control of distortion by combined effect of dc- lsnd and ttt in...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:17 No:06 160

173506-8484-IJMME-IJENS © December 2017 IJENS I J E N S

Control of Distortion by Combined Effect of DC-

LSND and TTT in MIG Weld Joints and Its Effect on

Residual Stress and Fatigue Behavior Heri Wibowo1,2,*, M. Noer Ilman1, Priyo Tri Iswanto1, M. Rifai Muslih3

1 Department of Mechanical and Industrial Engineering, Universitas Gadjah Mada, Indonesia 2 Department of Mechanical Engineering Education, Yogyakarta State University, Indonesia

3 National Nuclear Energy Agency of Indonesia (BATAN), Serpong, Banten, Indonesia

*Corresponding author: e-mail address: [email protected]

Abstract-- The use of thin plates sections in fabrication of ship

hull structures for weight savings is preferable but it tends to

produce weld distortion. This current research aims to study

distortion and residual stress control methods by combining

dynamically controlled low stress no distortion (DC-LSND) and

transient thermal tensioning (TTT) techniques. These combined

‘in-process’ treatments were conducted by quenching the weld

metal behind the welding torch using cryogenic liquid nitrogen

and simultaneously performing the secondary heating process

using flame torches at both sides of the weldline. Subsequently, a

number of experiments was carried out as follows: distortion

measurement, residual stress measurement, microstructure

examination, hardness measurement, tensile test and fatigue test.

Results show that combined effect of DC-LSND and TTT

treatment can effectively reduce distortion and residual stress

which lead to improved fatigue crack growth performance. In

addition, changes in strength and hardness of the weld joints are

also observed and these are associated with changes in

microstructures due to secondary heating and quenching during

welding.

Index Term-- DC-LSND and TTT, MIG welding, distortion,

residual stress.

1 INTRODUCTION

Welding is the main manufacturing process in

fabrication of ship structures since the ship structures are built

from many thin plates or panels which are welded to form

structures. In recent years, thin plates in such constructions are

increasingly used to reduce weight, increase ship performance

with higher speed and lower fuel consumption. However,

welding of thin plates tend to result in welding distortion so

that welding repair is required. Distortion is undesirable

deformation caused by a localized heating and non-uniform

cooling during welding which produce thermal stresses. The

presence of distortion reduces dimensional accuracy, loss of

structural integrity and premature damage. In addition,

distortion can cause undesirable impact on the fabrication cost

since additional work or repair needs to be performed to

reduce weld distortion. The estimated cost of labor in

repairing and adjusting distorted element is 30% of the total

cost of labor [1].

Efforts have been made by a number research workers

with the aim of minimizing the weld distortion. In welding

process treatment based on mechanical effects such as

vibratory weld conditioning (VWC) technique [2] and

stretching technique [3] can significantly reduce residual

stresses and distortion in welded thin plate structures but these

techniques require high loads. Furthermore, thermal treatment

in welding process such as static thermal tensioning (STT) [4]

can minimize welding distortion and decrease the rate of

fatigue crack propagation [5] but this technique is less

effective especially for long plate which long secondary

heaters as well. Another known as the double-side arc welding

(DSAW) technique can effectively reduce distortion but

requires complicated equipment [6].

Transient thermal tensioning (TTT) is a technique for

control of weld distortion by employing secondary heat

sources placed at both sides of the weld line. TTT treatment

provides thermal tensioning effect which reduces distortion

and residual stress in weld metal [7][8] and it improves the

fatigue performance [5][8]. The advantage of TTT over post

weld treatments is an in-process weld heat treatment which is

carried out prior to or during welding hence reducing time for

weld preparation and and also cost. The intensity and position

of secondary heat sources in TTT affect the effectiveness of

distortion mitigation.

A relatively new technique to minimize welding

distortion is the dynamically controlled low stress no

distortion (DC-LSND). This technique is carried out by

spraying active coolant of CO2 snow [9][10] or liquid nitrogen

[11][12] behind the torch. The cooling process can reduce

temperature quickly and produce abnormal welding

temperature distribution that provides control of distortion and

residual stress. However, this technique has disadvantages

such as embrittlement of the weld metal [10].

In the present investigation, attempts have been made

by combining TTT and DC-LSND techniques to reduce

distortion and residual stress in welding of A36 steels.

