mGo, Ira

Accepted 15 August 2013Available online 27 August 2013

Keywords:Austenitic stainless steelWeld repairsHeat affected zoneMicrostructure

properties of stainless steel 316L under repeated repair welding. The welding and the repair weldingwere conducted by shielded metal arc welding (SMAW). The SMAW welding process was performed

repaired once only. According to the GB50236-97 and GB50236-98 standards, no more than two repair welds should be performedin the same area.

Most of the investigations about stainless steels 316L studied onthe effects of alloying elements, various heat treatments and weld-ing techniques on micro structures, oxide lm, creep and fatiguebehaviors [718]. Many researchers paid attention to weld and

hile longitudinalnumber inthat usingl to decre

residual stress. Vega et al. [26] studied the effect of multiplein the same area in seamless API X52 micro alloyed steel piobtained that a fourth weld repair is also possible. The mechanicalproperties satised the requirements of the different standards.However their investigation did not refer to the corrosion proper-ties. Lin et al. [27] investigated repeated repair welding effect onthe micro structural and mechanical properties of AISI 304Lstainless steel. According to their investigation, an increase innumber of repair welding in AISI 304L caused uniform and pittingcorrosion. The number of weld repair did not have any signicant

Corresponding author. Tel./fax: +98 6314429937.

Materials and Design 54 (2014) 331341

Contents lists availab

an

elsE-mail addresses: Mansour.farzam@yahoo.com, farzam@put.ac.ir (M. Farzam).[3], IPS-C-PI-270(2) [4] and GB50236-98 [5,6] standards. In theDNV-OS-F101 Appendix C, sub-section G 300 it is expressed Weldseams may only be repaired twice in the same area. In the IPS-C-PI-270(2), it is stated a weld with unacceptable defects may be

input increase, transverse stress decreases wstress changes little and with the welding layerthe residual stresses decrease. They concludedple-layer and high heat input weld can be usefu0261-3069/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.matdes.2013.08.052crease,multi-ase therepairspe andOne of the important maintenance and repair processes isrepair welding. In the metal industry, the volume of repair andmaintenance is far more than the manufacturing. There is no lim-itation in the number of repairs in the welding procedures such asAPI-1104 [1] and ASME Section IX [2]. The references found inwhich the number of weld repairs is limited are: DNV-OS-F101

residual stress. Majority of these studies are based on simulationby nite element [1925], and so far very little research on the ef-fects on mechanical properties and corrosion repair welding hasbeen conducted.

Jiang et al. [25] studied the effect of welding heat input andlayer number on residual stress in repair welds for a stainless steelclad plate by nite element method. Based on their study with heatMechanical characterizationCorrosion

1. Introductionusing E316L ller metals. Specimen of the base metal and different conditions of shielded metal arc weld-ing repairs were studied by looking in the micro structural changes, the chemical composition of thephases, the grain size (in the heat affected zone) and the effect on the mechanical and corrosion proper-ties. The microstructure was investigated using optical microscopy (OM) and scanning electron micros-copy (SEM). The chemical composition of the phases was determined using energy dispersivespectrometry (EDS). The corrosion behavior in 1 M H2SO4 + 3.5% NaCl solution was evaluated using apotentiodynamic polarization method. Tensile tests, Charpy-V impact resistance and Brinell hardnesstests were conducted. Hardness of the heat affected zone decreased as the number of repairs increased.Generally an increase in the yield strength (YS) and the ultimate tensile strength (UTS) occurred withwelding. After the rst repair, a gradual decrease in YS and UTS occurred but the values of YS and UTSwere not less than values of the base metal. Signicant reduction in Charpy-V impact resistance withthe number of weld repairs were observed when the notch location was in the HAZ. The HAZ of weldingrepair specimen is more sensitive to pitting corrosion. The sensitivity of HAZ to pitting corrosion wasincreased by increasing the number of welding repair.

