JPS5814867B2 - Tough cast iron where part of the graphite is hypereutectoid spheroidal graphite - Google Patents

Description

[Detailed description of the invention] Cast iron can be classified into hypereutectic cast iron, eutectic cast iron, and hypoeutectic cast iron, each having three types of structures: hypereutectic, eutectic, and hypoeutectic. When molten cast iron solidifies, graphite precipitates when it reaches the initial grade line, eutectic point, and hypereutectic line.

By the way, spheroidal graphite cast iron is cast iron in which the three types of precipitated graphite, which are precipitated at the above-mentioned primary crystal lines and hypereutectoid lines, are all spheroidized.

By the way, AltSb is an element that disrupts the spheroidization of graphite.
, As, Bi, Pb, Se, Te, Sn, Ti, etc. are known, and in order to completely spheroidize graphite, the upper limit of allowable amount of each of these elements is generally defined as follows.

Al0.0 5 parts, Sb0.01 parts, As0.05 parts,
Bi O. 0 0 2%, Pb O. 0 2%, S
eO. 0 3%, TeO. 0 1%+ Sn 0.
0 8%t TiO. 0.7% Therefore, if the content of these disruptive elements is below the above upper limit, Mg
When about 0.06'Z of graphite is contained, it is generally possible to obtain cast iron in which graphite is completely spheroidized.

On the other hand, vermicular cast iron
A cast iron having worm-eaten graphite called sti ron is known.

This cast iron is made by adding a small amount of the above-mentioned disruptive elements, such as Ti, to the molten metal for spheroidal graphite cast iron, and adding a small amount of elements such as Ti.
It is manufactured by adding the alloy just before casting.

The graphite in this cast iron has a worm-eaten shape or a snowflake-like shape, and unevenness can be seen around the graphite, and as the amount of graphite increases, the mechanical properties deteriorate somewhat, but on the other hand, the vibration absorption ability decreases. Since it has become a dog, its characteristics are being used to put it into practical use.

The present invention is a tough cast iron having a graphite structure containing a mixture of hypereutectoid spheroidal graphite, fine graphite, and flake graphite, which is selected by eliminating the characteristics and defects of spheroidal graphite cast iron, flaky graphite cast iron, and vermicular cast iron. The purpose is to provide C.
0.2-4.0%; SiO. 5-4. o%; Ca
O. o o 1 or more and less than 0.25%; Al, S
b 5 A S 5 B 1 t P b t S e
t At least one kind selected from T e , S n , T I; 0.1 to 1.0; S0. O05
over 0.03%; oo. The total content of one or two selected from among the alkali metals and rare earth metals other than oos and below + Ca is 0.03% or less; the remainder is substantially Fe and a portion of the graphite is The above object can be achieved by providing tough cast iron made of spheroidal graphite.

Next, the present invention will be explained in detail.

In the cast iron of the present invention, only the hypereutectoid graphite is spheroidized due to the presence of Ca, and the eutectic graphite and primary graphite precipitated during the casting process are Al, Sb, As, and B 1 5 P.
b 5 S e , T e t S n I T i
This is a new cast iron that is made fine or flaky due to the inclusion of homodisruptive elements, and in which the spheroidization of eutectic graphite and primary graphite is suppressed due to the inclusion of alkali metals other than Ca and rare earth metals. .

The present inventor previously discovered that sulfur, which affects the graphite precipitation effect of graphite steel,
Clarifying the effects of oxygen and silicon (Journal of the Japan Institute of Metals 1)
(1968, Vol. 32, pp. 84-88) Furthermore, he obtained patent rights for the invention of calcium graphite steel (Patent Registration No. 257706, No. 266848).

According to the above research, when Ca-treated molten steel contains 0.03% sulfur, graphitization is inhibited, and when the content exceeds 0.13%, graphite does not precipitate and pro-eutectoid cementite forms at grain boundaries. It begins to precipitate within the grains, and the oxygen content decreases to o. oo
It was found that when the content exceeds s%, the precipitation of graphite is significantly suppressed and the pro-eutectoid cementite becomes stable.

In addition, we investigated the mechanism of precipitation of spheroidal graphite caused by Ca, and the promoting effect of silicon on the precipitation of graphite.

