Abstract
Solidification cracking is a significant problem during the welding of fully austenitic stainless steels. The present work is considered as the first trial to investigate and propose a mechanism of hot cracking formation when welding the Fan-shaped cracking test specimen, using the pulsed current gas tungsten arc welding process (PCGTAW). The specimen lateral expansions perpendicular to welding line due to thermal effects, plus the transverse expansion due to crack opening are sensed and recorded to detect the crack behavior with time. The stages of crack formation are filmed by a high-speed photography of the weld pool and solidification process at a speed of about 1000 fps. Additionally, some microscopic examinations using Scanning Electron Microscope (SEM) and Electron Probe Micro-Analyzer (EPMA) are performed on the welds. The results helped in establishing a proposed mechanism for the formation of hot cracks in full–austenitic stainless steel welds done on a Fan-shaped test specimen. The proposed mechanism suggests three stages during hot cracking formation; the crack initiation, propagation, and ceasing. The occurrence of a hot crack during welding mainly depends on the way by which the molten zone solidifies, and which solid phase will primarily solidify. This affects, in turn, the segregation of the chemical elements, which found to have a great role in crack initiation. Moreover, the weld metal structure type, together with the thermal stresses in conjunction with the applied strains on the weld joint play a great role in the crack expansion and ceasing. The present work is considered the first trial done to propose a mechanism of hot-cracking formation during welding the Fan-Shaped test specimen using Pulsed-Current Gas Tungsten Arc welding process.
Highlights
Hot cracking or solidification cracking has been investigated in castings, Pellini [1] and Won et al [2] and in welds, Medovar [3] for several decades
The results of the accurate experimental observations and measures on the crack formation of Fan-Shaped specimen; which clearly demonstrate that the solidification cracking of this specimen is a result of the accumulation of macroscopic tensile cross-strains in a microscopic inter-granular liquid film of segregation at the final stage of the weld metal solidification
Investigated points A to D are chosen on the following grain boundaries; at crack site, on fusion zone vicinity, on heat affected zone, as well as on the base metal as shown in the figure
Summary
Hot cracking or solidification cracking has been investigated in castings, Pellini [1] and Won et al [2] and in welds, Medovar [3] for several decades. Hot cracking refers to cracking that occurs during solidification of welding, casting at temperatures close to the melting point of the material. Houldcroft [7], due to its simplicity, reproducibility, and effectiveness (cracking sensitivity) It does not require special equipment as it is a selfrestraint specimen, where variable degree of strains along the axis of the specimen are generated [8, 9]. Of many researches had been involved to study – in general- the hot cracking mechanisms during welding, the present work is considered the first trial to investigate and propose a hot-cracking mechanism when welding the FanShaped specimen using the PCGTAW process
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