Author's note to forumites: I invite you all to please look at this draft article with the purpose of criticising it severely, and in this way you will help me (if you will be so kind) to upgrade it into something a bit more useful than it is now. This is the first of two articles, the second one being "Heat Treatment of Khukuri Steel", so logically all significant references to heat treatment in this first article has been deliberately suppressed.
If you bring out well-meaning criticism, and I hope you all do, please do it in such a way that I can easily react to it. Don't say eg. "It's not too clear, really..." because I have accessed as many pieces of information, including many websites suggested by forumites, as possible in the time and under the circum stances. Actually please suggest concrete improvements or correct existing sentences in your replies. I don't mean for these articles to be solely under my own authorship.
I personally believe this article is not finished yet, because in my own mind I still have questions. I will put these questions in the text, after the words: "Author still confused" (more than normally).
Please remember, this is not for eventual commercial publication. It's just for me, and for you, for our own interest and enjoyment...
KHUKURI STEEL
Compiled by Johan van Zyl with the kind assistence of forumites
Prologue - This article is not meant for those already in the know, but for young and not-so-young prospective collectors of khukuris, and all other khukuri enthusiasts who are naturally inclined to want to know more about the objects of their interest. Steel being what makes a khukuri able to do a proper job of work, KHUKURI STEEL is what this is all about.
Introduction to hammer-forging of khukuri blades
It is said by people familiar with forging as a method of shaping blade steel, that it is the only way, albeit old-fashioned, to achieve real strength and edge-holding ability in a blade. The blades of Nepalese khukuris are shaped in this way.
I find myself on my guard as I write these statements. I realise that if I am sympathetically inclined towards the objects of my interest, in this case khukuris, I might overlook shortcomings, and I might magnify good qualities in order to make my point. That is why I do not actively stop myself from criticising khukuris, or hearing khukuris being criticised. For that reason, I venture into this topic of khukuri steel to try to lay bare the relevant facts. I hope I might find that, at the end, khukuris do have some good points stacked in their favour!
There seems to be something special about forged blades. However, one seldom hears of blades, besides khukuris, being made the old-fashioned way. Today, most modern quality factory made and benchmade knives are ground out of bar stock or even investment cast. The famous makers don't seem to want to admit forging is a better method, if in fact the statement is true.
The blades of all well-made, traditional khukuris are forged. The cheaper Indian khukuris are also forged, as one can tell by looking along the length of the blade in the light. So why are some of the Indian-made copies of khukuris scoffed at most of the time? Certainly, it is because of poor acceptance by users due to poor performance in the field, not only in terms of overall quality of visible workmanship, but also because they bend or chip when used under harsh conditions.
..............Author still confused: Are there really no khukuris of good quality made in India? If so, Nepal is the only Eastern country from which the really good ones come.
In high quality khukuris there is superior quality control over the various stages of forging. One might say it is the eye of the expert kami (traditional Nepalese bladesmith), which ensures eventual success in the making of these knives.
What does hammer-forging do?
A properly hammer-forged and hammer-packed knife can hold a good edge and have a spring temper, claims Lewis & Combs (1992), even without heat treatment. When heat-treated, its edge-holding capacity is reportedly unsurpassed. These authors explain that hammer-forging aligns the crystalline structure of the steel to create a more resilient blade. They say a hammer-packed edge is not only tougher, but takes a higher degree of sharpness and holds it longer.
Well, I try hard to understand statements like these. You have to be able to look inside steel to comprehend clearly what is meant. There is a discipline (metallography), which does just that. This is the science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by such tools as low-powered magnification, optical micros copy, electron microscopy and diffraction or x-ray techniques. But it is not easy to explain what steel looks like inside. It is said that steel can be considered a solid "solution" of iron and carbon. The iron atoms are arranged in a cubic configuration, also called the crystalline structure, within which the carbon atoms are tucked away in the interstices. The atoms are in a state of thermal agitation, even at room temperature, and are moving in small orbits or oscillating back and forth with more and more vigour depending on temperature. If this is not confusing enough, it also seems that steel has grain, much like wood. The "flow" of the grain in steel, and the alignment of the crystalline structure of the metal, seems to be one and the same thing.
I assume, in grinding a knife blade from bar stock, that when you start working, the grain is aligned along the length of the steel. Then, I conclude, when a knifemaker grinds a curved blade, he actually cuts against the grain in some parts of the blade. For instance, when he makes a khukuri, using this method, a certain part of the blade will be cut at an angle into the grain.
