On the basis of diffusion considerations, explain why fine pearlite forms for the moderate cooling of austenite through the eutectoid temperature, whereas coarse pearlite is the product for relatively slow cooling rates.

Tempered martensitemicrostructure

Turning speeds are adjusted to the feed rate of the mini lathe (0.004/rev.), a depth of cut of 0.040, and a tool life of 180 minutes.

Make a copy of the isothermal transformation diagram for a \(0.45 \mathrm{wt} \% \mathrm{C}\) iron-carbon alloy (Figure \(10.39\) ), and then sketch and label on this diagram the time-temperature paths to produce the following microstructures: (a) \(42 \%\) proeutectoid ferrite and \(58 \%\) coarse pearlite (b) \(50 \%\) fine pearlite and \(50 \%\) bainite (c) \(100 \%\) martensite (d) \(50 \%\) martensite and \(50 \%\) austenite

Tempered martensitevsmartensite

Tempered martensiteproperties

Determine the spindle speed for turning, milling, drilling, and reaming with these charts and cutting speed calculators.

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