Effect of Heat Input and Number of Passes on Microstructural Evolution of Duplex Stainless Steel Overlay Welds

Abstract

The effect of the cooling rate and the dilution in overlay welds with a duplex stainless steel, on a commercial low carbon steel sheet, by means of the semi-automatic welding process with shielding gas was studied. To study the effect of cooling rate and dilution, coupons were welded with 0.6; 0.9 and 1.8 kJ/mm (keeping the electrical parameters constant and varying the welding speed) with one and two layers. On the welded specimens, the chemical composition was measured, the phase content was quantified and the precipitation of intermetallic compounds was observed by optical microscopy, scanning electron and X-ray diffraction. The results show that, in the coupons welded with one layer, as the heat input increases, the ferrite content increases associated with the dilution decrease. On the other hand, in coupons welded with two layers (with low dilution values), the ferrite content decreases, associated with the cooling rate and the longer time available for the transformation of ferrite into austenite. The microstructural balance in Corrosion Resistance Alloy Overlay Welding with duplex stainless steels is controlled, mainly, by the degree of dilution for one layer and the heat provided for two layers.

Key-words:
Duplex stainless steels; Corrosion resistance alloy overlay; Cooling speed; Dilution; Microstructural balance