4140 prioir austenite grain boundries dangerous in drilling equipment 1

[goodbadgood]

HI all

I have some questions regarding the micro structure of 4140 steel. It is widely used in the drilling equipment. Is it possible that prioir austenite grain boundaries can be present in quenched tempered conditions or is it possible to reveal the prior austenite grain boundries using 2% Nital?

1 more question presence of prior austenite grain boundaries are desirable or are dangerous to the integrity of the material.

Thanks

 

[metengr]

Read here

http://vacaero.com/information-reso...vealing-prior-austenite-grain-boundaries.html

 

[EdStainless]

Why would you care?
What is more of a concern is that the structure be fully tempered martensite. That is the desired structure.
The worry should be about retained austenite and similar issues.
In alloys with suitable grain refiners the final structure will always be fine grained, there is no reason to check.

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P.E. Metallurgy, Plymouth Tube

 

[goodbadgood]

Actually i have found 1 sample which extracted from drill collar and i found some indication of prior austenite grain boundaries along with tempered marensite and retained ausetnite after 2% Nital etch. This is the reason i was just checking that is it possible to reveal prior austenite grain boundries with Nital. Unfortunately i don't have picric acid to check that etchant.

 

[arunmrao]

How did you verify it to be retained austenite?


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[goodbadgood]

It looks like some black grain boundries inside but not clearly visible which gives a hint of retained austenite.
That is why i am confused because with nital you cannot see prior austenite grain boundries.

 

[steelmtllrgst]

Hi.

You can see prior austenite boundaries with nital in some cases, depending heavily on thermal history. In the as-cast coarse prior austenite state the boundaries are very clear with nital.

 

[redpicker]

If you have a drill collar made from 4140 material, I suspect that is your problem, not any prior austenitic grain boundries.

 

[goodbadgood]

yes i have a mud motor of which the top sub is fractured. Tensile properties of this material is also not matching so is this the material failure??

 

[EdStainless]

If the amount of grain boundary trash and/or retained austenite allow you to see the PAGB that easily then you have other issues.
Dirty steel, improper heat treatment, insufficient hot/cold reduction, and a few other things.
We Q&T 4140 to P110 properties regularly. All that you see is tempered martensite. If you see anything else you have problems.

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P.E. Metallurgy, Plymouth Tube

 

[redpicker]

yes i have a mud motor of which the top sub is fractured. Tensile properties of this material is also not matching so is this the material failure??

Well, if the tensile properties do not meet the required properties of the tool, yeah, I'd say that was bad material.

Most rotary shouldered connections need 120KSI yield and 40 Ft-Lbs Charpy Impact. If the material does not meet these properties, that is at least part of the problem.

In the section thicknesses used in mud motor top subs, it is unlikely that you will obtain these properties with 4140. Yes, it can be done, but most quality manufacturers will use a modified 4145 (with increased Cr & Mo for improved hardenability) to be absolutely sure there will not be a material problem. If the top sub was manufactured at a small shop using "commercially heat treated" 4140 bar stock, then downhole failure would be expected. There is a reason the quality manufacturers charge more for their tools.