Effect of tip velocity on weld solidification process of hot-work tool steel

In order to clarify the effect of tip velocity on the weld solidification process of hot-work tool steel (SKD61) during welding, information about microstructure evolution was obtained by the combination of a liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. From the experimental results, it was found that the solidification mode was changed from FA mode (L → L+δ → L+δ+γ → L+γ → γ) to A mode (L → L+γ → γ) at high tip velocity. Moreover, the effect of tip velocity on the microstructure selection during solidification between the primary δ, ferrite and the primary γ, austenite was theoretically proven by the Kurz, Giovanola and Trivedi model. Therefore, it was understood that the solidification cracking susceptibility of hot-work tool steel (SKD61) weld metal was increased due to the δ to γ transition of the primary phase.