GB2069898A

GB2069898A - Inoculation to a molten cast iron during pouring

Info

Publication number: GB2069898A
Application number: GB8006454A
Authority: GB
Original assignee: Metal Research Corp
Current assignee: Metal Research Corp
Priority date: 1980-02-26
Filing date: 1980-02-26
Publication date: 1981-09-03

Abstract

A molten cast iron is inoculated during pouring from a pouring passageway having a small volume and provided in a main body of the molten cast iron pouring vessel, by feeding a composite clad wire material (3) encasing an inoculant, preferably oppositely, to the molten cast iron flow. The wire material (3) comprises an inoculant containing ferrosilicon, calcium, magnesium, silicon and rare earths encased in a ferrous sheath. Spheroidal graphite cast iron results. <IMAGE>

Description

SPECIFICATION A process for inoculation to a molten cast iron The present invention relates to a process for inoculation to a molten cast iron and more particularly a process for inoculation to a molten cast iron when a molten cast iron is poured into a mold by using an apparatus for pouring a molten cast iron wherein a passageway for pouring a molten cast iron having a small volume such as a pressure type automatic pouring apparatus, a pot type pouring ladle and the like, is provided separately in a molten cast iron vessel and the molten cast iron is poured into a mold through the above described passageway.

The inoculation of a cast iron has been heretofore carried out by adding a granular inoculant to a molten cast iron flow upon charging a molten cast iron into a casting ladle. In addition, the process wherein a compressed and deformed compositie clad wire material wherein an inoculant is encased in an iron sheath material, is fed mechanically into a ladle, has been developed.

However, when a spheroidal graphite cast iron is produced in a pouring ladle by sandwich process which has been presently broadly conducted, there has been no appropriate process for adding an inoculant and it is necessary to rely upon the process wherein an inoculant is necessary to relay upon the process wherein an inoculant is added on the molten cast iron surface and this process is deficient in the stability.

Furthermore, when a secondary adding of the inoculant is needed in order to adjust the components prior to casting a cast iron, it is necessary to rely upon the above described process and the operability is very poor and the effect is low in the stability.

Recently, a furnace for automatically pouring a molten cast iron has been used but when such an apparatus is used, there has been no appropriate inoculation process and various processes in which a powdery inoculant is added on a molten cast iron flow in the vicinity of an opening for pouring a molten cast iron or a molten cast iron pool added with an inoculant is provided at the upper portion of the casting mold, have been attempted. However, any of these processes is low in the stability and the quantitive inoculation is difficult and the defect, such as deep chill is caused. In addition, the process wherein a previously inoculated molten cast iron is poured by an automatic pouring machine, has been carried out but the fading phenomenon can not be avoided and an excess amount of inoculant is not only necessary, but also defects in the quality are caused.

An object of the present invention is to provide an improved inoculation process which obviates the drawbacks caused by the prior processes for inoculation to the molten cast iron when pouring the molten case iron, by using a molten cast iron pouring apparatus wherein a pouring passageway having a small volume is separately provided in the main body of the molten cast iron vessel whereby the molten cast iron is poured into a casting mold through the above described pouring passageway.

This object can be attained by feeding a compressed and deformed clad wire material formed by encasing the inoculant with an iron sheet into the molten cast iron in the above described passageway oppositely to the molten cast iron flow upon pouring the molten cast iron into a casting mold by using the above described pouring apparatus.

The inventors have made a variety of studies with respect to the drawbacks of the above described prior processes and paid attentions to the passageway for pouring the molten cast iron where is just before pouring and is highest in the inoculating effect and the molten cast iron volume is substantially constantly maintained, and found that the inoculation can be carried out without causing the above described drawbacks by continuously feeding a compressed and deformed composite clad wire material encasing an inoculant in an iron sheet into the molten cast iron at a moderate feeding rate or spped when the molten cast is flowing in said passageway. The present invention has been accomplished by this discovery.

According to the present invention, it is possible to pour the molten cast iron in a mold in the state where the inoculating effect is highest and further by predetermining the diameter of the composite clad wire material and the feeding rate, the addition amount can be easily controlled. Furthermore, since the composite clad wire material is added at a low rate corresponding to the molten cast iron flow, the new formation of slag due to the rapid dissolution and inoculation does not substantially occur and the slag inclusion does not occur. Moreover, this is not the inoculation in the mold, so that the maximum effect can be simply obtained without changing any casting plan and by the addition of the minimum amount of inoculant.

