Today, almost no one area of human life, which would not have used iron. This material has been known to mankind for a long time and enjoys an excellent reputation as a practical matter. Iron casting - the basis of a large number of parts, assemblies and mechanisms, and in some cases even self-sustaining product, capable of performing the functions assigned to it. Therefore, in this article we will pay a lot of attention to these iron compounds. Also find out what are the types of cast iron, their physical and chemical properties.
DEFINITION
Iron - this is truly a unique alloy of iron and carbon, in which more than 90% Fe, and C - not more than 6.67%, but not less than 2.14%. Also, carbon from the iron can be in the form of cementite or graphite.
Carbon gives the alloy a sufficiently high toughness, but at the same time, reduces the toughness and malleability. In this regard, iron is a brittle material. Also, in certain brands of cast iron add special additive, which is able to give a mixture of certain properties. In the role of alloying elements can be: nickel, chromium, vanadium, aluminum. iron density index is 7200 kg per cubic meter. From what we can deduce that the weight of cast iron - a figure that can not be called small.
HISTORICAL INFORMATION
Crude iron has long been known to man. The first mention of the alloy dates to the sixth century BC.
In China in ancient times, iron was obtained with a relatively low melting temperature. In Europe, iron began to get over in the 14th century, when they first began using blast furnaces. At that time, a cast iron went to the production of weapons, ammunition, spare parts for construction.
In the field of Russian crude iron production of active principles in the 16th century and then rapidly expanded. In the times Petra I Rossiyskaya Empire in terms of production of crude iron was able to avoid all the nations of the world, but already a hundred years again began to take their positions on the market of ferrous metallurgy.
Iron casting was used to create a variety of artworks in the medieval era. In particular, in the 10th century Chinese masters cast a unique figure of a lion, whose weight exceeds 100 tons. From the 15th century in Germany, and then in other countries, cast iron received the widest distribution. Made of fences, grids, park statues, garden furniture, tombstones.
In the last years of the 18th century cast iron as much as possible involved in the architecture of Russia. A 19th century and commonly known as "Iron Age", as the alloy is very actively used in architecture.
FEATURES
There are different types of cast iron, but the average melting temperature of the metal compound is about 1200 degrees Celsius. This figure is 250-300 degrees less than that required for steel smelting. This difference is related to a fairly high carbon content, which results in less than its close relationship with an iron atom at the molecular level.
At the time of melting and the subsequent crystallization of carbon contained in cast iron, did not have time to fully penetrate into the molecular lattice of iron, and because iron was finally obtained very brittle. In this regard, it does not apply where there are constant dynamic loads. But while it's great for those parts that have high power requirements.
PRODUCTION TECHNOLOGY
Absolutely all kinds of cast iron produced in a blast furnace. Actually, the process of melting is rather tedious activity that requires serious material investment. One ton of iron requires about 550 kilograms of coke and almost a ton of water. Displacement ore charged in the furnace will depend on the iron content. Most often use ore, in which iron is not less than 70%. A smaller concentration of the element is undesirable as it would be economically detrimental to use.
THE FIRST PHASE OF PRODUCTION
iron melting takes place as follows. Mainly in the furnace are filled ore and coke coal grades that serve to meet and maintain the desired temperature inside the furnace shaft. Furthermore, these products are in the process of burning actively participating in chemical reactions as reducing iron.
In parallel with the furnace ships flood acts as a catalyst. This helps the rocks melt faster, which contributes to the rapid release of iron.
It is important to note that the ore before it is subjected to a special pre-treatment in the oven. Her broken crushing plant (fine particles melt faster). After washing to remove particles that do not contain metal. Then raw calcined thus removing sulfur and other foreign elements from it.
THE SECOND PHASE OF PRODUCTION
The charged and ready for action of the furnace fed natural gas by special burners. Cox heats the raw material. It sets carbon that combines with oxygen to form an oxide. This oxide is then involved in reducing iron from ore. Note that with an increase in the amount of gas in the furnace the chemical reaction rate decreases, and when it reaches a certain ratio and is completely stopped.
Excess carbon penetrates into the melt and closes a mixture with an iron, eventually forming a cast. All those elements not melted, are on the surface and eventually removed. This waste is called slag. It can also be used for the production of other materials. Forms of iron obtained in this way called casting and pork.
DIFFERENTIATION
Modern classification of iron alloys involves the division of data into the following types:
- Wit.
- Half-hearted.
- Gray flake graphite.
- High-strength spheroidal graphite.
- Edit.
Let's examine each type separately.
WHITE CAST IRON
So it called iron one that virtually all of the carbon is chemically bound. In engineering, this alloy is not used very often because it is hard but very brittle. He also can not be machined by different cutting tools, and therefore is used by injection of parts that need no treatment. Although this type of cast iron can grind wheels. White cast iron can be both plain and dipped. In this welding it causes problems as accompanied by the formation of different fracture during cooling or heating, as well as due to nonuniformity of structure form in the welding point.
White cast irons produced wear due to primary crystallization of the molten aluminum during cooling overflow. Most often it is used for work under dry friction conditions (eg brake shoes), or for the manufacture of parts with high wear resistance and heat resistance (roll mills).
By the way, white cast iron got its name due to the fact that the appearance of its break - light crystal, radiant surface. The structure of the iron is a collection of member burites, perlite and cementite secondary. If the iron is subject to doping, then it is converted into comfortite perlite, austenite or martensite.
HALF CAST IRON
Classification of cast iron would be incomplete if we did not mention this species of an alloy.
For a typical combination of said iron metal and eutectic graphite in its structure. In general, the complete structure is as follows: graphite, perlite, Ledebur. If the cast iron is subjected to treatment or alloying element heat, it will lead to the formation of austenite, martensite and acicular troostite.
This type of iron is rather brittle, so its application is very limited. The very name of the alloy is so named because of its break - a combination of dark and light areas of the crystal structure.
THE MOST COMMON ENGINEERING MATERIALS
GOST 1412-1485 Gray cast iron contains in its composition about 3.5% carbon, 1.9-2.5% silicon, up to 0.8% manganese, up to 0.3% phosphorus and less than 0.12% sulfur.
This graphite cast iron has a plate shape. It does not require special customization.
Graphite plates have greatly weakened the performance because gray cast iron and is characterized by a very low toughness and almost no elongation (My figure is 0.5%).
Gray cast iron was well treated. The structure of the alloy can be as follows:
- Ferrite graphite.
- Ferrite perlite, graphite.
- Perlite, graphite.
Pressed gray cast iron is much better than in tension. It is also very well welded, but it requires a preheat, and as the additive material needed to use special cast iron core with a high content of silicone and carbon. Without preheating the welding is difficult because the pale iron will take place in the welding zone.
It produces gray iron parts that are in the absence of shock charge (pulleys, deck, frame).
Designation of iron takes place according to the principle: MF 25-52. Two letters indicate that it is a gray cast iron, the number 25 - figure tensile strength (in MPa or kgf / mm2), the number 52 - tensile strength in bending moment.
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