Fracture behaviour of the 304 stainless steel with micro-EDMed micro-holes

Micro-electrical discharge machining (EDM) is an ideal technique for micro-hole drilling of 304 stainless steel. However, the local stress raiser at the holes and the concomitant microcracks generally leads to the strength degradation. In order to explore the appropriate approach of post-treatment to improve the degraded strength, a series of experiments were carried out to systematically understand the fracture behaviour of the 304 stainless steel with micro-EDMed micro-holes. In this study, array holes (3x3) with the diameter of 0.7 mm were fabricated by micro-EDM in the 304 stainless steel. The stress-strain curves and tensile fracture topography demonstrate that the fracture form of the micro-EDMed sample belongs to the combination of quasi-cleavage fracture and ductile fracture. By comparing the metallographic characterizations and the microhardness of specimens with and without micro-EDM, it is found that slippage occurs in the grains near the fracture of the micro-EDMed specimen and the elongation of grain is hardly observed. It is considered as the main reason that work hardening and grain refinement of the molten solidified layer formed during EDM limit the elongation of the surrounding grains.