Effect of welding parameters on Phase Transformations

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ISSN: 1298-0595
Vol.27; No.2 (2015)
Effect of welding parameters on Phase Transformations and
Rigidity of Welding Finite Element Method
Ala Abedinzadeh1, Amir Mostafapour2
1
Science and Research Branch, Islamic Azad University, Tehran, Iran
2
University of Tabriz
ABSTRACT
This study investigates the effect of phase transformations during welding
operations on the hardness of the weld parts in low carbon and medium carbon
Steelswith the use of software Tool ANSYS And MATLAB The software
coding using a three dimensional finite element study of the piece. This paper
examines a number of phase transformations during continuous cooling process
and the formation of martensite in the area affected by acne and pimples HAZ
and Deals. Changes in volume of austenite to martensite transformation process
can be used to determine the amount of martensite formed by the application
and the relationship between the amount of martensite and hardness, and The
hardness profile of the weld to weld determined by the distance from the center.
One of the major problems of welded structures composed of martensite in the
region HAZ and its role in the hardness of the weld. In this study it is shown
that the properties of low carbon steels with lower job martensite, but mediumcarbon steels with properties suitable job martensite. In this phase changes and
the formation of martensite and thermal conductivity have been independently
investigated. In this paper, the simulation the welding process and to measure
the hardness of the weld, act like has been implemented in two stages.
KEY WORDS: Martensite, hardness, phase transformations, Finite element
Background:
One of the major problems of welded structures composed of martensite in the
region HAZ and its role in the hardness of the weld. Formation of martensite
phase transformation and the effect on the stiffness and tension of welding
residual is very important. Stress Residual welding may develop cracks and
reduce the buckling and... Parameters such as welding, preheat and then and the
number of passes welding of structural changes resulting from effective.
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Austenite to martensite steel in some phase change cooling time has important
effects on stiffness and tension residue of the process and its distortion. The
martensitic phase transformation without diffusion or displacement Where
individual atoms and therefore does not require thermal activation and the
change of shear and by displacement of the mass of the atom Performed. The
martensite phase or displacement by a martensitic transformation where a
group of atoms are obtained alloys of iron - carbon steel, Atom Carbon in the
octahedral spaces Network bcc Confined and therefore soluble carbon bcc To
greatly increase the volume of the crystal lattice of bcc To bct Converts Where
the parameter c The larger of the two other network parameters a Is. [1]
Therefore when martensite formed is an increase in the volume of metal and
plastic deformation will occur this increase in volume and the critical role
distortion and stress Residual weld area and region HAZ It had.
Model the finite element method:
In this phase changes and the formation of martensite and thermal conductivity
have been studied independently.
In this paper, the simulation the welding process and to measure the hardness
of the weld Act like has been implemented in two stages.
1- Similar to determine the thermal history of the welding process and thermal
conductivity
2. The temperature history and determine the phase changes in each element
First step:
In this paper, the process of welding and thermal conductivity were investigated
in a three-dimensional plot of the thermal history of each element is at any time
to complete Back. The pieces were shown below. Since the piece is symmetric
so like Building on half of it has been done. These fragment 13,735 elements
and the length and width and height respectively 1 0, mm 10 0, mm 8 May Is.
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Figure 1 - View three-dimensional plot of simulated
To determine the effect of carbon on phase transformations in steel welding
process two types, one with low carbon (ck15) and the average carbon (ck45)
has been studied. The specific characteristics of the steel table (1) and Fig. (2) Is
shown. [2]
Table 1. Chemical composition of alloy steels ck45, ck15
Steel C
Si
Mn P
S
Cr
ck15 0.15 0.22 0.41 0.021 0.024 0.06
ck45 0.44 0.22 0.66 0.022 0.029 0.15
Figure 2. The graph of changes in physical properties depending on temperature
Elise temperature heat source and its:
The welding TIG During the welding process without the use of welding
electrodes with a heat source model is implemented. In welding TIG the
electrode is connected to the negative.
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In the car these four mechanisms of welding joints Is: [3]
1. Continuous electron kinetic energy in the arc
2. The influence of the thermal electron density on the surface working
3. Existence of radiation from the arc
4. The heat transfer surface of the plasma arc working
The first mechanism is the most energy sources.
In this model, of the model the double ellipsoidal heat source was used as the
method.
Thermal model Oval Dual diversity:
The welding TIG During the welding process without the use of welding
electrodes with a heat source model is implemented. In welding TIG the
electrode is connected to the negative.
