If you've browsed through the Byzer(長安)/Cloudhammer website, you've seen several different types of steel used in practical swords, and might be wondering which one is best suited for your skill level and use.
Some considerations:
Hardness: The harder a blade, the sharper and more wear-resistant it will be; but that comes with increased risk to chipping, breaking, or bending. Hardness is determined in large part by carbon content, but also other alloys.
Edge Retention: Edge retention and Hardness are highly-related, influenced mostly by carbon content. The better the edge retention, the more you can cut without having to sharpen.
Rigidity: How well a blade maintains straightness under pressure. They tend to feel stiffer.
Bend Tolerance: How far a blade can bend before losing straightness. Steels with high warp resistance are recommended for beginning cutters.
Impact Resistance: How much force it takes to break. This is an important consideration when cutting very hard targets.
The chart below compares various objective measurements, using the common T10 Clay-Tempered steel as a baseline.
| steel | HRC | Impact Resistance | Bend Tolerance | Pros | Uses |
| Longquan T10 clay tempered | 58-59/ 38-40 |
<15j | 15-20 | ||
| 9260 51crv4 |
57 | 108j | 90 | toughness, warp resistance | Iaido, Beginning cutting softer targets |
| Sup12 | 58 | 102j | 90 | toughness, warp resistance, edge retention | Iaido, Cutting up to medium targets |
| Sx105v | 58 | 80-90j | 60-70 | toughness, edge retention | Iaido, batto, cutting up to hard targets |
| sx105 dif hard |
61/45 | 15j | 20-25 | edge retention | iaido, batto, cutting up to very hard targets (experienced cutters) |
| s5 | 58 | 186j | 80-90 | toughness, edge retention | iaido, batto, cutting up to hard targets |
| z tuff | 59-60 | 50j | 50-60 | toughness, edge retention | iaido, batto, cutting up to very hard targets |
| cpm 3v | 60-61 | 45j | 50-60 | toughness, edge retention | iaido, batto, cutting up to very hard targets |
| W2 dif hard | 59-60/ 38-40 |
25 j | 30 | edge retention | iaido, batto, cutting up to very hard targets (experienced cutters) |
Spring Steels for Beginning Cutters:
As can be guessed from their names, German 51crv4 and American 9260 Spring Steels are typically used in the making of springs. They therefore have significant resistance to deformation under stress. With the right heat treatment, both can be bent to 90 degrees without warping.
Since a beginner will not always maintain good edge alignment, cuts against harder targets risk bending a blade. Spring steels are very forgiving, being able to flex while still maintaining their original shape. They are also durable steels, able to withstand repeated blows. These advantage is offset by a lower hardness rating of 57 HRC.
Harder Steels for Intermediate Cutters
The harder the edge, the more inclined a steel is to chip or break-- depending on the alloys. Intermediate level cutters maintain are expected to maintain.
Sup12 Japanese Spring Steel is a step up from 51crv4 and 9260. It has improved edge retention, with an HRC of 58, and also stiffer. While it can still resist bending to 90 degrees, the wielder will feel the shock of the blow more through the steel.
Sx105v Japanese tool steel is marginally less resilient than Sup12, with a slightly lower impact resistance and bending tolerance; however, it holds an edge even better with an HRC of 58.
s5 tool steel is the toughest steel Cloudhammer uses in blades. Typical applications are for concrete breakers and high impact dies, so it should come as no surprise that a sword made from s5 can take a beating. It's impact resistance of 186 joules is up to 15x greater than T10, and nearly 2x greater than 51crv4, Sup12, or sx105v.
All three of these steels combine durability with the hardness to cut through green bamboo targets.
What about Differentially-Hardened Steels?
For those who wish to cut harder targets, diferentially-hardened steels that create a natural hamon offering both beauty and excellent edge retention. This comes at a cost, however; differentially-hardened steels are more prone to chipping and breaking, and the process also makes them less flexible.
For example, through-hardened sx105v has an HRC of 58, Impact Resistance of 80-90j, and flexibility of 70-80 degrees. If differentially-hardenned, the edge HRC rises to 61, while the spine drops to 45. Furthermore, it's bending resistance falls to 20-25 degrees, and its impact resistance plummets to 15j.
In the hands of an inexperienced cutter, this can lead to bending, breaking, or chipping.
Therefore, Byzer/Cloudhammer does not recommend differentially-hardened sx105v or W2 cable steel for beginning cutters
Harder, Still Tough
For a combination of unparalleled edge retention and excellent toughness, Byzer/Cloudhammer now offers swords made of CPM 3v (HRC60-61, Impact Resistance of 45j) and Z-Tuff (HRC 59-60, Impact Resistance of 50j) powder steels.
These powder steels are scratch resistant and can hold an edge just as well as differentially-hardened steels, while being less vulnerable to chipping, bending, or breaking. However, they won't survive repeated impacts against an s5 blade, and also cost 3-4x more.
Bottom Line
Beginning Cutters, go with 51crv4 or 9260; Sup12 if you're feeling daring.These steels will cut through pool noodles, plastic bottles, and tatami mats; they're durable enough to repeatedly hit harder services.
For Batto single cuts on harder targets such as bamboo or dowels, Sup12, sx105v, s5, cpm 3v, or z tuff.
For experienced cutters on targets as hard as fresh bamboo, differentially-hardened W2 or sx105v.