Enhancement Mechanism of Cerium in 316LN Austenitic Stainless Steel During Creep at 700 °C

doi:10.1007/s40195-022-01467-7

Abstract

Abstract:

Effect of cerium (Ce) on creep strength and microstructure of 316LN austenitic stainless steel (316LN steel) at 700 °C/150 MPa was investigated by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and thermodynamic calculations. Addition of 0.032 wt% Ce to 316LN steel results in a prominent increase in creep life from 313 to 556 h. Ce enriches in titanium nitride nanoparticles, increases slightly the activity and diffusion coefficient of Mo, and facilitates the formation of fine and dense intragranular Laves phase precipitates. Thus the creep strength is remarkably enhanced by Ce addition in 316LN steel through the intragranular Laves phase precipitation strengthening. It reveals a new insight into the improvement effect of rare earth (RE) elements such as Ce on creep strength of austenitic stainless steels, which inspired the design of RE-microalloying heat-resistant steels.

Key words: 316LN austenitic stainless steel, Rare earth, Creep, Laves phase, Precipitation strengthening

Renxian Yang, Xin Cai, Leigang Zheng, Xiaoqiang Hu, Dianzhong Li. Enhancement Mechanism of Cerium in 316LN Austenitic Stainless Steel During Creep at 700 °C[J]. Acta Metallurgica Sinica (English Letters), 2023, 36(3): 507-512.

Figures/Tables 5

Table 1 Compositions of two studied 316LN steels (wt%)

Steel	C	Si	Mn	Cr	Mo	Ni	Ce	N	Fe
LN0	0.010	0.31	1.63	17.73	2.77	13.76	-	0.13	Bal.
LN1	0.013	0.26	1.80	17.76	2.83	13.65	0.032	0.13	Bal.

Fig. 1 Creep strain versus time curves a and creep rate versus time curves b at 700 °C/150 MPa. [Inset in a is the enlarged view of the black box showing the negligible primary creep stage]

Fig. 2 SEM images of the microstructure in LN0 steel after 5% a, 10% c, 20% e interrupt crept and rupture crept g, and that in LN1 steel after 5% b, 10% d, 20% f interrupt crept and rupture crept h

Fig. 3 STEM micrographs of the intragranular precipitates in LN1 steel after interrupt crept at 20% strain a and the enlarged view of an intragranular precipitate b corresponding with selected area diffraction pattern (SADP) c, elemental concentration distribution of Mo d and Si e; STEM images of an individual nanoparticle within matrix in LN1 steel after crept rupture at 700 °C/150 MPa f together with EDS line scanning analyses g. [Yellow arrows in a, b represent nucleus of intragranular particles, while black arrow in f marks the position of an EDS scanning line]

Fig. 4 Chemical driving force of Laves phase variation with Mo fraction a and the dependence of Ce content on the activity and diffusion coefficient of Mo b, calculated by Thermo-Calc software at 700 °C

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