I’ve used umpteen kilos of hard facing rods in the dim and distant past. I’m guessing they would be too brittle for shock loading?
Some engine valves were stellite faced – biggest problem I’ve had with those is the whole head dropping off! Not sure if that was hard valves running on hardened seat inserts, but it was a problem with one make of engine. Always the risk that the insert fell out first, I suppose.
A couple of pics of the valve head.

It started out at about 2 1/8“/2 3/16” diameter, IIRC. It bounced around for a while….
I know one fellow that removed what appeared to be a ball bearing from the combustion chamber of an engine which was run for some time (probably an hour or hours) after the valve dropped in. Engine was considered scrap on that one. My engine was repaired and is still in running condition.