Induction Surface Hardening

WEBINAR
07.05.2015
2:00-3:00 pm
1
prof. dr hab. inż. Jerzy Barglik
Silesian University of Technology, Poland

WEBINAR
07.05.2015
2:00-3:00 pm
2
CONTENTS
- Introduction
- Mathematical Modelling of Induction Surface
Hardening
- Metallurgical Aspects and Unbalanced Diagrams
- Review of practical applications
Conical mandrels
Internal surfaces of steel tubes
Steel sections
Circular saw
Gear wheels.
- Conclusions

WEBINAR
07.05.2015
2:00-3:00 pm
3
SHORT INFORMATION ABOUT SILESIAN UNIVERSITY OF
TECHNOLOGY
The Silesian University of Technology
₋ one of the biggest technical universities in Poland
⁻ thirteen faculties with 50 areas/directions of education and
almost 190 specializations
⁻ about 1900 scientific-didactic staff
⁻ about 30,000 students at the University
History:
- the Silesian University of Technology was founded on 24th May
1945 with setting up of four faculties: Mechanical, Electrical,
Metallurgical and Civil Engineering
- the first inauguration of the academic year at the University in
Gliwice took place on 29th October 1945 and 2750 students began
their studies
so far 138,000 engineers have graduated from the University
which has also granted 3,500 PhD and 550 DSc degrees
The Rector’s
insygnia
A lecture at the Faculty of
Electrical Engineering in the 1950s

WEBINAR
07.05.2015
2:00-3:00 pm
4
RESEARCH ACTIVITIES
• surface induction hardening,
• optimization of transverse flux induction heaters
• induction heating for semi-liquid state,
• levitation and semi-levitation melting,
• new constructions of induction furnaces,
• magnetohydrodynamic devices for transportation, stirring and purification
of liquid metal.

WEBINAR
07.05.2015
2:00-3:00 pm
5
STAGES OF THE PROCESS
Surface induction hardening represents the most
interesting application of induction heating making
possible to achieve thin surface layer with different
mechanical properties in comparison to those of the core
material .
The process consists of:
-fast heating the layer to be hardened up to a temperature
higher than the upper critical temperature making
possible to form austenite structure,
-holding the body at this temperature for a sufficient time
in order to obtain a structural equilibrium in the regions,
-subsequent fast quenching in order to cool intensively the
structure stable at high temperature or one convenient
transformation (martensitic structure).
T (°C)
T
T
T
T
Ac
max
min
finish
i
t
hardness (HV)
t 1
3
t
1
Ac 3
1
2
3 4
1
2
3
4
Th
2
t

WEBINAR
07.05.2015
2:00-3:00 pm
6
FEATURES
- possibility to localize the treatment within a surface layer of the
body facing the inductor,
- thickness of hardened layer depends on frequency of field current,
power density, material properties of material and the heating time;
- big volumetric Joule losses achieved by using of high frequency field
currents and short heating times, make possible to obtain requested
very thin hardened layer

WEBINAR
07.05.2015
2:00-3:00 pm
7
DEFINITION OF OPTIMAL PARAMETERS
There are no simple general rules that allow to define optimal parameters of
the process:
- distribution of the eddy-currents in the treated body and optimum values
of the heating time, the time interval between the end of the heating and
the beginning of the quenching and the quenching velocity.
Besides on the material properties, these elements depend on the shape of
the hardened body, the presence of holes, teeth or edges, the thickness of
the layer to be hardened, the distance between the inductor and workpiece
surface, the position of the inductor’s edges etc.

WEBINAR
07.05.2015
2:00-3:00 pm
8
HARDENED PROFILE
Also the results obtained with the most modern models of numerical
simulation, require a successive experimental verification and adjustment of
the inductor, usage of flux concentrators in order to achieve the results
required.
Moreover, in many cases, the hardened profile is not the one desired by the
designer (hardening of gears, crankshafts etc.) but the one that can be
obtained by the practice of induction heating.

