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Read the text and say what mechanical properties of materials depend on.




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 transverse 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 aluminum-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 aluminum are more ductile in such operations than other metals.

2. Find the following words and word-combinations in English in the text: важлива особливість; гаряче прокатування; гаряче кування; присутні у металах; продукція гарячої обробки; необроблений відливок; напрямок потоку; поперечний; оброблена деталь; здатність металу; вибір сплаву; розтягування; бляшанки з-під напоїв; неметалеві складові; належні виробничі процеси; зміна форми; обмежений.

3.Answer the following questions to the text.

1. What process improves the mechanical properties of metals?

2. What new properties do hot-worked products have?

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

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

5. What are the best strain-hardening alloys? Where can we use them?

6. What are the inner flaws in the metal?

7. Can the metal fracture because of the inner flaws?

8. What limits the change of the shape during forming operations?







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