2 MATERIALS AND METHODS

2.1 Materials and welding parameters

A metal inert gas (MIG) welding process was used to

join A36 carbon steel plates which have dimension of 400 x

100 x 4 mm. The weld groove was machined with the groove

angle of 30o, the root face of 2 mm and the root gap of 1.5

mm. The plates was prepared on a flat work table and welding

was applied without providing clamp on the workpiece. The

chemical compositions of the plates and the weld metals are

given in Table 1. The welding parameters used in these

investigations are shown in Table 2.



Table I

The chemical composition of A36 steel and weld metal (wt%).

C Si Mn P S Cu Ni Cr Fe

A36 0.159 0.243 0.733 0.023 0.003 0.0137 0.016 0.042 Bal.

Weld metal 0.116 0.430 0.859 0.02 0.011 0.0834 0.014 0.035 Bal.

Table II

MIG parameters.

Voltage : 23.5 volt

Current : 148 A

Welding speed : 4.4 mm/s

Wire speed : 140 mm/s

Electrode type : ER70S-6

Diameter electrode : 0.8 mm

2.2 Combined treatment of DC-LSND dan TTT

The combined treatment of DC-LSND and TTT as shown

in Fig. 1 was performed by cooling the regions of both

adjoining plates behind the welding torch using double

cooling similar to that performed in the DC-LSND treatment

and simultaneously heating both sides of the torch at

temperature of 200 oC at the distance of 38 mm from the weld

line in a similar manner to that performed in TTT treatment.

Each cooling nozzle was located at the distance of 30 mm

behind the weld torch. The flow rate of nitrogen liquid used in

this investigation was 200 ml/minute. A partition was placed

between the cooling nozzles and weld torch to protect the

weld metal from negative effect of liquid nitrogen while the

secondary heating torches were located at various distances of

40 mm and 80 mm in front of the weld torch, and 60 mm

behind the weld torch. All treatment processes above are

designated as DT40, DT80 and DT(-60). The symbols of “D”

and “T” represent DC-LSND and TTT respectively, followed

by two digits of number which represent the distance variable.

Fig. 1. a The skematic of combined treatment of DC-LSND and TTT, b dimensional of combined treatments in mm.

2.3 Measurements of distortion

After welding process, plates were marked with grids

with each dimension of 20 mm x 20 mm on the surface. The

distortions were measured at all marked grids using dial

indicator gauge, having the accuracy of 0.01 mm. The out of

plane distortion along longitudinal direction was obtained by

calculating the average distortion in longitudinal direction.

(b)

(a)



2.4 Microstructure Examination

Specimens were prepared through afour-step procedure

as follows: cutting, grinding, polishing, and etching.

Examinations were focused on the weld metal area (WM) and

heat affected zone (HAZ). The quantitative analysis of

microstructure was carried out by using point count according

to ASTM method [13]. This quantitative method obtained the

volume fraction of the microstructure in a particular area.

2.5 Hardness tests

Hardness measurements were performed along weld

metal (WM), coarse grain heat affected zone (CG-HAZ), fine

grain heat affected zone (FG-HAZ), partially transformed

region and unaffected base metal (BM) as shown in Fig.2.

They were tested by Vickers micro hardness with a load of

500 grf with the distance of 500 μm from one point to the

other.

Fig. 2. Hardness measurement

2.6 Tensile tests

Tensile tests were carried out along the longitudinal weld

line direction to assess yield and ultimate stresses of the weld

metals. The specimens of this tensile testing were machined

according to the standard of JIS Z2201 as shown in Fig. 3.

Fig. 3. Longitudinal tensile test specimen

2.7 Fatigue crack growth tests

The fatigue crack growth rate (FCGR) tests were conducted

by sinusoidal loads with stress ratio (R) of 0.1 and frequency of

11 Hz. Middle tension M(T) specimens were used following the

ASTM E 647 standard as shown in Fig. 4. The crack propagation

was measured by traveling microscope with a level of accuracy

of 0.1 mm. Futhermore, Paris Law was used for analyzing

fatigue crack propagation as follows:

nKCdN

da

(1)

where da/dN is fatigue crack growth rate, ΔK is stress

intensity factor whilst and C and n are constants.

