JPH02127954A - Production of cv graphite cast iron pipe by centrifugal casting method - Google Patents

Abstract

PURPOSE:To prevent the segregation of an anti-graphite-spheroidizing element by ladle-adding a specific ratio of a rare earth metal to a molten ordinary cast iron, adding a specific ratio of Mg into the molten metal under pouring into a die and centrifugally casting the molten metal under GNo of a specific value or below. CONSTITUTION:The rare earth metal is added at 0.003 to 0.01wt.% to the molten ordinary cast iron in the ladle 6. Since the amt. of the metal to be added is slight, the metal is added to the ladle in order to uniformly add the element at a good yield to the molten metal. The Mg is added at 0.01 to 0.04wt.% to the molten metal under pouring into a die 1 for centrifugal casting. The Mg is included into the molten metal flow and is thereby uniformly added thereto. This molten metal is poured into the die 1 and is centrifugally cast under <=40 GNo. to produce the CV graphite cast iron pipe. The segregation of the anti-graphite-spheroidizing element is suppressed by selecting the adequate GNo. The cast iron pipe having the CV graphite cast iron structure down to the inside surface of the pipe is produced by the neutralization effect of the inhibiting element of the rare earth metal together with the graphite spheroidization treatment agent Mg in the molten metal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a cast iron pipe made of CV graphite structure (caterpillar-like graphite structure) by centrifugal casting.

(Prior art) CV graphite cast iron usually has a graphite nodularity rate of 30 to 70%, and although it is slightly inferior to ductile graphite cast iron (hereinafter referred to as FCD) in terms of tensile strength and elongation, it is comparable to ordinary cast iron ( below,
It is extremely superior to FC (FC) material, and FCD
It is extremely easy to manufacture compared to wood. For this reason, in recent years,
It is attracting attention as a material that can meet the demands for higher quality and diversification of cast products.

In general, C graphite cast iron castings are made using a graphite nodularizing agent (typically Mg
There is. ), add a treatment agent (for example, Mg-Ti alloy material) containing a graphite spheroidization inhibiting source metal to the ladle, or add FCD molten metal and F in a predetermined ratio.
It is manufactured by placing Cv graphite cast iron molten metal obtained by mixing Cv molten metal with Cv molten metal.

(Problem to be solved by the invention) Although the mold centrifugal casting method is an extremely economical method for mass-producing cast iron pipes, the reality is that it is not often applied to the production of Cv graphite cast iron pipes. be.

This is because when manufacturing a cast iron pipe by die centrifugal casting using CV graphite cast iron molten metal produced by the method described above, the outer surface of the molten metal poured into the mold (i.e., the metal There is a large difference in cooling rate between the inner surface (the side in contact with the mold) and the inner surface, which delays solidification on the inner surface. This is because, due to the centrifugal force generated by the rotation of the mold, the spheroidization-inhibiting elements in the molten metal segregate to the unsolidified inner surface, which tends to generate and develop an FC structure on the inner surface. Since the FC structure formed on the inner surface side is significantly inferior in mechanical properties to the CV graphite structure, sufficient strength as a cast iron pipe cannot be obtained, and a sound product cannot be obtained. Incidentally, the outer surface side tends to have an FCD structure, but this does not pose a problem in terms of product quality.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for obtaining a cast iron pipe having a C■ graphite structure up to the inner surface of the pipe by a mold centrifugal casting method.

(Means for Solving the Problems) The present invention, which has been made to achieve the above object, has a method of adding 0.003 to 0.0
．． 01 wt% of rare earth metal is added to the ladle, and 0.01 to 0.04 wt% of Mg is added to the molten metal being poured into the centrifugal casting mold with respect to the above-mentioned base metal amount, and centrifugal casting is performed at GN of 040 or less. The structure of the invention is to do so.

(Function) Add 0.01 to 0.04wt of Mg to the heaven made of FC molten metal.
% is added for the following reason.

That is, in general, C graphite cast iron has a graphite nodularization rate in the range of 30% to 70%, and Mg, which is a graphite nodularizing agent,
When the amount of addition is less than 0.01 wt%, graphite does not become spheroidized and forms a flaky graphite structure (FC structure);
If it exceeds this, the entire structure becomes spheroidal and becomes a spheroidal graphite cast iron structure (ordinary ductile cast iron), which is not economical.

