KR910006024B1 - Grey cast iron having a good oxidation resistant property - Google Patents

Abstract

A grey cast iron for oxidation resistance consists of 3-4 wt.% C, 3-5 wt.% Al, 1 wt.% Si, and the remainder of Fe. It is reqired for cast iron in mould for cast and mould stool to reduce thermal creack and to annihilate crack propagation due to oxidation. This method is characterized by enhancing oxidation resistance and thermal fatigue resistance properties of normal grey cast iron by optimzation of silicon and aluminum content.

Description

Gray cast iron with excellent oxidation resistance and thermal fatigue resistance

Figure 1 is a photograph showing the change of austenite austenite according to the aluminum content.

Figure 2 is a photograph showing the surface oxide layer thickness and internal structure changes according to the aluminum content.

3 is a graph showing the tensile strength (at 700 ℃) according to the aluminum content.

4 is a graph showing the fatigue resistance according to the aluminum content.

The present invention relates to cast iron, in particular gray cast iron excellent in oxidation resistance and fatigue fatigue resistance that can be used in high temperature and oxidizing atmosphere, such as mold stool and mold.

In general, cast iron used in high temperature and oxidizing atmospheres such as mold and platen has excellent thermal conductivity to reduce cracking caused by thermal stress, excellent oxidation resistance to suppress crack propagation due to oxidation, and high tensile strength and easy Manufacturing processes and the like are required, and cast iron materials mainly used for such applications are known gray cast iron, nodular graphite cast iron and C / V (Compacted Verimicular) graphite cast iron.

However, each cast iron has advantages and disadvantages. In the case of general gray cast iron, cast iron, which is the first used for casting and surface plate manufacturing, has been used for ease of casting, good thermal conductivity, and low production cost, but has a very low tensile strength. It is easily cracked by thermal stress during the process and has a short life.

On the other hand, spheroidal graphite cast iron increases the tensile strength and elongation by spheroidizing the shape of graphite, making cracking more difficult than gray cast iron. I couldn't.

Accordingly, in recent years, the tensile strength and thermal conductivity have been obtained to produce molds and plates using C / V graphite cast iron having a median value between ordinary gray cast iron and nodular graphite cast iron.

However, in order to manufacture C / V graphite cast iron as well as spherical graphite cast iron, spheroidization treatment is essential during the casting process. Especially, C / V graphite cast iron has a rare earth metal input or fading time. Manufacturing process is difficult and production cost is high. In order of production cost, C / V graphite cast iron is the most expensive, followed by nodular graphite iron and gray cast iron.

Therefore, the most recently developed C / V graphite cast iron has an effect on the side of life extension, but it is difficult to manufacture and has a high production cost. Therefore, the present invention is to improve the oxidation resistance and fatigue resistance by appropriately controlling the amount of silicon and aluminum of gray cast iron in order to solve the drawbacks of the conventional cast iron material.

The present invention for achieving the above object will be described in detail.

The present invention relates to gray cast iron having excellent oxidation resistance and fatigue fatigue resistance, characterized in that, in a typical gray cast iron, the amount of silicon is 1 wt% or less and the amount of aluminum is 3-5 wt%.

The gray cast iron applied to the present invention is C, Si; As the conventional gray cast iron containing the balance Fe and unavoidable impurities, the C needs to be subjected to a separate heat treatment due to excessive crystallization of Fe ₃ C at 2.5% or less. Since mechanical properties deteriorate, it is preferable to set it as 2.5 to 4.5%, and it is more preferable to limit it to 3 to 4% especially in consideration of high temperature strength, oxidation resistance, and thermal fatigue resistance.

The aluminum increases the amount and the orientation of the primary austenite, thereby giving a higher temperature strength than the nodular cast iron by acting as a fiber in the structure. In addition, the thermal fatigue phenomenon of the cast iron material proceeds as the internal oxidation is performed by oxygen invasion between the graphite and the tissue, aluminum suppresses the thermal fatigue phenomenon by forming a dense oxide film on the surface of the cast iron to delay the internal oxidation Play a role.

Referring to Figures 1 and 2, the effect of the aluminum on the crystallization amount and orientation of the primary austenite and the effect on the oxidation will be described as follows.

As shown in FIG. 1, when aluminum contains 1wt% (hereinafter referred to as%), [(a)] means that the crystallization amount of primary austenite is small and does not have an orientation, but aluminum is 3% and 4% [(b )] And [(c)] also increase in amount and show one-way in particular.

In addition, as shown in FIG. 2, when [(c)] contains 4% aluminum, the oxide layer thinner than [(b)] when [(a)] does not contain aluminum and [2] contains aluminum. It can be seen that formed.

Accordingly, the present inventors have limited the lower limit of the aluminum based on the amount of crystallized crystallization of austenite austenite and its orientation. When the amount is 3% or less, the high temperature strength is low because it does not promote the development of primary austenite. 3% or more is preferable because it does not play a significant role in suppressing thermal fatigue due to high internal oxidation delay.

On the other hand, when the amount of aluminum is 5% or more, the intermetallic compound, that is, carbide is formed, which is not only light and brittle but also poor castability, so the upper limit thereof is 5%.

In addition, when the amount of the silicon is 1% or more, the process temperature is increased to suppress the primary austenite development, thereby decreasing the strength, so 1% or less is preferable. Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

The cast iron prepared as shown in Table 1 was measured, and the tensile strength was measured at 700 ° C., and the results are shown in FIG. 3, and the thermal fatigue characteristics thereof were measured, and the results are shown in FIG. 4.

TABLE 1

As can be seen in Figure 3 showing the high temperature strength value according to the aluminum content, the present invention having the composition of Table 1 is the amount and directionality of ultrafine austenite than conventional gray cast iron, nodular graphite cast iron and C / V graphite cast iron This increased and showed an excellent strength value, especially when the amount of aluminum is 4% or more, the value is larger than 150 MPa.

In addition, as can be seen in Figure 4 showing the thermal fatigue properties according to the aluminum content, the present invention having the composition of Table 1 shows that the thermal fatigue properties are superior to ordinary gray cast iron, nodular graphite cast iron and C / V graphite cast iron .

As described above, the present invention has the effect of providing gray cast iron having excellent heat resistance and fatigue resistance easily at a low price without the need for spheroidizing treatment.

Claims (1)

Gray cast iron having excellent oxidation resistance and thermal fatigue resistance, which is composed of C: 3 to 4%, Al: 3 to 5%, Si: 1% or less, balance Fe and unavoidable impurities.

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