JP2005095911A - Method for continuously casting spheroidal graphite cast iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the increase of inventories in respective kinds and storing cost by continuously casting the base materials having the same component composition and changing the cooling conditions thereafter to classify into various material qualities. <P>SOLUTION: A method for continuously casting a spheroidal cast iron is peculiarly provided with the following processes: (a) molten metal having the component composition (mass%) of 3.1-3.7% C, 2.5-3.2% Si, 0.1-0.6%Mn, 0.02-0.05% Mg, 0.1-1.0% Cu and the balance with inevitable impurities, is introduced into a continuous casting mold to cast a cast billet; (b) successively, the cast billet drawn out from the mold, is cooled, and this surface temperature is made to be 710-730°C; and (c) this cast billet is cooled by adjusting so that the average cooling rate for cooling to 600°C, becomes a specific cooling rate in the interval of 0.05-1.5°C/s. (d) Thus, the cast billet provided with a specific strength in the range of 400-750 MPa is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing spheroidal graphite cast iron. In particular, the present invention relates to a method for producing a spheroidal graphite cast iron continuous cast bar having a tensile strength of 400 to 750 MPa.

  In recent years, continuous cast bars of cast iron have been used in various industrial fields. For example, due to the features such as high dimensional accuracy of materials, continuous machining processes such as NC lathe processing and automatic cutting processing. As the most suitable cast iron material, its value is increasing.

Spheroidal graphite cast iron improves mechanical properties such as tensile strength and elongation as compared with ordinary cast iron by spheroidizing graphite in cast iron. In order to increase the strength of spheroidal graphite cast iron, a method of adding appropriate amounts of copper and manganese is generally used. JP-A-8-188812 discloses a method of adding antimony to increase the strength of spheroidal graphite cast iron.
JP-A-8-188812

  In the prior art method of adding copper and manganese to increase the tensile strength, it is necessary to change the amount of copper and manganese added according to the tensile strength. For this reason, product inventory for each type classified into tensile strength and component composition is required, so that the amount of inventory increases, and thus product storage costs also increase. In addition, in the method of adding antimony, the stock type and storage costs are increased in the same manner.

  Furthermore, spheroidal graphite cast iron has many varieties such as FCD400, FCD450, FCD500, FCD600, and FCD700 in the standard of JIS G5502 (spherical graphite cast product) even when the tensile strength is in the range of 400 MPa to 750 MPa. For this reason, possessing and managing products of all materials and all sizes of spheroidal graphite cast iron will increase inventory costs and management costs.

  Accordingly, the present invention solves the above-mentioned problems, and continuously casts a base material having the same component composition, and then separates it into castings of various materials by changing the cooling conditions, thereby increasing the inventory type and the storage cost. The purpose is to prevent.

In order to solve the above-mentioned problems, aspects of the present invention are as follows.
The first aspect of the present invention is a continuous casting method of spheroidal graphite cast iron characterized by comprising the following steps.
(A) Component composition (component composition is mass%) is C: 3.1-3.7%, Si: 2.5-3.2%, Mn: 0.1-0.6%, Mg : 0.02 to 0.05%, Cu: 0.1 to 1.0%, with the balance being Fe and inevitable impurities, the molten metal is led to a continuous casting mold to cast a slab,
(B) Next, the slab pulled out from the mold is cooled to a surface temperature of 710 to 730 ° C.,
(C) Next, an average cooling rate for cooling the slab to 600 ° C. is adjusted to a specific cooling rate between 0.05 to 1.5 ° C./s to cool the slab,
(D) A slab having a specific tensile strength in the range of 400 to 750 MPa is obtained.

  According to a second aspect of the present invention, the cooling is a method in which air is injected by one or more air injection devices in which a hollow tube provided with a slit is arranged in a ring shape around a slab. This is a continuous casting method of spheroidal graphite cast iron.

  A third aspect of the present invention is a continuous casting method of spheroidal graphite cast iron, characterized in that when the slab is cooled to 600 ° C., the cooling is performed on a roll provided with a heat insulating cover.

