Solidification behaviour of laser welded type 21Cr–6Ni–9Mn stainless steel

Abstract

The solidification mode and microstructures were characterised for various processing parameters for laser welding 21Cr-6Ni-9Mn stainless steel. Two heats with varying nitrogen content showed both primary ferrite and primary austenite solidification. Weld ferrite content varied from 1 to 11 vol.-%, and decreased as travel speed increased. Base metal nitrogen content affected both solidification mode and weld ferrite content. Nitrogen loss from the weld pool was found to range from 10 to 45%, and decreased with increasing travel speed. Solidification mode was dependent on both chemical composition and processing parameters. The solidification mode shifted from primary ferrite to primary austenite as travel speed increased due to increased undercooling. Solidification mode varied within welds with constant nitrogen content, and the change in solidification mode was attributed to changes in undercooling along the weld cross-section. It is proposed that the variation of solidification mode with undercooling is affected by both the solidification rate and thermal gradient.

Microstructure evolution and mechanical properties of multiple-layer laser cladding coating of 308L stainless steel

“…Therefore, the cladding metals solidify in FA mode in theory. However, some studies [10,16,18] have pointed out with the increasing of the cooling rate, the stability of the austenite phase as the primary phase exceeds the ferrite phase because of the change of undercooling in the dendrite. Meanwhile, Lienert and Lippold [19] have also pointed out that if Creq/Nieq>1.69 (WRC-1992 equivalent formulas, where Creq = Cr + Mo + 0.7Nb, Nieq = Ni + 30C + 20N), the solidification of the primary phase is the δ ferrite for pulsed laser welding of austenitic stainless steel.…”

Effect of austenitic fillers on microstructural and mechanical properties of ultra-low nickel austenitic stainless steel

“…10 The phase transformation in fusion zone (FZ) of stainless steel weldments including solidification changes, ferrite–austenite transformation and carbide precipitation are controlled by the ratio of chromium equivalent (Cr eq ) to nickel equivalent (Ni eq ) and the cooling rate. 11, 12 Hence, the constitutional diagrams are the prime method for predicting solidification mode and δ -ferrite content by employing the Cr eq to Ni eq ratio. The WRC-1992 diagram is considered as one of the most accurate predictive diagram.…”

Welding metallurgy of stainless steels during resistance spot welding Part I: fusion zone

“…The phase transformations in FZ of stainless steel weldments including solidification transformations, ferrite–austenite transformation and carbide precipitation are controlled by the ratio of chromium equivalent to nickel equivalent (Cr eq /Ni eq ) and the cooling rate. 17–20 The cooling rate of RSW is significantly higher than that of the conventional arc welding processes. Gould et al 21 proposed a simple analytical model predicting cooling rates of resistance spot welds, as follows where α is thermal diffusivity of the steel sheets, T P is the maximum temperature experienced in FZ during welding process, t s is the sheet thickness, t E is the electrode face thicknesses (i.e.…”

“…[17][18][19][20] The cooling rate of RSW is significantly higher than that of the conventional arc welding processes. Gould et al 21 proposed a simple analytical model predicting cooling rates of resistance spot welds, as follows…”