Fig. 4. Middle tension (M(T)) specimen

2.8 Measurements of residual stress

The measurements of residual stresses were performed

using the neutron diffractometer on 10 test points as shown on

Fig. 5. The measurements were taken in longitudinal, transverse

and normal directions with wave length of neutron beam of

1.836542 Å. The lattice plane used in this investigation was 211



direction and the diffraction angle of 103o. The strain lattice (εi)

was obtained from the change in planar spacing with the strain-

free spacing (do) as the referrence using Eq 2.

0

0

d

dd ii

(2)

where di is inter planar spacing where i is x,y,z direction, d0 is

strain free inter planar spacing.

Residual stresses (σi) were obtained by considering the strain

lattice, Poisson’s ratio and Young’s modulus using Hooke’s

equation as follows:

kjhklihkl

hklhkl

hkli vv

vv

E

1

211 (3)

where Ehkl is Young’s modulus and vhkl is Poisson’s ratio.

Fig. 5. Neutron test points of the residual stress measurement

3 RESULTS AND DISCUSSION

3.1 Thermal cycles

Fig. 6 shows the welding thermal cycle during a

welding process on the combined treatment of DC LSND and

TTT that extracted from the thermocouple data. Based on the

thermal cycle graph, in the area of 5 mm from the welding

center, there is a cooling effect on DC-LSND which will

accelerate the cooling process up to 500 0C. The cooling

process can be analyzed interpolagraphically, which will result

in the cooling rates from 800 0C to 500 0C on the DT40

treatment around 10.5 seconds and on the DT80 treatment

around 10.0 seconds. Compared to the cooling rate on as-

welded of 19 seconds, the combined treatment of DC-LSND

and TTT can accelerate the cooling rate in the area

surrounding the weld line. Based on the continuous cooling

transform (CCT) diagram [14], phenomenon of the change of

cooling speed will affect the micro structure and mechanical

strength of the weld.

The combined treatment of DC-LSND and TTT will

change the temperature distribution in the area surrounding the

weld line, particularly during the cooling process as shown in

Fig. 7. Cooling process and plate equalization temperature

strongly influence the level of distortion. This phenomenon is

aligned with some papers [8][15] which suggest the degree of

distortion and residual stress interconnected and affected by

the distribution of welding temperature. This study found that

the DT(-60) treatment tends to stabilize the temperature

around the weld metal compared to other treatments especially

those with the distance of 15 and 30 mm.This will affect the

distortion and residual stress becomes low after the welding

process.



Fig. 6. Welding thermal cycles on: a As-welded, b DT40, c DT80, and d DT(-60)

Fig. 7. Welding temperature distribution at cooling process on combined treatment of DC-LSND and TTT

3.2 Weld distortion

Fig. 8 shows the out-of-plane distortions of welded

plates produced with and without the combined treatment of

DC-LSND and TTT at various welding torch distances. It can

be seen all welded plates are suffered from out of plane

distortion which have convex shape with the maximum

distortion occurs in the middle of plate length. The combined

treatment of DC-LSND and TTT can reduce out-of-plane

distortion significantly. The lowest distortion is achieved by

the welded plate produced using the DT(-60) treatment with

the distortion around 3.3 mm or 65,5 % lower compared to

that present in as-welded welded plate which has the

(a)

(c)

(b)

(d)



maximum distortion of 9.60 mm. Although combined DC-

LSND and TTT treatment with the welding torch in front of

weld metal i.e. DT40 dan DT80 is proved to reduce distortion

but its effectiveness is not as good as one with the welding

torch placed at the back of the weld torch, i.e. DT(-60) can

significantly decrease the out of plane distortion. Combined

treatment of DC-LSND and TTT generate more stretching

effects than that of single treatment which oppose buckling

distortion during welding process.

Fig. 8. Out of plane distortion in the combined treatment of DC-LSND and TTT

3.3 Microstructures

Fig. 9. shows the microstructures of the weld metal on

as-welded condition and treated using combined DC-LSND

and TTT. It shows that changes of micro structures occur,

which can be examined by the type and size of grain due to

these treatments.

