Looking for history of 5160 spring steel

[Ian]

Alloy steel 5160 (a.k.a. AISI 5160) is a high carbon, chromium containing alloy that is often used to make excellent large knives and swords. It's main commercial use has been in the manufacture of leaf suspension springs for automobiles and trucks. In some parts of the world, such as the Philippines, these leaf springs are scavenged from old vehicles and the steel is forged into edged tools and weapons.

I have been trying to determine the history of 5160 steel, when it was first produced, and when it was first used in the leaf springs of vehicles. Have automobile springs always been made from 5160 steel? Searching the web has not yielded much information and I am obviously not looking in the right places. Perhaps someone can point me in the right direction or has a pertinent reference.

Why I'm interested in the 5160 story is that the composition of the alloy and its associated properties make it very useful for large knives and swords, and if we know that this alloy has been used in a particular piece we may be able to date it more precisely. The amount of scrap 5160 available may also be a determining factor. For example, in the immediate post-WWII period huge numbers of U.S. vehicles were made redundant and abandoned or destroyed in the Philippines, at which time large amounts of scrap 5160 would have been available relative to pre-WWII.

I'm hoping you have some answers.

Regards,

Ian.

[mariusgmioc]

Interesting topic!

Not the answers you seek but more of what you were saying.

In Nepal the leaf springs are the main source of raw steel material for the Kukris...

http://gurkhakukris.com/Content/cms/index.php?id=43

Moreover, as far as I know most modern combat-ready swords (like those made by Hanwei Forge for example) are made of this steel.

[Will M]

Wilkinson sword used steel very similar to 1095. Main sword manufacturers thought this was the best steel to use for swords. If modern makers use some other steels they probably use it due to availability or ease of manufacture as they are now made by stock removal, not forged and shaped..

[Ian]

Will,

I think the main attractions of 5160 are that it is a readily available, durable steel that can be hardened to take a keen edge, and that it is a type of spring steel that can be bent and it will return to its original state (up to a certain limit of course). The small amount of chromium in the alloy seems important in that respect.

The edged weapons and tools in many developing countries are still largely forged by locals from materials on hand, which is why scrap leaf springs are sought out. 5160 does not need to be folded or have an inserted edge because it has desired properties of toughness, edge retention, and springiness without being combined with other metals. For this reason, I know from personal experience that scrap springs have been widely used in the Philippines, Mexico, and Thailand. Interesting to learn from marius that Nepalese kukhri are also made from the same material.

Ian

[mariusgmioc]

Well Ian... yes and no.

While some smiths may use it for its availability, it definitely does not explain why big, major, modern companies use it. Hanwei for example has easy access to other high alloyed steels.

Its exceptional mechanical properties that makes it an almost ideal steel for swords and other bigger blades. From all I know, it has only two minuses:
1. it is rather sensitive to rusting and,
2. it is somehow harder to be worked.

[Edster]

Ian,

Interesting subject. Not sure if this addresses your needs, but I found them informative.

Try this one."Leaf Springs: Their Characteristics & Methods of Specification, 1912. Free Google Book.
https://books.google.com/books?id=6T...spring&f=false

Author says that the modulus of elasticity of all steels are virtually the same. Springs made with carbon steel "ride" the same as those of alloy steel of same dimensions. Alloy improved the resistance to repeated deflections. Other alloy additions modified other desirable qualities in manufacturing & use.

While not specifically addressed in text 5160's alloy composition enhances other qualities of the carbon steel, not springiness.

Steel grade standards developed first for structural steels and then to needs of the train and auto industries for consistency to engineering needs and design qualities.

Sword makers in Sudan & elsewhere transitioned from bloomery irons to a good material, i.e. carbon alloy steels from railroads or lorry springs when they became available after c. 1900. I guess it just happened that what steel that made good vehicle springs also made good swords.

Regards,
Ed

[Chris Evans]

Hi Folks,

An overview of 5160:https://www.azom.com/article.aspx?ArticleID=6743

A good article on how to best heat treat 5160: https://knifesteelnerds.com/2019/04/...at-treat-5160/

And where 5160 sits in terms of toughness among forging cutlery steels: https://knifesteelnerds.com/2020/02/...-knife-steels/

Ian: You could ask Larrin at Knife Steel nerds when 5160 came into generall usage: https://knifesteelnerds.com/


Cheers
Chris

[Ian]

Marius, Ed and Chris.

