Microstructure observation of nodular cast iron

(1) Sample preparation. Cut the samples of three components into 10 mm by wire cutting machine × 10 mm × 10mm cube sample, and then grind it with 80 #, 200 #, 400 #, 600 #, 800 #, 1000 # sandpaper in order. After the surface scratches are uniform and the direction is consistent, use the particle size of 2.5 μ M diamond polishing agent.

After polishing until the surface is bright and there is no scratch on the mirror, rinse the sample with alcohol. After drying, suck 4% nitric acid alcohol solution with a dropper to corrode the surface of the sample. After holding for 3 ~ 5 s, rinse it with alcohol immediately and dry it with cold air.

(2) Organize observation. The metallographic structure of three groups of nodular cast iron samples, including graphite morphology, spheroidization rate and the proportion of pearlite and ferrite in the matrix, was observed by mdj-dm front-view optical microscope. The microstructure of nodular cast iron samples was observed under Zeiss scanning microscope, mainly pearlite shape and lamellar spacing.

(3) Data processing. The graphite size, spheroidization rate and the proportion of pearlite and ferrite in the matrix were measured by digital evaluation method using image Pro Plus software. Spheroidizing grade and graphite size grade shall be determined according to gbat9441-2009 metallographic inspection standard of nodular cast iron (as shown in the table).

Spheroidizing rate classification of nodular cast iron:

  1. The graphite of nodular cast iron is regular spherical, and a few are agglomerated, and the spheroidization rate is more than 95%
  2. Most of the graphite of nodular cast iron is spherical, and the rest is agglomerate and a small amount of agglomerate flocculent, with a spheroidization rate of 90% ~ 95%
  3. The graphite of nodular cast iron is mostly spherical and agglomerated, and the rest is agglomerated flocculent, with a spheroidization rate of 80% ~ 90%
  4. Most of the graphite of nodular cast iron is in the form of mass and flocculent, and the rest is in the form of ball and worm, with the spheroidization rate of 70% ~ 80%
  5. The graphite of nodular cast iron is dispersed spherical, vermicular, agglomerate and flocculent, and the spheroidization rate is 60% ~ 70%
  6. The graphite of nodular cast iron is in the form of worm, flake, ball, mass and flocculent
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