2013 Elsevier Ltd. All rights reserved.

repair welding, focused on studying the effect or distribution ofArticle history:Received 6 June 2013

The purpose of this study is to evaluate changes in the mechanical, micro structural and the corrosionThe effect of repeated repair welding onproperties of stainless steel 316L

Iman AghaAli a, Mansour Farzam a,, Mohammad AliaAbadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadanb Faculty of Materials Engineering, Isfahan University of Technology, Isfahan, Iran

a r t i c l e i n f o a b s t r a c t

Materials

journal homepage: www.echanical and corrosion

lozar b, Iman Danaee a

n

le at ScienceDirect

d Design

evier .com/locate /matdes

effect on the impact strength but did affect the fracturecharacteristics. Silva et al. [28] evaluated the effect of welding heatinput on the microstructure, hardness and corrosion resistance ofAWS E309MoL-16 weld metal, with AISI 316L austenitic stainlesssteel plates. Their investigation revealed that as heat input in-creased, the corrosion rate reduced.

Jiang et al. [29] studied of effect of multiple repairs welds onresidual stress, microstructure and hardness for a stainless steelclad plate. According to their investigation as the repair times

increase, the content of short ferrite is increased, longitudinaland transverse residual stress decreased, the hardness in the diffu-sion layer is increased because more Fe and C are diffused to thediffusion layer. Therefore, the diffusion layer should be removedcompletely before re-repair, in order to decrease the risk of crackgeneration. Based on the considerations of microstructure, residualstress and hardness, it is proposed that this clad plate should notbe repaired more than 2 times.

Up to day a systematic investigation into the multiple weld re-pairs effect on the microstructure and mechanical properties ofAISI 316L stainless steel has not been performed. Hence this studyevaluates change in the mechanical, microstructural and corrosionproperties of stainless steel 316L under the multiple weld-repairseffect.

2. Experimental details

The material used was AISI 316L austenitic stainless steel,welded using AWS E316L-16 electrode. Tables 1 and 2 show chem-ical compositions of materials. V-shaped butt welds with dimen-sion shown in Fig. 1a were prepared. The method of weldingused was shielded metal arc welding (SMAW). Welding andremoving of the weld bead was conducted using a qualied techni-cian. Details of the welding procedure and parameters are shown

Table 1Chemical composition of the AISI 316L austenitic stainless steel base metal (weight%).

C Si Mn P S Cr Mo Ni

0.03 0.06 1.05 0.022 0.004 16.5 2.1 10.4

Al Co Ti Cu Nb V W Fe

0.005 0.15 0.019 0.31 0.014 0.034 0.06 Base

Table 2Chemical composition of the AWS E316L-16 austenitic stainless steel weld metal(weight%).

C Mn Si Cr Ni Mo Fe

0.025 0.8 0.9 18.5 12 2.7 Balance

332 I. AghaAli et al. /Materials and Design 54 (2014) 331341Table 3Welding parameter.

Pass Welding process Filler metal Current (A) Voltage (V) Weldin

Class Diameter (mm)

1 SMAW E316L-16 3.25 120 20 202 SMAW E316L-16 3.25 120 24 203 SMAW E316L-16 3.25 120 24 204 SMAW E316L-16 3.25 120 25 205 SMAW E316L-16 3.25 120 25 206 SMAW E316L-16 3.25 120 25 207 SMAW E316L-16 3.25 120 25 208 SMAW E316L-16 3.25 120 24 20

Note: The inter-pass temperature was maintained at 140C to avoid variations in the co

Fig. 1. (a) Dimensions of weldment specimens; (b) Schematic illustration showing rproperties of various specimens; (c) Schematic illustrations of tensile test specimen; (d)scale, and dimensions are in mm.)g speed (Cm min1) Welding heat input (kJCm1) Inter-pass temperature (C)

7.2 27 18.6 30 18.6 140 19 140 19 140 19 140 19 140 1

egions of interest when evaluating microstructural characteristics and corrosionschematic illustrations of impact test specimen. (Note that illustrations are not to8.6 140 1

oling rate among the passes.

