Alloy steel

[ingnava]

Hello All!

I have a Steel sample of a fractured pinion, and I wish to know what kind of Steel is, I have reviewed some standards but it doesn't match for any I have checked. Also, we have made a metallographic examination and the microstucture observed, doesn't correspond to the carbón content detected on the sample by spectroscopy.

The composition is: C 0.22, Si 0.29, Mn 0.93, P 0.019, S 0.036, Cr 1.05, Ni 0.97, Mo 0.0064, Al 0.030, Cu 0.028,

I hope you can help me to know which alloy correspond to this composition, and why the microstructure shows a pearlite content so high in comparison of the carbón content.

Thanks in advance for all your inputs

Regards

D. Nava

 

[CoryPad]

Was the pinion case carburized? Nitrided?

How much pearlite is present? What about martensite, bainite and ferrite?

The alloy looks similar to 16NiCrS4 according to EN 10084 Case hardening steels, although that standard has a carbon range of 0.13 to 0.19 percent by mass. Perhaps your part is carburized and you were not in the core of the part, so the core is between 0.13 and 0.19 but the measurement site is elevated to 0.22 (and the case could be ~ 1.0).

 

[DeleteriousPhases]

would you consider posting the pictures of the exam at all?

 

[Maui]

Did you take any hardness readings in the case (assuming it was case hardened) and in the core? What did you find?

Maui

 

[ingnava]

Hello all,

No, I could not say if the part is carburized or nitrided, and the analysis was taken at the center of the sample, (it is a coupon 3/4" dia, 1/2" h), so I don't think we are checking at the carburized, or nitrided Surface. The verified hardness was 255 HB.

Attached you will find a picture of the microstructure observed.

Again, thanks for all your help

D Nava

 

[redpicker]

What size of pinion? That is, what is the approximate diameter of the shaft and the hub?

Often, a manufacturer will use a proprietary grade for their specialty products, usually by modifying an existing grade to enhance a specific property. Such as increasing the carbon range to increase the core hardness for large sections.

rp

 

[ingnava]

Hello Redpicker,

I have no idea of the size of the pinion, because the customer only sent a coupon of the failed part. We supply to them heat treatment services, and they asked for help in the analysis of that part.

regards!

 

[metengr]

The microstructure appears to contain proeutectoid ferrite and other transformation products (bainite, fine pearlite and colonies of carbides).

 

[CoryPad]

Furthering metengr's contribution, those are the phases present when (large) carburized gears are slack quenched. You need the whole part to review to make a complete analysis.

 

[Maui]

Did they send you any photos of the fracture surface that you could share? I agree with Cory - you will need them to send you the entire failed part in order to perform a proper failure analysis. At the very least a section of the pinion containing the fracture surface and a piece of the case carburized (or nitrided) surface layer should be provided so that you can analyze fracture surface, the microstructure, the hardness at the surface, and the hardness profile through the case.

Maui

 

[ingnava]

Thank you all for your inputs, unfortunately, they didn't share more info, or parts of the piece. They don't even know if they manufactured the part! Anyway, your help was so useful, and I appreciated all.

My best regards!

Daniel