Effect of heat input and filler metals on weld strength of ...
Transcript of Effect of heat input and filler metals on weld strength of ...
Effect of heat input and filler metals on weld strength of gastungsten arc welding of AISI 316 weldments
Essam Ahmed1, Ramy Ahmed2, A EL-Nikhaily2, A R S Essa2,3
1. Metallurgical and Materials Engineering Department, Faculty of Petroleum and Mining Engineering, Suez University,43721 Egypt;2. Mechanical Department, Faculty of Industrial Education, Suez University,43721 Egypt;
3. Mechanical Engineering Department, Egyptian Academy for Engineering & Advanced Technology,Affiliated to Ministry of Military Production, Cairo 3056, Egypt
Received 7 January 2020; accepted 14 February 2020
Abstract The present work investigates the effect of filler metals and heat input on weld bead geometry and mechanical properties of alloy316 welded by using GTAW. ER309L, ER316L and ERNiCrMo-3 filler metals, are applied to study their effect on the weldment. Weld de-fects are examined using radiographic testing. The mechanical properties of welds are evaluated through uniaxial testing, hardness measur-ing, and bending test. The mechanical properties and cooling rate decrease with increasing heat input. Tensile strength, yield stress and per-centage elongation of weldments using three fillers are determined. Best results are obtained using ERNiCrMo-3. Besides, weld nugget area,cooling time and solidification time increases with increasing heat input. Finally, applying bending test on weld samples, cracks, tearing andsurface defects are not observed.
Key words TIG welding, filler metals, nugget area, stainless steel, cooling rate
0 Introduction
Stainless steels are widely used in different industriessuch as, medical, nuclear, petroleum and chemical indus-tries, due to their good mechanical properties and high cor-rosion resistance. Among the AISI 300 series alloying ele-ments such as Ni, N, Mn, Si and Mo are added with con-trolled other elements (B, S, P, etc.), for specific require-ments in different industries[1]. Gas tungsten arc welding(GTAW) is mostly adopted for a high level of weldquality[2]. In TIG welding, due to the continuous heat inputssamples dimensions at weld pool and heat affected zone(HAZ) are changed[3]. However, the welding processes arestrongly influenced by materials properties such as micro-structure, mechanical behavior and corrosion resistance[1].
Successful GTAW weldments of Monel 400 and AISI304 were developed using ER304, ERNiCrMo-3 and ERNi-CrMo-4 as welding wires[4]. It was concluded that thetensile strength and yield strength of ERNiCrMo-3 weld-ments were comparable to those of parent metals. The
tensile strength and yield strength of dissimilar ERNiCrMo-3 welded joint was better than ER304 and ERNiCrMo-4weldments. Meanwhile, the effect of welding wires on thecharacteristics of dissimilar welding SS 316L and carbonsteel A516 GR 70 was studied[5] using three different fillermaterials ER80-Ni1, ER309L and ER NiCrMO-3 (Inconel625). Inconel 625 filler metal was found more suitable toweld dissimilar SS 316L and carbon steel A516 GR 70 thanother different fillers. Best results concerning ultimatetensile strength and hardness were obtained using the ERNiCrMO-3 (Inconel 625) as welding electrode.
The effect of cooling rate on solidification and segrega-tion characteristics of super austenitic stainless steel(SASS)was studied [6], and it was found that grain size was refinedmore with increasing the cooling rate. Also, the secondarydendrite arm spacing decreased sharply at welding begin,then decreased slowly with increasing cooling rate, and thetransition cooling rate was 20°C/s. Furthermore, the effectof heat input on the cooling rate and pitting resistance equi-valent number(PREN) in super duplex stainless steel
Corresponding author: Ramy Ahmed, Ph.D. Mainly engaged in welding metallurgy. E-mail: [email protected]: 10.12073/j.cw.20200107001
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(SDSS) welds was studied[7], and it was found that grainsize and cooling rate increased with increasing heat input.Best results for PREN are obtained at an intermediate heatinput value of 1.4 kJ/mm.