The microstructure of weld metal on all welds in Fig. 9

exhibits acicular ferrite (AF), Witmanstatten ferrite (WF) and

grain boundary ferrite (GF). The as-welded condition shows

the dominant phase of GF. The application of combined

treatment of DC-LSND and TTT seems to change the size and

volume phase of microstructures but it still presents similar

microsturctures. The combined treatment of DC-LSND and

TTT have refined the size and increased the percentage of AF

more than as-welded condition. These treatments also reduced

the percentage of GF and changed some plates of WF. Some

works [16][17] reported that the phase change of the

microstructure is greatly influenced by the cooling rate. The

change of the phase is also supported by the measurement

results of the thermal cycle during welding (Fig. 6) which

shows the cooling time (Δt8/5) on combined treatment of DC-

LSND and TTT less than as-welded condition.

3.4 Hardness distribution

The results of the hardness measurement across weld

metal (WM), heat affected zone (HAZ), partially transformed

region and base metal (BM) are shown in Fig. 10. The HAZ

can be devided into coarse-grained (CG) and fine-grained

(FG) HAZ. In all welded joint specimens under study, the

hardness of weld metals are relatively higher than the base

metal and sharp increase in hardness occur at HAZ then the

hardness decreases gradually as the distance is away from the

HAZ and then the hardness becomes constant at BM. The

combined treatment of DC-LSND and TTT increase the

hardness of WM. The relatively high values of hardness in

WM are related to the high percentage of AF microstructureas

a result of increasing of the cooling rate. This statement is

corresponds with Sivaraos et al. [18] that microstructure is the

main factor influencing the hardness.



Fig. 9. Weld metal (WM) microstructures at : a As-welded, b DT80, c DT40, and d DT(-60)

Fig. 10. Hardness distribution on weld joints of A36 steels

3.5 Tensile Stresses

Fig. 11 shows the results of the longitudinal tensile

tests for the weld joints in as-welded condition and the

combined DC-LSND and TTT treatment. Weld metal is as

welded condition has strentgh of 567 MPa and yield stress of

400 MPa. The strengths of weld metals treated using DT40

and DT80 with the heating in front of the torch are similar to

that of as-welded weld joint. However, the treatment of DT(-

60) with the heating at the back of the torch significantly

increase tensile strength of about 567 MPa. This indicates that



the combined treatment of DC-LSND and TTT with the

heating at the back of the torch the welding acts as postweld

tends to be able to improve the tensile strength compared to

when it functions as the preheat. The high tensile stresses

under the combined treatment of DC-LSND and TTT are

associated with the increasing percentage of AF in the weld

metal as supported by the number of works [19][20].If related

to the microstructure of the weld metal on the combined

treatment of DC-LSND and TTT, the percentage of AF is

linear with its tensile strength.

Fig. 11. Tensile strength of weld joints in longitudinal direction

3.6 Fatigue crack growth rate

The fatigue crack propagation is measured in weld metal

area and presented by plotting the crack length (a) as the

function of the number of cycles (N) as shown in Fig. 12. It can

be observed that combined effect DC-LSND and TTT treatment

increase the fatigue life of the weld joints.

Fig. 12. Diagram of a-N function

Furthermore, the a-N curves can be analyzed in the form of

fatigue crack propagation rate (da/dN) as the function of the

stress intensity factor range (ΔK) as shown in Fig. 13. It shows

that at the beginning of fatigue crack propagation, the da/dN of

the combined treatment of DC-LSND and TTT has a lower

value than the as-welded condition. This crack propagation

retardation is likely to be associated with residual stresses and

this will be discussed in further section. Fatigue crack



propagation rates (da/dN) in stable crack region (region II) is

usually represented by Paris law (equation 1).

Fatigue crack propagation rate can be determened by the

taking the trend lines of da/dN - ΔK curves at region II which

have the slope of n and C value at the intersection with the da/dN

axis at ∆K=1 MPa√m. The values of n and C are given in Table

3. The results of da/dN indicate that the combined treatment of

DC-LSND and TTT have a lower fatigue crack growth rate than

as-welded condition at all ΔK values. This finding is relevant

with the work of D’Urso, et al. [21] which states that weld

treatment affects the crack propagation rate at low ΔK.

Fig. 13. Fatigue crack growth rate of welded joints

Table III

Paris constants

Environment C n

As-welded condition 1.3286E-12 3.585

DT(-60) treatment 3.4784E-13 3.921

The SEM fractography on welded joints of as-welded

condition and the combined treatment of DC-LSND and TTT

is shown in Fig. 14. In as welded condition, fractured surface

seems to be brittle cleavage fracture with a little secondary

crack are observed. Striations, typical of fatigue fracture are

not clearly seen. Fractured surface of the combined treatment

of DC-LSND and TTT striations like appearance.

