The Pros and Cons of Recycled Steellewis.yoole
Article written by: David Grinter
At one time in Australia, mild and recycled steels were all you could easily source. If you wanted a steel that was heat-treatable and forgeable, chainsaw bars, leaf and coil springs, axles and hydraulic rods, large bearing races, old files (known as OF) and railway spikes were the go-to. If you wanted a more ‘fancy’ steel such as O1 Tool Steel, you had to go to an engineering supplier and buy precision-ground stock for an arm and a leg. 440C Stainless Steel and other similar steels often had to be purchased from the US.
At that time, recycled steel was used because there was nothing else. We now have much more choice.
Recycled steel is often referred to as, ‘Mystery Steel’ because the exact manufacturer and composition of the steel may not be known. The composition of recycled steel can sometimes be identified from its previous use, and tables exist that help to indicate the type(s) of steel(s) it might be. Resources such as the Machinery’s Handbook give heat treatment instructions based on this kind of identification.
As a rough guide, files are often claimed to be W1 or W2 Tool Steel or a comparable steel. This is often true for older files. However, if they were produced in more recent decades, they may be case hardened with a mild steel core. Similarly, car springs may be 5160 or SUP9 Spring Steel or other similar steel, but depending on date of manufacture, they are just as likely to be case hardened or impulse hardened from an alloy that’s otherwise unhardenable. Old or good quality recycled hammer heads are a great head start for small tomahawks, but experience teaches us that some Chinese hammers crumble like cast iron when forged. Large bandsaw blades are often said to be made from L-6, but it would be a mistake to assume that’s always the case. Axles and hydraulic rods are likely to be similar to 4140 steel, a chromium/molybdenum steel, but in the range of roughly 0.40% carbon. This is the right carbon content for tooling or hammers, but won’t hold a good enough cutting edge for knives. 1045 Steel is a good option at this carbon content.
Steel Grades and Alloys
What do these numbers mean? There are many steel standards and naming conventions out there and ongoing attempts are being made to unify them nationally and internationally. Equivalence guides are often US-centric, adhering to the American Iron and Steel Institute (AISI)/Society of Automotive Engineers (SAE) standard. Plenty of knifemakers – US and Australian use this as an easy reference system, particularly as much English-language knife making literature comes from the US.
The comparability of recycled steels can also be based on their previous uses within different industries. There are plenty of examples out there from steel companies. For example, Hastings Machine Company. These tend to be US-centric.
A common US standard is the number series used by the SAE. The simple 10XX series is well known and easy to understand as the first two numbers indicate the alloying element and the proportion of it by weight, and the second two digits indicate carbon content by weight. For example, 1075 Carbon Steel essentially indicates a low alloy carbon steel with 0.75% carbon and 1080 Carbon Steel and 1095 Carbon Steel have 0.8% and 0.95% carbon respectively.
Another example is a favourite of recycled steel knife makers: 5160 Spring Steel. The 5 indicates that chromium is the main alloying element and 1 indicates how much of that element is contained. For example, 1% chromium by mass. The 60 means it is 0.60% carbon by mass. This is not a comprehensive analysis of 5160, though. It needs to contain manganese and silicon as well as limited phosphorus and sulphur.
This is shown as:
As you can see from the table, not all spring steel is 5160. 5160 and SUP9 are virtually the same composition and tolerances, but not identical. Also, 5160 is a US AISI/SAE standard and name, and SUP9 is Japanese. For those of us who like to nerd out on the minutiae of steels, based on its content, SUP9 equivalences under other naming conventions would be AISI 5150 (USA), 55Cr3 (Germany and ISO), 55CrMnA (China), 55C3 (France), 527A60 (England).
There are so many differences in nomenclature and composition across countries and standards that some steels may be seen as comparable or similar, but rarely equivalent, even though equivalence is a term in common use. In that sense, 5160 and SUP9 can be considered comparable.
As another example, we had our 52100* bearings checked with optical emission spectroscopy to determine the alloy content. It turned out to be close to AISI 52100 specification, but with higher manganese. Bearings are often believed to be 52100 steel, but may are only be case hardened, or in this case an alloy close to 52100 steel, but not quite 52100. The higher manganese and silica we discovered will affect heat treating as compared to AISI 52100.
We are really just dipping our toes in the ocean of detail within metallurgy here, as each element brings something to the finished blade. ‘Recipes’ can vary across countries and companies, but the point here is that knowing the composition of your steel is important, particularly when forging and heat treating.
Another challenge with recycled steel is that dimensions of the stock are not always right for the job. Making a hammer from a leaf spring is a task that would require a lot of forging to re-dimension the stock, or some forge-welding even for a small hammer or axe. Similarly, taking round or thick stock down to the right profile for knives requires a lot of forge work. Hydraulic rod also has a hard chrome surface that needs to come off before forging and you may find yourself burning highly toxic paint and zinc coatings. If you are using purely stock removal, prepare to use a lot of belts. Hand tools are not an option because these steels are heat-treated and will be too hard unless annealed first.
