JPH03107442A - Cast iron having excellent weatherability - Google Patents

Abstract

PURPOSE:To restrain the development of chilled structure even in a thin casting and to obtain pig iron having excellent weatherability by adding the specific element for improving the weatherability and element for restraining formation of white pig iron in the structure to the pig iron, reducing S content as low as possible and regulating carbon saturation degree in the specific range. CONSTITUTION:In the pig iron containing 2.8-3.6wt.% C, 1.6-3.2% Si, 0.2-1.0% Mn, 0.03-0.030% S, 0.05-0.5% P, 0.1-1.0% Cr, 0.2-2.0% Cu, 0.1-2.0% Ni, 0.001-0.005% Ca and 0.02-0.15% Al and having 0.8-1.1 the carbon saturation degree Sc shown with C%/(4.23-Si%/3.2), by adding Al thereto, this is restrained to develop hard and brittle chilled layer caused by the formation of white pig iron in the structure and also P and Cu of elements for improving the weatherability, are contained in the suitable quantities. Even in the thin casting having <=5% area ratio of carbide in the structure and <=10mm thickness, chilled structure can be prevented, and the casting having excellent machinability and weatherability, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to cast iron for use in architecture and structural/design components, and relates to cast iron that has excellent weather resistance in the atmosphere.

<Conventional technology> High-Si cast iron containing 4 to 15% Si, 12% Ni
Niresist cast iron containing ~25% Cr, 10~3
There is already a cast iron with corrosion resistance equivalent to that of high Cr cast iron containing 5% (e.g. Foundry Handbook 1 edited by Japan Foundry Association), but high Si cast iron has brittle and hard mechanical properties and is therefore unsuitable for construction materials. Machining is also difficult. Niresist cast iron is N
It contains a large amount of i and has excellent mechanical properties, but is expensive. High Cr cast iron has corrosion resistance close to that of stainless steel, but each has drawbacks that make it difficult to handle, such as being extremely hard and having low toughness. Not too much.

In this way, conventional corrosion-resistant cast iron has low cost and workability.

Due to its material quality, it was unsuitable for use as a building material.

On the other hand, in the field of steel materials, weathering 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 has low designability as a decorative member. There are also cases where this is cast into a predetermined shape as cast steel (for example, bridges and foundations, 813.P40~
) These weather-resistant cast steels have poor castability, poor reproducibility of complex design patterns and shapes, and higher manufacturing costs than cast iron castings, so they lack applicability as architectural design components. Ta.

In addition, conventional corrosion-resistant cast iron can be used for thin-walled products, especially with a wall thickness of 10+n.
It has been difficult to prevent chilling when casting into pieces with a diameter of less than m. When the casting becomes dull, breakage and cracking tend to occur in the casting, and there are also problems in application to construction materials, such as deterioration of weather resistance.

<Problem that the invention seeks to solve> The object of the present invention is to apply it to architecture from the above-mentioned viewpoint.

The aim is to provide cast iron that is inexpensive and has good castability with excellent weather resistance and workability for structural and design components, and is especially applicable as design components with thin walls and complex shapes and patterns. It provides weather-resistant cast iron.

<Means for Solving the Problems> The cast iron of the present invention is based on a cast iron composition with excellent castability and workability, and by incorporating a trace amount of alloying elements, it prevents the formation of chills and This improves the weather resistance of the rust layer that forms in the atmosphere.

That is, the present invention provides carbon saturation {Sc = C%/ (
4,23-St%/3.2) ) is 0.8 to 1.1%
So, CF 2.8~3.6%, St: 1.6~
3.2%, Mn: 0.2-1.0%, S: 0.
003~0.030%4t:o, o5~0.5%, C
r: 0.1-1.0%, Cu: 0.3-2.0
%, Ni: 0.1-2.0%, Ca: 0.001
~0.005%, Al: 0.02~0.10% by weight, and the remainder consists of Fe and unavoidable impurities, and preferably the area ratio of carbides contained in the metal structure is 5% or less. It is a cast iron with excellent weather resistance.

