[EN] This work compares the weldability of ductile iron when: (I) a root weld is applied with a tungsten inert gas (TIG) process using an Inconel 625 source rod and filler welds are subsequently applied using coated electrodes with 97,6 %Ni; and (II) welds on ductile iron exclusively made using the manual shielded metal arc welding technique (SMAW). Both types of welds are performed on ductile iron specimen test plates that are subjected to preheat and post-weld annealing treatments. Samples with TIG root-welding pass shown higher hardness but slightly lower ductility and strength. Both types of welding achieved better ductile and strength properties than ones found in literature.Cárcel Carrasco, FJ.; Pascual Guillamón, M.; Pérez Puig, MA.; Segovia-López, F. (2017). Comparative study of tig and smaw root welding passes on ductile iron cast weldability. METALURGIJA. 56(1-2):91-93. http://hdl.handle.net/10251/102690S9193561-

Cárcel Carrasco, Francisco Javier

Pascual Guillamón, Manuel

Pérez Puig, Miguel Angel

Segovia-López, Francisco

English

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Comparative study of tig and smaw root welding passes on ductile iron cast weldability

[EN] This work compares the weldability of ductile iron when: (I) a root weld is applied with a tungsten inert gas (TIG) process using an Inconel 625 source rod and filler welds are subsequently applied using coated electrodes with 97,6 %Ni; and (II) welds on ductile iron exclusively made using the manual shielded metal arc welding technique (SMAW). Both types of welds are performed on ductile iron specimen test plates that are subjected to preheat and post-weld annealing treatments. Samples with TIG root-welding pass shown higher hardness but slightly lower ductility and strength. Both types of welding achieved better ductile and strength properties than ones found in literature.Cárcel Carrasco, FJ.; Pascual Guillamón, M.; Pérez Puig, MA.; Segovia-López, F. (2017). Comparative study of tig and smaw root welding passes on ductile iron cast weldability. METALURGIJA. 56(1-2):91-93. http://hdl.handle.net/10251/1026909193561-

