Sammendrag
Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (
Vis fullstendig beskrivelse
