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  • In this context the present

    2018-11-15

    In this context, the present investigation describes the superiority of DP-GMAW process in welding of AISI: 310S austenitic stainless steel in comparison to the conventional P-GMAW process. The grade AISI: 310S austenitic stainless steel (ASS) is designed for high temperature service due to excellent high temperature properties and good ductility [8]. It resists NSC59984 in continuous service at the temperatures up to 1000 °C [9]. However, it is reported that the welding of high chromium grade AISI: 310S material is critical since it is susceptible to Intergranular corrosion attack because of chromium depletion near the fusion line of HAZ [10]. It is generally known that the increase of heat NSC59984 input enhances the chromium depletion. Thus, special attention should be taken in welding of grade AISI: 310S ASS material. From the literature review, it is well understood that there is limited published literatures about welding of grade AISI: 310S ASS [11]. Hence, it is felt that the dual pulse GMAW process is one of the welding techniques which may improve the weld joint characteristics of grade AISI: 310S ASS material.
    Experimental
    Results
    Discussion In view of the results discussed above, it is clearly understood that the DP-GMAW process is used to improve the mechanical and metallurgical properties and minimize the transverse shrinkage of AISI: 310 ASS weld joints in comparison to the P-GMAW process. Further, it is noticed that, in the case of AISI: 310S ASS weld joint prepared by DP-GMAW process, the severity of inter-granular attack in the grain boundary of HAZ region of the weld joint is reduced. Such an improved property obtained by using DP-GMAW is largely due to the combined effect of pulsed current and thermal pulsation of the process. The thermal pulsation effect primarily obtained in the DP-GMAW by varying wire feed rate (WFR) is shown in Fig. 9. It is observed that DP-GMAW shows the variation of WFR from the given WFR setting in the power source, but such variation is not observed in P-GMAW process. The variation of WFR in DP-GMAW is to maintain a constant arc length because there is a chance to vary the arc length at a given WFR during the thermal pulsation period. This behavior reflects in the current and voltage waveforms (Figs. 10 and 11). The variation of WFR also confirms the synchronization between high frequency pulse and thermal pulse. This synchronization of pulses stirs the weld pool, reduces the heat input of DP-GMAW process accordingly and improves the properties of weld joints. In order to confirm the variation of WFR during DP-GMAW under dynamic operating conditions, the waveforms of welding current and arc voltage were studied. The typical current and voltage waveforms at relatively low and high WFR of 4 and 9 m/min during DP-GMAW are shown in Figs. 10 and 11, respectively. From the figures it is observed that the arc voltage decreases during the thermal pulsation period, but the welding current increases due to the variation of WFR. These behaviors indicate that the DP-GMAW process introduces comparatively more thermal shock in the weld pool in comparison to the P-GMAW process. This is a beneficial effect to improve the characteristics of weld joints.
    Conclusions This study highlights the superiority of DP-GMAW in place of P-GMAW in welding of grade AISI: 310S ASS material. Some of the key observations of the study are as follows.
    Acknowledgment
    Introduction Friction surfacing is a solid phase cladding technique that uses a combination of heat and deformation to clean surfaces and metallurgically bonded metals. In its simplest arrangement, a rotating consumable bar is brought into contact, under low load, with stationary substrate in the initial dwell time stage, as shown in Fig. 1, when the rotating bar is preferentially heated by the frictional heat development due to relative motion between the rotating consumable rod and stationary substrate, facilitating to the consumable to plastic state. After the dwell time, the substrate that is mounted on a table is given linear translational motion to facilitate the deposition of the plasticized consumable onto the substrate by shearing, as shown in Fig. 2. Bonding occurs by the combination of self-cleaning between the two materials and the application of heat and pressure to promote diffusion across the interface, thereby forming a solid-phase metallurgical bond. The process relies on producing precisely the right temperature and shear conditions at the interface between the rotating bar and substrate via the plasticized layer. Friction surfacing has gained increasing interest in the area of reclamation of worn components during the recent past as it has been proved to be successful in building-up of worn-out shafts. The process can be performed in open air [1], in inert atmosphere [2] and underwater without sealing [3]. It is suitable for consumables which exhibit low thermal conductivity as well as high thermal conductivity alloys like aluminium alloys. Minimal dilution, narrow heat-affected zone, ability to deposit metallurgically incompatible materials and freedom from cracking are amongst the most important advantages of friction surfacing in comparison with conventional fusion welding based surfacing methods. Friction surfacing was first patented as a metal-coating process in 1941 by Klopstock et al. [4], but only recently it has been developed as a practical industrial process because of its repair and reclamation capabilities.