DEVELOPMENT OF A WELDING PROCEDURE FOR MIL A 46100
DEVELOPMENT OF A WELDING PROCEDURE FOR MIL A 46100ARMOR STEEL JOINTS USING GAS METAL ARC WELDINGDESARROLLO DE UN PROCEDIMIENTO DE SOLDADURA PARAJUNTAS DE ACERO DE BLINDAJE MIL A 46100 CON PROCESO GMAWDAVID MAZUERA ROBLEDOGrupo de soldadura, Universidad Nacional de Colombia – Sede Medellín, jdmazuer@unal.edu.coJOHN ALBERTO SUÁREZ GÓMEZGrupo de soldadura, Universidad Nacional de Colombia – Sede Medellín, johnsuar@gmail.comJORGE ENRIQUE GIRALDO BARRADAProfesor Asistente, Grupo de Soldadura, Universidad Nacional de Colombia – Sede Medellín, jegirald@unal.edu.coReceived for review May 14th, 2010; accepted December 2nd, 2010; final version December 27th, 2010ABSTRACT: A welding procedure (WPS) for MIL A46100 steel armor joints using the gas metal arc welding process (GMAW)was developed and qualified according to mechanical and non-destructive (NDT) requirements of military codes. Obtained resultswere compared to shielded metal arc welding (SMAW) procedures used to weld this type of steel. It was found that designedWPS is a suitable option to weld MIL A46100 armors according to the results obtained. In addition, a narrower heat affectedzone (HAZ) was obtained with designed WPS which should lead to a better in-service armor performance according to resultsof previous studies. Finally, an increase in Charpy v-notch (CVN) test impact energy compared to the SMAW procedure was found.KEYWORDS: Gas metal arc welding (GMAW), welding procedure specification (WPS), MIL A 46100 armor steelRESUMEN: Se desarrolló un procedimiento de soldadura (WPS) para unir láminas de acero para blindaje bajo especificación MIL A46100usando el proceso GMAW, el cual fue calificado mediante ensayos mecánicos y no destructivos (NDT) de acuerdo con los requerimientosde códigos militares. Los resultados obtenidos fueron comparados con procedimientos de soldadura para este material realizados con elproceso SMAW. Los resultados obtenidos mostraron que el WPS diseñado es una opción viable para la soldadura de blindajes de aceroMIL A 46100. Además, con el WPS diseñado se obtuvo una reducción en el ancho de la zona afectada térmicamente (ZAT) que deberíaconducir a un mejor desempeño en servicio de los blindajes de acuerdo con los resultados de estudios previos. Finalmente, se encontró unincremento en la energía absorbida en los ensayos de impacto Charpy V comparada con la de soldaduras realizadas con el proceso SMAW.PALABRAS CLAVE: Acero para blindaje MIL A 46100, especificación del procedimiento de soldadura (WPS), soldadura por arco conprotección gaseosa (GMAW)1. INTRODUCTIONHigh strength steel plates have been used since the90s to build armored combat vehicles and vessels dueto a good ballistic behavior accompanied by weightreduction in the armored structure as a consequence ofthe plate’s high mechanical strength. The MIL-A-46100specification is used to produce one of those highstrength steels which obtains its ballistic behavior fromits chemical composition accompanied by heat treatment(oil quench from 900ºC and air tempering at 200 ºC)which produces a tempered martensite microstructure.Due to a high hydrogen induced cracking (HIC)susceptibility, austenitic stainless steel and ferritic fillermetals are commonly used to weld MIL-A-46100 plates[1-2]. In a previous study by National University ofColombia [3], MIL-A-46100 steel was characterized.Various welding procedures using shielded metal arcwelding (SMAW) were assessed by [3] in order todetermine the most suitable and cost effective. It wasfound that a procedure using the E11018-M electrodemet the requirements for ballistic welds with highercost effectiveness. However, taking into account theHIC susceptibility, which demands a controlled usageof this kind of electrode as well as skilled personnel,another procedure using E312-16 filler was also foundas a suitable option to weld MIL-A-46100 steel armorswith the corresponding tradeoff in cost effectiveness.Dyna, año 78, Nro. 168, pp. 65-71. Medellín, Agosto, 2011. ISSN 0012-7353
