Microstructures

Microstructures
Points : Microstructures, Definition, Cementite, Ferrite, Pearlite Definition Austenite is the solid solution of carbon or iron carbide in gamma iron. The maximum amount of carbon which can be dissolved in plain carbon steels is about 2.0% at a temperature of 2075 F. the solubility decreases with temperature to 0.80% Cat 1333F.

Ordinarily austenite cannot he seen through tile microscope in examining plain carbon steels because it decomposes on cooling, and it is impracticable to examine it through the microscope at high temperature. Austenite although a solid, is just as truly a solution as salt in water, and like a liquid solution it can vary in composition, can be saturated, and can he in contact with excess solute. Cementite Cementite is the common name for iron carbide. Fe₃C. It is very hard and brittle, whereas austenite is relatively ductile and plastic, and only moderately strong. Since Mn₃C cannot he distinguished from Fe₃ C under the microscope, it will be considered part of the cementite and noted and recorded as that constituent. Ferrite Ferrite is a solid Solution. In this solid solution, alpha iron is the solvent for carbon (or iron carbide) to a very limited extent, as is indicated in areas GPQ in at room temperature Ferrite can hold only about 0.008% C is solution.It is soft and ductile: it is also a solvent for silicon, manganese, and some oilier elements. Pearlite Pearlite is the mechanical mixture of Ferrite and cementite. The carbon content is about 0.80% (or approximately 12.5% cementite by weight). Roughly speaking in pearlite seven-eighths of the mass consists of platelets or masses of ferrite one eighth of the mass is particles of cementite mechanically mixed with the ferrite. With certain etching reagents. pearlite. when viewed through the microscope. exhibits a “mother of pearl” iridescence.