I have been trying to smelt titanium bars for my next tool upgrade. There doesn't seem to be a titanium bar recipe in the forge though. I tried taking some titanium and coal up to the forge, hoping that the issue would resolve itself, but that did not work.  Is there some titanium bar quest unlock or is it a bug?  

There is a quest for it, if you found titanium ore I think you’ve gone deep enough in the mines already to meet that requirement. I believe you have to do Kiera’s quest to get honeycomb as well before the quest from Sven will unlock.