Why darkness observed on microstructure of pearlite?
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Bcz during etching dissolving take place which lead to pit formation. These pits don't reflect back the light. That's why darkness observe.
Bcz during etching dissolving take place which lead to pit formation. These pits don’t reflect back the light. That’s why darkness observe.
See lessThe colour depends on the etchant used. It is a lamellar structure, thus when an etchant is used, an electrochemical reaction takes place between the two adjacent layers. One corrodes faster than the other, thus developing a groove like structure. Under the microscope, this forms the contrast betweeRead more
- The colour depends on the etchant used.
- It is a lamellar structure, thus when an etchant is used, an electrochemical reaction takes place between the two adjacent layers. One corrodes faster than the other, thus developing a groove like structure. Under the microscope, this forms the contrast between the two regions. Thus one etches light and another etches dark.
- Using tinted etchants, under different light (other than white light) can also give you colored regions.
- This is true for any metallographic etching, and not just pearlite. The electrochemical reaction depends on the etchant used.
- Normally, for pearlitic etching (i.e. mild steel and carbon manganese steel) we generally use 2% nital or 4% picral solutions as etchants.
- Example : Ferrite appears white with 2% Nital in low Alloy steel but in duplex steel white is Austenite with electrolytic etching.
See lessDarkness and brightness depends on the etching of particular phase relative to other phase. In pearlite, the cementite appears black due to more etching and forming corrosion product which does not allow light to reflect back as explained by Jaiho.
Darkness and brightness depends on the etching of particular phase relative to other phase.
In pearlite, the cementite appears black due to more etching and forming corrosion product which does not allow light to reflect back as explained by Jaiho.
See less