Effect of heat input on the microstructure and mechanical ......heat input as well as the fact that a heat input of 0.051 kJ/mm responsible for excessive grain growth, the value of

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



185

(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]



186

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.



187

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]



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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Documents

Effect of heat input on the microstructure and mechanical ......heat input as well as the fact that a heat input of 0.051 kJ/mm responsible for excessive grain growth, the value of