I wrote about what is possible in heat treating and what isn’t in this article. Using cryo or other cold treatments means you get closer to martensite finish and retained austenite is reduced.

Quenching is an ancient method of rearranging the atomic structure of a material. However, grain growth is controlled by both time and temperature.

You can read more about bainite in this article. 1. This phenomenon is an especially important issue if the carbon content is greater than 0.5 wt%. Thermal tempering is a key feature of Prince Rupert’s drops, so if you want to learn more about the process, I recommend you check out this article. Martensite is a metastable phase, which means it is not predicted by thermodynamics and does not appear on any phase diagram. You can read more about Curie in this article. Normalize steel by using descending temperatures.

Usually, after quenching, steel is tempered. See the chart below for carbon and chromium “in solution” during holding of 52100 at 1545°F: You can see that the change in C/Cr in solution is very rapid within the first few minutes, and trying to target a specific hardness would be challenging if you are trying to hold for very short times, especially under 5 minutes. No easy way to get around that. . So the file ends up being a check for a heat treatment that completely failed (did not harden), but is not particularly useful for dialing in heat treatments or for checking consistency.

The alloy needs to be cooled rapidly. This is because of the size and number of interstitial sites in FCC vs BCC structures (you can read more about BCC and FCC crystal structures in this aricle). I’m glad to have been shown this blog at a Polish knife forum. more transformed retained austenite after first tempering means less fresh martensite which should means higher toughness . Backyard bladesmith discovered a new super heat treatment that can’t be matched. 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. would nanograined steels needs water or brine quenching regardless to alloying elements ? I have the CCT curves in roughly the order of increasing hardenability. How fine that microstructure is prior to austenitizing also affects how fine it is after austenitizing. With high carbon hypereutectoid steels there is a region where both austenite and carbides are present. I think enough stabilization of retained austenite may lead theoretically to great improvement in some low toughness steels . are also air hardening steels due to the Mo additions plus high Cr. Slowing down the rate of martensite transformation reduces the chance of warping and cracking. No heat treatment is capable of making high carbide CPM 15V into a high toughness steel. Quenching has been an important aspect of swordmaking for centuries, but Japanese swordsmiths had perhaps the most sophisticated quenching technique.

The steel … Austenite, the Face-Centered Cubic (FCC) form of iron which is usually represented by γ, can dissolve more carbon atoms than ferrite (the Body-Centered Cubic (BCC) form of iron, represented by α). CruforgeV – No CCT curve available for CruForgeV but with its 0.75Mn-0.75Cr its hardenability is somewhere around here, 1.2419 is an O7 type steel with 1.05C-1.0Mn-0.25Si-1.0Cr-1.15W [5] – Tungsten contributes little to hardenability. This multiplying factor for carbon can then be used with other alloy that is in the steel: So if the steel had 1%Mn the Mn multiplying factor would be about 1.75, and a factor for 0.5% Si would be about 1.22.

Will this be sufficient enough or aluminum plates is the only safe way to go with these modern steels; Personally, I had nothing but success with Elmax-quench plates and liquid nitrogen until now but if there is room for improvement…you know what i mean. Most people think quenching is just dunking red-hot steel into a bucket of water, but materials scientists can quench in water… For very simple CCT and TTT diagrams, the CCT is typically at somewhat lower temperatures and longer times than a TTT, so in cases where only TTT diagrams are available you may still be able to get an idea of relative hardenability from a TTT (comparing one steel to another).

These estimates are not perfect but can give a general idea of relative hardenability. Heat Treating is the most important factor for high performance knives. To determine the effects that quenching can have on a metal, materials scientists may use Jominy tests or time-temperature-transformation (TTT) curves. Therefore a steel with 0.2% carbon can have high hardenability without being able to reach a particularly high hardness; the steel can be allowed to cool in air and achieve more or less the same hardness as when it is quenched in water. https://www.patreon.com/Knifesteelnerds, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). This distorted crystal is very hard, but quite brittle. The three fastest cooling rates do not transform to any phases until they reach the “Ms” line around 230°C which represents martensite. All the atoms that join this cluster will have the same orientation, and they will form a grain. However, the bubbles from boiling reduces the thermal conductivity, ultimately leading to a slower quench. For reference, here’s the relevant portion of the iron-carbon phase diagram. If you go even lower you can perform a subcritical anneal from temperatures like 1250-1300°F. but decreasing grain size to that size can greatly detriorate hardenability for any steel , even deep hardening steels “i.e. For example, W1 or 1095 have low hardenability due to the high carbon content and low additions of hardenability elements, typically 0.3% Mn and Si. As seen in the chart, Mo is the most effective hardenability element. Martensite is the end product of conventional quenching on steel. Generally, the only way to control cooling speed is with the quenching medium (that’s the stuff in the bucket).

Some knifemakers are afraid of holding too long at austenitizing temperature because of concerns about grain growth. Retained austenite is actually a stable (well, sometimes metastable) phase. The temperature of the water also affects the vapor blanket formation. These are a special type of crystal: a single crystal. It is relatively common to see forging bladesmiths recommend descending temperature normalizing or grain refining cycles, such as 1600°F, then 1550°F, then 1500°F, etc. The best way to determine the optimal quenching speed for a material is to use a Time-Temperature-Transformation (TTT) chart.

Required fields are marked *. And Mn is preferentially located within cementite rather than ferrite. Metallurgy and Testing of Knives and Steel. With low carbon hypoetuectoid steel, during cooling the steel passes through the “austenite + ferrite” region: At points 1 and 2, the steel is fully austenite and the carbon content of the austenite is equal to the bulk composition of the steel, in this case 0.4%. Unlike the crystals you might normally think of, like gemstones, metals are “polycrystalline.” That means that metals are composed of many, many tiny crystals. Different steels have different critical cooling rates. W2 steel [11] – 1.0C-0.2Mn-0.2Si-0.1V – Very low hardenability, needs to be quenched in 3 seconds, W1 – 1.05C-0.25Mn-0.2Si – Very low hardenability, 0.70C-0.25Mn-0.25Si [5]- 1070 though with lower Mn than normal (typically around 0.7Mn). That leads to a difference in hardenability, in a somewhat similar way to grain size discussed before. Backscattered Electron. Even with 1.5% Cr 52100 still needs to be cooled in about 20 seconds. Metallurgy and Testing of Knives and Steel. I reviewed the literature in this article. Tool Steels: Properties and Performance. I hope I have illustrated this with my homemade animations, but if you want to look this up yourself, it’s called the Hall-Petch Effect. Since martensite is BCT and austenite is FCC, their different lattice parameters will easily show up on XRD.

Don’t feel bad if you don’t understand quenching either! TTT diagrams are better for intentionally forming bainite or pearlite by holding at specific temperatures.


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