JPH084895B2 - Method for manufacturing corrosion-resistant centrifugal cast iron pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the manufacture of corrosion resistant centrifugal cast iron pipes.

[0002]

2. Description of the Related Art Centrifugal cast iron pipes, especially ductile cast iron pipes, are buried in the ground to form water and sewer pipes, and are widely used for agricultural water and gas pipes and play an important role in the formation of national land. Is being used nationwide. Cast iron pipes have higher corrosion resistance than steel pipes, but because they are buried in the ground and exposed to a corrosive atmosphere and the pipes are constantly exposed to running water, anticorrosion paint is applied to the outer peripheral surface and the inner peripheral surface is coated. Cement lining is applied to make sure. However, the applications of centrifugal cast iron pipes are further expanding, and there is a tendency for the number of cases where the fluid passing through the pipes, such as chemical plants and marine pipes, to cause corrosive conditions more than ever before. Corresponding to this tendency, it is necessary to improve the corrosion resistance of centrifugal cast iron pipes so that they can be used under more severe conditions.

There are roughly two methods for improving the corrosion resistance. One is a method in which a non-ferrous metal having a high corrosion resistance such as Ni is added when the cast iron is melted, and the alloy is cast as alloy cast iron. The other is a method of forming a corrosion-resistant skin layer on a necessary surface of a cast product (for example, only the inner surface of a cast iron pipe) to prevent direct exposure of the cast iron material to a corrosive atmosphere. Techniques for forming a specific coating on a part of a cast product to provide it with special properties that cannot be obtained by cast iron have been actively proposed, for example, JP-B-53-18166 and JP-A-57-177.
850, Japanese Patent Application Laid-Open No. 63-1
Many are found such as in the publication No. 0058.

Further, as a manufacturing method for imparting corrosion resistance to a ductile centrifugal cast iron pipe, there is Japanese Patent Publication No. 2-45538. In this conventional technique, an Fe-Si powder for Si enrichment is uniformly baked on the inner surface of a die for centrifugal casting with a regular coating for coating, and the die is rotated while pouring the molten metal into the inner surface immediately. The Fe-Si powder is evenly dispersed and melted on the inner surface of the molten metal to provide corrosion resistance to the inner and outer layer surfaces of the cast iron pipe. Japanese Patent Laid-Open No. 62-235478
Cylinders for conventional plastic molding machines made of steel
And the adhesion alloy that coats the inner surface of the cylinder is B
Includes 1.0 to 5.0% by weight and the balance is Ni
Lower than the first dressing layer and the dressing layer
Co-Ni group or Ni group having a melting point,
The second layer on the first layer by centrifugal force
We propose a two-layer dressing layer that is a composite layer of dressing layers.
The first layer is limited to the single addition of B, and then the second layer
Layers are stacked to prevent Fe from entering, and as a result, solid-liquid two
It is said that it was possible to prevent the expansion of the layer coexistence temperature range.
It

[0005]

