JPS60250865A - Production of cv graphite cast iron pipe - Google Patents

Abstract

PURPOSE:To form surely CV graphite by adding Mg or Mg alloy to a molten metal for a spheroidal graphite cast iron, controlling the remaining content of Mg in the molten metal according to the wall thickness of a pipe then inoculating specific alloy powder and grains to the molten metal and casting centrifugally said metal. CONSTITUTION:The Mg or Mg alloy is added to the molten metal for the spheroidal graphite cast ironcontg. <=0.010wt% S component by a pressure addition method, etc. The remaining content of the Mg in the molten metal is controlled according to the wall thickness (t) of the cast iron pipe in this stage. The content is adjusted to 0.010<Mg%<=0.020 when t<=10mm., to 0.015<Mg%<=0.025 when 10<t<=25 and further to 0.020<Mg%<=0.030 when 25<t. While such molten metal is poured into a metallic mold for centrifugal casting, the powder and granular los Mg-Fe-Si alloy or the like having 30-160 mesh is inoculated thereto and the molten metal is centrifugally cast. The CV graphite is surely and stably formed in the struture by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a centrifugally cast cast iron pipe whose material is CV graphite cast iron (worm-like to semi-spheroidal graphite cast iron).

<Problems to be solved by the invention> CV graphite cast iron has various mechanical properties close to those of ductile cast iron, high fatigue strength, and good thermal conductivity close to that of ordinary cast iron. be. In addition, it has good flowability, high yield, minimal generation of dross and few casting defects as in the case of ductile cast iron, and good castability with fewer restrictions on molten metal composition and mold conditions. Furthermore, since the amount of Mg remaining in the molten metal is small, it is easy to become cementite-free (chill-free) as cast, and in some cases, annealing may not be necessary. As described above, CV graphite cast iron has been evaluated for its excellent properties in various respects, and has attracted attention in recent years.

If the CV graphite cast iron is subjected to centrifugal force casting, a cast iron pipe having the above-mentioned excellent properties can be obtained, but at this time, centrifugal force casting has a large effect of fading, and due to fading during casting, graphite It is difficult to obtain a cast iron pipe with stable mechanical properties because the shape is easy to vary.Also, depending on the amount of graphite nodularizing agent added, the cast iron material can become normal cast iron or ductile cast iron, which is unique to CV graphite cast iron. Since it is difficult to obtain CV graphite cast iron with a spheroidization rate of 30 to 70% that suitably has the following properties, it has not been put into practical use industrially.

<Means for Solving the Problems> The present invention has been made in view of the above points, and aims to provide an industrial manufacturing method with excellent productivity for CV graphite cast iron pipes with a spheroidization rate of 30 to 70%. The method is to add a Mg or Mg alloy graphite nodularizing agent to a molten metal for spheroidal graphite cast iron with an S content of 0.010% by weight or less, and remove 1t of residual Mg in the molten metal to form the desired cast iron. In weight% according to the wall thickness t of the pipe, when t≦10 days, 0.010 <l'1g%≦0.0
2010〈t≦25 when dragon 0.015 <Mg%≦
0.02525<t O,020<Mg%≦0.030
After the melt is poured into a centrifugal casting mold, powdery low Mg-Fe-5i alloy or rare earth-Ti alloy is poured into powder.
-Fe-5i alloy is inoculated and centrifugal casting is performed.

Effect> According to the above means, since the molten metal for spheroidal graphite cast iron with an S component of 0.010% by weight or less is used, the Mg yield in the molten metal can be kept constant when adding the graphite spheroidizing agent of Mg or Mg alloy. This makes it possible to keep the quality of the molten metal constant. In addition, since the amount of Mg remaining in the molten metal is controlled to a predetermined value depending on the wall thickness of the target cast iron pipe, the effect of fading after adding the graphite nodularizing agent is kept constant regardless of the sewing wall thickness. Furthermore, when pouring into the mold for centrifugal casting, the target 30 It is possible to form CV spheroidal graphite cast iron which has a spheroidization rate of ~70%, has no delt, and has promoted ferrite formation.

<Example> Examples of the present invention will be described in detail below.

First, the molten metal for spheroidal graphite cast iron used in the present invention has S of 0.
A molten metal whose composition is normally adjusted in addition to the specified 0.010''% or less is used.The preferred chemical composition of the molten metal is shown below.The unit is % by weight.

C:3. O~3.8% P: 0.08% or less Si
: 1.5~2.7% S: 0.010% or less:
0.2-0.8% The balance is essentially FeS 0.010%
The following provisions are made for the following reasons. S needs to be kept as low as possible in order to reduce the Mg required for graphite caterpillarization as MgS, and in order to keep the molten metal yield of Mg stable and constant, S should be kept at 0.010% or less. It can be suppressed.

Mg or Mg alloy is added to the above molten metal by an addition method with a stable yield such as a pressure addition method, but the amount of residual Mg in the molten metal due to this addition is determined by
It is managed like a table.

