Determine the validity of each of the following statements concerning the Fe-Fe_

Question

Determine the validity of each of the following statements concerning the Fe-Fe_3C steel system Toughness in steels is derived from having a continuous cementite matrix Carton is generally more soluble in austenite (y-Fe) than ferret (a-Fe) Austenite (y-Fe) is more ductile than ferrite (a-Fe) Strength in steels increases with increasing carbon concentration Hardness in steep increases with increasing cementite (Fe_3C) concentration Slow cooling of a stool containing 0 76 wt% carbon will produce a microstructure featuring a protected phase Strength in steels increases with increasing cementile/ferrite Interfacial area Marten site Is an equilibrium phase of steels.

Explanation / Answer

i) True, the greater the proportion of cementite, the greater the mechanical strength and the greater the difficulty to deform steel.

ii) Carbon atoms are larger in size and occupy octahedral interstitial sites in cyrstals for this reason, body centered cubic ferrite is much smaller for carbon atoms than face centered cubic austenite. Therefore, carbon is more soluble in austenite than ferrite.

iii) True, austenite is denser than ferrite and more ductile at higher temperatures.

iv) True, carbon is the most important commercial steel alloy. For this reason, increasing carbon content increases hardness and strength in steel.

v) True, hardness of steel increases with increasing cementite concentration.

vi) False, proeutectoid phase has carbon content less than 0.76 wt%.

vii) True, a carbon percentage increase results in increase of cementite/ferrite interfacial area and this increases the strength of steel.

viii) False, equilibrium phases are formed by slow cooling rates but martensite is usually formed by very fast cooling rates.

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