Thanks for your thoughts and suggestions. Much appreciated. I will report back here if I discover anything useful.

Ian.

[Ian]

Chris,

I sent off an email to Larrin Thomas, as you suggested. What a nice guy! He sent me a prompt reply which is copied below.

Hi Ian,

Finding steel history can be surprisingly difficult, and 5160 is not one I have looked into. I was unable to find the history of 5160. However, I looked some at some of SAE journals from the early 20th century and found a couple things. I found a reference to 5165 steel in the 1913 journal: https://babel.hathitrust.org/cgi/pt?...ew=1up&seq=638

5165 was not present in the 1912 SAE transactions: https://babel.hathitrust.org/cgi/pt?...iew=1up&seq=51

The chromium limits of 5165 were changed in 1919: https://babel.hathitrust.org/cgi/pt?...iew=1up&seq=14

However, 5165 was removed from the SAE specifications in 1922 "as there is apparently no use for it, and 5150 has been added for shafting material and for gear purposes." https://babel.hathitrust.org/cgi/pt?...ew=1up&seq=218

I found an ad from United Steel in 1919 advertising for "spring steel" which had four different brands including "Crucia" a Chrome-Carbon steel. https://babel.hathitrust.org/cgi/pt?...iew=1up&seq=88

So I didn't find 5160 but early versions of the steel date back to at least 1913. Perhaps with this starting point you can find something.

Larrin

And a further follow-up reply ...

Ian,

I found a reference to 5160 in a 1952 book, though it doesn't talk about 5160 as being the most common choice for springs, just one of the choices. https://babel.hathitrust.org/cgi/pt?...ew=1up&seq=483

Larrin

[mariusgmioc]

Very interesting. Thank you!

But actually this steel could have existed much earlier, maybe with small variations, only it was not analysed and documented.

It was only with Industrial Revolution that steels have started to be studied systematically. Prior to that it was only empirical study by trial and error.

After all, every 16th century rapier blade is a spring... but not even its maker knew its composition.

[David R]

Do you have an EN number for it?

[Chris Evans]

Originally Posted by David R

Do you have an EN number for it?

5160?

This website lists a number of equivalent standards, among which is EN - 60Cr3

http://www.zknives.com/knives/steels...&dlm=AISI&ss=1

Ian: Thank you for publishing Larrin's reply, which is very informative.

Cheers
Chris

[Chris Evans]

Originally Posted by Ian

. It's main commercial use has been in the manufacture of leaf suspension springs for automobiles and trucks. In some parts of the world, such as the Philippines, these leaf springs are scavenged from old vehicles and the steel is forged into edged tools and weapons.

Ian,

Leaf springs have been made from a variety of steels, not just 5160. Over the years I have seen mentioned 9260, L6 and the higher carbon content 10xx series including 1095.

So we must not make the assumption that just because many leaf springs were made from 5160, that all were of the same material.

As an aside, making swords and knives from discarded used leaf springs is not a very good idea because these springs develop micro fatigue cracks that are an invitation for later breakage in a sword of knife.

As another aside, the village blacksmiths in SE Asia tend to only harden the edges with a shallow edge quench and leave the rest of the blade soft, which mitigates the above risk, though it would not work all that well with thin bladed swords, at least not to our expectations.

Cheers
Chris

[Chris Evans]

Originally Posted by mariusgmioc

Very interesting. Thank you!

But actually this steel could have existed much earlier, maybe with small variations, only it was not analysed and documented.

It was only with Industrial Revolution that steels have started to be studied systematically. Prior to that it was only empirical study by trial and error.

After all, every 16th century rapier blade is a spring... but not even its maker knew its composition.

I very much doubt that the iron ores used to make bloomery iron would have contained the alloying elements required by the 5160 standard.

Cheers
Chris

[Ian]

Originally Posted by mariusgmioc

Very interesting. Thank you!