WEBINAR
07.05.2015
2:00-3:00 pm
9
THE MAIN FACTORS
The main factors influencing on the results of the induction surface
hardening process:
steel grade
value and distribution of the temperature in the hardened region
the speed of quenching
the type and geometry of the inductor-sprayer system.
usage of inductor with flux concentrators

WEBINAR
07.05.2015
2:00-3:00 pm
10
CONTENT OF CARBON
And the percent of martensite (the curve at 99% corresponds to
a complete hardening with a total transformation of austenite into
martensite); it shows that in practice, only a small improvement of the
hardness may be achieved when the carbon content of the steel
exceeds 0.6%. For this reason, only steels with a carbon content
between 0,4 to 0,6% are normally used.

WEBINAR
07.05.2015
2:00-3:00 pm
11
DEPENDENCE OF HARDNESS
ON CARBON CONTENT

WEBINAR
07.05.2015
2:00-3:00 pm
12
DIAGRAM IRON-CARBON-STEEL
1. It can be observed that the
carbon content influences on the
upper critical temperature AC3
above which the formation of
austenite takes place.
2. Also the value of the upper
critical temperature AC3 depends
on rate of heating.
3. For rapid induction heating the
hardening temperature must be
increased above the AC3 in order
to guarantee a minimum time
interval above the temperature of
austenite formation

WEBINAR
07.05.2015
2:00-3:00 pm
13
INFLUENCE OF ADDITIONS CONTENT
Critical temperatures
increase for steel containing
alloying elements promoting
the formation of carbides,
like titanium, silicon,
molybdenum, vanadium or
tungsten.
.

WEBINAR
07.05.2015
2:00-3:00 pm
14
TEMPERATURE DISTRIBUTION
Once the hardening depth and the steel grade are given, it is necessary
to heat all points of the layer to be hardened to a temperature above
the AC3 (or to higher values for rapid heating), while at the same time
keeping to lower temperature the internal layers.
This can be achieved with rapid heating at high or medium frequency
field current, which can give rise to considerable temperature gradients
in the layer to be hardened much higher than the ones achievable by
the flame hardening.

WEBINAR
07.05.2015
2:00-3:00 pm
15
NECESSITY OF EXPERIMENTS
The examination of the curves confirms the already mentioned
difficulty of an exact theoretical estimation of the hardening
parameters and the consequent necessity of the final experimental
verification.
SIMULATION VERIFIED BY WELL PLANNED EXPERIMENT

WEBINAR
07.05.2015
2:00-3:00 pm
16
ALGORITHM
INPUT DATE
ELECTROMAGNETIC FIELD
μ =μ(B)
B, pv
B = B + ΔB
μ (T)
 (T)
λ (T)
ρc(T)
αc(T) NON-STATIONARY t = t + Δt
αr(T) TEMPERATURE FIELD
HEAT STRESSES FIELD
yes u no
T = T + ΔT
NON-STATIONARY NATURAL
TEMPERATURE FIELD COOLING
NON-STATIONARY
TEMPERATURE FIELD INTENSIVE
COOLING
λ (T) HEAT STRESSES FIELD
ρc(T)
αc (T) u t = t + Δt
yes no
T = T - ΔT
EXPERIMENTAL DATA
METALLURGICAL
FIELD HV = f (vc)
HARDNESS (HV)
MICROSTRUCTURE
I
II
III
T
T

WEBINAR
07.05.2015
2:00-3:00 pm
17
ELECTROMAGNETIC FIELD
  ext
1
curl curl curl

 A+ v A J
  extcurl curl j - curl   A+ A v A J
extcurl curl j A+ A J
0A
BASIC EQUATIONS
symmetry plane z = 0
BOUNDARY CONDITIONS
external border
0 A n

WEBINAR
07.05.2015
2:00-3:00 pm
18
2D FORMULATION
0



A
n
Eddy current density
= jJ A ,
vp



*
J J
Volumetric Joule losses

WEBINAR
07.05.2015
2:00-3:00 pm
19
3D FORMULATION
curl , div 0, grad  J = T T H T
0 grad H H
0 3
1
d
4π V
V
r

 
J r
H
2 2
J
curl
w
 
 
J T
 grad B = T

WEBINAR
07.05.2015
2:00-3:00 pm
20
TEMPERATURE FIELD
    vdiv grad grad -
T
T c v T c p
t
  

