Hot Working of Steel

Text C

VII. Oral Practice

Ex. 19. Make up a plan to the text.

Ex. 20. Explain:

1. why carbon is the most important element;

2. when people began making things from metal;

3. what is called alloys.

VIII. Reading and comprehention.

Ex.21. Read the text without a dictionary for 5 minutes:

An important feature of hot working is that it provides the improvement of mechanical properties of metals. Hot-working (hot –rolling or hot - forging) eliminates porosity, directionality, and segregation that are usually present in metals. Hot –worked products have better ductility and toughness than the unworked casting. During the forging of a bar, the grains of the metal become greatly elongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakened in directions transverses to the flow. Good forging makes the flow lines in the finished part oriented so as to lie in the direction of maximum stress when the part is placed in service.

The ability of a metal to resist thinning and fracture during cold – working operations plays an important role in alloy selection. In operations that involve stretching, the best alloys are those which grow stronger with strain (are strain hardening) – for example, the copper – zinc alloy, brass, used for cartridges and the alumunium- magnesium alloys in beverage cans, which exhibit greater strain hardening.

Fracture of the workpiece during forming can result from inner flaws in the metal. These flaws often consist of nonmetallic inclusions such as oxides or sulfides that are trapped in the metal during refining. Such inclusions can be avoided by proper manufacturing procedures.

The ability of different metals to undergo strain varies. The change of the shape after one forming operation is often limited by the tensile ductility of the metal. Metals such as copper and aluminium are more ductile in such operations than other metals.

Notes:

Feature – особливість

porosity - пористість

flow – течія, потік

thinning – витончений (утонченный)

strain hardening – деформаційне укріплення (Деформационное упрочнение)

brass – латунь

to exhibit – проявляти (проявлять)

refining – очищення, очистка (очищение)

to segregate – розділяти

transverse–поперечний

tensile ductility – пластичність при розтягуванні

Ex. 22 Agree or disagree with the following statements:

1. Hot –worked products have better ductility and toughness than the unworked casting.

2. During the forging and welding of a bar, the grains of the metal become greatly elongated in the direction of flow.

3. The ability of a metal to resist thinning and fracture during hot – working operations plays an important role in alloy selection.

4. The best alloys are those which don’t grow stronger with strain.

5. Fracture of the workpiece during forming can result from inner flaws in the metal.

6. The ability of the metals from one group to undergo strain varies.

Ex.23. Answer the questions:

1. What process improves the mechanical properties of metals?

2. What new properties have hot – worked products?

3. How does the forging of a bar affect the grains of the metal? What is the result of this?

1. 4. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?

4. What are the best strain – hardening alloys? Where can we use them?

5. What are the inner flaws in the metal?

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