nd Design 54 (2014) 331341 333I. AghaAli et al. /Materials ain Table 3. Removal of the weld bead was done by milling (Drillingand milling machine, Model ZX7032). The fusion zone and line re-moved completely before re-repair. Sample which was weldedonce is assigned 0R and sample which was repaired once assigned1R and so on. Thus, ve different samples: original and with differ-ent number of welding repairs: 0R, 1R, 2R, 3R, 4R were prepared.Detailed microstructural observations were carried out in theheat-affected zone (HAZ) and base metal (BM) region of the spec-imens are shown in Fig. 1b. The specimens were polished mechan-ically and then were etched chemically in a Glyceregia solution (3parts glycerol, 5 parts HCl, 1 part HNO3). Glyceregia etchant attacksphases and outlines the carbides [30]. The surface of each speci-men was examined using optical and scanning electron micro-scope (SEM, VEGA-TESCAN-XMU). The chemical composition andelement distribution were determined using energy dispersiveX-ray spectrometry (EDS). According to ASTM: E-3 and ASTM: E-407, mechanical polishing with emery paper of grit Nos. 120,240, 400, 600, 800, 1000, 1200, and 2000 was conducted before -nal polishing with 0.25 lm Al2O3 suspensions and then etched for4560 s in the Glyceregia solution. The SEM specimens wereetched in the Glyceregia solution for 100120 s. The assessmentof the grain size of the HAZ was carried out according to ASTM:E-112 and ASTM: E-883 using an optical microscope coupled to adigital images analyzer. The hardness measurement was carriedout using Brinell test in accordance the ASTM: E-10. Consideringthe limitations, tensile tests were performed at room temperatureaccording the ISO 6892-1 standards [31]. The samples of the tensiletest were prepared to sub size dimension. The location of the ten-

Fig. 2. Microstructure of AISI 316L stainless steel. Etch Solution: Glyceregia; etching tisile test sample has been shown in Fig. 1c. The extension rate was0.05 mm s1. Several tests for each welding repair condition werecarried out. The impact properties of the specimens were testedat a temperature 25 C using an impact test machine. Thetests were performed using notch type A (V-notch by radius0.25 mm) specimens with standard size dimensions(55 mm 10 mm 10 mm: ASTM: E-23 standard) (Fig. 1d). Theelectrochemical corrosion properties of the specimen immersedin a corrosive solution (chemical composition: 3.5% NaCl + 1 molH2SO4) at 25 C were determined using a potentiodynamic method

me: 4560 s. (a) BM; (b) 0R HAZ; (c) 1R HAZ; (d) 2R HAZ; (e) 3R HAZ; (f) 4R HAZ.

Fig. 3. ASTM grain size number in HAZ as a function of the number of repairs forcentral area.

(AUTOLAB; ASTM: G-59). Platinum and the silver/silver chloride(Ag/AgCl) were used as counter and referenced electrode. Eachspecimen was scanned potentiodynamically at scan rate 1 mV s1

from an initial potential of 0.8 V to a nal potential of 1.4 V.

3. Results and discussion

3.1. Microstructural properties

Fig. 2 presents OM images of the original AISI 316L stainlesssteel BM, and the HAZ regions of the 0R, 1R, 2R, 3R and 4Rspecimens. The images show that the solidied microstructuresof the BM specimen, and the HAZs of the ve weld-repair speci-

mens, comprised of austenite matrix, ferrite precipitates and blackcarbide particles. BM had predominantly d-ferrite lathy morphol-ogy, characteristic in both ferriteaustenite (FA) and completelyferrite (F) (Fig. 2a). The morphology of d-ferrite was altered withnumber of welding. The evaluation of the microstructure, HAZ ex-posed to the lowest number of welding (R0) had predominantly d-ferrite lathy morphology similar to BM (Fig. 2b), but less lathy d-ferrite, and d-ferrite with vermicular morphology, ne short ferriteprecipitates and black carbide particles were detected. 1R, 2R had asimilar microstructure to the previous set of results, but less lathyd-ferrite and more d-ferrite with vermicular morphology werepresent (Fig. 2c and d). The evaluation of the microstructure HAZsof 3R and 4R show reduced percentage of d-ferrite lathy morphol-ogy and increased d-ferrite with vermicular morphology (Fig. 2e

334 I. AghaAli et al. /Materials and Design 54 (2014) 331341Fig. 4. Morphologies after Glyceregia chemical etching; etching time: 100120 s. (a) BM; (b) 0R HAZ; (c) 1R HAZ; (d) 2R HAZ; (e) 3R HAZ; (f) 4R HAZ.