The influence of welding current on AISI 316 weldedby gas tungsten arc welding(GTAW )was studied[8], and itwas concluded that ultimate tensile strength (UTS) andhardness Vickers(HV) increased with increasing heat input.The best result for UTS and HV was obtained using 100A.Also, sigma phase and Cr23C6 in 316 SS welded samples in-creased with increasing heat input. The influence of variouswelding variables such as heat input, bevel angle and shield-ing gas flow rate on weld sample of similar graded materialwelded by GTAW was studied[9], and it was concluded thatUTS and HV increased with increasing bevel angle, but de-creased with increasing the heat input and shielding gasflow rate. The best result for UTS and HV was obtained atlow heat input and high bevel angle. The effect of weldingelectrode on the characteristics of dissimilar AISI 420 and304L welds was studied[10] using three different filler rodsER312, ER316L and ER2209. The ER2209 rod producedwelds with highest impact toughness and lowest hardness.The effect of weld bead area on mechanical properties wasinvestigated[11], and it was found that the nugget area in-creases with increasing weld current and arc voltage, but de-creases with increasing welding speed.
The cooling rate is the temperature loss per unit time. Itis known that the cooling rate in the temperature range 800-500°C is important for phase transformation of stainlesssteel. It determines the final solidification mode or micro-structure of the weld metal and its properties[12].
The influence of multi-pass and welding current on thewelding strength and hardness value in 7A52 AA welds wasstudied[13], and it was found that welding strength decreasedwith increasing welding current. The HV between the weldregion (WZ) and the heat affected region (HAZ) was char-acterized by a gradual transition, but the HV gradually de-creased as the distance from the weld line increased.Moreover, optimization of dissimilar ST04Z galvanizedsteel and 5A06 Al alloy welds sample characteristics wasstudied[14] using four different laser power 1 000, 1 200,1 500 and 1 700 W. The best result for tensile strength wereobtained at 1 200 W.
Hence, the main objective of this work is to obtain thesuitable conditions that yield a reliable GTAW joint. This isachieved by changing the welding current and filler metalsfor welding stainless steel 316. The effects of welding vari-ables on welded joints, its mechanical properties and weldbead are studied in details.
1 Experiment
AISI 316 stainless steels with 200 mm×100 mm×4 mmas parent materials are considered for butt joint configura-tion using employing pulse current TIG welding process.Three filler metals (a-ER309L, b-ER316L and c-ERNi-CrMo-3) of 2.4 mm diameter are used. The chemical com-positions of the base metal and filler metals are listed inTable 1, and their mechanical properties are listed in Table 2.
Base metal samples are made using a standard 2 mmroot face butt joint configuration, as shown in Fig.1a. Be-fore welding, base metal and filler metals are cleaned withacetone. Parent materials are tack welded on both ends andon sample center before completing welding to avoid mis-alignment of the plates. Detailed applied parametric com-binations are presented in Table 3. Radiography testing(RT) is carried out in DELTA 800 Company. Surface hard-ness of weldments and base metal are measured by a Vick-ers hardness tester. Hardness profile of welded joint ismeasured every 1 mm over a single indentations line using1 kg load and 20 s loading time.
The mechanical properties, such as YS and UTS are de-termined by uniaxial tensile testing using a universal test-ing machine (Instron Model) at a strain rate of 10−3s−1. Thegeometry and dimensions of the applied standard tensilesample are shown in Fig.1. The deformability of weldedsteel is determined using a bending test according to(ASTM E190-92), and the specimen is put on two support-ing rollers and is pressed through between the rollers. Thedistance between the supporting rollers “ Lf” is equal toformer diameter “d” plus 3 times specimen thickness “a”.The backside of the specimen (tension side) is observed, tostop the test if a surface crack develops, and the angle towhich the specimen could be bent is measured. The heat in-put and nugget area during welding can be estimated byEq.1[2] and Eq.2[11], respectively.
