Observation and analysis of microstructure of gray cast iron

1.Metallographic observation

The metallographic sample is taken from the gray cast iron cylinder body, cut and sampled with a cutting machine, and the sampling position is shown in the figure. The removed samples were inlaid with epoxy resin, ground on 120 #, 280 #, 400 # and 500 # sandpaper respectively, and polished on MP-1 metallographic sample polishing machine. After the polished sample is cleaned by the ultrasonic cleaner, it is eroded with 4% nitric acid alcohol solution. The obtained corroded samples can be observed under the mr5000 metallographic microscope, and the distribution and size of various structures can be clearly distinguished.

According to GB / t7216-2009, the graphite in gray cast iron is divided into 6 types according to its distribution shape, and the length is divided into 8 levels. When observing the graphite distribution shape in gray cast iron, just polish the sample without erosion, zoom in 100 times, and distinguish the type and size of graphite by comparing with the standard picture.

The quantity of pearlite is divided into eight grades, which is similar to the graphite detection method. After the sample is eroded by 2% – 5% nitric acid alcohol solution, the content of pearlite is calculated through metallographic microscope inspection (pearlite + ferrite =

1 0 0 % ) 。

2.Scanning electron microscope observation and energy spectrum analysis

The preparation method of SEM observation and energy spectrum analysis samples is the same as that of metallographic samples, and whether they are corroded can be selected according to needs. Jsm-6490 scanning electron microscope is used to observe the cross-section and fracture morphology of the sample. At the same time, energy dispersive spectrometer can detect the type and content of elements in the micro area of the sample.

3.Phase analysis

D / max-2500v type Cu (KLA ray) lead X-ray diffractometer (XRD) was used for phase analysis. The scanning angle was 10-90 °, the scanning speed was 4 ° / min, the test voltage was 40kV, and the current was 40mA. The phase analysis of gray cast iron samples prepared under different processes and conditions was carried out.