66Mazuera Robledo et alOn the other hand, ref [3] found no weldments exhibitingsatisfactory ballistic behavior (e.g., projectiles impactingon weld beads and heat affected zone passed through theweldment), except in one case in which the bullet wasrejected by a weldement with a narrower heat affectedzone (HAZ); this ballistic response agreed with thefindings of [4-5]. Based on the latter observation, it isdesirable to design welding procedures (WPSs) thatreduce the HAZ width. In addition, the use of the SMAWprocess implies that a considerable amount of time willbe dedicated to tasks such as electrode change, interpasscleaning, and slag removal, which reduce the productionrates. Thus it is also desirable to look for WPSs which usesemiautomatic welding processes that allow a potentialincrease in productivity and production rates.In the current article, a welding procedure to weldMIL A-46100 steel plates was designed and qualifiedaccording to mechanical and non-destructive testingrequirements for military standards (ballistic tests werenot carried out due to limitations in access to the testingsetup) in order to evaluate its feasibility in comparisonwith the aforementioned SMAW procedures.2. REQUIREMENTS FOR WELDMENTS OFARMOR STEELSQuality requirements for the welding of MIL-A-46100steel are given by MIL STD 1185 [1] and SD-X12140[2] standards. For the sake of comparison, theauthors also selected some requirements used by [3]to complement criteria not specified in the militarystandards. Weldment requirements can be grouped intothree categories: (i) mechanical properties, (ii) weldsoundness, and (iii) in-service performance.2.1 Mechanical PropertiesMilitary standards cited in the former paragraph,established a minimum yield strength of 550MPa(80ksi) for the welded metal when ferritic filler isused, and a minimum tensile strength of 550 MPa(80ksi) in welds performed using austenitic fillermetals. In addition, the recovery of the parent metalhardness must be achieved at a distance of 15.9mm(5/8”) measured from the weld bead centerline. Forthe sake of comparison with results of [3], the authorsestablished energy absorbed in Charpy V notch (CVN)impact test as an additional acceptance criterion.Satisfactory weldments should exhibit the same CVNvalues obtained by [3].2.2 Weld SoundnessTo evaluate the quality of weldments, visual testing (VT)and radiographic testing (RT) were conducted. Acceptancecriteria from military standards [1-2] are listed below: Undercut: not allowed Slag inclusions: not allowed Tungsten inclusions: not allowed Cracks: not allowed Underfill: not allowed Misalignment: lower than 3mm (1/8”) Overlap: not allowed if greater than 10% of weldedlength. Porosity: maximum diameter 1.5 mm (1/16”) andmaximum 6 pores per 304mm (12”) of weldedlength. For cluster porosity (lower than 1/32”)maximum 8 pores per 25mm (1”) of welded lengthAdditional acceptance criteria not listed above for RTand VT were based on qualification requirements of AWSD1.1 [6] and ASME Section IX [7] according to [3].2.3 In-Service PerformanceTo evaluate in-service performance of welded armors,ballistic tests must be conducted according with theNIJ 0108.01 standard and the aforementioned militarystandards [1-2]. However, due to limitations in access to aballistic testing setup, a comparison with results obtainedby [3-5] was carried out based the HAZ width of sampleswhich showed satisfactory ballistic performance.3. MATERIALS AND EQUIPMENT3.1 EquipmentSample welds were conducted using a Kemppi Mark500HF machine and applied in mechanized mode [8]using a mechanical oxy-fuel cutting device adapted tocarry on the welding torch (Figure 1) in order to reduceproblems associated with a human welder.
Dyna 168, 201167developed through a quenching and temperingheat treatment. A scanning electron micrograph ofMIL-A-46100 steel is depicted in Figure 2.3.3 Filler MetalFigure 1. Device used for mechanized weldingA commercial voltmeter (0-50 V 0.01V) and a DCclamp meter (600 A 0.1A) were used to recordwelding current and voltage, respectively.GMAW filler metals to weld armor steel include AWSA5.5 ER308Mo and ER312; AWS A5.29 ER100S-1,ER100S-2, ER100S-2, and ER120S-1 [1-2]. Based onthe results obtained in a previous study by [3] usingE11018M, a ferritic filler exhibiting similar chemicaland mechanical properties was selected. The finalselection relied on ER100S-1 (ESAB spoolarc 95)wire based on commercial availability and the fact thatESAB trademarked filler is the only one that meets therequirements of the MIL-E-23765/2 standard [9].Mechanical and non-destructive test (excepting VT)were conducted by the metallurgy laboratory staff atNational University of Colombia.3.2 Base MetalMIL A-46100 specification covers different typesof armor steels meeting mechanical properties andchemical compositions that vary according to platethickness. The armors used in this work correspondto plates 4.5 mm thick. Mechanical properties andchemical compositions obtained experimentally aresummarized in Tables 1 and 2, respectively [3].Table 1. Mechanical properties