Dr. Dmitri Kopeliovich

Macro- (Macrography, Macrostructure) Examination is a method of examination of large regions of the specimen surface or fractured section with the naked eye or under low magnification. The following macrostructure details may be studied:

• Macro-segregation of the alloying elements or impurities (sulfur in steel, antimony in lead base babbit);

• Large non-metallic inclusions such oxides, sulphides or slag;

• Forging flow lines;

• Cast grain structure;

• Physical defects such gas pockets, shrinkage cavities, cracks.

Three different procedures are used for observation various characters of macrostructure:

• 1. Surface examination
• 2. Macroetching
• 3. Fracture Examination

The sample surface is usually ground (polish is not necessary)

The finish grinding is Grade 320 paper.

Large cracks, shrinkage cavities, gas pockets may be investigated.

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Macroetching helps to reveal much information of cast, hot-rolled and forged details.

Sulfur print is a macroetching technique of steel samples, allowing to determine sulfur distribution and segregation in the sample:

• The ground specimen is degreased and washed;

• Pieces of photographic paper (bromide) are soaked in 2-3% solution of sulphuric acid for two minute;

• The paper is taken from the solution and excess acid is removed from the surface;

• The paper is placed on the sample surface, providing an intimate contact between the sensitive side of the paper and the sample surface.

The sulphuric acid reacts with the sulphides in the steel specimen, forming hydrogen sulphide, which then reacts with the silver bromide of the photographic paper, forming dark traces corresponding the sulfur segregation;

• After 2-5 min. the paper and specimen are separated and the print paper is rinsed in water and fixed in hypo solution (20%) for 5 min.

• Finally the print is washed for 30 min and dried.

(quantities of the components are in weight parts)

• For steels

Crystal structure: Iodine10 parts, Potassium Iodide20 parts, Water100 parts

Flow lines, cracks, porosity: Hydrochloric acid50 parts, Water50 parts, Boiling for 5-15 min.

Dendritic structure: Copper ammonium chloride 9 parts, Water91 parts, Immersion for 0.5-4 hours.

• For stainless and austenitic steels: Hydrochloric acid 15 parts, Nitric acid5 parts, Water100 parts.

• For aluminum alloys: Hydrochloric acid 10 parts, Nitric acid1 part, Water200 parts.

• For copper alloys (dendritic structure): Ferric chloride 25 parts, Hydrochloric acid 25 parts, Water100 parts.

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Fracture examination is a method relating to observation of the broken surfaces of the failed part.

The appearance of the surfaces may be a result of brittle fracture, fatigue with its characteristic fracture, intercrystalline fracture, segregation, slag particles, cracks, starting from physical defects, rough surface, corrosion and other causes.

Fracture examination should take into account the working condition, the history of the part, possible overloads, applied to the part, misalignments and other working factors.

Fracture examination should be supported by other metallography examinations.

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• Metallographic examination - introduction
• Specimen polishing technique
• Etching metallographic specimens
• Metallurgical Microscope
• Scanning Electron Microscope
• Grain structure
• Solidification
• Phase transformations and phase diagrams
• Basic principles of heat treatment
• Chemical Composition Evaluation

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to Metallographic examination