Try this simple test. Take a .5" thick piece of the material to be tested ( your .5% Moly)and grind a couple of very tight grooves approximately .125" deep and .0625" wide and approximately 3" apart. (I would suggest that something thinner the than standard grinding wheel be used as this usually makes for too wide of a gap.) Perform the Dry MT and observe the particles VERY CLOSELY at the notch. The finer the mist of particles the better. The particles should stand straight out at the tip of the notch. Heat the plate to the approximate proposed test temperature and once again perform the Dry MT and observe the particles VERY CLOSELY at the notch. Note any difference if any. This should give you some idea as to whether or not you are getting enough field into the part. I have performed Dry MT at 650 degrees myself and found that the indications still show themselves quite well.