Is there any possibility of contamination by Si due grinding tool steel with SiC grinding paper? I have grinded and polsihed a microstructural sample with SiC paper. After polishing there was not any black, or pore like features. However, they started to appear after etching, please see image attached. Is it possible that these are SiC particles? The material is AISI H13 tool steel.
Thank you.
I do not think these are SiC particles. You may ultrasonicate the sample after polishing to knock out the emery particles. The H13 steel may have ~ 1% Si already. You cannot contaminate the steel with Si by just polishing with SiC because of very high bond strength between Si and C. Typically H13 will have relatively large carbide particles (that can be resolved under optical microscope) that are uniformly distributed in the tempered martensite matrix. These black spots (at least the smaller ones, if not all) could be carbides. The matrix is under etched. It is also possible that the carbides have been pulled out during polishing. Imaging under the SEM and performing an EDS analysis will resolve this issue, if you can do that!
Dear Ali,
Too much grinding or use of coarse particles can effect your microstructure. After etching the black spots may arise due to over burning of the sample due to etching. As some grain boundaries can also be seen in your microstructure, this does not imply that these black spots are SiC particles.
Thanks everyone.
Krishnan Raja I do have SEM and EDS facility. I will try investigate more with them.
The mesh size of abrasive particles present in the grinding wheel are below 200. So After the grinding, samples will polish at 250-300 mesh of SiC paper at least 30 minutes with 500 RPM. Farther go 320- 400 mesh for 1 hr. Then again you will polish the sample 500 mesh and 800 mesh for 2 hr. As same 1000, 1200., 1500, 2000, the mesh will use then diamond (cloth polish ) each 1 hr.
The RPM of the Polishing dish, not more than 500 in each case.
I really don't think that SiC particles glued to your metal surface during grinding or polishing but it can be diamond's ones if you ended your process with these medium (that is generally mandatory to obtain a "mirror surface" prior to etching).
I never use simple SiC paper polishing sequence...
A 2nd solution can be also corrosion (or oxydation) due to the basic or acid solution you used to echo your steel if you apply a too long duration. And your image shows different phases so maybe its also contains Si oxides or carbides in the matrix...
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