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A D V A N C E D
M A T E R I A L S
&
P R O C E S S E S | J U N E
2 0 1 6
5
CHTE UPDATE
Fig. 1 —
Magnetic parameter (MP) changes with surface hardness.
PROJECT STEPS
The team analyzed several surface hardness and case
depth measurement techniques, including eddy current,
meandering winding magnetometer (MWM), and alternat-
ing current potential drop (ACPD), before concluding that
Barkhausen noise testing and ACPD best support the proj-
ect objectives. (Note: More work needs to be done on ACPD
before insights can be shared.) Several widely used alloy
steels including AISI 8620/9310/1018/5120 were carburized
and fully characterized with destructive testing. Samples
were also tempered. The concentration profile, hardness
profile, and retained austenite percentage were experimen-
tally determined. The team is now determining correlations
among nondestructive test measurements and hardness
and microstructure for standards, and then verifying the
effectiveness of nondestructive test techniques in industry
applications.
THE PROCESS
CHTE measured the properties of steel with Barkhau-
sen testing and found a good correlation between surface
hardness and the Barkhausen noise result. Magnetic param-
eter (MP) was measured with the Rollscan 350 unit from
Fig. 2 —
Maximum slope ratio changes with case depth.
American Stress Technologies (AST). Carburized AISI 1018
samples were prepared using the surface removal method.
Samples display different surface hardness due to the car-
bon concentration difference. MP is sensitive to hardness as
shown in Fig. 1.
Due to the industry’s need for case depth evaluation,
additional testing with Barkhausen noise is being con-
ducted by CHTE, which includes the effects of grain size,
tempering condition, and microstructure. Working with
AST, researchers used the magnet voltage sweep method
for case depth testing. The Rollscan 350 unit can mea-
sure the MP by scanning the exiting voltage from 0 to 18
Vpp. Data is collected with software and the maximum
slope of the curve is recorded. With measurement from
two different frequencies, properties of the sample from
different depths can be evaluated. The slope ratio of the
two frequencies is then correlated with case depth as pre-
sented in Fig 2. Completion of this CHTE research project is
expected in December.
For more information:
Visit
wpi.edu/+chte, call
508.831.5592, or email Rick Sisson
(sisson@wpi.edu) or
Diran Apelian
(dapelian@wpi.edu).
The CHTE collaborative is an alliance between the indus-
trial sector and university researchers to address short-term
and long-term needs of the heat-treating industry. Member-
ship in CHTE is unique because members have a voice in se-
lecting quality research projects that help them solve today’s
business challenges.
Research projects are member driven. Each research
project has a focus group comprising members who provide
an industrial perspective. Members submit and vote on pro-
posed ideas, and three to four projects are funded yearly.
Companies also have the option of funding a sole-sponsored
project. In addition, members own royalty-free intellectual
property rights to precompetitive research and are trained on
all research technology and software updates.
CHTE is located in Worcester, Mass., on WPI’s New En-
gland campus. The university was founded 150 years ago this
year. 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.edu, or Diran Apelian at
dapelian@wpi.edu.
ABOUT CHTE