In this model, of the model The double ellipsoidal heat source method was
used [3]
Figure 3 - the ellipsoid heat source Dual Diversity
The welding heat source model is a combination of two ellipses Astragalus is
considered continuous motion used. The analytical solution for the model The
Limited almost impossible.
So often the way Numerical model to solve Used welding. Finite element
method is a reliable method for obtaining the temperature distribution during
the welding process that is used by many researchers.
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Temperature distribution in each of the oval Milk vetch is presented in the
form varies, so that the equations of the heat in the middle of front and rear as
follow [4]
(1)
(2)
In the above equations a , B, c 1, c 2 Fixed Experimental and f r, f f To Defined
Used. In the above equations extension f Front of the semi-circle Diversity and
extensions r about half of its dorsal.
Variable Q The amount of heat input Depending on the severity of the I and
voltage U and the efficiency η and is defined as follows.
Q = I. U. η
(6)
Fixed parameters the equations in Table (2) have come. [5]
Table 2. The constants The equations (2) and (1)
fr
c
b
a 2 a 1 Parameter
ff
0.67 1.33 5
3.5mm 10 5
Value
mm
mm mm
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Heat transfer:
Due to the high temperatures generated in the boiling heat transfer by
convection and by radiation is performed A., Due to the temperature
dependence of heat transfer coefficient and heat transfer coefficient to increase
the accuracy of the model is as follows: . [6]
0
<T <500 0 C α h = 0.0668T (W / m)
500 0 C <T α h = 0.231T - 82.1 (W / m)
For temperatures simple carbon steels A
equations . [7]
(7)
1,
A 3 Obtained from the following
A 1 = 723 - 10.7Mn - 16.9Ni + 29Si + 16.9Cr + 290As + 6.4W
A 3 = 912 - 203 - 15.2Ni + 44.7Si + 104V + 31.5Mo + 13.1W - 30Mn - 11Cr
- 20Cu + 700P + 400Al + 120As + 400Ti (8)
Phase transformations:
During continuous cooling of austenite structure fcc The martensite lattice
structure bct Phase change and increase the volume Result. The volume
changes during phase transformations in shape (4) have come.
Figure 4. Diagram of volume changes in temperature
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The martensitic transformation of the period t 8/5 And the percentage of
martensite transformation of two steel ck15, ck45 Using the diagram CCT The
two cases were austenitized at 900 and 1050 ° C for 5 min was plotted in the
figure below.
To determine the phase transformation to a three-dimensional plot of the
relationship Koistinen- Marburger Use . [8]
( M s ≥T ) f m (T) = f (1-exp (-k (M s -T))) (9)
F m (T): The amount of martensite at a specified temperature T
K: Constant factor in percent for carbon steel (k = 0.011)
T Temperature pieces per minute
M S : Austenite to martensite transformation temperature at which it begins
Back.
M s = 561- 474C- 33Mn -17Ni- 17Cr - 21Mo (1 0)
Temperature M S to change the phase steels ck15, ck45 Table (3) it is stated.
Table 3 transformation temperature of the metal to steel ck45, ck15
M f
C)
280
140
(0
Ms
C)
476
328
(0
A 3
C)
843
787
(0
A 1
C)
726
724
(0
steel
ck15
ck45
During the welding process, the strain resulting in an increase in the volume of
austenite to martensite microstructure during the transition phase. Therefore,
possible variations in the amount stated in the following manner. [9]
(11)
In this regard,
Volume changes due to phase transformations.
The relationship between volume and percentage of martensite martensitic
transformation is expressed as follows: back,
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(12)
In this regard, T C Δ The temperature during the cooling device Work and C
εΔ Constant volume of the steel ck45, ck15 Respectively 2.88 × 10 -3, 8 × 10 -3
Is.
And martensite hardness equation:
After determining the amount of martensite in the degree of difficulty of each
element must be determined which elements. The hardness of the martensite
carbon content in a way that depends on the hardness of martensite increases
with increasing carbon content.
For steels studied ck45, ck15 Relationship between hardness and martensite in
the form of (5) It is stated.
Figure 5. The relationship between hardness and percentage of martensite steel ck45
Using the Software MATLAB and between access to each of the following
statements concerning the hardness of martensite in steel CK45, CK15
Expressed .
HRC = 1.2124 × 10 -6 X 4 - 1.9846 × 10 -4 X 3 +8.2311 × 10 - 3 X 2 + 2.3226 ×
10 -1 X + 30.157
(13)
X Percentage of martensite
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HRC Hardness in Rockwell C
Results:
As stated earlier in this article, I will be the first welding process using heat as
ellipses Double Extra and thermodynamic properties ck45, ck15 And the
conductivity Variable temperature using software ANSYS A three-dimensional
simulation Then for each element of the History of temperature as a function of
time obtained The . For example, the temperature history of the work piece In
the figure below (6) Has come.
