My problem is as follows,
I have tested (tensile) stainless steel 316L wire(18 thou) at various strain rates to ascertain its rate dependant behaviour. Since the wire is highly cold drawn (>85% reduction in area) in the manufactured state, ant further increase in cold work, with increasing strain rate, reduces the level of martensite in the structure (put simply, work hardening reduces with increasing strain rate).
Thats a brief outline of the exercise.
The problem I am encountering involves the metallographical examination of the structure to see the reduced martensite with increasing strain rate.
I am using optical microscopy and am electrolitically (6Volts)etching the samples using 10 grams oxiliac acid & 100 ml water, a standard etchant to reveal the grain structure in austenitic stainless steels.
However this process has not been successful.
An etching time of 1min is advised by the standards (ASTM-407, I think).
But this etching time severly (I think) erodes the surface and certainly does not reveal any of the grain structure.
Under-etching with a time of about 25sec oes not seem to effect the surface at all.
Variations of these times does not improve matters.
I have also used Vialles reagent
Why am I not producing the grain structure?
Are the grains too small to be seen at 100x on an optical microscope?
There is another suggested etchant (acetic glyceregia) but this is too dangerous to be made up according to the Chemistry department in my college).
The specimens have been ground and polished to a fairly acceptable level and would in no way affect the visibility of the grain structure.
So, what am I doing wrong?
Would the use of Scanning electron microscopy, etching for 25 sec, improve the situation?
Please help
I have tested (tensile) stainless steel 316L wire(18 thou) at various strain rates to ascertain its rate dependant behaviour. Since the wire is highly cold drawn (>85% reduction in area) in the manufactured state, ant further increase in cold work, with increasing strain rate, reduces the level of martensite in the structure (put simply, work hardening reduces with increasing strain rate).
Thats a brief outline of the exercise.
The problem I am encountering involves the metallographical examination of the structure to see the reduced martensite with increasing strain rate.
I am using optical microscopy and am electrolitically (6Volts)etching the samples using 10 grams oxiliac acid & 100 ml water, a standard etchant to reveal the grain structure in austenitic stainless steels.
However this process has not been successful.
An etching time of 1min is advised by the standards (ASTM-407, I think).
But this etching time severly (I think) erodes the surface and certainly does not reveal any of the grain structure.
Under-etching with a time of about 25sec oes not seem to effect the surface at all.
Variations of these times does not improve matters.
I have also used Vialles reagent
Why am I not producing the grain structure?
Are the grains too small to be seen at 100x on an optical microscope?
There is another suggested etchant (acetic glyceregia) but this is too dangerous to be made up according to the Chemistry department in my college).
The specimens have been ground and polished to a fairly acceptable level and would in no way affect the visibility of the grain structure.
So, what am I doing wrong?
Would the use of Scanning electron microscopy, etching for 25 sec, improve the situation?
Please help