of MIL-A-46100 steel plates [3].Property [Units]Tensile Strength [MPa]Elongation [%]Charpy V-Notch @ -20 ºC [J]Hardness [Hv]Value16902528525Table 2. Chemical composition of MIL-A-46100 steelplates (Measured by [3] using GDS).ElementCVAlSnCuCrSiMnWt. TiPSPbNiMoFeWt. %0.0010.0310.0100.0020.0050.1920.243BalanceAs mentioned in the introduction, MIL A-46100 steelplates posses a tempered martensite microstructureFigure 2. Martensitic microstructure of MIL-A46100 steel, SEMmicrograph 3700X nital 5% [3]3.4 Shielding GasIn order to design and qualify a WPS to weldMIL-A-46100 steel plates in all positions, it is necessaryto use short circuit metal transfer (GMAW-S); thusa mixture of 75% Ar -25% CO2 was selected. Itspotential impact on cost effectiveness was also takeninto account.3.5 BackingCopper backing was selected to make a single passwelding procedure, which leads to a reduction of theHAZ width as consequence of both the lower heatinput (due to the use of only one pass), and the copper
68Mazuera Robledo et albacking itself (acting as chiller). The cross section ofbacking plates used is shown in Figure 3.4. EXPERIMENTAL PROCEDURETest plates of 152mm (6”) x 304mm (12”) have beenused for procedure qualification according to militarystandards [1-2]. These plates were thermally cutusing compressed air plasma to reduce microstructuralchanges of base materials as a consequence of thethermal cutting process. Weldments were carried outin mechanized mode using the device shown in Figure1 and the welding procedure parameters summarizedin Table 3.Reduced section and CVN specimens were cutaccording to the requirements and dimensions specifiedby [3]; taking into account that due to plate thickness,standard CVN specimens could not be prepared. FiveCVN specimens were prepared using the sampledimensions shown in Figure 4.Figure 4. Dimensions of CVN specimensAll specimens were prepared using a CNC EDM wirecut machine. CVN specimens were polished to obtaina surface roughness of 64µm.Figure 3. Cross section of copper backing platesTable 3. Welding procedure parameters.JOINT DESIGNRoot openingJoint geometry3mmsquareBASE METALSMaterial spec.ThicknessMIL A 461004.5mmFILLER METALAWS specificationAWS classificationA5.28ER100-S1SHIELDING GASCompositionFlow rateAr75%CO2 25%14 L/minELECTRICAL ansfer modeshort circuitTECHNIQUEStringer beadSingle passContact tube todistanceIn order to determine the hardness recovery distance,Vickers microhardness (500gf, 30s) measurementswhere conducted at 1mm deep from the top face ofwelded plates. The indentations were recorded at200µm pitch starting at the fusion boundary as shownschematically in Figure 5.Figure 5. Schematic showing microhardness testslocations5. RESULTS AND DISCUSSION5.1 Visual Testingwork18mmMISCELANEOUS PARAMETERSGroove positionflatTravel speed5mm/sVisual inspection of weldments produced with thedesigned procedure was satisfactory; results arepresented in Table 4.
69Dyna 168, 2011Table 4. Visual testing results.ParameterResultFace reinforcement1.5mm (1/16”)Root reinforcement1.5mm (1/16”)UndercutNot observedSurface porosityNot observedSurface cracksNot observedOverlapNot observedMisalignmentNot observed5.2 Radiographic TestingRadiographic testing revealed two pores of less than 2mm in diameter which is in the range for acceptancecriteria [1-2]. An example of radiographic film is shownin Figure 6, exhibiting weld soundness.5.3 Tensile TestsComparison between WPS using SMAW and GMAWprocesses is shown in Table 5. In this table, theoreticalvalues of tensile strength for all filler metal used havebeen included [10-12].From the data in Table 5 it was found that in all casesthe requirements for qualification are fulfilled. Anincrease in tensile strength (UTS) of welded metalwith respect to the filler metal was also found—thiscould be a consequence of an increase in carboncontent of welded metal due to dilution. It must beemphasized that in all cases failure occurred throughwelded beads.Table 5. Tensile tests results.FillerWelded metalUTS [MPa]Filler .4 Charpy V Notch Impact TestsTable 6 shows the CVN results of tests conducted at-20 ºC presented in units of Joules per millimeter ofsample thickness, taking into account that non-standardspecimens were used. In addition, CVN results at -40ºC obtained by [3] for SMAW procedures are alsopresented on Table 6. In order to compare results forER100S-1 and E11018M (which was selected as thebetter choice by [3]), experimental results are plottedon Figure 7 along with the CVN data provided by fillermetal manufacturers for all welded metal. It can beseen from Figure 7 that impact energy is always greaterfor ER100S-1welded metal in the range between -50ºC and -20 ºC, which corresponds with experimentalresults for MIL A46100 weldments.Table 6. CVN results.FillerEnergy [J/mm]ER100S-11.57 (@ -20 ºC)E11018M0.70 (@ -40 ºC)E312-160.29 (@ -40 ºC)Figure 7. Comparison between E11018M and ER100-S1CVN results including all weld metal data provided by thefiller metal manufacturers5.5. Microhardness TestsFigure 6. Radiographic example showing weld soundnessMicrohardness profiles for weldments produced usingER100S-1, E11018M, and E3121-16 are shown inFigure 8. It can be seen that the hardness recovery
