МИНИСТЕРСТВО ОБЩЕГО И ПРОФЕССИОНАЛЬНОГО ОБРАЗОВАНИЯ РОССИЙСКОЙ ФЕДЕРАЦИИ

ВОЛГОГРАДСКИЙ ГОСУДАРСТВЕННЫЙ ТЕХНИЧЕСКИЙ УНИВЕРСИТЕТ

Кафедра иностранных языков

METALS AND ALLOYS

Методические указания по английскому языку для студентов II курса факультета ФТКМ всех специальностей. Часть II.

РПК “Политехник”

1999

Unit III. Heat Treatment of Steel

Vocabulary

tempering отпуск

to relieve stresses снимать напряжение

to refine очищать от примесей, улучшать структуру

to reduce понижать, уменьшать

furnace печь

to range колебаться в известных пределах

tensile strength прочность на разрыв

yield point предел текучести

charge загрузка (печи)

ductility пластичность

distortion искажение, деформация

crystal lattice кристаллическая решетка

to eliminate устранять, ликвидировать

casting отливка

impact strength ударная вязкость

quenching закаливание (при быстром охлаждении)

tool steel инструментальная сталь

wear resistance износоустойчивость, сопротивление износу

Exercise 1. Choose the correct Russian equivalents to the English terms:

1. tensile strength 1 инструментальная сталь

2.crystal lattice 2. искажение, деформация

3. tempering 3. очищать от примесей, улучшать структуру

4.to reduce 4. прочность на разрыв

5.tool steel 5. кристаллическая решетка

6. to refine 6. понижать, уменьшать

7.distortion 7. отпуск

Exercise 2. Read and translate the verbs meaning repetition:

reuse; reappear; reread; replace; restart; rewrite; review; return; rearrange.

Exercise 3. Choose the correct English equivalents to the Russian terms:

I.малоуглеродистая сталь 1. charge

2. износоустойчивость 2. to eliminate

3. колебаться в известных пределах 3. yield point

4. ударная вязкость 4. low - carbon steel

5. предел текучести 5.to range

5. устранять, ликвидировать 6. wear resistance

6. загрузка (печи) 7. impact strength

Exercise 4. Read and translate the words meaning negation:

unusual; unlimited; unseparated; unsatisfactory; independent; indirect; impossible; disadvantage; regardless; useless.

Exercise 5. Translate the following word combinations:

to relieve internal stresses, a cooling rate, to reduce the distortions of the crystal lattice, to have a higher yield point, to improve mechanical strength, to retain ductility, to reduce brittleness.

Exercise 6. Translate the words of the same root. Define speech parts:

form-formation- former-formerly;- heat-heated-heating-heater; crystal- crystallize-crystallization- recrystallization- crystallography; cool-cooling-coolant-coolness; to apply-application-applied-applicable-appliance; to resist-resislance-resistanl-resistor; to quench-quenching-quenched-quenchant.

Exercise 7. Choose the correct terms:

1. Any operation or operations of 1. Work- hardening heating metal and cooling it in order to bring out

desired physical properties.

2.Reheating steel after the quenching 2. High- carbon steel operation to some temperature below

the critical range to produce desired physical properties.

3.The increase in hardness due to inelastic 3. Heat treating deformation below the recrystallization

temperature.

4.Steels having a carbon content of 0.5 4. Tempering. per cent or over.

Exercise 8. Translate the sentences into Russian and observe the different ways of expressing obligation:

1. Steel has to be widely used in engineering because of its high strength.

2. Forging should be carried out under the temperature above the critical temperature of (the metal.

3. Chromium and tungsten are to increase the hardness and strength of steel.

4. This specimen is to be subjected to the process of annealing and recrystallization in order to soften it

5. Special alloy steels can be used for parts requiring great wear resistance.

TEXT A

Steel undergoes heat treatment to improve its structure and to obtain higher or specified mechanical properties.

Heat treatment is the process of changing the structure of a metal by heating it to a predetermined temperature, holding it at this temperature for a prescribed period of time and cooling it at a prescribed rate¹.

The types of heat treatment applied in practice are: (1) annealing, (2) normalization, (3) hardening and (4)-tempering.

Annealing is one of the most important heat treating operations applied to steel. It relieves internal stresses in the metal, refines the grain and reduces the hardness. After annealing, steel becomes more plastic and ductile.

After the required heating temperature is achieved in annealing the metal is held for a certain time in the furnace to enable the required changes to take place throughout the mass of the workpiece.² This holding time³ in the furnace at the annealing temperature usually ranges from 30 to 60 minutes per ton of the charge.

The metal is commonly cooled, after heating and holding, with the furnace , a cooling rate from 150 to 200 deg С per hour is regular practice.

If the steel is subjected to cold working to increase the tensile strength and yield point but at the same time becomes work-hardened and brittle (loses its ductility), so-called recrystallisation, or process annealing is applied. Its purpose is to reduce the distortion of me crystal lattice produced by cold working.

Recrystallisation annealing consists in heating the steel to a temperature of about 600-700 °C, holding at this temperature for a prolonged period and slow cooling.

This treatment transforms the grains of steel, broken up or distorted in the process of deformation, back into their normal state (by recrystallisation) thus removing work-hardening and relieving internal stresses.

Л special highly efficient annealing process, called normalizing, is sometimes used for the elimination of internal stresses in steel and for its recrystallisation. It has essentially the same purposes as conventional annealing and, therefore, the structure of the steel after normalizing is similar to the structure of annealed steel.