 

-
0
T
n



       4 4
c c o r c c r r r-
T
T T T T T T T T p
n
     

            

     2 2
g cr g c o cr cr- ,
T
T T T T T T
n
    

       

   div grad grad 0
T
T c T c
t
  

  

v
   c c r r r s
T
T T T T p p
n
  

        


WEBINAR
07.05.2015
2:00-3:00 pm
21
STRESS FIELD
   u
1 1 2
E

 


  
 u
2 1
E




   2
u u u u u T mgrad div 3 2 grad 0u T          u+ f
m  f J B

WEBINAR
07.05.2015
2:00-3:00 pm
22
TEMPERATURE DEPENDENCE ON VELOCITY OF COOLING

WEBINAR
07.05.2015
2:00-3:00 pm
23
RELATIVE MAGNETIC PERMEABILITY

WEBINAR
07.05.2015
2:00-3:00 pm
24
OTHER MATERIAL PROPERTIES

WEBINAR
07.05.2015
2:00-3:00 pm
25
INITIAL MICROSTRUCTURE
Initial microstructure (before the heat treatment) has a decisive
influence on the final structure and hardness distribution.

WEBINAR
07.05.2015
2:00-3:00 pm
26
TTA DIAGRAM

WEBINAR
07.05.2015
2:00-3:00 pm
27
TTC DIAGRAM

WEBINAR
07.05.2015
2:00-3:00 pm
28
COMPLETE HARDENING
In particular the curves corresponding to cooling rates, higher or equal
to the critical one ,prevent the intersection of the perlite and bainite
transformation regions. c V
Therefore occurs the complete transformation of austenite into
martensite, with only some percentage of residual austenite if the steel
is highly alloyed, thus realizing the so-called complete hardening.

WEBINAR
07.05.2015
2:00-3:00 pm
29
INCOMPLETE HARDENING
The martensite is a hard and brittle constituent whose hardness is
higher, the higher is the content of carbon.
However, for lower cooling rates, one obtains various microstructures
corresponding to the presence of the various constituents determined
by the points of intersection between the cooling curve and the
transformation curve.
In particular, for cooling rates lower than the critical one, one obtains
an incomplete hardening in which the austenite transforms partially
into bainite and partially into martensite; for even lower rates one
obtains the normalizing of steels with medium alloying content,
whereas the curve 1 represents a complete annealing cycle.

WEBINAR
07.05.2015
2:00-3:00 pm
30
DIFFERENT MICROSTRUCTURES
In the hardening of workpieces of considerable dimensions, it must be
taken into account that the surface layers cool down with a rate higher
than the critical one, whereas the internal layers with velocities
progressively decreasing in the cross-section, from the surface towards
the core. This gives rise to different microstructures with constant
hardness in the region where the cooling velocities are higher than and
hardness gradually decreasing towards the core to the values
characteristic for the thermally unaffected material.

WEBINAR
07.05.2015
2:00-3:00 pm
31
ALGORITHM FOR CONTINUAL HARDENING

WEBINAR
07.05.2015
2:00-3:00 pm
32
BASED ON EXPERIMENT
In this case, the analytical calculation become extremely complex, even
under the consideration of constant material parameters. Therefore,
one must always refer to experimental diagrams.
In the two cases of non-moving workpiece and scan hardening, the
power of the high frequency generator necessary to harden a given
area will be substantially different.

WEBINAR
07.05.2015
2:00-3:00 pm
33
QUENCHANTS
The choice of the quenching fluid has the same importance as that of the heating
regime; this choice must be done taking into account the mechanical and
metallurgical properties required, the steel grade, and the shape as well as the
dimensions of the workpiece.
The most used quenching media are:
water,
oil,
synthetic polymers fluids,
other like aqueous emulsions of oil, solutions of water and salt, air, baths of salt
melts, some metal melts.

