The complex shapes produced by the casting processhave enabled Ductile Iron castings to replacenumerous steel fabrications. Nevertheless, there areapplications where a casting becomes part of a fabri-cation, which may imply joining different parts bywelding Ductile Iron to steel. For example, a DuctileIron casting could replace a complex steel fabricationand be welded to a section of the assembly whichrequires the properties of steel. Such practices haveunfortunately found limited applications in the industrydue to the inherent limitation created by the formationof carbides during solidification of the welded area.However, recent development at Linde Gas (AGA) inSweden, to which Rio Tinto was associated, opensnew avenues for welding Ductile Iron to steel.

Procedures developed by the American WeldingSociety recommend, for Gas Metal Arc Welding(GMAW), the use of high nickel rods with short arc-

metal transfer and pure argon as shielding gas,resulting in relatively low productivity. However,experimental work has shown that optimum resultsare achieved when using a special variant of high per-formance GMAW metal transfer in combination with ashielding gas containing both argon and helium withsmall amounts of some oxidizing components.

Figure 1 compares the microhardness profiles acrosswelds obtained a) with usual procedures and b) withoptimized procedures. The new welding proceduresresulted in the decrease of the hardness of the DuctileIron / weld interface from 600 VHN to 300 VHN.Microstructural examination related such a decreaseto the limited formation of carbides in the fusion zoneand the reduction of the thickness of this zone from ~0.6 mm to ~ 0.2-0.3 mm. Comparable results wereachieved with ferritic and pearlitic Ductile Irons.

111

ADVANCES IN WELDING DUCTILE IRON TO STEELby

Martin Gagné, Sorelmetal Technical Services

Suggestionsfor Ductile IronProductionSorelmetal

®

Figure 1. Microhardness Profiles of Welded Specimens.

a) non-optimized b) optimized

STEEL D.I. STEEL D.I.

Charpy V-notched impact tests were performed onwelded ferritic and pearlitic Ductile Irons. As seen inthe table above, the toughness of the weld - DuctileIron interface is nearly doubled with respect to typicalvalues reported in literature.

More information on the properties of the welds canbe found in the technical paper jointly published byLinde Gas and Rio Tinto, which is referenced below.

During the experimental program, a variety of plateand tube geometries were welded, Figure 2. As seenin this figure, a candidate component currentlyfabricated of a welded assembly of preformed steel to

which steel tubes are welded, as shown in Figure 2,is the rear axle of a heavy vehicle; the objective wasto replace the costly preformed steel section of theaxle by a Ductile Iron casting, to which steel tubeswould be welded. The Ductile Iron-to-steel weldingtechnology was successfully developed on prototypeparts, meeting all customer’s requirements.

For more details, ask your Sorelmetal TechnicalServices metallurgist, or your Sorelmetal agent for acopy of the technical paper (see below) published onthis technology or contact us via our websitewww.sorelmetal.com.

July 2006

MATERIAL FERRITIC DUCTILE IRON PEARLITIC DUCTILE IRON

Weld Parent Metal Interface 11 – 20 J 5 – 9 J

Parent Metal 12 – 14 J Not available

Weld Parent Metal Interface – (Literature (1)) 8 – 12 J 3 – 4 J

TABLE 1

CHARPY V-NOTCHED IMPACT RESISTANCE (+ 20°C)

(1) Iron Casting Engineering Handbook, AFS, 2003.

Figure 2. Examples of Ductile Iron-to-Steel Welded Assemblies.

Technical Paper: M. Gagné, S. Leclerc, S. Helgee, N. Stenbackaand J. Tani, “Welding Ductile Iron to Steel: A Reality ”, AFSTransactions, vol. 114, 2006.