Influence of isothermal aging on σ precipitation in super duplex stainless steel

Abstract

The time-temperature-transformation (TTT) curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on σ precipitation was studied by metallographic observation, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000°C, especially in the range of 800-900°C. The longer the aging time, the higher the amount of σ precipitation. The area fraction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850°C is the most sensitive transaction temperature, the incubation time for the formation of σ precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The σ phase is formed preferentially at the α/α/γ junction, and then grows along the α/α boundary in the matrix.

Evaluation of the of isothermal phases transformations and hardness measurements in SAF 2507 super duplex using Pulsed Eddy Currents

“…Figure 2b shows the microstructure for specimen (S-5), which was subjected to an isothermal treatment at 900°C for 5 minutes. During this time, the microstructure did not undergo signi cant transformations, such as the presence of deleterious phases, which is in agreement with the response found in the TTT diagram in the work of [37]. The precipitation of deleterious phases and other changes are seen in specimen (S-15) as shown in Fig.…”

A Comprehensive Material Model for the Super-Duplex Stainless Steel SAF2507 in a Welding Environment

“…In the case of welding, not every phase or precipitation needs to be considered, since several phases, such as, for example, the σ phase, need more time to form than is available during welding [17,18].…”

Effect of solution treatment on microstructure and properties of 00Cr32Ni7Mo3.5N

“…The σ phase is hard and brittle, and it is the most harmful precipitation phase in steel, which can significantly reduce the plasticity of steel [6][7][8][9]. Amit [7] and Wang [10] et al believed that it is the slow cooling rate during forging that transforms δ phase to σ phase, and the precipitation of σ phase in this process damages the hot workability. It was observed that the high content of α-phase stabilising elements in SAF3207, such as Cr, Mo, and Ni, can promote the precipitation of σ phase, making the hot workability problems more typical [4,11].…”