PARTICULATE COMPOSITE SURFACING OF STEEL BY TIG ARCING PROCESS

Abstract

With the advantage of its affordability and significant properties like strength, malleability & toughness, mild steel finds its usage in the diverse industrial application such as car body panels, nuts & bolts, metal chains, food cans, engine parts, bicycle rims and wire ropes. But in the due course of its usage, it wears out very quickly, meaning, it does not possess good wear resistant and hardness properties. The solution to the above problem is surface modification, which can be done through different techniques such as by changing surface chemistry like carburizing, nitriding & by surface deposition like thermal diffusion process, coating and by controlling the phase transformation on the surface like laser, electron beam & TIG arcing technique. Out of the above, one promising technique is making the layer of the surface as composite & the other is producing the desired phase on the surface by using TIG arcing process. But, there are certain limitations associated with these techniques which led to the current investigation. In this investigation, a layer of composite is developed on the surface of the Mild Steel, by using the activated tungsten inert gas (A-TIG) arcing process, in order to enhance the surface hardness. Surface composite has been prepared in two ways - (i) By trapping, i.e. ex-situ development, the hard phase particles - like SiC, Al2O3- into the surface and (ii) By in-situ growth of the hard reinforcement particles i.e. by adding the deoxidizers like Al, which takes away the oxygen present in the material and forms nonmetallic compound of Al2O3. Also, a composition was decided to develop the in-situ grown hybrid composite containing TiC & Al2O3 as the reinforcement particles. TIG arcing process has been used for melting the surface of base material. To take care of the inclusion and proper distribution of the reinforcement inside the weld pool, the weld pool flow was controlled -which is controlled by the addition of the oxide particles to the weld pool. In order to characterize the layer of composite formed on the surface, samples were examined under optical microscopy-to see the microstructural changes, EDS- to confirm the presence of reinforcement particles, FESEM analysis- to check the distribution of the reinforcement particles and XRD analysis- to check the presence of desired phase. Also, the microhardness values were calculated for the modified surfaces which was found to be enhanced by 2.9 times for SiC embedded sample, 1.9 times for Al & 2 times for the Al2O3 embedded samples. Surfaces were also modified with the fluxes prepared by mixing TiO2 and Al to form hybrid

composite containing TiC + Al2O3. The composition of these mixtures was decided based on the literature survey. Microhardness values for these mixtures embedded surfaces i.e. Mix 1 (sample 1), Mix 1 (sample 2), Mix 1 (sample 3), Mix 2 (sample 4) & Mix 3 (sample 5) were found to be increased by 1.8, 1.9, 2.13, 1.87 & 1.85 times respectively.