THE EFFECT OF SHIELDING GASES ON MECHANICAL PROPERTIES AND .
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013ISSN 2278 – 0149 www.ijmerr.comVol. 2, No. 4, October 2013 2013 IJMERR. All Rights ReservedResearch PaperTHE EFFECT OF SHIELDING GASES ONMECHANICAL PROPERTIES ANDMICROSTRUCTURE OF AUSTENITIC STAINLESSSTEEL WELDMENTSN R Anand1, Vijaysingh M Chavan1* and Nitin K Sawant1*Corresponding Author: Vijaysingh M Chavan, vijaysingh chavan@yahoo.co.inIn this study AISI 304 L type of austenitic stainless steels were welded using 308 L consumableelectrodes by the process of Gas Metal Arc Welding (GMAW). The aim of current study is toexamine effects of shielding gas compositions on mechanical properties and microstructure ofAISI 304 L weldments. A detailed study of gas metal arc welding of AISI 304 L stainless steel wascarried out with different shielding gas compositions such as 100% argon, 80% argon 20%CO2, 50% Argon 50% argon and 100% CO2. The mechanical properties were determined byperforming different tests, viz. Charpy V notch impact test, tensile test, hardness test, bendtest. Surface morphology had been analyzed by Scanning Electron Microscope (SEM). Theresults indicated that the shielding gas compositions have great influence on mechanicalproperties. Results revealed that increase in amount of CO2 in shielding gas resulted in highertensile strength and hardness values than the base metal. The study also indicated that shieldinggas composition also have an influence on toughness values which further depends upon -ferrite content in the weld metal. This -ferrite content decreases with increase in CO 2percentage of shielding gases. Decrease in -ferrite content has negative effects on toughnessvalues of weldments. The gas metal arc welding is found to be suitable for welding of AISI 304 Laustenitic stainless steels owing to their high welding speed and excellent mechanical properties.Keywords: Shielding gases, Austenitic stainless steel 304 L, GMAW, Mechanical propertiesINTRODUCTIONpressure vessels to structural purposes. Theinfluences that these materials have on theindustry are mainly due to their mechanicalstrength as well as their excellent corrosionThroughout several years, Austenitic StainlessSteels (ASS) have been employed in industrialapplications that range from pipes and1Department of Mechanical Engineering, College of Engineering, Pune, India.253
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013resistance, which can also be attributed to theaustenitic phase that appear in the matrix ofthe material when alloying elements like nickel,manganese, and nitrogen are combined athigh quantities. Similarly, several methods ofjoining, like welding, have been broadlyperformed for these metals because of the lowprice and high quality of this process.Additionally, for the industrial applications ofthe AISI/SAE 304 stainless steels, the weldingmethod is widely used due to its simpleassembly and which joins sheets, plates andpipes made up of this material. On the otherhand, it is also imperative to highlight thatduring welding many discontinuities areproduced, which acts as stress raisers that canlead to a decrease in the life of the weld.Therefore, the problems of this joining methodhave become an important issue of study inmanufacturing. The austenitic stainless steels(Fe-Cr-Ni) have excellent mechanicalproperties and corrosion resistance. Due tohaving combine properties, their usage invarious applications such as storage tanks,pipe, and pressures vessel valves, pumps,distiller etc have been increasing. Betterstrength, toughness and formability arerequired for this kind of applications mentionedabove (Kou, 2003). 300 series austeniticstainless steels are most popular steels andtheir most important and conspicuousproperties are their excellent toughness andcorrosion resistance (Liao and Chen, 1998;Budinski and Budinski, 1999; Kou, 2003; andShigley, 2004). Due to fcc structure ofaustenitic stainless steels, they have highertoughness values which is almost independentof temperature, thus brittle failure does notoccur like low carbon steels which have bccstructure. Austenitic stainless steels maintaintheir higher notch toughness even at cryogenictemperature. The mechanical properties ofaustenitic stainless steels provide an excellentcombination of better strength, ductility andtoughness over a broad temperature range(Liao and Chen, 1998; and Liao and ve Chen,1999). The selection of the shielding gas iscrucial for obtaining optimal properties of theweldments. Therefore, number investigationshave been performed to study the effect ofshielding gas composition on mechanicalproperties of austenitic stainless steelweldments. Determination of mechanicalproperties such as hardness, impacttoughness and tensile strength, etc., of thecomponent made from austenitic stainlesssteel weldments is crucial for its safe use.Those constructions can be exposed dynamicload during working in various applications,therefore, impact toughness behavior becomemore important under different workingcondition such as temperature andenvironment.The present study investigates the influenceof shielding gas composition on the notchimpact toughness of AISI 304 L austeniticstainless steels. Four different gascompositions were used for the purpose ofshielding. Optical and scanning electronmicroscopy studies and hardnessmeasurement were also carried out so as toanalyze effect of shielding gases.EXPERIMENTAL PROCEDUREAISI 304 L grade austenitic stainless steelplates of dimensions (125 mm x 250 mm x8 mm) were used in this study. Austeniticstainless steel grade 308 L wire with diameterof 1.2 mm was used as consumable electrode.254
