JPS5948842B2 - Graphite nodularizing agent for spheroidal graphite cast iron and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a graphite nodularizing agent for producing spheroidal graphite cast iron.

The present inventor, together with a co-inventor, previously added 01 to 0.15% MgO to molten iron having a hypoeutectic composition containing 02 to 0.08% So, and then added C.
aO0049~2.85% and CeO,001-0,15
disclosed a method for producing hypoeutectic cast iron in which graphite is spheroidized by adding Mg. The point is to alleviate the effects of elements.

In addition, the present inventor disclosed Fe80 to
The basic components are 10% and 80~5% of Ca, and also Fe and C.
Si has a strong affinity with a.

Refined steel made of a Fe-Ca-based alloy containing one or more selected from AI and Mn within a range of 55 to 5%, and optionally containing NiQ to 5%. Further, the Ca content is 1% in the refining agent and the refining agent.
Although steel refining agents containing up to 75 alkali metals, alkaline earth metals, or rare earth elements have been disclosed, these refining agents can also be used as graphite nodularizing agents for cast iron.

Furthermore, the present inventor has disclosed 5i
10-99.5%, AIo, 05-3%, Ca, Mg
Contains 4% or less of at least one selected from the group consisting of O, 0.25% or less of nonmetallic inclusions, and the remainder substantially consists of Fe, and the component composition of the nonmetallic inclusions is A1203.
1 to 12.5%, at least 1 of MgO, CaO
A high-purity ferrosilicon for steel modification comprising 3 to 60% of seeds, 3% or less of FeO, and the balance of SiO2 and unavoidable impurities has been disclosed.

This ferrosilicon can also be used as a cast iron graphite nodularizing agent.

By the way, as can be seen from the inventions of the present inventors,
Mg, Ca, and rare earth elements are the best elements for spheroidizing graphite in molten cast iron, but the amount of Mg, Ca, and rare earth elements used must be very small relative to the weight of the molten metal.
If Ca is used alone, it may cause a rapid reaction with molten cast iron, which is dangerous, so it is usually used diluted in a large amount of ferrosilicon and alloyed.

The advantage of being alloyed with ferrosilicon is that the amount is increased by ferrosilicon, making it easier to disperse more uniformly in the molten metal, and ferrosilicon also promotes graphite spheroidization, and the presence of Fe in ferrosilicon also reduces the specific gravity. If graphite is added as a nodularizing agent deep into the molten cast iron, it will not only take longer to float and contact with the molten metal, but also cause explosive vaporization due to the high vapor pressure of Mg and Ca at high temperatures. The yield of graphite spheroidization can be improved by suppressing it by alloying it with Si and making it diluted.

In addition, producing rare earth elements as simple metals is expensive, so producing them as silicides of rare earth elements, that is, mitshu metal silicide, is generally the cheapest in terms of cost, and is also the most excellent as a graphite spheroidizing agent. Because there is.

However, when using mitshu metal silicide as it is in molten cast iron, only a small amount is required, so in order to add it uniformly to the molten metal, it is often diluted in a larger amount of ferrosilicon and then used as an alloy.

Now, when the above-mentioned Mg, Ca, and rare earth elements are used as an alloy in ferrosilicon, the amount of inclusions contained in ferrosilicon and its component composition greatly affect the graphite nodularization of molten cast iron. The present inventors have previously discovered this, and have provided a steel modifier in which the composition of non-metallic inclusions as well as the composition of metallic elements in the alloy are limited, based on the above-mentioned Japanese Patent Application Laid-Open No. 11112/1983. That's what I did.

That is, as described in the above publication, if nonmetallic inclusions are contained in ferrosilicon, graphite spheroidization of cast iron is often hindered, so ferrosilicon with as few nonmetallic inclusions as possible is required.

For this reason, ferrosilicon with fewer nonmetallic inclusions and its manufacturing method have been proposed. For example, 5tal inEngli published in the Soviet Union in September 1969
In sh, a mixture of iron ore, limestone, quartz, etc. is added to a 75% Si ferrosilicon melt, and the nonmetallic inclusions in the melt are brought into contact with the molten slag of the mixture. A small amount of ferrosilicon and its manufacturing method are described.

