52100 Microstructural Questions

[sodeen]

The quick breakdown:

- 52100 Steel, through-hardened to a martensitic phase for bearings.

- Material from other sources with this part # are running fine, but this specific batch of material is growing/shrinking all over the place, going way out of round and out of flat.

- Cut and polished a sample, Nital Etched (5%) and here's what it looks like at 150x:




Doesn't look like the normal spiky pine-needles of martensite, that's for sure. I'm thinking that perhaps the dark areas are oversized spheres of Pearlite that didn't fully dissolve, but I'd love some other input. (Never was good at microstructures.)

For the record: It's cheap-ass Chinese Steel with questionable carbon smudges on the mill certification.

 

[EdStainless]

look at samples before heat treat.
check chemistry.
You are right, this looks wrong.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metengr]

Agreed; The large globules look like coalesced carbides from either over tempering or unheat treated material. Did you obtain hardness? I cannot define the large dark islands, you would have to view unetched and compare.

 

[metengr]

Here is the TTT diagram for 52100 steel

http://www.industrialheating.com/IH/Home/Images/ih0607-htdr-fig.1-lg.jpg

Here is the CCT diagram for 52100

http://www.industrialheating.com/IH/Home/Images/ih0607-htdr-fig.2-lg.jpg

 

[redpicker]

I'm thinking you are looking at a prior microstructure issue, not really a quality issue. Try a process anneal by heating to 1600F for an hour per inch and drop the furnace to 1200F holding an hour per inch plus an hour. Then, heat treat as usual.

While it is easy to blame "cheap-ass Chinese Steel", it is quite possible the steel quality if just fine, but they just used a annealing cycle that resulted in a microstructure that is very difficult to austentitze. My experience with Chinese producers shows that they are not nearly as "cut every cost" conscious as domestic sources. They do often have quality issues, but if you are using them as a supplier, making the assumption that they are just trying to make it cheap can often make you overlook many of the issues that cause the problems. Then there is the whole language/culture issue...

rp

 

[sodeen]

Didn't mean to offend any QA working in the Chinese Steel industry - just figured the cheap-ass moniker was a quick way to indicate that we're buying this stuff because it's the absolute cheapest we can get. All other things being equal, you get what you pay for in most cases.

Polishing and etching the pre-HT samples shows bands of light/dark material in the microstructure.

 

[mrfailure]

Sodeen,

The ideal microstructure for this steel should be carbides in a martensite matrix when heat treated. You should look at this structure at higher magnifications. ASTM A892 lets you rate the quality of the structure in terms of carbide size, network, and lamellarity by comparing structure at 1000X. Lower mag micrographs for this material are very misleading and subject to misinterpretation.

Aaron Tanzer

http://www.lehightesting.com