SIX - Metallographic examination

1, sample preparation, coarse grinding with coarser silicon carbide grinding wheel grinding, grinding surface to 2-3 mm. The internal organization of the proof alloy; Set sample is coarse grinding sample with sulfur circle insert samples, sample set samples should make all polished in a plane. Circle will be set with sample set samples, on special sample device of fine grinding, to eliminate coarse grinding water grinding crack. When the fine grinding of abrasive has two kinds: one is containing silicon carbide (120-180 mesh) and potassium permanganate solution; Another kind is boron carbide (180-220 mesh) with kerosene or a mixture of transformer oil. Polishing can be conducted on similar to the fine grinding device. Mill pad on the canvas, and drop into the zirconia powder (150 mesh) and potassium permanganate solution, no streaks of light should be after polishing grinding surface, further on the iron plate in woolen cloth fine grinding, to eliminate grinding polishing is the formation of the turbidity, drip continuously in the process of fine grinding abrasive (less than 3 micron boron carbide) and lubrication oil, transformer oil or edible vegetable oil), after fine grinding of grinding should be smooth as a mirror.

2, the corrosion of grinding

Porosity is A field of pore area percentage, namely X = A/B * 100%; X for porosity, A is the area of the field of pore, B is the area of the field. Generally choose a field of most pore and the known standard photos to compare and determine porosity. Dirt degree is to put the above 40 microns, irregular shape but the clarity of the edge of black holes. Graphite inclusions generally or tiny dot gathered in nests, its edge is clear, in the process of grinding, flake graphite inclusions are usually the pore, some national standards will even graphite inclusions as the secondary pore. Other defects, layered like dirt under a microscope, but longer than dirt, dirt than straight edges. Crack is thin and long black stripes. Not good pressure caused by the pore usually triangular or water chestnut, if pore focused particularly on the sharp edge of place, usually is not good. Owe to burn the pore generally smaller, about 5 microns, concentrated in the middle of specimen. Burnt generally does not affect the porosity, but serious when burnt, average porosity is larger, in 10-20 microns, and most of the surface.

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