Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 265-271; DOI: 10.3221/IGF-ESIS.37.35 265 Focused on Fracture Mechanics in Central and East Europe On monitoring of mechanical characteristics of hot rolled S355J2 steel D. Angelova, R. Yordanova, A. Georgiev, S. Yankova University of Chemical Technology and Metallurgy, Bulgaria donkaangelova@abv.bg, r.yordanova@uctm.edu A BSTRACT . Hot rolling normalization technology for producing sheets from a low-carbon steel, Steel S355J2, used in the Bulgarian Metallurgical Plant “STOMANA Industry SA” is under investigation. A newly introduced automatic application optimization procedure in this technology is an important step that leads to avoiding of traditional heat treatment, improving of steel mechanical characteristics, increasing of production efficiency, all resulting in high quality final products. On the basis of the final mechanical rolled-sheet characteristics - yield strengths, R e , ultimate tensile strengths, R m , absorbed energies in impact tests, K, and elongations after fracture - some energy-stress and energy-stress-elongation constructions-spaces have been plotted. These spaces can be used for general evaluation of the applied rolling technology and for prediction of steel-sheet mechanical behaviour . K EYWORDS . Hot Rolling; Low-Carbon steel S355J2; Rolled-sheet; Prediction of Steel-Sheet Mechanical Behaviour I NTRODUCTION evelopment of modern metallurgy and engineering is characterized not only by increasing production volume and enriching production range, but by sufficient improve in quality - increase of metal-product’s service life in combination with high reliability of structures machines and devices [1-3]. Industrial processing of metals (forming) by plastic deformation is one of the major and most important industries in the global economy. High quality metal product features a constant chemical composition, micro- and macrostructure, geometric shapes and sizes and guaranteed physical and mechanical properties. The quality of metal products depends primarily on their mechanical properties, their behavior in processing and exploitation, and their microstructure [1-5]. E XPERIMENTAL WORK AND RESULTS Conventional hot rolling technology for producing thick sheets hick sheets (30 mm and 40 mm) from a low-carbon steel, Steel S355J2+N, have been produced by normalization rolling in the Bulgarian Metallurgical Plant “STOMANA Industry SA” for more than 60 years [6-7]. The aim of this work is to investigate and control the technological process of forming of hot-rolled steel plate (sheet) of Steel S355J2+N in attempt to improve mechanical characteristics of the final product. D T