Have you ever wondered what makes one blade steel superior to another or what makes a particular blade steel better suited to a particular purpose that another blade steel? Or, have you ever wondered what the difference is between a stainless steel and a high carbon tool steel and why some people have a distinct preference for stainless steels while others prefer high carbon tool steels instead?
Well, I have too and thus, I decided to do some research into all of the various alloying elements that are incorporated into various blade steels to see how the addition of each element affected the resulting steel alloy and quite frankly, I was surprised to see just how much the addition or subtraction of as little of 0.1% of a particular element such as Vanadium can change the latent properties of a blade steel!
Researching Blade Steel and Steel Composition
Therefore, to start my research, I first identified all of the various elements that are added to blade steels to create the various alloys and I found that they consisted of Carbon, Chromium, Molybdenum, Vanadium, Tungsten, Manganese, Nickel, Cobalt, and Silicon. In addition, while I was aware that Carbon (expressed as C) is the element that transforms iron into steel, I discovered that steels with a Carbon content greater than 0.50% are considered high carbon steels but, steel can only absorb 0.80+% Carbon at most and thus, any remaining Carbon in the steel serves to increase hardness.
I also found that as it relates to blade steel, Carbon is the single most important alloying element due to the fact that a high carbon steel is significantly harder than low carbon steel and thus, it will hold and edge longer than a softer steel but, it is also significantly less tough and thus, it is more prone to break than a softer steel is. Also, I discovered that Chromium (expressed as Cr) increases the hardness and edge holding ability of blade steels and that steels containing more than 12.5% Chromium are considered stainless steels.
However, I also discovered that there is apparently some controversy on that particular subject because one source I read stated that steels containing more than 10.5% Chromium were considered to be stainless while another source I read stated that 11.5% Chromium is required to produce a stainless steel. Next, I discovered that the addition of Molybdenum (expressed as Mo) increases the hardness of certain tool steels and that during forging, Molybdenum combines with Chromium to form hard, double carbide, bonds which help improve both the abrasion and corrosion resistance of the steel.
Next, I discovered that Vanadium (expressed as V) is added to help produce a fine grain structure during heat treating which improves the wear resistance of the steel and also refines the size of the gain which increases toughness and enables the steel to be honed to a very keen edge. In fact, many people report that they are able to get knives using steels that contain Vanadium noticeably shaper than they can non-Vanadium steels such as ATS-34 or 154CM.
Next, I discovered that Manganese is added to almost all stainless steels as well as to most non-stainless tool steels to help increase the toughness and hardenability of the steel but, that it also produces a coarse grain structure. Next, I discovered that Tungsten (expressed as W) is added to only four of the common stainless steels but is added to several of the non-stainless tool steels to help produce a fine, dense, grain structure (similar to adding Vanadium) which tends to negate the tendency of Manganese to create large grain structure without compromising its tendency to increase toughness and hardenability.
Next, I discovered that Nickel (expressed as Ni) is added to several stainless steels and many of the non-stainless steels to increase the strength and toughness of the steel. Also, I found that Cobalt (expressed as Co) is added to a few, select, stainless steels (and none of the common, non-stainless, steels) because it permits quenching at higher temperatures and increases the strength and hardness of blade steels and, it also intensifies the individual effects of other elements in more complex steels.
Last, I discovered that Silicon (expressed as Si) added to some steels in order to increase the tensile strength of the steel.
The Average Knife buyer
So, what does all of this mean for those of you who are simply interested in purchasing a knife with the correct blade steel for your intended purpose? Well, first of all, the amount of Carbon contained in a particular blade steel will determine if it’s a tough steel or a hard steel.
For instance, a steel with 0.55% Carbon content (such as SAE 1055) is not likely to be a particularly hard steel and is usually heat treated to achieve a spring temper and thus, it's a good choice for high impact blades such as Parangs, Bolos, Goloks, and Machetes.
However, if edge holding ability is more important to you, then you need a steel with a with a Carbon content more along the lines of 0.95% to 1.50% which would make it a hard, high carbon, steel. Also, because it seems that most people prefer stainless steels over non-stainless steels due to their ease of maintenance, noting the presence and quantity of Chromium is another important factor when choosing a blade steel because steels containing greater than 12.5% Chromium are considered to be stainless and thus they require far less care to keep them corrosion free.
In addition, noting the presence of Molybdenum is also an important factor when choosing a blade steel because Molybdenum makes the steel more corrosion resistant and enables the blade to hold an edge longer. Furthermore, noting the inclusion of Vanadium into the steel is the fourth most important factor in choosing a blade steel because the presence of this element has a significant effect on the fineness of the crystalline structure of the steel and will result in a blade that will accept and hold a keener edge than steels that do not contain this alloying element.