Table 1 Chemical compositions of base metal and filler metals (wt.%)Material C Cr S Mn Mo Ni P Si Fe
316 SS 0.08 16−18 0.03 2.0 2−3 10−14 0.045 1.0 Balance
ER309L 0.04 22−25 0.03 0.5−2.5 0.75 12−14 0.040 1.0 Balance
ER316L 0.04 17−20 0.03 0.5−2.5 2−3 11−14 0.040 1.0 Balance
ERNiCrMo−3 0.03 20−23 0.015 0.2−0.5 8−10 60−65 0.020 0.4 Balance
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HI(kJ/mm) = η× (V × I×60)/ (S ×1 000) (1)
Na(mm2) = 33.312×10−6×[A1.55/v0.903
](2)
Where, HI is the heat input (in kJ/mm), η is the welding ef-ficiency (ηTIG = 70%), V is the arc voltage (V), I is thewelding current (A) and v is the welding speed (mm/min)and Na is nugget area (mm2).
The cooling rate[15] and cooling time[16] can be calcu-lated using Eq.(3) and Eq.(4), respectively.
(∂T∂t
)x=
(∂T∂x
)t
(∂x∂t
)T= −2πK
((T −To)2
Hnet
)(3)
t8/5 =HI2πλ
(1
500−To− 1
800−To
)(4)
where, (∂T/∂t)x is the cooling rate (℃/sec), K or λ is thethermal conductivity (W/mm·K), and T is the temperaturenear the pearlite nose on TTT diagram (550 ℃) and To isthe initial temperature of the plate to be welded (20 ℃).
The solidification time (ts) of welded joint depends onthe cooling rate and heat input. Hence, ts is also of great im-portance as it affects the microstructure and its properties.The solidification time can be calculated as follows[17]:
ts (s) = L×Hnet/2πkρc(Tm−To)2 (5)
where, ts is the solidification time (s), L is the heat of fusion(J/mm3) that is 2 J/mm3 for steel, ρc is the volumetric specif-ic heat (J/mm3·℃) and Tm is the melting temperature (℃).
2 Results and discussion
2.1 Radiography examinationTIG welding butt joints are processed using three filler
metals: ER309L, ER316L, ERNiCrMo-3, and different val-ues of welding current. The samples are examined visuallyimmediately after welding to visually inspect the exposedsurfaces. The samples macrographs are shown in Fig. 2,Fig. 3 and Fig. 4, and no serious surface defects could beobserved.
Visual inspection and radiographic testing (RT) indic-ate, that weld specimens made of GTA welding are freefrom macro/micro defects such as porosities, inclusions orinternal cracks. RT images of welding specimens usingthree filler metals and welding currents are shown in Fig. 5,Fig. 6 and Fig. 7.
2.2 Effect of welding current on welded jointsThe cooling rate (∂T/∂t)x, heat input (HI), cooling time
(t8/5) and solidification time (ts) after welding are very im-portant to determine the behavior of welds. HI, (∂T/∂t)x, t8/5and St are calculated according to previously mentionedequations; Eq.(1), Eq.(3), Eq.(4) and Eq.(5), respectively.Heat input increases with increasing welding current and arcvoltage but decreases with increasing welding speed, aspresented in Fig. 8a. The cooling rate (∂T/∂t)x decreaseswith increasing HI, as shown in Fig. 8b. Moreover, the cool-ing time and solidification time increase with increasingwelding current, as observed in Fig. 9a, Fig. 9b, respect-ively. However, both parameters decrease with increasingwelding speed.
(a)
(b)
100 100
100 5050
20
4 R12.5
200
4
2
Fig. 1 Schematics of (a) Butt joint configuration (b) Geo-metry of tensile test specimen(mm)
Table 2 Mechanical properties of AISI 316 and weldingwires
Base metal UTS/MPa Yield strength/MPa Elongation(%)
AISI 316 515 205 40
ER309L 590 415 45
ER316L 480 170 40
ERNiCrMo-3 780 500 35
Table 3 Applied gas tungsten arc welding parametersParameter Value
Welding process GTAW (Maunal)
Welding configuration Butt joint
Welding wires ER309L, ER316L and ERNiCrMo-3
Welding wire diametar 2.4 mm
Shielding gas Pure argon
Polarity DC negative electrode
Welding current 80, 100 and 130 A
Gas flow rate 7 L/min
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2.3 Weld bead geometryFig. 10 shows the weld nugget area of 316 SS square
weld samples under different heat inputs and filler metals.The weld nugget area increases with increasing HI (weld-
ing current). Meanwhile, and decreases with increasingwelding speed. Increasing the welding current leads to awider cross-section of all weld samples. Hence, increasingheat input increases depth and width of weld metal fusion.
