Effect of Zr addition on toughness and microstructure of coarse grained heat affected zone in Al deoxidised low carbon steel

Abstract

The effect of Zr addition on the toughness and microstructure of coarse grained heat affected zone (CGHAZ) in Al deoxidised low carbon steel was investigated. In this present work, the specimens (Zr free and Zr added) were subjected to weld thermal cycle with heat input of 54, 80 and 100 kJ cm 21 at 13508C peak temperature using thermal simulator. The typical inclusions were characterised by scanning electron microscopy, and the chemical composition of the inclusions was determined by energy dispersive spectroscopy. The nanoscale precipitates were analysed by transmission electron microscopy and energy dispersive spectroscopy. It was verified that the occurrence of Zr in steel mostly exists in the form of oxide inclusions, but a few in the form of solid solution state and Zr containing precipitates when the concentration of Zr is 0.015%. The improvement of CGHAZ toughness is obtained when the heat input is 80-100 kJ cm 21 . The possible reasons about the effects of Zr on the toughness of CGHAZ, including Zr containing inclusions, precipitates and microstructure characteristics, were also discussed.

Effect of Zr addition on toughness in the simulated heat-affected zone of high-titanium low-alloy steels

“…It was reported that TiN particles precipitated during steel solidification hindered the growth of the austenite grain by pinning at the grain boundary of austenites [7] and inducing the nucleation of Afs [8][9][10][11]. Titanium oxides [12][13][14][15], magnesium oxides [16][17][18], and zirconium oxides [19][20][21][22] in steels owing to the low misfit with ferrites were widely investigated. For example, the formation of the Mn-depletion zone on the surface of Ti 2 O 3 favoured the nucleation of Afs [13], and MgO particles had a low misfit with ferrites which reduced the nucleated energy barrier of Afs [23].…”