(Solved): 3. Using the isothermal transformation diagran for an iron-carbon alloy of eutectoid composition (F ...

3. Using the isothermal transformation diagran for an iron-carbon alloy of eutectoid composition (Figure 10.22), specify the nature of the final microstracture (in terms of microconstituents present and approximate percentages of each) of a small specimen 1 that has been subjected to the following time-temperature treatments. In each case assume that the specimen begins at $760^{?}\mathrm{C}\left(1400^{?}\mathrm{F}\right)$ and that it has been held at this temperature long enough to have achieved a complete and bomogeneous austenitic structure. (a) Cool rapidly to $700^{?}\mathrm{C}\left(1290^{?}\mathrm{F}\right)$, hold for $10^4\mathrm{s}$, then quench to room temperature. (b) Rapidly cool to $600^{?}\mathrm{C}$ (1110 'F), hold for 4 s, rapidly cool to $450^{?}\mathrm{C}$ ( 840 'F), hold for $10\mathrm{s}$, then quench to room temperature. (c) Cool rapidly to $400^{?}\mathrm{C}\left(750^{?}\mathrm{F}\right)$, bold for $2\mathrm{s}$, then quench to room temperature. (d) Cool rapidly to $400^{?}\mathrm{C}$ ( $750^{?}\mathrm{F})$, hold for $20\mathrm{s}$, then quench to room temperature. inure 10.22 The smplete isothermal ansformation diagram ir an iron-carbon loy of eutectoid imposition: $\mathrm{A}$, stenite; B, bainite; M, artensite; P. pearlite.