has a fixed structure under all conditions

exists in several crystal forms at different temperatures

responds to heat treatment

has its atoms distributed in a random pattern

below 10°K

above 100°K

around 0°C

around 100°C

austenite

pearlite

ferrite

cementite

alpha iron, beta iron and gamma iron

alpha iron and beta iron

body centred cubic a-iron and face centred cubic a-iron

alpha iron, gamma from and delta iron

face-centred cubic lattice

body-centred cubic lattice

hexagonal close-packed lattice

all of the above