Browsing by Author "Igwemezie, Victor"

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    Assessment of fatigue crack growth resistance of newly developed LTT alloy composition for the repair of high strength steel structures
    (Elsevier, 2024-06-11) Igwemezie, Victor; Mehmanparast, Ali; Ganguly, Supriyo
    Tensile residual stress (TRS) is a well-known factor that deteriorate the integrity of welded joints. Fatigue failure is accelerated by the existence of TRS introduced during the welding process. There have been efforts in the last two decades to develop filler alloys that can reduce TRS by introducing compressive residual stress (CRS) to oppose the TRS in high strength steel welded joints. These works are based on the theory of austenite (γ) to martensite (α’) transformation and the filler is often called a low transformation-temperature (LTT) alloy. Many studies have reported that the fatigue strength (FS) of weld joint made with LTT alloy is many times better than that of the conventional fillers. It is reported to be particularly useful in the repair of high strength steel structures. However, studies on the fatigue crack growth (FCG) behaviour of these LTT alloys is scarce. In this work, we developed Fe-CrNiMo based LTT weld metal composition, assessed its FCG behaviour and compared the results with that of a conventional welding wire (ER70S-6). It is found that ER70S-6 weld metal obtained under relatively fast cooling is extremely tough, but the associated heat affected zone (HAZ) has poor resistance to FCG which obscured the benefit of the tough weld metal. High heat input or condition that results to slow cooling of the ER70S-6 weldment deteriorates its resistance to FCG. Unfortunately, despite its low martensite start temperature of 231±7 and the anticipated beneficial effect of induced CRS, the LTT alloy studied had the lowest FCG resistance. The LTT alloy appears to have an intrinsic microstructural feature or a ‘fault line’ that reduced its resistance to FCG. While the LTT alloy weld metal has poor resistance to FCG, the associated HAZ resisted FCG more than the HAZ associated with ER70S-6 weld metal. It is observed that aligning the ER70S-6 weld metal perpendicular to the crack front produced the highest resistance to fatigue crack initiation and propagation. In the case of ER70S-6, it is believed that the weld metal induced a CRS at the notch tip which resulted to the high fatigue resistance. In the case of the LTT alloy, perpendicular alignment of the weld metal produced slight improvement.
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    Impact of cold-wire gas metal arc welding (CW-GMAW) parameters on microstructure and microhardness characteristics in repairing S275JR structural steel
    (Springer, 2025-03-23) Musa, Zahraddeen; Ganguly, Supriyo; Suder, Wojciech; Igwemezie, Victor; Rajamudili, Kuladeep
    This study investigates the influence of adding a cold wire during gas metal arc welding (CW-GMAW) for repair of S275JR structural steel. The research is aimed at improving repair productivity through increased deposition rates with enhanced performance. During weld repair, multiple passes induce large number of thermal cycles and a huge thermal gradient on the material which has an adverse effect on the material’s properties. This is largely due to the microstructural changes that occur during the process. In this work, a systematic approach has been adopted to explore the effects of varying gas metal arc welding (GMAW) parameters, including wire feed rate, welding current, voltage, travel speed, and specifically cold-wire feed speed on the heat affected zone (HAZ) microstructure and hardness. Macrostructural examination highlights significant alterations in the heat affected zone (HAZ) region, with marked microhardness changes in both WM and HAZ. Cold-wire addition led to a reduction in the HAZ area, depth of weld metal penetration, and significantly reduced the impact of imposing thermal cycles on the HAZ of the welded samples. Additionally, microstructural analysis was conducted using a standard optical microscope to correlate the observed hardness variations with microstructural transformations in the weld metal and heat affected zone (HAZ). The findings reveal that specific combinations of CW-GMAW parameters can significantly influence the microstructure and thereby hardness, suggesting that with careful control of these parameters, it would be possible to do faster repair with minimal loss of integrity for critical structural steels.