But actually this steel could have existed much earlier, maybe with small variations, only it was not analysed and documented.

It was only with Industrial Revolution that steels have started to be studied systematically. Prior to that it was only empirical study by trial and error.

After all, every 16th century rapier blade is a spring... but not even its maker knew its composition.

Hi marius:

Yes, I suppose chance may have led to an earlier use of a similar alloy, but 5160 is not just carbon and chromium added to iron. The detailed composition is given above. It seems unlikely that earlier smiths would have stumbled upon this precise formula, but I suppose anything is possible. There are non-destructive methods that can now test for mineral content, so your idea could be readily tested using old, well-dated pieces.

As for carbon steel alone being springy, that is absolutely true. The quality of a blade depends so much on its tempering, and properly quenched carbon steel can certainly exceed the quality of a poorly tempered 5260 blade. The addition of chromium adds durability toughness to the steel, making it less likely to fail under a load.

Ian

[Ian]

Originally Posted by Chris Evans

Ian,

Leaf springs have been made from a variety of steels, not just 5160. Over the years I have seen mentioned 9260, L6 and the higher carbon content 10xx series including 1095.

So we must not make the assumption that just because many leaf springs were made from 5160, that all were of the same material. ...

Very true. I am reading now some of the other materials used for leaf springs and will report back shortly.

... As an aside, making swords and knives from discarded used leaf springs is not a very good idea because these springs develop micro fatigue cracks that are an invitation for later breakage in a sword of knife. ...

Chris, would not some of these mirco-cracks be corrected during the forging process? The bar stock provided by a leaf would need to be worked extensively on the forge to get to a knife or sword blade.

... As another aside, the village blacksmiths in SE Asia tend to only harden the edges with a shallow edge quench and leave the rest of the blade soft, which mitigates the above risk, though it would not work all that well with thin bladed swords, at least not to our expectations. ...

Chris, I agree, but I don't think there are a lot of thin-bladed weapons or tools made from these sources. What I have seen are nearly all fairly sturdy pieces that are designed to last a long time. I know people who have had the same bolo for 20+ years and used it regularly.

[Chris Evans]

Originally Posted by Ian

Chris, would not some of these mirco-cracks be corrected during the forging process?

Maybe, but chances are against it. The inside surfaces of the crack become oxidized and are unlikely to weld shut, unless a flux is introduced.

The practice of recycling used leaf springs is not best practice because for starters one does not know the steel's composition and thus the heat treatment cannot be optimized. And then there's the matter of the said fatigue cracks.

In summary, it is one of those things that is widely done in the poorer regions of the world with the assumotion that near enough is good enough and things are OK until they are not.

This subject has been discussed over and over on blade smith forums and the experts always prefer new steel of a known composition. After all, plain and low alloy carbon steels are quite cheap.

Cheers
Chris

[Chris Evans]

Originally Posted by Ian

The addition of chromium adds durability toughness to the steel, making it less likely to fail under a load.

Ian

Chromium in small quantities increases the hardenability of the steel and what this means in practical terms is that a low thermal shock oil quench suffices, reducing the chances of cracks and warping. Plain carbon steels of the 10xx type require much faster quenches, traditionally in water or brine.

The matter of toughness is more complicated and I refer you to the excellent articles on Larrin's website. This one is very recent: https://knifesteelnerds.com/2020/02/...-knife-steels/

Cheers
Chris

[Ian]

Here are some interesting perspectives and a nice summary of the state of leaf springs in the early 1900s. It is apparent that the materials from which springs were being made was in a transition from plain carbon steel to alloys that had better properties suited to the greater performance demands of automobiles. At the time of publication (1912) the formulation of these new alloys was still being worked out. Although this book does not use the Society of Automobile Engineers' (SAE) terminology, it is clear that the usual steel used for leaf springs had been SAE 10XX stock, whereas some of the newer alloys included, among others, SAE 51XX materials. The advantages of these new alloys is clearly spelled out.

