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    • MIAB welding of alloy steel t http

    2018-11-01

    MIAB welding of alloy steel tube and establishment of operational windows based on visual inspection of welded tubes were reported by Arungalai Vendan et al. [11], in which the strength assessment and non-destructive evaluation of T11 welded tubes were also reported. Further bonding integrity of the welded samples was reported based on the macro and micro analyses of the welded samples in Refs. [12,13]. But no literature is available on detailed analysis of structure property correlation of MIAB welded T11 tubes. Hence an attempt is made to analyze the structural changes in welded tubes and to study its effect on the weld properties. Low alloy steels exhibit high strength with good toughness properties under quenching and tempering conditions. The ability to retain these properties of the buy Manumycin A metal in welded region is also important as it will help in improving its structural and functional properties. Considering that T11 tubes are usually used in high pressure applications, including boiler, pipeline and defence application, it is required to understand the suitability of MIAB welding process through a detailed study on microstructural characterization. In spite of typical application studies on MIAB welding, there are few literatures on the detailed microstructural analysis of MIAB welded T11 tubes. When the properties are retained, MIAB welding could qualify for high pressure part welding like boilers, submarines, ships, etc. This paper presents the study on the microstructural characterization of MIAB welded T11 tubes with hardness and strength assessment to correlate the weld properties. The description of the experimental setup and operating parameters are explained in the following section. The results of the experimentation are discussed through microstructural analysis, parameter influence, hardness and mechanical testing results in Section 3 and 4. When the properties are retained, MIAB welding could qualify for high pressure part welding.
    Experimental setup and process parameters Welding was carried out using a hydraulic MIAB welding machine available at Welding Research Institute, BHEL, Tiruchirappalli. The setup is shown in Fig. 3. The MIAB welding process is divided into four stages of operation, viz., arc initiation, arc stabilization, arc rotation and upsetting. The arc is initiated when the closed joints are slightly spaced to a definite interval according to the applied voltage. The arc gets initiated from the inner dimensions of the tube and moves to the external edges. This stage relates to the beginning of the arc rotation due to the interaction of magnetic and electric fields. The momentum of the arc gets established in Stage II. In Stage III, the arc velocity is stabilized and results in a visible arc ring around the gap between the joints. In budding stage, a thin layer of molten metal appears at the tube end and is accompanied by a shrill sound of arc rotation. The molten metal at the edges appears to break and is attributed to waving. This sets Stage IV for the upsetting force to be applied to fuse the metal joints. The joint setup for MIAB welding is shown in Fig. 4. An electromagnetic force FL is generated on the arc due to the axial component of current flow in the arc, and IL crosses the radial component of the applied magnetic field BL. Flashing will occur, and the plasticized material from the contact area flows to form a weld bead around the circumference of the joint. Of the different currents, the arc rotation current is of critical importance in determining the weld quality [14]. The faying edges start to be uniformly melted and gets ready for fusion. Any difference in current settings will lead to a bad weld, including lack of fusion. The values of current and time parameters for different stages of welding are listed in Table 1. The thickness of the tubes and the type of material dictate the choice of the operating parameter range and are decided based on the trial and error method. If the currents are in excess, the joints become irregular with the changes of welding current and welding time in each stage of MIAB welding. In the present study, the effect of arc rotation and upsetting on MIAB welded tubes are studied by varying arc rotation current, arc rotation time and upset current in two levels. The range of welding variables was obtained by trial and error method as the samples welded out as per the range show an improper weld bead formation.