Effect of Auxiliary Preheating of the Filler Wire on Quality of Gas Metal Arc Stainless Steel Claddings Amandeep S. Shahi and Sunil Pandey (Submitted June 8, 2006; in revised form November 9, 2006) Weld cladding is a process for producing surfaces with good corrosion resistant properties by means of depositing/laying of stainless steels on low-carbon steel components with an objective of achieving maxi- mum economy and enhanced life. The aim of the work presented here was to investigate the effect of auxiliary preheating of the solid filler wire in mechanized gas metal arc welding (GMAW) process (by using a specially designed torch to preheat the filler wire independently, before its emergence from the torch) on the quality of the as-welded single layer stainless steel overlays. External preheating of the filler wire resulted in greater contribution of arc energy by resistive heating due to which significant drop in the main welding current values and hence low dilution levels were observed. Metallurgical aspects of the as welded overlays such as chemistry, ferrite content, and modes of solidification were studied to evaluate their suitability for service and it was found that claddings obtained through the preheating arrangement, besides higher ferrite content, possessed higher content of chromium, nickel, and molybdenum and lower content of carbon as compared to conventional GMAW claddings, thereby giving overlays with superior mechanical and corrosion resistance properties. The findings of this study not only establish the technical superiority of the new process, but also, owing to its productivity-enhanced features, justify its use for low- cost surfacing applications. Keywords austenitic stainless steel, ferrite, preheated filler wire, UGMAW process, weld cladding 1. Introduction Increasing productivity of any welding process while maintaining or even improving the weld quality has been the task of researchers in the field of development of welding processes. Previous predictive studies on gas metal arc welding (GMAW) process have had various purposes. Researchers have attempted to model GMAW process in different metal transfer modes and tried to optimize it using different techniques (Ref 1-3) apart from accounting for wire melting rate in this process (Ref 4-6). 1.1 Cladding The term weld cladding usually denotes the application of a relatively thick layer (approximately 3 mm or 1/8th in.) of weld metal for the purpose of providing a corrosion-resistant surface (Ref 7). In modern industry, increasing use is being made of clad materials as a means of achieving the optimum balance of strength, special surface properties, and economy. Some of the typical base metal components that are weld-cladded include the internal surfaces of carbon and low-alloy steel pressure vessels, paper digestors, urea reactors, tube sheets, and nuclear reactor containment vessels. Among the various welding processes employed, GMAW process has become a cost- effective choice for cladding smaller- and medium-sized areas due to its superior quality, all position capability, and ease of mechanization. The characteristics and typical uses of various weld-surfacing processes are mentioned in Table 1. 1.2 Dilution It is defined as the ratio of the cross section of weld metal below the original surface to the total area the weld bead measured on the cross section of the weld deposit (Ref 8). Various combinations of procedural parameters like primary parameters viz. welding current, voltage, welding speed, and secondary parameters like polarity, electrode size, wire stickout, welding position/inclination, arc shielding, electrode oscilla- tion, welding technique, additional filler metal etc., which affect dilution, can be incorporated into a procedure (Ref 9). Various processes like SAW, GTAW, PAW, GMAW, ESW, FCAW, Strip cladding, Explosive welding (Ref 10-13), etc., have been used for cladding operation with an aim of minimizing dilution to as low value as possible without sacrificing the joint integrity. This requires a thorough understanding and proper control over a number of variables, which affect dilution. Use of hot filler additions (Ref 14) in various conventional processes like TIG, Laser, Plasma arc, etc., have been reported which affect dilution to a significant extent. 1.3 Auxiliary Preheating Arrangement in GMAW Process (Universal Gas Metal Arc Welding Process) This process makes use of a specially designed torch as shown in Fig. 1. It employs two contact tips and a secondary Amandeep S. Shahi, Department of Mechanical Engineering, Sant Longowal Institute of Engineering & Technology, Longowal, Punjab 148106, India; and Sunil Pandey, Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India. Contact e-mail: ashahisliet@yahoo.co.in. JMEPEG (2008) 17:30–36 ÓASM International DOI: 10.1007/s11665-007-9132-1 1059-9495/$19.00 30—Volume 17(1) February 2008 Journal of Materials Engineering and Performance