JPS62148068A - Metal mold centrifugal casting method for high strength ductile cast iron tube - Google Patents

Abstract

PURPOSE:To obtain a high strength ductile cast iron tube having high toughness bainite structure as matrix by using molten ductile cast iron having specified Si content and executing two step inoculations by Fe-Si series to the above- mentioned material to obtain high strength tube even only as cast condition and further specified cooling from austenite temp. range after pouring. CONSTITUTION:When the molten ductile cast iron having 2.4-3.0wt% Si content is poured into a mold 1 for centrifugal casting through a pouring runner 5 from a ladle 4, the inoculation by Fe-Si series is executed at chute part from the ladle 4 to a receiving port 5A of the runner 5 and at spout part from a tapping port 5B of the runner 5 to an inner surface of the metal mold 1. Then, the cast iron tube is formed by the centrifugal casting and during austenite range for its temp., hot water is supplied into the inner surface of rotating cast iron tube by a suitable means to cool rapidly until 300-450 deg.C, and after that it is cooled by air. In this way, the above-mentioned inoculation is desirable to be executed by 0.05-0.15wt% at chute part and 0.10-0.30wt% at spout part to the pouring cast iron amount.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing high-strength tag tile cast iron pipes by die centrifugal force casting, and in particular, to prevent crystallization of MW'i cementite as much as possible. This invention relates to a method for centrifugal force casting of molds.

(Prior Art) Increasing the strength of tag tile cast iron pipes has been desired from various fields, and one method for achieving this is austempering treatment. This is a method in which a strong bainite structure is obtained by rapidly cooling the austenitizing temperature (850 to 950°C) to 300 to 450°C using a salt bath furnace and maintaining the temperature constant in the bath. In addition, as another method, Nis Cr, M
There is also a method of obtaining a bainite structure in an as-cast state by containing alloying elements such as o.

However, the austempering method is difficult to heat treat large cast pipes, and is uneconomical as it must be kept in a bath for a certain period of time, and the use of an austempering furnace itself is not effective from an energy saving perspective. Undesirable. On the other hand, the method of adding alloying elements has the disadvantage that it is less economical because the alloying elements are expensive.

(Problems to be Solved by the Invention) Therefore, the inventor of the present invention, after performing centrifugal force casting of molten tag tile cast iron in a mold, rapidly cooled the cast iron pipe from the austenite temperature in order to avoid the formation of pearlite, and then cooled it in air. A mold centrifugal casting method for manufacturing high-strength tag tile cast iron pipes with bainitic structure was proposed.

However, even though a coating is formed on the inner surface of the centrifugal casting mold prior to pouring the metal into the inner surface of the mold, the insulation effect is not sufficient, so the molten metal is rapidly cooled and free cementite is generated. was there.

If an excessive amount of free cementite is generated, the free cementite is hard and brittle, leading to a deterioration in the strength of the pipe. Therefore, it is necessary to perform an annealing treatment to break down this, and then transform the base into a bainite structure by an austempering treatment. Ta.

Another method is to apply a large mold with a thickness of 1 to 2 ms on the inner surface of the mold using wet spray coating or sand resin coating to provide sufficient heat insulation and prevent the formation of free cementite, but the coating is labor-intensive. There is a problem in that productivity is poor.

The present invention was made in view of this problem, and when obtaining a high-strength tag tile cast iron pipe by the mold centrifugal casting method, a conventional coating mold of about 0.05 to 0.1 fin is applied to the centrifugal casting mold. To provide a mold centrifugal casting method capable of suppressing the generation of free cementite even when used as-cast and obtaining a high-strength tag tile cast iron pipe without problems in terms of strength as cast.

(Means for Solving the Problems) The feature of the present invention, which was taken to achieve the above-mentioned object, is that molten tag tile cast iron is poured from a ladle through a pouring gutter into a mold for centrifugal casting. When the temperature of the cast iron pipe is in the austenite range, hot water is supplied to the inner surface of the rotating cast iron pipe to achieve a temperature of 300 to 45
A casting method in which Si is rapidly cooled to 0°C and then air cooled.
．． Using molten tag tile cast iron containing 4 to 3.0% by weight, Fe-Si type inoculation was carried out between the ladle and the socket of the pouring gutter and from the outlet of the pouring gutter to the inner surface of the mold. It is in the point of doing.

(Example) Next, the mold centrifugal force casting method of the present invention will be described in detail.

FIGS. 1 and 2 show an example of a centrifugal casting apparatus for carrying out the present invention, in which 1 is a centrifugal casting mold, and a band 3 for stopping hot water is attached to the opening of the mold. ing.