Now in forging a piece of steel, the grain flow becomes aligned along the forging lines (Lewis & Combs). For instance, if you forge a khukuri blade, the grain flow now follows the curve of the blade. In this way the steel is strengthened by forging. Compare the strength of a hoop-shaped armrest of a chair made from rattan, in which the grain follows the curve due to the bending process, with an armrest made from a solid piece of timber machined out. My judgment is that the armrest in the case of the rattan will be able to withstand more abuse than the one made from a machined piece of wood.
.............Author still confused: Assuming Lewis & Combs is correct (that the grain flow is alligned along the forging lines), then I must assume that the end product, after heat treatment, still has grain which follows the curve. If the heat treatment cancels out the grain flow, then it is useless to mention the grain flow in the first place.
But this comparison of steel with wood might be regarded as too simplistic. However, I have seen pictures of irregularly-shaped forged objects which have been etched to show the grain flow, which illustrates very clearly that the flow follows the curves.
The materials used in khukuri bladesmithing
Various advertisements claim that khukuris are forged from high-carbon steel.
According to the Khukuri-FAQ website (Wallace), kamis prefer to use Mercedes Benz or Saab truck leaf springs, if they can get them, to make khukuris. Now vehicle leaf springs are made of the so-called carbon steelsand possibly also alloy steels, both of which are non-stainless.
Carbon is present in all steels, but in varying quantities. It is the most important hardening element in steel, and it also increases the strength of the steel. Knifemakers want knife-grade steel to have more than 0.5% carbon, which makes it "high-carbon" steel. The Encyclopaedia Britannica states that spring grade steels (the kind used in the manufacture of vehicle leaf springs) range from 0.85% to 10.5% carbon, used in a heat-treated condition.
Being the steels most often forged, carbon steels can be differentially tempered, and the kamis have allegedly been using this characteristic to good advantage, giving the steel a hard edge and a tough springy back. Tests done on a number of khukuri blades have shown that hardness is definitely not the same throughout.
Let me admit, I didn't know exactly and specifically which carbon and/or alloy steels are used in the manufacture of truck leaf springs. I read up on some material about steels compiled by collector and knifemaker Joe Talmadge, and consequently found that the springs might be made of one or more of the following:
5160 steel: This alloy steel, popular with forgers, has about 0.60% carbon. It is essentially a simple spring steel with chro mium added for hardenability. It has good edge holding qualities, but is known especially for its outstanding toughness. Quite often used for hard use knives, har- dened up near the 60s on the Rockwell "C" scale. I thought this might be a likely candidate used for the truck leaf springs.
1095 steel: This carbon steel (belonging to the AISI 10-series) is the most popular for knives. 1095 is, sort of, the "standard" carbon steel, and it performs well. It is reasonably tough and holds an edge very well. This is a simple steel having 0.95% carbon and 0.4% manganese as an alloying element. I felt that this might have been used in the manufacture of some truck leaf springs as well.
Joe Talmadge responded to my plea for further help, and suggested that 5160 steel is probably used in the making of truck leaf springs. Shortly afterwards I browsed through an information leaflet by the North Texas Blacksmiths Association, which states that vehicle leaf springs are made of 1085 and 5160 steels. At last I had some conclusive evidence. And the more I read up on the topic, the heavier the weight of evidence became, in favour of 5160 steel.
Regarding the preference the kamis have for Mercedes Benz and Saab truck springs, I asked myself on what grounds do they base that preference. Surely it is through experience in the forging of the various steels, in terms of the quality of the final product, that they are able to stand back eventually and declare they prefer this or that.
Concluding remarks
Hammer-forging allows the kami to change the shape of the steel. As an added bonus, the flow lines are arranged more or less parallel to the finished surface (as has already been pointed out), and the lines take an easy curve around corners. But as the spring steel is heated and hammered, it becomes more brittle and hard. That is why it is general procedure to bring the steel back to its original state by annealing (heating and then cooling slowly), if the desired shape is not yet reached.
Although it is said that some metals are harder to forge than others, I don't think there can be great variation in the "feel" of different vehicle leaf spring steels when hammering them on the anvil. But somewhere along the line quality checks must have been made on completed khukuris, and it must have been found that khukuris made from Mercedes springs conform best to the qualities desired in the best knives.
So what are these "desired qualities"? To put it in a nutshell, the blades must not bend when subjected to stress and the edges must be sufficiently hard. This is a big part of what separates real khukuris from wall-hangers.
But although the kamis seem to PREFER Mercedes and Saab, it does not imply they actually get it. Your next khukuri might be forged from a piece of Lada spring.
In the final account, it that so important? Whatever the case may be, I think we all accept that there's more to knife performance than merely the steel chosen to make the knife from. For one thing, the blade profile is important, in view of the task you need the knife for.
But perhaps the most important, after all, is the heat treatment. Some say the heat treatment is the soul of the blade. This is the topic of the follow- up article: HEAT TREATING KHUKURI STEEL.