<Function> Next, the reasons for limiting the range of constituent components of the weather-resistant cast iron of the present invention will be described with reference to some examples.

C, Si i C+ Si is a basic element in cast iron and does not affect the properties or castability of cast iron. In the case of the cast iron of the present invention, carbon saturation {Sc = C%/ (,1,23−
When Si%/3.2)) is in the range of 0.8 to 1.1, gray cast iron with good castability and graphite shape can be obtained. That is, Sc <0. In '8, the tendency to white pig iron increases, making the material hard and brittle. Moreover, when Sc > 1.1, not only does the amount of graphite become excessive, but also large quiche graphite is produced.
Degrades mechanical properties. Here, the amount of Si is limited to a range of 1.6 to 3.2% because if the amount is small, the castability and graphitization tendency will be deteriorated, and if it is too large, hard and brittle silicoferrite will be formed. Also, the amount of C is 2.8 to 3 from the relationship with Si.
．． It was limited to 6%.

S: S is harmful to weather resistance and has the effect of increasing the tendency of cast iron to become white, so it is desirable to reduce it as much as possible. Preferably, the upper limit should be kept below 0.015%, but 0.
It can be used if the content is up to 0.03%. On the other hand, the lower limit was set at 0.003%, which is within the range that can be achieved by general dissolution methods, in order to prevent cost increases.

Mn HMn has the effect of neutralizing the influence of S in cast iron, but its effect is low unless it is contained at 0.2% or more. On the contrary, 1.
Even if the content exceeds 0%, not only the effect will not be improved but also whitening will be promoted. Therefore, the Mn content is 0,
It was limited to 2-1.0%.

Ca; Like Mn, Ca has the effect of neutralizing S, and also has a deoxidizing effect, so it promotes graphitization and has the effect of making good gray cast iron. In this case, the Ca content is o
, if it is less than oot%, the effect is low, and on the contrary, even if it is contained in more than 0.005%, the effect does not improve, so 0.001 to 0
．． It was limited to a range of 0.005%.

FDP is an element useful for improving the weather resistance of cast iron, and its effect is recognized from 0.05% as shown in FIG. Also P
is an element that has the effect of improving the fluidity of molten metal and is also useful as cast iron for decorative parts. However, if the content exceeds 0.5%, the amount of iron phosphide produced will be extremely large, making the material hard and brittle, so the content is limited to a range of 0.05 to 0.5%.

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, if it is added in an amount exceeding 2%, no further effect can be obtained and the tendency for segregation increases, which is not preferable. Therefore, the Cu content is 0.2 to 2
．． It was limited to a range of 0%.

Ni: Ni has the effect of reducing segregation of Cr and stabilizing the rust layer. Even if added in large amounts, there will be no adverse effects, but the upper limit was set at 2.0% to prevent cost increases. On the other hand, since the effect of Ni cannot be obtained unless it is added in an amount of 0.1% or more, the lower limit was set at 0.1%.

Cr: When added alone, Cr does not have much effect on the surface weather properties, but when added in combination with P, Cu, and Ni, it becomes effective from 0.1% or more. on the other hand,
If it is added in an amount exceeding 1.0%, the tendency for whitening will increase significantly and a large amount of carbide will be formed.
It was limited to 0%. However, in the case of thin-walled cast iron with a wall thickness of 10 mm or less, if Cr is added in excess of 0.6%, it becomes difficult to prevent whitening. .6% is preferred.

At: At has the effect of suppressing whitening by fixing oxygen and nitrogen, which are elements that promote whitening dissolved in hot metal, as stable 81203 and AIN. Figure 3 shows the chill depth of cast iron, which is A! Shows the effect of content. A!
When the content is 0.02% or more, the chill depth is significantly reduced. This effect does not differ much up to 0.15% content, but if more is added, the fluidity of the hot metal decreases, so the content of AI is limited to 0.02 to 0.15%.

