JPH05171342A - Continuously cast cast iron tube - Google Patents

Abstract

PURPOSE:To continuously cast a cast iron tube made of spheroidal graphite cast iron without causing chilling. CONSTITUTION:This objective tube is a continuously cast cast iron tube which has a degree of carbon saturation [Sc=C%/(4.23-Si%/3.2)] of 1.15 to 1.35 and also has a chemical composition consisting of, by weight, 3.8-4.1% C, 2.7-3.8% Si, 0.1-0.4% Mn, 0.006-0.040% Mg, 0.0003-0.005% Ca, 0.0003-0.005% Bi, 0.0003-0.005% RE, and the balance Fe with inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous cast iron pipe.

[0002]

2. Description of the Related Art Continuous cast iron pipes are solidified and formed by cooling the molten metal by means of a casting mold device provided at the pouring port of a molten metal holding furnace. That is, the molten metal in the casting mold is rapidly cooled by the casting mold and the core when passing through the pipe forming passage formed by the casting mold and the core, and solidified into a tubular shape.

Here, as the cast iron pipe becomes thinner, the heat capacity of the molten metal becomes smaller, so that the molten iron is rapidly cooled. As a result, metastable solidification and chilling occur, and the graphite crystallization amount is significantly reduced and cementite crystallizes out. Hardens and becomes brittle.

Generally, the chemical composition of cast iron pipes (editor: Japan Institute of Metals, "Theory and practice of spheroidal graphite cast iron", Showa 41)
May 30, 2013, published by Maruzen Co., Ltd., p. 384), C: 3.0-3.8%, Si: 2.0-2.5%, Mn: 0.
2 to 0.4%, P: <0.1%, S: <0.015%, Mg: <
Although 0.03% is known, this component system can be applied to a cast iron pipe manufactured by a centrifugal casting method with a slow cooling rate during solidification, but when applied to a continuous cast iron pipe, it is significantly chilled.

Further, in JP-A-1-313147, in order to prevent chilling during casting of a continuously cast iron pipe, the chemical composition of the molten metal is Sc: 1.00 to 1.15%, C: 3.6 to 4.0%, Si. :
A method of inoculating 2.0-2.4%, Mn: 0.1-0.5%, and 0.1-0.3% Si into the molten metal has been disclosed, but this method also completely eliminates cast iron pipes with a wall thickness of 10 mm or less. It was difficult to achieve stable continuous casting without chilling.

[0006]

As described above, according to the prior art, it is extremely difficult to continuously cast a cast iron pipe without chilling, and chill prevention of the continuous cast iron pipe has not been substantially achieved.

An object of the present invention is to make it possible to continuously cast a cast iron pipe made of spheroidal graphite cast iron without chilling.

[0008]

The continuously cast iron pipe according to the present invention has a carbon saturation of {Sc = C% / (4.23−Si% / 3.
2)} is 1.15 to 1.35 and the chemical composition is C: 3.
8 to 4.1%, Si: 2.7 to 3.8%, Mn: 0.1 to 0.4
%, Mg: 0.006 to 0.040%, and Ca: 0.000
3 to 0.005%, Bi: 0.0003 to 0.005%, RE: 0.0003
.About.0.005%, and the balance is Fe and inevitable impurities.

[0009]

The reason for limiting the chemical composition range of the cast iron pipe of the present invention is as follows. (1) Carbon saturation {Sc = C% / (4.23-Si% / 3.2
)} (1.15 to 1.35)

C (3.8 to 4.1%) Si (2.7 to 3.8%) C and Si are basic elements in cast iron and affect the properties, graphitization ability and castability of cast iron. In the case of the cast iron pipe of the present invention, a sound continuous cast iron pipe made of spheroidal graphite cast iron in which chill does not occur in the carbon saturation range of 1.15 to 1.35 can be obtained. That is, when Sc is less than 1.15, the graphitization ability is insufficient and chill occurs in the continuous cast iron pipe, so Sc was set to 1.15 or more. Further, when Sc exceeds 1.35, not only the effect is saturated, but also a large amount of coarse quiche graphite crystallizes to deteriorate the mechanical properties,
In addition, since the graphite becomes excessive and the strength decreases, Sc is set to 1.35 or less.

