Steel Microstructure of Medium Carbon Steel 1

[metalfate]

Dear Metallurgist Master and Enthusiast...

Herewith attached microstructure of 0.45%C after Heat Treatment process. According to the submitters, the process step were:
- Steel Bar
- Hot Forging
- Carburizing
- Tempering
- Case Hardening
- Tempering
We have notice Pearlite and Ferrite microstructure. However, there were some big - irregular shaped pearlite (?) microstructure observed. Do any of metallurgist master here able to identify what is that? On what process does it develop?

Thank your for any comment and advice. Best of Luck.


Regards,

Metalfate

 

[metman]

If the larger bodies are pearlite, it could be from heating within the temperature range between the lower critical and upper critical tempertures.

Design for RELIABILITY, manufacturability, and maintainability

 

[redpicker]

This appears to be an occasional large grain in a fine-grained structure. However, this is just a guess. Trying to identify a microstructure without knowing magnification and sample preparation techniques is like trying to guess the number of monkeys in a closed barrel.

Is this the structure after case hardening and tempering?
Is this the microstructure of the core (or the case)?
Do you know the process times and temperatures of each of the processes?

I am aslo curious about section size. Peralite is a structure generally associated with slow cooling rates. Case Hardening after carburizing is a process that generally involves rapid cooling (quenching). The implication is that, even with quenching, the material represented by the photomicrograph experienced a slow cooling rate from the hardening temperatures. Is that correct?

rp

 

[mfgenggear]

it does not appeared to be quench & tempered?

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[mfgenggear]

"is like trying to guess the number of monkeys in a closed barrel."

LOL RP

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[metman]

Yes some guessing required but based upon the info provided, the surface hardening process is likely induction and the photomicograph then is the core material and obviously not the casehardened surface. Also the suface is not visible which is another clue that we are looking at the core.

Using redpicker's guess, the large grains could be discontinuous grain growth from one or more high temperature excursions.

Design for RELIABILITY, manufacturability, and maintainability

 

[CoryPad]

Why would this be made from steel with 0.45% carbon and then carburized? Very unusual choice.

 

[Mett87]

If it had been quenched from above austenitizing temperature there would be no directionality within the grains, in the photomicrograph attached directionality is quite clear. Also unless it was a very thick section you would expect martensite/ferrite in the core.

 

[metman]

Cory,
Exactly. That is why I forgot (subconsciously discounted) that he said it was carburized and thought he must have meant induction hardened for heat treat which would leave no matensite in the core.

Design for RELIABILITY, manufacturability, and maintainability