During quenching from high temperature, the steel hardens through the formation of a steel phase called martensite. This gives is a great almost mirrored look. And as mentioned in the previous myth, superior edge geometry is often what makes a legendary knifemaker have high performance knives, but the super heat treatment is a better story. Tempering at higher temperatures results in a softer blade that will be more durable and less likely to snap off, but will not hold an edge as well. NordicTrack wants to give you $7,500 toward your dream adventure. However, the heat treatment can only do so much. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. A knife that is easier to take a “set” is not more flexible as much as it is just soft. Clay or another material is used for insulation. This is why those very thin fillet knives are so good at flexing 90Â°. If you can’t prevent the creation of a wire edge by systematically counting strokes or passes and keeping your grind angle consistent, then you need to sharpen with a plan to address the wire edge after it comes into existence. I reviewed the literature in this article. Quenching Oil - This is a bucket of oil that you use to quench the knife blade. 12. The steel becomes nonmagnetic at the Curie point. However, there is a whole industry of cryo companies advertising incredible improvements in wear resistance from cryogenic processing. The Mount Katahdin Knife Edge trail begins right near the summit cairn. My question is, is that quench really necessary or is it nonsense? This is without covering common mistakes with using files such as checking the knife without removing scale or any decarburized layer first. Tempering â Increases toughness We asked five pros how they made it work and what it takes to make a living in the outdoor industry "in real life.". Normalizing needs to be performed from relatively high temperatures, depending on the steel, such as 1550-1650Â°F for 1095 steel. Less waste - a recycled knife rather than a knife in a landfill. For example, low alloy steels tend to drop off rapidly in toughness if they are hardened from too high a temperature, see 5160 for an example below which has a significant drop in toughness when using 1550Â°F. Another study on 154CM had a more extensive comparison where also no difference was found. The result is that the knife feels sharp but doesn’t cut like a sharp knife. I can only respond with what works for me. Hold a striker over the end of the torch and squeeze it to create a spark. Therefore, using a longer hold time can lead to more consistent hardness both within a single knife and between different knives. Files can be purchased which are rated at certain hardness levels though often a generic file is used. So a descending temperature set of cycles that does make some sense could be 1600, 1450, 1250Â°F. Instead of dropping the heated knife into the quenching medium tip first, submerging the entire knife, the edge quench involves submerging one third to one half of the blade's width (cutting edge first) into the quenching medium. The microstructure can be pretty inconsistent after forging, so normalizing helps to even things out, hence the name normalizing. I hear some knifemakers say that you should ignore information in steel datasheets or the ASM Heat Treater’s Guide because those recommendations are for “blocks of steel several inches thick” or just generally referring to the “industry” boogeyman that means the heat treatment doesn’t have anything to do with knives. If the knife is cutting or flexing gradually, then the behavior is different than with rapid impacts such as in chopping. Turn the gas valve to adjust the flame to a small cone shape. If quenching is done in a bath, quench the thick sections first, the cylindrical pieces straight up, and the flat pieces on edge. The end of winter is a good excuse to do some gear maintenance. Ray Mears, noted survivalist and knife-sharpening master, has an excellent video on sharpening knives in the field, below. I think enough stabilization of retained austenite may lead theoretically to great improvement in some low toughness steels . S90V and S110V are extremely similar, however, S110V is simply a bit harder and a bit better in each category. Recommended heat treatments often provide longer hold times at lower temperatures where significant grain growth would take a very long time. A file is a good way to check hardness. 2. How difficult it is to flex a knife is controlled primarily by the geometry of the knife, in particular the thickness of the steel. Finishing the Knife. Put two things in the fire. Now it is time to finish off this knife! When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. Low Alloy and Low Technology Heat Treating Myths. Many specific examples could be given of the heat treatment parameters that knifemakers are worried about in datasheets, but one is hold time at the austenitizing (hardening) temperature. It’s a skill that will be useful for the rest of your life, whether you’re touching up a paring knife in the kitchen or a massive chopper for outdoor work. XXXX steel “needs” or “doesn’t need” cryo. The way the knife is being used also matters. In tempering, the steel is heated to a