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Subject on This Issue:
* Steels & Properties
* Heat Treatment



Preparation of test specimen

  1. Clean the specimen to remove any scale/ pit or foreign material that might crush or flow under test pressure and so affect the result.
  2. Polish the tested surface with Alumina Surry to ensure the surface condition of the specimen before etching

Procedure of etching

  1. Differential the material of the specimen
  2. Refer to Table 1 to check what kind of etchant should be used for etching.
  3. Correct handling of chemicals.
  4. After preparing the etchant, place or fix the specimen securely by a tong special for etching.
  5. Immerse the specimen into the etchant by the duration of etching which is specified for certain material or purpose.
  6. Adjust the duration of etching until a clear microstructure has been observed.

Etchants for general purpose

Table 1. Etchants for different type of materials



Duration (s)


Tool steel
Oil hardened steel
Carbon steel
Wrought irons


2-10% Nital
2-10% by volume of conc. HNO3 in ethanol


10-15s or until the surface becomes
a silvery color


Stainless steel


Mix 50mL HCl, 25mL HNO3, 25mL of distil water




Pure Zinc, Impure Zinc


50% conc. HCl acid





Copper alloys

Alcoholic ferric chloride

5gm FeCl3, 2mL HCl, 95mL ethanol

Ammonia/ Hydrogen peroxide

1 part NH4OH, 1 part H2O2 3%, 2 parts distil water





5-20s or until surface is noticeably darkened


Aluminum alloys

Mixed acid reagent

95 mL Water, 1.5mL HCl, 2.5mL HNO3, 0.5mL HF 48%



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