The effect of annealing temperature between 750 ℃ and 780 ℃ on structure of two TRIP steel - 0.2C-1.5Si- 1.5Mn and 0.2C-1.5Si-1.5Mn-0.5Cu has been studied by color metallograph method
X-ray diffraction and scanning electron micrograph. The test results showed that for the TRIP steel containing 0.5Cu
the retained austenite volume fraction was 16.2%~17.2% when annealed at 750 ℃
760 ℃ and 780 ℃ and it was 15.2%~15.7% when annealed at 770 ℃;and for free Cu TRIP steel
when annealed at 760 ℃ and 770 ℃
the retained austenite volume fraction was 12.5%~12.9% and 14.6%~15.1% respectively which lower than that fraction 17.0%~17.5% and 16.0%~16.4% when annealed at 750 ℃ and 780 ℃ respectively. With the annealing temperature increased from 750 ℃ to 780 ℃ the ferrite volume fraction in steel decreased from ~70% to ~50%
and the bainite volume fraction in steel increased from ~ 10% to ~30%.