WEBINAR
07.05.2015
2:00-3:00 pm
34
SPEED OF QUENCHING

WEBINAR
07.05.2015
2:00-3:00 pm
35
INTERNAL STRESSES
1. As known, the martensitic transformation causes a volume increase.
2. Too fast or irregular transformation induces substantial internal
stresses which can cause deformations and cracks, especially in the
case of complex geometries or surface defects.
3. Temperature differences between the quenching curves of the
surface layers and the ones of the core, which cools down slower,
increase with high quenching rates.
4. It causes expansion of the internal mass against the hardened
surface layer and a higher internal residual stress with the possibility of
the workpiece distortion and formation of cracks.

WEBINAR
07.05.2015
2:00-3:00 pm
36
SPRAY QUENCHING
In the case of water quenching, especially with plain carbon steels,
optimal results are obtained with spray quenching, where the water
runs over the hot surface at high velocity, preventing the formation of a
vapor film which reduces the heat transfer between the workpiece and
the quenchant.
However, it may sometimes cause local unhardened areas.

WEBINAR
07.05.2015
2:00-3:00 pm
37
LOWER QUENCHING RATES
With lower quenching rates (oil or polymer solution quenching), the
difference between the internal and external temperatures is lower;
there with derives that before the surface layer has reached the point
Mf, causing the brittle casing of martensite, the most internal part of
the workpiece has been already transformed and has undergone the
consequent expansion.
Due to the lower internal mass which transforms after the surface layer
has finished its transformation, the above mentioned problems are
reduced proportionally.

WEBINAR
07.05.2015
2:00-3:00 pm
38
REDUCTION OF STRESSES
Sometimes, for bodies of complicated shape the quenching in air can
be utile in which, due to the low quenching velocity, the transformation
occurs practically contemporaneous in the whole mass of the piece, so
reducing the internal stress to a minimum and hence the risk of cracks.
In the case of quenching by immersion, the workpieces are always kept
in rotation and the quenching bath is maintained at controlled
temperature; due to its inflammability, the hardening in oil is always
done by immersion or in similar conditions.

WEBINAR
07.05.2015
2:00-3:00 pm
39
Steel tubes transporting mixtures of loose materials (for
example sands) and water have to be highly mechanically
resistant, particularly with respect to abrasion.
The basic way how to meet this demand is hardening of
their internal surfaces that may be realized by means of
induction heating, using movable internal or external
inductor and water sprayer.
INDUCTION HARDENING OF INTERNAL SURFACES
OF STEEL TUBES
It is necessary to harden
the internal surface of a
long steel tube.
This process can be
realized in two basic
ways: with internal or
external inductor.

WEBINAR
07.05.2015
2:00-3:00 pm
40
Electromagnetic field
depends on
• shape of the inductor,
• influence of the supplying
conductors (but these
feeders are usually placed
close to one another, so
that their contribution to
the resultant magnetic
field is low and may be
neglected).
The arrangement is taken
fully axisymmetric.
MATHEMATICAL MODEL

WEBINAR
07.05.2015
2:00-3:00 pm
41
ALGORITHM

WEBINAR
07.05.2015
2:00-3:00 pm
42
0
1
2
3
4
5
6
0 200 400 600
temperature (deg)
electricalconductivity
(MS/m)
0
500
1000
1500
2000
2500
3000
0 200 400 600 800
temperature (deg)
relativemagnetic
permeability(-)
B = 0.5 T
0
10
20
30
40
50
60
0 200 400 600
temperature (deg)
specificheatconductivity
(W/mK)
0
200
400
600
800
1000
1 10 100 1000 10000
time (s)
hardness(HV)
MATERIAL PROPERTIES

WEBINAR
07.05.2015
2:00-3:00 pm
43
0
100
200
300
400
500
600
700
800
900
0 100 200 300 400
time (s)
temperature(deg)
int 0 mm
int 83 mm
ext 0 mm
ext 83 mm
Bottom points
TIME EVOLUTION OF TEMPERATURE

