Fatigue Fracture of Pie Channel Weld of Sinter Screen: A Metallurgical Insight
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TECHNICAL ARTICLE—PEER-REVIEWED
Fatigue Fracture of Pie Channel Weld of Sinter Screen: A Metallurgical Insight Kaushal Kishore
. Manashi Adhikary . Anup Kumar
Submitted: 25 July 2020 / Accepted: 3 September 2020 Ó ASM International 2020
Abstract Sintering is an agglomeration process to convert iron ore fines into a larger mass suitable to be charged directly into the blast furnaces. A screen separates the incoming iron ore raw materials based on their size fraction. These screens are supported by pie channels. One of these channels failed during operation that led to unwarranted interruption in production. Owing to the criticality of the matter, detailed failure investigation was conducted. It involved visual observations, micro- and macro-fractography to determine the mode of fracture, chemical analysis and microstructure examination using optical and scanning electron microscopes aided with energy-dispersive x-ray spectroscopy and electron probe microanalyzer. The analysis revealed incompatible austenitic stainlesssteel filler metal was used for welding mild steel material along with poor welding workmanship as suggested by underfilling and presence of thick layer of welding slag. There was formation of un-tempered martensite in dilution zone (the interface layer between heat-affected zone/fusion zone). The formation of undesirable martensite in the dilution zone is correlated with the time–temperature transformation diagram where the nose of the C-curve got significantly shifted toward the right due to enrichment with chromium and nickel as revealed by electron probe microanalysis. It was concluded that the failure occurred in
fatigue mode due to deficiencies in welding and recommendations to prevent failures are also provided. Keywords Steel channel Fatigue striations Electron probe microanalysis Welding slag Martensite
Introduction Blast furnace is a counter-current reactor that relies on the close specification of raw materials like iron ore lumps, agglomerates like sinter and pellet, coke and fluxes [1]. These furnaces can only function smoothly if the size fraction of the charge materials is within close tolerance. For instance, iron ore fines below 10 mm size are seldom charged inside the blast furnace as it would lead to choking and the loss of permeability. Sintering of these fines is an effective process of agglomeration [2]. However, the process of sintering is a continuous one and any major failure of critical component often results in the breakdown up to the downstream processes. Recently, a pie channel which is used to provide mechanical support to the screen used to separate oversize material before the process of sintering failed during service. This led to an operational delay of approximately 15 h. Such a delay had huge implications from point of view of productivity. Thus, it became important to study and understand the failure and come up with corrective and preventive actions to ensure no similar failure occur in future.
K. Kishore (&) M. Adhikary A. Kumar Scientific Servi
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