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013The chemical compositions of base materialand filler material are given in Table 1.gas flow rate of 15 liters/min. Interpasstemperature was kept below 150 C due tolower thermal conductivity of austeniticstainless steels.Table 1: Chemical Composition of Baseand Filler Material UsedElementsBase Material304L Wt (%)The welding parameters used wereselected according to suggestions ofp ro d u ct ca t a lo gu e a n d e xp e rie n ce sobtained earlier. The welding parametersare shown in Table 2.Consumable308 L Wt 020P0.02500.021Cr18.130019.700Ni8.44009.300Cr Eq.20.140021.830Ni Eq.12.590014.140Table 2: Welding ParametersFigure 1: Edge Preparation for Weld JointS. No.ParameterValue1.Welding Current (I)2002.Voltage (V)283.Speed (mm/min)1204.Heat Input (KJ/m)2.85.Gas Flow (Lit/min)15As seen from the table, welding current iskept 200 Ampere and voltage is 28 volt.Constant welding speed of 120 mm/min wasmaintained. This welding system provides theconstant heat input of 2.8 KJ/m during weldingprocesses.The welded joints were sliced (as shown inFigure 2) using abrasive cutting and thenmachined to the required dimensions forpreparing tensile, impact test, bend andmetallographic specimens.The austenitic stainless steel 304 L plateswere prepared for welding by GMAW with thedimensions 250 mm (l) x 150 mm (w) x 8 mm(t). Butt joint configuration was used. Beforethis V shaped edges were prepared with 600included angles between two edges. Threedifferent passes of GMAW were performed.Welding process was carried out usingdifferent shielding gas compositions such as100% argon, 80% argon 20% CO2, 50%argon 50% CO2 and 100% CO2 with constantFigure 2: Extraction of Test Samples255
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013GMAW process has higher values than thatof FCAW process. The ferrite numbers in theweld metal were measured. The effect ofCO2 content in the shielding gas on ferritecontent is pronounced. The ferrite content inthe weld metal is decreased by increasingthe amount of CO 2 in the shielding gas.Carbon is austenite stabilizing element andwidens austenitic area in the weld metal(Kou, 2003). The increase of CO 2 content inthe shielding gas resulted in increasingamount of carbon in the deposited metal.Thus the ferrite number decreases, whichprovides larger austenitic area in the weldmetal due to increasing of Ni equivalentvalue. Higher percentage of CO 2 resulted inhigher oxygen potential therefore,consumption of Cr and Si increase due tooxidation, which causes lowering of Crequivalent value and narrowing ferrite areain the weld metal. The results obtained in thisstudy are consistent with earlier literature(Liao and Chen, 1998; and Liao and veChen, 1999). The amount of delta-ferrite wasestimated using Cr and Ni equivalent of theweld metal. Delta-ferrite is solidified firstlywhich decreases crack susceptibility duringcooling. The percentage of ä-ferrite in theweld metal was determined with the help ofWRC-1952 constitution diagram as functionof Cr and Ni equivalent value. The otherelements are also effective during cooling.According to earlier studies, about 3-4%volume ferrite prevents the weld metal fromsolidification cracking. Ferrite number of 4 ispreferable for preventing hot cracking duringthe cooling of the weld metal. Sometimes,cracks may be seen in deep and narrow ofweld metal during usage of the weldingmethods having higher heat input.Microhardness measurements were carriedout across the weld metal and base metal forwhich 1 Kg load was applied duringmeasurements. Microstructure examinationwas carried out on cross section of theweldments. The specimens were mountedlater flatted and then grounded using SiCabrasive paper with grit ranges from 180 to1200. Then the samples were lightly polishedusing lapping machine. Samples were thenwashed, cleaned by alcohol and then dried,followed by electrolytic etching in 10% oxalicacid at 9 V for 30 s. Metallographicexamination of samples were performed usingscanning electron microscopy. Chemicalcomposition of weld metal was determined byusing Spectrometry. Ferrite numbers of theweld metal were measured theoretically andalso by using ferrite-scope equipment.RESULTS AND DISCUSSIONThere were no any observations of spattersgenerated under all gas composition exceptlittle spatters generation using of 100% CO 2shielding. This indicates that a stable arc isobtained under all the gas composition. Betterweld bead appearance was obtained afterGMAW process which points out that GMAWprocess provides better appearance andweld quality. As mentioned in earlierinvestigation by Liao and Chen (1998) andLiao and ve Chen (1999) the spatter ratesincrease with increasing CO 2 content in theshielding gas composition. Higher CO 2content causes larger and numbers of spatterparticles. This spatter rate is increased byoxygen potential of shielding gas. Of course,an increase of CO2 content in the shieldinggas naturally results in increasing oxygenpotential of the gas. Welding current during256
