Explain what each of the following are and how each can be m

Solution

>> Bainite

Bainite is a plate-like microstructure or phase morphology (not an equilibrium phase) that forms in steels at temperatures of 250–550 °C (depending on alloy content)

A fine non-lamellar structure, bainite commonly consists of cementite and dislocation-rich ferrite. The high concentration of dislocations in the ferrite present in bainite makes this ferrite harder than it normally would be.

Bainite is an intermediate of pearlite and martensite in terms of hardness. For this reason, the bainitic microstructure becomes useful in that no additional heat treatments are required after initial cooling to achieve a hardness value between that of pearlitic and martensitic steels

How it is made

it is one of the decomposition products that may form when austenite (the face centered cubic crystal structure of iron) is cooled past a critical temperature. This critical temperature is 1000K (727 °C, 1340 °F) in plain carbon steels.

>> Coarse Pearlite

The more coarse the Pearlite, the more the layers will be able to stretch out, and the more ductile it\'ll be.

Pearlite is a microstructure occuring in Steel. It consists of alternating layers of Iron in Body Centered Cubicstructure (Ferrite), and Fe₃C (Cementite).

It is called Pearlite because of the fact that when viewed under low magnification, it looks a bit like mother of pearl.

How it is made

Firstly take some Austenite, basically any steel above 727C, and let it cool. Pearlite will only be formed if it\'s allowed to cool between 540C and 727C. At the lower temperature, it forms quite quickly, within 10 seconds. At the higher temperatures, it can take quite a bit longer, taking longer the closer it is to 727C.

To form Coarse Pearlite you have to stick it in another furnace, one that is kept between 600-700C.

>> Fine Pearlite

The finer the layers making up the Pearlite, the more they\'re going to resist slipping relative to each other, and the stronger the Steel is going to be.

How it is made

Firstly take some Austenite, basically any steel above 727C, and let it cool. Pearlite will only be formed if it\'s allowed to cool between 540C and 727C. At the lower temperature, it forms quite quickly, within 10 seconds. At the higher temperatures, it can take quite a bit longer, taking longer the closer it is to 727C.

Finer Pearlite is formed at lower temperatures than Coarser Pearlite, and thus it has to be cooled down quicker than the Coarse. Generally, if you wish to form Fine Pearlite, simply pulling it out of the furnace and letting it cool in the air will be sufficient

>> Speroidite

Annealing of pearlitic or bainitic microstructures at elevated temperatures just below eutectoid (e.g. 24 h at 700 C) leads to the formation of new microstructure – spheroidite - spheres of cementite in a ferrite matrix.

Composition or relative amounts of ferrite and cementite are not changing in this transformation, only shape of the cementite inclusions is changing.

Driving force for the transformation - reduction in total ferrite - cementite boundary area