Normalized steel castings have a higher yield point, tensile strength than if they were' annealed. Since normalizing requires less time than conventional annealing it is extensively replacing the conventional annealing in treating low- and medium-carbon steels. High-carbon steels undergo normalizing to eliminate the cementite (carbide) network.

The heat-treating process applied to impart high hardness to steel, to improve its mechanical strength and to retain its ductility comprises two operations- hardening and tempering.

al a prescribed rale- по заданному режиму throughout the mass of the workpiece - no всему сечению изделия ' This holding time... - Эта выдержка (в печи)

with the furnace - одновременно с охлаждением печи

Steel is hardened by heating to a temperature above the upper or lower critical point, holding at this temperature and quenching (rapid cooling). After quenching, a martensite structure is obtained or other transitional forms of austenite, for example, martensite + troostite.

Directly after quenching, the steel acquires a high hardness but, at the same time, high internal stresses develop in the steel and it becomes brittle. The next heat- treating operation-tempering—relieves the internal stresses to some extent and reduces the brittleness of the hardened steel. After hardening and tempering structural steels acquire higher strength, hardness and ductility. The purpose of hardening tool steel is to inscrease the hardness and wear resistance while retaining sufficient ductility.

Exercise 9. Make up a list of types of heat treatment of steel mentioned in the text Exercise 10. Read the text and find:

a) the definition of annealing b) the definition of hardening.

Exercise 11. Discuss the advantages and disadvantages of normalizing and conventional annealing.

Exercise 12. Define which of these statements correspond to the text. Use the expressions: that's right, that's wrong...

1. Annealing relieves internal stresses in the metal, refine the grain and reduces the hardness.

2. Normalizing requires much lime than conventional annealing.

3. The purpose of recrystallisarion is to reduce the distortions of the crystal lattice produced by cold working.

4. Tempering doesn't reduce the brittleness of the hardened steel.

Exercise 13. Answer the following questions

1. What is the purpose of heat treatment of steel?

2. How can heat-treating operations be divided?

3. What docs annealing relieve and reduce?

4. How docs the holding time in the in the furnace usually range?

5. What is the purpose of recrystallisation?

6. Does recrystallisation transform the grains of steel broken up or distorted in the process of deformation?

7. What is normalizing?

8. Why is normalizing extensively replacing the conventional annealing in treating low-and medium- carbon steels?

9. How is steel hardened?

10. What properties docs structural steel acquire after hardening and tempering?

Exercise 14. Get ready to retell the text. Make use of the answers to the above questions.

Text в

The father of the branch of science concerned with the changes in structure of steel was the Russian metallurgist Dmitry Konstanlinovich Chernov (1839-1921). Investigating the properties of steel after heating to various temperatures Chernov first established that at definite temperatures steel undergoes certain changes altering its structure and properties. These "critical temperatures" characterized by internal changes in the steel arc now known all over the world as the "Chernov points". One of these points called by Chernov point a, is notable for the fact that steel heated below this point (about 700°C) cannot be hardened no matter how rapidly it is cooled. Another point, b, is characterized by the fact mat as soon as the temperature of the steel reaches it (800 to 850°C), the steel rapidly passes from the coarse crystalline into the fine crystalline state, in which it possesses the best mechanical properties. If the temperature is raised still further, the metal crystals begin to increase again in size, and the higher the temperature, the more rapidly they grow.

The discovery of the critical points of steel was of very great importance for metallurgical theory and practice. Explaining the phenomena of tempering and hardening of steel and the structural changes taking place in steel when heated, it enabled to determine the hardening temperatures and to select the favourable conditions of forging and other types of steel treatment.

Exercise 15. Read the text and give it a suitable title. Give your reasons for the choice.

Exercise 16. Look through the text and find the definition of "Chernov points"

Exercise 17. Read the text and say:

a) what information is quite new to you b) what information you are already familiar with.

Exercise 18. Comment on this statement:

D. K. Chernov was the first who laid the foundation of the modern metallurgy and heat treatment of steel.

Exercise 19. Summarizing the information of Text A and В write an abstract using the key-patterns.

Exercise 20. Translate the following text in written form without using a dictionary:

We can alter the characteristics of steel in various ways. In the first place, steel which contains very little carbon will be milder than steel which contains a higher percentage of carbon, up to the limit of about 1,5 %. Secondly, we can heat the steel above a certain critical temperature, and then allow it to cool at different rates. At this critical temperature, changes begin to lake place in the molecular structure of the metal. In the process known as annealing, we heat the steel above the critical temperature and permit it to cool very slowly. This causes the metal to become softer than before, and much easier to machine. Annealing has a second advantage. It helps to relieve any internal stresses which exist in the metal. These stresses are liable¹ to occur through hammering or working the metal, or through rapid cooling.

On the other hand, we can make steel harder by rapid cooling. We heat it up beyond the critical temperature, and then quench it in water or some other liquid. The rapid temperature drop³ fixes the structural change in the steel which occurred at the critical temperature, and makes it very hard. But this hardened steel is more liable to ^fracture than normal steel. We therefore heat it again to a temperature below the critical temperature, and cool it slowly. This treatment is called tempering. It helps to relieve the internal stresses, and makes the steel less brittle than before. The properties of tempered steel enable us to use it in the manufacture of tools which need a fairly hard steel. High carbon steel is harder than tempered steel, but it is much more difficult to work.

Exercise 21. Make up some questions on the basis of this text and answer them.