1、 Metallographic observation
Metallographic structure observation includes sampling, grinding, polishing, etching, cleaning, microscope observation and other steps. Metallographic specimen size is Φ× L=20mm × 20mm。 The etching solution for matrix structure observation uses 2% – 4% nitric acid alcohol solution, and the soaking time is 12s; The etching solution of eutectic cluster is prepared by using 1g copper chloride, 4G magnesium chloride, 2ml hydrochloric acid and 100ml absolute ethanol, and the etching time is 1min. Wash and air dry quickly after etching. When air drying, pay attention not to touch the etching surface of the sample. Observe the matrix structure of three grades of gray cast iron with Zeiss metallographic microscope, and determine the graphite grade and pearlite content of three grades of gray cast iron with jx-2000 metallographic software.
2、 Fracture analysis
(1) Observation of fracture morphology
The tensile specimens and tension compression fatigue specimens of three grades of gray cast iron were mechanically cut and sampled 5 mm below the fracture surface, and the morphology of the two fractures was observed and analyzed by scanning electron microscope. The equipment used in this test are jeol-6360lv scanning electron microscope of Japan Electronics and field emission scanning electron microscope of Zeiss sura55 of Germany. The working principle is that the focused electron beam is emitted to the sample surface. After multiple reflections and refractions, various electronic signals are excited on the sample surface. After further receiving and processing these signals, the surface morphology of the sample is obtained. When observing the morphology, the voltage is usually 20kV and the aperture diameter is 60 μ m。
(2) Fracture composition analysis
The equipment used is Zeiss supra 55 field emission scanning electron microscope and energy spectrometer. Its working principle is that the focused high-energy electron beam is emitted to the sample surface, and the inner electrons of the sample are excited to produce X-rays at the same time. The wavelength of the generated X-ray reflects the element contained in the sample, and the intensity of the X-ray reflects the content of the element in the sample. In this test, the composition of alloy compounds on the fracture surface of tension compression fatigue samples was analyzed by energy spectrometer.