A knife is a knife, right? Wrong. Appropriate blade style, clip point, drop point, Tanto or flexible filleting blades are highly important. Ergonomics, ‘tacticool’ factor, fit and functionality are normally what attracts most of us to a good knife as well.
But just how much consideration is given to the actual steel composition of the blade? What type of steel is it? How do differing types take an edge? How hard are diverse steels to sharpen? Here, I will start with heat treatment and the Rockwell hardness scale, go through a few of the more popular types of blade steels as well as explain their composition, uses, properties and applications and conclude with a few words on care and black oxide.
Steel is not a naturally occurring element, it’s man-made. It is essentially comprised of varying percentages of iron and carbon, with a few other elements tossed in to suit whatever application, be it industrial, automotive, for tools, ships, firearms or appliances. Different steel compositions are designed for varying applications and these are often given a heat treatment.
This process of heating metal, often to extreme temperatures to, in the case of knives, achieve varying levels of hardness or to make forming operations of the subsequent product, such as machining or welding a little easier. Tempering of steel is a process carried out prior to high temperature heat treating. Initial tempering is conducted for a sustained few hours beforehand at a lower temperature, usually around 200-300 degrees to minimise brittleness in the latter stages of high temperature heat treating.
Later, heat treating to extreme temperatures, often in excess of 900 degrees, causes metal (in our case, steel) to undergo changes in its mechanical properties or molecular composition. Heating alters the microstructure which in turn gives the steel differing degrees of hardness resulting in (depending on percentage of other elements present) increased edge retention, corrosion resistance, ease of sharpening and eventual end use. The degree of hardness is measured using the Rockwell scale.
The scale was devised by brothers Hugh and Stanley Rockwell from Connecticut in 1914 when they applied for a patent on a differential depth machine which could quickly and accurately gauge the hardness of ball bearings. Basically, the Rockwell machine applied a load to a bearing surface to ascertain its hardness through attempted depth penetration and stress cracking.
The machine then displayed direct hardness values without the requirement for mathematical calculations. For us blade users, the values of Rockwell aid greatly in determining how the steel chosen by a manufacturer will perform for its specific task. Most knife and axe steels will value between 52-62 Rockwell. Large machete-type knives and axes will generally be made of slightly softer composition steel because their intended use is direct force impact, chopping.
Whereas a hunting or survival-type knife, with a shorter, more manoeuvrable blade can be made much harder to survive outdoors work exposed to the weather elements, but also because its use is for slicing and caping which are of course, slower, more deliberate movements.
This is a reasonably strong and deservedly popular steel for knives and machetes. The HC stands for High Carbon. It is used extensively by major manufacturers such as Buck, Kershaw, Gerber, Leatherman and others for not only blades, but handles as well.
It is stainless and is usually seen at 55 Rockwell making sharpening easy, but required frequently. With the correct heat treatment, 420HC can be elevated to about 58 Rockwell. 420HC is a cheap and readily available steel with a high resistance to corrosion. It is popular for use in diving knives and surgical instruments due to its high chromium content of 13 per cent.
This is a step or two above 420HC and is an excellent knife steel, but also sees use in bushings, bearings and valve ports. It contains roughly 14 per cent chromium and also 4 per cent molybdenum and about 1 per cent carbon. It’s a grand balance between toughness, hardness and corrosion resistance.
It was developed in 1959 and began being widely used for blades in the mid-1970s. It can be hardened to the 58-60 Rockwell bracket. This is tough, but not tough enough to become brittle when used with force. It is a popular steel for combination or serrated knife blades due to its ability to withstand sharpening with a rat-tail file without chipping. Leatherman use this steel exclusively in their interchangeable wire cutters on their multi-tools.
More commonly known as spring steel, 5160 is a slightly softer and more malleable and flexible steel which can be hardened to 57-58 Rockwell, making it ideal as a platform for axes as well as longer knife blades and machetes.
In industrial applications, it’s highly suited to tools and parts which require a high degree of impact resistance, such as leaf springs for automotive purposes. But why would you want a softer, more flexible steel in a hunting knife? Because it’s easy to sharpen.
If you’re like me and often take hunting trips which can easily run into a week’s length, with a little fishing thrown in, you’ll be using your knife a lot. Field dressing water buffalo or red deer, gutting barramundi or bass and general camp chores will be heavy work on your knife and being able to hone it up again quickly is of vast benefit.
And trust me, putting an edge on 5160 is easy. Note, there is not enough chromium in 5160 to make it a true stainless steel and it will patina with little use and is marginally more prone to rust.
S30V and S35VN
Now we are getting serious. These are the premium knife steels. S30V was developed by Dick Barber, of Crucible Industries, in New York in 2001. It is a wear and corrosion resistant steel which can be hardened supremely to between 59.5-61 on the Rockwell scale.
It takes time to resharpen if you are a novice, but once sharp, it retains its edge geometry for longer than almost any other steel used in the knife industry at time of writing. Because of its hardness, it would not be suitable for axe work, but for slicing, caping and field butchery, it excels. It is a type of powder steel, gaining great strength from fine microstructures in a rapid solidification process. This means it is also a dense steel. S30V was designed and developed in conjunction with collaboration from knifemakers.
S35VN was also developed by Crucible, this time by metallurgist Maria Sawford. It too is a powder steel and almost identical to S30V, but with a decrease in vanadium and an increase in niobium. This led to a steel which offered slightly better machining properties. S35VN was released in 2009.
These steels are quite expensive and are mostly only seen on high-end and custom knives. Buck refers to S30V as ‘the absolute best blade steel available.’ I’d have to agree.
Benefits to black oxide
I think no article on knives would be complete without a few words on black oxide, sharpening and knife care. When using any knives, especially ones which aren’t stainless like 5160, it is vitally important to clean out blood, scale or fur residue and give a light coating of gun oil or even Vaseline.
I prefer stones and a strop finish when sharpening my knives, but it’s a process which I actually enjoy. If you don’t enjoy it or don’t have the time, there is a myriad of commercial sharpeners available.
Diamond coated rat-tail files are absolutely invaluable when sharpening serrated or combination blades and they are ideal for sharpening gut hooks. Black oxide is mannetite comprised of sodium hydroxide, nitrates and nitrites and is used to coat the surface of ferrous materials.
Its main advantage is to increase corrosion resistance, so it is often used to coat lesser quality steels, although it is also often seen applied to 420HC, even if it doesn’t really need it. There is no discernible dimensional impact when using it and it’s far cheaper than paint, electroplating or cerakoting.
It also drastically lessens light refraction for tactical military applications and results in minimal build-up of residue. It will show scratches better than almost anything else, but I prefer to use it for its rust inhibiting qualities on blades and tools which I know will see heavy use outdoors.
Here’s hoping this brief rundown has helped you a little in your own knife selection.