2 cm
2 cm
2 cm
2 cm
2 cm 2 cm
80 A
100 A
130 A
Top s
urf
ace
Bott
om
surf
ace
Fig. 2 Visual inspection of butt GTAW joints of 316 AISI using different welding current values and ER309L as filler metal
2 cm 2 cm
2 cm 2 cm
2 cm 2 cm130 A
80 A
100 A
Top s
urf
ace
Bott
om
surf
ace
Fig. 3 Visual inspection of butt GTAW joints of 316 AISI using different welding current values and ER316L as filler metal
2 cm 2 cm
2 cm 2 cm
2 cm 2 cm
130 A
80 A
100 A
Top s
urf
ace
Bott
om
surf
ace
Fig. 4 Visual inspection of butt GTAW joints of 316 AISI using different welding current values and ERNiCrMo-3 as fillermetal
80 A 100 A 130 A
Fig. 5 Radiographic films of AISI 316 TIG welding using different welding current values and ER309L as filler metal
11
Accordingly, more heat of the arc transfers into the speci-men, and a deeper welding penetration takes place. Thisagrees with other publications[11, 18], where it is reported thatthe width of weldments increases with increasing HI.
2.4 Mechanical properties of weld specimensTensile testing is carried out to determine the strength
and plasticity of welded joints and to examine the influenceof weld defects on the joint performance. Tensile strength of
80 A 100 A
130 A
Fig. 6 Radiographic films of AISI 316 TIG welding using different welding current values and ER316L as filler metal
80 A 100 A
130 A
Fig. 7 Radiographic films of AISI 316 TIG welding using three different welding current values and ERNiCrMo-3 as fillermetal
800
600
400
80 A 100 A 130 A
Welding current
80 A 100 A 130 A
Welding current
70
60
50
40
30
ER309L
ER316L
ERNiCrMo-3
ER309L
ER316L
ERNiCrMo-3
Hea
t in
put/
(J·m
m−1
)
Cooli
ng r
ate
(°C
·s−1
)
(a) (b)
Fig. 8 Effect of welding current on (a) Heat input (b) Cooling rate of 316 SS welding.
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TIG welds using ER309L, ER316L and ERNiCrMo-3 aswelding rods is evaluated according to the ASTM E8 stand-ard. Tensile test results of TIG welded joints are shown inFig. 11. The base metal tensile strength is much lower thanthat of all weld metal samples. The ultimate tensile strengthand yield strength of all weld specimens decreases with in-creasing heat input. This is attributed to the slow coolingrate and high heat input, that lead to increase grain size ofthe weld region. This is consistent with hardness results andcooling rate. Weld specimens produced using ERNiCrMo-3filler metal show superior values of the ultimate tensilestrength and yield strength than specimens produced usingthe other two fillers (ER309L and ER316L). The UTS andYS values decrease with increasing heat input, solidifica-tion time and cooling time. Maximum values are obtainedusing ERNiCrMo-3 filler and low welding current (80A).On the other hand, the base metal shows minimum UTS andYS values. This agrees well with previous results[4 – 5]. The
percentage elongation of TIG weld samples are shown inFig. 11c. The elongation percent of all weld samples de-creases with increasing welding current, that is consistentwith the UTS and YS results.