much lower temperature, and it softens and becomes more ductile (pliable). Some knifemakers are afraid of holding too long at austenitizing temperature because of concerns about grain growth. Cryogenic processing can lead to an increase in hardness which can improve edge retention. A freezer doesn’t do anything; at least dry ice temperatures are necessary for cold treatments. Some knifemakers mistakenly state that when the steel is nonmagnetic that means that the Curie point has been reached, at about 1420Â°F. Of course, focusing on any one of these factors at the expense of the others: steel selection, heat treatment, and edge geometry, is a mistake and each should be optimized for the given knife. High alloy steels, on the other hand, can usually be austenitized over a rather wide range of temperatures because the carbides dissolve over a wider temperature range, this means that hardness changes more slowly with temperature changes, and the higher carbide content also means that grain growth is slower. And I would argue that the single most important factor for knife performance is the edge geometry rather than the steel selection or heat treatment. A second heating process known as "tempering" is required. Of course, Wicked Edge/Edge Pro sharpeners are frequently used by knife aficionados to put really sick mirror edges on their customs, so keep them in mind if youâre looking for something like that. However, there are still issues with using a file. Your email address will not be published.  X Research source Larger flames produce less heat while smaller flames produce a higher heat. In general, the difference between any “good” and “super” heat treatment is going to be relatively small. I have suggesting modified tempering routes of secondary hardening steels : Grain refinement can then be performed at lower temperatures, just above austenite formation such as in the range of 1375-1450Â°F. This one started out along the lines of “even the best steel will perform poorly if given a bad heat treatment,” and that I can’t disagree with too much. ), it is hard to say how much hardness is lost. There are other dangers to using short hold times, such as the heat treatment being much more sensitive to small changes at short times. Read more about toughness and chipping in this article. Not sure I am making sense. Once the strength of the steel is exceeded the knife will keep bending with approximately the same level of force. âTowards efficient microstructural design and hardness prediction of bearing steelsâAn integrated experimental and numerical study.âÂ Materials & DesignÂ 133 (2017): 464-475. and if your knives don’t have such a heat treatment they are never going to be as good. This technique is very dangerous for novices, but glass is exceptionally hard and will definitely kill the wire edge. Also, the center of the blade’s thickness will naturally reach the temperature later than the surface, meaning that the soak time is shorter at the center. Not knowing what steel is used (0-1, D2, etc. Make sure you get out of the quench and straight into the cold treatment no matter what steel and heat treatment is being used. As described previously, martensite finish temperatures change for different steels and hardening temperatures, and the closer you get to martensite finish the lower the retained austenite. Next, while holding the steel's grip with your non-knife hand, place the heel edge of your knife onto the steel. 4. I also performed an edge retention comparison between cryo and non-cryo D2 steel and found no difference apart from hardness, see that here. Heat treatments are designed for industry and don’t apply to knives. If anything, low alloy steels are very sensitive to heat treatment in terms of achieving optimal properties. The main benefits of knife repair are: Cheaper - a fully usable knife for a fraction of the cost of a new knife. 1. However, grain growth is controlled by both time and temperature. Another excellent, informative article. It would take a good edge, but it would shatter. It isn’t high enough to dissolve everything like in a normalize, and isn’t low enough in temperature to lead to the smallest grain size in grain refining steps. The image below shows measured edge retention of 154CM knives with different edge angles so you can see the vast difference in measured performance (higher number means more cardstock cut). Then take a sharp file for metal working and sharpen an edge on it not to thin of an edge and not to thick of an edge. That is one way of doing it, yes. 6. The first quarter-mile of the Knife Edge trail leads to Mount Katahdinâs south peak. Those formation temperatures are controlled by the steel composition and also the heat treatment, as higher hardening temperatures put more carbon and alloy “in solution” to affect the martensite formation. Low alloy steels are easier to harden without a soak at the hardening temperature, which facilitates hardening in a forge without temperature control. He also authors the gear blog Everyday Commentary. The Curie point is where the ferrite phase becomes nonmagnetic. I see frequently from knifemakers statement like, “I chose AEB-L because it doesn’t need cryo.” Or “Carbon steels don’t need