Micrograph of AISI 1045 steel-Segragation and bands in grains

[onurct]

Hello everyone,

I have a question about bands and islands found in grains of AISI 1045 steel after heat treatment of:

Austenization (inert atmosphere): At 880 C for 1 hour
Annealing: At 550 C for 1 hour

The chemical composition is: C: 0.45 %wt
Mn: 0.3-0.6 %wt
S: <0.03 %wt
Cr+Ni+Mo: < 0.6 %wt
Si: <0.4 %wt

In this micrograph,

The dark bands (waves) in red box and again dark relatively straight lines in blue boxes.

In this micrograph:

The white islands in grain with red box.

I couldn't figure out what they could be, so I'm asking for your help. If you can give some head-up, I'd appreciate a lot.

Thanks in advance

 

[Maui]

In your first image,

The dark bands (waves) in red box and again dark relatively straight lines in blue boxes

you are referring to appear to be pearlite. You can read about it here:

http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html

Maui

http://www.EngineeringMetallurgy.com

 

[metengr]

onurct;
Need more background information regarding the micrograph attachments. How was the 1045 steel sample above prepared for viewing? Was a section of the 1045 steel prepared using standard metallograhic techniques? How was the sample etched for viewing?

 

[NickE]

They look like SEM images, probably secondary electron detector.


Nick

 

[metengr]

onurct;
Another question - your stated heat treatment parameters are not typical for 1045 steel. Why was a subcritical anneal done at 550 deg C? Was the material held at 880 deg C to fully austenitize and then cooled to 550 deg C before furnace cooling?

 

[TVP]

onurct,

The white islands in the second image are carbide particles (cementite) that are partially spheroidized. Subcritical annealing of steels with pearlitic microstructures will transform the cementite in the pearlite into a spheroidal form. This transformation is a function of temperature, time, and the amount of strain stored in the material (deformation from prior processing). In order to completely transform all of the cementite into spheroids you would need to hold the sample at temperature for a longer time, or impart more strain on the sample by deformation (drawing rod through a die, etc.).

 

[onurct]

Thanks a lot for the responses.

Metengr,

FIB profile cuts and SEM, as NickE said. I dont know why it was done at 550 C. I'll ask. And yes, it was held at 880 C for fully austenitization and cooled to 550 C before furnace cooling.

 

[metengr]

I think before I would venture any further using the above images, I would perform a metallographic examination of the sample.