There is another part that you can’t see here which is the tang. The tang is the rest of the blade that runs through the hilt, sometimes up to the tang button.

The most important part of a knife is the blade and the most important part of the blade is the part you can’t see: the internal construction. Steel is made at a foundry; carbon is added to iron to make steel alloy. Carbon makes iron harder and sets the crystalline structure, for a visual aid, it looks similar to a wood grain but microscopic.

There are other elements that can be added to give steel different qualities. Guessing the most well known is adding chromium and nickel to make stainless steel (side note, no stainless steel is 100% stainless there is always something that will stain it.). The list is huge on what can be added into iron/steel, but carbon is the most important: the more carbon the harder it gets up to the point of being brittle. So there’s a very fine line, especially when you’re only talking about a range of between 0.20% carbon for mild steel, up to 3% carbon for cast iron, which is very brittle.

As stated before, the crystalline structure of the steel is very important. When making a blade there are two very different ways of doing so.

The first is the way man has been making blades since he figured out how to use metal: that is forging using heat. This is what a Bladesmith does.

The other is what is called “the stock removal method”, basically it’s grinding. Now of course you have to grind a forged blade as well, but it’s only to refine the shape and to polish it up; you don’t remove any of the internal structure.

By forging a blade, the crystals are actually compressed when you draw out the edge or the tip; in turn this makes them structurally stronger, which is good, because these are the working areas of a blade.
Compression occurs when steel is heated to approximately 1000℃, all the crystals relax and the steel becomes malleable. This principle is important, for an example, when the tang is formed; there is no loss of any structure or material where the blade and tang meet which is the weakest point of a blade.

The hardening and tempering of a blade is next most important process in making a knife.
When medium to higher carbon steel is cooled quickly or quenched (from being around 800-900℃), it will set the crystal structure in position and the steel will be the hardest it can be without stress fracturing this is known as dead hard (there are also many other reasons for this fracturing). But this is much too hard to be a functioning blade, it would be really hard to sharpen, and the first time you hit it on something with any substance it would break.

Tempering is heating the blade again but only to somewhere between 100-350℃. Doing this relaxes the structure to a point (depending on the temperature reached), that softens the blade enough so as to be flexible and resilient. There are many ways of tempering, and each Bladesmith would have his own secret formula.

A blade should be tempered to match the purpose of the knife; you can temper a blade so it is soft in the spine for shock absorption, but still keeping the edge tough, or a blade can be made to be flexible like a spring. There are heaps of possibilities.
Forging a blade does have downfalls as well but most of these are the human or smithing faults. If you over heat or burn the blade you’ll either damage the crystalline structure or remove carbon. Poor hammering technique means the blade will have to have either as much, or more grinding done to get to a finishing stage, than a stock removal blade.

So the simplest answer to the question “What makes a good knife?” is:
The best blades are forged from medium-high carbon steel with the right temper for the tool.

The Hilt, this is next area that would be taken into consideration.
Most of the concerns with the hilt are personal ones for the individual that will be using the knife. There are a few criteria that all hilts should cover:
The tang should at the very least extend half the length of the hilt, a full tang is optimal; this is to give the knife greater strength.

The grip/handle must have no movement and is either riveted, glued, pressed, bound or all of the above. It is very dangerous for the user to have a loose handle; this means that you won’t be able to control the knife 100%. Grip should fit the hand nicely and comfortably.
Overall the hilt should be well sealed to stop grime and moisture getting in and causing rust.
The remainder of the hilt design is purely aesthetic, and as there is a massive range of materials that can be used, you are only limited by your own imagination (and maybe budget!). Just remember the hilt has to fit the purpose of the knife.

Housing of the knife is also something that should be thought about. Whether it’s in a sheath, box or on a stand; there are points that must be considered.

The knife should be protected from dirt, grime, and moisture as well as impact and scratching. The blade should be held safely and securely, this is for the safety of the user and bystanders. There should always be some way of securing the knife in it’s housing, for the security of the user but also to stop theft or misuse.