91METALURGIJA 56 (2017) 1-2, 91-93J. CÁRCEL-CARRASCO, M. PASCUAL, M. PÉREZ-PUIG, F. SEGOVIA COMPARATIVE STUDY OF TIG AND SMAW ROOT WELDING PASSES ON DUCTILE IRON CAST WELDABILITYReceived – Primljeno: 2016-05-10Accepted – Prihvaćeno: 2016-10-10Original Scientific Paper – Izvorni znanstveni radJ. Cárcel-Carrasco; M. Pascual; M. Pérez-Puig; F. Segovia. ITM-Uni-versitat Politècnica de València (Spain). Camino de vera s/n, 46022 Va-lencia (Spain). Corresponding author, Email: fracarc1@csa.upv.esThis work compares the weldability of ductile iron when: (I) a root weld is applied with a tungsten inert gas (TIG) process using an Inconel 625 source rod and filler welds are subsequently applied using coated electrodes with 97,6 %Ni; and (II) welds on ductile iron exclusively made using the manual shielded metal arc welding technique (SMAW). Both types of welds are performed on ductile iron specimen test plates that are subjected to preheat and post-weld annealing treatments. Samples with TIG root-welding pass shown higher hardness but slightly lower ductility and strength. Both types of welding achieved better ductile and strength properties than ones found in literature.Key words: weldability, ductile cast iron, chemical composition, microstructure, mechanical propertiesINTRODUCTION The cast irons are useful materials due to the low-cost and non-massive production, wide design versatil-ity, ease of casting and machinability, and acceptable levels of mechanical behaviour. A relevant question that restrains a wider number of technical applications is their weldability. The poor mechanical properties of some castings are caused by the presence of graphite that produces discontinuities in the matrix and so leads to the presence of stress concentrators. The SMAW pro-cess is commonly employed in industry because it uses low cost fillers and can be more easily performed than other welding techniques. The welding filler is a deter-mining factor for the microstructure and mechanical properties of the welds. In processes with high thermal input alloying elements such as Cr and Mo, the pres-ence of dendritic or hard phases could result in reduced ductility and brittleness – even if the material is hard and strong [1 - 5]. The result is also influenced by pre-heating treatments and cooling rates. A subsequent an-nealing process also improves the properties. The aim of this work is to investigate the weldability of ductile cast iron using an Inconel 625 as highly alloyed weld filler in the root TIG welding pass versus the standard SMAW welding procedure.EXPERIMENTAL PROCEDURE The chemical composition of ductile cast iron is shown in Table 1. Figure 1a presents the microstructure of ductile cast iron before heat treatment. The mechani-cal properties of the casting material of this study are shown in Table 2. ISSN 0543-5846METABK 56(1-2) 91-93 (2017)UDC – UDK 621.791.052:669.163:66.014:620.1817=111Table 1 Chemical composition / wt. %C Si S + P Ni + Cu + Cr Mg Fe3,7 2,5 < 0,03 < 0,08 0,03 restTable 2 Mechanical properties of cast ironMechanical characteristics Ductile cast ironTensile strength, Rm / MPa 370Yield strength, Ry / MPa 320Break strain, A / % 6Toughness index, TI / MJ·m-3 11,1Elastic modulus, E / GPa 160Table 3  Chemical composition of fillers used to ductile iron welds / wt. %Filler Ni Cr Mo Ta Nb FeInconel 625 58 23 10 4,5 3,5 restNi97,6 97,6 restSample plates are produced by a sand casting process and subsequently milled to 300 / 95 / 10 mm to produce coupons. The specimens of ductile iron are welded using Figure 1  Ductile cast iron (a); SMAW ductile iron weld after annealing and cooling (b); SMAW top-beads on Inconel 625 - TIG root weld (c); and Inconel 625 root weld (d).92J. CÁRCEL-CARRASCO et al.: COMPARATIVE STUDY OF TIG AND SMAW ROOT WELDING PASSES ON DUCTILE... METALURGIJA 56 (2017) 1-2, 91-93TIG and SMAW processes. It is recommended for root welding pieces of greater thickness than 8 mm. The filler material is added with two SMAW passes over the TIG root weld. A second batch of test plates were welded to-gether using only Ni97,6 rod fillers. The composition of electrodes is shown in Table 3. All the welds are carried out on a series of test plates that were pre-heated to 350 °C because of the difficulty of welding the castings. Once the welds are finished, the plates were immediately annealed at 900 °C and cooled in a furnace.The Vickers microhardness (HV) test was performed in accordance with EN ISO 876. Mechanical properties (EN ISO 10002-1) measured were yield (Ry) and tensile strength (Rm), and break strain (A). A conventional toughness index (TI) is taken into account to discrimi-nate the differences between the ductile/brittle behav-iour of the cast irons welds. It is calculated from the expression TI = αRmA, where α is 5•10-3 (dimension-less). The results for the average values obtained from five samples per batch are shown in Table 4.Table 4 Mechanical properties of weldsFiller Ni97.6SMAWRoot           Beads TIG     +    SMAWRm / MPa 320 300Ry / MPa 310 285A / % 8 7TI / MJ·m3 12,8 9,0HV HAZ 194 210HV Interface 320 610        325HV WZ 227 520        160RESULTS AND DISCUSSIONIn the SMAW-only welds, Figure 1b reveals three defined zones: (a) the heat affected zone HAZ; (b) the weld zone (WZ) with the interface between both HAZ and WZ; and (c) the ductile iron base material zone (BM). In the latter zone it is possible to observe the fer-rite structure with uniformly distributed spheroid nod-ules that decrease in size as we near the HAZ. The HAZ and HAZ-WZ interface hardness are given in Table 4. It is the consequence of tempered martensite precipitated in the ferrite matrix which was not completely elimi-nated in the annealing treatment.Finally, Ni is the most common material in the WZ. The microstructure consists of uniformly distributed spheroids in an austenitic matrix with a hardness of 227 HV. Ry and Rm were 310 and 320 MPa. (86 % of the ductile cast iron Rm). The mechanical properties of the coupons welded with Ni electrodes are lesser than those from other authors [1, 6]. In latter references the ENi-CI electrodes contained less Ni and more C, and the welds were basically constituted by cementite-martensite (partially melted zone) and perlite-martensite (HAZ). This effect produced welds of low ductility (0,7 %) and greater brittleness (1,3 MJ·m-3) compared with the same welds in this work (8 % and 12,8 MJ·m-3). The fractures were localised between the partially melted and HAZ while fractures in this work occur between the base ma-terial and the HAZ.The microstructure of the cast iron weld in Ni97,6 electrode coated filler second pass zone on the Inconel weld root is shown in Figure 1c. Nodular graphite in the ferritic matrix is observed in the interface close to the base metal. In the WZ the precipitated nodules are smaller than in the interface [7, 8]. The hardness in the HAZ is 210 HV while mechanical properties are somewhat lower: 285 MPa (Ry), 300 MPa (Rm). However, the ductility is 7 % to A and 9 MJ·m-3 in the TI. The fracture is more ductile than in previous cases and usually occurs in the cast zone near the interface [9]. Weld ductility and Ni-based consuma-bles are closely related because: (a) the formation of brit-tle products in the WZ is prevented [10]; (b) the precipita-tion of graphite increases in the WZ and reduces both metal shrinkage and thermal stress during solidification – thereby causing a reduction in susceptibility to cracking; (c) improvements in tolerance to phosphorus and sulphur and reduction in the risk of hot cracking [6].Figure 1d shows the interface of the TIG-root. It is appreciable that small traces of white iron (W, blue zone) in a martensitic matrix (M, white needles) remain undissolved. The hardness level reaches from 520 HV (root) to 610 HV in the interface zone. This is below that obtained if air cooling were applied because the Cr con-tent in the Inconel has retained part of the carbides formed in the weld. More and smaller graphite nodules are shown in Figure 1d. The fracture was brittle in this zone and started near the interface. TI reaches 70 % of the SMAW-Ni weld coupons. Askari [6] reports that samples welded with electrode EN-CI on the root and post filled with EN7018 showed improved resistance – but that A reached 2,5 %. However, ductility deterio-rated and the toughness dropped to 5,3 M·m-3. The WZ hardness in the Ni-beads is less than the original casting (160 HV) but ductility and fracture strain are greater. The microstructure consists of smaller spherulites strung in an austenitic matrix because of Ni content.The microstructure and EDX-spectrum in Figure 2a corresponds to a weld obtained using only Ni97.6 elec-trodes. The interface zone reveals the high Ni content (diluted together with Fe). Si appears as the element that causes graphite precipitation. There is no trace of white iron and graphite is distributed in nodules of in-termediate size. This verifies that the structural constit-uents generate a solid union, as Figure 1b shows. The spectra and composition of the interface between the weld root with Inconel and Ni97.6 obtained using SMAW are shown in Figures 2b and 2c.Figure 2b corresponds to the second pass of the filler (Ni97,6). The absence of Cr directly influences the struc-ture of the welding interface dissolving the carbides, eliminating the white iron, and producing a substantial decrease in hardness. This contributes to the ductile be-haviour of the weld. The ferritic matrix microstructure is observed in Figure 2a. Tensile fracture occurs in this zone near the base material. Figure 3c corresponds to the inter-face of the root welded with Inconel 625 rod. The spec-93J. CÁRCEL-CARRASCO et al.: COMPARATIVE STUDY OF TIG AND SMAW ROOT WELDING PASSES ON DUCTILE...METALURGIJA 56 (2017) 1-2, 91-93trum shows less pronounced decreases in Cr. The result is a partial reduction in the presence of carbides as a conse-quence of an incomplete dissolution through annealing