JPH0635641B2 - Cast iron with excellent weather resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to cast iron for construction and structural / design members, and more particularly to cast iron having excellent weather resistance in the atmosphere.

<Prior art> As is well known, weather-resistant cast iron has a high content of Si of 4 to 15%.
Si cast iron, Ni-resist cast iron containing 12 to 25% Ni, Cr
There are already materials with excellent corrosion resistance such as high Cr cast iron containing 12 to 35% (for example, Foundry Handbook, edited by the Japan Foundry Association), but high Si cast iron has weak mechanical properties and is hard. Not suitable and difficult to machine. Ni-resist cast iron is Ni
It contains a large amount of and has excellent mechanical properties, but it is expensive. High Cr cast iron has corrosion resistance close to that of stainless steel, but has extremely hard and low toughness, etc., which are difficult to handle, and they are generally used only as industrial parts for special purposes. .

As described above, the conventional corrosion-resistant cast iron is unsuitable for use as a building member in terms of cost, workability, material, and the like.

On the other hand, in the category of steel materials, weather resistant steel is known as a structural member that is inexpensive and has excellent corrosion resistance (weather resistance), but this is generally a rolled steel material, and its designability as a design member is low. There are also cases in which this is cast into a predetermined shape as cast steel (for example, Hashizome and Foundation, 81-3, P40-). These weather-resistant cast steels have poor castability and reproducibility of complicated design patterns and shapes. However, it is lacking in applicability as an architecturally-prepared design member, such as poor production cost and higher manufacturing cost than cast iron castings.

<Problems to be Solved by the Invention> An object of the present invention is to provide a cast iron having excellent weatherability and workability, which is inexpensive and has good castability, as a structural, structural member for construction from the above viewpoints. In particular, the present invention provides a weather-resistant cast iron that is highly applicable as a design member having a complicated shape and pattern.

<Means for Solving the Problems> The cast iron of the present invention has a rust layer formed in the air by mixing a trace amount of alloying elements in the material, based on a cast iron composition having excellent castability and workability. It has improved weather resistance.

That is, according to the present invention, the carbon saturation {Sc = C% / (4.23−
Si% / 3.2)} is 0.8 to 1.1, C: 2.8 to 3.6%, Si: 1.6
~ 3.2%, Mn: 0.2-1.0%, S: 0.003-0.030%, P:
0.05% to 0.5%, Cr: 0.1 to 1.0%, Cu: 0.2 to 2.0%, N
i: 0.1 to 2.0%, Ca: 0.001 to 0.005% by weight
The cast iron having excellent weather resistance is characterized in that the area ratio of carbides contained in the balance of Fe and unavoidable impurities is 5% or less.

<Operation> Next, the reason for limiting the range of constituent components of the weather-resistant cast iron of the present invention will be described.

C, Si; C, Si is a basic element in cast iron and affects the properties and castability of cast iron. In the case of the cast iron of the present invention, the carbon saturation {Sc = C% / (4.23-Si% / 3.2)} is 0.8 to
In the range of 1.1, gray cast iron with good castability and graphite shape can be obtained. That is, when Sc <0.8, the tendency to self-pigment becomes high and the material becomes hard and brittle. Further, when Sc> 1.1, not only the amount of graphite becomes excessive, but also large quiche graphite is produced, deteriorating the mechanical properties. Here, if the Si content is small, the castability and graphitization tendency are deteriorated, and if the Si content is large, hard and brittle silicoferrite is formed, so the content is limited to 1.6 to 3.2%. Further, the amount of C is limited to 2.8 to 3.6% because of the relationship with Si.

S; S is detrimental to the weather resistance and has the effect of increasing the tendency of cast iron to form pig iron, and it is desired to reduce it as much as possible. The upper limit should preferably be suppressed to 0.015% or less, but if the content is up to 0.03, it can be used. On the other hand, the lower limit is the cost U
In order to prevent P, 0.00 of the practical range by the general dissolution method
It was set to 3%.

Mn, Ca; Mn acts to neutralize the effect of S in cast iron,
The effect is low unless 0.2% or more is contained. On the contrary, if the content exceeds 1.0%, not only the effect is not improved but also white pig iron is promoted. Therefore, the Mn content is limited to 0.2 to 1.0%. Like Mn, Ca has an action of neutralizing S and also has a deoxidizing action, so that it has the effect of promoting graphitization and making a good gray cast iron. In this case, the Ca content is 0.001%
If the content is less than 0.005%, the effect is low. On the contrary, if the content exceeds 0.005%, the effect is not improved.

P; P is an element useful for improving the weather resistance of cast iron, and as shown in FIG. 1, its effect is remarkably recognized from 0.05%, especially above 0.1%. Further, P has an effect of improving the fluidity of the molten metal and is an element useful as cast iron for design members. However, 0.5%
If it is contained in excess of 0.1%, the amount of iron phosphide generated will become extremely large and the material will become hard and brittle, so the composition range was limited to more than 0.1% and 0.5% or less.

Cu; Cu is an extremely important element for improving the weather resistance of cast iron.
As shown in FIG. 2, weather resistance is improved by containing 0.2% or more. On the other hand, even if added in excess of 2%, no further effect is obtained and the tendency of uneven bending increases, which is not preferable. Therefore, the Cu component range is limited to 0.2 to 2.0%.