Here, when C is less than 3.8%, Sc is 1.
Even if it is in the range of 5 to 1.35, chill is generated, and if it exceeds 4.1%, a large amount of quiche graphite is generated, which makes it difficult to control the components of the molten metal, so the content was limited to 3.8 to 4.1%.

Further, if Si is not contained in an amount of 2.7% or more, chilling occurs, and if it exceeds 3.8%, not only the effect is saturated, but also hard and brittle silicon ferrite is precipitated.
It was limited to 2.7-3.8%.

(2) Mn (0.1 to 0.4%) Mn is added to neutralize the chilling promoting action of S contained as an impurity in cast iron. In this case, the effect is low unless 0.1% or more is added, and conversely, when the content exceeds 0.4%, the chilling promoting action of Mn becomes strong and the tendency of chilling increases, so the content is limited to 0.1 to 0.4%. ..

(3) Mg (0.006 to 0.040%) If Mg is less than 0.006%, flake graphite crystallizes and 0.040%
If it is contained in excess of 0.005%, it will be chilled, so 0.006 to 0.040%
Limited to.

(4) Ca (0.0003 to 0.005%) Bi (0.0003 to 0.005%) RE (rare earth element) (0.0003 to 0.005%) Ca, Bi, RE (La, Ce, Pr, Nd, etc.) are each 0.0003 to. By containing 0.005%, chilling of cast iron pipe can be prevented. If it is less than 0.0003%, the effect is insufficient and chilling occurs, and if it exceeds 0.005%, chilling occurs due to excessive addition. Bi and RE are chilling-promoting elements, but by adding a small amount of Bi, RE, and Ca together, a graphite crystallization site is formed, and a remarkable chill prevention effect is obtained. Bi and RE are not only graphite site forming elements but also chilling promoting elements.

[0016]

EXAMPLE FIG. 1 shows the metal structure of the cast iron pipe of the present invention (magnification: 100
2) is a micrograph showing a metal structure (magnification: 100 times) of a cast iron pipe of a comparative example, FIG. 3 is a schematic view showing a continuous casting apparatus, FIG. 4 is a sectional view showing a casting apparatus, Figure 5
FIG. 3 is an end view showing a casting mold device.

A Wertlli type continuous casting apparatus 10 shown in FIG. 3 continuously casts the cast iron pipe of the present invention having the chemical composition shown in Table 1 into a spherical graphite cast iron pipe having an outer diameter of 76 mm (wall thickness 5 mm) and a length of 65 m. Manufactured. The holding temperature of the molten metal was 1390 to 1430 ° C, and the average drawing speed was 1 cm / sec. In the components of the cast iron pipe of the present invention in Table 1, P and S are unavoidable impurities.

[0018]

[Table 1]

As shown in FIG. 3, the continuous casting apparatus 10 is provided with a casting mold apparatus 13 attached to a casting port 12 formed in a lower portion of a side surface of a molten metal holding furnace 11. The continuous casting device 10 is
The molten metal is cooled by the casting mold device 13 to form a cast iron pipe 14, which is drawn and cast.

The continuous casting apparatus 10 comprises a guide roller 15 for supporting the cast iron pipe 14 on the outlet side of the casting mold device 13 and a drawing device 16 for intermittently drawing the cast iron pipe 14. The drawing device 16 includes a pinch roller 17 and a pressing roller 18.

As shown in FIGS. 4 and 5, the casting mold device 13 is
It is composed of a mold 19 made of graphite and a core 20 made of graphite as well.

The mold 19 is hollow, has a core-holding inner diameter portion 21 at the end on the casting side, and has a pipe outer surface forming inner diameter portion around the center axis of the mold over substantially the entire length excluding the core-holding inner diameter portion 21. 22 is provided.

