Fire

Yep-
ok- this is a fairly simple overview, as it can get damn complex, and I dont have my reference stuff sitting right here with me.

to start with, there are in general two kinds of knife grade steel- Carbon steel (or high carbon, or simple carbon, or whatever)
and stainless steel (440 stainless, surgical stainless, ect)
Both of these categories of steel have many, many different types and grades that fall under them- heres some of the pros and cons and some explanations

Carbon steels- these are fairly simple alloys, mostly just carbon and iron- in the U.S. the most basic carbon steels are called ten series, and designated by four numbers, all of which signify alloy content- for example, in the case of 1050 , the first two numbers designate that it is simple carbon steel, the second two show how much relative carbon content it has- in simple carbon steels, the more carbon, the more edge holding you can get out of the piece, and the higher rockwell, but the more brittle it gets- note that this is relative, without a good heat treat , its just accademic- more complex alloys add other elements and have different number designations- for example, 5160 adds a few things to make it springier (it makes exceptional swords), hence the 5 and 1 at the front- it has .06% carbon, hence the back two numbers-
there are also a boat load of specalized tool steels with names like A2, D2, L6. ect- they can be great if they are treated right and used in the right application- but in general, it is better to have a guy (or manufacturing plant) that knows how to get the most out of a simple carbon steel than to spring for a $30.00 a foot tool steel and then not do the right heat treat- its largely in what you do with it, which is why custom smiths charge so much, cause its one of the few trades left where know how can trump big machines-
Carbon steels are used in general because they hold a better edge than stainless, are easy to sharpen, handle shock much better than stainless, and can be forged and differentialy heat treated.....(more on that in the folding and RC section further down)
NOTE: carbon steel designations vary from country to country, with everyone having their own naming system, and there is also nothing stopping a company from producing their own steel that is virtualy identical to something else, except for a fraction of a percentage point difference in mix, and then naming it whatever they want- so if you see an unfamiliar steel, then read up on it, cause new ones are born every day- also remember the whole country differences thing on even simple, here its 1050, there it may be en50, unfortunately theres not much reason to it

Stainless steels:

stainless steel is an alloy of iron and carbon with at least 13% chromium in it- (at least here in the u.s., elsewhere it can be as low as 10%) the up side to stainless is low maintainence, the downside is that it does not, in general, hold as good and edge as carbon steel, and it is not as easy to sharpen- also, for large blades and swords, the same thing that makes stainless rust resistant also makes it brittle, so it is a VERY BAD THING TO MAKE A SWORD OUT OF- I shout because I see it done a lot, and it is to me like making a shotgun out of plastic tubing- messy and ineffective at best-
another strike against it as a sword steel is the fact that as far as I know, no stainless steel can be differentialy heat treated

Stainless works far better in small knives, and with the advent of better stainless alloys, the problems of sharpening and edgeholding are fading into the background - sadly, there does not seem to be corresponding hope for functional stainless swords -
Stainless steel is far more likely to be proprietary, and so has a bunch of designations, none of which nesessarily make any sense-
440 series- this is the top of the old style stainless- nothing compared to some of the hot shot alloys, but cheap and fairly easy to work with- it comes in three grades, A,B, and C , the latter being the best for knives

420 series- the el cheapo of stainless- not much to reccomend it except it doesnt rust

154CM- very good stuff, now seldom used as it is expensive, It has largely been replaced with the nearly identical ATS-34 which does the same thing and is cheaper- these two steels did more than anything to give stainless a better name as a knifemaking material than anything else- holds an edge well and is tough as nails-

Aus 6 and 8- have heard good things, ie its a nice new alloy that holds an edge well for stainless- but have not played around with knives made from this stuff myself

Surgical stainless- is a MYTH- there is no such thing, or standard- its just a lable manufactureres dreamed up years ago, that stuck

Like with carbon steels that are a myriad of new stainless steels comming out all the time- so it can be hard to keep current

Rockwell Hardness:
this is a measure of how hard a piece of steel is, determined by how far into it a diamond tipped needle thingy indents into it when put under serious force by a testing device-
for knife purposes they rate using the C scale - the higher it is the harder the steel, the better edge holding you will get, but the more brittle it becomes- for most knives 55-58 is fine- anything higher is a bit brittle for my tastes- swords should not be higher than 52 unless differentialy treated- optimum rockwell will vary based on the alloy in question as well-

Folded steel:
Properly called pattern welded steel, and commonly known as damascus steel, whole books have been written on the subject- back in the day ie the dark ages, folding the steel was a way to work out impurities, and maximize the strength of the resulting blade, while using as little scarce high carbon steel as possible- it has literaly thousands of variations and methods, but at its most basic it is acomplished by taking two types of steel, a high and low carbon piece, and folding them together untill you have several hundred layers-(swords were NOT folded a thousand times- this results in carbon migration and homogenous medium carbon steel that will not work as a sword. a sword may have thousands of layers, but those are composite blades made of many "layers of layers", ) idealy this should produce a stronger blade, much in the way that plywood has strength, this allows one to temper the blade to a higher rockwell without worrying about as much brittleness, as the low carbon steel will not harden and the "plywood effect " resists shock- when sharpened the extremly hard high carbon layers would stand out to form the edge, and provide the edge with micro serations, which some modern smiths call the Damascus Cutting Effect, or DCE- there is a lot of debate as to whether damascus blades are worth the trouble given the quality of modern steels, but they are certainly breathtaking in appearance, and much in demmand commercialy

Forged blades- blades that are worked with a hammer when hot- the masters of this in the U.S. are the mastersmiths of the ABS who literaly wrote the book on the subject- forging may or may not produce a better blade than stock removal, ( creating blades by grinding away the non knife bits) that debate is currently raging in a knife periodical near you! the general belief though, is that forging produces a slightly stronger blade, if done right, stock removal proponents hold that the benefit of forging a blade is so small as to be accademic.

I hope this helped some, its a confusing subject made worse by the fact that more than a few catalogs lable stuff wrong, and some foreign manufacturers , well, frankly, lie about their stuff- especialy be wary of cheap stuff from china and pakistan-

If you want more info I reccomend a few books

The Wonder of knifemaking, by ABS mastersmith Wayne Goddard

Step by step knifemaking, By David Boye

also pick up Blade magazine and /or knives illustrated

online- check the virtual blacksmith's junkyard, or anvilfire

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