CJ is right? A stainless steel machete with a thin blade is not well suited for chopping things anything wider as your finger. 420 HC steel is not something i would recommend for a tool that has to suffer impacts. 1075 or 1085 or S7 is much more suited for chopping tools. The benefits of a stainless chopper do not outweigh the possiblity of breakage. A little FeO will not hurt the plants, nor your food... The benefit of carbon steel is that in most cases it will bend instead of breaking all of a sudden.
Don't worry it's just a learning curve,i hope you will get a new machete and if you need to cut a thicker brand try chopping it sideways,slicing of smaller chips instead of straight on chopping. Chopping equals carbon steel, or tool steel, not cutlery grade stainless steel. If you really worry about rust prevention, soak the blade in mineral oil. You can still use it to cook and it will not rust away before your eyes. Or put on a nice patina from the start with hot vinegar or the likes.It will look cooler then red oxidation and it will resist new oxidation.
rule of thumb:
cutters and slicers: high end stainless steel (and some carbon as well).
Cutting choppers ( good impact resistant stainless steel if blade lenght is not longer then 5 inch).
Choppers (carbon or tool steel, but no stainless steel)
I concur with your guidance to the original poster. Stainless isn't the most ideal class of materials for an implement intended to be bashed vigorously against hard materials. You are very lucky the broken shard of blade didn't fly back into you, as can easily happen.
I would specifically argue for a softer blade and edge relative to your garden variety pocket knife. Microscopic cracks can and do form in hard use implements, the softer, springy temper tends to limit the depth and length of such microscopic fractures.
Because stainless steels tend to be fairly brittle by comparison to even a high carbon steel, even drawing down the hardness to below 50 HRC won't necessarily provide the same toughness and resilience that a medium or high carbon steel can (1060, 1070, 1085, etc.) will at around 53-55 Rockwell (which is a bit harder than I'd prefer for these blades).
The stains and minor scratches that a machete will tend to accrue are merely cosmetic. Hard use knives aren't really meant to be pretty. When heavily used, a machete will strip off any protective coatings or oxides on at least half the blade. Cleaned off after use, the blade will develop a dark oxide patina. With a light coat of oil applied, it will almost certainly not rust unless the sheath absorbs the oil from the surface and moisture condenses on the blade.
There are a number of truly excellent Central and South American style machetes, African style Pangas, Indonesian Gloloks, Bolos, Filipino Barongs and virtually all of the better made examples are of medium to high carbon steel with a nice springy temper. Hacking down a small diameter soft wood like pine won't phase a well made machete, even if it's probably the wrong implement for anything heavier than brush.
Check the online vendors such as Valiant if you favor the Eastern styles, Tramontina, Condor, Ontario and even Cold Steel will cover the styles found in the Americas and Africa.
Good luck and stay safe -
Happy 4th of July.
The OP said this was a felled log over a 4x4 path. It appears to me that any 4x4 could get over that. I think the OP really wanted to use his machete, so he rationalized that he "had to" cut and remove the log and it was more like that "he wanted to" use the machete to do that. I am not different in that aspect. I could have easily tried that same thing many years ago. Then my dad would have called me a dingbat, and told me how dangerous steel snapping like that could have really hurt me. Dad never had a problem hurting my feelings, but never wanted me to get hurt. As do I for the OP. 
