Influence of Argon Pollution on the Weld Surface Morphology

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mental investigations about weld joint quality can be deformation behavior. These publications do not mion. The punt for wel

quality. Low argon quality causes discoloration of tharea and changes to the surface morphology oftubes. The surface morphology of the pipe installationinuences the interaction of liquids and gases with the sur-face and through surface wear may cause impurities or hasan inuence on electrisation. It is a very important issue inbranches such as the pharmaceutical and food industries. A

http://dx.doi.org/10.1016/j.measurement.2015.04.0010263-2241/ 2015 Elsevier Ltd. All rights reserved.

Corresponding authors.E-mail addresses: [email protected] (G.M. Krolczyk), p.nieslony@

po.opole.pl (P. Nieslony), [email protected] (J.B. Krolczyk), [email protected] (I. Samardzic), [email protected](S. Legutko), [email protected] (S. Hloch), [email protected](S. Barrans), [email protected] (R.W. Maruda).

Measurement 70 (2015) 203213

Contents lists available at ScienceDirect

Measure

journal homepage: www.elseviefound in the open literature. Tseng and Hsu [1] investigateve kinds of oxide uxes. They showed the effect of

the problems related to the argon pollutargon as a shielding gas is very importaentionrity ofd jointe weldwelded1. Introduction

Precise characterization of surface morphology is ofprime importance in many engineering industries becausecertain functional properties of the materials are oftendetermined by the surface characteristics. Achieving thedesired surface quality is of great importance for the func-tional behavior of a part. Welding is the principal joiningmethod used by engineering industry. Examples of experi-

activated TIG process on weld morphology, angular distor-tion, delta-ferrite content, and hardness of 316L stainlesssteels. Dewan et al. [2] presents residual stresses, micro-hardness, microstructures, and uniaxial tensile propertiesin TIG welded of AISI-4140 alloys steel with SAE-4130chromiummolybdenum alloy. Wen et al. [3] presentsmicrostructural change and fatigue properties of linearfriction welding of Ti6Al4V joints with special attentionto the relationship between the microstructure and cyclica r t i c l e i n f o

Article history:Received 13 November 2014Received in revised form 30 March 2015Accepted 8 April 2015Available online 16 April 2015

Keywords:Surface metrologySurface morphologyTopography inspectionWavinessWeld qualityIn this paper the surfaces of butt welded joints in steel tubes were analyzed using an opti-cal 3D measurement system to determine the morphology and topographic parameters. Itwas established that pollution of the argon shield gas with oxygen did not inuence thewidth of the heat-affected zone. However, the composition of the shield gas signicantlyinuenced the surface asymmetry, Ssk, and its inclination Sku. The measurement of theseparameters enabled the selection of a higher quality surface, which was visually provenby the reduction in discoloration of the surface of the weld joint. High quality surfaceseliminate a potential habitat for bacteria and a future source of corrosion as well as provid-ing less resistance to uid ow.

2015 Elsevier Ltd. All rights reserved.Inuence of argon pollution on the

G.M. Krolczyk a,, P. Nieslony b, J.B. Krolczyk a,S. Barrans f, R.W. Maruda g

a Faculty of Production Engineering and Logistics, Opole University of TechnolbDepartment of Manufacturing Engineering and Production Automation, OpocMechanical Engineering Faculty of Slavonski Brod, J.J. Strossmayer Universityd Faculty of Mechanical Engineering and Management, Poznan University of Te Faculty of Manufacturing Technologies, Technical University of Kosice, 1 Bayf Turbocharger Research Institute, University of Hudderseld, Hudderseld HDg Faculty of Mechanical Engineering, University of Zielona Gora, 4 Prof. Z. Szald surface morphology

