JPS6059284B2 - How to inoculate cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the material quality of cast iron castings, and more particularly to a method for inoculating cast iron, which can easily and economically improve the material quality of cast iron castings.

Various methods have been used to improve the quality of cast iron, one of which is inoculation.

In addition to the method of using a so-called inoculant such as calcium-silicon, adding a cast iron ingot to molten cast iron or adding hot metal to molten metal is expected to produce an inoculating effect. There are two methods: pig iron inoculation method and hot metal inoculation method. The former method, which uses special inoculants such as calcium-silicon or iron-silicon, has excellent effects such as improved mechanical properties and reduced chill depth. If left untreated, these inoculants not only disappear over time, a so-called fading phenomenon, but also have the disadvantage of increasing costs. On the other hand, the latter method, pig iron inoculation method or hot metal inoculation method, has the effect of reducing the chill depth, is cheaper than the general inoculants mentioned above, and has the characteristics of no segregation. By adding hot metal to molten metal,
It has the disadvantage that the strength is reduced and no improvement in mechanical properties can be expected. That is, in order to improve mechanical properties when originally inoculated, it is essential to improve the shape and distribution of graphite, or to avoid the formation of ferrite bases. Although carbonization, pig iron inoculation, or hot metal inoculation are effective for graphitization, they have no effect on improving graphite structure, and there is no fundamental change in graphite shape or distribution or matrix structure.
Therefore, the mechanical properties are not improved, but rather deteriorated. The present invention was made in order to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a cast iron inoculation method that can easily and economically improve the material quality of cast iron castings. The present invention adds carbon 3.0 to 4.2% and silicon 1.5 to 3.2% by weight to the molten cast iron before casting.
Manganese 0.8% or less, phosphorus 0.08% or less, sulfur 0.
0.03% or less, and 0.01 to 0.5% of at least one selected from magnesium, calcium, yttrium, cerium, and other rare earth metals, with the balance substantially consisting of iron. The above objective was achieved by adding % of the amount. The present invention will be described below.
A case in which an alloy having the above composition is introduced in the form of chips will be specifically explained.

The alloy chips having the above composition contain no magnesium, calcium, yttrium, cerium or other rare earth metals.
．． It is characterized by containing 01 to 0.5% in the form of an alloy, which promotes pearlitization of the base. These additive elements do not have this effect at 0.01% or less, or 0.01% or less.
．． There is no difference in effectiveness even if it is increased to 5% or more. Also, the carbon content is 3.0 to 4.0% and the silicon content is 1.5 to 3.2%.
%, it has a composite graphite-based and silicon-based inoculation effect, and is expected to improve the base structure, which is different from normal pig iron inoculation. As a result, it contributes not only to the mere graphitization of carbide but also to the improvement of mechanical properties. In this case, it is best to use chips in consideration of ease of dissolution when poured onto the surface of the molten metal in the ladle, workability, and economic efficiency. It is possible to reduce the amount of melting by adding chips, but the amount of chips to be added is determined by the maximum heating temperature of the molten metal and the temperature of the molten metal, taking into account the casting temperature. For example, if the melting temperature of the molten metal is 15
When the lower limit of the casting temperature is 50°C and the lower limit of the casting temperature is 1330°C, the molten metal temperature decreases by about 10'C per 1% of the amount of chips added, so it is preferable that the amount of chips added is 20% or less. If only the inoculation effect is expected, it is sufficient to add 1% or more of the chips, but in order to also obtain the effect of making the base perlite and preventing the fade ink phenomenon, it is sufficient to add 5% or more of the chips. amount of input is required. In other words, in iron-silicon inoculation, if treated at high temperature and left unattended, the above-mentioned fading phenomenon will occur, but according to the method of the present invention, the temperature of the molten metal decreases, and therefore casting is not performed immediately. There is no fear that fading will occur due to the process, and not only the mechanical properties are improved by pearlitizing the base, but also the castings of good quality can be obtained by a simple and economical method, such as prevention of chilling. Furthermore, as the inoculating alloy ζ in the present invention, M as a graphite nodularizing agent satisfying the above-mentioned composition range is used.
Ductile cast iron in which trace amounts of g, Ca, Y, Cel, or Mitsushi metal remain can be used. Examples will be described in detail below.

Carbon 3.0% is added to the molten metal obtained by remelting FC-2 Xiangdan's flowing pig iron (carbon content: 3.0%, silicon content: 1.0%).
5% by weight, 2.2% by weight of silicon, 0.15% by weight of manganese, 0.01% by weight of phosphorus, 0.011% by weight of sulfur, 0.04% by weight of copper, 0.0% by weight of nickel, chromium 0.0
Inoculant alloy chips with a size of 10 to 14 mesh consisting of 5% by weight of magnesium, 0.065% by weight of magnesium, and the balance iron were charged. The input treatment amount is 5 to 2% saliva based on the original water. In addition to the input treated sample, an untreated sample and an inoculated sample to which 0.4% by weight of iron-silicon (75) was added were also prepared. The maximum heating temperature of the molten metal is 1550°C, and the casting temperature is 1350°C. The chips were added directly into the ladle after being held at 1550°C for 2 minutes. Iron-silicon inoculation was carried out in the same manner. The test casting was a 4.5k9 block (
The dimensions of the test section are 80 x 60 x 100). Each sample was taken from near the center of the thickness of the test casting, and the temperature of the molten metal decreased.
Brinell hardness, microstructure and tensile strength were tested. The microstructure of each sample is shown in FIGS. 1 to 7.