Table 4Major alloying-element concentration in BM and HAZ regions of the 0R, 1R, 2R, 3R and 4R specimens.

Specimen Phases Cr (wt.%) Ni (wt.%) Mo (wt.%) Mn (wt.%)

BM d-ferrite 23.91 4.64 4.39 0.15Austenite 14.97 10.52 2 0.2Total 16.5 10.04 2.1 1.05

HAZ 0R d-ferrite 22.08 5.46 3.67 0.76Austenite 17.15 9.27 2.53 0.84Total 16.7 10.18 2.2 1.03

HAZ 1R d-ferrite 22.28 4.91 3.69 0.72Austenite 16.72 9.38 2.19 0.84Total 16.76 10.24 2.23 1.03

HAZ 2R d-ferrite 22.59 4.74 4.39 0.7Austenite 16.24 9.72 2.18 0.85Total 16.81 10.29 2.25 1.04

HAZ 3R d-ferrite 22.83Austenite 15.71Total 16.85

HAZ 4R d-ferrite 23.95Austenite 15.48Total 16.89

Fig. 5. d-ferrite as a function of the number of repairs.

Table 5Brinell hardness values for each one of the repair condition and for different locations.

Weld HAZ 2 cm 3 cm 4 cm 5 cm

HBW BM 146 146 146 146 146HBW 0R 187 170 152 149 147 146HBW 1R 187 172 152 149 147 146HBW 2R 187 167 152 149 147 146HBW 3R 187 163 152 149 147 146HBW 4R 187 160 152 149 147 146

Fig. 6. Longitudinal section of specimens from tensile tests.

I. AghaAli et al. /Materials and Design 54 (2014) 331341 3354.7 4.86 0.6810.53 2.17 0.8610.33 2.28 1.04

4.5 4.93 0.611.71 2.16 0.8710.41 2.3 1.05

Table 6and f). Fig. 2 shows that the addition of d-ferrite, carbide blackdeposits in the area is distributed. However, these carbides aremore apparent in the austenitic grain boundaries and especiallyat the border of d-ferrite and austenite phases.

The assessment of the grain size in the HAZ was carried outaccording to ASTM: E-112. It should be noticed that each specimenwas analyzed with 10 elds of view per data with magnications of100 X and 200 X, in the central area. Fig. 3 shows ASTM grain size

Result of the tensile tests for the different repair conditions.

Yield strength(offset 0.2%) (Mpa)

Tensilestrength(Mpa)

Lf(mm)

Elongation (%)Lo = 40 mm

Failurezone

Base 270 554.4 64.15 60.37 Basemetal

R0 340.2 580.5 55.50 38.75 Basemetal

R1 392.4 585 58.00 45 Basemetal

R2 355.5 577.35 57.30 43.35 Basemetal

R3 327.6 576 57.05 42.62 Basemetal

R4 343 566.55 55.20 38 Basemetal

Fig. 7. Stress vs. elongation prole.

number (G) in HAZ for central area is largest for 1R. The grain sizenumber is a function of the number of repairs. At rst, the heat ofthe welding cause formation of new grains and the grain size num-ber is increased. After 1R, by repeating repair welding, the grainsgrow and get bigger and the grain size number is decreased.

Fig. 4 presents scanning electron microscopy (SEM) images ofthe original AISI 316L stainless steel BM, and the HAZ regions ofthe 0R, 1R, 2R, 3R and 4R specimens, respectively. According to Ta-ble 4, the ferrite phase has a higher percentage of chromium com-pared to the austenite phase, so ferrite passive layer is morecorrosion resistant than that of austenite. Increase or decrease ofalloying element results in a concentration gradient of alloyingelements (between base and the ller metal). However, signicantchange at percent of the element has not been observed due to theFig. 8. Average value of absorbed energy for each one of the repair condition.

