JPH0480344A - Alloy cast iron material excellent in wear resistance - Google Patents

Abstract

PURPOSE:To obtain allay cast iron material in which microsegregation is hard to occur and excellent in wear resistance by preparing an allay cast iron material having a specified compsn. in which each content of C, Cr and Mo is prescribed. CONSTITUTION:An alloy cast iron material having a chemical compsn. of, by weight, 2.3 to 3.4% C, 0.3 to 2.0% Si, 0.3 to 1.5% Mn, 0.3 to 3.0% Ni, 7 to 18% Cr, 1 to 8% V, 5 to 15% Mo, 0 to 10% W (where Mo+1/2W is regulated to 2 to 15%) and the balance Fe with impurities is prepd. Furthermore, this alloy cast iron material is cast into an objective shape, is subjected to rough working, is thereafter, for hardening the matrix, held to about 950 to 1150 deg.C (in the cast the cast iron material is used for an inner layer, to about 950 to 100 deg.C), is austenitized, is thereafter rapidly cooled by fog water cooling or the like, is hardened, is thereafter held to about 500 to 650 deg.C for about 2 to 10hr and is tempered; and the above treatment is executed for several times. In this way, a wear-resistant casting in which the microsegregation of V is hard to occur can easily be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an alloy cast iron material with excellent wear resistance used for rolling rolls, steel material conveying rollers, and the like.

(Prior art and issues) It is known that (1) forms a highly hard and fine MC type carbide and has wear resistance and toughness.
Publication No. 37949 discloses a wear-resistant alloy cast iron containing (■).

However, ■ carbide (more precisely, MC type carbide containing a large amount of ■) has a low specific gravity, so when casting large castings or performing centrifugal casting, it separates due to the difference in specific gravity, causing macroscopic non-uniformity. This causes uneven wear.

For this reason, the technique disclosed in the above publication attempts to prevent segregation by incorporating Nb, but since Nb is difficult to dissolve and cannot be added in large amounts, it cannot be said that prevention of segregation is sufficient. is the reality.

The present invention was made in view of this problem, and an object of the present invention is to provide a V-containing wear-resistant cast iron material that does not contain Nb and is less likely to cause macro segregation.

(Means for Solving the Problems) The wear-resistant cast iron material of the present invention, which has been made to achieve the above object, has a chemical composition of 2.3 to 3.4% by weight, C: 2.3 to 3.4%;
Si: 0.3-2.0% Mn: 0.3-1.5
%, Ni: 0.3-3.0% Cr: 7-18
%, ■: 1-8% Mo: 5-15%, W:
0-10% However, Mo+'/2W: 5-15% The balance is formed by Fe and impurities.

(Function) The wear-resistant cast iron material of the present invention selects a specific high-C, high-Cr component system, narrows the solidification temperature range (solid-liquid coexistence region), and makes segregation less likely to occur. It is characterized by the addition of heavy elements (mainly Mo) that easily generate double carbides, increasing the specific gravity of double carbides and suppressing specific gravity separation.Hereinafter, the reasons for limiting the chemical composition (wt%) will be explained. explain.

C: 2.3 to 3.4% If it is less than 2.3%, the solidification temperature range (solid-liquid coexistence region) becomes wide. Furthermore, the amount of carbide decreases, resulting in deterioration of wear resistance.

Castability also deteriorates. On the other hand, if it exceeds 3.4%, toughness decreases.

Si: 0.3 to 2.0% Add 0.3% or more to prevent oxidation of the molten metal and provide castability. Further, Cr dissolves in solid solution in carbides other than carbides (complex carbides containing a large amount of Cr) and has the effect of increasing the amount of carbides, but if it exceeds 2%, the material deteriorates.

Mn: 0.3-1.5% In order to fix S mixed as an impurity as MnS,
Add 0.3-1.5%. If it exceeds 1.5%, retained austenite increases and hardness decreases.

Ni: 0.3 to 3.0% Ni is added in an amount of 0.3% or more to strengthen the base and increase hardenability, but if it exceeds 3%, retained austenite increases and hardness decreases.

Cr: 7-18% Usually added to increase hardenability and oxidation resistance, but if it is less than 7%, the solidification temperature range becomes too wide. on the other hand,
If it exceeds 18%, the number of double carbides containing a large amount of Cr increases.

