RA in Ovako 146s

[karlmet]

Hi All,

I have attached a micrograph of Ovako 146s case hardened steel, I am estimating around 10% RA in the case (independent lab from H/T company state "No RA") I am also achieving hardness results to support the level of RA agains independent lab results of >800Hv! Is there a more accurate way of determining without the use of XRD etc?

Thanks

 

[karlmet]

http://imageshack.us/g/252/52862252.jpg/

The above link is of the samples from the HT comapany and from an independent lab (supposedly from the same sacrificial test piece). Microstructures look very different and a difference in hardness of approx 200Hv.

 

[TVP]

As you already know, x-ray diffraction is the most accurate method for determination of residual austenite content in steels. However, microscopy techniques are frequently used, and some of them are more accurate than conventional nital etching. If you have access to a Scanning Electron Microscope, this can be particularly helpful when observing etched microstructures. Here are some links with good information on this subject:

Color tint-etching for multiphase steels

http://www.asminternational.org/sta...b9b1410=0&bcsi_scan_filename=amp16102p027.pdf

Imaging of Phases in Steels

http://www.georgevandervoort.com/met_papers/IronandSteel/imaging_phases_in_steels.pdf

Martensite and Retained Austenite

http://www.georgevandervoort.com/met_papers/IronandSteel/Martensite_RetainedAustenite.pdf

Etching Techniques for the Microstructural Characterization of Complex Phase Steels by Light Microscopy

http://www.mtf.stuba.sk/docs/internetovy_casopis/2008/4mimorc/hairer.pdf

 

[karlmet]

Thanks, some interesting info.Klemm's tint etch could be worth trying as an alternative. Any idea on the claimed >800Hv? As no carbide network is visible and the material has been tempered I would have thought this would be near impossible to achieve?

 

[TVP]

Agreed, I have only seen 800 HV in cast iron that has been exposed to extremely rapid cooling.

 

[karlmet]

Thanks TVP,I'm awaiting response on these claimed results.