Formability of micro sheet hydroforming of ultra-fine grained stainless steel

The formability of ultra-fine grained stainless steel is investigated in micro hydromechanical deep drawing. The materials used are ultra-fine grained stainless steel and SUS304-H with thickness of 20 and 50 m. The micro cups are successfully fabricated for the ultra-fine grained stainless steel but it cannot be fabricated for SUS304-H with thickness of 20 μm. The fracture type of ultra-fine grained stainless steel foil is the shortage of tensile strength at plain strain state and does not change with a decrease of the thickness. In contrast, the fracture type of SUS304-H foil changes to the bending deformation with decreasing the thickness due to its low ductility. The ultra-fine grained metal foil is required to obtain the high formability and fabricate the sharp micro cups.