FIG. 1 shows the microstructure of an untreated sample with no chips added, and its Brinell hardness was 207. FIG. 2 shows the microstructure of the untreated sample shown in FIG. 1 which has been corroded. FIG. 3 shows the microstructure of a sample containing 5% by weight of chips, and its Brinell hardness was 201. FIG. 4 shows the microstructure of a sample to which 1% of chips were added, and its Brinell hardness was 197. Figure 5 shows
The microstructure of a sample containing 15% by weight of chips was shown, and its Brinell hardness was 197. Figure 6 shows 2 chips.
The microstructure of the sample containing % of the slag was shown, and its Brinell hardness was 192. FIG. 7 shows the microstructure of an iron-silicon inoculated sample tested for comparison, whose Brinell hardness was 197. As is clear from FIG. 2, the formation of carbide is observed in the untreated sample without the addition of chips. As is clear from FIG. 3, in the sample with chips added, no carbide was formed even when the amount of chips added was 5% by weight, indicating the effect of reducing chill. In addition, in another experiment, it has been confirmed that the effect of reducing chill appears from an input amount of chips of 1% by weight. Furthermore, as is clear from FIGS. 3 to 6, as the amount of chips introduced increases, eutectic graphite and coarse graphite gradually decrease, and flaky graphite becomes uniformly distributed. The base tissue in this case is perlite. The hardness of each sample is 10 to 15 wr from the casting edge to the thick center and further to the top! Measurements were taken at intervals of n and 40 Twt.

The Brinell hardness described above indicates the value at the center of the wall thickness. The hardness decreases slightly with increasing chip input. Although data is not listed, as the amount of chips added increased, the difference in hardness between the inside and outside became smaller, and the so-called wall thickness sensitivity became smaller. Figure 8 shows the test results of tensile strength with respect to changes in hardness. As is clear from the figure,
Tensile strength is improved by increasing the amount of chip input, and it is shown that the tensile strength is improved and the degree of maturity is improved. The reason why the untreated sample has a high tensile strength is because it contains carbides as shown in FIG. 2, which impairs machinability and is not practical. Furthermore, since the iron-silicon inoculated sample was left to reach the casting temperature after high-temperature treatment, a fading phenomenon occurred, the tensile strength was low, and the microstructure was also unfavorable as shown in FIG. On the other hand, the sample according to the present invention is preferable because there is no fading phenomenon because the temperature immediately decreases when chips are added and the sample is cast as it is. In this example, ductile cast iron chips, which are a type of industrial waste, are used as the inoculant, so the inoculant is extremely inexpensive.

Although ductile cast iron chips were used as the inoculant in the above embodiments, the scope of the present invention is not limited to this, and the same applies as long as it satisfies the composition described in the claims. You can expect the following effects.

Further, in the above examples, the graphite spheroidizing agent was magnesium, but the graphite spheroidizing agent is not limited to this, and may be cast iron containing other graphite spheroidizing agents such as calcium, yttrium, cerium, Mitsushi metal, etc. Similar effects can be expected. Further, the shape of the inoculant is not limited to chips, and may be granular or lumpy. As explained above, in the production of cast iron castings, the present invention inoculates the molten cast iron before casting by adding a cast iron piece containing a graphite nodularizing agent, which is simple and economical. It has the excellent effect of improving the properties of cast iron castings.

Furthermore, since cast iron containing a graphite nodularizing agent can be used as the inoculant for cast iron, it has an excellent effect of being extremely inexpensive.

[Brief explanation of the drawing]

Fig. 1 is a micrograph showing the microstructure of the center of the wall thickness of an untreated sample with no chips added, Fig. 2 is a photomicrograph showing the microstructure of the corroded sample shown in Fig. 1;
Figures 3 to 6 are micrographs showing the microstructure of the center of the thickness of various samples manufactured by the cast iron inoculation method according to the present invention, and Figure 7 is the thickness of the sample inoculated with iron-silicon. FIG. 8, which is a micrograph showing the microstructure of the center part, is a diagram showing the relationship between the amount of chips added and the tensile strength in each sample.

Claims (1)

[Claims] 1 3.0 to 4.2% carbon by weight in molten cast iron before casting
, silicon 1.5-3.2%, manganese 0.8% or less,
0.08% or less of phosphorus, 0.03% or less of sulfur, and at least one selected from magnesium, calcium, yttrium, cerium, and other rare earth metal elements.
1. A method for inoculating cast iron, characterized in that 5 to 20% by weight of an alloy containing 01 to 0.5% by weight and the remainder substantially consisting of iron is injected.