Improvement of Surface Ridging Resistance of an Ultra-purified Ferritic Stainless Steel by Optimizing Hot Rolling Condition

doi:10.1007/s40195-016-0421-2

Abstract

Abstract:

The effects of the finisher entry temperatures (FETs) on the surface ridging behavior for an ultra-purified 21%Cr ferritic stainless steel have been investigated. The results indicate that decreasing the FET facilitates the formation of in-grain shear bands in the hot rolled slab. The in-grain shear bands supplied recrystallization nucleation sites in grains during subsequent annealing through coalescence of subgrains, which is beneficial to refine the microstructures and intensify the {111}//ND textures. This effect will evolve to the final cold rolled and annealed sheet. The micro-texture analysis indicates that the formation of grain colony in the final sheet is weakened by decreasing the FET. Then, the surface ridging resistance of FSS is enhanced due to the optimizing of micro-texture distribution.

Key words: Ferritic steels, Surface ridging, Micro-texture, Electron backscattered diffraction (EBSD)

Chi Zhang, Li-Wen Zhang, Zhen-Yu Liu. Improvement of Surface Ridging Resistance of an Ultra-purified Ferritic Stainless Steel by Optimizing Hot Rolling Condition[J]. Acta Metallurgica Sinica (English Letters), 2016, 29(6): 561-567.

Figures/Tables 10

Table 1 Chemical compositions of the tested steel (wt%)

C	Si	Mn	P	S	Cr	Nb	Ti	N
0.006	0.12	0.17	0.007	0.007	21.5	0.17	0.14	0.008

Table 2 Process parameters for the rolling and annealing processes

	Reheating	Rough rolling (°C)	Finish rolling (°C)	Annealing after hot rolling	Cold rolling reduction	Annealing after cold rolling
No. 1	1200 °C, 1 h	1100-1030	970-850	950 °C, 5 min	80%	950 °C, 3 min
No. 2	1200 °C, 1 h	1050-960	750-680	950 °C, 5 min	80%	950 °C, 3 min

Fig. 1 Surface morphologies of the final sheets after tensile test by a strain of 15%

Table 3 Surface ridging data detected after tensile straining by 15%

	Average roughness, \(R_{\text{a}}\) (μm)	Maximum peak, \(R_{\text{p}}\) (μm)
No. 1	1.94	6.00
No. 2	1.33	4.24

Fig. 2 Orientation maps of the hot rolled and annealed sheets: a No. 1, b No. 2

Fig. 3 Micro-texture of the cold rolled and annealed sheets at center layer of No. 1 specimen: a orientation map, b distribution of specific orientations

Fig. 4 Micro-texture of the cold rolled and annealed sheets at center layer of No. 2 specimen: a orientation map, b distribution of specific orientations

Fig. 5 Orientation maps for the sheets of No. 2 after hot rolling and partial annealing at 950 °C for 90 s

Fig. 6 TEM images showing crystallization in the hot rolled sample (No. 2) annealed at 950 °C for different time: a 10 s, b 60 s, c 75 s, d 90 s

Fig. 7 TEM images showing crystallization in the hot rolled sample (No. 1) annealed at 950 °C for different time: a 30 s, b 60 s, c 105 s

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