The first reason is that the thicker the wall, the longer it takes to pour the metal, and the greater the effect of Mg fading, making it difficult to stably obtain the desired CV graphite structure. That is, if the residual amount of Mg is kept constant regardless of the wall thickness, the graphite structure will become flaky in the case of a thick wall, while on the other hand, in the case of a thin wall.

It becomes spherical. Furthermore, the residual amount of Mg in Table 1 is the same as that in Table 2.
As shown in the table, this is based on the results of an investigation into the relationship between the residual Mg (% by weight) in the molten metal and the spheroidization rate (%) with respect to the wall thickness t (+ui) of the cast iron pipe. The molten metal used had an S component of <0.010% or less as described above.

Table 2 The molten metal adjusted to a predetermined Mg residual amount is rotated at a predetermined rotation (G
Molten metal (N020 to 80) is poured into a centrifugal casting mold, and during this pouring, inoculation with specific alloy powder particles is performed.

For the inoculation, it is preferable to use a granular low Mg-Fe-3i alloy or a rare earth (hereinafter abbreviated as RE) -Ti-Fe-3i alloy. More specific components are the composition of the low MgFe-3i alloy in weight%: hg:t~3%;
34445%, the remainder being essentially Fe, and RE-
For Ti-Fe-3i alloy, RE: 3-5%, Ti1l
-2%, 34445%, and the balance is preferably Fe. By using such an alloy as an inoculant,
C1 spheroidal graphite cast iron having a targeted spheroidization rate of 30 to 70% and in which non-chilling and ferrite formation are promoted can be formed.

The particle size of the above-mentioned powder and granules is 30 to 30% due to ease of dissolution into molten metal
It is preferable that the amount is 160 mS, and the amount added is preferably 0.1 to 2 wt% of the amount of molten metal to be poured. If it is less than 0.1%, the effect will be small, while if it exceeds 0.2%, it will be difficult to dissolve into the molten metal and it will become scum.

Regarding the centrifugal casting of the molten metal, it can be cast either directly into a centrifugal casting mold as usual, or after applying sand resin or wet spray coating to the inner surface of the mold. good. However, for direct casting into a mold, it is suitable to have a tube thickness of 10 mm or less, and in this case, the cooling rate is faster than when using a sand oven or wet spray, so the amount of Mg remaining can be reduced. -11 less, usually 0.01
It may be less than 5”%.

Next, specific examples will be listed and explained.

(1) The CVV lead cast iron pipe of Example 1.2 was manufactured using the molten metal shown in Table 3 (ladle analysis before casting) under the manufacturing conditions shown in Table 4.

In addition, the Mg amount of the source water in Example 1 was 0.020%, and in Example 2
The Mg content of the source water was 0.025%.

(2) Among the cast iron pipes obtained, Example 1 was annealed (950°C x 0.5 hours) L, and Example 2 was left as cast, and the structure at the center of the pipe thickness was observed.

FIG. 1 shows Example 1 (magnification 100), and FIG. 2 shows Example 2 (magnification 100). In FIG. 1, there is a CV graphite rougherite structure, while in FIG. 2, it is CV graphite + ferrite + pearlite, and it was confirmed that the desired structure was formed.

(3) Samples were taken from Example 1.2 and their mechanical properties were examined as shown in Table 5.

For comparison, Table 5 also includes data regarding ferrite ductile pipes. It can be seen from Table 5 that Examples 1 and 2 according to the present invention have the same fatigue limit ratio of the material as the ferrite ductile pipe.

Next (Effects) As explained above, the method of the present invention adds M or Mg alloy to the molten metal for spheroidized graphite cast iron, and the effect of fading is always kept constant according to the wall thickness of the target cast iron pipe. By controlling the residual amount and inoculating with specific alloy powder particles during pouring, the desired CV graphite can be reliably and easily formed stably in the structure, and C■ graphite cast iron can be formed. Its utility value as an industrial production method for pipes is significant.

[Brief explanation of drawings]

FIGS. 1 and 2 are metal assembly t's micrographs showing the structure of a CV graphite cast iron pipe according to an embodiment of the present invention. Patent applicant Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] 1.3 Add a graphite spheroidizing agent of Mg or Mg alloy to the molten metal for spheroidal graphite cast iron containing 0.010% by weight or less of the component, and adjust the amount of residual Mg in the molten metal according to the wall thickness t of the intended cast iron pipe. In weight%, at 1510m 0.010 <Mg%≦0.020
10 <When t≦25 fins 0.015 <Mg%≦0.
After adjusting to 02525<t O, 020<Mg%≦0.030, the molten metal is poured into a centrifugal casting mold while powdery low Mg-Fe-5i alloy or clay 11i-Ti
- A method for manufacturing a CV graphite cast iron pipe, which comprises inoculating Fe-3i alloy and performing centrifugal casting.