  In the fourth aspect of the present invention, an average cooling rate for cooling the slab to 600 ° C. is adjusted to a predetermined cooling rate between 0.05 to 1.5 ° C./s, and the graphite pearlite and ferrite are used. Spheroidal graphite characterized by controlling a base area ratio of a metal structure and casting a slab having a predetermined tensile strength in a range of 400 to 750 MPa in a same lot using a molten metal within the range of the component composition. This is a continuous casting method of cast iron.

  In the present invention, C: 3.1-3.7%, Si: 2.5-3.2%, Mn: 0.1-0.6%, Mg: 0.02-0.05%, Cu: A continuous cast bar containing 0.1 to 1.0% and the balance being Fe and inevitable impurities is air-cooled to maintain the surface temperature of the cast bar at 710 to 730 ° C., and then the average cooling rate up to 600 ° C. is 0. By adjusting and cooling between 5 and 1.5 ° C./s, it is possible to produce a spheroidal graphite cast iron continuous cast bar having a tensile strength of 400 to 750 MPa. It is possible to create different materials by changing them.

  Embodiments of the present invention will be described below. The manufacturing method of the spheroidal graphite cast iron continuous cast bar of the present embodiment has a component composition (component composition is mass%): C: 3.1-3.7%, Si: 2.5-3.2%, Mn: 0.1 to 0.6%, Mg: 0.02 to 0.05%, Cu: 0.1 to 1.0%, with the balance being Fe and unavoidable impurities in a continuous casting mold The slab is cast, then the slab drawn from the mold is cooled to a surface temperature of 710 to 730 ° C., and then the average cooling rate of the slab to 600 ° C. is 0.05 to 1. The slab is cooled to a specific cooling rate of 5 ° C./s to obtain a slab having a specific tensile strength in the range of 400 to 750 MPa.

  In the present embodiment, the component composition of spheroidal graphite cast iron (the component composition is mass% hereinafter) is C: 3.1 to 3.7%, Si: 2.5 to 3.2%, Mn: 0 0.1 to 0.6%, Mg: 0.02 to 0.05%, Cu: 0.1 to 1.0%, with the balance being Fe and inevitable impurities.

Below, the reason for limitation of the chemical component etc. in this invention is demonstrated.
C: 3.1-3.7% C is an important element for crystallizing graphite with cast iron. However, if the content is less than 3.1%, chill is likely to occur, and if it exceeds 3.7%, dross is likely to occur when spheroidizing treatment is performed. Therefore, the addition amount is in the range of 3.1 to 3.7%.

  Si: 2.5-3.2%. Si is an element for promoting graphitization and has an effect of improving castability. If the content is less than 2.5%, the fluidity of the molten metal during pouring deteriorates. If it exceeds 3.2%, the toughness decreases. Therefore, the amount of Si added is in the range of 2.5 to 3.2%.

  Mn: 0.1 to 0.6% Mn has an effect of deoxidation and desulfurization, and is an element that promotes pearlization. If the content is less than 0.1%, the heat treatment effect cannot be expected, and if it exceeds 0.6%, the toughness deteriorates. Therefore, the amount of Mn added is in the range of 0.1 to 0.6%.

  Mg: 0.02 to 0.05% Mg has a function of spheroidizing graphite. If the content is less than 0.02%, the effect of spheroidizing graphite is small. Even if the content exceeds 0.05%, the effect is small, which causes generation of chill. Therefore, the amount of Mg added is in the range of 0.02 to 0.05%.

  Cu: 0.1 to 1.0% Since Cu is a pearlite forming element, it is necessary for the effect of promoting base strengthening. If it is less than 0.1%, the effect is not obtained, and if it exceeds 1.0%, the toughness deteriorates. Therefore, the addition amount is in the range of 0.1 to 1.0%.

  When manufacturing a cast rod, it is necessary to adjust the components in order to control the structure according to the size and shape, for example, if the cylinder is a cylinder, the diameter is large or small. For example, for C, it is necessary to change the addition amount depending on the size of the slab, and when the diameter is 300 mm, the addition amount is reduced to about 3.3%, and when the diameter is 40 mm, the addition amount is increased to about 3.6%. It is necessary to. In the case of Cu, when the slab is 300 mm or more, it is desirable to add 0.4 to 0.8% for structure control.

