MECHANICAL AND TRIBOLOGICAL CHARACTERIZATION OF CLADDING ON LOW CARBON STEEL FABRICATED BY GMAW USING COLD METAL TRANSFER (CMT)

Abstract

Weld cladding has emerged as an innovative technique for enhancing the surface properties of carbon steel, with widespread applications across multiple industries, including chemical processing, marine, mining, agriculture, and power generation. The low carbon steel has become an in-demand material in different industrial applications due to its versatility and cost-effectiveness. Despite its unparalleled advantages, it cannot be utilized in wear-resistant applications without surface altercation, which can be achieved by cladding stainless steel over low-carbon steel. Low-carbon steels can be clad with stainless steel to enhance their mechanical wear properties. Studies were carried out to investigate the impact of process parameters on weld bead geometry and dilution% during cold metal transfer (CMT) cladding of super duplex stainless steel 2507 over low carbon steel. Response Surface Methodology (RSM) with a Central Composite Design matrix was used to optimize the process parameters (welding current, welding speed, and nozzle to work-piece distance (NTD)). The adequacy of the model was checked using an ANOVA analysis. The ideal input parameters were 200 A of welding current, 4.64 mm/s of welding speed, and 14 mm of NTD. The welding speed is the most dominant parameter, followed by the welding current and NTD. The cladding samples were prepared using the optimal parameters. The CMT-clad layer's microstructure, microhardness, and wear properties were also evaluated. The results indicate a dense crack-free and non-porous clad surface was obtained under optimal conditions. The tribological performance of the Austenite stainless steel clad over low carbon steel plate samples prepared at different CMT welding speeds (3, 4, 5, and 6 mm/sec) was studied. A ball-on-disc reciprocating tribometer was used to examine the wear characteristics of the cladding surface by varying the normal loads (30N, 40N & 50N) and frequencies (5Hz, 10Hz & 15Hz). The wear resistance of the cladding surface is enhanced by 30-40% compared to a base material. Results show that the wear rate varies with applied load and frequency due to the metastability of austenitic stainless steel during plastic deformation; the austenite changes into martensite. The cladding and worn out surfaces were examined through optical and field emission scanning electron microscopy (FESEM) to study the wear mechanisms. The comparison of the Cold Metal Transfer (CMT) welding and pulse MIG welding processes to study the weld-clad bead of 308L stainless steel over low-carbon steel was also carried out. To investigate the mechanical and wear properties of CMT weld-clad samples, welding speed (3, 4, 5, and 6 mm/sec) was used as the input process parameter, while maintaining constant current (175 A), nozzle-to-workpiece distance, and shielding gas flow rate (15 l/min). Microstructural examination of weld beads was conducted using optical microscopy and FESEM. Results showed that increasing welding speed enhanced microhardness and wear resistance of the clad surface. Notably, the CMT cladding process demonstrated superior mechanical and wear properties, reduced residual stresses, and lower heat input compared to pulse MIG welding, attributed to minimal dilution.