The place to start with mystery steels is a magnet test. It is a simple way of determining if your sample is even ferrous before going any further, but keep in mind that stainless steel may be only weakly magnetic.
One of the best initial tests is a simple spark test. Depending on the appearance of the sparks generated by grinding the steel on an abrasive wheel or belt, you will know roughly whether they are worth pursuing in terms of carbon content and alloying materials. This is important because you don’t want to waste good tool steel on a scroll or create a beautiful knife from cast iron!
Below is a useful guide to what to look for when spark-testing and you will be able to tell if it is worth beginning experimentation depending on the spark characteristics.
Of course, the above images are only a rough guide, and the sparks may be affected by the type of abrasive used, the pressure applied, or other factors. It can help to grind some samples of known steel and compare the sparks with your mystery steels.
After some experimentation with heat treating, normalising cycles, hardness testing, break testing, you can tell if the material will do the job even if you don’t know the exact alloy.
The important thing to remember is that this steel has been recycled for a reason. It may be perfectly good or it may be cracked or fractured. There are a number methods of testing your stock for cracks such as Magnetic particle testing (MPT), Liquid penetrant inspection, Eddy current testing (ECT) method, X-ray testing and Eddy current array (ECA).
Without testing your recycled steel, you can’t be 100% confident in it and the steel may fail at some point. It doesn’t happen often, but those of us who use recycled steel will have experienced such failures at one time or another and it is very frustrating. You really don’t want your hammer shattering or your knife cracking in heat-treat after all the work you have put into it.
Once you know your steel is free of fracturing, how do you find out what the exact makeup of the steel is? Optical Emission Spectroscopy (OES) is the only way to be sure of the actual alloy content of mystery steel and getting it done isn’t that difficult. It can cost as little as a few hundred dollars and the metallurgy department of a university may be a good place to start. These tests are available at a price, but kind of negate the saving if economy is your reason for using it – unless you have a lot of the same steel.
This is not intended to discourage anyone from using recycled steel. There is some good free steel out there. If you have the tools to shape it, something like a recycled forklift tine is a source for a huge amount of steel for tooling or a post anvil. They are usually something similar to 4140 or 4340. Depending on the dimensions a striker (or a power hammer) will make working larger pieces a lot easier. If you find the right stack of leaf springs of the right composition you may have enough steel for a lifetime of forging swords and choppers, which is where Freerk Wieriga sourced the steel that goes into many of his projects. It’s important to remember that Freerk has honed his skills over many years and ensures his stock is sound. The late Rudy Ruana swore by Studebaker leaf springs above all others (reportedly 9260 rather than 5160) and made beautiful knives that performed very well.
So is the saving of cheap or free recycled steel worth the potential increase in labour, forge fuel and uncertain result? Are you even saving? Do you want to save?
If you are interested in ornamental ironwork and general forging then – yes, as long as we are talking about mild steel and wrought iron. For a good series on forging useful pieces from a bucket of scrap see the Hook of the Week series at Black Bear Forge.
Assuming you are reading this because you want to create good knives: – yes and no. Recycled steel is cheap or free, and with the proper tools and understanding, some of the best swords and knives in the world can be produced from it. Another great example is Island Blacksmith who makes $5000 tantos exclusively from recycled steel. http://islandblacksmith.ca/2016/12/testing-reclaimed-steel-for-knife-making/.
If you enjoy the process of experimentation that goes along with recycled steel like so many of us do, then it is a good choice for you and you will learn a lot.
If you want to learn about knife making, using a known knife steel is the best place to start. If you want to make the best knife you can with guaranteed edge-holding, stain-resistance and toughness that can be precisely heat treated, then it is essential you choose the right knife steel and understand its properties. You will know what alloy you are using; you will be able to follow tried-and-tested processes and learn from other peoples’ experience, and if you run into problems – especially with heat treatment you will be able to troubleshoot the problems you are having. If you don’t know what alloy of steel you are using it’s very difficult to get specific advice on how to get the results you want or what it is in your process that’s causing issues.
So, if you are looking for steel that is designed especially for knives and comes in the desired dimensions with a spec-sheet and a guarantee right out of the box, then there is now a great range available in Australia on our website.
The choice of steel for knife makers in Australia has never been better. At Gameco Artisan Supplies we import specialist steels in bulk from time-to-time, making them accessible to knife makers and blacksmiths at a great price. From simple carbon steels that are quenchable in oil straight from the forge to the latest in powder metallurgy requiring precision heat and cryogenic treatment.
There is plenty of information on the steels in our range on our website so that you know what its specific properties are. You can also purchase the Knife Engineering: Steel, Heat Treating, and Geometry Book for more information on edge geometry, steel selection, and heat treatment. We have larger sizes for tooling – ideal for hot-work punches and hammers, tomahawks and axes. We stock specialist blade and tool steels in a range of dimensions to suit your needs.
Check out the range, or give us a call if you don’t see what you are looking for. We may still be able to help.
If you are new to knife making, check out our beginner guides for steels, tools and techniques on our Makers’ Space Blog Page.