Metal Microstructure Analysis

Ferrite has bcc unit cell, shows a yield point clearly and be brittleness at low temperature.

Perlite has layers structure between Fe3C and ferrite has the trait of being tough, tenacious and strong but easily to be corrosion.

Austenit has fcc unit cell, demonstrated a yield point clearly without brittleness on the State of the icy, it is soft, quite powerful and non-magnetic.

Martensite has solid solution phase is over saturated carbon units in a cell of the body centered tetragonal (bct). The higher the degree of saturation of carbon, the greater the ratio of unit cell axis unit and the more hard and more brittle.

Bainite has properties between martensite and ferrite.

Cementite is a compound of metal Fe and Fe3C, form C is hard and brittle.



Picture above describe about boiler tube ferrite and pearlite micro-structure at normal conditions.



Picture below describe about Micro-structure of tube degradation initial condition due to overheating.



Micro-structure classification based on ERA technology.



Crack / creep(sample).







There has been a growing and carbide spheroidization as picture below (sample)





Graphitization as picture below (sample)






Cracks in the outer surface of the tube shows the indication swelling hydrogen damage. On the conditions of high temperature local overheating, there will be the reaction of hydrogen gas with Fe3C (cementite) ferrite forming (Fe) and gas CH4 are moving towards methana limit metal granules gradually more and more giving rise to enormous pressure producing inter-granular cracking. Early indications that the rift has been shown in the photo on the outer surface of the tube (see picture below)








Some example metal micro-structure of creep, corrosion and hydrogen damage as picture below.









Source:
Harianto PLN Puslitbang