Among the conventional techniques, adding a corrosion-resistant component to the molten component itself requires a large amount of molten metal to be treated. Therefore, even if 1% of alloying element is added, the addition amount is large. It becomes too much and the manufacturing cost rises sharply.
Corrosion resistant metals are considerably more expensive than iron such as Ni, Cr, Cu, etc. In order to realize a visible improvement in corrosion resistance, a minimum addition amount of 5% or more is required and the economic burden is not small. Next, many techniques have been proposed to improve the properties of only a part of the cast product, but all of the cited prior arts use effective components such as Te, V, and B for cementing free carbon in cast iron. Since it is a target, it is only for the purpose of partially hardening cast iron to improve wear resistance. In order to dramatically improve the corrosion resistance of cast iron, it is necessary to say that a considerable gap still remains by simply utilizing the white pig iron content of carbon. In addition, it is considered that the conventional technology for centrifugal cast iron pipes can surely form Si enriched layers on the inner and outer surfaces if properly implemented.
Since Si itself is added to the molten metal as a deoxidizer and there is a special technical term called inoculation, the timing of addition when it has a high affinity with oxygen at high temperatures is limited to a very narrow range. There is a concern that it may be.
Due to this difficulty, the layer thickness of the tomographic Si layer formed on the inner surface cannot be kept constant due to a slight timing shift, and it is considered that it is difficult to avoid considerable variations in corrosion resistance. Surely, Si is a ferrite-forming component for cast iron, and silicoferrite, which is a solid solution of Si in ferrite, is a famous corrosion-resistant (heat-resistant) material, but the starting component was 2.3% Si. It is not known how much the corrosion resistance can be improved by increasing Si to about 3.0%. In addition, plast
Prior Art Related to Internal Corrosion Resistance Enhancement of Cylinder for Molding Machine
For, the temperature was measured by adding only a small amount of B to the Ni base.
While making adjustments, first of all, with the Fe from the base metal,
The focus is on cutting off the exchange. But the book
As for the ductile cast iron pipes that the target applies to,
It occurs between the molten cast iron that is the base material and the additive material.
Select the composition of components mainly for the reaction and add in powder form
And promotes the reaction between the interfaces as the additive material melts.
Therefore, it is better to form a completely integrated alloy layer for corrosion resistance.
It is judged that priority is given to the improvement of sex. In order to solve the above-mentioned problems, the present invention has significantly improved corrosion resistance on the inner surface.
In addition, it is an object of the present invention to provide a method for manufacturing a corrosion-resistant centrifugal cast iron pipe which is reliably and reliably provided relatively easily and relatively economically.

[0006]

The method for producing a corrosion-resistant centrifugal cast iron pipe according to the present invention is a method of pouring and casting molten ductile cast iron at a temperature of at least 1300 ° C. while rotating a centrifugal casting mold at a high speed. Immediately after the hot water is completed, Ni is used as a base and
Cr in eutectic relationship and the eutectic point to lower temperature side
Induction to B, and over a powder blended with other ingredients to have at most eutectic point to 1200 ° C. or less, such as Si on the inner surface the entire length of the casting evenly sprayed, high rate ductile iron pipe surface
The austenite phase containing Ni as a solid solution is used as a matrix.
And cast a corrosion-resistant alloy layer reinforced with precipitated Cr carbide.
The above-mentioned problems have been solved by forming the structure on the iron side continuously and integrally.

[0007]

The casting temperature of the cast iron melt in the centrifugal casting method is usually set as a control target of around 1350 ° C. Therefore, it is assumed here that the pouring temperature is 1300 ° C. or higher, and the melting point is at least 100 ° C. lower than this temperature. Require additional powder with. The melting point of Ni alone is 1455 ° C.,
Cr alone is 1880 ° C, and corrosion resistant metals are generally 13
Although the temperature is higher than 00 ° C, for example, Ni and Cr have eutectic points near 1345 ° C, and when C and Si are increased, the eutectic line flows to the low temperature side, and the compound ternary or quaternary phase diagram Although the details have not been confirmed yet, the experimentally confirmed result shows that powders having a melting point of 1200 ° C. or lower can be sufficiently obtained by adding and adjusting Ni, mainly Cr, Si, C and the like. . That is, when the molten metal of 1300 ° C or higher is cast into the mold, the molten metal in contact with the mold (corresponding to the outer peripheral surface of the casting) is deprived of the retained heat and rapidly begins to solidify, but the inner surface of the molten metal still remains. Since it is in a completely molten state, if the metal powder is evenly distributed over the entire length, the powder is immediately melted by the heat of the molten metal, forming an alloy layer with high corrosion resistance inside the cast product. To do.