and the furnace cooling. Several authors have found that when large amounts of C, Cr, Fe, Mo and Ni are present in combination with high temperatures and post air-cool-ing the formation of γ - (Fe, Ni), martensite, Ni - Fe - Cr - C phase, Cr7C3 and other complex carbides is possible [1, 4, 11, 12]. In this research, the use of very low C con-tent electrodes, the complete solubility of graphite above 800 ºC, and the moderate presence of Mo-Nb-Ta in the composition of Inconel 625 cause most of the Cr to be dissolved (as Figure 2b shows). There is a reduction in hardness at the interface (325 HV) although it remains hard. The fracture is brittle and starts at the root zone – but the result is a substantial increase in ductility since the A is 7 % and the TI is 9 MJ/m3.CONCLUSIONSIn this work has been studied that it is possible to weld short ductile cast iron sections using the TIG tech-nique and Inconel 625 for the root welding pass.For TIG-root Inconel welding coupons, the anneal-ing treatment does not significantly change the initial weld conditions and maintains part of the white iron structures with martensite in ferritic matrix. There is an increase in hardness in the welding zones – but not with respect to mechanical strength, ductility, and toughness.The toughness, ductility, tensile, and the yield strength of the ductile cast iron coupons welded exclu-sively using Ni electrodes and SMAW method are bet-ter than those made with TIG Inconel root welding fol-lowed by Ni-SMAW passes – but the differences in mechanical and toughness properties between both welding methods are not dramatically different. Inconel root TIG welding exhibits somewhat lesser properties but better behaviour and structural quality than those reported by other authors.AcknowledgmentWe would like to give thanks to Language Transla-tors Service of the Languishes Department of Universi-tat Politècnica de València, Spain.REFERENCES[1]  Jeshvaghani, R. Arabi, E. Harati, and M. Shamanian. “Ef-fects of surface alloying on microstructure and wear beha-vior of ductile iron surface-modified with a nickel-based alloy using shielded metal arc welding.” Materials & De-sign. 32.3 (2011): 1531-1536.[2] Hou, Q. Y., et al. “Effects of molybdenum on the micro-structure and wear resistance of nickel-based hardfacing alloys investigated using Rietveld method.” Journal of Materials Processing Technology. 209.6 (2009):2767-2772. doi:10.1016/j.jmatprotec. 2008.06.025.[3] Karamış, M. B., and K. Yıldızlı. “Surface modification of nodular cast iron: A comparative study on graphite elimi-nation.” Materials Science and Engineering: A. 527.20 (2010): 5225-5229.[4] Amirsadeghi, A., and M. Heydarzadeh Sohi. “Comparison of the influence of molybdenum and chromium TIG surfa-ce alloying on the microstructure, hardness and wear resi-stance of ADI.” Journal of Materials Processing Techno-logy. 201.1 (2008): 673-677.[5]  Abboud, J.H. “Microstructure and erosion characteristic of nodular cast iron surface modified by tungsten inert gas.” Materials Materials & Design 35 (2012): 677–684.[6]  Askari-Paykani, Mohsen, Mehrdad Shayan, and Morteza Shamanian. “Weldability of ferritic ductile cast iron using full factorial design of experiment.” Journal of Iron and Steel Research International. 21.2 (2014): 252-263.[7]  El-Banna, E. M., M. S. Nageda, and MM Abo El-Saadat. “Study of restoration by welding of pearlitic ductile cast iron.” Materials letters. 42.5 (2000): 311-320. doi:10.1016/S0167-577X(99)00204-9.[8]  El-Banna, E. M. “Effect of preheat on welding of ductile cast iron.”. Materials Letters. 41.1 (1999): 20-26. doi:10.1016/S01 67-577X(99)00098-1.[9]  Bayati, H., and R. Elliott. “Influence of matrix structure on physical properties of an alloyed ductile cast iron.” Ma-terials Science and Technology. 15.3 (1999): 265-277. doi: 10.1179/026708399101505833.[10]  Pascual, M., Cembrero, J., Salas, F., and Martínez, M. P. “Analysis of the weldability of ductile iron.” Materials Letters. 62.8 (2008): 1359-1362. doi:10.1016/j.matlet.200 7.08.070[11]  Shamanian, M., SMR Mousavi Abarghouie, and SR Mousa-vi Pour. “Effects of surface alloying on microstructure and wear behavior of ductile iron.” Materials & Design. 31.6 (2010): 2760-2766. doi:10. 1016/j.matdes.20 10.01.017.[12]  Gaxiola, A.J., Pérez-López, M.J. and Almanza E. “Effects of welding conditions by TIG and post weld heat treatment in ductile cast iron on the corrosion resistance.” Materials Science Forum. 755 (2013): 21-27. doi:10.4028 /www.scientific. net/MSF.755.21. Note:  The responsible translator for English language is theService of the Languishes Department of Universitat Politècnica de Valèn-cia, SpainFigure 2  Interface zone in the weld made with a Ni electrode (a), filler weld interface of the top pass (b), root weld interface (c)

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Comparative study of tig and smaw root welding passes on ductile iron cast weldability

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