Technology
The High-End Material
Supracor - the name is descriptive. The supermaterial offers enormous abrasion resistance and can also be used for knife blades. Specialist Dieter Wilhelmy tells us what we need to know about this material.
Powder metallurgy steel has made great strides in recent years - in mechanical engineering and with high-quality knives. Most responsible for this is the American manufacturer Crucible Steel, which developed milestones like CPM 440V.
The next entwicklungsstufe(?) was CPM 420V, which possesses even better abrasion resistance with still higher amounts of carbon, vanadium and molybdenum. With a knife blade a higher Schnitthaltigkeit(?) means. Both steels just received new designations: CPM S60V and S90V.
Crucibles flagship, however, is Supracor, as it is known in Europe, which in the USA is called CPM MPl-1. Supracor is the most highly alloyed powder metallurgy steel in the world. With a carbon content of 3.75 percent and an enormously high chrome content of 24 percent with likewise considerable vanadium and molybdenum Supracor sets yardsticks. Nearly 40 percent of the material isnt iron. The primary carbide portion is 46 percent (CPM 440V: 24 percent). That means that nearly half of the material consists of extremely hard carbides (carbon compounds).
Already the chemical composition calls for respect. This respect grows substantially the first time you try to work on Supracor. Supracor is available only as round material (for example with a diameter of 50 millimeters); flat material is not available. Therefore flattening tires must be cut from the round material in longitudinal direction. While this sounds simple, it is extremely difficult in practice. Supracor cannot be sawed with carbide tipped saw bands. In fact Supracor has a hardness of 42 HRC in the annealed, thus unhardened, condition.
Only the wire eroding remains. With wire eroding by means of a thin wire and a tension put on funkenerosiv(?) the material is evaporated. In this fashion even the hardest materials can be cut, if they are conductive. However this procedure is not very cheap. Wire erosion machines are CNC machines and accordingly expensive. From this a high machine hour price results.
In addition this procedure takes a very long time. Example: A 230 millimeter long cut in 50-mm round material takes approximately two hours. Depending upon number cutting times result beziehugsweise thickness of the strips up to 24 hours, in order to cut only one piece of open round material. To the very expensive materials price you add enormous cut costs.
The resulting flat pieces are polished on a surface grinding machine primarily with CBN disks. Then the desired outline is roughly before-cut out-polished, and/or with a diamond disk. With a corundum friction disk it goes also, however only under substantial wear of the disk. Then the blank is continued to work on as usual at the Bandschleifer. Applies also here: With corundum volumes it goes, however the consumption of the volumes is very high.
Necessary drillings in Supracor succeed only with tungsten carbides drill, and the service life of the drills is very small also here. Also milling of Supracor with full tungsten carbide drills is extremely material intensive: The drill service life up to the wear limit (full tungsten carbide drill K 05) amounts to with one 10-mm drill and 0.5 millimeters of spantiefe only two minutes! One must clarify oneself: Supracor consists nearly to the half of carbides. The fact that thereby the tools wear very fast is clear.
In relation to these difficulties during processing the advantages of Supracor stand: A measurer from Supracor moderately on approximately 60 HRC hardened (the maximum is with 67 HRC), offers an almost unbelievable schnitthaltigkeit. Compared with a measurer from CPM 420V the abrasion resistance lies approximately twice as highly. Used by a hunter (expert), a CPM-420V-Messer can be still in working condition also after a half year. A Supracor measurer can hold the sharpness for a whole year. In practice also some Spielereien are possible: With a Supracor measurer hardened on 67 HRC at a CPM-420v blade (59 HRC) splinters were already scraped off.
The table of the manufacturer offers objective verschleisszahlen (see to box the schnitthaltigkeit). These values were determined under reproducible, standardized conditions.
A further outstanding characteristic of Supracor is the extremely high corrosion resistance. Due to the composition (the matrix holds lots of free chromium) this strength is also no miracle.
The Achilles heel of this superalloy is the small notched-bar impact-strength. It amounts to only approximately a third of CPM 420V (CPM 420V has the same notched-bar impact-strength as 1,4125 = 440C). Should one all-went with a measurer cut and not lever or similar abuse commit. Before a Supracor blade breaks, all bells in the head should ring. Differently expressed: It belongs to already a due portion of courage will to break a Supracor off blade. Naturally play also thickness and processing as well as the thermal treatment sound a large role.
Not easy is also sharpening a Supracor knife: the production of the sharpness takes place at the best korundstein current on one slowly (90 revolutions per minute), which runs additionally in a wasserbad. Functions! One does not need a diamond stone. However the abrasion at the korundstein is higher when sharpening Supracor than with all other steel, and the procedure lasts longer.
Apropos sharpness: a band sharpener is absolutely unsuitable, in order to produce at a high-quality measurer the sharpness - not only with Supracor blade. The sharpening temperatures, which thereby in the thinnest place, speak at the cut, arise, can lie far over 1000 degrees Celsius. It can come even to melting the steel. These temperatures play themselves mind you in the small one off (within the in order range), but preferentially exactly at the point of the cut - where the knife to cut is. From the enormously high temperatures - results casually expressed - alloy mixing machine, which everything else as the ideal condition of the steel represents. Then one their optimal gumption ability does not bring oneself.
Even with hand-guided whet-stones these extreme temperatures can occur. Result: Always beautifully slowly with the speed, and always well hand loops cool with water, also with!
After this digression, back to the Supracor: This material is manufactured only in relatively small quantities. That has to do with the fact that only very few economically justifiable applications exist. Differently expressed: Supracor is very expensively and very difficult to work on, and the thing makes relatively uneconomic for the industry.
In order to say it completely clearly: I personal keep at present CPM 420V in the sum of its characteristics (in addition also the price belongs) for the best cutlery steel. Supracor will remain always a Exote(?) under the cutlery steels - but a challenge for each knifemaker.