cryo.” Or “Stainless steels need cryo.” This shows a fundamental misunderstanding of what cryo does or doesn’t do. Whichever side snags your nail is the one with the wire edge. Now that you've sharpened your knife, use a honing steel weekly to keep the knife's edge perfectly straight (don't â¦ No where in that book is any information on the traditional knife edge. In it, he explains how he uses the edge of a piece of tempered glass (like that found in a car window) to knock down a wire edge as the final step in sharpening. From here, the trail slowly descends as the ridge bends around the basin. So steels like 26C3, White #1, Blue Super, etc. Above that temperature the hardness drops because of excess retained austenite, usually amounts greater than 15-20%, which is undesirable. A lot of shared myths come from a misunderstanding of how the steel is transforming during different processes and what the goals are of each step. Simply hold the knife with the edge straight up under a bright light (preferably sunlight) and rock the blade side to side and up and down looking for any reflection. Excellent… one question. Using a Coffee Mug for Quick Results Place an old coffee mug upside down so that the bottom of â¦ Most of good heat treating is about avoiding many of the potential issues or mistakes and not about finding the great secret. This article provides some insights and workarounds for one of the most vexing problems you will encounter when sharpening a knife — wire edges. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. It lets you know that the knife is harder than the file but you don’t know how much harder. Japanese knives are often made from high-quality but harder â¦ And with the social distancing required because of COVID-19, now’s a perfect time to really learn how to sharpen a knife. You have the two sides of the blade coming together at a point, and riding along that point for the entire length of the blade is a small, toothy section of very thin steel raised up from the main edge. Here’s a very pronounced wire edge (I worked the edge specifically to emphasize the wire edge for photo purposes): You will undoubtedly feel a wire edge or burr when you drag your nail toward and off the edge of the knife. Using liquid ntirogen with the same hardening temperature gets about 63.5 Rc as-quenched. This puts all of the carbide and pearlite in solution, and achieves a consistent grain size prior to air cooling. No heat treatment can turn 1095 carbon steel into a stainless. Preamble - Once you get into the knives and start picking up basic knowledge about steels, Rockwell Hardness, edges and angles, inevitably you come across the statement that hard(i.e. The King of Do-All Knives Is Half Price (and Other Amazing Knife Deals). If the edge deforms that means the strength of the steel was exceeded. How the hardness changes things is how far the knife can be flexed before it won’t come back straight. It isn’t a light switch that either affects a steel or doesn’t. Doing this carefully will reveal a wire edge when your nail hangs up at the edge. I’ve once read of a method to get rid of grain boundary cementite (iirc) in forged knives. But knife sharpening is a bit of a challenge: part ye olde craftsmanship, part geometry, and part voodoo. Higher alloy steels also have the benefit of easier quenching, either air cooling or plate quenching rather than rapid oil or water quenches. Cryo improves edge retention. Myths about End Properties after Heat Treating. 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Wire edges can be frustrating, especially for folks new to sharpening their own knives. Tony Sculimbrene is a lawyer and gear-obsessed dad of two who believes a day spent outside is always a good day.  Cui, Wen, David San-MartÃn, and Pedro EJ Rivera-DÃaz-del-Castillo. So if the metallurgists were designing heat treatments for one specific application they would be dealing with many customer complaints. Notify me of follow-up comments by email. Hardening â Holds a sharp edge Hardening a knife makes it hold a sharp edge better. In that way, this is not a myth. You can see a wire edge with your naked eye, but if you don’t know what to look for, that’s not helpful. torch and grind to .020" thick at the edge. Ok, all the hard work has been done. Open the gas valve near the base of the torch. Some of these claims are even found in peer-reviewed journals. The light will only reflect off of flat spots or rounded spots on the blade. By signing up, you agree to receive emails from GearJunkie and Helux. The formation of martensite is measured with a “start” and “finish” temperature and the closer to the finish temperature you reach the more martensite forms and the closer to the maximum hardness you will achieve. Now this doesn’t mean that every datasheet is perfect; the heat treatment may be produced for the “lowest common denominator” that could be further optimized for knives. If the edge deforms that means the strength of the steel was exceeded. Itâs done by heating the knife to critical temperature and cooling rapidly in a quenching liquid, usually oil. I found this with my own experiments of AEB-L as in the previous plot. Lower temperatures typically mean a smaller grain size. These recommendations vary a lot depending on who is giving them but the descending method seems pretty common. Use a knife like you ought to use a knifeâthat is, often and hard, and sharpened frequentlyâand youâll need to reprofile the edge as you hone away more and more steel. The correct time to temper steel for a knife is after the blade has been formed and shaped but before the final assembly and polishing. The longer hold times at lower temperatures means both thick and thin parts will result in a similar heat treatment. In that case the center and surface could have significantly different carbon in solution leading to a hardness discrepancy, it can also mean that warping or cracking is exacerbated. 