JPH0987797A - High strength ductile cast iron material - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To improve toughness and surface roughness of a ductile cast iron material used for rolling materials for rolling, large machine parts and the like. SOLUTION: The chemical components are in a weight ratio of C: 3.0 to 4.
0%, Si: 1.0 to 4.0%, Mn: 0.3 to 1.3
%, P: 0.1% or less, S: 0.05% or less, Ni:
1.0-4.0%, Cr: 2.0% or less, Mo: 0.1
~ 2.0%, Cu: 0.1-4.0%, Mg: 0.1
A ductile cast iron material excellent in toughness and roughening resistance, characterized in that it is 1.0%, Bi: 0.0005 to 0.05%, and the balance impurities and substantially Fe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ductile cast iron material having improved toughness and surface roughening resistance, and a graphite structure having an extremely fine and uniform distribution.

[0002]

2. Description of the Related Art Ductile cast iron is one in which graphite is spheroidized by performing spheroidizing treatment such as addition of Mg, and mechanical properties are improved as compared with flake graphite cast iron. Japanese Unexamined Patent Publication No. 6-116677 discloses a ductile cast iron material in which spheroidal graphite is finely dispersed by adding Bi to the ductile cast iron to improve toughness and surface roughness. However, in the case of JP-A-6-116677, although the graphite structure can be improved by finely dispersing the spherical graphite,
No improvement in matrix structure is obtained.

[0003]

For example, when the ductile cast iron material is applied to a member to which a large load is applied, such as a rolling roll, the material strength thereof is particularly important. Further, since the rolling roll comes into contact with the rolled material during use, irregularities on the roll surface are also likely to be a problem. Therefore, it is necessary to further improve the toughness and surface roughening resistance of the ductile cast iron material, for that purpose, it is considered effective to uniformly finely disperse graphite and to make the matrix structure pearlite or bainite. . As the method, it is easiest to raise the casting solidification rate and quench it, but in the case of large castings such as rolling rolls, since a sufficient solidification rate cannot be obtained especially inside, spherical graphite coarsens. , The matrix tends to be ferritic, and it is difficult to improve the toughness and the surface roughening resistance. An object of the present invention is to provide a ductile cast iron material having improved toughness and roughening resistance by making graphite finely dispersed even when a sufficient cooling rate is not obtained and making the matrix pearlite or bainite. It is a thing.

[0004]

Means for Solving the Problems In the present invention, graphite particles are made fine by adding Bi, and a matrix is made into pearlite or bainite by adding Cu, and the chemical composition is C: 3.0-4. 0%, Si: 1.0-4.
0%, Mn: 0.3 to 1.3%, P: 0.1% or less,
S: 0.05% or less, Ni: 1.0 to 4.0%, Cr:
2.0% or less, Mo: 0.1 to 2.0%, Cu: 0.1
~ 4.0%, Mg: 0.1-1.0%, Bi: 0.00
It is a ductile cast iron material excellent in toughness and rough surface resistance, which is characterized by comprising 0.05 to 0.05% and the balance impurities and substantially Fe.

[0005]

With the above composition, the graphite is finely dispersed uniformly and the toughness and surface roughness are improved.
The reason why the alloy components are limited to the above range will be described below. C:
Regarding the limitation of 3.0 to 4.0%, if the amount is less than 3.0%, the crystallization of graphite is insufficient, and if it exceeds 4.0%, the amount of graphite becomes excessive and the toughness and the surface roughening resistance deteriorate. . Si:
Regarding the limitation of 1.0 to 4.0%, Si is an essential element for crystallization of graphite, and if it is less than 1.0%, the eutectic carbide crystallization amount becomes excessive and the toughness deteriorates. On the other hand, if it exceeds 4.0%, the toughness and the surface roughening resistance deteriorate due to the brittleness of the matrix.

Regarding the limitation of Mn: 0.3 to 1.3%,
Mn is a matrix pearlite promoting element,
If it is less than 0.3%, the effect of forming pearlite is not recognized.
If it exceeds 3%, the toughness and surface roughness will deteriorate due to the brittleness of the matrix. P: Regarding the limitation of 0.1% or less, P was set to 0.1% or less from the viewpoint of making the material brittle. S: Regarding the limitation of 0.05% or less, S is set to 0.05% or less from the viewpoint of making the material brittle.

Regarding the limitation of Ni: 1.0 to 4.0%,
Ni is an element that improves the matrix structure and is an element that promotes graphitization, as is clear in Nihard cast iron. 1.0%
If it is less than 4.0%, no improvement effect is observed, and if it exceeds 4.0%, the spheroidization of graphite is hindered. Cr: Regarding the limitation of 2.0% or less, Cr is a white pig iron promoting element and also a pearlite promoting element. In the present invention, since Cu, which is a strong pearlite formation promoting element, is added, the amount of eutectic carbide is excessive (white pig iron) and the toughness is 2.0% in the range where deterioration does not occur.
Below.

