In-Situ Observation of Growth Behavior of Niobium Carbide during Dual-Phase Rapid Solidification of SUS347H

Abstract

In order to improve solidification cracking susceptibility, the crystallization of a heterophase such as the niobium carbide in the brittle temperature range is one of the effective techniques. In such a system, not only the growth behavior of dendrites during the rapid cooling but also the crystallization behavior of heterophase is very important. Therefore, diffraction patterns of a dual-phase mode Nb-bearing stainless steel during rapid cooling were investigated by in-situ two-dimensional time-resolved X-ray diffraction for the first time in order to reveal the microstructure formation. We discuss the growth behavior of dendrites with crystallization of niobium carbides. Subsequently, the niobium carbide formed epitaxially to the dendrite of the preferred in-plane orientation, having a small distorted orientation. With undercooling of several degree Celsius, the coherent growth on the d-ferrite was stable for niobium carbide.

Analysis of crystallisation and growth behaviour of NbC on solidification process of SUS347H weld metal

“…2. From in situ observations by synchrotron radiation of the behaviour of welding solidification of Fe-18Cr-1Nb-0?2C- (5)(6)(7)(8)(9)(10)(11)(12)Ni weld metal, it was found that 5%Ni weld metal solidified as FA mode and NbC crystallised at temperatures 60-70 K below the initiation of solidification. Similarly, 8%Ni weld metal also solidified as FA mode and NbC crystallised at temperatures 70-80 K below the initiation of solidification.…”

“…First, it was assumed that c/NbC eutectic phase consisted of the phase fraction of c phase df c and that of NbC df NbC . In this case, the overall differential mass balance between df c and df NbC is given by 24,25 df c zdf NbC ~{df L (12) The mass balance for Nb is given by…”

“…Furthermore, from Nb concentration C L Nb estimated as the solution of equation ( 20), the phase ratio of NbC df NbC in c/NbC eutectic phase is obtained by solving equation (19). Therefore, by substituting equation (12) and the phase ratio of NbC df NbC into equation ( 21), the following differential equation for the concentration of solute i other than Nb and C in liquid phase during c/ NbC eutectic solidification is developed…”

“…In this study, first, in order to investigate the solidification process of SUS347H weld metal, the behaviours of the phase selection among d, c and NbC phases during welding solidification process were investigated by in situ observations of welding solidification process. [3][4][5][6][7][8][9][10][11][12][13] Second, in order to predict the change in microsegregation in the liquid phase during welding solidification of SUS347H steel, a new numerical model in which the crystallisations of d, c and NbC phases were developed. Third, the validity of the developed numerical model was verified by the comparison of the experimental results from the in situ observation with the calculated results.…”

Analysis of crystallization and growth behavior of NbC on solidification process of SUS347H weld metal

“…Nb C In order to investigate the solidification cracking susceptibilities of SUS347H weld metal containing high niobium and carbon contents, it is important to analyze the crystallization behaviors of not only and phases but also niobium carbide during welding solidification. In the present study, the behavior of the phase selection for , phase and niobium carbide on Fe-18%Cr-0.2%C-1%Nb- (5)(6)(7)(8)(9)(10)(11)(12)%Ni weld metals during welding solidification was investigated by the developed in-situ observation technique of welding solidification process using synchrotron radiation. On the other hand, to evaluate the micro segregation in liquid phase on SUS347H weld metal during welding solidification, which has influence on the solidification cracking susceptibility, the numerical model to calculate the micro segregation in liquid phase considering the crystallization of , and niobium carbide was developed.…”