Fig. 14. SEM micrography of: a as-welded condition, b DT(-60) treatment



3.7 Residual stress

The longitudinal dan transverse residual stresses

measurements were done along the transverse distance from

the weldline. The combined DC-LSND and TTT treatment

with the secondary heating sources located at the distance of

60 mm behind the weld torch, i.e. DT(-60) treatment was

selected in this investigation because it effectively reduces

weld distortion.

Fig. 15 a shows longitudinal residual stresses in as-welded

condition and the combined DT(-60) treatment. In general,

both welded plate specimens show tensile residual stress in

weld region and its adjacent area and whilst the regions away

from the weldline form compressive residual stress static

equilibrium.

Fig. 15 b shows the transverse residual stress in as

welded condition and the weld treated with combined DC-

LSND and TTT treatment. It can be seen that the tensile

residual stress at the weld centre, i.e. 185 MPa as shown in as

welded condition is reduced 110 MPa due to combined DC-

LSND and TTT treatment.. The decrease of the tensile

residual stress was caused by the change of the gradient

temperature as a result of the cooling treatment on DC-LSND

as suggested by by Guan [22]. As disscussed previously, the

magnitude and distribution of residual stress influence fatigue

behavior. It can be argued that better fatigue crack growth

resistance in the the weld treated using combined DC-LSND

and TTT is caused by its lower transverse residual stress present

in the weld region as shown in Fig. 15. The condition of stresses

at the crack tip can be seen from stress intensity factor, K. Based

on superposition approach, the total stress intensity factor Ktotal

is the sum of stress intensity factor due to residual stress, Kres and

that generated by applied stress, Kapp. Accordingly, low (or even

compressive) residual stress will reduce Ktotal hence reducing

fatigue crack growth rate.

Fig. 15. Results comparison of residual stress in : a longitudinal direction, b transverse direction

(b)

(a)



4 CONCLUSIONS

The distortions, residual stress, and mechanical

properties on combined treatment of DC-LSND and TTT have

been investigated. The main results are summarized as

follows:

(1) The combined treatment of DC-LSND and TTT

accelerate the cooling rate in the area surrounding the

weld line and effect to reduce out of plane distortion on

weld joints.

(2) The use of combined treatment of DC-LSND and TTT

increase the hardness, refine the microstructure by

increasing phase of acicular ferrite, and improve the

tensile strength on weld metal.

(3) The fatigue crack growth rate can be improved by

combining DC-LSND and TTT treatments. It is

associated with decreasing of transverse residual stress on

weld metal.

(4) The DT(-60) treatment has decreased the longitudinal and

normal residual stress on surrounding weld area that

impacts on the decrease of distortion.

REFERENCES [1] L. F. Andersen, “Residual Stresses and Deformations in Steel

Structures,” Dep. Nav. Archit. Offshore Eng. Univ. Denmark, 2000. [2] J. Xu, L. Chen, and C. Ni, “Effect of vibratory weld conditioning on

the residual stresses and distortion in multipass girth-butt welded

pipes,” Int. J. Press. Vessel. Pip., vol. 84, no. 5, pp. 298–303, May 2007.

[3] N., S. Triyono, S. H., and Muhayat, “Effect of Stretching During

Welding Process on the Weldability of Dissimillar Metals Resistance Spot Welded between Carbon,” Adv. Mater. Res. . 2014,

Issue 894, p206-211. 6p., p. 20, 2014.

[4] M. N. Ilman, Kusmono, M. R. Muslih, N. Subeki, and H. Wibowo,

“Mitigating distortion and residual stress by static thermal

tensioning to improve fatique crack growth performance of MIG

AA5083 welds,” J. Mater. Des., vol. 99, pp. 273–283, 2016. [5] N. Subeki, M. N. Ilman, and P. T. Iswanto, “The Effect of Heating

Temperature in Static Thermal Tensioning ( STT ) Welding on

Mechanical Properties and Fatigue Crack Propagation Rate of FCAW in Steel A 36,” Int. Conf. Eng. Sci. Nanotech., vol. 30057,

2017.

