JPS60169515A - Manufacture of wear resistant casting - Google Patents

Abstract

PURPOSE:To manufacture a casting with much superior wear resistance by inoculating W carbide into molten cast iron contg. W to disperse densely and uniformly crystallized lump W carbide in the cast iron. CONSTITUTION:When molten cast iron contg. 2.5-5.0% C, <3.5% Si, <3.5% Mn and 25.0-80.0% W or further contg. <=10% Ni, Cr, Co or other element substituted for part of Fe is cast, <=0.05% powder of W carbide such as WC and W2C is inoculated into the molten cast iron in a melting furnace, during charging into a casting mold or in the casting mold. Fine lump WC of 5-100mum grain size is uniformly crystallized and dispersed by 15-75vol% in the matrix of the resulting casting. Thus, a casting with very high hardness and superior wear resistance is obtd. It is suitable for use as the material of a roll for rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cast article having excellent wear resistance and having a structure in which massive crystallized tungsten carbide is densely and uniformly dispersed in the matrix.

Wear-resistant materials include, for example, various alloys in which hard carbides are precipitated in the matrix by a combination of chemical composition and heat treatment, cemented carbide made by bonding and sintering tungsten carbide with metals such as nickel and cobalt, and alumina. , ceramic sintered bodies such as silicon carbide, etc. The wear-resistant material according to the present invention differs from such various conventional materials by crystallizing a large amount of fine lumpy tungsten carbide in the matrix, thereby achieving high +Ir1J wear resistance. It embodies the ε-character.

In other words, in our research on wear-resistant materials, the present inventors found that iron-based alloy melts adjusted to a certain chemical composition containing a large amount of glue/Gestene (W) contain a large amount of H during the casting and solidification process.
Observing the crystallization of the massive tungsten carbide of 7H, the cast product has a structure in which the massive crystallized tungsten carbide is densely and uniformly dispersed in the matrix, and has excellent wear resistance, and is suitable for use in rolling rolls, for example. It has been found that it is suitable for various purposes.

The casting is made of c 2.5-5.0%, Si 3.5% or more.
r-184n3.5% or morer:,,W 25.0-80.
The iron-based alloy has four basic components of 0% IA, and in the base, bulk crystallized tungsten carbide with a grain size of about 5 to 1 (l Opm) occupies about 15 to 75% by volume. It can be obtained as a casting with a fine structure.

However, the crystallized tungsten carbide produced during the casting and solidification process tends to be in the form of coarse lumps or a series of lumps, and such a structure causes embrittlement of the material and deterioration of wear resistance, making it difficult to use for rolling. It becomes unsuitable as a roll or other structural material. In order to provide wear resistance as well as other properties such as strength and toughness, it is necessary for a large amount of massive tungsten carbide to form a dense and uniformly dispersed structure. As a result of further research on this point, the present inventors have found that inoculating the molten metal with tungsten carbide particles during casting is effective in uniformly dispersing the tungsten carbide produced in bulk.

The present invention has been made based on the findings described in section 2.
C'2.5-5.0%, Si3.5% or less, Mn35%
Hereinafter, in the casting of an iron-based alloy containing W25.0 to 800%, the molten metal is inoculated with tungsten carbide particles, thereby finely and uniformly dispersing the massive crystallized tungsten carbide in the matrix.

According to the present invention, inoculation with tungsten carbide particles is performed in casting a molten iron-based alloy containing W adjusted to a predetermined chemical composition.

The timing of the inoculation may be in the furnace immediately before pouring the hot water, or in the ladle during or after pouring the hot water.
It may be sprinkled into the mold or may be carried out during pouring into the mold.

The tungsten carbide particles used for inoculation are WC,
It may be W2C or a double carbide such as tungsten/chikun carbide. These carbide particles may be used in combination as appropriate. Its particle size is 10-25077
Preferably, it is m. , particle size is 1. If the particle size is less than 76.1 μm, the particles will completely dissolve and spread easily, and once they spread, the inoculation effect will disappear. on the other hand,
If coarse particles exceed 250 μnl, they will remain as particles in the molten metal, so the effect of inoculation will be reduced in this case as well. If the particle size is within the range of 10 to 250 μm, the inoculated carbide particles will collapse and disperse and be evenly distributed in the molten metal, or the uniformly distributed particles will dissolve but not diffuse. It is presumed that the crystallized carbides act as residual particles or crystallization nuclei, thereby avoiding the coarsening and agglomeration of crystallized carbides and forming a fine and uniformly dispersed structure.