Samardzic c, S. Legutko d, S. Hloch e,

Proszkowska St., 45-758 Opole, Polandersity of Technology, 76 Proszkowska St., 45-758 Opole, Polandijek, Trg Ivane Brlic-Mazuranic 2, 35000 Slavonski Brod, Croatialogy, 3 Piotrowo St., 60-965 Poznan, PolandSt., 080 01 Presov, Slovak Republic, UKtreet, 65-516 Zielona Gora, Poland

ment

r .com/ locate/measurement

The welded material was pipes 50 1.5 of an auste-

Sv maximum valley depth

204 G.M. Krolczyk et al. /Measurement 70 (2015) 203213material often used in the food and pharmaceutical indus-tries is stainless steel where the working surfaces ofdevices are in direct contact with food and drugs ingredi-ents. This type of material has been used for many yearsdue to its good mechanical properties [4] and good corro-sion resistance [5]. According to Tsisar et al. [6] martensiticsteels have a tendency toward weld cracking during cool-ing when hard brittle martensite is formed. Kim et al. [7]investigated the effects of shielding gas on the pitting cor-rosion of hyper duplex stainless steel welds. They reportedthat the pitting resistance of a solution heat-treated weldwith a combination of Ar and N2 as the shielding gas isgreatly increased due to an increase of austenite in theweld material and heat affected zone (HAZ). Furtherresearch on the process of welding stainless steels hasbeen dealt with by many researchers. Chern et al. [8] inves-tigated the effects of the specic uxes used in the tung-sten inert gas process on surface appearance, weldmorphology, angular distortion, mechanical properties,and microstructures when welding duplex stainless steel.Yajiang et al. [9] studied Fe3Al and Cr18Ni8 steel in thetungsten inert gas arc welding process. Micro-cracks, frac-ture and dislocation morphology in the weld zone wereanalyzed by scanning electron microscope, electron probemicro-analyzer and transmission electron microscopy.Zhang et al. [10] investigated the effect of tungsten inertgas welding and subsequent post-weld heat treatment onthe microstructure evolution and pitting corrosion behav-ior of duplex stainless steel. However, these publicationsdo not mention the geometrical parameters of the weldsurface morphology.

Surface prolometry has been known for many years asa method of topography inspection. Gharbi et al. [11]investigated the inuence of the main process parameterson the surface nish quality during the direct metaldeposition process. Their work was carried out using anYb-YAG disk laser and a widely used titanium alloy

Nomenclature

GPS geometric product specicationsHAZ heat affected zoneIFM innite focus measurementSa average roughnessSdr developed interfacial area ratioSdq Root Mean Square (RMS) Surface SlopeSku kurtosis(Ti6Al4V). Koszela et al. [12] presented textured cylinderliner surface topographies and computer software forvisualization of oil pockets array on machined surface.Mathia et al. [13] described problems of surface topogra-phy characterization and future trends in surface metrol-ogy. Parthasarathi et al. [14] studied characterization ofworn surface topography in a prototype fast breeder reac-tor. Safara Nosar and Olsson [15] investigated 3D surfacetopography images and surface proles behind the initialstages of material transfer between stainless steel and toolsteel in metal forming operations. Wieczorowski [16] pre-sented a novel spiral method of surface prolometry.nitic stainless steel 1.4301 (DIN EN 10088-1). The elemen-tal composition of the welded material is given in Table 1.

The welding method used was orbital welding which isa mechanized version of the tungsten inert gas arc welding(TIG) process. This method is used to weld pipes or station-ary tubes. The tungsten electrode contained in the weldhead rotor rotates (orbits) around the weld joint circumfer-ence. The welding speeds were 125 mm/min. The TIG pro-cess can be an autogenous process in which the edges ofthe weld joint are heated by the arc and fused together,without the addition of ller material. Alternatively, llermaterial may be added to the weld pool. The device forchecking the weld quality by the measurement of argoncontaminants was an Orbitec Oxy-2 residual oxygen ana-lyzer. Residual oxygen measuring devices can control andRepresenting surface properties using topographicparameters is accepted as being superior to using 2Dparameters. The surface parameters can be used withinfunctions describing surface behavior. In order to establisheffective quality control of the weld zone, it has beenrecommended that an extensive investigation is needed.This should include the clarication of the deteriorationproblems of surface weld joints which are important inpractical use [17].

This paper focuses on research problems related to themorphology of the surface after orbital welding. The mainpurpose of this study was to determine the inuence ofargon pollution as a key process factor in controlling sur-face integrity parameters. A secondary aim of this studyalso was to present the quality of the welds.

