One of my longer-lived test fortresses survived for many (20+) years on mithril and d-steel. Tungsten is a pretty decent material aside from its weight, so an artifact reactive plate of that is going to be useful for some time, more because of its superior coverage than anything else. The best way to find out is to just run with it. I find that artifact armor tends to outperform its material more often than not. Also, it is a chest plate - you can always put the chainmail of your choosing underneath it.
Tungsten is, as Putnam mentioned, a remarkably hard metal. Tungsten carbide, an alloy of equal parts tungsten and carbon, is harder than steel, and is used in modern machinery and armor-piercing rounds. Unfortunately, it takes very high temperatures to manufacture (hotter than magma). Lower temperature synthesis is possible, but requires some very advanced technology (flourine gas, teflon gaskets, lots of risk of dwarves being melted by acid, etc). That's not to say that tungsten carbide won't ever be a part of LFR, but it will need some serious tech advances beforehand and some creativity on my part to make it seem reasonable. If it does come, it won't be until a very late tier, at which point I must weigh the possibility that the required investment might outpace the potential reward, as I'm not sure how tungsten carbide would compare to something like voidshard - there doesn't seem to be a natural place for it to fall. At this point, it might or might not be included - we'll see how things work out moving forward.
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For now, the advanced alchemy lab is focused on investigating new materials (with some help from the experimental materials workshop), specifically looking at the first dwarven forays into magnetism and limited use of electricity, which will get a foot in the door to what has always been the sort of "end goal" of the tech tree - mechanical constructs. This tier of the tech tree will look more like traditional, almost steampunk research and development, with investment of highly varied reagents, trial, and error. Mad, bearded scientists test their hypotheses with alcohol, elaborate contraptions, and unstable prototypes, a la Da Vinci or Tesla (much of the inspiration comes from these two inventors). What that means for you is hybrid weapons, experimental combat technologies, more potential disasters and lab accidents, and some other stupid dwarf tricks thrown in for good measure.
Imagine a dwarf tinkering for years with a new weapon/contraption, whilst all of his colleagues think him insane, who goes down in history not for his contribution to the military, but for some very unusual cheese that he accidentally created as a byproduct of his research. That's kind of what this tier is going to look like.