Formations In Steel Flashcards
(7 cards)
Ferrite
Iron which contains little to no carbon. It is very soft and ductile. It does not harden when cooled rapidly. It forms smaller crystals when cooled from a bright red heat at a rapid rate. Also called alpha phase iron.
Pearlite
A mixture of ~87.5% ferrite and 12.5 cementite. The thickness of alternate plates and the distance between them is governed by the rate the steel is cooled, where a slower cooling rate produces a coarser structure. Soft steels contain ferrite and pearlite, and the hardness increases with the proportion of pearlite. Hard steels are a mix of pearlite and cementite.
Cementite
This is a definite carbide of iron (Fe3O) which is harder than normal steel. Cementite increases (generally) with the proportion of carbon present. The hardness and brittleness of the steel. It contains 6.6% C and occurs in the form of a network or globular or massive form. It is magnetic below 25*C. It decreases the tensile strength but increases the hardness and cutting qualities of the steel.
Martensite
Characterized by its hard brittle mass of fibrous/needle like structures and is the main constituent of hardened steels. It is produced by the rapid quenching of high carbon steel from a slightly higher temp than the max temp of critical interval (where steel undergoes phase change and recrystallizes). This structure is weaker than austenite but is magnetic.
Austenite
A solid solution of iron-carbon which is stable on writhing a particular range of compositions and temperatures (usually above 727C). It is formed when carbon steel with more that 1.1% carbon is quenched rapidly from ~1000C. The amount of austenite increases with the proportion of carbon usually to 1.6-1.8%. These steels cannot be hardened by usual heat treatment methods and are non-magnetic.
Troostite
A structure consisting of very finely divided iron carbide produced by tempering a martensitic steel between 205 and 450C or by suppressing the thermal change point fully. It’s basically very fine pearlite.
Sir it’s
Evenly distributed carbide of iron particles in a mass of ferrite. Formed when a fully hardened steel is tempered between 550 and 650C. It is very strong and has a high degree of toughness.
