Abstract
Effect of manganese content on burring and tapping in 0.2C-1.5Si-(1.0-2.0)Mn (mass%) high strength TRIP-aided sheet steels with polygonal ferrite matrix (TDP steels) was investigated for automotive applications. Burring test was performed on a machining center with rotational speed of 3500 rpm and cutting feed rate of 10 mm/min, using disc specimen of 50 mm in diameter. Moreover, tapping test was performed on a machining center with rotational speed of 20 rpm and cutting feed rate of 20 mm/min after burring. The hardness of flange after burring was evaluated by hardness increment (ΔHV) expressed by ΔHV=HVmax–HV0, where HVmax and HV0 are a maximum hardness after deformation and a base material hardness (an initial Vickers hardness).
The hardness increment (ΔHV) increased with increasing of manganese content. The lower the initial carbon concentration in retained austenite (Cγ0), the higher the hardness increment (ΔHV). Strain induced transformation and work hardening contributed to the toughness of flange after burring with TDP steel having a tensile strength of 980 MPa grade.
