Key Takeaways & Executive Findings
- •• The hot deformation behavior of 2707 HDSS was characterized by a balance between work hardening and dynamic recovery at low strains, followed by distinct softening mechanisms depending on strain rate. • Dynamic recovery dominates at high strain rates, while dynamic recrystallization becomes prevalent at medium and low strain rates, with ferrite completing dynamic recrystallization at 1 s-1. • The deformation activation energy was determined as 645.46 kJ·mol-1, and the hot processing map at strain 0.8 indicates reduced hot workability due to high alloying content. • Microstructural analysis reveals that austenite softening is influenced by ferrite, primarily undergoing dynamic recovery, but austenite at α/γ phase boundaries tends to dynamically recrystallize.
Abstract
The hot deformation behavior of 2707 hyper duplex stainless steel (HDSS) was investigated through a hot compression test at 950 °C to 1,250 °C at strain rates of 0.01 s-1 to 10 s-1. Observations from the flow stress curves reveal a balance between work hardening and dynamic recovery at the beginning of the deformation and subsequently demonstrate various softening mechanisms with the increase of strain. At high strain rates, dynamic recovery is the prevailing mechanism, whereas, at medium and low strain rates, dynamic recrystallization becomes dominant. The constitutive equation was constructed, and the deformation activation energy was calculated to be 645.46 kJ·mol-1. The hot processing map was drawn based on the dynamic material model at a strain of 0.8. The results indicate that the hot workability of 2707 HDSS decreases due to its high alloying content. The microstructure evolution of 2707 HDSS at 1,050 °C was identified by means of electron backscatter diffraction and transmission electron microscopy. The results demonstrate that the ferrite completes dynamic recrystallization at the strain rate of 1 s-1. The softening process of austenite is influenced by ferrite and mainly experiences dynamic recovery. The austenite located at the α/γ phase boundaries tends to undergo dynamic recrystallization.
1. Introduction
Hyper duplex stainless steel (HDSS) 2707 contains two main phases, austenite (γ) and ferrite (α), which have different hot deformation behaviors due to different softening mechanisms [1]. As a new steel, 2707 HDSS contains higher content of Cr than 2507 and 2205 super duplex stainless steels (SDSS). Thus, the 2707 HDSS has better corrosion resistance and higher strength than 2507 and 2205 SDSS [2]. Due to the excellent mechanical properties of 2707 HDSS, it can serve as a cost-effective substitute for super austenitic stainless steel in extremely corrosive environments [3-5].
Deformation temperature and strain rates are the main factors influencing the hot deformation of duplex stainless steel [6]. In the temperature range of hot deformation, the γ and α phases have different softening mechanisms [7]. Kang et al. [6] studied the hot deformation behavior of S32760 SDSS by combining thermal simulation tests with model verification. Results show that phase fraction is an important factor affecting the hot deformation behavior of the materials. Besides, it is commonly considered that ferrite would undergo dynamic recovery due to the high stacking fault energy [8], while austenite owning low stacking fault energy would undergo dynamic recrystallization [9].
A study on the thermal processing of 2205 DSS at low strain rates was conducted by Momeni et al [10]. Experimental results showed that at high deformation temperatures, ferrite underwent dynamic recovery and transformed into continuous dynamic recrystallization, while the dynamic recrystallization of austenite was delayed due to the influence of phase boundaries. Kingklang et al. [11] investigated the hot working behavior of 2507 SDSS and found that the optimum process window was at a temperature range of 1,000-1,100 °C and a strain rate of 0.1-1 s-1. Moreover, they found that the primary softening mechanism at high temperature of 1,200 °C was the dynamic recrystallization in the austenite. Chen et al. [12] investigated the hot processing characteristics of 2205 DSS and determined that the optimal processing window of the tested steel was 1,373-1,473 K and 0.01 s-1.
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Ai-qin Wang, Pei Liu, Chen-lu Liu, Hang Wang, Jing-pei Xie (2025). Hot deformation behavior of 2707 hyper duplex stainless steel. China Foundry. https://doi.org/10.1007/s41230-025-3078-5
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Frequently Asked Questions
What is the deformation activation energy of 2707 hyper duplex stainless steel?
The deformation activation energy of 2707 HDSS was calculated to be 645.46 kJ·mol-1.
What are the dominant softening mechanisms in 2707 HDSS at different strain rates?
At high strain rates, dynamic recovery prevails, while at medium and low strain rates, dynamic recrystallization becomes dominant.
How does the high alloying content affect the hot workability of 2707 HDSS?
The high alloying content decreases the hot workability of 2707 HDSS, as indicated by the hot processing map.
What is the optimal processing window for 2707 HDSS?
The paper does not specify an optimal processing window for 2707 HDSS, but it provides a hot processing map at strain 0.8 that can be used to identify suitable conditions.
What microstructural changes occur in ferrite and austenite during hot deformation?
Ferrite completes dynamic recrystallization at a strain rate of 1 s-1, while austenite mainly undergoes dynamic recovery, but austenite at α/γ phase boundaries tends to dynamically recrystallize.
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