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The Center for Heat Treating Excellence
(CHTE) at Worcester Polytechnic Institute
(WPI) in Massachusetts is conducting a cut-
ting-edge research project aimed at demon-
strating the benefits and limitations of induction tempering versus
furnace tempering. Results will enable manufacturers that use a
tempering process for their products to choose the optimal tech-
nology required to reduce tempering cycle time and process costs
while maintaining or improving product quality.
“This is the first time a project like this is being
undertaken,” says CHTE member Lesley Frame,
manager of materials engineering and develop-
ment at Thermatool Corp., East Haven, Conn.
“Currently, widely available, detailed compara-
tive data for induction and furnace tempering
does not exist. The industry has been reliant on
dated gas furnace-tempering data, which does
not provide a sufficient guide for developing in-
duction heat treating recipes.”
Tempering requires a balance between
desired hardness and tensile strength,
while increasing toughness and maintain-
ing a uniform microstructure. Further, in-
dustry requires minimized residual stress
and distortion in heat treated parts. Be-
cause stresses and distortion are affected
by temperature changes, it is necessary
to understand how internal stresses
might develop during rapid-heating
processes like induction tempering.
This study will provide CHTE members
with information on the best recipe to
maximize part performance. The expecta-
tion is that members will be able to apply
the data to process designs to improve
efficiency and productivity and eliminate
trial-and-error experimentation.
Rick Sisson, WPI professor of mechanical
engineering and director of CHTE, said the
project will take the guesswork out of deci-
sion-making and help industry work more
effectively. “For the first time, industry will have the answers it
needs to determine when furnace tempering will best meet appli-
cation needs and when induction tempering is the best process,”
explains Sisson.
Research objectives
One of the project’s main goals is to compare induction and fur-
nace tempering processes at a fundamental level in terms of the
effects of power (kW), frequency (kHz), temperature, and time on
the microstructure and hardness of quenched and tempered
steel. In the study, 1 ft long by 0.5 in. diameter (300 by 13 mm)
AISI 1045 carbon steel and AISI 4140 alloy steel rods are being
tested. Steel microstructures will be characterized using optical
and scanning electron microscopy, x-ray diffraction, and trans-
mission electron microscopy.
Microstructures, residual stress distri-
bution, and mechanical properties
(hardness, impact toughness, and tor-
sional properties) of induction-tem-
pered
steel
samples
and
furnace-tempered samples will be
compared. Based on hardness test re-
sults, impact toughness and torsional
fatigue behavior of selected samples
will be determined and correlated with
the microstructure.
Induction-tempering tests will be con-
ducted at Thermatool Corp. and furnace
tempering will take place at CHTE. Re-
sults are expected in late 2014.
Induction tempering offers
an alternative to furnace
tempering.
ADVANCED MATERIALS & PROCESSES •
MARCH 2014
40
Demystifying Induction Tempering
HTPRO
4
About CHTE
The CHTE collaborative is an alliance between the industrial sector and university researchers to address short-term and long-term
needs of the heat treating industry. Membership in CHTE is unique because members have a voice in selecting quality research proj-
ects that help them solve today’s business challenges.
Member research process
Research projects are member driven. Each project has a focus group comprising members who provide an industrial perspective. Mem-
bers submit and vote on proposed ideas, and three to four projects are funded yearly. Companies also have the option of funding a
sole-sponsored proprietary project. In addition, members own royalty-free intellectual property rights to precompetitive research, and
are trained on all research technology and software updates.
CHTE also periodically undertakes large-scale projects funded by the federal government or foundations. These endeavors keep mem-
bers informed about leading edge technology.
CHTE current research portfolio
Other projects now in progress include:
Nondestructive testing, alloy life improvements, gas quench steel hardenability, and cold spray nanomaterials.
For more information about CHTE, its research projects, and member services, visit
wpi.edu/+chte, call 508/831-5592,
or email Rick Sisson at
sisson@wpi.eduor Diran Apelian at
dapelian@wpi.edu.
CHTE member
Lesley Frame,
Thermatool
Corp.