Fig. 9. Fracture surface of specimens from impact test for each one of the repair conditio

336 I. AghaAli et al. /Materials and Design 54 (2014) 331341n; (a) base metal, (b) as-welded, (c) rst, (d) second, (e) third and (f) fourth repairs.

nd DI. AghaAli et al. /Materials ause of the similar ller with base metal. Considerable differencesbetween the percent of manganese in the ferrite and the austeniteand total were observed. This is due to the lack of manganese a so-lid solution. Nevertheless, increased number of repair does not al-ter the solubility of manganese. Table 4 shows as the number ofrepair is increased, the solubility of chromium and molybdenumin the ferrite phase is increased. The solubility of nickel and man-ganese at ferrite phase is decreased. Chromium and molybdenumsolubility in the austenite phase is also decreased and the solubilityof nickel and manganese in the austenite phase is increased.

Fig. 5 shows the amount of d-ferrite tends to decrease with anincrease in number of repairs. Silva et al. [28] have concluded thatreductions in the level of d-ferrite have been attributed to a slowercooling rate when the welding heat input is increased. Thisassumption is based on the theory that the cooling rate has a sig-

Fig. 10. SEM micrographs of impact surface in beginning of fracture: (a) baseesign 54 (2014) 331341 337nicant inuence on solidication and solid state transformationsof stainless steel weld metals, especially for levels of d-ferriteabove 14% [32]. Slower cooling rates would result in lengthy d toc transformation, thus causing a greater percentage of d-ferritetransformation into austenite. Assuming that the heat weldingdoes not melt the HAZ; increase in repair number promotes condi-tions for the d to c transformation.

3.2. Hardness evaluation

Brinell hardness results are reported in Table 5. According toASTM: E-10, the test force was 29.42 KN (3000 Kgf), ball diameter10 mm, and test duration was 1015 s. Weld hardness value ismore than the other regions because of differences in percent ofalloying elements. Due to the use of same ller in all welding pro-

metal, (b) as-welded, (c) rst, (d) second, (e) third and (f) fourth repairs.

cesses, hardness remained constant. Table 5 shows the hardnessvalue of HAZ as a function of weld repair. The Brinell hardness ofHAZ has a tendency to decrease with increase in the number ofrepair.

3.3. Tensile tests

The tensile samples were prepared and tested as shown inFig. 6. The results of the tensile tests are presented in Table 6and Fig. 7. This behavior indicates a gradual increase in yieldstrength (YS) and ultimate tensile strength (UTS) reaching maxi-mum value in the 1R, followed by a slight decrease in the second,third and fourth repair. The variation in the YS and UTS can beattributed to the contribution of the HAZ grain size and grain

renement (Fig. 3). The change in elongation may be looked atthe similar manner.

3.4. Impact properties analysis

Impact test was conducted using ASTM: E-23. Fig. 8 shows theimpact strength of BM was higher than that of the HAZ, but falls asthe number of weld repairs increased. Fig. 9 shows the fracto-graphs of the fracture surfaces of different weld repair. The fracturesurfaces were dull and brous. Fig. 10 shows details of the frac-tured surface morphologies in beginning of fracture. Increasednumber of weld-repairs leads to change of the fracture from planarfracture to appearance of ridges. This behavior can be attributed tochanging fracture toughness value with the number of weld re-

338 I. AghaAli et al. /Materials and Design 54 (2014) 331341Fig. 11. SEM micrographs of impact surface in the center or the end of fracture: (a) base metal, (b) as-welded, (c) rst, (d) second, (e) third and (f) fourth repairs.

pairs. Fig. 11 shows the fractured surface morphologies in the cen-ter (or the end) of fracture. The fractured surface of specimens con-tains planar fracture, in-depth ridges and shear dimples.

3.5. Corrosion properties analysis

Fig. 12 shows the polarization curves and the measured data ofthe electrochemical parameters are presented in Table 7. The re-sults show that the corrosion potentials for the BM specimen, thewelded specimen and repaired specimens varied from 0.337 to0.298 V. The important parameter in pitting corrosion and cre-vice corrosion is difference between breakdown potential (EB, thelowest potential at which pitting occurs) and protection potential(EP, repassivation potential). When a pit has been initiated, the po-tential must be decreased down below the protection potential to

showed the average hardness of lathy d-ferrite morphology waslarger than the average value of vermicular d-ferrite morphology.Padilha and Guedes [37] showed that the increase in the volumet-ric fraction of d-ferrite leads to a higher value of hardness. Vegaet al. [26] studied the effect of multiple repairs in the same areain seamless API X52 micro alloyed steel pipe and reported a similarresults.

