Assuming any of the following:
And let's assume the nail is rather thick - 3 millimeters or thicker.
What happens if I cut such a tree or log with a chainsaw and the chainsaw meets the nail? Would it likely cut no problem or will any damage likely happen?
Have you tried? Basically a good, sharp chainsaw will pretty much chew through nails and wire embedded in timber.
That doesn't mean you want to do it!
You want to ensure your saw avoids contact - even briefly - with metal obstacles in your wood. Because such contact will very very quickly blunt your saw. And if you value your time at all, you don't want to be chainsawing with a blunt saw.
An expert (which I am not) may be able to give you a fuller answer, involving safety issues, and damage to the saw itself ... but basically your number one problem is that you will blunt the teeth on your saw.
To add on to what Tea Drinker says, which is what happens on contact with metal, I don't ever use a chainsaw without wearing goggles, a helmet with mesh visor, protective chaps, heavy-duty gloves (make sure they don't go up past your wrist, or they will be easy to catch onto), and tight-fitting heavy-duty long sleeve shirt. I've never had any accidents. I think safe is better than sorry, especially when working on clients' properties, to give them a feeling of security.
You will go dull within seconds of hitting steel. I haven't had a chain fly off for this reason, but it is possible, so always dress prepared, and don't let yourself get comfortable. It's very inefficient time and money wise to have to happen chainsaw blades every few minutes, so if you have a tree which is riddled with steel, it's best to leave it.
Also of note: in areas like where I am, where hunting is a big thing, it's common to find lead bullets buried in the tree, and they can be anywhere in the diameter, depending on how long ago the shot was fired. These will dull the blades, but not nearly as much as steel. Just note that lead poisoning is not fun, so watch that you don't inhale the sawdust or rub it into your skin.
It can damage the chain blade. If this happens to you, use a sharpener to sharpen the affected blades.
I always find nail at the lower area of the tree where people like to hang things.
The same thing can happen if it hits wire or rocks, etc. Even with this, my chains usually last 5 to 10 cords of 18" firewood before I need to replace them
Pay close attention to what and where you are cutting. You will be fine.
The biggest danger is that the saw will bounce back. The user's manual for the Stihl E20 electric chainsaw says:
Kickback may occur when the nose or tip of the guide bar touches an object, or when the wood closes in and pinches the saw chain in the cut. Tip contact in some cases may cause a lightning fast reverse reaction, kicking the guide bar up and back towards the operator. Pinching the saw chain along the top of the guide bar may push the guide bar rapidly back towards the operator. Either of these reactions may cause you to lose control of the saw which could result in serious personal injury,'
I have heard of kickback happening to other people in my area, the saw can bounce back into your face or shoulder.
