Hardness pearlite, martensite, tempered

Bainite. In a given steel, bainite microstructures are generally found to be both harder and tougher than pearlite, although less hard than martensite. Bainite properties generally improve as the transformation temperature decreases. Lower bainite compares favorably with tempered martensite at the same hardness and can exceed it in toughness. Upper bainite, on the other hand, may be somewhat deficient in toughness as compared to fine pearlite of the same hardness (33). 

Figure 10.32 Hardness (at room temperature) as a function of carbon concentration for plain carbon martensitic, tempered martensitic [tempered at 371°C (700°F)], and pearlitic steels.

In contrast to the pearlite structure, which is lamellar (Figure 2.15), tempered martensite contains the carbide particles as a spheroidal dispersed phase. While the tempered martensite is soft and tough, the parent martensite is hard and abrasion resistant. 

To summarize, the relative hardness of the various phases discussed thus far (Brinell hardness values in parentheses) martensite (300-700) > tempered martensite (300-450) > bainite ca. 400) > fine pearlite (100-300) > coarse pearlite (100-220) > spheroidite (90-180). The hardness and brittleness of cementite is much greater than ferrite, whereas the latter has significantly greater ductility. 

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