  In the production method of the spheroidal graphite cast iron continuous cast bar of this embodiment, the continuously cast cast bar is cooled using jet air so that the surface temperature of the cast bar is set to 710 to 730 ° C, and then the average cooling to 600 ° C is performed. It is characterized by adjusting the speed between 0.05 to 1.5 ° C./s and cooling to obtain a cast bar having a tensile strength of 400 to 750 MPa.

  When producing the spheroidal graphite cast iron by the continuous casting method, the present inventors investigated the relationship between the metal structure of the base around the spheroidal graphite and the cooling rate for the cast product having the component composition according to the present invention.

  FIG. 4 shows a continuous cooling transformation curve (CCT curve). In FIG. 4, F represents ferrite, P represents pearlite, and M represents martensite. FIG. 4 shows that the pearlite transformation region exists in the range of 720 to 600 ° C., and that the ratio of ferrite and pearlite varies depending on the cooling rate. That is, when the cooling rate (CR) is less than 0.1 ° C./s, ferrite accounts for 70% or more (perlite is 30% or less), and when the cooling rate is 0.1 <CR <5, ferrite and pearlite are mixed. (Perlite 30-90%) and CR> 5 results in a martensite structure.

  As for the temperature inside the casting rod during casting, the temperature was estimated by performing solidification analysis by a computer. When the surface temperature is 720 ° C., the temperature at the center is, for example, 735 ° C. for a 50 mm diameter casting rod, 750 ° C. for a 100 mm diameter casting rod, and 800 ° C. for a 300 mm diameter casting rod.

  This embodiment will be described with reference to FIG. The spheroidal graphite cast iron melt 13 held in the tundish 15 is introduced into the water-cooled mold 17 through the opening of the tundish 15, and the cast bar 11 solidified by passing through the water-cooled mold 17 is pinched roll 29. It is pulled out to the right in the figure. Next, the casting rod 11 is cooled by the blast air while moving on the support roll 27 while passing through the air jetting device provided with one or more.

  For example, in FIG. 1, the first air injection device 19, the second air injection device 21, the third air injection device 23, and three air injection devices are provided. Air injection is performed using any one or more of the first to third units. Then, the casting rod 11 is cooled and the surface temperature is controlled to 710 to 730 ° C.

  In the present embodiment, the surface temperature of the casting rod 11 after passing through the air injection device is controlled to 710 to 730 ° C. This is because if the temperature is lower than 710 ° C., the temperature is lower than the transformation start temperature, and if it exceeds 730 ° C., the center diameter of the large-diameter slab exceeds 800 ° C., and it is difficult to obtain a desired cooling rate essential for structure control.

  Next, the casting rod 11 is cooled by adjusting the average cooling rate up to 600 ° C. to 0.05 to 1.5 ° C./s. When adjusting to a predetermined cooling rate, it is used when controlling the surface temperature to 710 to 730 ° C., for example, using one or more of the first to third units to cool by air injection It is desirable to do. Or you may cool by injecting water in mist form. In short, the average cooling rate up to 600 ° C. may be adjusted to 0.05 to 1.5 ° C./s. The average cooling rate is a value obtained by dividing the temperature difference from the predetermined temperature to the predetermined temperature by the time required for cooling.

  In the manufacturing method of the spheroidal graphite cast iron continuous casting rod of the present embodiment, one or more air injection devices in which a hollow tube provided with a slit for injecting air is arranged in a ring shape are provided, and the air injection device When cooling by injecting air from the slit and cooling the slab surface by adjusting the amount of blast air, the average cooling rate of the slab is controlled.

  The air injection device of this embodiment will be described with reference to FIGS. 2 (a) and 2 (b). The air injection device 41 is formed by forming a hollow cylindrical tube into a ring shape. FIG. 2A shows a state in which the blast air 43 is blown through the slit to the cylindrical casting rod 11 passing through the air jet device 41 provided in a ring shape. Since the blast air 43 is blown out from a slit provided around the inner circumference of the ring-shaped tube at a uniform pressure and a uniform flow rate, the surface of the casting rod 11 located at the center can be cooled uniformly.

