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Quenching is a heat treatment when metal at a high temperature is rapidly cooled by immersion in water or oil. Quenching makes steel harder and more brittle, with small grains structure.

Tempering is a heat treatment applied to steel and certain alloys. Hardened steel after quenching from a high temperature is too hard and brittle for many appli­cations and is also brittle. Tempering, that is re-heating to an intermediate temperature and cooling slowly, re­duces this hardness and brittleness. Tempering tempera­tures depend on the composition of the steel but are fre­quently between 100 and 650 °C. Higher temperatures usually give a softer, tougher product. The color of the oxide film produced on the surface of the heated metal often serves as the indicator of its temperature.

Annealing isa heat treatment in which a material at high temperature is cooled slowly. After cooling the metal again becomes malleable and ductile (capable of being bent many times without cracking).

All these methods of steel heat treatment are used to obtain steels with certain mechanical properties for cer­tain needs.

Vocabulary:

to immerse — погружать

to apply — применять

intermediate — промежуточный

oxide film — оксидная пленка

annealing — отжиг, отпуск

cracking — растрескивание

 

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Exercise 1. Answer the questions:

1. What can be done to obtain harder steel?

2. What makes steel more soft and tough?

3. What makes steel more malleable and ductile?

4. What can serve as the indicator of metal tempera­ture while heating it?

5. What temperature range is used for tempering?

6. What are the methods of steel heat treatment used for?

 

Exercise 2. Translate into English the following words and word combinations:

1. температура нормализации

2. мелкозернистая структура

3. быстрое охлаждение

4. закаленная сталь

5. состав стали

6. окисная пленка

7. индикатор температуры

8. медленное охлаждение

 

 

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Чётко указываем группу,  фамилию, номер темы (на листке с заданиями).

ТЕМА 4 METALWORKING(1) (Работа с металлом)

 

Прочитайте слова, постарайтесь запомнить их перевод.

1. useful — полезный

2. shape — форма, формировать

3.rolling — прокатка

4.extrusion — экструзия, выдавливание

5.drawing — волочение

6.forging — ковка

7.sheet — лист

8.to subject — подвергать

9.amount — количество

10.condition — состояние, условие

11.perform — выполнять, проводить

12.to harden — делаться твердым, упрочняться

13.at least — по крайней мере

14.common — общий

15.billet — заготовка, болванка

16.orifice — отверстие

17.die — штамп, пуансон, матрица, фильера, во­лочильная доска

18.cross section — поперечное сечение

19.window frame — рама окна

20.tube — труба

21.hollow — полый

22.initial — первоначальный, начальный

23.thick-walled — толстостенный

24.mandrel — оправка, сердечник

25.impact — удар

26.loosely — свободно, с зазором

27.fitting — зд. посадка

28.ram — пуансон, плунжер

29.force — сила

30. gap — промежуток, зазор

31. to determine — устанавливать, опреде­лять

 

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«METALWORKING PROCESSES»

Metals are important in industry because they can be easily deformed into useful shapes. A lot of metalworking processes have been developed for certain applica­tions. They can be divided into five broad groups:

Rolling,

Extrusion,

Drawing,

Forging,

Sheet-metal forming.

During the first four processes metal is subjected to large amounts of strain (deformation). But if deformation goes at a high temperature, the metal will recrystallize — that is, new strain-free grains will grow instead of deformed grains. For this reason metals are usually rolled, ex­truded, drawn, or forged above their recrystallization temperature. This is called hot working. Under these conditions there is no limit to the compressive plastic strain to which the metal can be subjected.

Other processes are performed below the recrystalli­zation temperature. These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks.

Rolling

Rolling is the most common metalworking process. More than 90 percent of the aluminum, steel and copper produced is rolled at least once in the course of produc­tion. The most common rolled product is sheet. Rolling can be done either hot or cold. If the rolling is finished cold, the surface will be smoother and the product stronger.

Extrusion

Extrusion is pushing the billet to flow through the orifice of a die. Products may have either a simple or a complex cross section. Aluminum window frames are the examples of complex extrusions.

Tubes or other hollow parts can also be extruded. The initial piece is a thick-walled tube, and the extruded part is shaped between a die on the outside of the tube and a mandrel held on the inside.

In impact extrusion (also called back-extrusion) (штамповка выдавливанием), the workpiece is placed in the bottom of a hole and a loosely fitting ram is pushed against it. The ram forces the metal to flow back around it, with the gap between the ram and the die determin­ing the wall thickness. The example of this process is the manufacturing of aluminum beer cans.