70Mazuera Robledo et alfor GMAW weldments occurred three millimeterscloser to the fusion boundary when compared to thoseproduced using SMAW. The narrower HAZ suggests abetter in-service performance of ER100S-1 weldmentsaccording to the ballistic results obtained by [3-5].5.6 Microstructural AnalysisFinally, a welded metal microstructure is shown inFigure 10. The morphology of this region is referredto as acicular ferrite [13-15] and is developed dueto the manganese content exceeding 1.2 wt% in thewelded metal as well as small amounts of aluminumand titanium. This microstructure is responsible for thehigher toughness observed in CVN tests of ER100S-1weldments [16-17].Figure 9 shows a macrograph of the welded jointin which the HAZ can be observed easily. Hardnessvariation shown in Figure 8 is the consequence ofmixed microstructures along the HAZ due to thetemperatures reached at each point which inducedlocalized heat treatments (different from point to point).The highest hardness found near the fusion boundarycorresponds to two microstructures: (i) coarsemartensite grains formed due to the high temperaturereached exceeding AC3 which caused grain growth,and (ii) a martensitic microstructure developed in aregion reaching a temperature just above AC3 in whichgrain growth was avoided. A stepped hardness dropis observed at around 2 mm from the fusion boundary.In this region, peak temperatures were between AC1and AC3 and thus former tempered martensite on basemetal was dissolved and transformed into a mixture offerrite and martensite during cooling. From that point,hardness is progressively recovered in a region havingdifferent microstructures depending on the temperatureachieved, causing an over-tempering of base material.Using copper backing in the GMAW weldments,a narrower low hardness zone (approximately 4-5mm than that found in SMAW weldments) wasobtained, which is beneficial for ballistic performanceof the HAZ, and thus reduces the vulnerability of theweldments.Figure 9. Optical macrograph showing weld cross section,nital etchFigure 10. Welded metal microstructure showing acicularferrite, optical micrograph nital etch6. CONCLUDING REMARKSFigure 8. Microhardness profilesThe designed welding procedure using GMAW withER100S-1 filler metal and copper backing was foundto be a suitable option for welding MIL A 46100 armorsteel plates, based on results obtained in mechanicaland non-destructive tests. It met the qualification
Dyna 168, 2011requirements of military codes. However, two aspectsmust be commented on: First, the use of single passwelds using copper backing reduced the width of theHAZ which should improve in-service behavior of thewelded joint according to results published in previousstudies; and second, the higher values of absorbedenergy found in Charpy V notch tests (which are dueto the development of an acicular ferrite microstructureof the welded metal) would lead one to expect, from aqualitative point of view, satisfactory ballistic behaviorof the welded metal; nevertheless, ballistic and crackingsusceptibility tests must be conducted to determinewhether this hypothesis is true or not.Additional advantages such as a lower number ofdiscontinuities and a potential increase in productionrates can also be expected when a semi automaticprocess such as GMAW is used as evidenced in thiswork; however, a complete discussion about this topicis presented elsewhere.REFERENCES[1] DEPARTMENT OF DEFENSE, MIL STD 1185. MilitaryStandard. Welding, high hardness armor, DoD, 1979.[2] DEPARTMENT OF DEFENSE. SD-X12140D. Welding,homogeneous armor, metal-arc general requirements for,DoD, 1987.[3]UNIVERSIDAD NACIONAL DE COLOMBIASEDE MEDELLÍN. Estudio de la soldabilidad de acerosmicroaleados utilizados en la construcción y reparación deembarcaciones, Grupo de Soldadura, 2005.[4] REDDY, G. M., MOHANDAS, T. Ballistic performanceof high-strength low-alloy steels weldments. Journal ofmaterials processing technology, 57, 23-30, 1994.