When adding Mg to the molten metal, it is added to the molten metal flow that is being poured from the ladle into the mold, so Mg is caught up in the molten metal flow and can be added uniformly.

Rare earth metals are also used as graphite spheroidization aids and graphite spheroidization inhibiting elements (eg, Ti).

It is effective in neutralizing the influence of Pb) and adjusting the graphite structure. If it is less than 0.003 wt%, the effect of the spheroidization-inhibiting elements segregated in the unsolidified portion of the inner surface of the cast iron pipe cannot be neutralized, and the inner surface of the cast iron pipe becomes a flaky graphite structure (FC structure). 0.01
If it exceeds wt%, it is not economical because a corresponding improvement in effect is not observed.

Incidentally, since the rare earth metal is added in a very small amount as mentioned above, it is preferable to add it to the molten metal in a ladle in order to uniformly add it to the molten metal with a good yield.

G No. is the acceleration due to centrifugal force expressed as a multiple of gravitational acceleration. When GNα exceeds 40, the segregation of spheroidization-inhibiting elements in the unsolidified portion on the inner surface of the cast iron pipe becomes excessive, and the inner surface of the tube becomes an FC structure. Although the lower limit is not particularly specified, it is needless to say that it is at least a value that allows smooth centrifugal casting without causing defects such as poor hot water circulation or raining due to insufficient centrifugal force.

(Example) Although the tenba used in the present invention may be any FC molten metal, a preferable chemical composition is shown below.

Carbon Light It: 4. Owt%~5.5 wt%Mn
: 0.2wt%~1.5wt%P: 0.7w
Less than t% S: Less than 0.05wt% remainder substantially Fe The reasons for limiting each of the above components will be described below.

Carbon equivalent: 4. Owt%~5.5 wt%5.5w
When it exceeds t%, the strength decreases significantly, while 4. Ow
If it is less than t%, it will separate from the eutectic component and the castability will drop significantly.

Mn: 0.2 wt% to 1.5 wL% Mn is an element added for deoxidation, but if it is less than 0.2 wt%, the deoxidizing effect is not sufficient, while if it exceeds 1.5 wt%, the deoxidation effect will be insufficient. It is not economical as there is no improvement in the effectiveness of the method, and it also becomes fragile.

P: less than 0.7 wt%, S: 0.05 wt
Anything less than % makes the material brittle, so the lower the content, the better.
It is preferable to keep P at less than 0.7 wt% and S at less than 0.05 wt%.

The Mg added to the molten metal in the present invention is the base of Mg metal.
based alloy materials (e.g. Cu-Mg, Ni-Mg,
Ni-51-Mg, Ca-31-Mg, Mg-5
t-Fe) can be used.

And in the present invention? Ig metal or its alloy material is added to molten metal that is being poured from a casting ladle into a mold, and CV graphitization treatment of the molten metal is performed until the molten metal solidifies. For this reason, since it is necessary for the above-mentioned additive to dissolve quickly when added to the molten metal, it is desirable that the particle size thereof be 5.5 mm or less.

In addition, rare earth metals added to Tenba in the present invention include:
In addition to rare earth metals (for example, Ce is a rare earth metal used as a single element), complex compounds containing rare earth metals, such as Mitsushi metal and cerium-reinforced metals having chemical compositions as shown in Table 1, are used. It's okay.

Since the amount of the first addition is very small, it is preferable to add it in a ladle in order to uniformly add it to the top surface with a good yield. In this case, the ladle used for addition may be a casting ladle (so-called triangular ladle) or a distributing ladle in centrifugal casting equipment. However, if the casting ladle is used for pouring, the FC material and the C2 graphite cast iron material can be separately blown using the FC molten metal in the distribution ladle.

The shape of the rare earth metal or its composite compound may be such that it can be dissolved in the atmosphere by the above-mentioned addition operation.

Hereinafter, specific manufacturing examples will be described.

<Example A> Figure 1 schematically shows the cast iron pipe casting situation of this example.
The source hot water was poured into a casting ladle 6 (indicated by a dotted arrow in the figure). At this time, as rare earth metals, Mitshu metals (total rare earth metals (T, RE) as shown in Table 1 above) are used.
A quantity of 98.38% and a shape of 5 mmφ x 200 ma/liter was poured into the casting ladle 6.

