Koh-ichi Sugimoto

314 Effect of Retained Austenite Characteristics on Burring in TRIP steels

Effect of retained austenite parameters on burring of (0.1-0.4)C-(1.0-2.5)Si-(1.0-2.0)Mn (mass%) ultra high-strength TRIP-aided sheet steels with porigonal ferrite matrix (TDP steels) having different retained austenite parameters was investigated for automotive applications. Thermal drilling is a process that uses friction to produce bushing in steel tubing and sheet. The combined rotational and downward force of the thermal drilling tool bit creates friction heat. The height of the bushing was roughly 3 to 4 times the original steel thickness. The bushing are ideal for thread applications, as the strength of threads was significantly increased. Hole notches of 5mm diameter were produced by mechanical punching for hole-expanding test. The stretch-flangeability was evaluated using hole-expanding ratio. The hole-expanding ratio of burring were completed in TDP steels. The higher tensile strength, the lower hole-expanding ratio of mechanical punching. In TDP steels, the burring resulted in much higher stretch-flangeability than the mechanical punching. We found that compared with mechanical punching, the burring contributed to the improvement of the tensile strength of 1100MPa class TDP steel with porigonal ferrilte matrix.