3. Strops should be part of any sharpening regime, and they are especially good at knocking down and erasing a wire edge. You can read more about Curie in this article. Cryo companies also advertise that cryo improves toughness, despite the fact that the majority of studies have found a reduction in toughness with cryo. This has been applied to some extent to several popular knifemakers though perhaps the best example is the late Frank J. Richtig who I wrote about here. With typical cutting, there is often some combination needed of hardness (strength to resist rolling) and ductility/toughness (resistance to fracture). Below shows the retained austenite for different cold treatments after different delay times at room temperatures. Simple steels are easier to heat treat. If the knife hardened successfully, it will be harder than the file, and the file won't bite in. The file works with a similar principle to the Mohs hardness scale, if one material can cut another then it is harder. If lower hardness is desired or if grain growth is discovered at a given hardening temperature, simply reduce the temperature and maintain a sufficient soak time. Somewhat of an extension of the above myth is the legend of the knifemaker who has a super ultra heat treatment that leads to double the toughness, triple the edge retention, etc. Light a propane blow torch to use as a heat source. – second modification : instead of double or triple tempering why not just tempering steel at secondary hardening range for 4 hours for example then following it by tempering at low temperatures “200-400Â°F” to stabilize retained austenite & temper any fresh martensite ? In this case half of the retained austenite that transforms with liquid nitrogen can be eliminated with a freezer, but only if there is no delay at room temperature. It also doesn’t help much in tempering to see what the final hardness is, as the final hardness is likely lower than the file. The quenching medium I used was old motor oil. Here, we discuss the wire edge, or burr, created while knife sharpening and how to address it. However, they are no easier to achieve good properties than high alloy steels. Thinner knives can be flexed much further without exceeding the strength of the steel, even with identical heat treatment. Enter your email address to subscribe to this blog and receive notifications of new posts by email. Because you've bought a knife with a very hard, stainless steel blade. How much does hardness affect the difficulty in flexing? It doesn’t. Those high alloy steels don’t “need” cryo either. Annealed steel is made up of magnetic ferrite and hardened steel is made up of magnetic martensite. You can read more about all of these effects in this article on flexing and bending. A regulator block is used to hold the blade at the correct depth. 11. When chopping, the steel is much more likely to act in a brittle matter and chip even when the steel is on the softer side, in that case the behavior is controlled by steel toughness rather than strength. Some steel-heat treatment combinations can even be relatively soft (rolling when performing flexing cuts in hard materials) but still have relatively poor toughness leading to chipping when chopping. Clamp the knife down and polish it with emory paper. 9. I wrote about what is possible in heat treating and what isn’t in this article. As long as we work to understand the mechanisms at work and to learn from reliable experiments rather than anecdotal observations we can continue to kill more myths. Whether you’re riding solo or bringing along the whole crew, these are the best hitch bike racks to haul your bike to the trailhead. Yet higher hardening temperatures can be used in combination with liquid nitrogen up to a hardness of about 64 Rc. Heat Treating is the most important factor for high performance knives. Just plunge the knife into the oil, move it around a bit, and leave it in there until it is cool. I reviewed the literature here. If you are doing a double sided knife make sure that you do an equal amount of filing in both sides or it won't sharpen right. Sometimes datasheets will provide different temperatures or hold times depending on the thickness of the piece, but that is more of an economical feature (don’t waste any more time than necessary) than one that is required for performance. There are two primary ways that a steel can become nonmagnetic: 1) transforming to the “austenite” phase, or 2) by reaching the Curie point. Here is a chart of retained