  FIG. 2B shows a cross section of the hollow cylindrical tube of the air injection device 41. In the air injection device 41, a slit 45 is provided on the inner side of the ring-shaped tube over the entire circumference. Further, a pipe (not shown) for receiving cooling air is connected to the hollow portion 47 of the ring-shaped tube, and a flow meter, a pressure gauge, a control valve, etc., not shown, are also provided.

  In order to control the surface temperature of the casting rod, adjustment of the blast air is performed by adjusting the shape and size of the tube, the shape and size of the slit, the pressure and flow rate of the blast air, and the size and shape of the casting rod. What is necessary is just to select the most suitable one. Further, when a plurality of air injection devices are provided, precise control becomes possible. Moreover, when providing two or more, what is necessary is just to select the optimal conditions similarly to the above also about the space | interval which provides an air injection apparatus.

  The manufacturing method of the spheroidal graphite cast iron continuous cast bar of this embodiment adjusts the average cooling rate up to 600 ° C. to a predetermined cooling rate between 0.05 and 1.5 ° C./s, and uses graphite, pearlite and ferrite. The base area ratio of the metal structure is controlled, and cast slabs having a predetermined tensile strength in the range of 400 to 750 MPa are cast in the same lot using a molten metal within the range of the component composition.

  The same lot refers to a slab manufactured in one cycle operation from the start to the end of casting in a continuous casting method in which a predetermined amount of molten cast iron is repeatedly supplied to the tundish to obtain a continuous slab. Represent.

(Embodiment 1)
The metal structure and tensile strength when the cooling rate is changed will be individually described below.
In the first embodiment, the cooling rate to 600 ° C. of the cast rod after cooling by the air injection device is set to 0.5 to 1.5 ° C./s, and the base of the metal structure is 90% or more of the pearlite and the remaining part in the area ratio Is a coexisting structure of ferrite, and is characterized by obtaining a cast bar having a tensile strength of 700 MPa or more.

  That is, air cooling is performed so that the surface temperature of the casting rod is in the range of 710 to 730 ° C. Then, the casting rod is forcibly cooled by adjusting the air pressure and the air volume and controlling the average cooling rate up to 600 ° C. to 0.5 to 1.5 ° C./s. As a result, it is possible to obtain a spheroidal graphite cast iron continuous cast bar having a metal structure base of coexisting pearlite with an area ratio of 90% or more and the balance of ferrite with a tensile strength of 700 MPa or more.

For metal structure bases, find the perlite area ratio P (%) using the following formula, for example, according to the casting manual (edited by the Japan Foundry Association, published by Maruzen Shoten on January 20, 1985). Can do.
P (%) = A _P ÷ (A _G + A _F + A _P ) × 100
Where A _P : Perlite occupation area
A _G : Occupied area of graphite
A _F : Occupied area of ferrite

(Embodiment 2)
In the second embodiment, the cooling rate of the cast rod after cooling by the air injection device is set to 0.3 to 1.0 ° C./s, and the base of the metal structure has an area ratio of 80% pearlite and the balance. A cast bar having a ferrite coexisting structure and a tensile strength of 600 MPa or more is obtained.

  That is, air cooling is performed so that the surface temperature of the casting rod is in the range of 710 to 730 ° C. Thereafter, the air pressure and the air volume are adjusted to control the average cooling rate up to 600 ° C. to 0.3 to 1.0 ° C./s. As a result, it is possible to obtain a spheroidal graphite cast iron continuous cast bar having a metal structure base of coexisting pearlite with an area ratio of 80% or more and the balance of ferrite with a tensile strength of 600 MPa or more.

(Embodiment 3)
In Embodiment 3, the average cooling rate up to 600 ° C. of the cast rod after cooling by the air injection device is 0.1 to 0.5 ° C./s, and the base of the metal structure is pearlite with an area ratio of 40 to 60%. And the balance is a coexisting structure of ferrite, and a cast rod having a tensile strength of 500 MPa or more is obtained.