Lastly, it is important to note the presence or absence of Manganese in the blade steel because Manganese combined with Carbon often indicates a tough steel rather than a hard steel such as SAE 1085 and 1095 (indicates 10 series steel with 85% or 95% Carbon respectively) and, although high carbon tool steels are not stainless, they are an excellent choice for heavy duty tactical knives, combat knives, and survival knives as well as Parangs, Bolos, Goloks, and Machetes.
Although I personally prefer stainless steels, most advocates of high carbon tool steels state that they find high carbon steels easier to sharpen than stainless steels which is understandable due to the lack of hard, double-carbide, bonds created between Chromium and Molybdenum. But, with the correct type of whet stones, sharpening knife blades made from stainless steels can be just as easy as sharpening knife blades made from high carbon tool steels.
I have read statements by several American Blade Smiths who prefer to hand forge their blades from high carbon tool steels that such blades will take a finer edge and hold it longer than a blade made from stainless steels. In addition, I have read comments from some users who have stated that they have had knives made from stainless steels break or shatter when subjected to impact or lateral forces in sub-zero conditions.
Call me a cynic but I tend to view all such statements with skepticism (although they may very well be true!) because there are many different ways to temper and heat treat the various types of stainless and high carbon tool steels and proper heat treatment is every bit as significant to the performance of the steel as its chemical composition. Consequently, I believe that a properly composed and treated stainless steel is capable of rivaling the performance of the best forged, high carbon, tool steel blades although, I have to admit that I do not have any significant evidence to support my belief.
However, simply being aware of the various alloying elements and their properties is not enough information to judge a particular blade steel by and thus, it is also necessary to have something to compare that information to before it truly makes sense. Therefore, consider the composition of the following popular blade steels as a reference for your assessment of other blade steels:
- S30V – The top American blade steel designed by custom knifesmith Chris Reeves and made by Crucible Industries LLC. Consists of, 1.45% Carbon, 14.0% Chromium, 2.0 % Molybdenum, and 4.0% Vanadium.
- VG-10 – The top Japanese blade steel originally developed for use in high-end chef's knives and so named because the “G” stands for “gold” which indicates that it is the “gold standard” of Japanese blade steels. Contains 0.95% – 1.05% Carbon, 14.50-15.50% Chromium, 0.90-1.20% Molybdenum, 0.10%-0.30% Vanadium, 0.50% Manganese, and 0.30% – 0.50% Cobalt.
- 154CM – The former top American made blade steel still in widespread use. Contains 1.05% Carbon, 13%-14.5% Chromium, 4.0% Molybdenum, 0.5% Manganese, and 0.49% Nickel.
- 440C – The top American made blade steel before it was replaced in popularity by 154CM. Contains 0.95-1.2% Carbon, 16-18% Chromium, 0.75% Molybdenum, and 1.0% Manganese.
- AUS-8 – A Japanese blade steel commonly considered to be a mid-grade stainless steel a step above entry level but is not generally considered to be a premium blade steel. Contains 0.70%-0.75% Carbon, 14% Chromium, 0.1%-0.3% Molybdenum, and 0.75% Manganese.
- D-2 – An SAE grade, American made, semi-stainless, tool steel commonly used for making dies, industrial cutting blades, and high impact tools and when used for knife blades, it hold an edge exceptionally well. Contains 1.4%-1.6% Carbon, 11%-13% Chromium, 0.7%-1.2% Molybdenum, 0.6% and, Vanadium 1.1% Manganese.
- 1095 – An SAE grade, American made, high carbon, tool steel that is commonly used for machetes, hatchet heads, axe heads, shovels, and rakes, ect. Contains 0.90% – 1.03% Carbon and 0.30% – 0.50% Manganese.
Thus, by examining the above mentioned blade steels and comparing them to the above mentioned criteria, you can see that all of these popular blade steels are considered high carbon steels and that all of them except D2 (which is considered to be a semi-stainless steel) and 1095 are considered to be stainless steels. In addition, upon examining CPM S30V (which is considered to be the top American stainless blade steel), you can see that it contains only the four key elements Carbon, Chromium, Molybdenum, and Vanadium whereas VG-10 (which is considered to be the “gold standard” of Japanese blade steels) contains Cobalt which none of the other blade steels listed above contain.
Also, note that both S30V and D2 have the highest Carbon content of all of the steels listed and thus, they are an excellent choice for hunting knives and that AUS-8 has the lowest Carbon content of all of the steels listed which makes it an excellent choice for large, heavy-duty, general purpose blades and that 440C has an unusually high Chromium content which makes it extremely corrosion resistant.
Lastly, note that the high carbon tool steel SAE grade 1095 contains nothing but Carbon and Manganese and thus, it is a very tough steel but is also highly prone to corrosion due to the lack of Chromium or Nickel. Thus, by understanding what alloying elements are commonly incorporated into blade steels and how those alloying elements affect the properties of the steel, you can gain a considerable amount of insight into how a particular blade steel will perform in the field and for what particular purpose it is best suited.