Microstructure and hardness of welded low-carbon steel

Zavarivanje je interdisciplinarna tehnologija spajanja istovrsnih ili raznovrsnih materijala, taljenjem ili pritiskom, sa ili bez dodavanja dodatnog materijala. Cilj provođenja zavarivanja je da se dobije homogen zavareni spoj. Postupci elektrolučnog zavarivanja su bili među prvim postupcima koji su se razvili u 20. stoljeću. U ovom radu provedeno je proučavanje literature koja opisuje teorijske osnove različitih postupaka zavarivanja. Posebna pažnja je posvećena detaljnom proučavanju postupka zavarivanja netaljivom elektrodom pod zaštitom plina (TIG). U eksperimentalnom dijelu rada samostalno je provedeno zavarivanje niskougljičnog čelika st 35.8 (Č.1214, DIN17175, W. Nr. 1.0305, EN-P235GH) TIG postupkom. Nakon zavarivanja provedena je analiza mikrostrukture optičkim mikroskopom. Mikrostrukturna analiza je provedena na osnovnom materijalu, zoni utjecaja topline i zoni taljenja. Uočeno je da osnovni materijal imaferitno-perlitnu mikrostrukturu, dok je u zoni utjecaja topline prisutna također feritno-perlitna mikrostruktura s mjestimično prisutnim Widmanstattenovim feritom. U zoni taljenja zamijećena je lijevana mikrostruktura koja se sastoji od ferita i bainita. Zona taljenja je pokazala najveće vrijednosti tvrdoće (228,7 HV10).Welding is an interdisciplinary technology of joining identical or diverse materials, by melting or pressing, with or without the addition of additional material. The aim of process welding is to obtain a homogeneous welded joint. Arc welding processes were among the first processes to be developed in the 20th century. In this thesis, a study of the literature describing the theoretical foundations of different welding procedures was obtained. Special attention is paid to the detailed study of the process of welding with a non-fusible electrode under gas protection (TIG). In the experimental part of the work, low-carbon steel st 35.8 (Č.1214, DIN17175, W. Nr. 1.0305, EN-P235GH) was independently welded by TIG process. After welding, microstructure analysis was performed with an optical microscope. Microstructural analysis was performed on the base material, the heat affected zone and the melting zone. It was observed that the base material has a ferrite-perlite microstructure, while in the heat affected zone a ferrite-perlite microstructure with Widmanstatten ferrite is also present in places. A cast microstructure consisting of ferrite and bainite was observed in the melting zone. The melting zone showed the highest hardness values (228.7 HV10)