Hardness of welded joints is measured along the crosssection parallel to the base plate surface, as shown in Fig. 12(ASTM E384-09). The hardness at the center of the weldedregion shows a minimum hardness value for each sample.This is due to the heat input from the welding process, thatcauses annealing and recovery leading to hardness decrease.Moreover, the increase of the heat input decreases the cool-ing rate of weld metal. The hardness increases gradually inthe heat affected zone “HAZ” from the fusion line to theparent metal. This can be attributed to the low cooling ratenear the fusion line, that subsequently causes grain growth.On the other hand, higher cooling rates near to the parentmetal leads to a finer grain size, and also to microstructuraland chemical homogeneity[1]. Highest hardness is obtained
80 A 100 A 130 A
Welding current
0.04
0.03
0.02
ER309L
ER316L
ERNiCrMo-3
Nugget
are
a/m
m2
20 mm
(a) (b)
Fig. 10 The weld nugget area of 316 SS square weld samples under different heat inputs and filler metals (a) Macrostruc-ture of weld specimen (b) Nugget weld area of 316 SS specimens
80 A 100 A 130 A
Welding current
80 A 100 A 130 A
Welding current
7
6
5
4
3
2.0
1.5
1.0
ER309L
ER316L
ERNiCrMo-3
ER309L
ER316L
ERNiCrMo-3
Soli
dif
icat
ion t
ime/
s
Cooli
ng t
ime/
s(a) (b)
Fig. 9 Effect of welding current on (a) Cooling time (b) Solidification time of 316 SS welding.
13
80 A 100 A 130 A
Welding current
350
300
250
200
580
560
540
520
48
46
44
42
40
ER309LER316LERNiCrMo-3
ER309LER316LERNiCrMo-3
ER309LER316LERNiCrMo-3
Basemetal
80 A 100 A 130 A
Welding current
Basemetal
80 A 100 A 130 A
Welding current
Basemetal
UT
S/M
Pa
YS
/MP
a
Elo
ngat
ion (
%)
(a)
(c)
(b)
Fig. 11 Mechanical test results of TIG welded joints (a) Tensile strength (b) Yield strength (c) Percentage elongation.
240
220
200
180
160
140−10 −8 −6 −4 −2 0 2 4 6 8 10
Distance from weld zone/mm
80 A100 A130 A
80 A100 A130 A
Har
dnes
s/H
V
(a)
80 A100 A130 A
240
220
200
180
160
140−10 −8 −6 −4 −2 0 2 4 6 8 10
Distance from weld zone/mm
Har
dnes
s/H
V
(c)
240
220
200
180
160
140−10 −8 −6 −4 −2 0 2 4 6 8 10
Distance from weld zone/mm
Har
dnes
s/H
V
(b)
Fig. 12 Vickers hardness profiles of 316 SS TIG joint cross sections for different values of welding current using (a) ER309L(b) ER316L and (c) ERNiCrMo-3 as filler rods.
14 CHINA WELDING Vol. 29 No. 1 March 2020
in specimens welded using ERNiCrMo-3 filler rod and 80Awelding current.
The bend test (root bend test and face bend test) of AISI316 weld specimens at different welding current with
ER309L, ER316L and ERNiCrMo-3 as filler rods is carriedout. By increasing the bending angle up to 180°, no visualdefects could be observed, as shown in Fig. 13 as an ex-ample.
3 Conclusions
AISI 316 weldments using three filler rod materials andat different welding current values are successfully pro-duced by GTAW process. The following could be con-cluded:
(1) Visual inspection and radiographic testing indicatethat the weldments are free from macro/micro defects.
(2) The heat input, cooling time, solidification time andweld nugget area increase with increasing welding current.The cooling rate decreases with increasing welding current.
(3) Using ERNiCrMo-3 as filler rod produced weld-ments with higher ultimate tensile strength and yield stressthan using ER309L or ER316L.
(4) The ultimate tensile strength, yield stress and elong-ation percent decrease with increasing heat input. Highestvalues are obtained using ERNiCrMo-3 filler rod at compar-atively low welding current (80 A).
(5) The hardness is lower in weld zone than that of inheat affected zone and base metal. In general, it decreaseswith increasing heat input (welding current). Highest val-ues are obtained using ERNiCrMo-3 filler with low heat in-put (80 A).
(6) After sample bending up to 180°, no cracks, tearingor surface defects could be observed.
Acknowledgement
The authors would like to thank the Petrojet Company
(Suez, Egypt) which is deeply acknowledged for providingwelding process and collaboration.
References
Gopinath Shit, Kuppusamy M V and Ningshen S. Corrosionresistance behavior of GTAW welded AISI Type 304L.Transactions of the Indian Institute of Metals, 2019, 72:1 −15.
