Rank the following iron–carbon alloys and associated microstructures from the most ductile to the most brittle: (a) 0.20 wt% carbon with coarse pearlite (b) 0.20 wt% carbon with spheroidite (c) 0.75...

Rank the following iron–carbon alloys and associated microstructures from the most ductile to the most brittle:

(a) 0.20 wt% carbon with coarse pearlite

(b) 0.20 wt% carbon with spheroidite

(c) 0.75 wt% C with fine pearlite

(d) 0.75 wt% C with coarse pearlite Justify this ranking.

Briefly explain why the hardness of tempered martensite diminishes with tempering time (at constant temperature) and with increasing temperature (at constant tempering time).