Overview of Intermetallic Sigma (𝜎) Phase Precipitation in Stainless Steels

Table 1

Chemical composition and lattice constant of the 𝜎 phase [10].

Alloy	Lattice parameter (Å)	Composition of phase (wt%)					Formula
		Fe	Cr	Ni	Mo	Si
Fe-Cr	𝑎0=8.799, 𝑐0=4.544						Fe-Cr
Fe-Mo	𝑎0=9.188, 𝑐0=4.812						Fe-Mo
17Cr-11Ni-2Mo-0.4Ti	—		30	4.3	9	0.8
17Cr-11Ni-0.9Mo-0.5Ti	—		33	4.5	5.4	0.7
Type 316	𝑎0= 8.28~8.38, 𝑐0= 4.597~4.599	55	29	5	11	—	(FeNi)x(CrMo)y
Type 316L	𝑎0=9.21, 𝑐0=4.78
20Cr-25-34Ni-6.5-8Mo	𝑎0=8.87, 𝑐0=4.61	35/37	17/26	15/21	21/28	—
25Cr-20Ni	—	40	46	9.4	—	3