Phase evolution of AISI 321 stainless steel during directional solidification

Abstract

The phase evolution of AISI 321 stainless steel was studied by directional solidification and quenching techniques. Two interfaces, solid/liquid and the peritectic reaction interface, were found to exist in the directional solidification structure. With increasing growth velocity the solid/ liquid interface changed in the sequence of planar, cellular, dendritic and the primary phase changed from austenite to ferrite. The phase and morphology selection was verified by the interface response functions (IRFs) and the maximum growth temperature criterion. The ferritic island banding structure was observed, not only in the austenite cellular primary growth condition (3 mm s 21 ), but also in the dendritic ferrite primary growth one at relatively low growth velocity (5 mm s 21 ). It is deemed that the former resulted from the nucleation of ferrite in the continuous matrix of austenite phase, yet the latter is the residual primary ferrite attributed to the growth of austenite. Both of them do not come from the nucleation near the solid/liquid interface.

Microstructure and volume shrinkage during directional solidification of peritectic steel

“…The region with the largest volume shrinkage drew closer to the ZST-ZDT brittle zone, increasing the crack-formation tendency of peritectic steel. (7) We proposed a novel explanation for the regulation mechanism. The reduced cooling rate of the initial solidification during the continuous casting of peritectic steel delayed a massive type of peritectic transformation away from the ZST-ZDT brittle zone, reducing the probability of crack formation…”

“…Mazumder and Trivedi [6] concluded that the tree-like structure resulted from the coupling between convection and phase transitions at the leading edge of the solid-liquid interface. Liang et al [7] studied the phase evolution of AISI 321 stainless steel by directional solidification and found that two interfaces, a solid/liquid and a peritectic reaction interface, exist in the directionally solidified structure.…”

Effect of Titanium Addition on As-Cast Structure and High-Temperature Tensile Property of 20Cr-8Ni Stainless Steel for Heavy Castings

“…The equilibrium solidification model of ingot S1 was the FA model (liquid → liquid + δ-ferrite → liquid + δ-ferrite + γ-austenite → δ-ferrite + γ-austenite). Liang et al also indicated that the equilibrium solidification model of AISI 321 stainless steel was the FA model, according to the ratio of Ni equivalent and Cr equivalent [33]. In ingot S2 and ingot S3, the austenite formed after solidification, and the equilibrium solidification model was the F model (liquid → liquid + δ-ferrite → δ-ferrite).…”

Directionally solidified structure of peritectic steel

“…A peritectic alloy is an alloy with peritectic phase transformation during solidification, such as Fe-C, Cu-Zn, Pb-Bi, Ti-Al, Fe-Cr-Ni and Nd-Fe-B. Owing to its unique mechanical properties and functional characteristics, it is extensively applied in mechanics, buildings, oceans, superconductor engineering, and other fields [1][2][3][4][5]. The peritectic phase transformation occurs during the solidification of peritectic alloys, involving the nucleation, competition, and growth of parent and peritectic phases with different physical characteristics.…”