Epoxy resin composition, prepreg, and fiber reinforced composite material

An epoxy resin composition comprising component [A], which is an epoxy resin, component [B], which is dicyandiamide, component [C], which is aromatic urea, and component [D], which is a boric ester, and fulfilling any of the conditions from (i) to (iii) given below:

• (i) to meet requirement [a] and requirement [b],
• (ii) to meet requirement [c] and requirement [d], and
• (iii) to meet requirement [c] and requirement [e],
• where requirements [a] to [e] are as follows:
• [a]:
• the time period after reaching 100° C. until reaching the peak top in the heat flow curve is 60 minutes or shorter when an epoxy resin composition is analyzed in a nitrogen stream at a constant temperature of 100° C. using a differential scanning calorimeter,
• [b]:
• the time period after reaching 60° C. until reaching the peak top in the heat flow curve is 25 hours or longer when an epoxy resin composition is analyzed in a nitrogen stream at a constant temperature of 60° C. using a differential scanning calorimeter,
• [c]:
• the average epoxy equivalent over all epoxy resins is 165 g/eq or more and 265 g/eq or less,
• [d]:
• component [A] contains an epoxy resin [A1] that is represented by formula (I) and/or formula (II) and accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass:
• wherein R1, R2, and R3 each are a hydrogen atom or a methyl group, and n is an integer of 1 or greater,
• wherein n is an integer of 1 or greater, and
• [e]:
• component [A] contains a tri- or higher functional glycidyl amine type epoxy resin [A2] that accounts for 10 parts by mass to 50 parts by mass of the total epoxy resin quantity, which represents 100 parts by mass.