I think the grenade damage values are good. Especially the first two tiers. (Higher level frags might be too powerful compared to HE grenades, but I won't judge before I see actual higher level content. Either way, that would be easy to rebalance by increasing shrapnel amount and decreasing shrapnel damage.)
Hmm. You could change grenade crafting to something like this:
Old progression
Mk1 grenades - 1x TNT (15)
Mk2 grenades - 1x RDX (22)
Mk3 grenades - 2x TNT (30)
Mk4 grenades - RXD+TNT(37)
Mk5 grenades - 2x RDX (44)
New progression
Mk1 grenades - 1x TNT (15)
Mk2 grenades - 2x TNT (19)
Mk3 grenades - 1x RDX (30)
Mk4 grenades - 2x RDX (38)
Mk5 grenades - 1x HMX (44)
Mk6 grenade? - 2x HMX (55) - optionally
- Secondary explosive has 25% difficulty modifier. RDX has 30 skillreq instead of 22. Tier 3 explosive would have 44 skillreq.
- The low skill requirements of the blueprint would be retained with similar skill progression.
- Grenade acquiring would be easy to control by modifying the rarity of explosives.
- Crafting Mk2 grenades would now be viable, which really isn't the case with the old progression. Mk3 is better, same component price, more common components.
Vendors:
The amount of TNT currently available in shops is good (making it even more common wouldn't hurt though), but RDX might be a little bit too common. Lucas always has one, Gort always has 2 and you can randomly find plenty more in shops (Len, Johan, Colton, Blaine?). Maybe change that a little.
This way grenade crafting would still be a nice boon, you could craft a few Mk3s or even Mk4 with it early on, but it wouldn't be something you could completely rely on.
PS. give us a blueprint for flashbangs! 
PPS. Question! Grenades don't have impact speed listed, how will they work with energy shields? I'm going to assume their impact speed would be at least high or very high.
That's not even close to ok. The way the grenades were balanced was that you should encounter new grenade level about every 5 character levels (earlier if you have high intelligence to craft them), this is why you can't find/buy mark 5s in the current content.
The fact that you can craft the highest level grenade with 44 chemistry (which a level 7 character can pull off with no intelligence bonus) is insane.
Here's how I'm changing it:
Mk2 and Mk3 grenade recipes are swapped. Hexogen requirement is increased to 50. Secondary explosives diff mod increased to 125%.
This will result in:
Mk1 grenades - 1x TNT (15)
Mk2 grenades - 2x TNT (33)
Mk3 grenades - 1x RDX (50)
Mk4 grenades - RXD+TNT (68)
Mk5 grenades - 2x RDX (112)
Much closer to what was intended. You will be able to craft mark 5s approx on level 20, earlier if you have high intelligence.
Btw, impact speed of the fire damage of grenades is high, while shrapnel impact speed is medium.