Further, the amount of tungsten carbide particles to be inoculated is preferably 0.05% or more based on the amount of molten metal.

If the inoculation amount is less than 0.05%, the nucleation effect will be insufficient,
This is because it is difficult to obtain a sufficient industrial effect.If the amount of inoculation is increased, the fluidity of the molten metal may decrease due to the temperature drop of the molten metal due to heat absorption by the administered particles, or the presence of a large amount of collapsed and dispersed tungsten carbide particles. There is no particular problem in increasing the amount of inoculation as long as the required fluidity is maintained. This is because the surplus tungsten carbide particles do not participate in the nucleation effect, but remain as they are and contribute to improving wear resistance. However, even if the dose exceeds 20%, the effect hardly increases, which is economically disadvantageous.

tail Next, the reason for limiting the composition of the cast alloy will be explained.

C: 2.5-50% C is necessary for the formation of crystallized tungsten carbide. If the content is less than 25%, individual lumpy tungsten carbides cannot be crystallized, and continuous iron-tungsten double carbides are formed.

Moreover, when it exceeds 50%, graphite crystallizes in the base and becomes brittle. Therefore, it is set at 25 to 50%.

Si: 3.5% or less It has the effect of preventing the crystallization of sword-shaped tungsten carbides in the matrix and the accompanying embrittlement, and improving the fluidity of molten metal during casting. However, if it is contained in a large amount, (116) will become noticeable, so it should be kept at 35% or less.

Mn: 3.5% or less It has the effect of purifying the molten metal, but if it is too much)
f (as it causes embrittlement of the ground, it should be 35% or less.

W: 25.0-80.0% It is the most important element constituting the product of the present invention.

At least 250% is required to fully crystallize primary tungsten carbide. On the other hand, if it exceeds 800%, the melting point will be high and melting and casting will become difficult. Therefore, 2
50-800%.

The cast alloy in the present invention has four basic constituents of each of the above elements, and if necessary, in addition to the basic constituent elements, any one element selected from the group of Ni, Cr, Co, and other elements may be added for the purpose of improving the material quality. Or appropriate amounts of two or more elements (
(total amount of about 10% or less), and the remainder is an iron-based alloy consisting essentially of Fe. For example, one or both of Cr and N1 is contained as an optional element for the purpose of strengthening the base. In that case, the Cr content is preferably 5.0% or less in order to avoid embrittlement due to crystallization of chromium double carbides. Further, in the case of N1, it is appropriate to limit the amount to 6.0% or less when considering the effect of addition and cost.

The chemical composition of the cast alloy in the present invention is shown in Fig. 4.
When applied to the e-C-W ternary system phase diagram, it can be seen that the liquid phase surface of the corresponding composition is in the range of about 1700 to 1200°C, and tungsten carbide crystallizes as a primary crystal.

According to the present invention, a casting having the above-mentioned chemical composition is made such that massive crystallized carbides with a grain size of approximately 5 to 100 μn (circular equivalent value) occupy approximately 15 to 75% of the total volume in the matrix. It can be obtained as a casting having such a structure, and its hardness is extremely hard, for example, 900 to 1/100 in terms of TTv.Examples of the structure of the casting according to the present invention are shown in FIGS. 1 and 2. (The inoculant is WC particles).The crystallized carbide is a fine lump exhibiting a geometric crystal habit, and is densely and uniformly distributed in the base. The extracted carbide is WC, and contains almost no elements such as Fe and C+-.

There is no particular restriction on the casting method according to the present invention, and the casting method according to the present invention can be obtained, for example, as a solid columnar body or as a hollow cylindrical body. In this case, since wear resistance is a surface issue, a hollow cylindrical body may be cast and, if necessary, another type of metal may be cast as a core material in the hollow hole to form a two-layer structure. In this way, the required material properties can be met while reducing the amount of tungsten used, which is expensive as a constituent element of the molten metal and an inoculant. Furthermore, a centrifugal force casting method is used to cast hollow cylindrical castings, and by separating bulk crystallized carbide by specific gravity using centrifugal force, it is also possible to form a structure in which crystallized carbide is densely distributed in the surface layer.

