Influence of Finish Rolling Temperature on Microstructure and Mechanical Properties of a 19Cr1.5Mo0.5 W Ferritic Stainless Steel

doi:10.1007/s40195-020-01035-x

Abstract

Abstract:

A 444-type heat-resistant ferritic stainless steel containing 0.05 wt% Ce (rare earth element) and 2 wt% (Mo + W) was adopted as an experimental material to study the effect of finish rolling temperature on microstructure and texture evolution as well as on mechanical properties and formability. The rolling processes contain hot rolling at two different finish rolling temperatures (860 °C and 770 °C) and annealing, cold rolling and subsequent annealing. It was found that the microstructures after hot rolling and annealing could be refined by lowering finish rolling temperature. The resultant microstructures after cold rolling and annealing were hereditarily refined. Lowering finish rolling temperature can weaken α-fiber texture in hot-rolled or cold-rolled ferritic stainless steel strip, while γ-fiber texture in the final product was homogeneously strengthened. Additionally, enhanced mechanical property and formability in terms of strength and average plastic strain ratio could be obtained via decreasing finish rolling temperature.

Key words: Ferritic stainless steel, Finish rolling temperature, Microstructure, Texture, Mechanical property, Formability

Hou-Long Liu, Ling-Ling Liu, Ming-Yu Ma, Li-Qing Chen. Influence of Finish Rolling Temperature on Microstructure and Mechanical Properties of a 19Cr1.5Mo0.5 W Ferritic Stainless Steel[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(7): 991-1000.

Figures/Tables 11

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

C	Si	Mn	Cr	Nb	Ti	N	Mo	W	Ce
< 0.01	0.44	0.34	19.6	0.47	0.14	< 0.009	1.55	0.45	0.05

Fig. 1 Main orientations of ferritic stainless steel in φ2?=?45° ODF section

Fig. 2 Optical micrographs for microstructures in the hot-rolled sheet a and annealed sheet c with finish rolling temperature of 860 °C and the hot-rolled sheet b, annealed sheet d with finish rolling temperature of 770 °C

Fig. 3 Optical micrographs for the cold-rolled sheet a and annealed sheet c with a finish rolling temperature of 860 °C and the cold-rolled sheet b, annealed sheet d with a finish rolling temperature of 770 °C

Fig. 4 Constant φ2 = 45° ODF sections for the hot-rolled sheet a and annealed sheet c with finish rolling temperature of 860 °C and the hot-rolled sheet b, annealed sheet d with finish rolling temperature of 770 °C

Fig. 5 Constant φ2 = 45° ODF sections for cold-rolled sheet a and annealed sheet c with a finish rolling temperature of 860 °C and the cold-rolled sheet b, annealed sheet d with a finish rolling temperature of 770 °C

Fig. 6 Crystal orientation maps and grain size distribution of the annealed sheet with finish rolling temperature of 860 °C a, c, 770 °C b, d

Fig. 7 Engineering stress-strain curves of the final products with different finish rolling temperatures

Table 2 Mechanical properties for cold-rolled and annealed sheets under two hot rolling conditions

Finish rolling temperature (°C)	Yield strength (MPa)	Tensile strength (MPa)	Elongation (%)	Yield strength ratio
860	354	527	32.1	0.67
770	367	542	32	0.68

Table 3 Formability of the final sheets with two hot rolling processes

Finish rolling temperature (°C)	r₀	r₄₅	r₉₀	r_m	Δr	n	R_a (μm)	R_t (μm)
860	1.64	0.95	1.36	1.36	0.82	0.21	0.538	4.138
770	1.84	1.36	1.51	1.52	0.32	0.21	0.352	2.673

Fig. 8 Surface roughness profiles of the final annealed plates with finish rolling temperature 860 °C a, 770 °C b

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