... Steels contain various percentages of carbon, depending on the purposes for which they are intended. When used for springs approximately one per cent of carbon has been found best. In the early eighties [i.e., 1880s] the Pennsylvania Railroad Company made long and costly investigations into the merits of the various carbon steels then on the market. These investigations were conducted by their chief chemist, the late Dr. Charles P. Dudley. It was found that steels having carbon ranging from .95 to 1.10%, or practically one per cent, were the most efficient from all points of view. The spring steel specification then prepared has since become standard for vehicle springs also. It is universally recommended in all branches of the spring industry, having withstood the hardest service. As a simple carbon steel it has so far had no rival, and may be looked upon as the acme in that class of material. It is the only material used in Dragon Brand springs.

The advent of the motor car forced springs into a service more severe and exacting than any they had been called upon during the past. The speed and weight of the new vehicle produced shocks and deflections unknown before. There has consequently arisen in recent years a need for a steel even better than the carbon stock described above.

It has been found that a carbon steel can be greatly improved by the addition of very small percentages of the heretofore less used elements, such as silicon, manganese, chromium, nickel, vanadium, tungsten, etc. Steels containing these elements singly or in various combinations, in addition to carbon, are called "Alloy" steels.

It is not our purpose here to extol the virtues of any one alloy steel. All have their inherent advantages and purposes for which they are admirably suited, while many undoubtedly have bad points. New elements and combinations are constantly appearing. In the course of time, by the natural processes of selection, the best alloy will survive, and, as in the case of the carbon steels, will be looked upon as standard.

It is often supposed that an alloy steel will, in itself, improve the riding qualities of a spring. It is imagined, for instance, that to replace a poor riding carbon spring by an alloy spring of the same dimensions would result in a marked betterment of the riding qualities. This is an error which we most emphatically contradict. The new spring will ride exactly the same as the old one. It will, however, possess one vast advantage in that its "life" will have been remarkably lengthened. The alloy is a hardier material, better able than the plain carbon spring to resist repeated deflection. In everyday language, the spring "will last longer." This is the only superiority which can be claimed for an alloy steel legitimately. The increased cost of the better material is returned in greater endurance and greater resistance to fatigue. …

It is a matter of everyday experience that if we double the load upon a spring its deflection will be doubled. In a simple spring the deflection varies directly as the load. That relation will, however, not hold true indefinitely, for when a load is increased beyond a certain point the steel is injured. To make this clear examine Figure1f again and imagine it to be a spring of one leaf. Suppose we increase the load on the bar by increments of 50 pounds, releasing it to its free height after each increase of load. It will be found that each additional 50 pounds produces practically the same increase in deflection and that each time we release the bar we find it to have resumed its original shape. But as we keep on adding weight continually, we will notice that our differences in deflection are no longer the same and uniform, but that they have suddenly increased, each being larger than that preceding. We will also notice that if we now release the load the bar no longer has its former shape; it has been permanently bent. This point in the experiment, at which the bar is permanently bent and at which the deflections begin to increase in greater proportion than the load is called the elastic limit of the material. That limit can best be measured by stating the stress which exists at the time. Each kind and quality of metal has its own elastic limit. Wrought iron can be stressed to about 25,000 pounds per square inch without injury, structural steel to from 30,000 to 40,000 pounds, carbon-spring steel after treatment to 110,000 pounds.

If we now examine an alloy steel in the same way we note a marked and truly wonderful increase in the elastic limit. This increase in the elastic limit, together with the accompanying ability to resist fatigue, are the essential characteristics of alloy steels. We can point out a certain Silico-Manganese steel, made in the electric furnace, which has an elastic limit of 220,000 pounds per square inch. The vast advantage of such a steel can easily be comprehended. A bar of it held in a vise could be bent just twice as far without injury as a carbon steel bar of the same dimensions. This does not mean that a spring of this alloy will merely last twice as long as a similar carbon spring. The ratio between the two is very much greater than this. For in addition to having a high elastic limit these steels also possess remarkable anti-fatigue properties. Instead of only doubling the life of the spring by employing alloy steel we increase its life many fold. …

From Landau D (ed.) Leaf Springs: Their characteristics and method of specification. Sheldon Axle Company: Wilkes-Barre, PA, 1912.

[Chris Evans]

Hi Ian,

Thanks for sharing that interesting information - All I can say is that we have come some way way from those days.....

Cheers
Chris