The cast iron of the present invention, which has been adjusted to have the above-mentioned composition range, suppresses delting even when thin-walled castings with a wall thickness of 10 nm+m or less are cast, and exhibits good weather resistance and workability.

Next, the preferred 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 exhibits excellent weather resistance is that the alloying elements dissolved in the iron base concentrate on the iron surface as rust occurs, forming a dense protective film. Therefore, if the alloying elements segregate or become dissolved in a predetermined amount in the base iron, the weather resistance performance will deteriorate. On the other hand, carbides in cast iron are composed of these alloying elements (Cr and P in the cast iron of the present invention).
As a result, the amount of solid solution of the alloy in the isthmus is reduced and the weather resistance performance is deteriorated. In addition, when the amount of carbides increases, the material becomes hard and brittle, which deteriorates the excellent workability that is a feature of this weather-resistant cast iron. As shown in 3rd M,
As the area ratio of carbides in cast iron increases, the hardness increases significantly, and when the area ratio approaches 10%, machining becomes difficult with ordinary machine tools. For these reasons, the amount of carbide produced in the cast iron of the present invention is preferably small, and the carbide area ratio is preferably 5% or less.

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

<Example> Thin-walled castings having the chemical compositions shown in Table 1 and having thicknesses of 3 mm and 5 mm were produced. The results of examining the cyclostructures of test steels A to E are shown in FIG. 6 for a 3 mm wall thickness material.

Comparison +AO and E have a large amount of cementite crystallized,
It's chilled. In contrast, the cast irons A, B, and C of the present invention
is a good gray cast iron with no delification observed at all. In addition, the comparative material E, which had a wall thickness of 5 mm, also had a large amount of cementite crystallized and formed a delta.

Also these cast iron meat J! J! -5mm section samples at one location in the critical industrial zone and at two locations (X, Y) in the industrial zone.
Figure 5 shows the results of the annual atmospheric exposure test. Compared to the conventional ordinary cast iron material F, the cast irons A, B, and C of the present invention exhibit less corrosion and clearly have improved weather resistance. Also,
Comparative material that has been converted into a model.

It is also clear that the amount of corrosion is smaller than that of E, and that it has the effect of improving the weather resistance of the - layer by preventing chilling.

<Effects of the Invention> As described above, according to the present invention, not only thick objects but also thick objects with a wall thickness of 10
Even when thin-walled castings of 1 m11 or less are cast, no chill occurs, and cast iron with excellent weather resistance and machinability can be obtained. Therefore, it is an extremely useful material for architectural, structural and decorative parts such as interior and exterior wall materials, handrails, bridge members, gate posts, roof tiles, gates, and other thin walled design parts.

In addition, if this weather-resistant cast iron is coated with paint, etc.
The rust layer that forms in defective areas and locally deteriorated parts of the paint film due to long-term use forms a protective film with excellent weather resistance, which has the effect of suppressing the spread of rust and extending the life of the paint. Therefore, it is a useful material in this respect as well.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between P content and corrosion amount in the atmospheric exposure test, Figure 2 is a graph showing the relationship between Cu content and corrosion amount, and Figure 3 is the relationship between carbide area ratio and hardness. , Figure 4 is a graph showing the relationship between chill depth and AI content, Figure 5 is a graph showing the amount of corrosion during two years of atmospheric dew testing, and Figure 6 is 100 times that of a 3mm thick casting. This is a photograph of the metallographic structure of .

Claims (1)

[Claims] 1 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: 0.05-0.5
%, Cr: 0.1-1.0%, Cu: 0.3-2.0%
, Ni: 0.1-2.0%, Ca: 0.001-0.0
Cast iron with excellent weather resistance, characterized by containing 0.05% by weight and 0.02 to 0.10% by weight of Al, with the remainder consisting of Fe and unavoidable impurities. 2. The cast iron with excellent weather resistance according to claim 1, wherein the area ratio of carbides contained in the metal structure is 5% or less.