Author(s):
1. Ivana Ivanić, 1University of Zagreb, Faculty of Metallurgy Sisak, Croatia
2. Gorazd Kosec, Acroni d.o.o., Slovenia
3. Mirko Gojić, Croatia
4. Stjepan Kožuh, 1University of Zagreb, Faculty of Metallurgy Sisak, Croatia
5. Borut Kosec, University of Ljubljana, Faculty of Natural Science and Engineering, Slovenia

Abstract:
Niomol 490 K steel belongs to the group of High Strength Low Alloy Steel (HSLA). The aim of this study was to determine the transition temperature of the Charpy impact toughness of welded Niomol 490 K steel. The samples for testing of the Charpy impact toughness were heat treated in order to obtain different microstructures. Metallographic samples were prepared according to the classical procedure. For microstructure analysis an optical microscope and scanning electron microscope were used. Heating that appears at the deposition of the next welding layer was simulated by short heating into the two-phase region (austenite and ferrite). It is found that impact toughness is highly dependent on steels microstructure. The transition temperature of the Niomol 490 K steel in the initial state was about -67 ° C. After water quenching from 920 °C, the Charpy impact toughness of the upper level was reduced to about a half of the value than that of the steel in the initial state. After reheating to 750 °C, the toughness was reduced by approximately half of the value that in water quenched sample. The fracture surface in the region of a completely ductile fracture shows the areas of shear decohesion. The transition from the brittle to the ductile fracture shows that the crack propagation path expands with the plane slip to the first tiny dimples.

Key words:
High Strength Low Alloy Steel, welding, microstructure

Thematic field:
SYMPOSIUM A - Science of matter, condensed matter and physics of solid states

Date of abstract submission:
25.07.2018.

Conference:
Contemporary Materials 2018 - Savremeni Materijali

Applied paper from author