Effect of Velocity of Atmospheric Laminar flow Plasma on Microstructure and Properties of Ductile Iron

The surface quenching of QT450 ductile iron was carried out by using a self-developed laminar plasma system for surface quenching.The size,microstructure,hardeness of quenching zone was studied by optical microscope（OM）,microhardness tester,X-ray diffraction（XRD）,and scanning electron microscope（SEM）.The results showed that the quenching zone was composed of cementite,fine pearlite,martensite and partially retained austenite.The cross section from the outside to the inside of the samples was mainly composed of quenching zone,heat affected zone and matrix.Under these conditions,when the scanning rate was 500 mm/min,the size of the molten zone was the largest and the hardness was the highest.