Figure 6: Elements of temperature versus time history
For example, elements of the thermal history of the weld surface in the form of
(7) are expressed.
Figure 7 - The history of central Germany boiling temperature versus time
Temperature distribution diagram for welding pieces Figure (8).
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Figure (8) - Temperature distribution diagram of the welding zone
Accurate to express the results of simulation, modeling and mesh sample in
Figure (9) is considered.
Figure (9) - Typical mesh and named
Then determines the temperature history for each element in Software
MATLAB Using a using equations 8, 9, 10, 12 in each element is determined
by the amount of martensite And then using the relationship in terms of
Rockwell 13 hardness C Expressed A. For the validation of simulation the
practical test is performed to evaluate the hardness of the metal and x Make the
hardness testing, hardness and percentage of martensite as a practical
measurement and simulation results the following table is used for comparison.
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Table 4. Results of hardness and percentage of martensite steel welding CK45
Rockwell Of
The
hardness martensite maximum
temperature
58
100
1750
58
100
1650
57
98
1550
55
95
1490
52
90
1150
49
80
860
46
65
720
Number
ninety
N1
N2
N3
N4
N5
N6
N7
Simulation of welding processes for the steel ck45, ck15 the amount of
martensite obtained by welding two pieces obtained as follows: The following
results show that the properties of low carbon steels with higher carbon
martensitic steels properties of martensite job creation, but a little more difficult
as a result of higher welding.
Table 5. The percentage of martensite steel obtained for two ck45, ck15
E6
E5
E4
E3
E2
E1
Germany
24
65
91
95
98
98
Drsdmartnzyt
ck15
4
11
16
18
21
22
Drsdmartnzyt
ck45
In steel ck45 After determination of martensite formed in each element using
the software ANSYS And use of relevant difficult to determine the percentage
of martensite The difficulty of each element based on the distance from the
center of the weld on the surface of the element to be determined . Figure 10
shows the percentage of martensite in terms of distance from the center of the
weld.
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Figure 10 - The martensite transformation in terms of distance from the line of
welding
Figure (11) In terms of hardness Vickers hardness can be seen in various
welding .
Figure 8. Vickers hardness of welding in welding in different areas
Effect of welding parameters:
The relationship between hardness and martensite for each piece of nodes in
the simulated welding table (6) is expressed.
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Table 6 - Results of hardness and percentage of martensite steel welding CK45
Energy
Weld 600 [J / mm]
Of
The
martensite maximum
temperature
84
2470
65
2360
54
2140
46
1900
42
1620
36
1380
Energy
Weld 400 [J / mm]
Of
The
martensite maximum
temperature
100
1750
98
1680
95
1550
90
1410
85
1340
75
1100
Germany
E1
E2
E3
E4
E5
E6
To investigate the effect of welding parameters on the structural change of the
mode is used for simulation. In the first case, the welding current of 200 m.a
and a voltage of 12 V and a welding speed of 3 mm per second and the rate of
return of 5.0 is used in this case, the energy input of 400 joules boiling mm. In
the second case, the welding current of 300 m.a and a voltage of 20 V and 5.0
welding speed of 5 mm per second and the rate of return is that in this case the
energy J 600 mm weld input. To increase energy and reduce the cooling rate of
martensite formed for welding with high input energy decreases. For maximum
results, and the percentage of martensite in the table (7) is shown.
Table 7 - The hardness of martensite and welded to two different modes
Rockwell Of
The
hardness martensite maximum
temperature
58
100
1750
58
100
1650
57
98
1550
55
95
1490
52
90
1150
49
80
860
46
65
720
Number
ninety
N1
N2
N3
N4
N5
N6
N7
Conclusion
Similar The welding process with oval heat source Dual-like species Phase
transitions in three-dimensional finite element simulation of welding TIG And
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determine the martensite transformation from welding area and determine the
percentage of martensite hardness profile of the steel Carbon and carbonaverage results obtained.
1- The phase transformation in low carbon steels in the region of weldments
HAZ Consequently there is less job martensite properties of martensite resulting
in lower areas.
2 - In the medium-carbon steels with high job martensite properties in the weld
region and a high percentage of martensite and hardness in the weld region was
observed in the weld region back.
3. In medium carbon steels welding job because of the properties of martensite,
embrittlement of the weld is high.
4. Due to the increased energy and reduce the cooling rate of the weld with a
high percentage of martensite formation, decreased energy and reduces the
hardness of the welding back.
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