On page 897 of the above-mentioned 5tal in English, the total amount of nonmetallic inclusions and their chemical composition in 75% ferrosilicon obtained by subjecting standard molten 75% ferrosilicon to aluminum removal treatment are listed as shown in Table 1 below. .

From Table 1 above, standard 75% ferrosilicon is 1 to 3
% of Al and about 0.8 to 1.2% of nonmetallic inclusions, and the nonmetallic inclusions are mainly composed of about 17 to 20.5% of Al2O3 and about 73 to 76% of SiO2. It can be seen that it is an aluminum silicate.

Also, 01~ as stated in the notes for the standard 75% ferrosilicon.
By applying the slag treatment according to 3 and D, respectively,
For example, the content of AI is 2.63% for the sample.
It can be seen that the total amount of nonmetallic inclusions has decreased from 1.19% to 0.224%.

However, even if the slag treatment by 01 to 3 or D is applied to the molten ferrosilicon, the total amount of nonmetallic inclusions will decrease depending on each treatment, but the amount of nonmetallic inclusions in the ferrosilicon after the treatment will be The composition of aluminum silicate in the remaining nonmetallic inclusions did not change significantly;
For example, in the case of D treatment, Al20320 before treatment.
It can be seen that 4% decreases only slightly to 15.4% after treatment.

In this case, SiO2 before and after treatment is 73.6%, respectively.
It is 78.0%.

That is, in conventional high-purity ferrosilicon with reduced non-metallic inclusions, the AI content therein is 0.14%, as described in 5tal above, and the non-metallic inclusions are reduced. The total amount of the nonmetallic inclusions is 0.224%, which is a very small amount, but the nonmetallic inclusions are
It is clear that the main component is aluminum silicate consisting of 5% or more.

However, when producing spheroidal graphite cast iron using the high-purity ferrosilicon described in 5tal above, the spheroidization of graphite may be incomplete due to the large amount of aluminum silicate in the nonmetallic inclusions contained in this ferrosilicon. It may happen.

The purpose of the present invention is to provide a novel graphite nodularizing agent for spheroidal graphite cast iron, which eliminates and improves the drawbacks of conventionally known graphite nodularizing agents for cast iron, and a method for producing the same, and which disrupts graphite nodularizing. Graphite spheroidizing agent for spheroidal graphite cast iron with limited content and composition of nonmetallic inclusions as well as metallic elements,
That is, Si20-60%, AIo, 01-2%, Mg
4 to 16%, rare earth elements 5% or less, Ca 5% or less, nonmetallic inclusions 0.25% or less, the remainder substantially consisting of Fe, and the nonmetallic inclusions are A120315% or less,
MgO.

Contains 1 to 60% of at least one selected from oxides of rare earth elements CaO1, 3% or less of FeO, and the balance is Si.
Consists of O2 and unavoidable impurities, MgO-Al2
The above object can be achieved by providing a graphite spheroidizing agent for spheroidized graphite cast iron, which is characterized by a minimal amount of O3-based spinel-type nonmetallic inclusions, and a method for producing the same.

Next, the reason for limiting the component composition in the present invention will be explained.

In the present invention, it is not economical to add Si as an alloy component with less than 20%, while if Si is more than 60%, the production cost is high and it is uneconomical to use. It is necessary to keep it within the range of ~60%, and it can be used most preferably within the range of 40-50%.

In the present invention, if Al is less than 0.01%, it is difficult to produce it industrially at low cost, while if it is more than 2%, it inhibits graphite spheroidization. It needs to be within the range of 2% to 2%.

In the present invention, if Mg is less than 4%, the amount of spheroidizing agent added is too large, which not only lowers the temperature of the molten metal but is also uneconomical, whereas if it is more than 16%, manufacturing becomes difficult and costs increase. Mg needs to be within the range of 4 to 16%.

