10.5 PREHEATING

Quiz
1) See the figure below for possible solutions.
The thought process behind these is as
follows:
a) 100% coarse pearlite: We want to keep
the temperature above the nose of the IT
curve in order for the diffusion process to
allow larger growth of the eutectoid (pearlite)
structure.
b) 100% tempered martensite: We want first
to form 100% martensite, which would be by
cooling rapidly enough to miss the nose of
the IT curve, and to pass completely through
the Mf temperature. Then perform a
tempering heat treatment at low
temperatures for a short (1 hour) period of
time.
c) 50% coarse pearlite + 25% bainite + 25%
martensite: To do this, we will need to have a
three step process. First, cool to a
temperature above the nose of the IT curve
and hold until you have converted 50% of the
austenite to coarse pearlite. Second, rapidly
cool to a temperature below the nose, but
above the Mstart temperature, and hold until
50% of the remaining austenite is converted
to bainite (this makes 50% of 50% = 25%
bainite). Finally, rapidly quench through the
Mf temperature to completely convert the
remaining austenite to martensite
http://oregonstate.edu/instruct/engr322/Homework/AllHomework/W98/ENGR322HW6.html