HOT TOPICS Issue #1, 2009 Welding of Ductile Iron

Introduction carbon content, molten iron tends to Welding is defined as a process for solidify with a carbidic structure that joining separate pieces of material, limits the toughness of the weldment. usually metal, in a continuous metallic This initial limitation restricted the use bond. One of the most common of cast iron parts in many fabrications misunderstandings by the Engineering that could have taken advantage of the community is that Ductile Iron cannot be casting process and its properties. welded to itself or to other dissimilar Ductile irons with properties competing ferrous materials. On the contraire, with those of steel would find many new ductile iron is weldable and engineered applications if it could be welded into many different applications and without becoming brittle. market segments that require welds. However, special consideration is Avoiding the formation of this carbidic required for selection of the correct zone is a difficult task. Studies have welding process, proper joint design, been conducted and reported in Modern welding materials and setup. Casting toward an improved bond between ductile iron and steel, whereby There are many different welding industrial manufacturing processes could processes available. These include but be introduced. Laboratory and are not limited to Arc, Pulsed Arc, application welding tests were Friction, Laser, Resistance, Plasma, performed with industrial equipment and Spray, Impact and Fusion Welding. Not commercially available consumables all of these methods are appropriate for using a multi-pass approach to minimize Welding of Ductile iron due to inherent the interactions between the base process and/or design limitations. materials and the heat involved during Processes for welding ductile iron have the welding process. been developed in the past, but A shielding gas containing both argon improving the quality would enlarge the and helium in combination with small range of applications, specifically in the amounts of some oxidizing components heavy vehicle industry. Control of was used. heating rates and cooling rates of the weld zone is critical and will influence The welding procedures included pre- microstructure significantly. welding heat treatments from 300-320C (572-608F) and post-welding cooling Metallurgical Aspects followed by heating to 600-620C (1,112- While welding steels has been rapidly 1,148F) maintained for two hours.1 and successfully introduced in all industrial sectors, the difficulty of Filler Metal Welding Joint Design welding cast irons was recognized early. The Weld Zone of a traditional filler When welded, ductile iron is liquefied in metal welded section can be broken the welded area and because of its high down into several distinct regions. The

Rob Logan, Elkem Metals Inc. and Member of DIS Research Committee 1

regions that are typically evaluated for It is important when designing a welded metallurgical bonding, microstructure application to ensure the weld zone has a and defects include: proper dilution balance appropriate for the applicable parent material and filler Weld Toe – area at end of weld beads, metal.2 susceptible to cracking Penetration Area – depth of weld into Typical Weld Defects 3 parent metal As with the Ductile Iron casting process, Partially Melted Zone (PMZ) or Fusion potential for welding defects is also Zone – hottest liquid region and greatest present. General Categories of Defects concern for influence on ductility include: Heat affected Zone – non liquid region adjacent to PMZ 1. Defects involving inadequate bonding. Weld Dilution 2. Defects from the introduction of foreign inclusions. Weld Dilution 3. Geometric effects. One method of measuring weld quality 4. Metallurgical effects. is analyzing the weld dilution. The root causes of weld defects can be attributed to one or more of several conditions:

1. Lack of welding know-how and experience. C A 2. Welding process characteristics. 3. Base metal defects or compositions. B 4. Materials selection and properties. 5. Welding environment (joint design, fit up, temperature, support, etc.)

Welded Applications Image Analysis is often used to identify 1. Closed Coupled Catalytic Exhaust the area of the weld metal and the Manifolds original parent material location. Each Strict requirements for low emissions are area is measured and a weld dilution is now standard throughout the automotive determined. industry and are particularly challenging Area A, B and C is the entire Weld for cold start light off conditions. One Bead. commonly used design technology Area A is the non penetrated portion of achieving these requirements are closed the weld bead. coupled catalytic converters. It has been Area B and C are considered to be the proven in high volume applications that Area of Penetration. Dilution Factor = durable welds can be made by joining a (B+C) / (A+B+C). machined SiMo Iron Manifold to a 400 The weld dilution will vary for each series stainless steel catalyst can. This weld design and application but will welding design approach allows for a influence the microstructure and tightly packaged and lighter weight mechanical properties of the weld zone. Rob Logan, Elkem Metals Inc. and Member of DIS Research Committee 2

solution to be achieved. This joining is deoxidizing coatings are not required. accomplished by using a pulsed shielded The work pieces do not require pre- or metal arc welding process, shielding gas post-heat treatment to minimize the and a high Ni, welding wire filler metal effects of the HAZ.7 44HT.4 References and Sources 1) Welding ductile iron to steel: a new welding process will allow ductile iron castings to be welded to steel, making fabrications using both metals a reality, Modern Casting, June 2007 Article, M.Gagne, S. Leclerc, Rio Tinto Iron and Titanium Inc. N.Stenbacka, J.Tani, Linde Gas. 2) Online Welding Handbook. http://www.esabna.com/EUWeb/oxy_ha ndbook/589oxy15_4.htm 3) Ductile Iron Welding, Carl Loper, Q1 2. Ductile Pipe 2007 DIS News. Field Welding of Ductile Iron Pipe has 4) Dissimilar Welding of Simo Ductile been a standard procedure developed in Iron Exhaust Manifold Exhaust the 1990’s. Procedures have been Manifold to Stainless Steel Catalytic developed and published by the Ductile Converter Using NI-ROD FM 44HT, 5 Iron Pipe Research Association and are SAE Paper 2000. available online by searching pipe 5) Field Welding and Cutting of Ductile 6 producer websites. Iron Pipe. Ductile Iron Research Pipe welding technology development to Association, 12-98. address problems with tension anomalies 6) U.S. Pipe HP LOK Field Weld and sub-optimal interweld pass fusion Brochure and Welded Outlets BRO-063. has been recently patented. The 7) Highly Ductile Reduced Imperfection invention discovered that ductile iron-to- Weld for Ductile Iron and Method for ductile iron welds can be reliably formed Production Same, Patent #, at mission-critical junctures by PCT/US2002/016813 by US PIPE AND compensating for the brittle nature of the FOUNDRY COMPANY IN (US) heat affected zone through enhancing ductility of the weld itself. The invention provides a highly durable weld without soundness problems such as tension anomalies, multilayer fusion imperfections, or pinholes; and a method of forming such a weld. The weld is created using high nickel weld wire (filler metal or consumable electrode, or both) welded in a pure inert gas (or mixture of pure inert gasses and even reducing gasses). Additions of weld metal alloys, flux coring, and Rob Logan, Elkem Metals Inc. and Member of DIS Research Committee 3