In the second invention, if the rare earth element exceeds 5%, not only will the cost increase, but graphite spheroidization will not be further promoted, so the rare earth element needs to be 5% or less.

In the present invention, if the content of nonmetallic inclusions is more than 0.25%, graphite spheroidization is inhibited, and therefore it is necessary to keep the content to 0.25% or less.

If Al2O3, which is a non-metallic inclusion, exceeds 15%, graphite spheroidization is similarly inhibited, so Al2O3 must be kept at 15% or less.

In the present invention, it is difficult to manufacture a graphite nodularizing agent containing less than 1% of at least one selected from MgO and CaO in the nonmetallic inclusions, and there is no need to increase the content of the nonmetallic inclusions to more than 60%. The content of at least one selected from MgO and CaO in the inclusions must be within the range of 1 to 60%.

In the present invention, it is difficult to produce a graphite nodularizing agent in which at least one of MgO, CaO, and oxides of rare earth elements in the nonmetallic inclusions is less than 1%; Therefore, at least one selected from MgO and CaO1 rare earth element oxides in the nonmetallic inclusions must be in the range of 1 to 60%.

In the present invention, if FeO exceeds 5%, graphite spheroidization is inhibited, so it is necessary to keep it below 5%.

Next, a method for producing the graphite spheroidizing agent of the present invention will be explained.

After removing as much non-metallic inclusions in a normal molten ferrosilicon as possible by a known method if necessary, adding Ca or a Ca alloy to the molten metal to reduce the content of non-metallic inclusions to 0.25% or less, Then, Mg or Mg alloy is added to the molten metal together with or before or after the rare earth element or rare earth alloy.
%, AIo, 01-2%, Mg 4-16%, Ca 5% or less, rare earth elements 5% or less, non-metallic inclusions 0.25% or less, the balance substantially consisting of Fe, and the non-metallic inclusions A1□0315% or less, MgO, CaO1 1 to 60% of at least one selected from oxides of rare earth elements, FeO 3% or less, the balance being SiO2 and unavoidable impurities, and MgO-Al2O3 system. It is possible to produce a graphite nodularizing agent for spheroidal graphite cast iron that has minimal spinel-type nonmetallic inclusions.

According to the invention, normally commercially available ferrosilicon is prepared in a ladle using a mixture of iron ore, limestone and quartz in a known manner, for example as described in 5tal September 1969.
Alternatively, after removing most of the nonmetallic inclusions in the molten metal by refining in an acidic furnace using silicate-limestone slag, Ca or Ca alloy is added to reduce the content of nonmetallic inclusions in the molten metal. It is necessary to keep it below 0.25%.

Adding Mg or Mg alloy to conventional commercially available molten ferrosilicon, or molten ferrosilicon from which most of the nonmetallic inclusions have been removed by conventional methods, and then adding Ca or Ca alloy, or together with Mg or Mg alloy. Ca
Alternatively, a Ca alloy is added to adjust the Mg and Ca contents in the molten metal to predetermined values.

However, the above conventional method (the above-mentioned Japanese Patent Application Laid-Open No. 53-111
Including the manufacturing method of No. 12.

), by adding Mg, MgO-Al
The present inventors have newly discovered that 2O3-based spinel-type nonmetallic inclusions are generated and these interfere with the spheroidization of graphite.

Furthermore, it was also found that it is not easy to reduce the spinel-type inclusions with Ca.

Therefore, according to the present invention, Ca is first added to the molten metal before adding Mg, and Al2O3 is reduced to <At by Ca as shown in the following reaction formula.

Al2O3+3Ca=3CaO+2A 1 Thus, Al2O3 in the molten metal is extremely reduced.

By adding Mg or Mg alloy to such a molten metal, it is possible to achieve extremely low non-metallic inclusions, especially Mg.
0-AI.

It was possible to produce a graphite spheroidizing agent containing very few spinel-type nonmetallic inclusions of the 03 series, and the production method of the present invention was completed.

In the graphite spheroidizing agent of the present invention, a part of Ca can be replaced with alkaline earth metals Ba and/or Sr other than Ca, which also have the ability to spheroidize graphite.

