Работы по юриспруденции

TEXT “CAST IRON” №1

 Steels and cast irons are both primarily iron with carbon as the main alloying element. Steels contain less than two percent carbon, while all cast irons contain more than two percent carbon. In addition to carbon, cast irons also must contain silicon, usually from one to three percent, and thus they are actually iron-carbon-silicon alloys.

Due to high carbon content and the silicon in cast irons they are actually excellent casting alloys. Cast irons, however, are not ductile enough to be rolled or forged.

The most common types of cast iron are grey iron, ductile iron and malleable.

Grey iron have excellent wear - resistance. Hardness of grey iron can be increased by adding some alloying elements or by heat - treatment. Grey iron serves well in different kinds of machines because of its good fatigue resistance.

Ductile iron is stronger and more shock-resistant due to its specific structure, i.e. contains magnesium as an additional alloying element.

White iron is produced from both grey or ductile iron by cooling selected areas of casting on the mould. The principle disadvantage of white iron - its brittleness - can be reduced somewhat by carbon content or by thoroughly stress - relieving. Because of its extreme hardness white iron is used in applications requiring wear and abrasion - resistance.

Malleable iron is white iron after an extended (one to six days) heat treatment, it is malleable and easy machined.

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Тестовые задания к тексту

 I. Выберите вариант завершения предложения, соответствующий содержанию текста

1. Grey iron is widely used in machinery of different kinds due to...

a) high stiffness and hardness   b) good fatigue resistance:

c) excellent machinability          d) long service life

2. In order to obtain white iron from grey or ductile iron it is necessary.

a) to relieve stresses in the above types of cast iron

b) to change the molecular structure of grey or ductile iron

c) to cool the definite areas of a casting in the mould

d) to reduce caibon content in the initial material

3. Malleable iron is usually produced by means of.

a) special kind of treatment of grey iron

b) cooling the selected, areas of the ductile iron casting in the mould

c) prolonged (one to six days) thermal treatment of white iron

d) increasing carbon content in grey iron

4. Cast irons can be hardly subjected to rolling or forging because of

a) chemical composition,

b) extreme hardness and stiffness

c) specific molecular structure                                        

d) insufficient ductility

5. Besides carbon the most important element in chemical composition of cast iron is

a) manganese

b) nickel

c) silicon

d) phosphor