The mass fractions of total ferrite and total cementite in an iron-carbon alloy are 0.91 and 0.09, respectively. Is this a hypoeutectoid or hypereutectoid alloy? Why?

hypoeutectoid

Explanation:

ferrite: pure form of iron

cementite: It is iron carbide with 93.3% iron and 6.67% carbon

hypoeutectoid: Eutectoid steel with carbon fraction less than 0.8%

hypereutectoid: Eutectoid Steel with carbon content more than 0.8%

For the mentioned iron-carbide alloy,

% of carbon in iron-carbide alloy = percentage of cementite * percentage of carbon in cementite

% of carbon in iron-carbide alloy = 0.09 * 0.0667

= 0.6%

so the alloy is hypoeutectoid