[1]
Dilip Kumar Singh, Gadadhar Sahoo, Ritwik Basu, et al.Investigation on the microstructure-mechanical propertycorrelation in dissimilar steel welds of stainless steel SS304and medium carbon steel EN8. Journal of ManufacturingProcesses, 2018, 36:281 − 292.
[2]
Yelamasetti Balram, Vishu Vardhan T, Sridhar Babu B, etal. Thermal stress analysis of AISI 316 stainless steelsweldments in TIG and pulse TIG welding processes.Materials Today: Proceedings, 2019, 19:1 − 6.
[3]
Balram Yelamasetti, Sravan Kumar, Sridhar Babu B, et al.Effect of filler wires on weld strength of dissimilar pulseGTA monel 400 and AISI 304 weldments, Materials Today:Proceedings, 2019, 19: 1-5.
[4]
Abdollah Bahador, Esah Hamzah, Mohd Fauzi Mamat.Effect of filler metals on the mechanical properties ofdissimilar welding of stainless steel 316l and carbon steelA516 GR 70. Jurnal Technology (Sciences & Engineering),2015, 75:61 − 65.
[5]
Hao Y S, Li J, Li X, et al. Influences of cooling rates onsolidification and segregation characteristics of Fe-Cr-Ni-
[6]
80 A 100 A
130 A
20 mm 20 mm
20 mm
Fig. 13 Bending test specimens of weldments using ERNiCrMo-3 welding wire and different welding current values.
15
Mo-N super austenitic stainless steel. Journal of MaterialsProcessing Technology, 2020, 275:1 − 9. Huei-Sen Wang. Effect of welding variables on cooling rateand pitting corrosion resistance in super duplex stainlessweldments. Materials Transactions, The Japan Institute ofMetals, 2005, 46:593 − 601.
[7]
Navid Moslemi, Norizah Redzuan, Norhayati Ahmad, et al.Effect of current on characteristic for 316 stainless steelwelded joint including microstructure and mechanicalproperties. 12th Global Conference on SustainableManufacturing, 2015, 26:560 − 564.
[8]
Balaji C, Abinesh K, and Sathish R. Evaluation ofmechanical properties of stainless steel weldments usingtungsten inert gas welding. International Journal ofEngineering Science and Technology, 2012, 4:2053 − 2057.
[9]
Aziz Barıs Basyigit, Mustafa Gökhan Murat. The effects ofTIG welding rod compositions on microstructural andmechanical properties of dissimilar AISI 304L and 420stainless steel welds. Metals, 2018, 8:1 − 14.
[10]
Shultz B L, Jackson C E. Influence of weld bead area onweld metal mechanical properties. Welding ResearchSupplement, 1973, 54:26 − 37.
[11]
Debasish Das, Dilip Kumar Pratihar and Gour Gopal Roy.[12]
Cooling rate predictions and its correlation with graincharacteristics during electron beam welding of stainlesssteel. The International Journal of Advanced ManufacturingTechnology, 2018, 97:2241 − 2254. Shu F Y, Tian Y, Zhao H Y, et al. Microstructure andmechanical properties of multi-Pass TIG welded joint ofthick Al-Zn-Mg alloy plate. Material Research Express,2019, 6:1 − 9.
[13]
Yu X Q, Ding F, Huang J k, et al. The characteristic ofinterface microstructure for aluminum-steel butt joint by arcassisted laser welding-brazing. Material Research Express,2019, 6:1 − 12.
[14]
Merchant Samir Y. Investigation on effect of heat input oncooling rate and mechanical property (hardness) of mildsteel weld joint by MMAW process. International Journal ofModern Engineering Research (IJMER), 2015, 5:34 − 41.
[15]
Oystein Grong, Metallurgical modelling of welding, TheInstitute of Materials, London: 1994.
[16]
Charlotte Weisman, Welding Handbook, Fundamentals ofWelding, American Welding Society, Miami, Florida, 1976.
[17]
Aziz Barıs Basyigit , Adem Kurt. The effects of nitrogen gason microstructural and mechanical properties of TIG weldedS32205 duplex stainless steel, Metals, 2018, 8: 1-13.
[18]
16 CHINA WELDING Vol. 29 No. 1 March 2020