Is this tempered martensite? 1

[Naruwan]

Dear all,
can anyone advise me is the microstructure in the picture that I had attached tempered martensite? Thanks!

 

[metengr]

Naruwan;
There is not enough information to provide a recommendation on the microstructure. Appearances can be deceiving.

What is the material?
What was the heat treatment?


PS; I have noticed you are posting with increased frequency questions that a materials engineer/consultant should be able to answer on their own. My only advice is to be careful with your questions because we are not here to provide free consulting advice. Also, as with any free advice, it is worth what you paid for it!

 

[TemperedMartensite]

It doesn't have the classic look - what is the etchant, alloy, heat treatment?

 

[CoryPad]

Probably a mixture of tempered martensite and lower bainite.

 

[Naruwan]

metengr, thanks for your advise. This material is ISO 3183-3 which is equivalent to API 5L grade X65.

TemperedMartensite, I had etched with 2% nital. This material was made to be a pipe and was bent by heating it to 1050 Deg C and water quenched. No normalizing was done afterwards. I was quite surprised not to see fully tempered martensite structure as the wall thickness was 20mm only.

CoryPad, actually I concluded that the microstructure was a mix of tempered martensite with scattered ferrite. Do correct me if I am wrong. Thanks!

 

[CoryPad]

I had a longer look this time. Probably all three phases are there.

 

[metengr]

Based on the chemistry of this steel, there should be little to no bainite for the stated heat treatment.

 

[CoryPad]

I wrote two posts without truly taking in all the information. Low carbon, little to no alloy, and water quenching do mean bainite in unlikely. However, it could be possible if the part was not truly quenched in water (Tmax ~ 100 [°]F), but was allowed to cool more slowly through a higher temperature range.

 

[QC1971]

Can someone help me understand where the tempering of the martensite would occur. If it was bent at 1050C and water quenched this would be essentially a normalizing treatment. The material should have fully austenized at that temperature and formed fresh untempered martensite upon cooling correct?

 

[metengr]

Correct. You can get autotempering in certain low alloy steels. However, in this case, I would expect close to 100% untempered martensite.

 

[QC1971]

So how would you explain the tempering? It seems to me like there had to be another heat treatment performed on this material to temper the martensite since martensite would not form until it was below the tempering temperature for the material.

 

[stanweld]

What was the chemistry and hardness? I assume this to be an induction bend with continuous water quenching after heating/ forming and no tempering. In a manner of speaking, some tempering effect is produced by the induction heating of material immediately adjacent to the quenched section. Whereas X65 may have a wide variation in carbon content and microalloying, the structure may also be a simply a low hardness martensite with some ferrite. Bainite is quite possible with some X65 chemistries.