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013Weld Chemistry and FerriteContentpercentage in the gas increases consumptionof Cr, Si and Mn.Weld metal composition and ferrite contentwas determined for each sample. Themeasured chemical composition of the weldmetal is listed in Table 3. It is observed thatthere is great influence of shielding gases onweld metal composition which further becomesresponsible for ferrite content in weld metal.As seen from the table, carbon and nickelcontent in the weld metal increase withincrease in the CO2 content of the shieldinggas. The weld chemistry plays important rolein phase balance which further defines themechanical properties.The amount of -ferrite in the weld metal iscalculated using the composition of basemetal, filler metal as function of Cr equivalentand Ni equivalent for which W RC-92constitution diagram was used. The calculationof -ferrite ratio gives the values from 6% to11% however, those are estimated values.Ferrite contents by using ferrite-scopeapparatus was from 6 to 12. All the estimatedand measured values of ferrite content arelisted in Table 4.Table 4: Average Ferrite ContentTable 3: Chemical Composition and Crand Ni EquivalentsS.No.Weld Samples withShielding GasWeight Percentage (Argon 060.0070.007 319.02818.89118.79311.309811.274011.5320Cr Eq.Ni rriteContent(byFerriteScope)1.100% Argon11122.80% Argon 20% CO2893.50% Argon 50% CO2784.100% CO266Microhardness Test ResultsThe microhardness (VHN) test was performedon the etched transverse cross-section of theweld zone using a load of 1 Kg, which wasapplied for duration of 15 sec. The mean valueof three different measurements was taken asexact value for the hardness. It has been foundthat, weld metal shows highest hardness. HAZshows intermediate hardness whereas basemetal is having lowest hardness. Hardnessvalues of all 304 L weldments taken in thecentre of weld metal are higher than that ofthose taken in HAZ and base metal. It wasfound that the higher values were especiallyobtained nearer to surface, i.e., away from weldcenterline. According to the previous studies,It is well known that nickel and carbon arestrong austenite stabilizing elements.Therefore, the CO2 increase in shielding gasresulted in decrease of Cr equivalent on theother hand, increasing of Ni equivalent. Inaddition to that, an increase of CO 2257
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013Table 5 (Cont.)the weld metal produced in multipass weldingprocess was shown work hardened state withdislocation density exceeding as comparedwith the dislocation density of in fully annealedaustenitic stainless steels. The increase indislocation density is because of repeatedthermal cycles experienced by the solidifiedmetal during multipass welding (Shamsul andHisyam, 2007).Distancefrom WeldCenter (mm)Microhardness 229.0226.8228.2226.4C1 100% Argon shieldingTensile Test ResultsC2 80% Argon 20% CO2 shieldingTensile test results mainly showed that thefracture occurs away from the joint in eachsample plate. Among the four shielded weldmetals, tensile strength of weld metal ishigher than the base material. In particular,for 100% CO 2 gas shielded weld test platethe value of tensile strength is highest, i.e.,594 MPa. The tensile strength of a test platewelded with shielding gas mixture of 80%Ar and 20% CO2 is found to be intermediateand the magnitude of ultimate tensilestrength was found to be 580 MPa. Thetensile strength of weld sample with 50%argon and 50% CO 2 was found to be 588MPa. Finally the value of ultimate tensilestrength for weld with 100% argon asshielding gas was found to be 575 MPa.C3 50% Argon 50% CO2 shieldingC4 100% CO2 shieldingTable 5: Microhardness Values AcrossWeld JointDistancefrom WeldCenter .9262.7258.2–1273.2266.4264.2257.9Microhardness VHNTable 6: Tensile test TensileStrength(MPa)FractureLocation1.100 % Argon254575Base Metal2.80% Argon 20% CO2282580Base Metal50% Argon 50% CO2294588Base 8.2267.9257.83252.8246.8245.9243.84.100% CO2310594Base Metal3.5253.2247.2244.7243.45.Base Metal234585Base Metal3.258