To explain an embodiment of the present invention, a ceramic mold (inner diameter 3 Q mjll x height l Q
Castings (A) and (B) were obtained by casting Q yrrm ). Inoculation of the molten metal was carried out in the mold in the furnace immediately before tapping.

(1) Molten metal composition: C4, 10%, Si 0.54%,
Mn0.8%, W42.0%, Ni2.8%, CrO,
88%, remainder F e .

(11) Casting temperature: 1550°C (iii) Inoculant: W2C particles, particle size 10-63
μ+11 (1■) Inoculation timing and inoculation amount Casting (A): 08% inoculation to the molten metal in the mold Casting (B) 10% inoculation to the molten metal in the furnace just before release.

As a comparative example, a casting (C) was obtained under the same casting conditions as above except that no inoculation was performed.

(1,1 structure) 2 marks 3 from the bottom of each casting (A), (B) and (C)
The structures at the 0-H position are shown in FIGS. 1 to 3, respectively. In the comparative example (Fig. 3) in which no inoculation was carried out, the crystallized crystals were coarse and continuous in the form of blocks, but inoculation was carried out in the present invention example (A) (Fig. 1) and (B)(
Figure 2) shows that the crystallized carbides are extremely fine, dense, and uniformly separated.
! It has an organized structure.

In addition, the average grain size of the crystallized carbide in each structure of the present invention examples (A) and (B) is approximately 44 ltm, and the volume ratio is approximately 42 ltm.
% (according to lm11 grid intersection measurement method).

11J] Wear resistance A plate specimen was prepared from each casting (Δ), (13), and (C), and an abrasion test was conducted using an Okoshi type rapid abrasion tester under the following conditions to determine the abrasion resistance of each casting. The evaluation was based on the wear volume (specific wear amount) per unit load and unit sliding distance. .

(a) Mating material (rotating ring): SUJ 2, hardness (HRC
)62.0 (b) Zuburi speed: 3. '477Z/sec. Sliding distance: 200y horn.

(c) Final load: 176 to 18.5 kgf.

Table 1 shows the test results. The same table shows the conventional material Ni.
Glen cast iron (C3, 22%, Si0.75%, Mn0.
68%, Ni4.38%, Cr1.64%, hh035
%, balance Fe) and chilled castings (C3, 99%, Si
0.29%, 1023% Ni, 3.38% Ni, CrO,
The test results of the same abrasion test for 98% Mo, 0.22% Mo, and the balance Fe are also shown. The casting of the present invention has wear resistance superior to that of the comparative casting (C), N1 grain cast iron, and chilled casting.

Table 1 010 JI for each of curved castings (N, (B) and (C))
Tests were conducted on both sides using SZ 2242, and the absorption energy of glossy ruby was confirmed.

Casting (A): 0.40 kqf -yn casting (B)
: 0.3 5 kqf ・7 nol casting L)' 0
．． 30/cg (・711) It can be seen that the casting of the example of the present invention has excellent impact resistance.

As shown in (2), the castings obtained by the present invention have a structure in which ultrafine lumpy carbides are densely and uniformly dispersed in the matrix, are extremely hard, have high wear resistance, and have #dJ. It also has excellent properties, such as those related to steel, etc. ni
Roll 3 such as 1 rolling roll and conveyance roll in i: (
t, each pusher 11. It is suitable as a material for making IJs, dies, and other various types of metals that require wear resistance.

[Brief explanation of the drawing]

Figures 1 to 3 are micrographs (×/IO
), Figure 4 is a phase diagram of the 1-c-C-W ternary system. Agent: Patent Attorney Shinhachibe Miyazaki

Claims (1)

[Claims] (1) C2,5-5,0%, Si3.5% or less, Mn
35% or less, W250-80.0%, remainder substantially Fe
, or in the casting of iron-based alloys in which a portion of Fe is replaced with one or more alloying elements, by inoculating the molten metal with tungsten carbide particles, fine lumpy crystals are formed in the matrix. A method for producing a wear-resistant casting, characterized by forming a structure in which extracted tungsten carbide is uniformly dispersed.