I think you'll end up doing more damage to the cardboard than to the knife.
No kidding.
Cardboard contains abrasive particles, and so it might dull a knife edge (or wear the finish off) faster than say, paper or meat will. But will it 'damage' the knife? No. Hell no. As folding knives go, Emmersons are damn-near indestructible.
The CQC-14, (just so others won't have to look it up like I did) is the snub-nosed Emmerson folder. Like all Emmerson blades it can perform defensive roles, but its primary design consideration was for certain locales where it is illegal to carry a larger blade. On that basis I would not consider it just a defensive knife.
Regarding the other steels, 154CM is a stainless steel, 1095 is a carbon steel and D2 is a tool steel. The differences are functionally and metallurgically complex, but suffice it to say that 154CM is less likely to rust or corrode as quickly as the other two, and this makes it an ideal choice for a knife that you carry around all day. 1095 and D2 might technically be tougher, but 154CM is as tough as stainless steel gets, and especially in a knife of that size I wouldn`t worry about it.
On that note, it's easy but not altogether reasonable to get hung up on the kind of steel a knife uses. The heat-treatment of the steel, and especially the geometry of the blade, are much more important to durability, and edge retention, and cutting ability. (When was the last time you sharpened a swiss army knife?) My most useful knife is a wee little Gerber STL 2.0, made out of 440A stainless. Most serious knife users, including myself, will tend to scoff at that, since 440A is generally considered soft and obsolete. But if the knife works, well, it's definitely a knife then, isn't it? The same goes for your Emmerson; as long as it cuts, and you enjoy cutting with it, I wouldn't get too bogged down in details.
