Effects of Silicon on the Microstructure and Mechanical Properties of 15-15Ti Stainless Steel

doi:10.1007/s40195-020-01068-2

Abstract

Abstract:

Effects of silicon on the microstructure and mechanical properties of 20% cold-worked 15-15Ti austenitic stainless steels are systemically investigated by uniaxial tensile tests, scanning and transmission electron microscope observations, and strength calculations. The results reveal that a large number of deformation twins are formed in the 20% cold-worked steels with various silicon additions. The volume fraction of deformation twins and the density of dislocations increase with silicon content, while the twin thickness slightly decreases. A better strength-ductility combination is achieved by silicon addition, since the yield strength of the steel with 2% silicon is 61 MPa higher than that of the steel with 1% silicon, while their uniform elongations are almost both equal to 16%. The yield strength of the 15-15Ti stainless steels is predominantly contributed by the solid solution, dislocation and deformation twin strengthening effects, which can be enhanced by silicon addition.

Key words: Austenitic stainless steel, Silicon, Microstructure, Mechanical property

Hao-Yu Yi, Tian Liang, Min Wang, Xiang-Dong Zha, Ying-Che Ma, Kui Liu. Effects of Silicon on the Microstructure and Mechanical Properties of 15-15Ti Stainless Steel[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(11): 1583-1590.

Figures/Tables 13

Table 1 Chemical compositions of steels investigated (wt%)

	Si	Ni	Cr	Mn	Ti	Mo	C	Fe
R1	1	15	17	1.5	0.36	1.5	0.06	Bal
R2	1.5	15	17	1.5	0.36	1.5	0.06	Bal
R3	2.0	15	17	1.5	0.36	1.5	0.06	Bal

Fig. 1 Typical OM microstructures of the 15-15Ti SS samples: a R1; b R2; c R3

Fig. 2 Typical XRD profiles of the 15-15Ti SS samples

Table 2 XRD characterization results of steels investigated

	D (nm)	\(\varepsilon\)	b (nm)
R1	113.3	0.254112	0.25
R2	103.8	0.197435	0.25
R3	85.4	0.170405	0.25

Fig. 3 Typical SEM microstructures of the 15-15Ti SS samples: a R1; b R2; c R3

Fig. 4 Typical microstructures of the 15-15Ti SS samples: deformation twin lamella of a R1, b R2 with SAED pattern (inset) and c R3; TiC particles in the d dislocation region with SAED pattern (inset) and in the e deformation twin region of R2; Cr23C6 particle with SAED pattern (inset) on the f grain boundaries of R2; g typical dislocation structure in R3

Fig. 5 Tensile engineering stress-strain curves of the 15-15Ti SS with various silicon contents

Table 3 Microstructure characteristic parameters of steels investigated

	Grain size d (μm)	SPP size, x (nm)	SPP content, f_spp (vol%)	Twin thickness, t (nm)	Twin content, f_T (vol%)	Dislocation density, ρ (10¹⁴ m^-2)
R1	17.7 ± 1.2	233 ± 13	0.22 ± 0.03	11.5 ± 4.6	8.9 ± 3.1	4.36
R2	17.3 ± 1.0	234 ± 21	0.18 ± 0.03	12.0 ± 3.9	10.3 ± 2.7	5.13
R3	20.9 ± 1.5	269 ± 33	0.23 ± 0.04	10.0 ± 3.2	11.5 ± 2.8	5.48

Table 4 Free contents of carbon and titanium of steels investigated (wt%)

	Free [C]	Free [Ti]
R1	0.032	0.25
R2	0.037	0.27
R3	0.031	0.24

Table 5 Values of some physical parameters for 15-15Ti steel [22]

M	α	b (nm)	μ (GPa)
3	0.26	0.25	68

Table 6 Experimental and calculated strengths of the investigated steels (MPa)

	σ_SS	σ_GB	σ_d	σ_TB	σ_SPP	σ_cal	σ_y
R1	144	127	279	53	8	611	621
R2	157	129	302	59	7	654	666
R3	164	117	313	80	7	681	682

Fig. 6 Contributions of solid solution, grain boundary, dislocation, twin boundary and SPP to the yield strengths of the three 15-15Ti SS samples

Fig. 7 Work hardening rate Θ versus true strain curves for the 15-15Ti SS samples with various silicon contents. The cross indicates the uniform elongation for the samples

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