Text C: «METALWORKING AND METAL PROPETIES» An importantfeature of hot working is that itprovides theimprovement of mechanicalproperties of metals . Hot-working (hot-rolling or hot-forging)eliminates porosity, directionality, andsegregation that are usually present in metals. Hot-worked products have better ductility and toughness than the unworkedcasting. During the forging of a bar, the grains of the metal become greatlyelongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction andweakened in directionstransverse to the flow. Good forging makes the flow lines in thefinishedpart 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 frominner flaws in the metal. These flaws often consist of nonmetallicinclusions such as oxides or sulfides that aretrapped in the metal duringrefining. Such inclusions can beavoided by proper manufacturing procedures.
The ability of different metals toundergo strain varies. The change of the shape after one forming operation is often limited by thetensile ductility of the metal. Metals such as copper and aluminum are more ductile in such operations than other metals.
General understanding:
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?
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 a metal fracture because of the inner flaw?
8. What limits the change of the shape during forming operations?
Exercise 2.5. Find the following in the text:
1. важная особенность горячей обработки
2. улучшение механических свойств металла
3. необработанная отливка
4. направление максимального напряжения
сопротивляться утончению и разрушению
6. проявлять большее деформационное упрочнение
7. разрушение детали при штамповке
8. внутренние дефекты в металле
9. неметаллические включения
металлов подвергаться деформации
11. ограничивается пластичностью металла при растяжении
Exercise 2.6. Translate into English:
1. Горячая обработка металла улучшает его механические свойства и устраняет пористость и внутренние дефекты.
2. Удлинение зерен в направлении текучести при ковке значительно улучшает прочность металла в этом направлении и уменьшает его прочность в поперечном.
3. Хорошая проковка ориентирует линии текучести в направлении максимального напряжения.
4. Деформационное упрочнение металла при холодной обработке очень важно для получения металлов с улучшенными свойствами.
