# MODELING OF INDUCTION HARDENING PROCESSES PART 2: QUENCHING AND by 9jjVQuZ

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```									      MODELING OF INDUCTION
HARDENING PROCESSES
PART 2: QUENCHING AND HARDENING

Dr. Jiankun Yuan
Prof. Yiming (Kevin) Rong

Acknowledgement: This project is partially supported
by Delphi and CHTE at WPI. Dr. Q. Lu was involved
in the early work of the project.

http://me.wpi.edu/~camlab
Objectives
• To develop a numerical modeling system for analyzing quench
cooling and hardening processes based on temperature field data after
induction heating.
• To provide temperature distribution in workpiece at any time in a
quenching process
• To provide continuous cooling curves (CCC) of any location in
workpiece, for phase transformation analysis.
• To build an algorithm to analyze phase transformation in quench
cooling processes, based on time-temperature-transformation (TTT)
and CCC curves.
•To provide time traces of volumetric content of martensite, pearlite
and bainite formed in cooling.
• To formulate a relationship between martensite content and hardness
values, and to provide hardness patterns formed after quenching
process.
• To investigate key parameters (input AC power, frequency and gap
between coil and workpiece) effects on final hardening patterns.
Principle: Phase Transformation
Phase transformation kinetics from austenite to pearlite, bainite and martensite
Koistinen-Marburger model for martensite content determination
TTT diagram
f m  (1  f p  fb )(1  er ( M s T ) )
r= 0.01-0.015
(fs,ts)
Avrami model for fp, fb determination in isothermal
(fe,te)
transformation
 ktn
f 1  e
 ln(1  f s )        Generally
ln               
n(T )      ln(1  f e )        fs=0.5%, fe=99.5%                                  TTP curve
t 
ln  s 
t                                                  ti
 e
Ms
 ln(1  f s )
k (T ) 
t sn (T )

For continuous cooling , fp, fb can be determined
using following expressions

fi  (kntn 1ekt )i ti
n

•Ms: Martensite start temperature
N
f   f i                                 •Martensite can only be formed from austenite
i 1                                 after WP temperature lower than Ms
Principle: Hardeness Analysis

Principle: Relationship between martensite content and hardness

fm
HRC
Aim of
hardening
0.5         47.2              analysis
0.8         50.3

0.9         53.7

0.95        56.3

0.99        58.8

0.47%                                HRC  82 .47 ( f m ) 2  99 .21( f m )  76 .187

General expression:
HRC  a( f m ) 2  b( f m )  c
Page 144, <<Steel and its Heat treatment>>, Karl-Erik Thelning
Coefficients a,b,c varying with carbon content

For AISI 1070, 0.7% carbon, a=80.91,b=97,c=81.61
Case Study:Temperature Field Variation in Water Quenching Process

t=0.5s
Total quenching time
t=2s
tq = 40s

f=9600Hz
s=1.27mm
J=1.256e6 A/m2

t=8s                                  t=40s
Case Study: Cooling Curves and Hardening Pattern

Surface points                                                      Inside points
along contour
line T=8150C

Material: Carbon
Steel, AISI 1070

Hardness pattern form
Automotive parts from
numerical simulation
Delphi Inc.,
Sandusky,Ohio
Case Study: Gap Effect - Hardening Pattern Variation with Tolerance
Tolerance= - 0.0025”             Tolerance= 0”

S=1.2065mm                      S=1.27mm

f=9600Hz                        f=9600Hz

J=1.265e6                       J=1.265e6

Tolerance= + 0.0025”

Fig. Hardening depth variation with gap
S=1.3335mm                              between coil and workpiece under three
f=9600Hz                                different frequencies.
J=1.265e6

• Hardening depth decreases with air gap distance
Power Effect - Hardening Pattern Variation with Coil AC Current Density

s  1.27mm                     s  1.27mm
J  7 106 A / m 2            J  1.256 107 A / m 2
f  9600Hz                    f  9600Hz
th  7s                        th  7 s
t q  40s                      tq  40s

(a) J  7 10 6 A / m 2        (b) J  1.256 10 7 A / m 2

s  1.27mm                      s  1.27mm
J  2.25 107 A / m 2           J  3 107 A / m 2
f  9600Hz                      f  9600Hz
th  7s                         th  7 s                 Fig. Hardening depth variation with input
t q  40s                       t q  40s                current density with f=9600Hz, s=1.27mm

• Case depth increase with input AC
power
(c) J  2.25 10 7 A / m 2     (d ) J  3 10 7 A / m 2
Hardening Pattern Variation with Input AC Frequency

s  1.27mm                s  1.27mm
J  1.256 107 A / m 2    J  1.256 107 A / m 2
f  5000Hz                f  9600Hz
th  7 s                  th  7 s
tq  40s                  tq  40s

(a) f=5000Hz                (b) f=9600Hz

s  1.27mm                                         Fig. Hardening depth variation with input
J  1.256 10 A / m
7      2
current frequency with J=1.256e7 (A/m2),
f  15000Hz                                        s=1.27mm
th  7 s
tq  40s

•Case depth decrease with input AC frequency.

(c) f=15000Hz
Summary
•   A quenching and hardening modeling system was developed with the
following capabilities.
(1) Provide workpiece temperature distribution at any time.
(2) Provide cooling curve data of any location in workpiece.
(3) Simulate the phase transformation process and predict volume
fraction of Pearlite, Bainite, Martensite formed in cooling process.
(4) Provide desired hardness pattern through proper simulation of coil
design and optimum combination of control parameters.
(5) Investigate parameters effects on final hardness pattern, including
gap effect, AC frequency effect and current density effect.
•   Applied the developed system to investigate the hardening process on a
complex surface of an automotive spindle.

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