[5] REDDY, G. M., MOHANDAS, T., PAPUKUTTY, K.K. Effect of welding process on the ballistic performance ofhigh-strength low-alloy steel weldments. Journal of materialsprocessing technology, 74, 27-35, 199871[6] AMERICAN WELDING SOCIETY, D1.1 Structuralwelding code- Steel, 119-179, AWS, 2002.[7] AMERICAN SOCIETY FOR MECHANICALENGINEERS, ASME boiler and pressure vessel code.Section IX welding and brazing qualifications, 12-47,ASME, 1998.[8] CARY, H, Arc welding automation, Marcel Dekker, 9-23,1995.[9] DEPARTMENT OF DEFENSE, MIL-E- 23765/2.Military Standard. Electrodes and rods-welding, solid, lowalloy steel, DoD, 1979.[10]AMERICAN WELDING SOCIETY, A5.9 Specificationsfor corrosion-resisting chromium and chromium-nickel steelbare and composite metal cored and standard arc weldingelectrodes and welding rods, AWS, 1977.[11] AMERICAN WELDING SOCIETY, A5.28 Specificationfor low alloy steel filler metals, AWS, 1979.[12] AMERICAN WELDING SOCIETY, A5.5 Specificationfor Low Alloy Steel Covered Arc Welding Electrodes, AWS,1996.[13] LINNERT, G, Welding metallurgy carbon and alloysteel, 787-802, AWS, 1994.[14] GRONG, Φ, METALLURGICAL MODELING OFWELDING, 406-444, University of Trondheim, 1994.[15] KOU, S, Welding Metallurgy, Second Ed, Wiley, 216243, 2003.[16] LOSZ, J, CHALLENGER, K, Haz microstructuresin HSLA steel weldments, First United States – Japansymposium on advances in welding metallurgy, 207-225,1990.[17] FUKADA, Y, Comiso, Y, Toughness improvementin weld metal of carbon and HSLA steel in Japan, FirstUnited States – Japan symposium on advances in weldingmetallurgy, 177-205, 1990.
WPS is a suitable option to weld MIL A46100 armors according to the results obtained. In addition, a narrower heat affected zone (HAZ) was obtained with designed WPS which should lead to a better in-service armor performance according to results of previous studies. Finally, an increase in Ch
6.3 Mechanised/automatic welding 114 6.4 TIG spot and plug welding 115 7 MIG welding 116 7.1 Introduction 116 7.2 Process principles 116 7.3 Welding consumables 130 7.4 Welding procedures and techniques 135 7.5 Mechanised and robotic welding 141 7.6 Mechanised electro-gas welding 143 7.7 MIG spot welding 144 8 Other welding processes 147 8.1 .
seam butt welding resistance butt welding flash butt welding resistance butt welding shielded unshielded other process plasma laser resistance butt welding inert gas welding submerged arc welding atomic hydrogen shielded metal arc welding (coated electrode) esepl w w w . e u r e k a e l e c t r o d e s .
the welding processes most often used in today's industry including plasma arc cutting, oxyfuel gas cutting and welding, Gas Metal Arc Welding (GMAW), Flux-Cored Arc Welding (FCAW), Shielded Metal Arc Welding (SMAW), and Gas Tungsten Arc Welding (GTAW). Flat welding positions and basic joints will be practiced. Pipe and tube welding
3. Classification of Underwater Welding Underwater welding may be divided into two main types: a) Wet welding b) Dry welding Fig. 3.1 Classification of underwater welding 3.1 Wet welding 3.1.1. Wet welding with coated electrode Wet welding is performed at ambient pressure with the welder-diver in the water and no physical barrier
2. DISSIMILAR METALS WELDING This section briefly presents the different consider-ations of welding procedure specifications for fusion welding of dissimilar metals, focusing on the GMAW Table 1. Welding procedure requirement for ferrous metal [10,11]. Considerations Fundamentals Service consideration Filler metal selection Welding process .
10.6 Braze-welding 460 Exercises 466 11 Joining processes (welding) 467 11.1 Fusion welding 468 11.2 Oxy-acetylene welding 468 11.3 Manual metal-arc welding 490 11.4 Workshop testing of welds 504 11.5 Miscellaneous fusion welding processes 506 11.6 Workholding devices for fusion welding 509 11.7 Resistance welding 515
Welding residual stresses and stress relieve Formation of the weld metal Solidification of the weld metal Phase transformations during welding Basics of welding methods used in welding of zirconium alloys TIC Laser Welding Electron Beam Welding Upset shape welding Resistance Appendix C -R
affected zone. Welding processes that are commonly used with the corrosion-resistant alloys are shown in Table 1. In addition to these common arc welding processes, other welding processes such as plasma arc welding, resistance spot welding, laser beam welding, electron beam welding, and submerged arc welding can be used. Because of
