Материаловедение: свойства металлов. Матросова Т.А - 45 стр.

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45
Normalizing may be done to improve machinability, to refine the grain
structure, and to homogenize the part. For example, homogenization of steel
castings may be done in order to break up or refine the dendritic cast structure and
facilitate a more uniform response to subsequent heat treatment. In the case of
wrought products, normalization can reduce large grain size where large and small
grains exist, thus developing a more uniform grain structure. Toughness can be
increased. This is frequently desirable in the use of "as-rolled" medium carbon
steels.
A broad range of ferrous products can be
normalized. All of the standard, low-, medium-, and
high-carbon wrought steels can be normalized.
Stainless steels, austenitic, and maraging steels are
not usually normalized. The normalizing may increase
or decrease the strength and hardness of a given steel
depending on the carbon content and the thermal and
mechanical history of the part.
Gears, bolts, nuts, washers, and other parts in
which low distortion is an important criterion should
be made in the following general operation sequence:
rough machine, normalize, finish machine,
carburize, heat treat, grind.
Spheroidizing produces globular carbides in a ferritic matrix. The iron-base
alloy is held for a prolonged period of time (10 to 12 hours) at a temperature near but
slightly below the A, temperature, and then slowly cooled (furnace-cooled). A
spheroidized steel (fig. 16.1.) has minimum hardness and maximum ductility. The
structure improves machinability markedly. Normalized steels are one of the better
starting spheroidized materials because their fine initial carbide size accelerates
spheroidization.
Glossary
№ English word Translation
1. normalizing нормализация
2. heating нагрев
3. iron-based на основе железа
4. alloy сплав
5. upper верхний
6. iron-carbon железо-углерод
7. phase diagram фазовая диаграмма
8. cooling охлаждение
9. still спокойный
10. ordinary обычный
11. relieve снимать
Fig. 16.1. The microscopic
structure called spheroidite

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