A Novel Cu-Modified 20Cr Lean Duplex Stainless Steel with Exceptional Combination of Mechanical Properties and Corrosion Resistance

doi:10.1007/s40195-025-01864-8

Abstract

Abstract:

Over the past few years, the Cu element has attracted much attention in duplex stainless steels. It undoubtedly holds advantageous in regulating the two-phase proportion and austenite stability and is also one of the crucial factors affecting the corrosion resistance. However, the systematic research on the impact of Cu addition to lean duplex stainless steels remains insufficient. In this study, a novel Cu-alloyed Mn-N-type 20Cr lean duplex stainless steel was developed and the effect of Cu on the strain hardening capacity and corrosion resistance was analyzed. The results show that the Cu addition increases the volume fraction and stability of the austenite, retards the martensitic transformation, and extends the transformation-induced plasticity effect to a wider strain range. Compared to the Cu-free steel, the plasticity of Cu-containing steel can be increased by ~ 26%. Additionally, the addition of Cu redistributes the Cr and N elements in the ferrite and austenite phases, thereby improving the corrosion resistance of the lean duplex stainless steel.

Key words: Lean duplex stainless steel, Alloying, Strain hardening behavior, Phase transformation, Corrosion

Zheng-Hong Liu, Ying Han, Jia-Peng Sun, Ming-Kun Jiang, Ying Song, Guo-Qing Zu, Xu Ran. A Novel Cu-Modified 20Cr Lean Duplex Stainless Steel with Exceptional Combination of Mechanical Properties and Corrosion Resistance[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(8): 1361-1370.

Figures/Tables 14

Table 1 Chemical composition of the 20Cr LDSSs in this study (wt%)

Steel	C	Cr	Mn	Ni	Si	N	Cu	Fe
2Cu	0.02	20.11	3.16	0.95	0.33	0.25	2.08	Bal.
0Cu	0.02	20.33	3.08	0.98	0.32	0.24	-	Bal.

Fig. 1 EBSD microstructures of the experimental steels after full recrystallization annealed at 1000 °C: a and c IPF maps, b and d phase maps (red-BCC, green-FCC); a and b 0Cu steel, c and d 2Cu steel

Fig. 2 a Overall grain size distribution and b the austenite grain size distribution of the experimental steels

Fig. 3 a Variation of engineering stress-strain curves and b the detailed mechanical performance indicators of the experimental steels at room temperature

Fig. 4 Variation of true stress-strain curves and the corresponding strain hardening rate curves of the experimental steels at room temperature

Fig. 5 EBSD phase maps and corresponding KAM maps of the experimental steels after tensile interruption tests (ε = ~ 0.23): a 0Cu steel and b 2Cu steel

Fig. 6 The EBSD phase maps and corresponding KAM maps of the experimental steels after fracture: a 0Cu steel and b 2Cu steel

Table 2 Chemical composition of the ferrite and austenite in the experimental steels (wt%)

Steel	Phase	C*	N*	Si	Cr	Mn	Ni	Cu
0Cu	γ	0.027	0.31	0.306	19.72	3.79	1.22	-
0Cu	α	0.0017	0.02	0.382	22.12	3.25	0.87	-
2Cu	γ	0.027	0.33	0.313	19.88	3.77	1.22	1.86
2Cu	α	0.0017	0.02	0.386	22.68	3.29	0.85	1.49

Fig. 7 TEM micrographs of the deformed 0Cu steel: a ε = ~ 0.23, b-d tensile fracture

Fig. 8 TEM micrographs of the deformed 2Cu steel: a-c ε = ~ 0.23, d tensile failure

Fig. 9 Schematic diagram of austenite deformation mechanism for the experimental steels

Fig. 10 Potentiodynamic polarization curves of the experimental steels in 3.5 wt% NaCl solution

Table 3 Electrochemical parameters obtained from the potentiodynamic polarization curves of the experimental steels tested in 3.5 wt% NaCl solution

Steel	i_corr (mA/cm²)	E_corr (mV)	E_b (mV)
0Cu	0.01634	− 874.08	− 10.82
2Cu	1.51 × 10^-3	− 441.17	962.15

Fig. 11 OM images of pitting corrosion surfaces in the experimental steels: a 0Cu steel and b 2Cu steel

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