[6] C. Yang, H. Zhang, J. Zhong, Y. Chen, and S. Chen, “The effect of DSAW on preheating temperature in welding thick plate of high-

strength low-alloy steel,” Int. J. Adv. Manuf. Technol., pp. 421–428,

2014. [7] J. Souto, E. Ares, and P. Alegre, “Procedure in reduction of

distortion in welding process by high temperature thermal transient

tensioning,” Procedia Eng., vol. 132, pp. 732–739, 2015. [8] M. N. Ilman, Kusmono, and P. T. Iswanto, “Fatigue crack growth

rate behaviour of friction-stir aluminium alloy AA2024-T3 welds

under transient thermal tensioning,” Mater. Des., vol. 50, pp. 235–243, 2013.

[9] R. Holder, N. Larkin, L. Kuzmikova, L. Huijun, Z. Pan, and N. J,

“Development of a DC-LSND welding process for GMAW on DH-36 Steel,” 56th WTIA Annu. Conf., vol. 2011, pp. 1–13, 2011.

[10] C. Shen, “Low distortion welding for shipbuilding industry.”

Material and Mechatronic Engineering, University of Wollongong, 2013.

[11] R.S. Sudheesh and Siva N. Prasad, “Parametric Studies on Effect of

Trailing Liquid Nitrogen Heat Sink on TIG Welding of Steels,” Adv. Mater. Res. . 2014, vol. 875, no. February, pp. 1595–1599,

2014.

[12] S. R. Kala, N. Siva Prasad, and G. Phanikumar, “Studies on multipass welding with trailing heat sink considering phase

transformation,” J. Mater. Process. Technol., vol. 214, no. 6, pp.

1228–1235, 2014.

[13] R. J. S. R. E. Bishop, Modern Physical Metallurgy dan Materials

Engineering. Jordan Hill, Oxford: Elsevier Science Linacre House,

1999.

[14] D. Radaj, Heat Effects of Welding : Temperature field, Residual

Stress and Distortion. Verlag-Berlin: Springer, 1992. [15] G. Fu, M. Igor, M. Duan, and S. F. Estefen, “In fl uence of the

welding sequence on residual stress and distortion of fi llet welded

structures,” Mar. Struct., vol. 46, pp. 30–55, 2016. [16] C. Borchers et al., “Microstructure and mechanical properties of

medium-carbon steel bonded on low-carbon steel by explosive

welding,” Mater. Des., vol. 89, pp. 369–376, 2016. [17] Y. Wu, Y. Cai, H. Wang, S. Shi, X. Hua, and Y. Wu, “Investigation

on microstructure and properties of dissimilar joint between SA553

and SUS304 made by laser welding with fi ller wire,” Mater. Des., vol. 87, pp. 567–578, 2015.

[18] Sivaraos, F. Darwis, K. Kadirgama, M. Shajahan, M. Amran, and

M. A. Lajis, “Hardness and microstructural investigation of laser welded SS400 steel performed by CO2 laser cutting machine,” Int.

J. Mech. Mechatronics Eng., vol. 15, no. 3, pp. 17–22, 2015.

[19] L. Fan, D. Zhou, T. Wang, S. Li, and Q. Wang, “Materials Science & Engineering A Tensile properties of an acicular ferrite and

martensite / austenite constituent steel with varying cooling rates,”

Mater. Sci. Eng. A, vol. 590, pp. 224–231, 2014. [20] K. Digheche, Z. Boumerzoug, M. Diafi, and K. Saadi, “Influence of

Heat Treatments on the Microstructure of Welded Api X70 Pipeline

Steel,” Acta Metall. Slovaca, vol. 23, no. 1, p. 72, 2017. [21] G. D. Urso, C. Giardini, S. Lorenzi, and T. Pastore, “Journal of

Materials Processing Technology Fatigue crack growth in the welding nugget of FSW joints of a 6060 aluminum alloy,” J. Mater.

Process. Tech., vol. 214, no. 10, pp. 2075–2084, 2014.

[22] Q. Guan, D. L. Guo, and C. Q. Li, “Low stress no distortion (LSND) welding - a new technique for thin materials,” Weld.

World, vol. 8, pp. 49–55, 1994.

control of distortion by combined effect of dc- lsnd and ttt in...

Documents