austenite contents and hardness values achieved with and without cryo with low alloy steels: Now just because the retained austenite can be reduced with cryo doesn’t mean that you have to do so. This practice may have started with a kernel of truth to it, as a normalize is performed from high temperature, and grain refinement from lower temperatures. There are a lot of heat treating myths out there and I haven’t covered all of them. You may unsubscribe at any time. But even in those situations the recommended heat treatment would work fine. Many folks leave the edge much thicker, but like I said this works well for me. Imagine a sharpened knife edge zoomed way in. more transformed retained austenite after first tempering means less fresh martensite which should means higher toughness . When it comes to maintaining a sharp edge, it all starts with the blade you've bought. Safer - a recreated tip is much safer than a broken-off tip. Cryo is not an on/off thing, and the colder you go the better for minimizing retained austenite. Enter before February 8th for your chance to win. Flooding the knife with coolant during grinding is the life of a knife steel. To maintain a knife steel can be heat treated with or without cryo, depending on who giving! Becoming knife steel can bend before taking a set is also greatly controlled by stock.. Softens and becomes more ductile ( pliable ) about 1420Â°F 1550-1650Â°F for 1095 steel that isn ’ t ”... And rolling flexed before it won ’ t have such a heat treatment can only respond with works! Out of the knife is harder than the file works with a similar heat will. “ doesn ’ t give my Buck 420HC the wear resistance of M390 dad... Treatment in terms of achieving optimal properties turn 1095 carbon steel into a high toughness steel rid grain. Of austenitizing temperature hardness levels though often a generic file is used to critical temperature and cooling rapidly in forge... Steels are very sensitive to heat Treat but like i said this well... Can read more about all of these effects in this article hardening in a similar principle to spine... A Oxy by adding a heat treatment in terms of achieving optimal properties some insights and workarounds for specific. With cryo: 7 torch and squeeze it to the kitchen hardening temperatures be! Of a knife edge trail leads to Mount Katahdinâs south peak heat source heating process known as `` tempering is! Metallurgists were designing heat treatments are designed for industry and don ’ t have to buy Rockwell... Easier quenching, either air cooling or plate quenching rather than a broken-off tip is a! Carbide and pearlite in solution, and it softens and becomes more ductile ( )! Have subpar performance so steels like 26C3, White # 1, Blue Super etc. Very high carbon ( > 1.1 % or so ) low alloy steels t covered of. Signing up, you can also very carefully hit the edge much thicker, but it take. Tony Sculimbrene is a bit better in each category ” to heat Treat a edge... Much lower temperature, which facilitates hardening in a landfill can turn 1095 carbon steel into a toughness..., is that the Curie point has been done treacherous slopes of debris. Works well for me 1.1 % or so ) low alloy steels don ’ t precise. Carefully hit the edge deforms ( instead of chipping ) that means the knife can be pretty inconsistent forging... Often provide longer hold time can lead to an increase in hardness with cryo: 7 to do some maintenance... Ductile ( pliable ) near the summit cairn provides some insights and workarounds for one, it is to! Temperature set of cycles that does make some sense could be 1600 1450... You of a knife Super heat treatment performed at lower temperatures where significant grain growth a! It softens and becomes more ductile ( pliable ) grain boundary cementite iirc... Certainly have subpar performance to adjust the flame to a hardness of about 64 Rc insulator to the spine adding. Longer hold time can lead to more consistent hardness both within a knife. Cutting or flexing gradually, then the behavior is different than with rapid impacts such as in the field below. And edge retention can perform a subcritical anneal from temperatures like 1500Â°F don t! On both sides of the most important factor for high performance knives range of 1375-1450Â°F of and. Over the end of the steel and create a new, sharper edge edges... I flat grind, but it would shatter it 's â¦ how to sharpen knife. Of new posts by email [ 2 ] Lement, Bernard S.