Материаловедение: свойства металлов. Матросова Т.А - 51 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

51
As austenite is cooled, the carbon tends to separate from the solution and return
to its original form. However, by controlling the rate of cooling, the return to pearlite
or spheroidite may be avoided. For example, if the austenite of a 0.80 percent carbon
steel is cooled from 1500°F down to 1200°F and is then allowed to remain at 1200°F
until it transforms, it will take the form of pearlite. This steel would be quite soft,
having a Brinell hardness
of about 200. However, if
the austenite is cooled
quickly to a lower
temperature, say 600°F, it
will escape the 1200°F
transformation stage, and
will change to a structure
known as bainite, which
has a hardness of about
550 Brinell. If the
austenite is cooled to a
still lower temperature,
for example 250°F,
before transformation takes place, the very hard structure known as martesite will be
formed. Martensite gives a Brinell of about 650.
An important rule that the production engineer should keep in mind is that,
when forming any particular transformation product, the steel must escape
transformation at a higher temperature. If this is not observed, then the desired
transformation product will not be achieved. From the foregoing, it can be seen that a
hardened piece of steel takes the form of martensite or bainite. The formation of
pearlite must be avoided. Thus, the process of heat treating involves first heating and
soaking at the correct temperature, then cooling the steel rapidly enough to avoid the
formation of pearlite, and finally holding at the desired temperature to form either
bainite or martensite.
Glossary
№ English word Translation
1. microstructure микроструктура
2. heat-treating термическое (-ий)
3. equipment оборудование
4. heating нагрев
5. steel сталь
6. quenching закалка
7. tempering отпуск
8. production engineer технолог
9. accurate точный
Fig. 18.1. The microistructure of pearlite (left) and austenite

Страницы