Transformation of the δ-Ferrite in SS2343 Austenitic Stainless Steel upon Annealing at 1050 °C, 1150 °C and 1250 °C

Abstract

The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the volume fraction of δ-ferrite in the as-cast state and its transformation after subsequent annealing were investigated. Monitoring of morphological transformations of δ-ferrite in the microstructure show the progress of δ-ferrite dissolution. Annealing tests were conducted at 1050 °C, 1150 °C and 1250 °C with soaking times of 5 and 40 min. The thermodynamic prediction and metallographic identification of δ-ferrite are presented. The ferrite fractions were measured using a magnetic method and determined to be in the range between 10.7% and 14.6%. The volume share of δ-ferrite decreased with an increase in temperature and the time of annealing. About 50–55% the δ-ferrite was effectively transformed. The δ-ferrite phase, originally present in a dendritic morphology, tends to break up and spheroidize. The morphology varies from vermicular, lacy and acicular shapes to globular for higher temperatures and for longer exposure times. In the δ-ferrite after annealing, concentrations of Cr and Mo decrease, and conversely the concentration of Ni increase, all by small, but significant, amounts. The observed changes in the solute concentration can be explained in terms of the transformation of ferrite into austenite and sigma phases.

Heat Treatment of Iron- and Aluminum-Based Alloys

“…This study identified the key factors in designing optimal welding processes that avoid any secondary phase precipitation in the weld bead, as well as in the heat-affected zone. In [2,3], thermodynamic calculations were used, and the numerical results were in good agreement with the experimental results. This underlines the important role of simulations in the study of heat treatments.…”

“…Arh et al [2] investigated the solidification behavior of laboratory-cast austenitic SS2343 stainless steel in terms of the volume fraction of δ-ferrite in the as-cast state, and its transformation after subsequent annealing. Their study suggests different types of annealing to reduce the δ-ferrite content by approximately 50%.…”

Deformation-Induced Martensitic Transformation in Laser Cladded 304 Stainless Steel Coatings

“…Based on these element mappings, the dendritic structure can be recognized, and it can be seen that there was a Cr-rich, Ni-depleted, and in comparison, a lower Cr, Ni-rich region, Figure 4c,d. This constellation indicates δ-ferrite for the Cr-rich region, since it shows a very low solubility for Ni [22]. Accordingly, the second phase should be γ-austenite enriched with Ni, which is stabilized by the high Ni contents.…”

“…the dendritic structure can be recognized, and it can be seen that there was a Cr-rich, Nidepleted, and in comparison, a lower Cr, Ni-rich region, Figure 4c,d. This constellation indicates δ-ferrite for the Cr-rich region, since it shows a very low solubility for Ni [22].…”

Effects of Stabilization Heat Treatment on Microstructure and Mechanical Properties of Si-Bearing 15Cr–9Ni–Nb Austenitic Stainless Steel Weld Metal

“…It can be seen that the original large piece of δ ferrite has been mostly transformed into austenite, and the δ/γ interface has disappeared, leaving the precipitations originally located at the interfaces. The δ → γ transition during heat treatment has been observed in some studies [19]. The diffusion of elements across the δ/γ interfaces controlled the δ → γ transition [20].…”