Steady-State Creep Behavior of Super304H Austenitic Steel at Elevated Temperatures

doi:10.1007/s40195-015-0331-8

Abstract

Abstract:

Creep behavior of Super304H austenitic steel has been investigated at elevated temperatures of 923-973 K and at applied stress of 190-210 MPa. The results show that the apparent stress exponent and activation energy in the creep deformation range from 16.2 to 27.4 and from 602.1 to 769.3 kJ/mol at different temperatures, respectively. These high values imply the presence of a threshold stress due to an interaction between the dislocations and Cu-rich precipitates during creep deformation. The creep mechanism is associated with the dislocation climbing governed by the matrix lattice diffusion. The origin of the threshold stress is mainly attributed to the coherency strain induced in the matrix by Cu-rich precipitates. The theoretically estimated threshold stresses from Cu-rich precipitates agree reasonably with the experimental results.

Key words: Super304H steel, Cu-rich precipitate, Creep, Threshold stress

Ping Ou, Long Li, Xing-Fei Xie, Jian Sun. Steady-State Creep Behavior of Super304H Austenitic Steel at Elevated Temperatures[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(11): 1336-1343.

Figures/Tables 11

Table 1 Chemical composition of the Super304H steel (wt%)

C	Mn	P	S	Si	Ni	Cr	Cu	Nb	N	Al	B	Fe
0.08	0.787	0.022	0.001	0.29	8.88	17.98	3.066	0.58	0.07	0.012	0.0026	Bal.

Fig. 1 SEM microstructure of the aged Super304H steel a and EDS result of the primary MX particles b

Fig. 2 Diffraction contrast image of Cu-rich precipitates in Super304H steel aged at 973 K for 500 h

Fig. 3 High-resolution TEM image a and corresponding FFT diffractogram b of Cu-rich precipitate in Super304H steel aged at 973 K for 500 h

Table 2 Young’s modulus, shear modulus of the austenitic matrix and experimental threshold stress σ th at different temperatures

Temperature (K)	E (GPa)	μ (GPa)	Experimental σ _th (MPa)
923	138	53.5	162.7
948	136	52.7	152.9
973	134	51.9	137.4

Fig. 4 Plots of \(\ln \dot{\varepsilon }\) versus \(\ln (\sigma /\mu )\) for the Super304H steel crept at different temperatures

Fig. 5 Plots of \(\ln \dot{\varepsilon }\) versus 1/T for the Super304H steel crept at different applied stresses

Fig. 6 Plots of \(\dot{\varepsilon }^{1/5}\) versus σ for the Super304H steel crept at different temperatures

Fig. 7 Plot of \(\ln (\dot{\varepsilon }/D)\) versus \(\ln [(\sigma - \sigma_{\text{th}} )/\mu ]\) for the Super304H steel

Fig. 8 Plot of \(\ln (\sigma_{\text{th}} /\mu )\) versus 1/T for the Super304H steel

Table 3 Bulk modulus of the Cu-rich precipitate, lattice parameter mismatch and coherency strain between the Cu-rich precipitate and austenitic matrix, Burgers vector of the austenitic matrix, theoretical threshold stress σ th and Orowan stress σ Or at different temperatures

Temperature (K)	B (GPa)	δ (%)	ε (%)	b (nm)	Theoretical σ _th (MPa)	σ _Or (MPa)
923	110.2	0.487	0.2975	0.2574	159.3	250.8
948	109.3	0.488	0.2982	0.2576	157.3	247.3
973	108.0	0.485	0.2925	0.2577	152.0	243.6

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