Hardening and Tempering of Malleable Iron,Hardening and Tempering of Malleable Iron,Hardening and Tempering of Malleable IronA typical procedure for producing a hardened pearlitic malleable iron consists of, first, air quenching castings after firststage
annealing, which results in retention of about 0.75% combined carbon in the matrix; second, reheating and holding
for 1 h at 885 °C (1625 °F) to reaustenitize the matrix and homogenize the combined carbon; and then quenching in
heated (50 to 55 °C, or 120 to 130 °F) and agitated oil, thereby developing a matrix consisting of martensite without
bainite and having a hardness of 555 to 627 HB. Figure 3 shows the effects of austenitizing temperature and quenching
medium on the hardness of ferritic and pearlitic malleable iron. The appropriate austenitizing temperature for pearlitic
malleable iron is 885 °C (1625 °F), and for ferritic malleable iron it is 900 °C (1650 °F). If direct oil quenching is used,
caution must be exercised to prevent cracking due to high combined carbon.
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