[0008]

EXAMPLES Examples of the present invention and comparative examples will be described. In FIG. 1, the die for centrifugal force casting has a diameter of 250 mm and a length of 500.
Using the 1 mm test mold, diatom the inner surface of the mold,
40 kg of ductile molten cast iron 3 in which Mg was pressed into a cast iron component of C3.2% and Si1.7% was cast at 1320 ° C.
Immediately after casting, the main melting point was Ni and the total melting temperature was 106
2 kg of low melting point metal powder 4 adjusted to 0 ° C,
The trough 5 was inverted and sprayed uniformly over the entire length of the inner surface of the cast body. Table 1 shows the Fe-Cr powders simultaneously cast under the same conditions except for the low melting point metal powder used in this example.
It is a powder component.

[0009]

[Table 1]

2 is an enlarged photomicrograph (magnification 40) of a cross section near the surface of the embodiment and FIG. 3 of the comparative example. The white portion in FIG. 2 is an austenite phase containing Ni of 20 to 50% and is on the parent phase. Cr carbides are precipitated in. The black part on the left is the pearlite phase of the cast iron material, and fine cementite is precipitated at the boundary. Calculated from the magnification of the photograph, the alloy layer of the austenite phase is about 1.5 to 2 mm. Figure
In No. 3 , innumerable cavities are overlapped on the entire surface, and it is not completely welded to the black cast iron material on the left side, and is easily peeled off. The Fe-Cr powder is integrated with the inner surface of the cast product. It can hardly be said that a corrosion resistant alloy film was formed. The low-melting metal powder used in this example is one of the self-fluxing alloys composed of the components shown in Table 1, which is called Ni braze and is already on the market. The melting point is 1200 ° C. It does not matter if it is a compounded material mainly composed of the following corrosion resistant metals.

[0011]

As described above, according to the present invention, since a skin layer having extremely high corrosion resistance is integrally formed on the inner surface of the cast iron pipe by simply adding a few post-processes at the time of centrifugal casting, the corrosion resistant centrifugal cast iron pipe is Very easy to manufacture.
In particular, it is effective for corrosion resistance in an oxidizing atmosphere, which conventional cement linings could not cope with, and the inner peripheral surface that remains exposed after mild inner surface maintenance exhibits acid resistance.
More specifically, the difference from the prior art is obtained by the present invention.
The alloy layer is Ni 20-50% (other than Cr, B, Si,
A matrix of austenite phase that dissolves the remaining Fe)
However, the cast iron in the molten state, which is the base material during casting, and
Choosing the composition of the constituents, mainly the eutectic reaction with Ni
Depends on the melting temperature of the alloy material added in powder form
To a certain level, and after melting, the reaction between the interfaces
We succeeded in forming a completely integrated alloy layer with an emphasis on response
Of. The present invention is a preferred component of low melting point and before and after solidification
Utilizing the behavior peculiar to cast iron in
C entered from molten cast iron using the knight phase (γ iron) as a base
Precipitates a strong carbide with Cr contained in the adhesion metal
To form a continuous structure in which the base material (cast iron) and the alloy layer are integrated.
And is completed by mutual atom substitution.
The fact that the perfect alloy layer was worn leads to a remarkable effect.
It is.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a micrograph showing a metal structure of an example of the present invention.

FIG. 3 is a micrograph showing a metal structure of a comparative example.

[Explanation of symbols]

 1 Mold for centrifugal force casting 3 Molten cast iron 4 Powder

Claims (1)

[Claims] 1. A centrifugal casting mold is rotated at a high speed while molten molten ductile cast iron at a temperature of at least 1300 ° C. is poured.
Immediately after pouring is completed, Ni is used as a base and has a eutectic relationship with Ni.
Cr, and induce the eutectic point to a lower temperature side
Has a eutectic point below 1200 ° C at the highest for B, Si, etc.
As described above, the powder containing other components is evenly distributed over the entire length of the inner surface of the cast body, and Ni is applied to the inner surface of the ductile cast iron pipe at a high rate.
The austenite phase in solid solution is used as a matrix and precipitates
Corrosion resistant alloy layer strengthened with Cr carbide and cast iron side structure
A method for producing a corrosion-resistant centrifugal cast iron pipe, which is characterized in that it is continuously and integrally formed.