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013Impact Test Resultsspray test was carried out using 5% NaClsolution with pH about 6.8. The results of saltspray corrosion test were found satisfactory.After each interval of 24 hours, samples wereinspected for four successive days. After 24,48, 72, 96 hours any white or red colored rustis not observed, thus this test also concludedsatisfactory results for all four samples of 304L stainless steel welds.The impact energies of the weldments byGMAW were given in Table 4, which show thatimpact energy decreases with decreasing -ferrite containing in the weld metal. It isknown that the austenite has FCC structureand delta ferrite a Body Centered Cubic(BCC) structure. FCC metal has a high notchtoughness which is almost independent oftemperature, thus brittle fracture does notoccur. On the other hand, the notch toughnessof BCC metal is strongly dependent ontemperature; therefore, brittle fracture issevere at low temperature, while at highertemperature it shows ductile rupture. It is alsoobvious that notch toughness of all weld metalis affected by delta ferrite and oxygenpotential and higher oxygen potential resultsin a degradation of notch toughness.Metallographic ResultsScanning electrode microscopy studies wereshown in Figures 3-6. These micrographswere taken from the weld metals. Themicrostructure of weld metal and ä-ferrite ratiocan be assessed using one of the Schaeffler,De-Long and WRC diagrams. The latest WRCconstitution diagram is used for present studywith consideration of chemical composition ofbase metal and filler materials after welding.Owing to non-equilibrium rapid solidificationcondition in welding process, peaktemperature in fusion zone is much higher thanthe upper limit of phase balance between Fe and -Fe phase. The austenite starts toprecipitate at the grain boundaries of ferriteduring the cooling. Since the - transformationis diffusion controlled process, because offaster cooling in welding process there is lackof sufficient time for completion oftransformation. As a result a large portion ofprimary -Fe is retained in joints. Typicalmicrostructures of fusion zone and weld metalare shown in figures. Almost all jointscomposed of dark -ferrite dendritic structurein matrix of austenite. However, different grainsizes can be observed in all the joints.Obviously, maximum ferrite number of 11 wasobserved by using constitution diagrams forthe weld sample welded with 100% argonTable 7: Impact Strength of WeldmentsS.No.Shielding GasImpact Strength inWeld Metal (Joules)1.100% Argon722.80% Ar 20% CO2623.50% Ar 50% CO2584.100% CO255Bend Test ResultsBend tests (root bend test and face bend test)were carried out on sample piece of each testplate. It is found that sample has not braked atthe weld line even there were no signs ofcracking at the weld interface. The strip hasshown even radius without any sharp anglechange. Thus, both bend tests showedsatisfactory results.Salt Spray test ResultsThe salt spray corrosion test was carried outusing standard test method IS 9000/1983. Salt259
Int. J. Mech. Eng. & Rob. Res. 2013Vijaysingh M Chavan et al., 2013Figure 6: SEM of Weld Metal Shieldedwith 100% CO2Figure 3: 100% Argon Shielding WeldFigure 4: SEM of Weld Metal Shieldedwith 80% Ar 20% CO2shielding. This highest ferrite content wasconfirmed by using ferrite-scopemeasurement technique. Ferrite-scopeindicated ferrite number 12 for this weld joint.For weld samples welded using 80% argonand 50% argon, ferrite number was 8 and 7respectively by using constitution diagram.Ferrite-scope indicated ferrite number of 9and 8 respectively for these samples. Thesevalues of ferrite number were foundintermediate between those values of argonshielded and CO 2 shielded samples.Minimum ferrite number was observed forweld sample welded using 100% CO 2shielding using constitution diagram whichwas around 6. This lowest value of ferritenumber was confirmed by using ferrite-scope.Ferrite-scope indicated ferrite number of 6for the sample welded with 100% CO 2shielding. These micrographs were takenfrom both fusion zone and the weld metals. Itis clearly seen that -ferrite contentdecreases with the increasi
Consumable 308 L Wt (%) The austenitic stainless steel 304 L plates were prepared for welding by GMAW with the dimensions 250 mm (l) x 150 mm (w) x 8 mm (t). Butt joint configuration was used. Before this V shaped edges were prepared with 600 included angles between two edges. Three different passes of GMAW were performed. Welding process was .
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Make sure that the blank shielding wire (5) is not removed. Twist this blank wire with the shielding (4) as shown below. Figure 2.3 - Blank shielding wire and shielding braid Blank shielding wire Outer sheath (jacket) (1) Filling threads (2) Power elements (3) Copper wire shielding (4) Blank shielding wire (5) Shielding foil (6) Isolation .
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developing, welding parameters change and new shielding gases are introduced. The purpose of this handbook is to give a useful overall picture of the shielding gases available for gas arc welding. The handbook describes the significance of shielding gases on the welding process and their
RADIATION SHIELDING DESIGN 2010 2010 Shielding Construction Solutions 1 ACMP 2010 SAN ANTONIO, TEXAS – MAY 23, 2010 DANIEL G. HARRELL SHIELDING CONSTRUCTION SOLUTIONS, INC. . Graphic Image. DESIGN Shielding Material Data Shielding Design Sketch Specific Points Use & Occupancy Distance Obliquity Effective Thickness Unusual Conditions