2 is a cast iron pipe cast on the inner surface of the mold 1. Molten tag tile cast iron is poured into the inner surface of the mold 1 from a ladle 4 through a pouring gutter 5 that is movable in the axial direction. In this case, the area from the ladle 4 to the socket 5A of the pouring gutter 5 is called a chute, and the area from the outlet 5B of the IE hot water gutter 5 to the inner surface of the mold is called a subo 1-. Reference numeral 6 denotes a coating mold formed on the inner surface of the mold 1, and in the present invention, it is not necessary to form it particularly thick, and the coating mold may have a thickness of <0.05 to 0.111 as usual.

The molten tag tile cast iron used in the present invention has the following composition in weight percent.

C: 3.2-3.7% P: 0.07% or less Si
: 2.4-3.0% S: 0.015% or less Mn
: 0.6% or less Mg: 0.015 to 0.03
0% balance substantially Fe In the above composition, the components other than Si have particular characteristics as a molten tag tile cast iron composition.

Since this is not a specific limitation, the reason for the limitation will be omitted.

Si has a graphitization promoting effect, and if it is less than 2.4%, excessive crystallization of free cementite cannot be suppressed even by specific inoculation described below. On the other hand, if it exceeds 3.0%, F
A large amount of Si becomes solid solution in e, resulting in embrittlement.

In addition to the above-mentioned components, 0.15 to 0.25% of 11IO or 2 can be contained in place of a part of Fe.

Due to the inclusion of such components, Barley 1 appears in the CCT diagram.
The formation region can be shifted to the long-time side, and the generation of pearlite can be prevented as much as possible during the quenching process of the cast iron pipe, and a cast iron pipe with extremely good strength can be obtained.

The molten tag tile cast iron flows from the ladle 4 to the mold 1 via the pouring gutter 5? )E? & will be done. At this time, the mold 1 may have a thin coating of about 0.05 to 1 mm formed on its inner surface as described above. In the present invention, the Fe--Si system is inoculated into the molten metal flow at the chute section and the sport section. By performing two-stage inoculation, the inoculation action can be significantly promoted and the occurrence of chill can be effectively prevented.

Incidentally, as inoculation in the sport portion, dry coating may be performed in which an inoculant is previously sprayed on the inner surface of the mold 1. In addition, in order to add the inoculant to the molten metal flow at the spout section, the inoculant can be pneumatically transported and sprayed onto the molten metal flow using a lance 8 installed in parallel at the bottom of the pouring gutter 5, as shown in Fig. 3. .

The inoculant was a regular F with Si content of 50% and 75%.
e-Si is used. The preferred amount of Fe--Si added is 0.05 to 0.15% by weight relative to the amount of poured metal, and is 0.05 to 0.15% in the chute portion, and 0.0 to 0.30% in the subboard portion. In either case, if the amount is less than the predetermined amount, free cementite tends to crystallize (on the other hand, if the amount exceeds the predetermined amount, undissolved Si becomes scum and mixes into the molten metal, which may cause casting defects.

After casting molten tag tile cast iron as described above, when the molten metal solidifies and is red-hot, that is, when the temperature of the inner surface of the cast iron pipe 2 is in the austenite range (usually 850 to 950°C), the temperature of 95°C or higher is Inject hot water into the inner surface of the tube.

Hot water efficiently removes the heat of vaporization and easily vaporizes and disappears.
It is suitable as a medium for rapidly cooling the cast iron pipe 2. In addition, it is preferable to supply an appropriate amount to the inner surface of the cast iron pipe 2 in order to take away the heat of vaporization and dissipate it, since it can automatically shift to an air-cooled state after being rapidly cooled to a desired temperature. The amount of hot water that disappears when rapidly cooled to a predetermined temperature can be easily calculated from the size of the cast iron pipe and the pipe temperature at the time of water injection.

The hot water is supplied from the opening of the mold 1 to the hot water supply gutter 7 as shown in Figure 2.
The molten metal may be supplied to the inner surface of the cast iron pipe 2 from the pouring channel 5, and a supply pipe having a large number of nozzle holes opened in the axial direction of the pipe is arranged in parallel, and the supply pipe is connected to the inner surface of the cast iron pipe over the entire length of the cast iron pipe. and insert it.
It may be sprayed and supplied from the nozzle hole in the form of a shower.

The tube, which has been rapidly cooled to 300-450° C. with hot water, is then air-cooled in a mold 1. The reason for air cooling to 300 to 450°C is to prevent the pearlite formation region from passing through the CCT diagram. Rapid cooling to less than 300°C may cause martensite to occur, while cooling to over 450°C may result in pearlite.
Rapidly cool to 0°C range.

