Snaping the steel and looking at it is a good way for most of us to get an approximate idea of grain size, since the most common way for hardened steel to break is by cracking around the grains in the grain boundaries (intergranular separation). But for anything greater than 60X under the microscope this is a problem because at higher magnifications the focal points become too tight, so you would only be able to get one micro-thin level into focus while everything above or below that would be blurry. For microscope work you need a perfectly flat and level surface.
My pictures need a lot of improvement yet, since I do not have a press to accurately level the work (and inverted scope would be nice as well
), and my polishing equipment is still limited (you can still see plenty of scratches that shouldn't be there).
To accurately determine grain size, and the quality of the other features we are observing, requires much more effort than what most are aware of. I often see folks dipping blades or steel in ferric chloride and claiming they are observing grain, this is false. What they are observing is the transition zones from one microstructure (phase) to another. Tempered martensite etches very differently from fine pearlite, which etches differently from course pearlite or spheroidal carbides. All you are observing at that level are the shades of gray produces by the different rates of etching, and the only grain you can readily observe is the fibrous anisotropic flow lines of the steel if it has been heavily cold worked or is particularly loaded with inclusions (e.g. wrought iron).
To produce the real deal you need to cut your steel into cross section with no heat at all (water cooled) since heat would change things in there. Then I rough polish the surface to 600 grit on a belt (keeping it cool), and then finish polishing on 800x, 1200x, 2000x, 4000x, 6000x. Next you do need to etch to bring out the structures, but ferric chloride, while great for damascus, really sucks at revealing microstructure. I currently use a nital etchant that is 95% alcohol and 5% nitric acid. It only takes a several seconds to darken the surface and reveal the microstructure and different features can be highlighted depending upon the time in the etch. Then the work piece is mounted on a slide with some modeling clay, this hold things in place but also lets you level the piece, and put under the microscope.
As you can see, if you really want to look at this stuff you have to work at it, and a quick dip in FeCl doesnt show much. My digital camera has a USB connection into my computer so that I can down load direct, but more importantly I can do all my shooting remotely without vibrating the microscope assembly. I am now working on a way to accurately determine actual grain size using Adobe Photoshop as soon as the image is on my screen (image layers are quite handy).
I have pictures of my scopes on my website at this page:
http://www.cashenblades.com/Info/lab/lab.html
But it doesnt show the camera mounted on the trinoc, since I needed it to take the photo
As you can see Reg, as per our discussion in another thread, it is only common sense for most knifemakers to use what is available and works for them, I will readily admit that the levels I have gone to are ludicrous to anyone who is not neurotically off the deep end about the metallurgical end of things. But if I get get information from it, I might as well share it to make some of my efforts worth while.
Apologies- I just noticed that you cannot see the images on my page with mozilla unless you click them individually. I need to look into this.
. But the images were there and ready so I thought, what the heck, folks got to be interested in what is inside of those blades.