The present inventor has conducted further research and found that even if Ca spheroidal graphite steel contains a certain amount of elements that inhibit graphitization and spheroidization, such as sulfur and oxygen, when an appropriate amount of silicon is added,
It was found that graphite precipitated along the hypereutectic line easily becomes spheroidized, and furthermore, a considerable amount of disrupting elements, for example: -XO. 1~
The present invention was conceived based on the finding that, unlike the case of M,9 spheroidal graphite cast iron, the spheroidization of hypereutectoid spheroidal graphite is not affected even if the content is about 0.6%.

The present inventor considers the reason why the spheroidization of hypereutectoid spheroidal graphite is not affected even if there is a considerable amount of disrupting elements as described above, as follows.

In other words, graphite that precipitates along the hypereutectic line is different from graphite that precipitates directly from a liquid, such as primary graphite and graphite that precipitates at the eutectic point, because graphite precipitates from the solid γ-austenite. This seems to be due to the fact that free growth and development is restricted by the crystal habitat along the axis.

The present invention was completed based on this knowledge, and has the following features compared to conventional spheroidal graphite cast iron and flaky graphite cast iron.

■． When purchasing raw material pig iron and iron scrap, there are few restrictions on disruptive elements, so you can choose from raw materials with a wide range of compositions.

2. Since hot metal with a high carbon and high silicon composition can be used, the castability is good, the shrinkage rate is low, and a feeder is not required, so the molten metal yield is good.

3. The content of spheroidizing elements is low, and there are few casting defects such as l-'os and shrinkage.

Next, the present invention will be explained using experimental data.

First, ordinary pig iron and titanium-containing pig pig were mixed as appropriate to adjust the amount of titanium, and 2.5 kg of the mixture was melted in a high frequency furnace.

When the temperature reached 1450°C-1500'C, approximately 500g of the cast mixture was cast into a 20mmφ CO2 mold to serve as a specimen for sampling the source water components.

A specified amount of calcium silicide powder was added to the remaining molten metal at the same time as 1/3 of the amount of calcium fluoride powder, and about 500 gr of the powder was cast into a 002 mold.

A prescribed amount of the same calcium agent as above was further added to the remaining molten metal, and about 500g of it was again cast into the CO2 mold.

In this way, the amount of calcium silicide added is gradually increased, and four different amounts of calcium silicide are added from one molten metal.
A specimen of the seeds was taken.

Sulfur o. o11%, oxygen o. Figure 1 shows the relationship between the amount of calcium silicide added and the structure when the titanium content in the source water containing 0.05% is varied within the range of 0 to 0.6, and the titanium content is different for each case. FIG. 2 shows microphotographs of the sample shown in FIG. 1 that has been corroded with 5% Nital (magnification 150) and one that has not been corroded (magnification 75).

These figures show that even when calcium silicide is about 4%, titanium is o. When the titanium content is 10% or less, the graphite spheroidization rate is as good as 5 ob or more, and some spheroidal graphite exists within the range of 0.35 to 0.1% titanium.

Furthermore, when the amount of calcium silicide added is increased to 6 parts, the titanium content increases from 0.1 to 0. It was revealed that spheroidal graphite was present within the range of 6%.

As mentioned above, the maximum allowable limit of titanium in magnesium spheroidal graphite cast iron is o. o7fO, it can be seen that the influence of titanium is alleviated in calcium spheroidal graphite cast iron.

As is clear from Figure 2, when there is a trace of titanium, almost complete spheroidization is shown, but at 0.34% titanium, only the hypereutectoid graphite becomes spheroidized, and the graphite at the austenite grain boundaries becomes flaky. I understand.

The use of calcium silicide and a large amount of calcium alloy is not industrially possible due to cost and workability.

Therefore, in order for this to be industrially successful, Patent No. 30044 is required.
No. 1 (iron-calcium based alloy) or Patent No. 858399 (clad wire rod for adding calcium to molten steel)
The amount of calcium alloy added can be reduced to about 1% by a method such as the following.

When using such iron-calcium based alloys and calcium-added clad wire rods, there is no problem in that alkaline earth metals and rare earth metals other than calcium may be contained in an amount equal to or less than calcium.

