Quenching is a heat treatment when metal at a high temperature is rapidly cooled by immersion in water or oil. Quenching makes steel harder and more brittle, with small grains structure.
Tempering is a heat treatment applied to steel and certain. Hardened steel after quenching from a high temperature is too hard and brittle for many applications and is also brittle. Tempering, that is re-heating to an intermediate temperature and cooling slowly, reduces this hardness and brittleness. Tempering temperatures depend on the composition of the steel but are frequently between 100 and 650 C. Higher temperatures usually give a softer, tougher product. The colour of the oxide film produced on the surface of the surface of the heated metal often serves as the indicator of its temperature.
Annealing is a heat treatment in which a material at high temperature is cooled slowly. After cooling the metal again becomes malleable and ductile (capable of being bent many times without cracking).
All these methods of steel heat treatment are used to obtain steels with certain mechanical properties for certain needs.
Additional vocabulary:
to immerse – погружать
intermediate – промежуточный
oxide film – оксидная пленка
annealing – отжиг, отпуск
quenching – закалка охлаждением
tempering – отпуск после закалки, нормализация
Questions:
- What can be done to obtain harder steel?
- What makes steel more soft and tough?
- What makes steel more malleable and ductile?
- What can serve as the indicator of metal temperature while heating it?
- What temperature range is used for tempering?
- What are the methods of steel heat treatment used for?
Translate into English the following words and word combinations:
- температура нормализации
- мелкозернистая структура
- быстрое охлаждение
- закаленная сталь
- состав стали
- оксидная пленка
- индикатор температуры
- медленное охлаждение
Complete the following sentences:
- Tempering is a heat treatment applied…
- Hardened steel after quenching from a high temperature is too hard and…
- Higher temperatures usually give…
- After cooling the metal again becomes…
- All these methods of steel heat treatment are used to obtain steels…
Text 4.
HOT WORKING OF STEEL
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 if 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 facture 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 cal 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.
Additional vocabulary:
feature – черта, особенность
to provide – обеспечивать
improvement – улучшение
porosity – пористость
directional – направленный
to segregate – разделять
casting – отливка
elongated – удлиненный
to weaken – ослабевать, ослаблять
transverse – поперечный
flow – течение, поток
finished – отделанный
thinning – утончение
strain hardening – деформационное упрочнение
brass – латунь
beverage – напиток
can – консервная банка
to exhibit – проявлять
inner – внутренний
inclusion – включение
trapped – заключенный
refining – очищать, очистка
tensile ductility – пластичность при растяжении
Questions:
- What process improves the mechanical properties of metals?
- What new properties have-worked products?
- How does the forging of a bar affect the grains of the metal? What is the result of this?
- How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?
- What are the best strain-hardening alloys? Where can we use them?
- What are the inner flaws in the metal?
- Can a metal fracture because of the inner flaw?
- What limits the change of the shape during forming operations?
Find the following in the text:
- важная особенность горячей обработки
- улучшение механических свойств металла
- необработанная отливка
- направление максимального напряжения
- способность сопротивляться утончению и разрушению
- проявлять большее деформационное упрочнение
- разрушение детали при штамповке
- неметаллические включения
- способность металлов подвергаться деформации
- ограничивается пластичностью металла при растяжении
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.
5. Внутренние дефекты металла – это неметаллические включения типа оксидов или сульфидов.
6. Изменение формы при штамповании металлических деталей ограничивается пластичностью металла при растяжении.
THEME 3