Alternative Heat Treatments for Complex-Alloyed
High-Cr Cast Iron Before Machining
V.G. EFREMENKO, K.M. WU, YU.G. CHABAK, K. SHIMIZU, O.B. ISAYEV,
and V.V. KUDIN
Four heat treatment schedules were applied to 14.6 wt pct Cr-2.2 wt pct Mn-1 wt pct Ni cast
iron to improve its machinability: (a) one-step continuous annealing [holding at 1123 K
(950 °C), 2 hours, cooling at 20 to 150 K/h], (b) three-step isothermal annealing [1123 K
(950 °C), 2 hours + 923 K (650 °C), 6 hours + 998 K (725 °C), 15 hours], (c) two-step isother-
mal annealing [923 K (650 °C), 6 hours + 998 K (725 °C), up to 25 hours], (d) quenching [1123
K (950 °C), 2 hours] and tempering [998 K (725 °C), up to 15 hours]. Heat treatments (a) and
(b), which include high-temperature holding at 1123 K (950 °C), result in secondary carbide
precipitation, and lead to a ‘‘martensite/austenite’’ or ‘‘martensite/austenite/pearlite’’ matrix
and a bulk hardness of 56 to 62 HRC with poor machinability. Heat treatments (c) and (d)
provide a matrix of ‘‘ferrite + granular carbides’’ with a bulk hardness lower than 40 HRC.
Quenching and tempering result in the elimination of retained austenite to 11.6 vol pct. The
kinetics of spheroidization and coagulation of eutectoid carbides and carbides as precipitated
from martensite are presented and discussed. Drill testing showed that after quenching and
tempering, cast iron has a superior machinability compared with other heat treatments.
Ó The Minerals, Metals & Materials Society and ASM International 2018
cast irons (HCCIs) are widely
used in many industrial areas (such as crushing, grind-
ing, milling, and pumping or transportation) where
advanced abrasive/erosive resistance is vital for machine
parts and components.
In general, HCCIs are used in
the as-cast shape, however, in some cases, machining is
required to ﬁt the casting into a machine or to provide
the required shape/surface roughness (mill rolls, knives,
slurry pump impellers and sheaths etc.).
diﬃcult to be machined, machining may shorten the tool
life because of the hard carbide M
, lower thermal
conductivity of cast iron, and due to austenitic matrix
which becomes harder under machining.
strategies have been developed to facilitate the
machining of HCCIs for example (a) using expensive
PCBN or ceramic-coated hard carbide tools,
heating the ingot [up to 573 K (300 °C)] during machin-
ing to soften the ingot,
(c) alloying the HCCIs with
lead (up to 0.2 wt pct) and/or sulfur (up to 0.4 wt pct) to
enable chip formation
and (d) applying heat
treatment for preliminary HCCI softening.
The latter strategy is often adopted because of its
simplicity and accessibility. Heat treatment increases the
HCCI machinability by reducing its hardness to a
suitable level (below 40 HRC
) and providing a
‘‘ferrite + granular carbides’’ microstructure that is
optimal for high-carbon alloys before tool machining.
The commonest heat treatment for the enhancement of
the machinability of HCCIs is one-step continuous
This treatment consists of isothermal
holding in the range of 1123 K to 1273 K (850 °Cto
1000 °C) for 5 to 10 hours with subsequent continuous
cooling at 30 to 100 K/h.
The isothermal holding
is aimed at destabilizing primary austenite by sec-
ondary-carbide precipitation (termed ‘‘destabiliza-
). The austenite depletion with carbon and
chromium reportedly accelerates the austenite transfor-
mation into a ‘‘ferrite + granular carbides’’ structure.
Continuous annealing is applicable to cast irons that are
alloyed with 12 to 20 wt pct Cr and up to 1 wt pct Ni
(Mn); it provides a hardness of 250 to 320 HB
and eliminates austenite in the structure. The elimina-
tion is important, as austenite decreases the HCCI
V.G. EFREMENKO and YU.G. CHABAK are with the
Priazovskyi State Technical University, Mariupol, 87555, Ukraine.
Contact e-mail: email@example.com K.M. WU and O.B.
ISAYEV are with the The State Key Laboratory of Refractories and
Metallurgy, Hubei Province Key Laboratory of Systems Science on
Metallurgical Processing, International Research Institute for Steel
Technology, Wuhan University of Science and Technology, Wuhan,
430080, China. K. SHIMIZU is with the Muroran Institute of
Technology, Muroran, 050-8585 Japan. V.V. KUDIN is with the
Zaporozhye National Technical University, Zaporozhye, 69061,
Manuscript submitted December 22, 2017.
Article published online June 5, 2018
3430—VOLUME 49A, AUGUST 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A