Page 125 - SSAB Welding Handbook Edition 2

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Welding handbook 21.0 Microstructures in the heat affected zone (HAZ) and the unaffected parent metal

The picture to the left in fig. 21.3 represents upper
bainite where the iron carbides are formed between
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ferrite formations. A bainitic structure with a more
finely distributed carbide formation that has many
different orientations supports a higher toughness
than a structure with larger carbide formations and
fewer orientations. The bainite type to the right in
fig. 21.3 is called lower bainite.

Upper banite Lower banite

Fig. 21.3: Illustration of bainite. Gray sections represent ferrite and
orange sections represent carbides.

Upper bainite is established at higher temperatures
during the cooling process than lower bainite. The
different types of bainite are often mixed in the
microstructure. Work has been carried out to
divide bainite into more subgroups. However,
upper and lower bainite are the most established
methods for dividing bainite into subgroups.

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all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications. 125
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.