effect of heat input on the microstructure and mechanical ......heat input as well as the fact that...
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 6 (2018) pp. 184-188
© Research India Publications. http://www.ripublication.com
184
Effect of heat input on the microstructure and mechanical properties of a
Welded joint-A Review
Saadat Ali Rizvi1 1Mechanical Engineering Department, Indian Institute of Technology (BHU),
Varanasi, and faculty member in UP, .JM.I, New Delhi India
Mumtaz Ahamad2 2 faculty member in UP, .JM.I, New Delhi India
Abstract
In this review paper an attempt has to be made to understand the effects of different heat input values on microstructure of parent metal (PM),the coarse heat affected zone (CGHAZ), Fine grain heat affected zone (FGHAZ), fusion zone (FZ), and various mechanical properties of welded joints. Usually heat input categories in three values. Low heat input, medium heat input, and high heat input depending on the values of welding parameters. Mechanical properties and microstructure of a weldment are too much influenced by the heat input. From various research papers, it is very clear that on low heat input microstructure of a welded joint is fine and there is an improvement in mechanical properties. But on increasing the heat input value microstructure of welded joint becomes coarse and there is a decrement in mechanical properties. Keywords: Microstructure, Mechanical properties, welded joints, SEM, fracture mode.
Introduction
Welding, nowadays, is used in producing most of the steel
structures in engineering industries. Welding offers a variety
of advantages such as uncomplicated setup, low
manufacturing cost, and high welded joint efficiency. Heat
input is known as "the electrical power supplied by the weld
arc to the workpiece." usually, however, heat input can
approximately if the arc efficiency is not taken into
consideration be characterized as the ratio of the arc power
supplied to the electrode over the arc travel speed, and it is
expressed as the following equation:
Where A= welding current in ampere; V-= arc voltage in volt;
and S= welding speed or arc travel speed in mm/min or
cm/min. In this approach, unit of heat input is J/mm, KJ/mm,
J/cm, or KJ/cm where J stands Joule, and KJ stand kilo Joule
respectively. Ramy Gadallah et al [1] determined the effect of
heat input and residual stress on fatigue crack propagation.
For this author generate a finite element (FE) model and they
informed that on the change in Heat Input there is one changes
in RS distribution, welding distortion, and welding
penetration. However, the change in welding HI has no
considerable influence on the magnitude of the induced
welding RS.
Figure 1. Influence of the change in Heat Input on the
distribution of longitudinal welding RS [1].
Jinfeng Wang et al [2] studied the energy input effect on the
mechanical properties and microstructure of DP1000 steel
welded by laser and they concluded that as there is a
decrement in energy input, the weld bead width and the width
of softening region became narrowed, and there in an
increment in mechanical properties as the energy input
decreased and they also added that as there is an increment in
energy input, the grain of this zone became coarse, and the
joints mechanical properties became poorer.
Figure 2. Macrosection of the welded joints. (a) Energy input
was 325 J/mm, (b) energy input was 217 J/mm, (c) energy
input was 163 J/mm, (d) energy inputwas130J/mm, (e) energy
input was 108 J/mm, and (f) energy input was 93 J/mm [2]
E. S. Mosa et al [3] determined the effect of heat input and
shielding gases on mechanical properties and microstructure
of SS304L steel. They considered 98% Ar and 2% N2 as
shielding gas and they mentioned in their result that
microstructure revealed changing in solidification structure
from ferrite to austenite 98% Ar and 2% N2 is used as
shielding gas and result also revealed when heat input
increased then the size of dendrite and inter-dendritic spacing
in the welded joint increase to. The ferrite number decreased
with increasing the heat input and using a mixture of 98 % Ar
and 2 % N2
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 6 (2018) pp. 184-188
© Research India Publications. http://www.ripublication.com
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(a) Low heat input
(b) high heat input
Figure 3. Dendritic structure of WM at low heat input [3]
Leonardo N. Tufaro et al [4] determined the Heat Input effect
on AA5052 Friction Stir Welds (FSW) Characteristics and it
was observed from the result that an increase in power with
shoulder diameter, as well as a lower level of defects in the
stirred zone, related with an improved plastic flow. Hardness
also decreased with tool diameter, due to a higher thermal
effect on the microstructure.
Chellappan Muthusamy et al [5] studied the Heat Inputs effect
on Mechanical properties and microstructure of AISI 410S
Martensitic Stainless Steel weldment, welded with Gas
Tungsten Arc Welded (GTAW).
