Unit 3 (Total Score – 14 points)

I. Прочитайте текст и скажіть, чому нагрів стали є важливим у процесі кування.

The Importance of Heating Steel in Forging Practice (Score – 6 points)

If a piece of steel is heated, it becomes softer and its tensile strength is reduced, and, at the sаmе time, its plasticity, and, consequently, its malleability, are increased.

As a result of improper heating practices and insufficient furnace productivity, a considerable loss of efficiency of. forging units can still be observed in a number of forging plants because of the time lost in waiting for the steel to reach the required temperature. Moreover, this so-called heating waiting time is sometimes included in the time specified for producing the forging. But innovators in industry have proved that, by improving the organization of furnace operations, the time lost by forging units – the so-called "hot-metal waiting time" – can be completely eliminated.

As a rule, the productivity of a furnace should be from 15 to 20 per cent greater than that of the forging unit with which it operates, so as to be able to "speed up" the latter.

Heating the metal is one of the main operations in forging practice and is considered as being of equal importance with the forging operation itself.

Proper heating and forging result in the lightening of the work of blacksmiths and forge hammer operators and ensure high efficiency of the forging installations. At the same time, power (steam, compressed air and electricity) and fuel can be economized, ensuring high quality of the forgings and reducing their cost.

П. Дайте відповіді на такі питання:

1. When does a piece of steel become softer? (Score – 2 points)

2. In the result of what can the considerable loss of efficiency of forging units still be observed?

Ш. Складіть анотацію до тексту. (Score – 6 points)

(Total Score – 14 points)

Unit 4 (Total Score – 16 points)

I. Прочитайте текст и намагайтесь зрозуміти його зміст. Дайте опис процесу ковальської зварки. (Score – 6 points)

Forge Welding

Forge Welding is a process whereby two pieces of metal heated to a plastic condition, are joined together under external pressure. Steel being heated to a definite temperature, becomes highly plastic; if the temperatures of two pieces of steel is raised until their surfaces become pasty, and they are then pressed or hammered, they will be welded, i.e., form a single piece of steel.

If two pieces of steel are properly welded together, the tensile strength of the resulting single piece of steel at its welded joint must be equal to that of the parent metal, that is, to the tensile strength of either or its two separate pieces.

As a matter of fact, however, it is impossible to attain a perfectly close contact of all the particles of the steel being welded; and for this reason, the tensile strength of a welded piece of work at its joint is usually less than that of its two separate components.

Welding is employed chiefly when the forging of a whole piece of work presents difficulties. In such cases, separate parts of work are forged and then welded together. Welding is also widely practiced in repairing operations

Forge welding consists of the following separate opera­tions: (1) preparing the ends of the pieces to be welded together; (2) heating them for welding; (3) welding the ends together; (4) hammering and finishing the weld joint. The weld joint must be thoroughly hammered. In order to retain the same cross-section of the work after welding and hammering, the ends of the pieces to be welded must be first upset and then hammered, depending on the welding method employed. After the ends have been prepared for welding, they must be heated to the welding temperature.

This is usually done in the forges or in special welding furnaces. As a rule, forge furnaces are not suitable for heating steel for welding and are unable to ensure the required welding temperature. The best fuels for weld heating are charcoal and coke.

Welding temperatures range from 1,275 to 1.400°C, i.e. they are considerably above the initial temperature of ordinary forging. This high temperature ensures the better joining of the parts being welded.

The welding temperature depends on the chemical composition of the steel: the greater the content of carbon and alloying elements in the steel, the lower must its welding temperature be. The heating of steel to be welded demands considerable attention and care. It is absolutely necessary that the places to be welded together are free of scale, slag, etc., i.e., the surfaces of the steels to be welded must be absolutely clean.

Not all metals possess what is called weldability. For instance, lead cannot be welded. By no means do all steels possess good weldability. The less alloying element in a steel, the better it welds. Pure iron is highly weldable, but any alloy­ing element lowers this property. The higher the carbon content, the poorer the weldability of a steel. The weldability of steel likewise decreases with the increase of the phosphorus, sulphur, chromium and copper content, etc.

A manganese content up to 0.6-0.8 per cent improves weldability, and for this reason manganese steels intended for welding may have an increased carbon content.

П. Дайте відповіді на наступні питання: (Score – 4 points)

1. What is a forge welding?

2. When does the steel become plastic?

3. What welding operations do you know?

4. What does the welding temperatures depend on?

5. What; is necessary for the correct welding of the surfaces?

Ш. Розкажіть, що ви знаєте про "weldability". Які метали мають ії та що сприяє цьому. (Score – 6 points)

(Total Score – 16 points)