Table 2 (Note) Unit: Weight %, balance is substantially Fe, and Mg M as a source
While adding g 5i-Fe alloy (Mg: 6.74 wt% 5 particle size 42 mesh to 150 mesh) from the charging hopper 7, the mold was centrifugally cast using GNα30 to form an outer diameter of 500 mm and a pipe length of 2500 + n [II, pipe Thickness 6mm,
A cast iron pipe with a back type of 200 kg was manufactured. In addition, in the figure, 2 is a core, and 5 is a rotating roller. Further, the arrow in the figure indicates the direction in which the casting ladle 6 is tilted.

Figure 2 shows Mitsushmetal and Flg when manufacturing a cast iron pipe of the above dimensions by centrifugal casting according to the above operation.
-3I-Fe alloy materials are shown in the structures of cast iron pipes obtained when various proportions are added. In addition, the amount of M8 added in the figure shows the value determined as the Mg content from the Mg-3i-Fe alloy material used. The amount of rare earth metal added is also calculated from the amount of Mitsushi metal added.

From the figure, it can be seen that the addition of Mg, which is a spheroidizing agent, alone cannot prevent the formation of FC structure on the inner surface of the cast iron pipe. In order to obtain a C■ graphite cast iron structure, Mg
It is also understood that it is necessary to add and coexist rare earth metals to neutralize the influence of the spheroidization-inhibiting elements segregated on the inner surface of the tube.

Next, for the FC source water in Table 2, rare earth metal 0.00
Cast iron pipes with the same dimensions as above were manufactured by centrifugal casting with various GNα while adding 6 wt % and Mg 2 O, 01 wt % to the top in the same manner as above.

Figure 3 shows the structure of the cast iron pipe obtained by the above operation and the G N
From the same figure, it was confirmed that centrifugal force casting at ONα of 40 or less results in a good Cv graphite structure up to the inner surface of the tube.

<Example B> Table 3 shows other examples and comparative examples. In Examples 1, 2 and 3, C■
Although it was possible to obtain a cast iron pipe consisting of a graphite cast iron structure, in a comparative example, the amount of rare earth metal added was 0.002%, which is outside the scope of the present invention.
As a result, the inner surface of the tube did not have a C■ graphite cast iron structure but an FC structure.

(Next page) (Effect of the invention) As explained above, according to the manufacturing method of the present invention, by selecting an appropriate GNα during centrifugal force casting, elements that inhibit graphite spheroidization in the molten metal are removed from the unsolidified state during casting. Prevents excessive segregation on the inner surface of the tube.

Furthermore, by adding a rare earth metal to the molten metal together with a graphite spheroidization treatment agent, the rare earth metal neutralizes the influence of the graphite spheroidization inhibiting elements segregated on the inner surface of the tube, and the inner surface becomes an FC structure. Therefore, a cast iron pipe having a CV graphite cast iron structure up to the inner surface of the pipe can be easily manufactured by the mold centrifugal casting method.

In addition, since the rare earth metal is added to the FC molten metal in a ladle, and Mg is added to the molten metal flow from the ladle into the mold, it is possible to omit the CV graphitization process at the top before casting. I can,
Since a drop in molten metal temperature can be prevented and the amount of slag produced is also reduced, the work of removing slag from the ladle can be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the cast iron pipe casting situation of an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the relationship between Mg addition amount and rare earth metal addition amount and graphite structure at a constant GNα, and Fig. 3 It is an explanatory view showing the relationship between No. and graphite structure. Patent applicant: Kubota Iron Works Co., Ltd. Agent: Patent attorney Yasu 1) Toshio Diagram

Claims (1)

[Claims] (1) A rare earth metal of 0.003 to 0.01 wt% based on the amount of the source metal is added in a ladle to the source metal consisting of molten ordinary cast iron, and 0.01 to 0.04 wt% of the amount of rare earth metal is added to the amount of the source metal. Mg
was added to the molten metal being poured into the centrifugal casting mold, and GNo.
A method for manufacturing a CV graphite cast iron pipe using a centrifugal force casting method, characterized in that centrifugal force casting is performed at a temperature of 40°C or less.