During the air cooling stage, the cast iron pipe 2 may be in a rotating or non-rotating state. By air cooling within the mold 1, the cast iron pipe 2 can slowly pass through the bainite generation region, and the austenite in the base can be turned into bainite.

Next, specific examples will be listed and explained.

Inner diameter 200 x 50001 x wall thickness 7.5t (Dragon)
Production example of tag tile cast iron pipe (1) For centrifugal casting, a 0.071 m coating mold (composition of rainbow liquor flower and bentonite) was formed on the inner surface using /8 hot water with the following components (wt%) excluding Si%. Injected into the mold. When injecting the molten metal, inoculation was performed as shown in Table 1.

The mold rotates at GNI 140 during injection, and after injection it reaches 0th floor 6.
I revved it to 0. The inner surface temperature of the cast iron pipe was measured with an infrared thermometer, and hot water was injected at the pipe temperature shown in Table 1. 1st
The amount of hot water in the table is the amount required to rapidly cool the tube temperature to a target of about 400°C.

・Molten metal composition excluding St C: 3.4-3.5% S: 0.01% or less Mn:
0.3~0.4% Mg: 0.03~0.05
%P 70.04-0.06% The remainder is substantially Fe (
Table 1 Note: 2 and 5 are examples of the present invention. The inoculant is Fe-Si with 50% Si, and the inoculum amount is the amount of Fe-Si supplied (%) relative to the amount of poured water.

(2) The cast iron pipes that were rapidly cooled by supplying the hot water shown in Table 1 were air-cooled in the mold as the hot water vaporized and disappeared.

After being air-cooled to room temperature, the tube was balataned and the structure of the tube was observed, and the tensile strength and amount of bainite, cementite, and pearlite (area %) were determined. The results are shown in Table 2. Note that the observation sample was taken at a position 2500 ui from the tube end.

Table 2 (3) From Table 2, when the Si content is 2.5 to 3.0% and two-stage inoculation is performed (Th2.5), the production of cementite and pearlite is 5% or less. I was able to do that. With this level of production, there is no need for annealing, and the as-cast tube can be used as a high-strength tag tile tube.

(Effects of the Invention) As explained above, the mold centrifugal force casting method for high-strength tag tile cast iron pipes of the present invention uses molten tag tile cast iron with a specific Si content, and performs two-stage inoculation with Fe-Si system. As a result, even if a centrifugal force casting mold with a normal thin layer coating is used, the formation of free cementite in cast iron pipes can be suppressed as much as possible, and even as-cast iron pipes can be used. It has high strength and does not require annealing heat treatment to decompose free cementite. In addition, since the cast iron pipe is cooled from the austenite temperature with hot water, it can efficiently remove the heat of vaporization from the pipe and rapidly cool it, and when the vaporization disappears, it can be easily air-cooled. !50℃
Since the base is rapidly cooled to , and then air-cooled, the base can be made into a highly tough haynite structure without producing pearlite or martensite as much as possible.

[Brief explanation of drawings]

1 and 2 are cross-sectional views schematically showing a centrifugal casting apparatus for carrying out the present invention. FIG. 1 shows the state of pouring molten tag tile cast iron, and FIG. 2 shows the state of hot water supply. FIG. 3 is an explanatory view showing the installed state of the inoculant supply lance. 1...Mold for centrifugal force casting, 2...Cast iron pipe, 4...
Hand, 5... Shoyo gutter, 6... Coating mold, 7... Hot water supply gutter. Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) A cast iron pipe is centrifugally cast by pouring molten tag tile cast iron into a centrifugal casting mold from a ladle through a pouring gutter, and when the temperature of the cast iron pipe is in the austenite range, rotating cast iron This is a casting method in which hot water is supplied to the inner surface of the tube to rapidly cool it to 300-450°C, and then air-cooled, and the Si content is 2.4-3.
Using tag tile cast iron molten metal containing 0% by weight, Fe-Si type inoculation is performed between the ladle and the pouring gutter socket and from the pouring gutter outlet to the inner surface of the mold. High strength tag tile cast iron pipe mold centrifugal casting method. (2) Fe-Si type inoculation is 0.05 to 0.15% by weight based on the amount of poured metal between the ladle and the spout of the pouring gutter.
0.10 between the outlet of the pouring gutter and the inner surface of the mold.
Claim 1 characterized in that the amount of 0.30%
The method for centrifugal force casting of high-strength tag tile cast iron pipes.