The passageway for pouring the molten cast iron provided separately in the main body of the molten cast iron vessel to be used in the present invention is not limited by the shape of the vessel, unless the molten cast iron in the passageway is mixed with the molten cast iron in the main body 1 a or 2a of the molten cast iron vessel even if the molten cast iron in the passageway is stirred as shown by the pouring nozzle I b in a pressure type automatic pouring apparatus 1 as shown in Fig. 1 or the pouring opening 2b in a pot type pouring ladle as shown in Fig. 2. The composite clad wire material 3 to be used in the present invention has been disclosed in Japanese Patent No. 858,399 in which an inoculant involving ferrosilicon, calcium, magnesium, silicon and rare earth metals and the like is encased in iron or iron alloy sheet or pipe.

In the present invention the rate of feeding the above described clad wire material 3 into the molten cast iron is preferred to be 5-1 8 m/min. and when said rate is less than 5 m/min, the inoculation amount is deficient and the depth of chill layer becomes larger, while when said rate exceeds 1 8 m/min., the sheath material is not completely dissolved in the molten cast iron pouring passageway and a part of said clad wire material is fed to the main body of the vessel and the actually inoculated amount becomes uneven in relation to the temperature of the molten cast iron and the feeding rate and the homogenization of the product is hindered.

The present invention will be explained in more detail.

For better understanding of the invention reference is taken to the accompanying drawings, wherein: Fig. 1 is a schematic view for explaining an embodiment for carrying out the present invention in a pressure type automatic pouring apparatus.

Fig. 2 is a schematic view for explaining another embodiment for carrying out the present invention in a pot type pouring ladle, and Figs. 3(a) and (b) are microscopic photographs (magnification: 115 times) of the textures of spheroidal graphite cast irons obtained by the process of the present invention and the conventional process.

The following examples are given for the purpose of illustrations of this invention and are not inteded as limitations thereof.

EXAMPLE 1 3 tons of molten cast iron of FC25 (Japanese Industrial Standard) melted in a low frequency induction furnace at 1,490-1 ,5200C was charged in pressure type automatic pouring apparatus (capacity 4.9 tons) and the composite clad material (containing FE-Si as the inoculant) having 4.9 mm was fed at a rate of 12 m/min. to effect the inoculation in an amount corresponding to about 0.1% of Si and then the inoculated molten cast iron was taken out by a sampling dipper from the molten cast iron and the molten cast iron was cast into a mold for a wedge-shaped chill test piece.For the comparison, when 400 kg of the same molten cast iron as that charged into the automatic pouring apparatus was charged into pouring ladle, Fe-Si (75%) having a grain diameter of 3-8 mm was added in the conventional manner in an amount of 0.3% by weight to effect inocculation and then the molten cast iron was taken out by a small sampling dipper and a wedge-shaped chill test piece was formed as the conventional sample.

When the molten cast iron was charged into the ladle from a melting furnace and cast in a mold, the indication of the inspection was 4 minutes after inoculation because of the loss time of transferring the ladle or pouring of the given amount of the molten cast iron in the given number of molds and the depth of the chill layer at this time is shown in the following Table 1.

TABLE 1

Depth of Chemical component chill layer in Time after wedge-shaped inoculation C Si Mn S Cr test piece mm Non-treatment (original 3.38 1.77 0.73 0.025 0.15 33.0 molten cast iron) Conventional 4 min. " " " " " 5.0 product Example 1 O r, " I, ,1 r, 2 As seen from the above result, the sample of the present invention can effect the effective inoculation even in the automatic pouring apparatus and further the result thereof is more excellent than the product obtained by conducting the inoculation by using the conventional ladle.

It has been well known that the fading phenomenon occurs, that is when an inoculant to a molten cast iron, the effct of the inoculant is lost with lapse of time, and the inoculation has been carried out so as to cover this phenomenon.

However, when the molten cast iron is poured into a mould little by little while maintaining å large amount of molten cast iron as in the pressure type automatic pouring apparatus, even if the molten cast iron previously inoculated is used, the fading phenomenon occurs and the secondary inoculation is needed before casting. If an excess amount of inoculant is added in order to prevent the secondary inoculation, the excessive inoculation results in lowereing of the quality or occurrence of unfavourable shrinkage.

