Materials science

MARTENSITE AND FERRITE
If pre-eutectoid steel is heated to a temperature between the As1 and Asz critical points, the ferrite transforms into austenite. After cooling, austenite turns into martensite, and ferrite remains in the hardened roll. As a result of quenching steel in water, a martensite + ferrite structure of technical hardness is formed. Such a search is incomplete.


MARTENSITE AND TROSTITE
If carbon steel is heated to the normal tempering temperature and it is smelted in oil rather than water, then a mixed structure of martensite and trostite is formed. (Fig. 37 shows the martensite-trostite structure X500 in tempered steel)
T he formation of such a structure occurs as follows. During rapid cooling in oil, point "a" in the figure is t= 500-600ºС

at temperature , trostite separates on the edges of austenite grains, trostite is formed from austenite, then martensite is formed from austenite remaining at a temperature lower than point "b" in Figure 38.


OF ROLLED AND RELEASED STEEL
MICROSTRUCTURE


RELEASED MARTENSITE . After quenching the steel subjected to martensite at a low temperature (up to 200ºС), a martensite microstructure is formed in the steel. Quenched martensite is similar to quenched martensite, but the needles (plates) in quenched martensite are shiny, while those in quenched martensite are dull. Figure 39 shows the martensite: a)- after tempering, bright martensite needles of austenite in a dim view, b)- post-tempering and low tempering, dull martensite needles in a bright view of austenite.
The change in color of martensite needles is due to the change that occurs in the martensite at low temperature.
When martensitic structural steel is heated to 200ºС, very small particles of cementite are released from the superheated solid solution of carbon in α-iron. However, these are still bound to the initial phase (α-solution). This reduces the tetragonality of martensite.
Released trostite After tempering steel subjected to martensite at 330º-450ºС, a released trostite microstructure is formed.
The product of martensite decomposition is released trostite, which is a highly dispersed mixture of ferrite particles, small round grains of cementite, and short plates.
LIQUID SORBIT . Martensitic steel at 500º-600ºС
after discharge at , a sorbitol microstructure is formed in it.
The product of martensite decomposition is sorbitol. It is a mixture of round grains of ferrite and cementite, and has a coarser texture than trostite.
Sometimes sorbite retains the shape of the martensite needles obtained by tempering the hardened steel. In this case, it is difficult to distinguish sorbite from martensite at normal magnification.