WEBINAR
07.05.2015
2:00-3:00 pm
44
MAIN WINDOW

WEBINAR
07.05.2015
2:00-3:00 pm
45
INDUCTION HARDENING OF CONICAL MANDRELS
BASIC ARRANGEMENT

WEBINAR
07.05.2015
2:00-3:00 pm
46

WEBINAR
07.05.2015
2:00-3:00 pm
47
INPUT DATA
• Mandrel: ra = 0.012 m, rb = 0.020 m, l = 0.4 m,
• Coil: rc = 0.025 m, w = 0.017 m, h = 0.03 m,
• Current density and frequency:
Jext = 7·106 A/m2, f = 440 kHz,
• Velocity: v = 0.002 m/s
• Temperatures: Tstart = 20 °C, T0a = 20 °C, T0w = 10 °C,
• Convective heat transfer coefficients:
heating a = 20 W/m2K, cooling w = 500 W/m2K.

WEBINAR
07.05.2015
2:00-3:00 pm
48
Time evolution of the temperature at selected points
0
200
400
600
800
1000
1200
0 50 100 150 200
time (s)
temperature(deg)
40 mm
80 mm
120 mm
160 mm
200 mm
240 mm
280 mm
320 mm
360 mm

WEBINAR
07.05.2015
2:00-3:00 pm
49
HARDNESS DISTRIBUTION
650
670
690
710
730
750
770
790
0 100 200 300 400
axial distance (mm)
hardness(HV)

0 0.05-0.05
0.0
5
-0.05
y
artificial boundary inductor
workpiece
hardened surface
A
z
B
C
x
STEEL SECTION FOR PLASTIC WORKING

r = 1
workpiece
inductor
elsewhere r = r (B)
v
3D ARRANGEMENT
Ac1 = 730 °C, Ac3 = 780°C, Ms = 325°C.
Known are temperature dependencies of its physical properties (electrical and thermal conductivities, specific
heat).
Axial length of the body is 0.118 m.

0
100
200
300
400
500
600
700
800
900
1 10 100 1000 10000
time of cooling (s)
HV
HARDNESS DISTRIBUTION
Inductor: massive conductor of rectangular cross-section 3*9 mm that carries current of density J = 10.5 A/mm2
and frequency f = 20 kHz. Its velocity is 2 mm/s.

Time evolution of temperature at selected point of the line passing through point A (-0.02, 0.0398),

Time evolution of temperature at selected point of the line passing through point B (-0.01, 0.0294),

Time evolution of temperature at selected point of the line passing through point C (0, 0.019),

The saw is used for cutting iron material. It is made from steel 40 HM produced in Poland its diameter is r = 1 m,
thickness t = 0.012 m and the number of teeth is 315.
CIRCULAR SAW

PARAMETERS
Field current I = 850 A,
frequency f = 40 kHz.
Convective heat transfer coefficient a for air
was taken 25 W/m2K.
Ac1 = 740 °C
Ac3 = 780 °C.

TEMPERATURE DISTRIBUTION ON TIME

The highest
temperature is
reached at point III (at
the top of the leading
edge).
TEMPERATURE DISTRIBUTION

WEBINAR
07.05.2015
2:00-3:00 pm
61
GEAR WHEELS
One typical example of hardening a geometrically complex workpiece is
the simultaneous hardening of gears, where the purpose of the process
is to obtain a uniform hardened layer along the whole surface, namely
at the tip, along the flanks, and the roots of the teeth.
In this case, the choice of the frequency results to be of fundamental
importance not only from the “electrical” point of view, but also the
thermal one.

WEBINAR
07.05.2015
2:00-3:00 pm
62
INFLUENCE OF FREQUENCY ON TEMPERATURE

WEBINAR
07.05.2015
2:00-3:00 pm
63
SIMULTANEOUS CONTOUR HARDENING
1 – Joule losses
2 – generator power
3- optimal frequency
4 – optimal frequency
5 – heatig time

WEBINAR
07.05.2015
2:00-3:00 pm
64
INDUCTION HARDENING
OF GEAR WHEELS

WEBINAR
07.05.2015
2:00-3:00 pm
65
GEAR WHEELS
The gear-wheels as the most typical case of the induction hardening of
complex geometries.
In gear spin hardening the entire gear part is brought up to the
hardening temperature by means of an inductor surrounding it and is
subsequently cooled.

