The thermal-fatigue behavior with 800 cycles of ambient-1 000℃ for 1. 5 mm cold-rolled sheet of 409

429 and 441 super ferrite stainless steels produced by pre-treaded metal-90 t K OBM S-VOD-LF-slab CC flow sheet for auto exhaust pipeline has been studied. Results show that the thermal-fatigue (crack length with 800 cycles- 1. 2mm) of steel 429 (/%: 0. 009C

0. 86Si

15. 3Cr

0.47Nb) and steel 441 (/%: 0. 008C

0.45Si

17. 9Cr

0. 39Nb

0. 18Ti) is better than the thermal-fatigue (crack length with 800 cycles- 2. 0 mm) of steel 409 (/% : 0. 007C

0. 40Si

11. 2Cr

0. 14Nb

0.10Ti) ； during reversing ambient-1 000 °C heating-cooling process

the Fe atoms in weak region of steel are first oxidized to form oxides and peel off from base metal

led to form crack

and the formed Fe

2

SiO

4

• Cr

2

O

3

oxide films near crack prevent crack further developing.