In carbon steel, for example, Widmanstatten structures form during ferrite sometimes occur in carbon steel, if the carbon content is below but near the eutectoid composition ( ~ 0.8 % carbon ).
32.
When steels with exactly 0.8 % carbon ( known as a eutectoid steel ), are cooled, the austenitic phase ( FCC ) of the mixture attempts to revert to the ferrite phase ( BCC ).
33.
Below around 700 �C ( 727 �C in eutectic iron ) the austenite is thermodynamically unstable and, under equilibrium conditions, it will undergo a eutectoid reaction and form pearlite an interleaved mixture of cementite ( Fe 3 C ).
34.
While cementite is thermodynamically unstable, eventually being converted to ferrite and graphite at higher temperatures, it does not decompose on heating at temperatures below the eutectoid temperature of the metastable Iron-Carbon phase diagram, which is of the order of 1000 K.
35.
An emerging alternative alloy of depleted uranium is stakalloy, formed of niobium ( 0.01-0.95 wt . % ), vanadium ( 1-4.5 wt . %, between gamma-eutectoid and eutectic ) and uranium ( balance ).
36.
Hypereutectoid steels are typically too brittle to be useful in a finished product, but by the end of forging the steel typically had a high carbon-content ranging from 0.8 % ( eutectoid tool-steel ) to 0.5 % ( hypoeutectoid spring-steel ).
37.
For a eutectoid carbon steel of thin section, if the quench starting at 750 �C and ending at 450 �C takes place in 0.7 seconds ( a rate of 430 �C / s ) no pearlite will form and the steel will be martensitic with small amounts of retained austenite.
38.
The edge-steel itself will generally end up with a composition that ranges from eutectoid to slightly hypoeutectoid ( containing a carbon content under the eutectoid composition ), giving enough hardenability without sacrificing ductility The skin-steel generally has slightly less carbon, often in the range of 0.5 %.
39.
The edge-steel itself will generally end up with a composition that ranges from eutectoid to slightly hypoeutectoid ( containing a carbon content under the eutectoid composition ), giving enough hardenability without sacrificing ductility The skin-steel generally has slightly less carbon, often in the range of 0.5 %.
40.
In a hypereutectoid composition ( greater than 0.8 % carbon ), the carbon will first precipitate out as large inclusions of cementite at the austenite grain boundaries until the percenage of carbon in the grains has decreased to the eutectoid composition ( 0.8 % carbon ), n at which point the pearlite structure forms.