Since double carbides containing a large amount of Cr such as W, V, and Mo are not very hard, it is preferable that the relative proportion of the double carbide to the total amount of carbides is small.

(2): 1 to 8% Forms MC type carbide with high hardness and increases wear resistance, but if it is less than 1%, the effect is small.

On the other hand, from the viewpoint of preventing specific gravity separation, addition of 8% or less is preferable.

Mo: 5-15% Part of it forms a solid solution in the matrix and increases hardenability.

Further, it forms double carbides with (1), and when added in an amount of 5% or more, it has the effect of suppressing the specific gravity separation of (2), but if it exceeds 15%, eutectic carbides increase, leading to a decrease in strength.

W: 0 to 10%, however, MO+y2W: 5 to 15% It has the effect of increasing the high temperature softening resistance of the base.

In addition, it has the same effect as Mo and can be substituted with Mo at a ratio of Mo:W=1:2, but since the atomic weight (therefore specific gravity) is about twice as high as that of Mo, addition of more than 10% In this case, the specific gravity of the molten metal increases, and the difference in specific gravity between the double carbide and the double carbide increases, which actually promotes the segregation of the molten metal. Furthermore, M6C type carbide increases, which is not preferable.

In addition to the above-mentioned components, the alloy cast iron material of the present invention is made of Fe and unavoidably mixed impurities.

(Example) The alloy cast iron material of the present invention is used as a wear-resistant material for various uses. For example, it is used as a cast material for the outer layer of a composite roll for hot rolling. In this case, as the inner layer (shaft core) material, a tough cast iron material such as high-grade cast iron or ductile cast iron, or a cast steel material such as graphite cast steel is appropriately used.

In addition, as a manufacturing method for the composite roll, after casting the outer layer by centrifugal force casting, a centrifugal force casting mold containing the outer layer is stood up to form a stationary mold, and the molten metal of the inner layer material is poured into the mold. There is a method of welding and integrating the outer layer and the inner layer using hot water, and it is commonly used because it is simple.In addition, when welding the outer layer and the inner layer, in order to prevent ingredients from mixing from the outer layer to the inner layer, , it is preferable to provide an intermediate layer between the outer layer and the inner layer.

The alloy cast iron material of the present invention is cast into a desired shape,
After rough processing, heat at 950-1150°C (
However, when the inner layer is cast iron, it is held at a temperature of 950 to 1100°C to austenite, then rapidly cooled by spray water cooling, quenched, and then tempered several times by being held at a temperature of 500 to 650°C for 2 to 10 hours. be exposed. In addition, if the casting is small, it can be hardened by simply air cooling after casting.
No special cold treatment is required.

Next, specific examples are listed.

(1) An alloy cast iron material having the composition shown in Table 1 is melted in a high-frequency furnace, and is made into φ200 x length 200 x thickness 50 (own).
A cylindrical material was centrifugally cast under the following conditions.

0 casting conditions Mold rotation speed...GNα=140 Mold wall thickness...120ml11 Coating mold thickness...1.5mm Casting temperature...Listed in Table 1 Next Table 1 (2) After casting, the material was heat treated three times at 540"CX10Hr, and the hardness was measured as shown in Table 2 below.

Table 2 (3) When the material was cut in the axial direction, the cut surface was corroded with aqua regia, and the macrostructure was observed by daylight, no segregation was observed in any of the examples, but in the conventional example, the inner surface 5m from
It is a high concentration V-containing layer up to 5 to 20 mm.
A layered segregation consisting of a mixed layer of high concentration and low concentration was observed over the period.

(Effect of the invention) As explained above, the alloy of the present invention has Cr: 7 to 18%,
Mo + '74W: Because it has a specific composition containing 5 to 15%, the macro of Wear-resistant castings that are less likely to cause segregation can be easily produced.

Claims (1)

[Claims] (1) Chemical composition in weight%: C: 2.3 to 3.4%, Si: 0.3 to 2.0%, Mn:
0.3-1.5%, Ni: 0.3-3.0% Cr: 7-
18%, V: 1-8% Mo: 5-15%, W: 0-10% However, Mo + 1/2 W: 5-15% The remainder is essentially Fe and has excellent wear resistance. Alloy cast iron material.