Mo: Regarding the limitation of 0.1 to 2.0%,
Mo has the effect of maintaining quenching and tempering resistance.
If it is less than 0.1%, no improvement effect is observed, and if it exceeds 2.0%, the amount of eutectic carbides becomes excessive and the toughness deteriorates. C
u: 0.1 to 4.0%, Cu has the effect of strongly promoting pearlite formation of the matrix without turning it into white pig iron. It suppresses the precipitation of ferrite in the matrix and promotes the precipitation of pearlite or bainite even when a sufficient solidification rate cannot be obtained as in the case of a large cast product such as a rolling roll. Moreover, it has an effect of suppressing eutectic carbide (white pig iron). If it is less than 0.1%, the effect of promoting pearlite or bainite cannot be obtained, and it is 4.0%.
If it exceeds, Cu segregates at the grain boundaries and the toughness deteriorates.

Bi: About 0.0005 to 0.05%, Bi is an element generally preferred in ductile cast iron materials because it inhibits crystallization of graphite and spheroidization when added to cast iron materials. Not conventionally added. However, when a small amount of Bi is added, there is no adverse effect such as inhibition of crystallization of graphite, and graphite can be dispersed uniformly and finely even in the interior where the cooling rate is slow. Where Bi
If added in an excessive amount, the amount of graphite will decrease rather than the effect of uniform fine dispersion, and the tendency of embrittlement of cast iron will become more prominent.
Therefore, the range is set to 0.0005 to 0.05%. In addition to the above components, the component according to the present invention is formed of the remaining impurities and substantially Fe.

Next, an example of basic data leading to the present invention will be described. This basic data is obtained by preparing a test piece by casting a mold as shown in FIG. 1 with a molten metal having the chemical composition shown in Table 1 so that the content of Cu is cast. The amount of ferrite and the tensile strength were measured using a test piece taken from a position of 100 mm). The results of this basic test are explained below. Fig. 2 shows the amount of ferrite (area ratio) and C
The relationship with the amount of u added is shown. The amount of ferrite was measured by a generally known image analysis method. Cu is 0.1
% Brings a suppressing effect on ferrite precipitation,
It has been found that when the content exceeds 3.0%, the amount of ferrite (area ratio) is 0%, that is, the matrix is all pearlite. FIG. 3 shows the relationship between the tensile strength and the amount of Cu added. C
A significant increase in tensile strength was observed by adding u (0.1-4.0%). If it exceeds 4.0%, Cu segregates at the grain boundaries, and the strength deteriorates.

[0011]

[Table 1]

[0012]

[Example] Product body diameter 800 mmφ, body length 2500 mm,
A ductile cast iron-integral roll having a total length of 5120 mm was manufactured as described below and subjected to various investigations. As a ductile cast iron material, a metal mold of the present invention shown in Table 2 which has a chemical composition is used.
It was cast at a casting temperature of 50 ° C. Table 2 shows the molten metal chemical components of the ductile cast iron-integrated roll produced in the present invention. After cooling completely, the roll was pulled out from the mold, and the same shape as the above-mentioned roll manufacturing method was used with the molten metal chemical components (with Bi, without Cu, without Bi, without Cu) shown in Table 3 as comparative examples. Rolls were manufactured and the manufacturing qualities of both were comparatively investigated.

[0013]

[Table 2]

[0014]

[Table 3]

FIG. 4 shows micrographs of microstructures of three persons (1 from the surface).
00 mm position) is shown. 4 (a) has Bi and Cu, FIG. 4 (b) has Bi, no Cu, and FIG. 4 (c) has B.
This is the case without i and Cu. It was confirmed that in the case of adding Bi and Cu, the target graphite was uniformly finely dispersed and crystallized, and the matrix was entirely perliteed. Further, Table 4 shows the production quality of both rolls. The Bi- and Cu-added roll of the present invention simultaneously achieves an increase in material strength and a finer graphite structure.

[0016]

[Table 4]

As described above, in the roll of the present invention, B
i (0.0005-0.05%) and Cu (0.1-0.1%)
The addition of 4.0%) makes it possible to uniformly disperse and crystallize graphite and to make the matrix pearlite, which is extremely effective in improving toughness and also improving rough skin resistance. It is also effective. Although the application of the rolling roll has been described in the present embodiment, the material of the present invention is not limited to this, and can be widely applied to, for example, large machine parts requiring high strength.

[0018]

As described above, the ductile cast iron material according to the present invention has a significantly higher toughness than the conventional ductile cast iron material because graphite is uniformly finely dispersed and crystallized, and the matrix is entirely pearlite. In addition to the improvement, the rough skin resistance was also improved.

[Brief description of drawings]

FIG. 1 is a view showing a mold for producing a test piece,

FIG. 2 is a diagram showing the relationship between the amount of ferrite and the amount of Cu added,

FIG. 3 is a diagram showing the relationship between tensile strength and the amount of Cu added,

FIG. 4 is a metallographic photograph (× 50) of a roll of the present invention and a comparative roll.

Claims (1)

[Claims] 1. Chemical ratio by weight of C: 3.0 to 4.0% Si: 1.0 to 4.0% Mn: 0.3 to 1.3% P: 0.1% or less S: 0.05% or less Ni: 1.0 to 4.0% Cr: 2.0% or less Mo: 0.1 to 2.0% Cu: 0.1 to 4.0% Mg: 0.1 to 1. 0% Bi: 0.0005 to 0.05% A ductile cast iron material excellent in toughness and surface roughness, which is characterized by being composed of the balance impurities and substantially Fe.