2. Material and methods

2.1. Welded material and welding method

Sz maximum height of surfaceTIG tungsten inert gasSp maximum peak heightSq root mean square roughnessSsk skewnessdocument the amount of oxygen in the area of the weldwhen they are linked to the weld controller. In the con-troller it is possible to set a limit on the amount of residualoxygen present. A schematic diagram of the experimentalarrangement is shown in Fig. 1.

2.2. Surface morphology analysis

Surface morphology analysis was performed using anInnite Focus Measurement Machine (IFM). The IFM is anoptical 3D measurement device which allows the acquisi-tion of datasets at a high depth of focus. The IFM method

%S

0.015

G.M. Krolczyk et al. /Measurement 70 (2015) 203213 205Table 1Chemical composition of 1.4301 austenitic stainless steel.

Element %C %Si %Mn %P

wt. (%) 0.07 1.00 2.00 0.045allows for the capture of images with a lateral resolutiondown to 400 nm and a vertical resolution down to20 nm. The IFM 4.2 software version was used to collectand present the measurement data. The surface morphol-ogy was measured from the functional side from theinside of pipe. The surface morphology analysis was car-ried out in the OUTech Surface Integrity Lab.

Before performing the Surface Morphology analysis, thequality of welds was checked by means of the X-ray exam-ination (Fig. 2). It was found that all the welds presented inFig. 2 were performed correctly, and there is no incompati-bility which might occur during welding.

3. Results and discussions

3.1. Variation in surface morphology

Correct shield gas formation gives a guarantee of thehighest quality of welds during TIG welding of highly

Fig. 1. Schematic diagram of ex%Cr %Ni %N Others

17.5019.50 8.0010.50 0.11 alloyed and stainless steels. From the point of view of theefciency of the welding process and the properties ofthe executed joints, an appropriate choice of shield gas isextremely important. The most common choice is argonwhich is heavier than air and non-reactive. Its principaltask is to protect the weld area against the ingress andunfavorable inuences of impurities coming from the sur-rounding atmosphere. In addition, argon inuencesphysicochemical phenomena forming in the weld arc dur-ing the welding process. Thus, it directly inuences a num-ber of factors determining the proper progression of thewelding process. The quality of shield gas argon is deter-mined by measuring the level of pollution (typicallyexpressed as parts per million (ppm)), mainly oxygen, inthe gas fed to the welding zone. The examination resultspresented in Fig. 3, concerning the impact of argon pollu-tion on the quality of welds were carried out under lab-oratory conditions. The measurements were performedfor seven different levels of pollution giving visible discol-oration of the weld area. Experimental studies were carried

perimental arrangement.

; 400 p

206 G.M. Krolczyk et al. /Measurement 70 (2015) 203213out from the inside of pipe. The research consisted of mea-suring the surface of the steel including the weld.Waviness measurement was performed using IFM.

The brown area visible in Fig. 3 is a result of metal oxi-dizing at high temperature but it is much bigger than theHAZ where the microstructure will be altered. This dis-colored region can harbor bacterial contamination and bean initiation point for corrosion. Argon is an inert gas,which means that it does not react with the weld puddleand does not cause oxidation of the tungsten electrode.Its low ionization potential (15.8 eV) facilitates ionizationof the gas space between the tungsten electrode and thewelded material. Low thermal conductivity in comparisonwith other gases reduces the cross-section of the arc col-umn. This brings about an increased concentration of heatin the arc core, which increases the depth of fusion in anarrow area. The concentration of energy in the arc coreand resultant high surface tension of the weld pool undera shield of pure argon causes high levels of sprue on theface of the weld. The welding arc under a shield of pureargon lacks stability, thus argon with the addition of activegases, particularly oxygen, is used for welding. However,an excess of oxygen in the mixture results in the introduc-tion of the excessive amounts of heat into the weldedmaterial. This then intensies the physicochemical phe-

Fig. 2. X-ray image of a weld joint: 800 ppm (a); 600 ppm (b)nomena in the welding zone. Hence, the degree of argonpurity inuences the quality of the weld. In addition tothe obvious impact on the quality and durability of theweld, the excessive amount of heat introduced into thewelded material brings about the changes in the surfacemorphology. The surface morphology, alongside the 3Dfunctional roughness parameters, inuences the perfor-mance of the engineered surface. In industrial practice,the geometric product specication (GPS) of the surfacecan be an important issue. In particular waviness and sur-face texture parameters can greatly inuence the interac-tion between machine elements and the interaction ofuids with the surface.

