FLOW TURNING, GRINDING AND HYDRO FORMING OF MARAGING STEEL TUBES.

Extruded tubes of 18 Ni-300 maraging steel were flow turned to 88% thickness reduction in three passes without intermittent annealing. During flow turning each element of the blank was displaced radially from its original position and cracks/voids were produced not only at the inclusion-matrix interfaces but also in the matrix itself suggesting that certain regions of the martensite platelets/laminates have relatively lower ductility. Blanks cut fro the flow-turned tubes were centrally ground and subsequently hydroformed after interference fitting over a die core. The hardness was maximum at the flow turned and ground surfaces but decreased inwards. The effect of forming pressure on the bead depth, bead strain and hardness variation have been investigated. During hydroforming the bellows fractured in shear, tear and mixed modes. (Edited author abstract