The core 20 has a flange portion 23 which is inserted into the mold 19 and which is fitted to the core holding inner diameter portion 21 of the mold 19 at the end of the casting side and has a substantially total length excluding the flange portion 23. A pipe inner surface forming outer diameter portion 24 is provided around the center axis of the mold and forms a pipe forming passage 25 between the pipe outer surface forming inner diameter portion 22 of the mold 19. Further, the core 20 is provided with a molten metal injection passage 26 communicating with the pipe forming passage 25 at each of a plurality of positions (four positions in this embodiment) around the center axis of the mold in the flange portion 23. Each molten metal injection passage 26
The cross-sectional shape of the passage is arc-shaped. In addition, it is preferable that the thickness g of the joint portion 27 sandwiched between the adjacent molten metal injection passages 26 is as small as possible in terms of strength, and the passage area of each molten metal injection passage 26 is larger.

That is, in the casting mold device 13, the flange portion 23 of the core 20 is fitted and fixed to the core holding inner diameter portion 21 of the mold 19, and the molten metal injection passage 26 and the pipe forming passage 25 are communicated in a straight shape. ..

In the casting mold device 13, the water cooling jacket body 30 made of copper is fitted to the outer peripheral portion of the casting mold 19 and the insert ring 31 made of brick is fitted to the outer circumferential portion of the casting mold 19 on the casting side. I am trying. As a result, in the casting mold device 13, the portion of the water cooling jacket body 30 is used as a cooling portion for solidifying the molten metal, the portion of the insert ring 31 is used as a non-cooling portion, and the holding furnace 11 is attached to the furnace wall 11A.

Further, the continuous casting apparatus 10 of this embodiment is
A hole-shaped recess 20A is provided at the end of the core 20 on the casting side so that the molten metal that has flowed into the mold 13 is not overcooled.

Therefore, the microstructures of the cast iron pipes of the present invention example and the comparative example are shown in FIGS. 1 (A), 1 (B), 2 (A) and 2 (B). In Comparative Examples C and D, carbides crystallized out and became chilled, whereas in Inventive Examples A and B, good spheroidal graphite structures free of carbides were shown, and the effectiveness of the present invention is clear. ..

That is, according to the present invention, a thin-walled spheroidal graphite cast iron pipe having a wall thickness of 5 mm can be produced without chilling during continuous casting of the cast iron pipe.

Further, according to the present invention, because of its strong graphitizing ability, not only cast iron pipes but also other continuously cast iron products can be produced without chilling.

[0030]

As described above, according to the present invention, a cast iron pipe made of spheroidal graphite cast iron can be continuously cast without chilling.

[Brief description of drawings]

FIG. 1 shows the metal structure of the cast iron pipe of the present invention (magnification: 100
2) is a micrograph showing the same.

FIG. 2 is a metal structure of a cast iron pipe of a comparative example (magnification: 100
2) is a micrograph showing the same.

FIG. 3 is a schematic view showing a continuous casting device.

FIG. 4 is a cross-sectional view showing a casting mold device.

FIG. 5 is an end view showing the casting mold device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Hiromasa Shinaka, 1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture, Kawata Steel Co., Ltd. Chita Works (72) Inventor, Hiroshi Saito, 1-1, Kawasaki-cho, Handa-shi, Aichi In Kawata Steel Co., Ltd. Chita Works (72) Inventor Sokabe Akira 1-1, Kawasaki-cho, Handa City, Aichi Prefecture In Kawata Steel Co., Ltd. Chita Works (72) Inventor Yuichiro Sato 1 Shimoshin Nisso-cho, Toyama City, Toyama Prefecture −93 Daiheiyo Steel Co., Ltd.Toyama Works (72) Inventor, Yuzuru Watanabe 1-93 Shimoshin Nissocho, Toyama City, Toyama Prefecture Daiheiyo Steel Co., Ltd. Toyama Works

Claims (1)

[Claims] 1. The degree of carbon saturation {Sc = C% / (4.23-Si)
% / 3.2)} is 1.15 to 1.35, and the chemical composition is wt% C: 3.8 to 4.1%, Si: 2.7 to 3.8%, Mn: 0.1 to.
0.4%, Mg: 0.006 to 0.040%, and Ca:
0.0003 to 0.005%, Bi: 0.0003 to 0.005%, RE: 0.
A continuously cast iron pipe containing 0003 to 0.005% and the balance Fe and unavoidable impurities.