3.2. Variation in surface texture

The study of the dependence of the waviness of theweld joint surface on the degree of pollution of the argonshield was performed using the IFM by means of theFocus-Variation method. Figs. 4 and 5 show the measuredsurface waviness for different levels of pollution of argon.It is possible to isolate two zones: Zone A and Zone B.Zone A is a zone of 3.5 mm in width, which correspondsto the width of the face of the weld. Because all the ana-lyzed weld joints were formed with the same technologicalparameters, Zone A does not change its width. The width ofZone B being the heat-affected zone in the welding process,was dened as the width where the waviness deviatedfrom the base level. The maximum width of Zone B forthe analyzed welding parameters was set to 7 mm anddivided into 7 subzones of 1 mm wide.

The results of the measurements of the surface wavi-ness, in spite of the fact that they are characterized by con-siderable uctuations in Zone A, display stability in Zone B.The surface waviness in Zone B is a measure of morewidely spaced components of surface texture and was upto 40 lm from the base surface. The magnitude of wavi-ness depended on the subzones for all the samples, thelargest values were observed for subzone B1, analogously,the smallest ones for subzone B7, most distant from thesource of heat. Moreover, in Figs. 4 and 5 it is possible toobserve a decrease in the waviness values as the argonshielding gas becomes purer. For 8 ppm, the maximum

pm (c); 200 ppm (d); 60 ppm (e); 20 ppm (f); and 8 ppm (g).deviation of surface waviness from the base level in zoneB was about 10 lm. For pollution levels of 600 and800 ppm, it was 30 and 60 lm, respectively.

The selected amplitude and hybrid surface roughnessparameters of the weld joint area from subzones B1B7are presented on Fig. 6. On these graphs two characteristicareas can be distinguished. The rst area includes samplesfor which signicant changes in roughness parameters, asa function of distance from the heat sources (subzones),were not obtained (Fig. 6a and b region A). This areaincludes welds executed with essentially pure argonshields (8 and 20 ppm pollution), and, what is interesting,joints executed with very high pollution levels in the shieldgas (600 and 800 ppm). The other area includes samplesfor which the roughness values distinctly decrease withdistance from the joint penetration area (Fig. 6a andb region B). In these cases, the difference in values forSa and Sq between subzones B1 and B7 is 56 lm. A similar

Fig. 3. Surface morphology of weld area depending on the argon pollution: 800 ppm (a); 600 ppm (b); 400 ppm (c); 200 ppm (d); 60 ppm (e); 20 ppm (f);and 8 ppm (g).

G.M. Krolczyk et al. /Measurement 70 (2015) 203213 207

208 G.M. Krolczyk et al. /Measurement 70 (2015) 203213characteristic was observed for parameter Sz (Fig. 6e).Welds executed with shield gas pollution levels of 8, 600and 800 ppmwere characterized by the an almost constantvalue of parameter Sz = 26 lm with uctuations limited to5 lm (Fig. 6e region A) in zone B. For the remaininggases, Sz ranged from 58 to 35 lm with uctuations of515 lm (Fig. 6e region B). On this basis we can con-clude that the quality of surface in the heat-affected zonedepends on the purity of argon, and primarily on the valueof doping with oxygen. It was observed that for a very puregas, and for the gas with the highest levels of O2 a surfacein Zone B was obtained with constant and rather smallvalues of roughness. For gases belonging to the60400 ppm group roughness values decreased withdistance from the source of heat. The phenomenon of

Fig. 4. Inuence of argon pollution on th

Fig. 5. Inuence of argon pollution on tconstant values of Sa, Sq and Sz for argon highly contami-nated with oxygen is related to the change in the ioniza-tion conditions and formation of the electric arc. Theeffect is interesting for technological reasons and it shouldbe subject to further research. The largest heights of eleva-tions and depths of depressions were assessed based onparameters Sp and Sv (Fig. 6c and d respectively). For bothanalyzed parameters it was observed that the lowest val-ues of Sp and Sv were obtained for very pure argon(8 ppm), as well as for the gas with a large dope of oxygen(600 ppm). The position of the subzone for which the mea-surement was performed did not have signicant inuencein this case. For this group of shielding gases, for parameterSp, average values of about 1518 6 lm were obtained.For the remaining group of gases, i.e. 20, 60, 200 and

e weld joint area (400800 ppm).

he weld joint area (80200 ppm).

