You can use optical microscopy if the amount of retained austenite is substantial (>15% or so). If it's less than that, x-ray diffraction is the most accurate method, so far as I'm aware.
Question 1) Generally, yes but, like Swall stated, not always.
Question 2) You can get an approximate yield strength measurement by performing a hardness test on the material. There is a pretty good correlation (plus or minus 15%, usually) between the YS and the hardness of a material. In my...
From my understanding, EDS is unable to give very accurate composition data for low atomic number elements, even if they can be detected. Due to the low ED response, the software tends to overestimate how much of the element is actually present. If I'm remembering that correctly, that's probably...