However, the residual amount of calcium is 0.001 or more o. If the residual amount of alkali metals other than calcium and rare earth metals is 0.025% or more, a part of the primary graphite and the graphite precipitated at the eutectic point will become spheroidized. It is not preferable because the characteristics are damaged.

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

If C is less than 2 modulus, castability deteriorates, while if it is more than 4.0 modulus, it becomes brittle, so C needs to be within the range of 2.0 to 4.0 modulus.

Ca is o. If it is less than 1%, it becomes difficult to spheroidize graphite, while if it is more than 0.03%, it is uneconomical and the spheroidization rate of graphite becomes 50% or more, which is not preferable.
Ca needs to be within the range of 0.001 to 0.03.

The total number of disrupted elements is o. If it is less than i%, graphite will become completely spherical, while if it is more than 1.0%, it will be difficult to produce spheroidal graphite, so the total amount of disrupting elements will be 0.1 to 1.0%.
Must be within the range.

Si is o. If it is less than 5%, graphite will not precipitate, while if it is less than 4%, graphite will not precipitate.
．． Si is 0.5 to 4.0 because it becomes brittle when it is more than 0 coefficient.
Must be within the range of %.

If the amount of S is more than 0.0301%, it becomes difficult to make the graphite into spheroids, which is not preferable, and if the S amount is less than 0.005%, the spheroidization rate of the graphite becomes 50% or more, which is not preferable.

Therefore, S is o. Exceeds oos% o. o30I) or less.

Oxygen is o. If it exceeds oos%, graphitization becomes difficult, so the oxygen content needs to be 0.008% or less.

The sum of alkali metals and rare earth metals other than Ca is 0.
If the amount is more than 0.03%, some of the graphite other than the hypereutectoid spheroidal graphite will become spheroidized, approaching complete spheroidal graphite cast iron, and the cast iron of the present invention cannot be obtained, so the above-mentioned total must be 0.03% or less.

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

Example 1 Aged pig iron or charcoal pig was used as the melting raw material, and approximately 100K was melted in a high frequency induction furnace lined with magnesia. The maximum heating temperature was 1550°C, and the processing temperature of the calcium alloy after tapping was 14500°C ~ The final casting temperature was 1500°C and 1410°C.

Add 1% calcium alloy by diluting 75k9 portions in a ladle.
and 1/3 of that amount of calcium fluoride were added.

The chemical composition of the additive alloy and the chemical composition of the cast iron are as follows.

The microscopic structure was similar to the case of 0.34% titanium and 4% calcium silicide as shown in FIG. 2, in which only the hypereutectoid spheroidal graphite was spheroidized, with ferrite surrounding the graphite.

Tensile strength is 3 5. 8 kg/my? t, elongation 25,
The hardness was 82.4 of Rb.

Example 2 FC melted at 1480-1515°C in a low frequency induction furnace
After pouring hot metal for No. 30 into a ladle with a capacity of 1000 kg and removing the slag, 0.8% calcium silicide clad wire with an outer diameter of 8 mm and containing 50% CAS was added using a wire feeding machine at a speed of 25 m/min.

The chemical composition and mechanical properties after addition were as follows.

The microscopic structure was strong cast iron containing uniform flaky graphite and some spheroidal graphite.

[Brief explanation of the drawing]

Figure 1 shows that the relationship between the Ti content in the molten metal and the amount of CaSi added has no effect on the graphite structure of cast iron, and Figure 2 shows the addition of CaSi and CaF2 to molten metals with different titanium contents. It is a micrograph showing the structure of cast iron.

Claims (1)

[Claims] 1 020-4.0; Si0.5-4. OL:I);
CaO. OO1% or more o. o less than 25%; A7, Sb
, As, BitPb+SetTe, Sn, Ti at least one selected from 0.1 to 10; S0
．． Exceeding section 005 and 0.03% or less; oo. oos% or less; total content of one or two selected from alkalis other than Ca and rare earth metals 0.03%
Below: Tough cast iron in which the remainder is substantially Fe and a portion of the graphite is hypereutectoid spheroidal graphite.