unnormal microstructure

[fusitexa]

hi,

could anyone tell me how the unnormal microstructure form in the attached file?
what i know about the material is: its grade is SAE1018, and the raw material is round bar.
does that make the properties worse, any idea is appreciated.

 

[fusitexa]

sorry, i made a mistake and upload again.

 

[redpicker]

I've seen that referred to as acicular ferrite and pearlite. For 1018, it is formed at somewhat more rapid cooling rates that produce the more common ferrite and pearlite structure.

As to whether or not it makes properties worse, it really depends on what properties you are interested in and what you consider worse.

rp

 

[stanweld]

Was this the only anomoly or were there many more similar structures. I would suspect some minor segregation as the culprit if only one.

 

[fusitexa]

rp， thanks for your reply.
stan, no, there are many similar structures.

 

[metengr]

There is nothing abnormal with this microstructure, as mentioned previously it is produced by more rapid cooling rates. It is typical to see some variability in grain size with variable cooling rates because of section thickness and geometry affects.

 

[stanweld]

Agree with metengr, anomolous structure is cooling rate dependent. Is the anomolous structure concentrated toward the surface?

 

[fusitexa]

stan, they are uniformly distributed in it.

 

[HT007]

The appearance is acicular ferrite within the big size pearlite. The fast cool rating and over heating or long soaking time during normalization are the main reasons. If it uniformly and widely appears in the matrix, it damages the impact property severely.

 

[jp2v]

I'd say it's pearlite and bainitic ferrite.

 

[metman]

Looks like Widmanstatten Structure

Design for RELIABILITY, manufacturability, and maintainability

 

[dbooker630]

I agree about the Widmanstatten appearance; too much of this and machining can be troublesome.