ANALYSIS OF THE SOLIDIFICATION PROCESS OF AUSTENITIC STAINLESS STEEL WELD METAL USING SYNCHROTRON RADIATION

A numerical model to predict the solidification microstructure and solidification cracking susceptibility of austenitic stainless steel weld metals was proposed. It was predicted using the developed numerical model that Fe-20 %Cr-14.4 %Ni, Fe-20 %Cr-12.7 %Ni, Fe-20 %Cr-11.5 %Ni and Fe-20 %Cr-9.8 %Ni weld metals solidified as A mode (L -> L + gamma ->gamma), AF mode (L -> L + gamma -> L + gamma + delta ->gamma + delta), FA mode (L -> L + delta -> L + delta + gamma ->delta + gamma) and FA mode, respectively. Also, it was found that the effect of Ni content on the solidification cracking susceptibility of Fe-20 %Cr-(9.8-14.4) %Ni weld metal, determined via trans-Varestraint testing, agreed with the results calculated using the model. In addition, in order to verify the validity of the developed numerical model, time-resolved in-situ observation of welding solidification process using synchrotron radiation has been carried out by changing the welding speed from 1 mm/s to 10 mm/s for Fe-20 %Cr-12.5 %Ni and Fe-20 %Cr-1 1.4 %Ni weld metals. It was found that the solidification mode of Fe-20 %Cr-12.5 %Ni weld metal transited from FA mode to AF mode by the higher welding speed and that of Fe-20 %Cr-11.4 %Ni weld metal maintained FA mode under the welding speed range of 1 mm/s to 10 mm/s. These results also coincided with the calculated results for Fe-20 %Cr-12.5 %Ni and Fe-20 %Cr-11.4 %Ni weld metals using the developed numerical model.