The impact strength of BM was higher than that of the HAZ, butfalls as the number of weld repairs increased. Repeating repairwelding changes the fracture mechanism from a planar fractureto ridges present. The change of morphology of d-ferrite from lathyto vermicular (and d-ferrite dispersion) may be the reason for thechanges mentioned. The micro voids presence may be related tod-ferrite. Another reason for decrease in the absorbed energymay be related to repeat welding which reduced percentage of d-

I. AghaAli et al. /Materials and Dstop the pit from growing and repassivate the surface. The BMspecimen has the highest corrosion and breakdown potentials.On the other hand corrosion potential and breakdown potentialand its relevant current density of weld are decreased. With therst repair welding, corrosion current density decreased and differ-ence between breakdown potential and protection potential (EB EP) increased. With each repair, corrosion current decreased andEB EP increased. Such behavior has been reported for AISI304L but their corrosion current density did not reduce [27].

3.6. Discussion

The multiple repair welds has great effect on the mechanicalproperties and corrosion. It is induced by the heat input. Whensolidication occurs in the primary ferrite phase (FA) or completelyferrite (F), the decrease in the cooling rate leads to a decrease in thed-ferrite level from the solidied liquid metal, and an increase inthe ferriteaustenite solid state transformation. Slower coolingrates would result in lengthy d to c transformation. Increase in re-pair number promotes conditions for the d to c transformation. Theferrite phase has a higher percentage of chromium compared to theaustenite phase, so ferrite passive layer is more corrosion resistantthan that of austenite.

Increase in EB EP indicated a reduced pitting and crevice cor-rosion resistance and decreased corrosion current density indi-cated an increased uniform corrosion resistance. Such behavior isdue to the changing morphology and volume of d-ferrite. By per-forming a repair welding, volume of d-ferrite is reduced. Uniformcorrosion is decreased with the decreasing percent of d-ferrite asdemonstrated [28]. The effect of d-ferrite on corrosion resistancecan also be attributed to the difference in the chemicalcomposition of d-ferrite and austenite. The presence of two phasescan form an activepassive region, accelerating the attack on theFig. 12. Potentiodynamic curves of AISI 316L stainless steel, base metal and HAZ ofthe different welding repair in 1 M H2SO4 + 3.5% NaCl solution at 25 C.austenite matrix [28,33]. Increase in EB EP implies the enhance-ment to chloride sensitivity of the HAZ of repeated welding. Itsresult is the transformation of the original lathy ferrite phases toa ne distributed short ferrite precipitates in the austenite. The re-peated weld repair process prompts a greater transformation of thelathy ferrite phase to short ferrite precipitates, and thereforeincreasing pitting corrosion [15,27]. The greater sensitivity of the4R is the result of the higher grain boundary energy induced bythe repeated welding repair process. This is due to more transfor-mation of the lathy d-ferrite phase to d-ferrite of vermicularmorphology, therefore increasing corrosion attack. However, theuniform corrosion resistance increased due to the reducing d-fer-rite phase.

The grain size number is a function of the number of repairs.After the rst repair, increasing the number of weld repairs pro-motes grain growth in the coarse grained heat affected zone(CGHAZ). The bead technique generates overlap beads producinggrain renement in the CGHAZ of the previous bead and decreasingthe residual stresses due to the input of additional thermal energy[34]. This is the reason that the one repair presents the maximumvalue of YS and UTS.