For the purpose of the secondary inoculation powdery or very fine granular inoculant may be added to the molten cast iron, but according to this process, the inoculant floats on the molten cast iron surface, so that the loss due to oxidation is much and slags are formed and unevenness occurs owing to the adding manner of the inoculant and the inoculating effect is not stabilized.

In the present invention, even in the case where a small amount of the inoculant is added, it is possible to accurately dissolve the given amount of inoculant in the molten cast iron and to give the maximum inoculating effect. Furthermore, since the chill can be decreased by the addition of a small amount of inoculant, even when castings having a large difference of the thickness are cast, the castings having no chill layer at the portion having a thin thickness can be obtained without lowering the quality at the portion having a large thickness.

EXAMPLE 2 3 tons of the molten cast iron previously inoculated with 0.3% of Fe-Si in a conventional process was charged into pressure type automatic pouring apparatus (capacity: 4.9 tons) and left to stand for 30 minutes. Then, the same clad wire material as used in Example 1 was fed into the molten cast iron just before pouring in an amount corresponding to 0.05% by weight at a rate of 8-1 0 mm/min. The inoculated molten cast iron was taken out by a dipper and a wedge-shaped chill test piece was formed and the chill depth was measured with respect to the said test pieces. The obtained result is shown in th following Table 2.

TABLE 2

Depth of Time after Chemical component chill layer in inoculation ~ wedge-shaped (min.) C Si Mn S Cr test piece mm Conventional 5 3.35 1.80 0.75 0.028 0,14 5 process FeSi (0.3%) 30 " " pp pp ,, 15 Example 2 0 pp pp " pp pp 5 As seen from this result, since the inoculant is added into the molten cast iron at the pouring passageway according to the process of the present invention, the fading phenomenon does not occur and the excellent inoculating effect is always obtained.

EXAMPLE 3 400 kg of molten cast iron produced in basic lining cupola furnace (capacity: 4.9 tons) was subjected to spherodizing treatment by sandwich process in a pot type pouring ladle and then the same clad wire material (corresponding to 0.03% Si) as used in Example 1 was fed into the molten cast iron flow in the pouring passageway at a rate of 6-8 m/min. to cast a spheroidal cast iron article.

For the comparison, 0.1% by weight of FeSi (75%) was dispersed on the molten cast iron surface and stirred by the conventional process and then the molten cast iron was cast in a mold to form a casting. The texture of both the castings were compared. Figs. 3(a) and (b) are the microscopic photographs of a magnification of 1 5 times of the textures of the product of the present invention and the conventional product and it can be seen from these photographs that the casting obtained in this example more satisfactorily proceeds in the ferrite formation (white portion in the photograph) than the conventional casting.

As mentioned above, the inoculation process of the present invention is the organic combination of the apparatus for pouring the molten cast iron having the particularly defined structure with the composite clad wire material, and the automatic inoculation to the automatic pouring apparatus, which has been heretofore considered to be difficult, has been made feasible and since the inoculation is carried out in the given volume of the pouring passageway at the constant rate just before pouring even in the inoculation in spheroidal graphite cast iron and usual cast irons, the satisfactory inoculating effect can be obtained in a small amount of inoculant and the inoculating process is simple, so that the operation is easy and the automatic operation can be easily effected and the practical effect is high.

Claims

1. An inoculation process to a molten cast iron wherein the molten cast iron is poured into a casting mold by using an apparatus for pouring the molten cast iron wherein a pouring passageway having a small volume is separately provided in a main body of a molten cast iron pouring vessel and the molten cast iron is poured into a casting mold through the above described pouring passageway, which comprises feeding a composite clad wire material encasing an inoculant in an iron sheet oppositely to the molten cast iron flow in the above described pouring passageway.

2. The process as claimed in claim 1 , wherein the clad wire material is fed oppositely into the molte cast iron flow in a rate of 5-1 8 m/min.

3. An inoculation process to molten cast iron substantially as hereinbefore described with reference to the accompanying drawings.

New claims or amendments to claims filed on 25 November 1980 New or amended claims:

1. An inoculation process to a molten cast iron wherein the molten cast iron is poured into a casting mold by using an apparatus for pouring the molten cast iron wherein a pouring passageway having a small volume is separately provided in a main body of a molten cast iron pouring vessel and the molten cast iron is poured into a casting mold through the above described pouring passageway, which comprises feeding a composite clad wire material encasing an inoculant in an iron sheet to the molten cast iron flow in the above described pouring passageway.