Next, the present invention will be explained with reference to examples.

Example 1 Commercially available JIS2 using a 5-ton low frequency induction furnace backed with silica stone
No. ferrosilicon and steel scrap were mixed and melted to produce 4 tons of molten metal, and quicklime and silica stone were added to form CaO/Sin.
After smelting with a ratio of 0.8 (7) and adding Ca alloy, one ton of each was poured into a preheated magnesia-backed small ladle, and the silicides of Mg metal and rare earth metal were poured. Graphite spheroidizing agents of the present invention as shown in Table 1 below were produced by adding various amounts.

Note that the nonmetallic inclusions in the same table are the values obtained as a result of residual fragrance analysis conducted using the chlorine method.

Example 2 For comparison, commercially available JI No. 32 ferrosilicon was melted in a 5-tun low-frequency furnace also backed with silica stone, and the graphite nodularizing agent of the present invention obtained in Example 1 with heat numbers 1 to 4 was melted in a ladle. After adding Mg alloy and rare earth element silicide, calcium silicon was added to make Mg9.5%, Cab,
8%, rare earth elements 0.85%, All, 32%, 5i
46.5% balance Fe graphite spheroidizing agent (Such a manufacturing method is conventionally known, and products made by this method are commercially available.

) was used to conduct a graphite nodularization test of molten cast iron.

The amount of graphite nodularizing agent added to each 1 ton of molten metal was 1%.

Then, the resistance force was measured for a test piece that was cast immediately after adding one ton of the spheroidizing agent to the molten metal, and a test piece that was cast 15 minutes after the addition.

The results are shown in Table 2.

The commercially available products in the same table are graphite nodularizing agents produced by the conventionally known method.

In Table 2, the tensile strength of the specimens cast immediately after adding the graphite nodularizing agent is the highest when using the commercially available graphite nodularizing agent, and the tensile strength using the graphite nodularizing agent of the present invention is slightly lower. The tensile strength of the specimens cast 15 minutes after the addition of the graphite nodularizing agent was far superior to the specimen using the graphite nodularizing agent of the present invention.

That is, it can be seen that the graphite spheroidizing agent of the present invention, after being added to the molten metal, causes the spheroidized graphite to collapse much more slowly than when a commercially available product is used.

It can be seen from the above that the graphite spheroidizing agent of the present invention is extremely superior to conventional ones.

Claims (1)

[Claims] I Si20-60%, AIo, 01-2%, Mg4
~16%, rare earth elements 5% or less, Ca 5% or less, non-metallic inclusions 0.25% or less, the remainder substantially consisting of Fe, and the non-metallic inclusions are Al203 15% or less, M
gO. Contains 1 to 60% of at least one selected from oxides of rare earth elements, CaO1, 3% or less of FeO, the remainder consisting of SiO2 and inevitable impurities, MgO-
A graphite nodularizing agent for spheroidal graphite cast iron characterized by having minimal Al2O3-based spinel-type nonmetallic inclusions. 2. After removing as much non-metallic inclusions as possible from the normal molten ferrosilicon, add Ca or Ca alloy to the molten metal and adjust the temperature and holding time so that A1□03 in the non-metallic inclusions becomes 15% or less. , adjust the amount added to reduce to AI, then add Mg or Mg alloy to this molten metal together with or before and after the rare earth element alloy to reduce Si to 20-60%.
, AIo, 01 to 2%, Mg 4 to 16%, Ca 5% or less, rare earth elements 5% or less, nonmetallic inclusions 0.25% or less, and the balance substantially consists of Fe, and the nonmetallic inclusions are Al20315. % or less, at least one selected from oxides of rare earth elements such as MgO and CaO1 to
60% FeO, 3% or less of FeO, the balance being SiO2 and unavoidable impurities, and a graphite spheroidizing agent for spheroidal graphite cast iron characterized by obtaining a graphite nodularizing agent containing very little Mg0-A1□03-based spinel-type nonmetallic inclusions. Method for producing graphite nodularizing agent.