Spyderco Edge-U-Cation® - SPYDERCO SALT SERIES
Enter H-1
H-1 steel is a radically different alloy that combines the extreme corrosion resistance and toughness of conventional austenitic stainless steels with enhanced levels of hardness that allow it to perform well as a knife blade material. Instead of carbon, H-1 uses nitrogen to help create its steel-like properties. Nitrogen, like carbon, is a small atom and has a similar ability to influence changes to iron’s ferrite structure. Unlike carbon, however, it does not increase the steel’s vulnerability to corrosion.
In addition to nitrogen, H-1’s unique alloy composition also includes chromium, manganese, molybdenum, nickel, phosphorus, and sulphur. Its finely tuned recipe of elements not only allows it to be precipitation hardened during the production process, it also enables it to harden further during the manufacturing of finished parts.
A true austenitic steel, H-1 does not require conventional heat treating. Instead, it acquires its “base” hardness through the rolling process. It begins as a 7mm-thick sheet and is progressively rolled down to the required finished thickness—typically 3.0mm or 2.5mm, depending upon the Spyderco model. The extreme compressive forces of this rolling process transform some of the austenite to hard martensite, increasing the overall hardness of the material without sacrificing its toughness or corrosion resistance.
Amazingly, H-1 also has the ability to “work harden.” The mechanical processes used to shape and grind finished blades also affect its hardness, most likely through the selective transformation of additional austenite to martensite.
According to an article in Scientific Reports, “…retained austenite can subsequently be transformed to the more stable martensite phase with the application of high stresses and temperatures; thereby increasing the toughness and ductility of the substrate. This means that under extreme operating conditions, when the pressures on the substrate, and the temperature to which is it exposed, are high enough, the transformation of retained austenite will be triggered, thereby achieving additional work hardening of the steel in-situ.”
This phenomenon may explain why the terminal cutting edge of a fully serrated H-1 blade has a significantly higher Rockwell hardness than the rest of the blade, and the cutting edge of a PlainEdge™ blade.
This remarkable property of H-1 was quantified in testing done by Crucible® Industries in the mid-2000’s. According to Spyderco founder Sal Glesser, “When Dick Barber was working at Crucible, we had discussed the properties of H-1 quite a bit. Crucible had micro hardness testing equipment that could be used to test hardness at .001 increments. That's how he tested H-1 and that's where the results came from.”
Sal went on to summarize Barber’s testing by explaining, “They were getting over 60 at the edge of the blade, 58 at the spine and various hardness in between as they went from the spine to the edge. The serrated edge version was higher, which Mr. Barber attributed to the extra "work" (heat) required to serrate the edge over just sharpening, as on the plain edge.”
Spyderco also confirmed the work hardening property of H-1 while developing specialized manufacturing processes for it. Again, to quote Sal, “We know when we try to drill a hole, the bit starts to melt about 20 thou (.020-inch) in. When we try to mill a ramp for a lock, the bit goes south about 50 thou (.050-inch) in.”
For this reason, some knife designs using H-1 had to be modified. For example, the Cobra Hood™ attachment featured on the Assist™ models with VG-10 blades could not be included on the Assist Salt™ model. Drilling and tapping a hole in the spine of the H-1 blade was simply too difficult due to the material’s work-hardening property.
The PlainEdge Challenge
Although the 60 HRC figure the Crucible report cited for the cutting edge of PlainEdge H-1 seems very promising, the actual cutting performance of that edge configuration was less impressive. CATRA (Cutlery and Allied Trades Research Association) machine testing revealed that its cutting performance was actually only on par with lower grades of martensitic stainless steel.
Again, to quote Sal, “CATRA testing on abrasion resistance puts the plain edge in the AUS-8 range.” Subsequent feedback from countless customers using H-1 knives in the field supported this comparison. H-1 blades in PlainEdge format, while incredibly corrosion resistant and highly serviceable cutting tools, don’t offer the same edge retention as Spyderco’s more conventional steels.
Based on customer feedback and our own extensive in-house testing, the typical sharpening processes used for PlainEdge blades also do not generate enough stress or heat to promote the work hardening necessary to improve edge retention over time.
Conversely, H-1 blades with fully serrated SpyderEdge™ blades turned out to be outstanding performers. In Sal’s words, “The serrated H-1, such as the Jumpmaster™, in CATRA tests, have shown to be exceptional, with better performance than plain or serrated steels of any that we've tested. Field tests have shown this to be true as well.” This statement is also backed by more than a decade of customer feedback praising the cutting performance and edge-retention properties of our serrated H-1 blades.
LC200N
As remarkable as H-1 is, we realized that, in the PlainEdge format, it does not offer the same edge retention as conventional martensitic steels. Although it still makes an extremely serviceable cutting tool, in that edge configuration it requires more frequent sharpening. Consistent with our obsession with Constant Quality Improvement (C.Q.I.), we therefore began exploring other exotic corrosion-resistant alloys for use in the Salt Series.
One material that showed tremendous promise was LC200N. Also known as Cronidur 30 and Z-FiNit, LC200N is a state-of-the-art, high-nitrogen alloyed tool steel specifically formulated to offer superior corrosion resistance and extreme toughness, even at high levels of hardness. The advanced processes used to produce this steel give it a fine, homogenous microstructure and allow it to be readily machined and polished. Its unique qualities make it the material of choice for applications that involve high static and dynamic loads in corrosive environments, and it is actually used by NASA for the ball bearings used in aerospace equipment.
Based on these unique qualities, LC200N was the perfect addition to the Salt Series. Since it is a martensitic steel and achieves its hardness through conventional heat treating, it can achieve a better edge hardness than H-1 in a PlainEdge format. For PlainEdge fans seeking extreme corrosion resistance and superior edge retention, it’s the perfect solution.
LC200N also offers the advantage that it can be full-flat ground in production. Because of its work-hardening properties, the process of grinding H-1 blades without warping is extremely challenging. For this reason, the blades of H-1 knives are simultaneously hollow ground from both sides to equalize the stresses in the steel. LC200N, however, doesn’t present this challenge and can be readily flat ground using standard methods. A full-flat grind creates low-friction edge geometry that further enhances cutting performance. It also reduces the overall weight of the knife and refines its balance in the hand.