Fergana polytechnic insitute mechanical engineering faculty department of mechanical engineering and automation

Ferrite- (F) is a solid solution 
of carbon in alpha 

iron. The maximum amount 
of carbon that can be dissolved in alpha iron is 0.025 
percent at 727°C. As the temperature rises above 727°C, 
the amount of soluble carbon in alpha iron decreases and 
becomes zero at 911°C. 
Ferrite is the softest among iron-carbon alloys, its 
Brinell hardness HB = 80-100 kg/mm 
2 
, plasticity 

= 40-50%. Its crystal lattice consists of concentric 
cubes. 
Sementite- (S) 
is a chemical compound of iron with 
carbon (Fe 
3 
C), i.e. iron carbide, which contains 
6.67% will be carbon. Cementite is the hardest 
among iron-carbon alloys, its hardness according to 
Brinell is HB = 800-1000 kg/mm 
2 
, plasticity 

= 0%, 
melting temperature is about 1600°C. Cementite is not a 
stable compound — it decomposes when heated to form 
ferrite and graphite: 
Internal structure of steels
The crystal lattice of cementite is complex and consists of several octahedra. 
Austenite- 
(A) is a solid solution 
of carbon in gamma 

iron, named after the 
English researcher R. Austen. The austenite crystal lattice is in the form of a centered 
cube, its plasticity 

= 40-50%, Brinell hardness 
HB = 160-200 kg/mm 
2 
. 
pearlite- 
(p) 
is a mechanical mixture formed by the breakdown of small grains 
of cementite with ferrite during slow cooling of austenite , i.e. p = F + TS. This 
compound is also called eutectoid. The microsand made of eutectoid steel and 

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treated with sodium picrate solution looks like mother of pearl when viewed under 
a metal microscope, hence the name pearlite (the Russian translation of mother of 
pearl is pearl).. pearlite can be plate-like and granular.. cementite in plate-like 
pearlite in the form of plates. and in granular perlite it is in the form of grains. The 
amount of carbon in pure perlite is 0.8%. The mechanical properties of granular 
pearlite are higher than those of plate-like pearlite, and its Brinell hardness is in the 
range of HB = 200-250 kg/mm 
2 
.