![]() These steels are typically used by forging bladesmiths, traditional folders, and some production fixed blades. I’m going to give the ratings first and then give more explanation about how the ratings were created. These images are taken from my book Knife Engineering. The 25 dps sharpened knife saw almost no edge damage with 2 ft-lbs while a 15 dps edge saw a significant chip with only 0.3 ft-lbs and catastrophic chipping with 1.4 ft-lbs. Below shows pictures of a 61 Rc knife that was impacted with a 3/16″ rod at different energy levels. This is a major tradeoff between improved cutting ability and edge retention with an acute angle vs a strong and chip resistant edge with an obtuse angle. So setting edge geometry for the type of knife and intended use is very important. A more obtuse edge angle is much more resistant to chipping than an acute edge. Things are similar with resistance to chipping and edge deformation. Using 10 dps sharpening (20 degrees inclusive on the chart) leads to about 5x the edge retention of 25 dps. For example, see the chart below for how much edge retention can change with edge geometry for a single steel (in this case 154CM and CPM-154). The reason is because sharpening and edge geometry will also greatly control properties. This does not predict which knife will cut longer or be more resistant to chipping. Or even a 7 in both categories.Īnother important caveat before we get to the ratings are that these are for the steel only. There is no such thing as a steel that is a “10” in both toughness and edge retention. Therefore I will be showing the ratings of the steels graphically in terms of toughness-edge retention balance, where steels that are high and to the right have the best combination, and you choose the steel based on the level of toughness or edge retention necessary for the knife. Toughness and edge retention are generally opposing properties and it is difficult to improve both of them at the same time. Or even if they try to be more open to importance of toughness, the good reputation of the high edge retention steels means that they get inflated toughness ratings along with it. Many steel ratings seem to over-emphasize edge retention. One important concept I want to hammer home is that there isn’t one property that is most important. I did a large study of different knives with identical sharpening and edge geometry. I will be focusing on CATRA edge retention which measures abrasive wear of knives. Edge retention is the ability of a knife to maintain cutting ability during cutting. In the context of a knife this would be chipped edges or broken knives. Toughness is a measure of how much resistance a steel has to fracturing. I reserve the right to change my ratings based on new information. There are still a few things I don’t know but we have enough information to make educated guesses where data isn’t available. And I’ve done a lot of experimental work on knife steels where I feel more confident in my own ratings. Both of those things are no longer an issue as I now have way too many articles and a book. At the end of the article I gave a list of reasons why I hadn’t made my own ratings chart, two big reasons were: 1) I didn’t yet have articles explaining what edge retention and toughness even is (this was early on in Knife Steel Nerds), 2) I didn’t have good experimental numbers on many steels. I wrote an article about knife steel ratings available online in 2018, where I concluded that none of them were very good. ![]() If you want to learn more than keep reading past the ratings. Most of the discussion of how the ratings were generated, various caveats and details, etc. That way you can get into the steel ratings quickly. There is also data to demonstrate that casting processes which solidify directionally (centrifugal, for example) lead to improvements in rupture strength and thermal fatigue resistance.įor guidance in selecting the appropriate cobalt-based alloy in your application, contact us.I have a (relatively) short introduction before getting into the ratings with a few important things to put them into context. While not as strong as nickel alloys at lower temperatures, above about 1700☏ / 930☌ cobalt alloys show higher strength. ![]() The materials are more weldable than nickel-based alternatives. ![]() Due to the high cost of these alloys, they are used where severe conditions prevail and require high temperature strength and hardness, excellent wear, galling, corrosion, and/or erosion resistance.ĭue to the high chromium content (25% – 30% for the grades listed below) cobalt-based alloys provide superior corrosion resistance at high temperatures. Cobalt based metals are alloyed with chrome, nickel, and tungsten.
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