TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The amount of Cu contained in the ferritic stainless steel base material is about 1.5 wt.% to about 7.5 wt.% (preferably 1.5 wt.% to about 3.4 wt.%). The ferritic stainless steel base material further comprises Al, Ti, C, and N. The ferritic stainless steel base material comprises about 10 to about 30 wt.% of Cr, less than or equal to 0.3 wt.% of Al, about 0.1 to about 2.0 wt.% of Mn, about 0.02 to about 0.5 wt.% of Ti, less than or equal to 0.2 wt.% of C, less than or equal to 0.1 wt.% of N, about 0.01 to about 0.5 wt.% of La, about 1.5 to about 7.5 wt.% of Cu, and the rest of Fe. The spinel-structured oxide comprises at least one of an oxide of formula (Cu, Cr)3O4 and an oxide of formula (Cu, Mn)3O4. The spinel-structured oxide comprises at least one of an oxide of formula CuCr2O4 and an oxide of formula Cu1.3Mn1.7O4. The spinel-structured oxide comprises an oxide of formula CuCr2O4. Preferred Method: The heat treatment is performed for about 10 minutes to 500 hours. EXAMPLE - A ferritic stainless steel base material (test) having a composition of Fe-23Cr-0.02Al-0.4Mn-0.05Ti-0.01C-0.007N-0.1La-1.8Cu was prepared as follows: 4459.76 g of Fe, 1350.80 g of Cr, 1.12 g of Al, 24.77 g of Mn, 4.38 g of Ti, 0.6 g of C, 64.52 g of Fe-7.75N-60Cr-alloy, 5.85 g of La, and 108.54 g of Cu were mixed to prepare a metal mixture with a total mass of 6 kg. The mixture was vacuum induction melted using ULVAC FMI-1-158 vacuum induction melting furnace, homogenized at 1150 degrees C for 24 hours by heat-treatment, and forged at 1150 degrees C to a thickness of 37 mm. Subsequently, the resultant was hot-rolled at 1050 degrees C (50% hot-rolling), cold-rolled at room temperature (80% cold-rolling), and heat-treated (recrystallization) at 900 degrees C for 5 minutes to prepare Sample 1. Sample 1 was additionally oxidized at a temperature of 800 degrees C for 100 hours to prepare Sample 3. A control ferritic stainless steel base material having a composition of Fe-23Cr-0.02Al-0.4Mn-0.05Ti-0.01C-0.007N-0.1La was prepared as follows: 4567.87 g of Fe, 1350.80 g of Cr, 1.12 g of Al, 24.77 g of Mn, 4.38 g of Ti, 0.6 g of C, 64.52 g of Fe-7.75N-60Cr alloy, and 5.85 g of La were mixed to prepare a metal mixture with a total mass of 6 kg. The mixture was vacuum induction melted using ULVAC FMI-1-158 vacuum induction melting furnace, homogenized at 1150 degrees C for 24 hours by heat-treatment, and forged at 1150 degrees C to a thickness of 37 mm. Subsequently, the ferritic stainless steel base material was hot-rolled at 1050 degrees C (50% hot-rolling), cold-rolled at room temperature (80% cold-rolling), and heat-treated (recrystallization) at 900 degrees C for 5 minutes to prepare Sample 2. Sample 2 was additionally oxidized at a temperature of 800 degrees C for 100 hours to prepare Sample 4. A fatigue fracture test was performed using a low cycle fatigue method in order to evaluate fatigue strengths of Sample 1 of test example and Sample 2 of control example. The maximum fatigue strength in the case of Sample 1 was about 350 MPa at room temperature, about 230 MPa at 600 degrees C, and about 130 MPa at 700 degrees C meanwhile, maximum fatigue strength in the case of Sample 2 was about 320 MPa at room temperature, about 120 MPa at 600 degrees C, and about 80 MPa at 700 degrees C. That is, the fatigue strength of Sample 1 was increased about 13% at room temperature, about 87% at 600 degrees C, and about 90% at 700 degrees C compared to those of Sample 2.