Hardening and tempering

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SUPPLEMENTARY TEXTS FOR READING

Текст А

Read the additional text about metals and retell it in Russian.

Read and translate the following sentences with Participle II.

Independent tasks

Read Text E again. Answer the questions without looking into the text.

1) When did people begin to use metals?

2) Why are metals the most important engineering materials?

3) What three most useful engineering properties do metals combine?

4) What was the first metal produced by people?

5) How will you call metals which are used in industry?

6) What is the most important engineering metal?

7) In what form are engineering metals most often used in industry?

8) What metal is largely used in the form of a simple metal?

1) Metals have served man to create new machines.

2) The first definition of metals was given by M.V. Lomonosov.

3) Metals have found wide application because of their properties.

4) There are some classifications of metals based on their properties and composition.

5) An alloy is a simple metal combined with some other elements.

6) Some metals are called refractory metals.

7) Metals are found in the form of ores.

8) There are many methods used to separate metals from ore.

9) Impurities are separated and removed as slag.

10) About two thirds of all elements found in the earth are metals.

11) Cast iron is produced in cupolas.

12) Ore is a metal combined with some impurities.

13) Metals used in industry are called engineering metals.

There are many superstitions (суеверий) about iron. The Romans (римляне) believed, if you drew (рисовать, проводить) three circles in the air around anyone and three on the ground with a bit (кусочек) of iron, that person would be bewitched (заколдован). It is interesting to note that wedding rings (обручальные кольца) in Ancient Rome were made of iron.

We find a lot of superstitions among the Creeks and the Egyptians. But we do not have to go back to Roman days for curious superstitions and beliefs (поверий). We can find them nowadays (today). There is still a superstition among some people to-day about horseshoes (подковы). They believe that horseshoes bring good luck or bad luck. Though people were superstitions about iron it turned out (оказалось) to be a much better metal for making tools than bronze. And so the Bronze Age gave ways to the Age of Iron.

Hardening means making harder. Steel which contains more than 0.75 per cent carbon becomes very hard and very brittle when hardened. High carbon steel is hardened by carrying out the following operations. The steel is first slowly heated to a proper temperature. Having been heated to red color, it is then rapidly cooled in oil, water, brine or some other liquid. The process of cooling is called quenching the steel, thus the hardening operation consists of heating and quenching. Alloy steels are usually hardened by special ways. The hardness produced by heat treatment depends upon the: 1) amount of carbon in steel; 2) temperature of heated steel; 3) speed of cooling.

The critical temperature, or critical point, is the temperature at which a piece of steel is properly hardened. When steel is heated to the critical temperature, the grain becomes very fine, that is the crystals get smaller, some other changes in the physical properties of steel take place, too, in this condition. The critical temperature is different for different kinds of steel. It depends upon the amount of carbon in steel. The more carbon the steel contains, the less it should be heated for hardening. In other words, the more carbon the steel contains, the lower is the critical point. The critical temperature may be tested with a magnet. Steel is magnetic until it reaches the critical temperature, then it is non-magnetic. Thus, a piece of steel to be hardened may be heated until it becomes non-magnetic; it should be then rapidly cooled (quenched).

Temper is the hardness, toughness and brittleness of a metal. Tempering, also called drawing the temper, means taking some of the hardness and brittleness out of hardened steel so that it could do good work. Having been tempered, the steel becomes stronger because its grain gets finer; as we already know, steel with a coarse grain is weaker than steel with a fine grain. Hardened steel is too hard and too brittle for many tools. A hardened cutting tool will break easily while cutting with it; it is therefore better to have a cutting tool tough and not too hard. Tempering brings about this condition.

Having hardened the steel, it is polished and heated. The different temperatures will show in the form of different colors on the polished surface. Each temperature or color is a different hardness or temper. The temperatures for tempering are from 400 to 600 degrees of Fahrenheit. When the right color appears, the steel is cooled (the speed of cooling is not important here). Thus the steel is a little softened and will be tougher and less brittle.

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