WEBINAR
07.05.2015
2:00-3:00 pm
66
VARIOUS PATTERNS
1. The gears are rotated during heating to ensure an even distribution
of energy.
2. It is possible to through harden the gear part down to the tooth root
(in the same way as the case hardening) or to harden the outer surface
at either a uniform or irregular depth from the surface.
3. The best pattern is usually a uniform thickness of the hardened layer
along the contour.
4. Different patterns may be acceptable or sometimes desirable
depending on the application. Breaks in the hardened layer may be
accepted on the tips of the teeth where mechanical loading is very low,
while on the flanks and roots it must be continuous in order to
withstand big contact pressure and tensile stresses from loading.

WEBINAR
07.05.2015
2:00-3:00 pm
67
MAIN PARAMETERS
The main parameters which play a dominant role in obtaining the
required hardness pattern are:
Field current frequency,
Its power density,
heating time,
quenching conditions and
Geometry of the system.
In particular, contour hardening can be obtained by single-frequency or
dual-frequency processes.

WEBINAR
07.05.2015
2:00-3:00 pm
68
SPIN HARDENING METHODS

WEBINAR
07.05.2015
2:00-3:00 pm
69
SINGLE FREQUENCY TREATMENT
The single-frequency single-shot hardening process is a spin hardening
in which all teeth are simultaneously contour hardened by means of a
single frequency inductor. It requires the use of high induced power
densities and very short heating times in order to avoid the diffusion of
heat from the surface layer to the lower material and the consequent
through hardening of the teeth.
The process requires a convenient choice of the operating frequency in
order to obtain suitable values of the induced power densities at the
flanks, tips and roots of the teeth.

WEBINAR
07.05.2015
2:00-3:00 pm
70
JOULE LOSSES
f = 10kHz
f = 500kHz

WEBINAR
07.05.2015
2:00-3:00 pm
71
OPTIMAL PARAMETERS
As regards frequency, the
following formula has been
proposed for a rough estimate
of the optimal value:
with M – module of the
gear in mm.
1- specific surface power , 2 - heating time,3 - frequency
1 3 2
5
opt 2 2
3 10
, kHz
K
f
M M

 

WEBINAR
07.05.2015
2:00-3:00 pm
72
PULSING SINGLE FREQUENCY
The single frequency contour hardening with pre-heating (the so called
also “Pulsing Single Frequency” process) has been developed consisting
of several consecutive stages
preheating with a reduced power up to approximately 550 - 750 ºC
(dependent on the material),
a short final heating with higher specific power to the hardening
temperature,
quenching and a low-power heating stage for tempering.

WEBINAR
07.05.2015
2:00-3:00 pm
73
PREHEATING
Pre-heating allows to reach a convenient heated depth at the roots of
the gear, enabling to attain an adequately high austenitizing
temperature in the
root circle during the final heating, without overheating the tooth tips;
this process cycle allows in many cases to reach the desired
metallurgical results and to decrease distortion in some materials. The
preheating time, dependent on size and shape of the gear, is followed
by a soak time which allows to achieve a nearly uniform temperature
distribution across the teeth of the gear and a contour-like hardened
profile by using high power density at the final heating stage.

WEBINAR
07.05.2015
2:00-3:00 pm
74
MICROSTRUCTURE
It is well known that the microstructure conditions of the
metal prior to the gear hardening are of fundamental
importance for the repeatability of the mechanical and
metallurgical results of the heat treatment. In particular,
initial conditions characterised by homogeneous fine-
grained quenched and tempered martensitic microstructure
with hardness of 30-34 HRC, are particularly favourable for
assuring a fast and consistent metal response to the heat
treatment, reduced distortion and minimum amount of the
grain growth, resulting in higher hardness and deeper case
depth in comparison to the ferritic/perlitic initial
microstructure.

WEBINAR
07.05.2015
2:00-3:00 pm
75
HARDNESS PROFILES
With pre-heating
With pre-quenching
And tempering

WEBINAR
07.05.2015
2:00-3:00 pm
76
DUAL FREQUENCY HARDENING
As previously mentioned, the use of two different frequencies is the
logical solution for obtaining a uniform hardened depth along the
contour of the gear. However, the range of the gear diameters suitable
for the dual frequency process is limited to gears with diameter lower
than 250 mm for economic reasons, due to the very short heating
times and the corresponding high power densities, which require the
use of frequency converters at medium and high frequency with unit
output power ranging from several hundreds of kW to some MW.

WEBINAR
07.05.2015
2:00-3:00 pm
77
SEPARATE FREQUENCY PROCESS
In these processes two frequencies are applied separately in sequence
to the same workpiece: pre-heating is accomplished in the first step of
the heating cycle by applying a low power density at MF (usually in the
range 3 -10 kHz), while during the final heating stage a high power
density at HF is used for contour hardening. The selection of suitable
values of the frequency of the final pulse, in the range 30 - 450 kHz -
depending on the type of gear, its size and material – and the heating
time allows to obtain the desired hardened depth.
In the great majority of cases the MF and HF frequency converters are
connected to two different coils, which are spatially separated,

WEBINAR
07.05.2015
2:00-3:00 pm
78
DUAL FREQUENCY CYCLE

WEBINAR
07.05.2015
2:00-3:00 pm
79
PREHEATING
The gear is preheated to a temperature which is usually 100-350ºC
below the critical temperature AC1, depending upon type and size of
the gear, tooth shape, prior microstructure, required hardness pattern
and distortion (which increases with preheating temperature) and
available power source.
Obviously, the higher is the pre-heating temperature, the lower is the
power for the final pulse. However, the increase of the pre-heating
temperature can produce an increased distortion.

WEBINAR
07.05.2015
2:00-3:00 pm
80
CONTOUR HARDENING
After preheating the contour hardening with HF is effected. Heating
times are in the range from tenths of seconds to seconds, depending
on the module, and the final stage requires a very fine control of time
and power.
To avoid through heating of the tooth, the final austenitizing operation
must be very short (often < 1 second), which requires very fast transfer
of the work piece from one inductor to the other and very high power
switching speeds.

WEBINAR
07.05.2015
2:00-3:00 pm
81
ONE INDUCTOR ONLY
A refinement of the dual-frequency method uses one common
inductor, which is first connected to the MF power supply circuit and
then switched into the HF circuit.
A limit of this technique is the time required for power switching,
typically about 0.5 second.

WEBINAR
07.05.2015
2:00-3:00 pm
82
PRE-HARDENING
As in the single frequency process, the heating cycle can comprise a
pre-quenching and tempering stage of the tooth area before the actual
hardening step; this stage is used for improving the final metallurgical
results also when the prior microstructure of the steel is not
particularly suitable for hardening.

WEBINAR
07.05.2015
2:00-3:00 pm
83
DUAL FREQUENCY CYCLE

WEBINAR
07.05.2015
2:00-3:00 pm
84
HARDENED PROFILES
MF pre-heating
Thickness 15 mm
Module 2.5 mm
pre-quenching
Thickness 30 mm
Module 3 mm

WEBINAR
07.05.2015
2:00-3:00 pm
85
DUAL FREQUENCY HARDENING

WEBINAR
07.05.2015
2:00-3:00 pm
86
CONCLUSIONS
1. Surface induction hardening has provided to distinct improvement of quality of
steel elements.
2. It is characterized by fast heating and immediate quenching
3. Heating depth can be easily changed by: field current frequency, power and heating time.
4. Numerical simulation seems to be a powerful tool supporting effective implementation of
the process to industry
5. Energy efficiency is the important factor deciding about practical implementation of the
surface induction hardening.

WEBINAR
07.05.2015
2:00-3:00 pm
87
ACKNOWLEDGEMENT
.
Acknowledgement
The presentation was elaborated within the framework of
ongoing Polish grant project PST 21/RM4/2014 and Tempus
project

Induction Surface Hardening

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Induction Surface Hardening

Similar to Induction Surface Hardening (20)

More from Leonardo ENERGY

More from Leonardo ENERGY (20)

Recently uploaded

Recently uploaded (20)

Induction Surface Hardening