I. Reading Activity and Speech Practice. Text B:Steel and its Alloys

I.1 Read the text given below and find in it the following information:

· kinds of alloys;

· constituencies of steel;

· alloying elements;

· properties of alloy steels;

· names of the technological processes mentioned in the text.

The value of alloys was discovered in very ancient times; brass (copper and zinc) and bronze (copper and tin) were especially important. Today the most important are alloy steels, which have a lot of special characteristics.

The most important metal in industry is iron and its alloy steel. Pure iron is soft, ductile and malleable, useful only as an ornamental material. However, the addition of carbon hardens it greatly and changes its properties. Steel is known as an alloy of iron and about 2% or less carbon. It is strong, stiff, but corrodes easily through rusting, although stainless and other special steels resist corrosion. The amount of carbon in

a steel influences its properties considerably. Steels of low carbon content (mild steels) are quite ductile and are used in the manufacture of sheet iron, wire, and pipes. Medium-carbon steels containing from 0.2 to

0.4 % carbon are tougher and stronger and are used as structural steels. Both mild and medium-carbon steels are suitable for forging and welding. High-carbon steels contain 0.4 to 1.5%carbon, are hard and brittle and are used in cutting tools, surgical instruments, razor blades and springs. Tool steel, also called silver steel, contains about 1% carbon and is strengthened and toughened by quenching and tempering.

Steel for special applications may contain other alloying elements besides carbon. This modifies and improves the physical properties of the base steel. For example, small percentages of nickel, chromium, manganese and vanadium may be used for strengthening steels for construction work. Heat treatment (i.e. tempering) and mechanical working at cold and hot temperatures may also give steel alloys superior qualities, such as strength, hardness, toughness, wear resistance, corrosion resistance, electrical resistivity and workability.

The inclusion of other elements affects the properties of the steel. Manganese gives extra strength and toughness. Steel containing 4% silicon is used for transformer cores or electromagnets because it has large grains acting like small magnets. The addition of chromium gives extra strength and corrosion resistance, so we can get rust-proof steels. Heating in the process of carbon or nitrogen-rich materials is used to form a hard surface on steel (case-hardening). High-speed steels, which are extremely important in machine-tools, contain chromium and tungsten plus smaller amounts or vanadium, molybdenum and other metals.

Steel making processes are known as melting, purifying (refining) and alloying at about 2,900 ºF

(1,600 Cº). Molten steel may be first cast into ingots. Later ingots are worked into finished products. This may be done by two major methods: hot-working and cold-working. The latter is generally used for making bars, tubes, sheets, and strips. Molten steel may also be cast directly into products.

II.2 Choose the right option to complete the sentences.

1. Steel is a general name for ….

a. non- metals b. ferrum c. iron-and carbon alloys

2. Pure iron is used ….

a. as an ornamental material b. for construction work

c. in machine tools

3. Physical properties of iron may be modified by the addition of ….

a. iron ore b. hydrogen c. carbon

4. Steel for special applications usually contains ….

a. carbon b. various alloying elements c. vanadium

5. Heat treatment and mechanical working at cold and hot temperatures result in … of steel.

a. a different carbon content b. better qualities

c. finished products

6. Melting, purifying and alloying are stages of steel ….

a. cold-working b. refining c. making

7. Bars, wire, tubes, sheets, and strips are the results of ….

a. melting steel b. hot-working c. cold-working

III.3. a Consider the advantages and disadvantages of various steels carefully; use the information given in the text.

b. Decide which steels you will use for making the objects named below.

Knives, nails, hammers, cables, automobile bodies, ships, containers, machine tools, bank vaults,

aircraft undercarriages.

IV.4 Explain how you understand the following statements from the text.

1. The most important metal in industry is iron and its alloy – steel.

2. Steel is known as an alloy of iron.

3. Steel for special applications may contain different alloying elements beside carbon.

4. There are different steel making processes known in modern metallurgy.

IV.5 Choose any of the following situations and get ready to speak on it.