  That is, air cooling is performed so that the surface temperature of the casting rod is in the range of 710 to 730 ° C. Thereafter, the air pressure and the air volume are adjusted, and the average cooling rate up to 600 ° C. is controlled to 0.1 to 0.5 ° C./s. As a result, it is possible to obtain a spheroidal graphite cast iron continuous cast bar having a metal structure base of pearlite having an area ratio of 40 to 60% and the balance being a ferrite coexisting structure and having a tensile strength of 500 MPa or more.

(Embodiment 4)
In the fourth embodiment, the average cooling rate up to 600 ° C. of the cast rod after cooling by the air injection device is set to 0.05 to 0.1 ° C./s, and the base of the metal structure is ferrite having an area ratio of 80 to 100%. And the balance is a coexisting structure of pearlite, and a cast bar having a tensile strength of 400 MPa or more is obtained.

  That is, air cooling is performed so that the surface temperature of the casting rod is in the range of 710 to 730 ° C. Then, it moves on the installation roll with a heat insulation cover, and controls the average cooling rate to 600 degreeC to 0.05-0.10 degreeC / s. As a result, it is possible to obtain a spheroidal graphite cast iron continuous cast bar having a metal structure base of 80 to 90% in area ratio of ferrite and the remaining pearlite coexisting structure and having a tensile strength of 400 MPa or more.

  3 tonnes of spheroidal graphite cast iron having the composition of the present invention shown in Example 1 of Table 1 as shown in FIG. 3 were poured into a tundish (TD) of a horizontal continuous casting facility to cast a cast iron casting rod having a diameter of 100 mm. . As shown in FIG. 1, the first to third ring-shaped air injection devices are arranged, air is injected from the slits of the air injection device, and the casting rod coming out of the mold is continuously cooled from the circumferential direction. .

  Air was injected using the first and second air cooling devices, and the surface temperature of the casting rod was controlled to be in the range of 710 to 730 ° C. Thereafter, using a third air cooling device, air pressure and air volume are adjusted to perform blast cooling at a wind speed of 30 to 40 m / s, and the average cooling rate of the cast rod up to 600 ° C. is 1.0 to 1.1. 2 tons of cast rods were produced by controlling the temperature to be ℃ / s.

  Observation of the surface layer portion, intermediate portion (1/4 position of the diameter), and central portion of the obtained cast rod revealed that the pearlite was predominant (95% pearlite) in any part. Further, when a test piece was collected from the middle part and examined for mechanical properties, the tensile strength was 766 MPa, the elongation was 4.2%, the hardness was HB (Brinell hardness) 255, and the characteristics equivalent to FCD700 were obtained. I found out that I have it.

  In addition, the tensile strength and elongation were calculated | required by the method of JISZ2241. The hardness was determined by the method of JIS Z2243.

  A cast iron casting rod having a diameter of 100 mm was cast by adding 2 tons of molten spheroidal graphite cast iron having the composition of the present invention shown in Example 2 of Table 1 to the tundish (TD) used in Example 1.

  In the same manner as in Example 1, air was injected using the first and second air cooling devices, and the surface temperature of the casting rod was controlled to be in the range of 710 to 730 ° C. Thereafter, using a third air cooling device, air pressure and air volume are adjusted to perform blast cooling at a wind speed of 20 to 30 m / s, and the average cooling rate of the cast rod up to 600 ° C. is set to 0.5 to 0.7. A cast bar was produced under the control of ℃ / s.

  Observation of the surface layer portion, the middle portion (1/4 of the diameter), and the metal structure of the center portion of the obtained cast bar revealed that the pearlite main body (perlite 80%) was found in any part. Further, when a test piece was collected from the middle part and examined for mechanical properties, the tensile strength was 650 MPa, the elongation was 7.0%, the hardness was HB (Brinell hardness) 241 and the characteristics equivalent to FCD600 were obtained. I found out that I have it.

  A cast iron casting rod having a diameter of 100 mm was cast on the tundish (TD) used in Example 2 by adding 2 tons of molten spheroidal graphite cast iron having the composition of the present invention shown in Example 3 of Table 1.

  In the same manner as in Example 1, air was injected using the first and second air cooling devices, and the surface temperature of the casting rod was controlled to be in the range of 710 to 730 ° C. Thereafter, the third air cooling device is used to adjust the air pressure and the air volume, and the average cooling rate of the casting rod up to 600 ° C. is controlled to be 0.2 to 0.3 ° C./s. Manufactured.