Fig. 6. Selected amplitude (ae) and hybrid (f and g) surface roughness parameters of weld joint area B17 subzone.


210 G.M. Krolczyk et al. /Measurement 70 (2015) 203213400 ppm, the values of Sp were much higher, within therange 2545 lmwith maximum values in the B1B4 zones.A similar characteristic can be observed for parameter Sv:In the heat-affected zone the maximum values of depres-sions of Sv are lower than Sp by about 40%. Doping argonwith oxygen within the range 60400 ppm still leads toan intensication of surface disturbances, with measuredmaximum depressions in the range 2229 lm.

The Root Mean Square Surface Slope parameter Sdq ispresented in Fig. 6f. This parameter is a general measure-ment of the slopes which comprise the surface. It is oftenused to differentiate surfaces with similar average rough-ness, Sa. It was found that in spite of the considerablevariation in parameter Sa (ranging from 1.4 to 7.7 lm)shown in Fig. 6a, the structure of the examined surfacesis similar. The degree of change of parameter Sdq is smalland it peaks at 0.190.32. Therefore, it is the same orderof magnitude. The degree of purity of the applied shieldinggas did not inuence the change in the surface structure. Aconrmation of this conclusion can be seen in the imagesof surface morphology characterization presented in Fig. 8.

Fig. 7. The maps of kurtosis (Sku) versus skewness (Ssk) for selecteTo differentiate surfaces of similar amplitudes and aver-age roughness we could use an Sdr parameter. It is knownthat Sdr increases with the spatial intricacy of the texture.In Fig. 6g, two groups of surfaces can be distinguished. Therst group includes surfaces formed with shield gas pollu-tion levels of 8, 60 and 200 ppm. In this area Sdr is rela-tively stable at approximately 2.3%. The other areaincludes surfaces for which changes of amplitude and aver-age roughness values are higher. For this case we obtainSdr = 33.5%. These latter surfaces were formed duringwelding with gases with high proportions of oxygen,namely 400, 600 and 800 ppm. The surface protected withgas of 20 ppm is of a different character. With distancefrom the weld area, i.e. from subzone B1, parameter Sdrdecreases from 3.5% to 2.3 for B5. For the more distant sub-zones (B6 and B7), parameter Sdr takes intermediate values,namely 2.7%. When comparing the selected areas with theareas related to parameters Sa, Sq or Sz (Fig. 6a, b and e,respectively), certain relations were observed. For thegroup of parameters Sa, Sq and Sz, whose values basicallydo not change as a function of subzone, the spatial

d subzones B1 (a), B3 (b), B5 (c) and B7 (d) of weld joint area.

G.M. Krolczyk et al. /Measurement 70 (2015) 203213 211intricacy of the texture is stable and low. For the group ofparameters which do appear to be functions of the distancefrom the welds, parameter Sdr takes higher values and isnot as stable.

(a) 800 ppm

(c) 400 ppm

(e) 60 ppm

(g) 8 ppmFig. 8. Surface morphology characterizatThe distribution of values of the coefcient of surfaceasymmetry Ssk and the coefcient of its inclination Sku ispresented in Fig. 7. The values of these parameters arestrongly inuenced by single elevations and depressions

(b) 600 ppm

(d) 200 ppm

(f) 20 ppm

ion depending on argon pollution.

ence is slight.

(8 and 20 ppm pollution) contribute to the forma-tion of surfaces with high values of Ssk and Sku close

212 G.M. Krolczyk et al. /Measurement 70 (2015) 203213The values of the characteristic surface parameters (Sa,Sq, Sp, Sv, Sz) changed signicantly moving away from theweld. Additionally, the values of skewness Ssk are negativefor higher values of argon pollution. This indicates that themajority of the material is localized near the peaks of thesurface.

