Product Code: ICA10_1905

Joonas Pekkarinen, Lappeenranta University of Technology; Lappeenranta Finland
Veli Kujanpää, Lappeenranta University of Technology; VTT- Technical Research Centre of Finland; Lappeenranta Finland
Presented at ICALEO 2010

This study is focused to determine empirically, which microstructural changes occur in austenitic stainless steels when heat input is controlled by welding parameters. Test welds were done bead-on-plate without shielding gas using 5 kW fiber laser. In this study austenitic stainless steels used were 1.4372 (AISI 201), 1.4404 (AISI 316L)and 1.4547 (high-alloyed 6 % Mo). Two of these steels, 1.4372 and 1.4404, solidify usually as primary ferritic mode and 1.4547 solidifies as primary austenitic mode. As generally known, the microstructural properties austenitic stainless steels welds are dependent on solidification mode.
In this study it was noticed that the welding speed affects austenitic stainless steels welds microstructure. In 1.4372 and 1.4404 steels solidification mode was changed towards primary austenitic solidification mode when welding speed was increased caused by increase in weld solidification growth rate and cooling rate. For 1.4547 steel changes in microstructure were mostly concerned on micro segregation of molybdenum. It was noticed that micro segregation of molybdenum decreased when welding speed increased caused by finer microstructure.
In practice, chances in solidification mode effect on filled wire selection. When high welding speeds are used filled wire is desirable choose so that weld solidifies as primary ferritic mode. In that way chance of hot crack formation decreases significantly. Decrease of micro segregation at high welding speeds is beneficial because then it is possible to use lower alloyed filled wire than usually and still get sufficient molybdenum concentration through the whole weld.

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