Thanks for the great information. I am checking out Huawei now. 1095 seems to be a pretty common steel in sword building. What steel do you recommend or prefer?
You're very welcome. Steels and metallurgy is an incredibly deep topic - many lengthy books have been written on the topic. By that I just mean it's a deep rabbit hole to go down. But I can give an introduction that I hope will be helpful. Apologies in advance if anything below is at all overly simplistic or basic, I don't mean to be condescending at all, just trying to start at the start.
Firstly, I must emphatically say that the quality of the heat treatment is FAR more important than the type of steel, if we're talking about modern high carbon steels.
With that out of the way, some basics: steel is simply iron + carbon. Carbon is the element which allows steel to be quenched to form a structure hard enough to hold a decent edge. 10xx series steels like 1095 are often called 'simple' high carbon steels - they are (mostly) just iron + carbon. 1095 is iron + 0.095% carbon 1075 is iron + 0.075% carbon etc. Some, such as 1084 have some other alloys (manganese) included, but you can basically think of 10xx series steels as iron + a percentage of carbon.
In order to hold an edge, a carbon steel is heated to a critical temperature, then cooled quickly. Most people have seen in a movie where a blade is brought to a glowing heat, then thrust into water. Water is actually a pretty terrible quenchant - most smiths quench carbon steels in a specific oil, where the viscosity of the oil is tuned to cool the steel at the appropriate rate.
The process of quenching a blade - hopefully - forms a structure in the steel which is harder than it's soft (annealed) state. In simple carbon steels this structure is usually martensite. The hamon, for example, delineates the transition from the martensitic edge, and the pearlitic/ferritic spine of a Japanese sword. The steel is however the same steel, just in a different structural form.
10xx series steels are fantastic steels. If heat treated appropriately, a 1095 blade should in theory form a harder edge than say a 1060 blade - the slightly higher carbon levels allowing for the additional hardness. The differential hardening process used in making Japanese swords, where the 'clay' on the spine forms a heat sink (ie holds heat in while the exposed edge cools faster) leaves a 'softer', tougher spine (the pearlitic/ferritic structure), which is more likely to bend/take a set, than shatter/snap.
Once quenched to harden, the blade will be tempered - which is essentially heating it back up a little, to relax some of the stresses/brittleness which forms in quenching. Most smiths have shattered a hardened blade by dropping it prior to the tempering process. So tempering is basically 'undoing' some of the quenching process, to trade some hardness for toughness.
Hopefully that give you an idea of the heat treatment process - the blade is hardened, but then needs to be tempered to make it tougher. Making it tougher by necessity makes it a little softer. This is emblematic of the bladesmithing conundrum -
everything is a trade-off.
This trade-off repeats itself with steel types. The addition of chromium to steel aids with corrosion resistance: stainless steels typically have above 1% chromium. In longer blades however, stainless steels are almost always too brittle to resist impact - which is why stainless wallhangers are dangerous (likely to shatter). D2 is often called a 'semi-stainless' steel, because it's chromium levels are approaching stainless territory. If well heat treated, it can make a VERY hard blade, but is still tough enough for longer blades. It won't however make the prettiest hamon.
W1, W2 and T10 are shallow hardening tool steels which make gorgeous hamon - that's why they're often used to make Japanese swords. The 'W' in the name is intended to indicate that they can be water (brine) quenched.. though it's far better to use a fast oil. They are incredible steels for Japanese swords.
'Spring steels' like 5160, 9120 or 80crv2 have some manganese, chromium and vanadium alloys which make them incredibly tough - hence the name. They can be hardened enough to hold a good edge, but remain springy/tough, and are therefore exceptional sword steels. Again however, they won't produce a nice hamon - the alloy levels interfere with that.
Howard Clark is famous in the smithing world for using L6 tool steel to create incredibly tough Japanese swords - they have a bainitic spine, while retaining the martensitic edge. Again though, not as pretty as a simple high carbon steel or shallow hardening tool steel.
Like I said before, everything is a trade-off. All of the above are fantastic steels for long blades, if heat treated properly. However the more exotic or difficult the steel and heat treat, the more expensive it will be. Whatever wizardry Howard Clark performs on his L6 blades doesn't come cheap. While a 10xx, W2/T10 or spring steel blade from Hanbon forge or Huawei will be far more reasonably priced.. and may be a little prettier.
Ultimately, these differences is steels should be of little concern to the end user. Unless you're cutting hard targets regularly, the distinction between a simple carbon Japanese sword and a fancy L6 or other steel blade will not impact on you. Particularly when discussing the above vendors, the difference in fittings, and fit and finish will be far more noticeable and meaningful to a committed JSA practitioner.
I could go on about this stuff forever, but I hope that's given a helpful insight into my views - which are not those of a super-duper expert or anything - I would highly recommend further research if you're interested. Walter Sorrels is another american smith who specialises in Japanese blades, and has a bunch of informative videos on youtube, perhaps starting there is a good idea, if anyone is so inclined.
What do you suggest, Musashi?
