An Innovative Large-Scale Preparation Method for ODS Steel: Zone Melting with Built-In Precursor Powder

doi:10.1007/s40195-025-01875-5

Abstract

Abstract:

To develop a melting-based larger-scale fabrication process for oxide dispersion strengthened (ODS) steel, this study proposed a method of zone melting with built-in precursor powder (ZMPP), followed by hot forging and aging treatments. A 50 kg ingot was successfully prepared, highlighting the scalability of this innovative process. Microstructural analysis revealed a predominantly lath martensite matrix with a small amount of ferrite in the hot-forged ODS steel, without oxide particle aggregation. Aging at 750 °C resulted in the formation of sub-micron-sized Cr₂₃C₆ particles at grain boundaries and martensitic lath interfaces, accompanied by a high-density (7.64 × 10²³ m⁻³) nano-scale (~ 6 nm) Y-Si-O complex oxides after 25 h. Additionally, the hot-forged sample exhibited a high yield strength (871 MPa) but limited ductility (5.0%). Aging treatments led to an increase in ductility but a decrease in yield strength. Notably, prolonged aging maintained the strength level of steels while enhancing ductility, with a 23.3% total elongation observed after 25 h. The novel ZMPP method, preparing high-quality ODS steels with uniform microstructure and good mechanical properties, provided a new avenue for large-scale production of ODS steels.

Key words: Oxide dispersion strengthened (ODS) steel, Zone melting, Built-in precursor powder, Particle precipitation, Mechanical properties

Haoyu Cheng, Chenyang Hou, Jianlei Zhang, Xiaodong Mao, Yuanxiang Zhang, Yanyun Zhao, Chulun Shen, Changjiang Song. An Innovative Large-Scale Preparation Method for ODS Steel: Zone Melting with Built-In Precursor Powder[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(8): 1397-1409.

Figures/Tables 18

Table 1 Chemical compositions of commercial P91 alloy steel (wt%)

C	Si	Cr	Mo	Nb	V	Fe
0.1	0.3	9.25	0.95	0.087	0.22	Bal.

Fig. 1 Schematic diagram for the method of zone melting with built-in precursor powder (ZMPP)

Fig. 2 EPMA micrograph of the as-cast a and microstructure analysis of the hot-forged ODS steel: b EPMA micrograph, c XRD pattern, d EBSD orientation color map and e EPMA elemental distribution maps

Fig. 3 XRD patterns of the aged ODS steel samples at 750 °C for different durations

Fig. 4 SEM micrographs of the aged ODS steel samples at 750 °C for different durations: a 3 h, b 10 h, c 20 h, d 25 h

Fig. 5 EPMA elemental distribution maps for the aged samples at 750 °C for 3 h a, 25 h b

Fig. 6 EBSD orientation color maps for the aged samples at 750 °C for 3 h a, 25 h b

Fig. 7 TEM images and TEM-EDS analysis of the as-forged ODS steel sample: a BF image of the martensite matrix, b further magnified image of the martensite matrix, c SAED pattern of the precipitates, d TEM-EDS analysis of the precipitates, e SAED pattern of the matrix

Fig. 8 TEM images and EDS results of the aged ODS steel sample at 750 °C for 3 h: a BF image of the martensite matrix, b further magnified image of the Cr-rich precipitates, c SAED pattern of the precipitates, d high-resolution image of nano-oxide precipitates, e FFT pattern of nano-oxide precipitates, f TEM-EDS analysis of the Cr-rich precipitates

Fig. 9 TEM images of the aged ODS steel sample at 750 °C for 25 h: a BF image of the matrix, b high-resolution image of nano-precipitates, c FFT pattern of nano-precipitates

Table 2 Statistical analysis of nanoparticle size and number density in the aged ODS steel samples at 750 °C for 3 h and 25 h

Samples	Size (nm)	Number density (m⁻³)
750 °C-3 h	4.9 ± 1.2	4.81 × 10²³
750 °C-25 h	6.2 ± 1.8	7.64 × 10²³

Fig. 10 Microhardness a and engineering stress-strain curves b of the ODS steel samples under various conditions

Table 3 Tensile properties of the ODS steel under various conditions

Samples	Yield strength (MPa)	Tensile strength (MPa)	Total elongation (%)
As-forged	871 ± 8	1253 ± 13	5.0 ± 2.3
750 °C-3 h	529 ± 10	669 ± 7	11.0 ± 2.1
750 °C-10 h	493 ± 9	644 ± 12	13.5 ± 4.3
750 °C-20 h	496 ± 2	645 ± 2	21.9 ± 0.6
750 °C-25 h	506 ± 2	660 ± 5	23.3 ± 0.2

Fig. 11 Tensile fracture surfaces of the aged ODS steel samples for different durations: a 3 h, b 10 h, c 20 h, d 25 h

Table 4 Elemental content analysis (wt%) of the ODS steel samples

Samples	C	Si	Nb	Mo	Cr
Hot-forged	0.10	0.29	0.08	0.91	9.10
750 °C-3 h	0.07	0.21	0.08	0.88	8.71
750 °C-25 h	0.06	0.19	0.07	0.80	8.60

Table 5 Values of θ, β, βcosθ, and 4sinθ for samples in different states

Peaks	Samples	θ	β	βcosθ	4sinθ
(110)	Hot-forged	22.260	0.345	0.320	1.515
	750 °C-3 h	22.320	0.281	0.260	1.519
	750 °C-25 h	22.280	0.286	0.265	1.517
(200)	Hot-forged	32.340	0.903	0.763	2.140
	750 °C-3 h	32.430	0.513	0.433	2.145
	750 °C-25 h	32.400	0.560	0.473	2.143
(211)	Hot-forged	41.010	0.789	0.595	2.625
	750 °C-3 h	41.070	0.538	0.406	2.628
	750 °C-25 h	41.020	0.576	0.435	2.625

Table 6 Contributions of four strengthening mechanisms to the yield strength of the ODS steel in different states

Samples	σ_s (MPa)	σ_g (MPa)	σ_d (MPa)	σ_p (MPa)
Hot-forged	224.48	142.86	312.98	-
750 °C-3 h	92.11	137.65	187.85	102.80
750 °C-25 h	46.37	133.52	171.64	139.61

Table 7 Mechanical properties and precipitation behavior of ODS steels prepared by different processes

ODS steel	Preparation methods	Oxides	Size of oxides	Yield strength (MPa)/Elongation (%)
ODS-316L-D150 [45]	Powder metallurgy + hot extrusion	Y₂O₃	Submicron	320/39
ODS-EUROFER 97 [46]	Powder metallurgy + hot isostatic pressing	Y₂O₃	1-40 nm	633/3.3
CNI-I-ODS [47]	Vacuum induction melting	Y₂O₃, Y(O, C)-phase	550-900 nm	482/22.7
9Cr-ODS [14]	Fe₂O₃ oxygen carrier melting	Y-O rich particles	0.2-1.1 µm	730/11.3
T91-ODS [48]	Vacuum induction melting	Y₂O₃	2-5 µm	−/10.2
T91-ODS [49]	Y₂O₃ colloidal + vacuum melting	Y₂O₃	Microns	-
ODS-316L [16]	Precursor powder + sub-rapid solidification	(Er, Ti)- oxides, Ti-O rich particles	100-350 nm, < 10 nm	411/33
Sample of 750 °C-25 h in this work	Zone melting with built-in precursor powder (ZMPP) + forging + aging	Y-Si-O	6 nm	506/23.3

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