AISI 8620 steel is a hardenable chromium, molybdenum, nickel based low alloy
steel often used for carburizing to develop a case-hardened part. The well balanced
alloy content permits hardening to produce a hard wear resistant case combined with
core strength on the order of 862 mPa (125,000 psi). It has excellent machinability
and responds well to polishing applications. With the balanced analysis, this steel
provides, uniform case depth, hardness and wear properties, and gives the advantage
of low distortion. [7] The standard carburization for AISI 8620 is at 900 oC to 925 oC
(1650 to 1700o
F) in an appropriate carburizing medium (Cp = 0.8-1.2 wt% C) and
quenched in oil to enhance the surface hardness. Improved carburized case and core
properties can be obtained by furnace cooling from carburizing at 900 oC to 925 oC
(1650 - 1700o
F) and then reheating to 860o
C (1575o
F). Carburizing is accomplished at
the same range of 900 oC to 925 oC (1650 to 1700o
F) in a carburizing environment,
followed by oil quench. [8] Fig.1 depicts an schematic illustration showing the
locations on the Fe-C phase diagram of the conventional heat treatment in the core of
the surface-carburized AISI 8620 steel.[9] During the heat treatment at 900 °C (points
a and b), both the carburized surface (0.8% C) and the core of the specimen (0.2% C)
remained in the austenitic single-phase region. Oil quenching from 900 °C to room
temperature produced a microstructure that nearly all martensite throughout both the
core and the case.