Ni; Ni has the effect of reducing the bias of Cr and stabilizing the rust layer. Addition of a large amount will not adversely affect, but the upper limit was set to 2.0% to prevent cost increase. On the other hand, the effect of Ni cannot be obtained unless 0.1% or more is added, so the lower limit was set to 0.1%.

Cr: Cr has little effect on the weather resistance when added alone, but when it is added in combination with P, Cu and Ni, it becomes effective from 0.1% or more. On the other hand, the Cr content was limited to 0.1-1.0% because the addition of more than 1.0% markedly increased the tendency to white pig iron and formed a large amount of carbides.

The weather-resistant cast iron of the present invention, which is cast by adjusting the composition range as described above, will form black-brown rust within a few years at the earliest, and five years at the latest, by exposure to the atmosphere. In this rust layer, there is a dense and stable layer in which Cu, P and Cr are concentrated, and this serves as a protective film for cast iron to suppress the progress of corrosion.

The preferable range of the carbide area ratio in the weather resistant cast iron of the present invention will be described below.

The reason why the cast iron of the present invention has excellent weather resistance is that the alloy elements solid-soluted in the iron matrix are concentrated on the iron surface with the generation of rust to form a dense protective film. Therefore, unless the alloying element is unevenly distributed or is dissolved in the base metal in a predetermined amount, the weather resistance is deteriorated. On the other hand, carbides in cast iron absorb a large amount of these alloying elements (Cr and P in the present weather-resistant cast iron), resulting in a decrease in the amount of solid solution of alloy in the base iron and deterioration in weather resistance. . Further, when the amount of carbides becomes large, the material becomes hard and brittle, so that the excellent workability characteristic of the present weather-resistant cast iron is also deteriorated. As shown in FIG. 3, when the area ratio of carbides in cast iron is high, the hardness is remarkably increased, and when the area ratio is close to 10%, it becomes difficult to machine with a general machine tool. For these reasons, it is better that the weather-resistant cast iron of the present invention has a smaller amount of carbide formed, and the carbide area ratio is preferably 5% or less.

Next, the present invention will be described based on examples.

<Examples> The results of performing the atmospheric exposure test for two years on the weather-resistant cast iron of the present invention at two locations (A, B) in the industrial zone and at one location in the critical industrial zone will be described below.

Table 1 shows the chemical compositions of the cast iron of the present invention and the comparative material used in the test. Symbols A to E are weather-resistant cast iron produced in the composition range of the present invention, and symbols F to H are comparative materials.

Figure 4 shows the results of the atmospheric exposure test. The weather-resistant cast iron of the present invention has a remarkably small amount of corrosion as compared with ordinary cast iron and ordinary steel, and it can be confirmed that it has weather resistance performance equivalent to or higher than that of weather resistant steel, and is sufficient as a weather resistant steel material. It is clear that it is satisfactory.

Further, FIG. 5 shows the results of EPMA analysis of the rust layer formed on the test material for five representative examples. The rust layer of the weather-resistant cast iron of the present invention contains Cu as in the weather-resistant steel. It can be confirmed that a concentrated layer of P, Cr exists.

All of the weather-resistant cast iron used in the test showed almost no carbide formation, hardness of 33 to 39 Hs, and good workability.

<Effects of the Invention> As described above, according to the present invention, by adding a trace amount of alloying elements to cast iron, Cu, P, and Cr are concentrated during exposure to the atmosphere and are excellent in stability and weather resistance. Forming a rust layer,
Since excellent corrosion resistance is exhibited without using high alloy cast iron, it is possible to obtain weather-resistant cast iron that is inexpensive and has excellent castability and machinability. Therefore, it is an extremely useful material as a weather-resistant design member for construction, structure / design member, for example, inner / outer wall material, balustrade, bridge dyeing member, gate pillar, roof tile, gate and the like.

Incidentally, when this weather resistant cast iron is coated with paint or the like, a rust layer formed in a defective portion or a locally deteriorated portion of the coating film due to long-term use forms a protective film having excellent weather resistance,
It also has the effect of suppressing the diffusion of rust and extending the life of the coating, which is also a useful material in this respect.

[Brief description of drawings]

Fig. 1 is a graph showing the relationship between the P content and the corrosion amount in the atmospheric exposure test, Fig. 2 is also a graph showing the relationship between the Cu content and the corrosion amount, and Fig. 3 is the relationship between the carbide area ratio and the hardness. FIG. 4 is a graph showing the amount of corrosion in the atmospheric exposure test for two years, and FIG. 5 is a graph showing the EPMA analysis result of the formed rust layer.

Claims (2)

[Claims] 1. Carbon saturation {Sc = C% / (4.23-Si% /
3.2)} is 0.8-1.1%, C: 2.8-3.6%, Si: 1.6-3.
2%, Mn: 0.2 to 1.0%, S: 0.003 to 0.030%, P: 0.1%
Over 0.5%, Cr: 0.1-1.0%, Cu: 0.2-2.0%, Ni:
Cast iron with excellent weather resistance, characterized by containing 0.1 to 2.0% and Ca: 0.001 to 0.005% by weight respectively, and the balance Fe and unavoidable impurities. 2. The area ratio of carbide contained in the metal structure is 5%.
The cast iron having excellent weather resistance according to claim 1, wherein: