Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
Intensive Quenching of Steel Parts: Equipment and Method
N. KOBASKO, M. ARONOV, J. POWELL, J.VANAS
IQ Technologies, Inc., Akron, USA
www.intensivequench.com
Euclid Heat Treating Co, Euclid, USA
www.euclidheattreating.com
Abstract: - The paper discusses an intensive quenching (IQ) method and IQ equipment. It is shown that
film boiling is absent and a main mode of heat transfer is nucleate boiling during intensive quenching of
large steel parts in electrolytes (water salt and alkaline solutions). In such condition during immersion of
steel parts into water solutions, the heat transfer coefficient is extremely high and the part surface
temperature drops to a quenchant saturation temperature within 1 or 2 seconds. It is recommended that
when quenching intensively low and medium carbon steels the steel chemical composition should be
tailored to provide an optimal quenched layer after complete cooling. Due to providing the optimal
quenched layer, very high residual surface compressive stresses form. Since the martensite finish
temperature is about 100oC for low carbon and medium carbon steels, significant cooling rate within the
martensite range is achieved. Due to this fact, the superstrengthening of a material in the part surface
layers is observed. Both the high residual surface compressive stresses and the superstrengthening of
material increase service life of steel parts. It is shown that water salt solution Na2(NO3) of optimal
concentration prevents corrosion of the parts being quenched and IQ equipment.
Key – Words: - Intensive quenching, Nucleate boiling, Optimal quenched layer, Service life, Corrosion,
Environment.
1 Introduction
To develop correctly intensive quenching process
for steel parts, it is necessary to take into account
a dependence of the martensite start temperature
and martensite finish temperature on carbon
content in steel (see Fig. 1).
Fig. 1 Martensite start temperature MS and
martensite finish temperature MF versus carbon
content in steel.
ISSN: 1790-5095
153
As known, a self-regulated thermal process takes
place during quenching of steel parts. The selfregulated thermal process is characterized by a
very slow rate of the surface temperature change.
During this process, for example, surface
temperature changes from 110oC to 104 oC and
core temperature changes from 850oC to 200oC
[1]. During quenching of high carbon steel in
water, the transformation of austenite into
martensite can be delayed if the martensite start
temperature is below 100oC. The martensite
transformation in this case starts when natural or
forced convection begins. During natural
convection, the cooling rate within the martensite
range is very low. Because of this neither the
superstrengthening effect nor high surface
compressive stresses are observed [1]. The forced
boiling didn’t impact the phase transformation.
The final result is like after conventional cooling
in oil. In the contrary, when quenching low
carbon steels, having martensite finish
temperature about 100oC, very intensive
quenching will be produced within the martensite
range since during cooling in water salt solution
film boiling is absent and MF is above saturation
temperature. Let’s consider these processes in
ISBN: 978-960-474-105-2
Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
more detail on the basis of inverse heat
conduction problem solution.
Table 1 Time required for the surface of steel spheres of different sizes to cool to different temperatures
when quenched from 875oC in 5% water solution of NaOH at 20 oC and moving at 0.914 m/s [2].
Size,
Time,
inches
seconds
(m)
700oC
600oC
500oC
400oC
300oC
250oC
200oC
150oC
4.75”
0.040
0.070
0.11
0.13
0.15
0.17
0.28
1.60
(0.1206) 0.050
0.065
0.08
0.12
0.19
0.24
0.35
1.10
0.040
0.062
0.09
0.12
0.18
0.23
0.32
0.78
0.042
0.065
0.08
0.12
0.24
0.27
0.35
0.60
Average 0.043
0.066
0.09
0.12
0.17
0.21
0.29
0.95
1.90
0.47
0.34
0.22
0.13
0.10
0.060
0.030
7.15”
0.94
0.44
0.33
0.27
0.16
0.12
0.090
(0.1816) 0.050
0.60
0.35
0.27
0.24
0.12
0.09
0.060
0.040
1.15
0.42
0.31
0.24
0.14
0.10
0.070
Average 0.040
11.25”
(0.2858)
Average
0.055
0.030
0.043
0.12
0.11
0.12
0.18
0.21
0.19
0.32
0.33
0.33
0.60
0.54
0.57
0.98
0.73
0.96
1.51
1.04
1.28
Table 2 Thermal conductivity of supercooled austenite versus temperature
T, ºC
100
200
300
400
500
600
700
17.5
18
19.6
21
23
24.8
26.3
W
λ,
mK
W
λ,
mK
17.5
17.75
18.55
19.25
20.25
21.15
21.90
2.66
1.70
2.18
800
27.8
900
29.3
22.65
23.4
Table 3 Thermal diffusivity a of supercooled austenite versus temperature
T, ºC
100
200
300
400
500
600
700
800
900
a ⋅ 10 6 ,
m2
s
4.55
4.63
4.70
4.95
5.34
5.65
5.83
6.19
6.55
a ⋅ 10 6 ,
m2
s
4.55
4.59
4.625
4.75
4.95
5.10
5.19
5.37
5.55
Note: λ and a at 500°С mean average values for the range of 100°С - 500°С (analogously for other
temperatures). Data provided in Table 1, Table 2, and Table 3 are used at solving inverse problem.
ISSN: 1790-5095
154
ISBN: 978-960-474-105-2
Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
2 Analyzing of quenching processes
on the basis of inverse heat
conduction problem solution
To solve an inverse problem and to get accurate
results of calculations, very accurate experimental
data are needed.
Previously we use our
experimental data, however in this paper we will
use accurate experiments of French [2]. Many
authors checked these data and they are worthy to
analyze (see Table 1). Table 1 provides surface
temperature versus time for steel spheres, which
were quenched in 5% water sodium hydroxide
solutions. The steel spheres were heated to 875oC
and quenched in the solutions at 20oC. Software
IQLab was used for solving inverse heat
conduction problem (IP). The IQLab software
comprises
the
latest
achievements
in
computational science including Tikhonov
method [3, 4]. Tables 1, 2, and 3 provide the
surface temperature and thermal properties of
steel, which were used to solve inverse problem
(IP). To restore surface temperature during a self–
regulated thermal process after 150oC, equations
(1), (2), and (3) were used [5] which allow
calculating a duration of the self – regulated
thermal process and overheats at the beginning
and at the end of the process [6]:
⎡
ϑ ⎤K
τ = ⎢Ω + b ln I ⎥ ,
ϑ II ⎦ a
⎣
where ϑ = Tsf − TS is overheat; m = 10/3;
β is between 3 and 7.36.
After a reconstruction of the surface temperature
(see Fig. 2), the core temperature was calculated
using the boundary conditions of the first kind.
Having these data, heat flux densities were
calculated by solving inverse heat conduction
problem. Results of calculations are presented in
Fig. 3. It should be noted that the boiling
process in water starts if the heat flux density
is within 0.1 - 0.4 MW/m2 and overheat is
about 4oC. That is true when the part surface
is heated from the room temperature to the
saturation temperature and over. During
quenching these values could be less.
(1)
where b=3.21;
0.3
1 ⎡ 2λ (ϑ0 − ϑ I ) ⎤
ϑI = ⎢
⎥ ;
β⎣
R
⎦
ϑ II =
1
β
[α conv (ϑ II + ϑuh )]0.3
(2)
(3)
These equations were obtained analytically
assuming that the heat transfer coefficient is a
function of the heat flux density, i.e.
α nb = βq 0.7
(4)
It was noticed that the duration of transient
nucleate boiling changes from 60 s to 68 s when
β changes from 3 to 7.36.
or
α nb = β mϑ m −1 ,
ISSN: 1790-5095
Fig. 2 Surface and core temperature versus time
during transient nucleate boiling when quenching
spheres 120.65 mm in diameter in 5% water
sodium hydroxide solution: a) is for β = 3; b) is
for β = 7.36.
(5)
155
ISBN: 978-960-474-105-2
Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
Heat flux densities during quenching of the
sphere of 120.65 mm in diameter are presented in
Fig. 3.
at 20oC. It means that no film boiling will take
place under these conditions. Experiments of
French support this fact (see Table 1).
Now let’s see how heat transfer
coefficients during quenching are changing. It
should be noted that there are two kinds of heat
transfer coefficients: a real heat transfer
coefficient, which is calculated from equation (6)
α nb =
q
Tsf − TS
(6)
and an effective heat transfer coefficient, which is
calculated from equation (7).
α ef =
q
Tsf − Tm
.
(7)
Historically heat treaters are using in the practice
equation (7).
Fig. 3 Heat flux densities versus time during
quenching of the steel sphere in 5% water sodium
hydroxide solution at 20oC: a) is the heat flux
when β = 3; b) is heat flux when β = 7.36.
Note that values β = 3 and β = 7.36 were used
only for overheat calculations and reconstruction
of the surface temperature, but not for equation
(4) or (5). We think that during quenching these
values significantly differ from empirical data,
which were received for boiling at heating small
elements in liquid to produce boiling processes.
Such difference is explained by the existence of
shock boiling and by an extremely high gradient
of the temperature.
In Fig. 4, the heat flux density is provided
as a function of the part surface temperature. As
we can see from Fig. 4, the heat flux is equal to
zero at the beginning of the quench. It increases
further to maximum value of about 13 MW/m2,
which is less than the first critical heat flux
density for 5% water sodium hydroxide solution
ISSN: 1790-5095
156
Fig. 4
Heat flux densities versus surface
temperature during quenching the steel sphere
(120,65 mm in diameter) in 5% water sodium
hydroxide solution at 20oC: a) is heat flux when
β = 3; : b) is heat flux when β = 7.36.
ISBN: 978-960-474-105-2
Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
Fig. 5 and Fig. 6 present heat transfer coefficients
versus time and surface temperature for sphere
quenched in 5% water sodium hydroxide solution
at 20oC.
and there is a moment of time when they reach
maximum value and then decrease very slowly with
time (see Fig. 5).
3 Optimal quenched layer and
equipment to provide it
An optimal quenched layer provides an optimal
residual stress distribution after intensive
quenching: high compressive residual stresses at
the surface and small residual stresses at the core
of steel parts. Such distribution of residual
stresses is achieved if ratio (8) is fulfilled, i.e.
DI
= const. ,
Dopt
Fig. 5 Real and effective heat transfer coefficients
versus time for steel sphere 120.65 mm in
diameter quenched in 5% water sodium
hydroxide solution at 20oC from 875oC.
(8)
0.5
⎛ abτ M ⎞
⎟ ,
DI = ⎜⎜
⎟
ln
θ
Ω
+
⎠
⎝
(9)
where DI is an ideal critical diameter; a is an
average value of thermal diffusivity of steel; b is
a constant which has the following numbers for
cylinders and spheres: 23.132 and 39.48; τ M is a
cooling time from the initial temperature to the
martensite start temperature which provides 50%
martensite at the core (see Fig. 7); Ω = 0.48 for
a cylinder and Ω = 0.72 for a sphere; θ is
dimensionless temperature; the constant in Eq.(8)
varies between 0.3 and 0.5; Dopt is a real
diameter of the steel part.
Fig. 6 Real and effective heat transfer coefficients
versus surface temperature for steel sphere 120.65
in diameter quenched in 5% water sodium
hydroxide solution at 20oC from 875oC: a) are
real and effective heat transfer coefficients for β
= 3; b) are heat transfer coefficients for β = 7.36.
As we can see from Fig. 6, heat transfer coefficients
increase with the decrease of the wall temperature
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157
Fig. 7 CCT diagram of AISI 1045 steel to
evaluate cooling time τ M
ISBN: 978-960-474-105-2
Proceedings of the 7th IASME / WSEAS International Conference on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT (HTE '09)
To provide an optimal quenched layer in steel
patrs after quenching and the effect of
superstrengthening, three companies in the State
of Ohio built production equipment which is
shown in Fig. 8.
91cm×91cm×182cm (36”×36”×72”) integral
quench atmosphere furnace equipped with an IQ
water quench tank of 41.6 m3 (11,000 gallons).
The furnace is equipped with an intermediate
chamber connecting the heating chamber with the
IQ tank to ensure that quenchant vapor does not
contaminate the furnace atmosphere. As a
quenchant the water solution of Na2(NO3) is used.
The described above method of quenching and
equipment make steel parts cheaper and stronger
and environment cleaner.
Conclusions
1. It has been established that the heat
transfer coefficients during transient
nucleate boiling can achieve a value of
200,000 W/(m2K) and greater.
2. During transient nucleate boiling, the
surface
temperature
changes
insignificantly and maintains at a level of
the saturation temperature.
3. Method of quenching for low and
medium carbon steels is proposed which
provides high residual compressive
stresses at the surface of steel parts due to
the optimal quenched layer and very
intensive quenching within the martensite
range.
4. Equipment for intensive quenching of
steel parts has been manufactured and
implemented into production.
Fig. 8 Equipment for intensive quenching of steel
parts:
Fig. 8 a) shows a production IQ system
for batch quenching consisting of a 6,000-gallon
stand-alone IQ water tank equipped with four
props
and
a
36”x36”x48”
atmosphere
furnace. The IQ system shown in Fig. 8b is
capable of quenching loads of up to 3,000 lb. Fig.
8b presents a production IQ system for batch
quenching consisting of a 1,900-gallon standalone IQ water tank equipped with one prop and
Ø23”x23” atmosphere pit furnace and load
transfer mechanism. The IQ system is capable of
quenching the load of up to 800 lb. Fig.8c
presents
a
picture
of
the
production
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158
References:
[1] N.I.Kobasko,
Steel
superstrengthening
phenomenon, JAI, Vol. 2, No. 1, 2005.
[2] H.J. French, The Quenching of Steels, Amer.
Society Treat. 1930.
[3] A.N.Tikhonov, V.B.Glasko, Application of
Regularization Method in Non-Linear
Problems, Jour. of Comp.Math. and
Math.Physics, Vol. 5 (No. 3), 1965.
[4] V.V.Dobryvechir, N.I.Kobasko, E.N.Zotov,
W.S.Morhuniuk, Yu.S.Sergeyev, Software
IQLab, ITL, Kyiv, Ukraine, www.itl.kiev.ua
[5] N.I.Kobasko, Intensive Steel Quenching
Methods, in a Handbook Theory and
Technology of Quenching, Liscic, B., Tensi,
H.M., and Luty, W., (Eds.), Springer-Verlag,
New York, 1992, pp. 367 - 389.
[6] Kobasko, N.I., Self- regulated thermal
processes during quenching of steels in liquid
media, IJMMP, Vol.1, No 1, 2005, pp. 110 124.
ISBN: 978-960-474-105-2