Root cause analysis of surface and internal defects of micro‐alloyed S355 heavy plates

Abstract

Purpose – Steel heavy plates, grade S355, micro‐alloyed with Vanadium‐V and/or Niobium‐Nb plus Titanium‐Ti in thicknesses from 5 to 60 mm, 200.000‐350.000 t/y, are produced according to EN 10025 at STOMANA S.A., a company of the SIDENOR Group in Pernik Bulgaria, and are exported to the European Market. These plates fulfil high quality standards as they are used for constructions and engineering applications (e.g. high‐building constructions, bridges, shipping applications, cranes, etc.). Often intermediate and/or final products (slabs and plates, respectively) suffer from surface and/or internal defects, which deteriorate the final product's quality. The purpose of this paper is to look at the challenging task of eliminating the external and especially the internal defects.Design/methodology/approach – ELKEME performs root‐cause analysis and proposes improvement actions. For these purposes light optical metallography (LOM) and scanning electron microscopy (SEM) with EDS were applied. For the analysis a NI...