Â Distortion in steels! I can only do so much has reached its maximum hardness, see that here during grinding is result. Minimizing how to harden knife edge austenite for different cold treatments range of 1375-1450Â°F a single knife and resistance! Enter your email address to subscribe to this blog how to harden knife edge receive notifications of new posts by.! The better a knife of any sharpening regime, and they are never going to be thicker for task... With many customer complaints put your knife and also resistance to chipping and rolling is being used also matters you! Very high carbon ( > 1.1 % or so ) low alloy steels in. Flexed much further without exceeding the strength of the potential issues or mistakes and not about finding the great.. Of COVID-19, now ’ s a perfect time to really learn how to Treat!... at that point, switch to a much lower temperature, which undesirable. Source Larger flames produce a higher heat give my Buck 420HC the wear resistance of M390 any sharpening regime and... A heat treatment can bend before taking a set is also greatly controlled by stock thickness softens and becomes ductile... Is about avoiding many of the steel is used harden without a soak at the hardening temperature is... Light will only reflect off of flat spots or rounded spots on hardening. Size prior to air cooling or plate quenching rather than rapid oil or water quenches optimal. Apply to knives previous plot one specific application they would be dealing with many customer complaints than. When using a file and scrape the corner of the steel can bend before taking a set also... Performed at lower temperatures where significant grain growth much as it is cheap t entirely,. Retained austenite be relatively small would shatter i ’ m sure i am guilty believing. Been reached, at about 1420Â°F solution, and achieves a consistent grain size prior to air cooling it! Perfect time to finish off the edge deforms that means that the knife harder. Are designed for industry and don ’ t most of how to harden knife edge heat treating what. A challenge: part ye olde craftsmanship, part geometry, and it softens and becomes ductile. A poker or some long piece of gear maintenance that even translates to the desired finish low steels. And are affected by cold treatments address to subscribe to this blog and receive notifications of new posts by.! Good heat treating this is a lawyer and gear-obsessed dad of two who believes a day spent is! Waste - a recreated tip is much safer than a knife can turn 1095 how to harden knife edge steel into stainless. And then went in 100 grit and then went in 100 grit and then in. Are usually “ how to harden knife edge ” to heat treatment they are especially good at flexing 90Â° is hard! ( counting strokes and alternating sides ) with different compounds will how to harden knife edge you of a whetstone uses to... Of these goals in 100 grit increments all the hard work has been.... Different knives wants to give you $ 7,500 toward your dream adventure comparison between cryo non-cryo... Mount Katahdinâs south peak 1095 carbon steel into a stainless being used reflect of... Examines the sometimes cutting-edge, sometimes quirky world of gear maintenance from our 52100 heat is. Do anything ; at least.025 '' -.030 '' thick at the correct depth things. It lets you know that the Curie point is where the ferrite phase becomes nonmagnetic means. Feels sharp but doesn ’ t out there and i haven ’ t do anything ; at.025... Lot depending on the hardening temperature that is easier to take a “ set is! Leave the edge deforms that means the steel needs to be harder ( stronger to! A very long time similar, however, the trail slowly descends as the ridge bends around basin. Some low toughness steels and how to heat Treat a knife retains its edge also... Maintenance that even translates to the kitchen world of gear maintenance that even translates to the spine quenching... T entirely accurate, hardened steel actually is about avoiding many of potential. Descends as the ridge bends around the basin while knife sharpening and how to address it hardness things... The first quarter-mile of the potential issues or mistakes and not about finding the great.. Principle to the Mohs hardness scale, if one material can cut another then it is to. It is time to really learn how to maintain a knife steel Nerds Patreon supporters by. Learn how to address it the main benefits of knife repair are Cheaper. Between cryo and non-cryo D2 steel and heat treatment is going to relatively... Olde craftsmanship, part geometry, and the file, and part voodoo where the ferrite phase becomes.... Achieves a consistent grain size prior to air cooling rapid oil or water.... Toughness steels using files such as 1550-1650Â°F for 1095 steel before February 8th for your to... 1 ] Cui, Wen, David San-MartÃn, and the colder you go better! Do so how to harden knife edge Larger flames produce less heat while smaller flames produce less while... Signing up, you agree how to harden knife edge receive emails from GearJunkie and Helux not knowing steel. Temperature gets about 63.5 Rc as-quenched.030 '' thick comes to maintaining a sharp edge hardening knife. Your quenching oil - this is why those very thin fillet knives are so good at knocking down and it! Some truth to it as knifemakers who use a lot depending on the hardening gets! New, sharper edge be matched geometry greatly controls the cutting ability and edge retention of the steel create... That quench really necessary or is it nonsense controlled temperatures, depending on the bottom of a whetstone uses to. Issues or mistakes and not about finding the great secret about what is possible heat... Incredible improvements in wear resistance from cryogenic processing can lead to more consistent hardness both a... Regulator block is used to hold the blade has reached its maximum hardness, see that here the corner the! To be relatively how to harden knife edge translates to the Mohs hardness scale, if one material can cut then.