Static and fatigue behavior of plug-welded dissimilar metal welds between carbon steel and austenitic stainless steel with different thicknesses
© Triyono et al.; licensee Springer 2014
Received: 6 July 2014
Accepted: 21 August 2014
Published: 18 September 2014
Plug welding was used on the parts of the structure in which spot welding cannot be implemented, such as the complex structure and the construction with the profile stiffener. The objective of the present work is to define the static and fatigue behaviors of the plug-welded dissimilar metal welds between carbon steel and austenitic stainless steel with different thicknesses because the detailed recommendations on it were limited.
Carbon steel SS400 with a thickness of 3.0 mm and 1.0-mm-thick austenitic stainless steel SUS304 were plug welded using varied hole diameter in a range of 7 to 13 mm where the welding current and the diameter of welding wire were kept constant at 80 A and 1.0 mm, respectively. The welding joints were exposed to tensile shear tests, and the transition of interfacial fractures to tearing fractures was defined as the optimum condition. Tensile peel, fatigue, and corrosion fatigue tests were carried out on the optimum specimens.
The optimum plug welding joints were obtained at the hole diameter of 8 mm where the tensile peel and tensile shear load bearing capacity were 8.6 and 17.2 kN respectively. The endurance limit of fatigue conducted in air was 2 kN, whereas corrosion fatigue samples at this load fail at about 1,000,000 cycles.
AWS's formula for plug weld can be applied to the plug-welded dissimilar metal welds between carbon steel and austenitic stainless steel with different thicknesses. Endurance limit of this joint in corrosive environments is about half of the endurance limit in normal environments.
Welding of dissimilar metals between carbon steel and stainless steel has been widely used in engineering practice over the years. It is more economical compared to the ones made of stainless steel only. The importance of corrosion resistance in the structures is also the reason for the implementation of dissimilar metal welds. Dissimilar metal weld is generally more challenging and often causes problems due to differences in the physical, mechanical, and metallurgical properties of the base metal to be joined.
The stiffened thin plate structure, where the thinner plate is reinforced by a thicker plate called a frame, has been claimed as being a cost-effective way of achieving a high-performance vehicle structure (Gean et al. 1999). This structure is generally welded by resistance spot welding due to its advantages in welding efficiency and suitability for automation (Hou et al. 2007). The parts of the structure in which spot welding cannot be implemented, such as the double sheeting structure, complex structure, and the construction with the profile stiffener, plug welding was applied instead of spot welding. Welding schedule of plug welding has been offered by American Welding Society (AWS) (2004) and previous study (Tsuruta et al. 1952). According to this recommendation, the weld quality is achieved when the hole diameter of plug welding is 8 + t (in mm), where t is the thickness of the joined plate (in mm). It is very useful in finding good weld schedules for equal-thickness welding, but confusing in that for unequal-thickness plate welding and generally developed by and practiced within individual manufacturers (Agashe and Zhang 2003). Some of them use the thickness of thinner material, and others use the average of joined material thickness in that empirical formula. There are a lot of scientific papers dealing with static and fatigue behaviors of spot-welded dissimilar metal joints (Alenius et al. 2006; Hasanbasoglu and Kacar 2007; Jamasri et al. 2011; Vural et al. 2006), but only a few studies have been published concerning those of plug welded. The objective of the present work is to investigate the static, fatigue, and corrosion fatigue of plug-welded dissimilar metals between 3.0-mm carbon steel and 1.0-mm austenitic stainless steel.
Materials and welding processes
The chemical composition (wt.%) and mechanical properties of test materials
Yield strength (MPa)
Tensile strength (MPa)
Metallographic evaluation and mechanical test
The transverse section of weld passing through the weld nugget was prepared by standard metallographic procedure. Due to the nature of dissimilar metal welds, a two-stage etchant was used for etching. In the first stage of etching, 2.5% alcoholic nitric acid solution was used to reveal the microstructure of carbon steel side. The microstructure of austenitic stainless steel side and weld metal were revealed using 10 ml nitric acid, 20 ml hydrochloric acid, and 30 ml water. Microstructure investigations were carried out using an optical microscope.
The corrosion rates of the raw material and plug-welded surface were evaluated using Potensiostat/Galvanostat Model 273 (Princeton Applied Research, Oak Ridge, TN, USA). The samples were mounted in epoxy to expose only one surface with an area of 133 mm2 for electrochemical tests. A saturated calomel electrode (SCE) was used as the reference electrode and a platinum wire was used as the counter electrode. All electrochemical tests were carried out at room temperature. The polarization was conducted in natural seawater at a potential scanning range from −800 to +300 mV with a speed of 20 mV/min. Tafel lines were drawn on corresponding graphical plot of E versus log I to obtain the corrosion current (Icorr) value.
Results and discussion
The most important factors that affect plug weld quality are strength, depth, and area of weld penetration (American Welding Society 2002). In order to determine weld quality of plug-welded dissimilar materials, the strength of weldment was also determined. Structures employing plug weld are usually designed so that the welds are loaded in shear when the parts are exposed to tension or compression loading. In some cases, the welds may be loaded in tension, where the direction of loading is normal to the plane of the joint, or a combination of tension and shear (Hasanbasoglu and Kacar 2007).
Because the tearing failure mode was guaranteed, the optimum plug welding joints were obtained at the hole diameter of 8 mm where the tensile peel and tensile shear load bearing capacity were 8.6 and 17.2 kN, respectively. The endurance limit of fatigue conducted in air was 2 kN, whereas corrosion fatigue samples at this load failed at about 1,000,000 cycles.
The authors would like to express their sincere gratitude for the financial support of the Ministry of National Education of Indonesia and Indonesian Railway Industry.
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