I. Reading Activity and Speech Practice

Text C: Ferrous Metals. Cast Iron.

I.1Scan the text and learn about iron and its alloys as much as possible.

As it is known, metals can be divided into ferrous and non-ferrous. The former contain iron and the latter do not contain it. It is to be noted that pure iron* is ductile, soft and relatively weak. It is not normally used as an engineering material because of its low strength. That is why iron has to be combined with other elements such as carbon, silicon, phosphorus, etc. The two most important forms of ferrous metals are cast iron and steel which are both alloys, and mixtures of iron and carbon. And carbon is the most important of all elements present in ferrous alloys*. Steel and cast iron differ in the quantity of carbon content: iron-carbon alloys with more than approximately 2% by weight of carbon are cast irons.

Cast iron is the cheapest of all the ferrous metals. Cast iron is a general term to be applied to iron-carbon alloys containing more than 2% of carbon. Cast iron without the addition of alloying elements is weak in tension and shear, strong in compression and has low resistance to impact.

Grey cast iron is an alloy of iron and carbon in which the carbon is present in free or graphite state. Grey cast iron has its term because of special colour of its fracture; it is soft, easily machined* and only moderately brittle. It is used for the parts not to be subjected to great tensile stresses.

However, many castings* that were formerly made of grey cast iron are now made of malleable iron because malleable castings do possess a degree of toughness and this is probably why they have been so named. Malleable iron castings can be made much thinner in section. But they are seldom used in the form they come from the moulds *, as they are hard and brittle and therefore they should be annealed*. Malleable iron is the most easily machined of all the ferrous metals.

Malleable iron before annealing is usually spoken of as the “white” iron. White iron is difficult to machine because most of the carbon present is in chemical combination with iron. It is desirable to use it in those machines which require some resistance to abrasion*. The tensile strength of white cast iron is about 30,000pei (pounds per square inch).

Vocabulary to the text:

1. pure iron* - чистое железо;

2. ferrous alloys * - железистые сплавы;

3. machined* - подвергнутый механической обработке;

4. castings* - отливка;

5. moulds * - литейная форма;

6. annealed* - отожжённый;

7. abrasion* - шлифовка.

I.2 Answer the questions to the text “Cast iron”.

1. What is the difference between ferrous and non-ferrous metals?

2. What properties does pure iron possess?

3. Why is cast iron more useful for industrial purposes?

4. What kind of alloy is grey cast iron?

5. Does it differ in any kind of properties from cast iron? And from pure iron?

6. What is “white” iron?

7. Why it is desirable to use “white” iron in machines that require resistance to abrasion?

I.3 Choose the correct ending to the following statements.

1. Ferrous metals contain …

a. iron b. steel c. copper

2. Pure iron is …

a. soft and weak b. ductile and elastic c. heavy and hard

3. Cast iron and steel are alloys of ….

a. manganese and iron b. iron and carbon

c. ferrum and copper

4. Cast iron is … of all the ferrous metals.

a. the most expensive b. the most popular c. the cheapest

5. Grey cast iron has got its name because of special ….

a. taste, colour and weight b. colour, shape and structure

c. colour and fracture

6. Grey cast iron is usually used for the parts do not to be subjected to great ….

a. high and low temperatures b. tensile stresses

c. tension and load

7. “White” cast iron is usually malleable before …

a. casting b. annealing c. melting

8. “White” cast iron is desirable to use in these machines which require some

a. resistance to abrasion b. heat resistance

c. resistance to wear

I.4 Prove the sentences with the help of the text

1. Pure iron is seldom used as an engineering material.

2. It is usually combined with other chemical elements.

3. Steel and cast iron differ from each other by their chemical composition.

4. Carbon is the basic alloying element.

5. Grey cast iron is a specific kind of ferrous alloys.

6. Malleable iron is the most workable alloy.

7. “White” iron requires special environment to use.

I.5 Complete the chart according to the text. Get ready to comment on its contents. Use the word-groups;

Pure iron

+ Carbon, silicon, phosphorous

… iron

Grey … M… iron

W… iron

I.6 Make a report on the problem of ferrous metals and their use in modern industry.

Section IV

Дата добавления: 2015-10-30