2380.6 wt% C, fine pearlite0.6 wt% C, coarse pearlite0.25 wt% C, coarse pearlite0.25 wt% C, spheroiditeThe 0.25 wt% C, coarse pearlite is stronger than the 0.25 wt% C, spheroidite since coarsepearlite is stronger than spheroidite; the composition of the alloys is the same. The 0.6 wt% C,coarse pearlite is stronger than the 0.25 wt% C, coarse pearlite, since increasing the carboncontent increases the strength. Finally, the 0.6 wt% C, fine pearlite is stronger than the 0.6 wt%C, coarse pearlite inasmuch as the strength of fine pearlite is greater than coarse pearlitebecause of the many more ferrite-cementite phase boundaries in fine pearlite.10.31 This question asks for an explanation as to why the hardness of tempered martensitediminishes with tempering time (at constant temperature) and with increasing temperature (atconstant tempering time). The hardness of tempered martensite depends on the ferrite-cementite phase boundary area; since these phase boundaries are barriers to dislocationmotion, the greater the area the harder the alloy. The microstructure of tempered martensite
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