).
In contrast to the white nodular vanadium carbide distributed in a high density, the distribution of vanadium carbide is hardly seen in the substructure shown in FIG. 1b). On the other hand, there is almost no difference in the distribution of vanadium carbide in the structure of the castings made of the alloy of the present invention shown in FIGS. 2(at) and 2(b). It can be seen that gravitational segregation of carbides was prevented.

As described above, it is clear that the alloy of the present invention has less uneven structure of the MC type carbide due to the 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 drawings]

The attached microscopic photograph (X200) shows the casting structure, and the first
Figures (Ikl and (bl) show the upper and partial inspection structures of the conventional cast iron casting, and Figures 2 (al and (b)) respectively correspond to the upper and lower parts of the casting made of the alloy cast iron of the present invention in Figure 1. Showing microscopic tissue. 1st (a) (a) (b) (b)

Claims (1)

[Claims] 1.11% 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 characterized by comprising niobium 2-B, the balance iron and inevitable impurities. 2.Charcoal s2.4~3.6, silicon 0.5~
1.5, -Nungan 0.3 to 1.0, Chromium 3 to 8, Molybdenum 9 or less, Tungsten 8 or less, Vanadium 2 to
8, Niobium 2-8, Nickel 3 or less and Cobalt 0
．． A wear-resistant alloy cast iron characterized by comprising one or two of Nos. 5 to 3, and the remainder iron and unavoidable impurities.