Thanks for the details about how you do all this Kevin. I'm sure it's standard prep to those
who understand these things but it's new to many of us.
Now, how did you get a picture of austenite?
:biggrin: Great! Somebody asked the question I was hoping for:biggrin:, I am not surprised it was you that caught that Dan!
Indeed how does one micrograph a phase that is only stable above 1335F? Once again there would not be a story if I simply had access to the best labs where they actually have the ability to look at very hot things, but I had to get much more "creative".
I was writing an article for the ABS about austenite an realized that I really needed some images of the phase. Obviously I couldn't go to austenite at 1500F and do all the polishing handling and prep, or have my equipment survive, so I made austenite come to me!
With more and more alloying the stable temperature of austenite gets lower and lower, until you have things like "austenitic stainless steels" which are nonmagnetic at room temperature.
Now this may sound like the problem was solved as soon as I sectioned of a sample of 304, but it was not that easy. The stuff is stainless so nital etchant won't touch it:2:.
I have more than a couple metallography books setting around so I looked up the appropriate etchant for austenite and stainless steel. Remember I mentioned that you needed to choose your etchant according to what you wanted to look at, well there are literally entire books devoted to all the combinations of chemicals to make different etches containing everything from potentially explosive compounds to potentially lethal gasses. In the later half the 20th century a man by the name of Beraha added a whole new level of sophistication to the types of color contrasting etches, so it is really a science unto itself.
I did find one electrolytic recipe for stainless that used items that were both safe and obtainable, but where could I find oxalic acid?? I looked at my wifes rhubarb patch and the mounds of oxalis growing near my house but thought that would be way too much work (don't laugh I once produced a potassium based mix I needed from nettle ashes). Something chewed a the back of my brain that I should go to the lumber yard, and when I was there it clicked... WOOD BLEACH! (pure oxalic acid).
I brought it home, made a solution and then stripped the wires on the end of a little AC/DC adapter I had and voila! I could see austenite with my own eyes for the first time! All these years I could make it and feel it under my hammer I knew it was there but to see it with my own eyes was pretty cool!