Figure 4. The microstructure of HAZ near to fusion line
under different heat input [5]
Figure 5. Fractographs of impact tested surface of weld
deposit under different heat inputs [5]
Xiao-Long Gao et al [6] studied the heat inputs effect on
mechanical properties and microstructure of pulsed laser
welded joints in Ti6Al4V/Nb, two dissimilar alloys and in
their result authors concluded that as there in increment in
heat input, the width of the heat-affected zone (HAZ) at the
side of Ti6Al4V increases significantly and underfill defects
moved out from the fusion zone (FZ) and mechanical
properties and microstructure of weldment heterogeneity in
the FZ of the welded joints increases with the increasing in
heat input.
Figure 6. Microhardness profiles of the weld cross-section for
various heat inputs. A 22.5 J mm−1, b 45 J mm−1, and c 67.5
J mm [6]
K.Monika et al [7] determined the heat inputs effect on the
mechanical quality of MIG welded dissimilar joints and
authors mentioned in their results that there is an increment in
tensile strength as there is a decrement in heat input and they
also added that there is an increment in hardness as there is a
decrement in heat input.
Figure 7. Strength and hardness of a welded joint at low and
high heat input [7]
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 6 (2018) pp. 184-188
© Research India Publications. http://www.ripublication.com
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Adam Grajcar et al [8] studied the heat inputs effect on
hardness distribution and microstructure of Si-Al trip-type
steel welded by laser. For their experimental works they
considered the heat input applied value from 0.037–0.053
kJ/mm and authors measured that there is no significant
impact on the microstructure and microhardness of the laser-
penetrated area of weldments.
And also they mentioned in their result that Heat Affect Zone
width and Fusion Zone increases along with increasing in the
heat input as well as the fact that a heat input of 0.051 kJ/mm
responsible for excessive grain growth, the value of this
parameter should be limited to about 0.045 kJ/mm. Lichan Li
et al [9] determined the effect of welding heat input on
microstructure and grain size of 316L SS welded joint. In their
experimental work, they described that on increasing the
amount of heat input. Zhiqiang Zhang et al [10] investigated
the heat inputs effect on mechanical properties and
microstructure of DSS welded joint welded by EBW process.
In their result, they summarized that on increase in heat input
promotes the growth of grain boundary austenite and the
formation of fine intragranular austenite. The EB had
significantly higher microhardness than the BM and the EB
weld had relatively lower toughness than the BM on changing
the value of heat input.
Figure 8. Macrostructure of penetration areas made with
process heat input of 0.051 kJ/mm (a); 0.043 kJ/mm (b); 0.037
kJ/mm (c) 0.051 kJ/mm [8]
Figure 10. SEM fractography of the EB welds with different
heat inputs of (a) 0.43, (b) 0.46, (c) 0.50 kJ/mm, and (d) BM
[10]
Xiao-Nan Wang et al [11] determined the effect of different
heat input on microstructure and fracture behavior of DP steel
welded joint and they concluded that the microstructure of
welded joints with different heat inputs was same but S-
CHAZ was unlike. With heat input increased, the decay of
martensite and precipitation of carbides were more significant,
such that the hardness decreased and they further added that
with the increasing heat input strength and elongation of
welded joints first increased and then decreased.
Figure 11. Tensile fracture of SEM with different heat inputs
[11]
Minghao SHI et al [12] determined the high heat Inputs effect
on Impact toughness and Microstructure of coarse grain heat
affected zone (HAZ) in Zr bearing low carbon steel and they
informed that Excellent impact toughness (more than 100 J) of
CGHAZ with heat input of 1 000 kJ/cm was obtained and
Impact toughness of Coarse grain heat affected zone with 400
kJ/cm (230 J) is the highest, because austenite grain size of
CGHAZ with 400 kJ/cm favors the growth of acicular ferrite
inside grain. They also added that Austenite grain size of
CGHAZ increases with heat input increasing due to long
holding time at peak temperature.