The physical appearance of the surface morphology wasvisually examined as part of the characterization process.Seven images obtained by using a Focus-Variation areshown in Fig. 8. The samples had a smooth surface, butsome particular features were revealed on the surface.For example, several areas of the surfaces were character-ized by isolated peaks around the weld (Fig. 8f and g), andin the zone most distant from the face of weld (Fig. 8c).These single peaks changed the statistical result of themeasurement of 3D parameters in subzone B1 and B2,which are characterized by the greatest uctuations ofchanges in subzone B7 for the 400 ppm sample.

4. Conclusions

The results obtained show that the method used tomeasure the surface topography of a welded joint hasallowed the functional characteristics of that surface tobe extracted. This has been possible largely thanks to theproper design of the experiment and experimental meth-ods. The quality of the argon shielding gas inuences theform of the product surface. The use of surface parametersenabled the impact of the proportion of oxygen, on thequality of the surface in the zone affected by heat fromthe welding process, to be shown. Based on the experimen-tal observations, the authors formulated the followingconclusions:

I. The application of argon with pollution levels below20 ppm eliminates discolorations on the surface ofwelded stainless steel pipe joints, and thus elimi-nates of a potential habitat for bacteria and a futuresource of corrosion.on the surface. The majority of surfaces, regardless of theanalyzed subzone and the purity of the shielding gas, arecharacterized by small values of parameters Sku and Ssk.For Ssk, the range from 0.5 to 0.5 was obtained, and forSku it is an area from 2 to 4. As can be seen in Fig. 7, surfaceswith negative values of skew and low values of Sku are pro-duced for subzones near the weld area with high values ofshield gas pollution (Fig. 7a and b). Basically, a differentconguration of parameters Sku and Ssk was observed for8 ppm, and particularly for 20 ppm (Fig. 7 region A). Forsubzone B1 Sku takes the value 47.5, and Ssk = 3.25. It ismuch greater than for the remaining cases. This suggeststhat the structure of this surface signicantly differs fromthe others. The known problem of ionizing the arc andstabilizing its location with little O2 in the shield gas wasprobably responsible for this effect. Also higher values ofSsk and Skuwere obtained for 8 ppm, which to some extentproves the role of O2 in the process of shaping this struc-ture. Practically, surfaces with zero or positive skewnesswere generated for last subzone B7, where the heat inu-Acknowledgments

The authors sincerely thank the Thomas G. Mathia andRafa Tomczak for their valuable contributions to the pre-paration of this manuscript.

References

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III. It was found that, on the basis of the analysis ofselected amplitude parameters (Sa, Sq, Sz), that forshield gases with medium levels of pollution withoxygen (60, 200 and 400 ppm), the surface textureparameters decrease their values with distance fromthe face of the weld. For pure gases (8 and 20 ppm)and also highly contaminated gases (oxygen levels600 and 800 ppm), roughness parameters stayed ata constant level equal to the values obtained forthe zone most distant from the face of the weld.

IV. It was observed that in spite of considerable differ-ences in the obtained values of Sa or Sz parameters,the surface texture assessed based on parameter Sdqis similar, and the level of purity of the appliedshielding gas did not inuence the surfacemorphology.

V. The composition of the shielding gas signicantlyinuences the values of the coefcients of surfaceasymmetry Ssk and its inclination Sku. Purer gases

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[14] N.L. Parthasarathi, U. Borah, S.K. Albert, Effect of temperature onsliding wear of AISI 316 L(N) stainless steel analysis of measuredwear and surface roughness of wear tracks, Mater. Des. 51 (2013)676682.

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Influence of argon pollution on the weld surface morphology1 Introduction2 Material and methods2.1 Welded material and welding method2.2 Surface morphology analysis

3 Results and discussions3.1 Variation in surface morphology3.2 Variation in surface texture

4 ConclusionsAcknowledgmentsReferences

Influence of Argon Pollution on the Weld Surface Morphology

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