Influence of Metallic Sodium on Repair Weldability for Type 316FR Stainless Steel

Abstract

The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to 7.99 mg/cm 2. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.

A generalised hot cracking criterion for nickel-based superalloys additively manufactured by electron beam melting

“…Solidification cracking operates in the solidification interval when the liquid to solid transformation takes place in the melt pool through the dendritic mode of solidification. This type of cracking is accompanied by a dendritic fracture surface, which are features that represent melting [21].…”

“…Liquation cracking occurs in the heat-affected zone (HAZ) [20][21][22] that affects the deposited layers exposed to reheating cycles during metal AM processes [23,24]. For additively manufactured Ni-based superalloy IN718, it was reported that the liquation cracks were accompanied with the precipitation of Laves phases which distinguishes them from precipitate-free solidification cracks [23].…”

Investigation of grain growth and microstructural evolution in electron beam melting additive manufacturing process

“…It is proposed, based on prior studies, that this region contains rapidly solidified liquid film that filled in the gaps between grains during the terminal stage of solidification[281]. The presence of such features implies that cracking occurred at the terminal stage of solidification, and not during the subsequent cooling stage, thus confirming this as a case of solidification cracking[138,140,152,282].…”

“…Solidification cracking operates in the solidification interval when the liquid to solid transformation takes place in the melt pool through the dendritic mode of solidification. This type of cracking is accompanied by a dendritic fracture surface with nearly no trace of melting [140]. Liquation cracking occurs in the Heat-Affected Zone (HAZ) [139][140][141] that affects the deposited layers exposed to reheating cycles during metal AM processes [142,143].…”

“…This type of cracking is accompanied by a dendritic fracture surface with nearly no trace of melting [140]. Liquation cracking occurs in the Heat-Affected Zone (HAZ) [139][140][141] that affects the deposited layers exposed to reheating cycles during metal AM processes [142,143]. For additively manufactured Ni-based superalloy IN718, it was reported that the liquation cracks were accompanied with the precipitation of Laves phases which distinguishes them from precipitate-free solidification cracks [142].…”