Effect of retained austenite phase on springback of cold-rolled TRIP steel sheets

We examined the effects of retained austenite phase on the springback of cold-rolled transformation-induced plasticity (TRIP) steel sheets through a series of V-bending tests. Prior to testing, the intercritically annealed TRIP steel sheets were heat-treated at different austempering temperatures (300, 350 and 400 °C) to obtain three specimens with different retained austenite phase fractions.Results show that the amount of springback in TRIP steel decreased as the fraction of retained austenite phase increased. The amount of springback was reduced by about 30% when the fraction of retained austenite phase increased by 5%. When the area fractions of the retained austenite phase of TRIP steel were less than 3%, we observed micro-cracks in the near-surface points of a V-shaped specimen where compressive and tensile stresses were concentrated. The dependency of material's direction upon springback was very weak in the V-bending test where no constraint such as a blank holder exists during testing.

► The fraction of retained austenite (γR) influences the formability of the TRIP steel.
► The forming balance increases by 20% when the fraction of γR increases by 5%.
► The amount of springback is reduced by 30% when the fraction of γR increases by 5%.
► When the fraction of γR decreases, fatigue fracture may occur during cold forming.