  When the metal structure of the surface layer part, the intermediate part (1/4 of the diameter), and the central part of the obtained cast bar was observed, the ratio of ferrite and pearlite was almost the same (60% pearlite) at any part. . Further, when a test piece was collected from the middle part and examined for mechanical properties, the tensile strength was 522 MPa, the elongation was 11.6%, the hardness was HB (Brinell hardness) 187, and the characteristics equivalent to FCD500 were obtained. I found out that I have it.

  A cast iron rod having a diameter of 100 mm was cast by adding 2 tons of spheroidal graphite cast iron melt having the composition of the present invention shown in Example 4 of Table 1 to the tundish (TD) used in Example 3.

  Air was injected using the first, second, and third air cooling devices, and the surface temperature of the casting rod was controlled to be in the range of 710 to 730 ° C.

  Then, it moved on the installation roll with a heat retention cover, and it controlled so that the average cooling rate of the casting rod to 600 degreeC might be set to 0.05-0.06 degreeC / s.

  When the metal structure of the surface layer portion, the intermediate portion (1/4 position of the diameter), and the center portion of the obtained cast bar was observed, the ferrite main component (92%) was found in any portion. Further, when a test piece was collected from the middle part and examined for mechanical properties, the tensile strength was 458 MPa, the elongation was 24.4%, the hardness was HB (Brinell hardness) 159, and the characteristics equivalent to FCD400 were obtained. I found out that I have it.

  C: 3.1-3.7%, Si: 2.5-3.2%, Mn: 0.1-0.6%, Mg: 0.02-0.05%, Cu: 0.1 When producing a continuous cast bar containing 1.0 and the balance being Fe and inevitable impurities, a spheroidal graphite cast iron continuously having a tensile strength of 400 to 750 MPa by changing cooling conditions from a base material of the same component composition Can cast casting bars.

It is the figure which showed the casting method of this invention. It is the figure which showed the air injection apparatus of this invention. It is the figure which showed the component composition etc. of the Example of this invention. A continuous cooling transformation curve (CCT curve) was shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Casting rod 13 Molten metal 15 Tundish 17 Water cooling mold 19 Air injection apparatus 21 Air injection apparatus 23 Air injection apparatus 25 Thermal insulation cover 27 Support roll 29 Pinch roll 41 Air injection apparatus 43 Injection air 45 Slit 47 Hollow part

Claims (4)

A continuous casting method of spheroidal graphite cast iron, comprising the following steps.
(A) Component composition (component composition is mass%) is C: 3.1-3.7%, Si: 2.5-3.2%, Mn: 0.1-0.6%, Mg : 0.02 to 0.05%, Cu: 0.1 to 1.0%, with the balance being Fe and inevitable impurities, the molten metal is led to a continuous casting mold to cast a slab,
(B) Next, the slab pulled out from the mold is cooled to a surface temperature of 710 to 730 ° C.,
(C) Next, an average cooling rate for cooling the slab to 600 ° C. is adjusted to a specific cooling rate between 0.05 to 1.5 ° C./s to cool the slab,
(D) A slab having a specific tensile strength in the range of 400 to 750 MPa is obtained.   2. The spherical shape according to claim 1, wherein the cooling is a method in which air is injected by one or more air injection devices in which a hollow tube provided with a slit is arranged in a ring shape around a slab. Continuous casting method of graphite cast iron.   3. The continuous casting method of spheroidal graphite cast iron according to claim 1, wherein when the slab is cooled to 600 ° C., the cooling is performed by moving on a roll provided with a heat insulating cover. The average cooling rate for cooling the slab to 600 ° C. is adjusted to a predetermined cooling rate between 0.05 to 1.5 ° C./s, and the base area ratio of the metal structure composed of graphite, pearlite and ferrite is controlled. The cast slab having a predetermined tensile strength in a range of 400 to 750 MPa is cast in the same lot using a molten metal within the range of the component composition. Continuous casting method of spheroidal graphite cast iron.
(P0305068)

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