Generally, the Brinell hardness of HAZ has a tendency to de-crease with increase in the number of repair. This behavior canbe attributed to the bigger grain size, the reduction in the levelof d-ferrite and the morphology of d-ferrite. In 0R and 1R, thereduction in grain size is the dominant factor, whereas in 2R, 3R,and 4R all the factors are responsible for reduction in hardness.Hardness increases in the rst repair due to the generation ofnew grain. Hardness decrease in the subsequent repairs is due tograin growth, reduction of ferrite and the change in morphologyof d-ferrite. The increase in hardness after the rst repair and a de-crease in the second and third repairs, because of an apparent grainrenement generated in the HAZ and grains grow during secondand third repair as demonstrated [26,35,36]. Silva et al. [28]

Table 7Electrochemical properties of AISI 316L stainless steel BM and weld-repair specimenswhen immersed in 1 M H2SO4 + 3.5% NaCl solution at 25 C.

Ecorr (V) icorr (A cm2) EBEP (V)

Base metal 0.298 3.07 106 0.7860R 0.318 2.01 106 0.7911R 0.333 1.69 106 0.8332R 0.337 1.61 106 0.9103R 0.320 1.01 106 0.9224R 0.329 9.47 107 0.928

Ecorr: corrosion potential, icorr: corrosion current density, EBEP: difference betweenbreakdown potential and protection potential.

esign 54 (2014) 331341 339ferrite. According to research conducted by Ylmaz and Tmer[38], toughness is directly related to the amount of ferrite.

nd Design 54 (2014) 331341Based on the Jiangs [25] study, using multiple-layer and highheat input weld can be useful to decrease the residual stress.Although the residual stress is not studied in this paper indepen-dently but the results of tensile and hardness tests represent theresidual stress decreased with increasing frequency of repair. Theharness has a close relation with the strength [39,40], which meansthe local strength in HAZ has been degraded because of the multi-ple heating.

4. Conclusions

This paper investigated the effect of repeating repair welding onmicrostructure, hardness, tensile strength, impact strength andcorrosion resistance for a stainless steel 316L by experimental,the following conclusions are obtained:

(1) The microstructures of the BM specimen, and the HAZs ofthe weld-repair specimens, comprised of austenite matrix,ferrite precipitates and black carbide particles. Heat inducedof welding repair changes the structure and amount of d-fer-rite. Repeating repair welding will transform d-ferrite mor-phology to ne short ferrite precipitates and will reducethe amount of ferrite.

(2) Brinell hardness of HAZ decreased with increasing numberof repair welding. The analysis showed reduction of the per-centage of d-ferrite is the main reason for such behavior.

(3) The tensile test results showed that repeating repair weldingdid not have much adverse effect on yield and ultimate ten-sile strength. The yield strength and the ultimate tensile ini-tially increased and then decreased, this was due to grainsize and grain renement effect. The grain size decreasedduring the rst repair and later increased with increasingnumber of repairs.

(4) The impact test showed a signicant fall in the absorbedenergy values as the number of weld repairs increased. Thiswas due to the change in the fracture mechanism because ofthe transformed d-ferrite morphology and the increasedgrain boundary energy and decreased d-ferrite phase.

(5) The HAZ of weld-repair specimen is sensitive to pitting cor-rosion when immersed in 1 M H2SO4 + 3.5% NaCl solution.Repeating repair welding causes the sensitivity of HAZ topitting corrosion and crevice corrosion increased. This isdue to more transformation of the lathy d-ferrite phase tod-ferrite of vermicular morphology, therefore increasing cor-rosion attack. However, the uniform corrosion resistanceincreased due to the reducing d-ferrite phase.

(6) Based on the compressive considerations of residual stress,microstructure, hardness, tensile strength, impact strengthand corrosion resistance, it concludes that the stainless steel316L can be repaired for 4 times in chloride-free environ-ment. But in chloride environment, because of damagingeffects of chlorine and formation of stress corrosion cracking(SCC), repairing more than 2 is not suggested. According tothe results in chlorine-free environment, there is no limitto numbers of repairs.

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I. AghaAli et al. /Materials and Design 54 (2014) 331341 341

The effect of repeated repair welding on mechanical and corrosion properties of stainless steel 316L1 Introduction2 Experimental details3 Results and discussion3.1 Microstructural properties3.2 Hardness evaluation3.3 Tensile tests3.4 Impact properties analysis3.5 Corrosion properties analysis3.6 Discussion

4 ConclusionsReferences