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 6 (2018) pp. 184-188
© Research India Publications. http://www.ripublication.com
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Figure 12. Charpy impact toughness of parent metal (PM),
and CGHAZ with heat input of 100 kJ/cm, 200 kJ/cm, 400
kJ/cm, 800 kJ/cm and 1 000 kJ/cm [12]
Honggang Dong et al [13] investigated the Heat Inputs effect
on Mechanical properties and microstructure of HSLA Steel
Joint and they mentioned in their result that impact toughness
of HAZ was not monotonously improved with the increase of
welding heat input and result revels increasing the welding
heat input could suppress the formation of martensite And
reduce the microhardness of HAZ.
Figure 13. SEM images of the impact fractures in base metal
(a) and in HAZ under different welding heat inputs of (b) 0.25
kJ/mm, (c) 0.46 kJ/mm, (d) 0.57 kJ/mm, (e) 0.67 kJ/mm, and
(f) 0.77 kJ/mm [13]
Mohammed Asif M et al [14] determined the effect of heat
input on microhardness, corrosion and mechanical properties
of UNS S31803 Duplex stainless steel welded by friction
welded. They informed that higher the heat input the better
was the preservation of joint strength. At room temperature,
toughness decreased as heat input increased. Microhardness
increases with an increasing in heat input due to grain
refinement. They also added that the Corrosion resistance of
weld was better than that of base material and it is increased
with an increase in the heat input.
Figure 14. Distribution of microhardness in DSS at different
heat input [14]
Fuyang Gao et al [15] studied the effect of different heat input
on mechanical properties and microstructure of Titanium
alloys welded by EBW. In their experimental work, they
mentioned that that for small heat input (SHI) weld metal,
martensite α’ phase was wide and intertwined and the residual
ß was relatively high. For large heat input (LHI), martensite α’
was relatively small. The microstructure of the HAZ was not
same at all point. For small heat input (SHI), ß phase collected
infusion line, and the heat affected zone (HAZ) of small heat
input had more residual ß phase than that of LHI. They also
added that a value of microhardness at the center of weld
metal of SHI reduces greatly because of α phase.
HongLiang Li et al [16] find out the heat inputs effect on arc
constancy and weld bead quality by FCAW of E40 steel in
underwater welding. In this experimental work, they defined
that heat input changes the chemical composition of weldment
and UTS and Toughness of weldments increases on increasing
the heat input. It is due to solid solution strengthening of
alloying elements. They also added that heat input has no
important effect on the hardness of CGHAZ.
Figure 15. Microstructure of weld metal and coarse-grained
heat affected zone at different heat inputs [16]
Wan Shaiful Hasrizam Wan Muda et al determined the effect
of heat input on microstructure and mechanical properties at
HAZ of ABS grade steel and they reported in their result that
formation of microstructure at CGHAZ was consisting of
pearlite (P), grain boundary ferrite (GBF), and Widmanstatten
ferrite (WF). Grain coarsening was observed at the CGHAZ
of all the joints, and it was found that the extent of grain
coarsening at CGHAZ has also increased as increment in the
heat input.
Figure 16. shows the micrograph of weldment at different
heat input [17]
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 6 (2018) pp. 184-188
© Research India Publications. http://www.ripublication.com
188
Subodh Kumar and A.S. Shahi studied the effect of heat input
on mechanical properties and microstructure of AISI 304
welded joints by GTA welding and they concluded that joints
fabricated at low heat input shows higher ultimate tensile
strength (UTS) than those welded by medium and high heat
input respectively. Significant grain coarsening was observed
in the heat affected zone (HAZ) of all the welded joints and
extent of grain coarsening in the heat affected zone increased
with increase in the heat input. It was also found that average
dendrite length and inter-dendritic spacing in the weld zone
increases with increase in the heat input which is results in
changing in the tensile properties of the weld joints.
CONCLUSIONS
This study investigates the effect of heat input on the
mechanical behavior and microstructure of welded joints of
different steels welded with various welding. Based on the
review of various papers, the following conclusions are
drawn:
Mechanical properties of different welded joints are significantly affected by heat input. In some cases on
increasing the heat input value tensile strength
increases but after sometimes it starts to decreases.
At low heat input UTS having highest value at compared to welded with medium and high heat
input.
Microstructure is also affected by heat input. At low heat input microstructure of weldments are fine but
as the value of heat input increases, the
microstructure of weldments start to become coarse.
As the microstructure of weldments starts to become coarse, the Toughness value of weldments decreases.
On increasing the heat input coarsening of grain start at CGHAZ.
Hardness of weldments is also influenced by the heat input.
Corrosion resistance power of weldment is also affected by the heat input.
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