History and Properties of 52100 Steel
I’ve started posting early test most current listings for things like heat treatment experiments, retained austenite measurements, etc. on Patreon. The data may ultimately be posted to the website, in case you want to see it because it comes then jump on Patreon. 52100 History 52100 is often a not hard steel with 1% carbon and 1.5% chromium, and small amounts of Mn and Si. 52100 steel has been around use since a minimum of 1905 [1]. It was developed for use within bearings. High carbon steels (0.8-1.0% C) were primarily used before late 1800’s or early 1900’s [2], and chromium addendums to bearing steels were being made. 1% Cr steels are already found in bearings since at least 1903 [1]. These early chromium-alloyed bearing steels were produced in Germany by Fichtel & Sachs and also by Deutsche Waffen- und Munitionsfabrik [1]. French-produced chromium steels were also employed in bearings in the similar time frame [2]. 52100 remains the most common bearing steel [3], and so the steel design has certainly stood test of energy. The steel passes by all kinds of other names such as 100Cr6, 1.3505, GCr15, En31, and SUJ2. Update 5/8/2019: Nick Dunham posted the subsequent concerning the good the SAE designation of 52100 (the name came later compared to steel, naturally): It appears that in 1919, the SAE Iron & Steel Division chose to replace 5295 with 52100 as part of their seventh report [1]. 5295, therefore, was introduced as 52-95 inside the third report (1912) [2], and dashes were removed within the fifth report (1913-1914) [3]. It was an impression steel from the beginning – another report says of 51- and 52- series chromium steels, “the utilization of such a steel is bound almost entirely to ball and roller bearings.” [2] The third report was also the creation of the two-digit series prefix [2]; in the second and third reports (1911), only two-digit codes were used, numbered 1-23 (including cast iron). No chromium steels were listed [4]. This just isn't to state that chromium steels did not exist yet, however the SAE specifications failed to exist yet. End Update Ed Fowler is owed some credit in popularizing 52100 like a knife steel nowadays. He has produced many knives in 52100 and wrote extensively about its virtues in Knife Talk columns in blade magazine. Ed was introduced to 52100 within the form of ball bearings provided for him by Wayne Goddard [5], another influential knifemaker who regularly wrote for Blade magazine. Because bearings were a comparatively common form of high carbon scrap steel, its use in knives extends back much further, needless to say. Knives produced as far back as the 1940’s in 52100 are actually reported, including knives by William Scagel [6]. 52100 Design The obvious difference between 52100 along with other high carbon steels utilised by forging bladesmiths is its high chromium content of just one.5%. The Cr addition is designed for several reasons, which I have described below. Quench Speed One function of the Cr addition is good for “hardenability,” a step of how fast steel must be quenched from hot temperature to realize full hardness. A simple carbon steel including 1095 uses a quickly water quench to fully harden, the place where a hard steel phase called martensite is actually created. 1095 has nearly 1% carbon like 52100 but with no chromium addition. If quenched in slow oil or able to air cool, then some volume of “pearlite” forms which cuts down on the hardness of steel in accordance with full martensite. Pearlite can be a mixture of 0.02 wt% carbon ferrite and 6.67 wt% carbon cementite (Fe3C) that forms in alternating bands, so which has a simple carbon steel the carbon must diffuse on the short distance for that bands of ferrite and cementite to form. Chromium can also be enriched in the cementite, so in a very chromium-alloyed steel the chromium must diffuse in to the cementite to create pearlite. Chromium is a much bigger atom than carbon therefore it diffuses less quickly. Therefore which has a chromium addition pearlite formation is suppressed and hardenability is increased. This hardenability effect can result in seen with a Time-Temperature-Transformation (TTT), also called Isothermal Transformation (IT) graph where the “nose” of the transformation (called ferrite+carbide) is pushed to longer times in 52100 relative to 1095. This allows bearings to be fully hardened in order that they have adequate strength and therefore resist deformation during use. The core of an impact cools slower as opposed to surface during quenching, therefore the higher hardenability allows larger bearings to get used. 52100 remains to be not a high hardenability steel, however, and just isn't considered a genuine “oil hardening” steel like O1 (instead of water hardening). For large bearings requiring higher hardenability, modified versions of 52100 were developed. A higher Mn version was introduced within the mid-1930s, along with a Mo-alloyed version after WWII [7]. However, neither of the versions have observed significant utilization in knives. The “nose” with the curve inside TTT for 1095 actually extends from the chart as the time is really short. Very fast quenching must avoid soft pearlite The “nose” from the 52100 TTT is a about 3 seconds, allowing more gentle quenching to realize full hardness Effect of Chromium on Carbide Size Carbides take time and effort particles in steel that improve wear resistance but reduce toughness or potential to deal with cracking. Therefore, greater amounts of carbides are desirable for applications that need high wear resistance. Applications requiring high toughness usually require carbides to get as small as possible and have a small volume fraction of which. A typical high carbon steel like 1095 forms hard particles of iron carbides called cementite, with three iron atoms for every carbon atom: Fe3C. High chromium steels form a chromium carbide for example Cr7C3 or Cr23C6. Some erroneously feel that 52100 forms one of those chromium carbide types. However, it doesn't plenty of chromium to make those types of carbides. Some in the chromium is instead enriched inside cementite, forming M3C where M can talk about either iron or chromium. The cementite in 52100 contains about 9 wt% chromium [8]. The addition of Cr reduces the carbide size. Smaller carbides means better toughness and capacity fracture. 52100 is renowned for its tiny carbide size and high density of carbides, even though compared to other carbon and alloy steels like 1095. The carbide dimensions are reduced by way of a similar mechanism on the rise in hardenability. Prior to delivering steel towards the end customer, the steel is annealed to become soft for machining and arrange it for final heat treating. One method for annealing would be to slow cool the steel from hot temperature to form pearlite, then an intermediate temperature treatment the place that the pearlite structure is “spheroidized” in order to create small round carbides [9]: Because Cr is a component with the carbides which diffuses more slowly than carbon, the spacing between cementite in pearlite is smaller, and therefore the rate of “spheroidization” and growth from the round carbides is reduced. Here are images [10] comparing 52100 (top) with 1095 (bottom), where the white particles are carbides. The 1095 is quite fine, nevertheless the 52100 features a greater density of carbides along with the maximum carbide size is small compared to 1095. 52100 1095 Carbide Fraction and Carbon in Solution When comparing steels on the same high hardening temperature however with increasing carbon content, the level of carbon in solution remains constant though the quantity of carbide increases. You can see that by looking at the iron-carbon phase diagram below; the black circle exactly in danger represents the carbon in solution which does not change with increasing carbon content. However, with higher carbon the road extends further into the “austenite + cementite” field indicating that more cementite occurs. The phase diagram represents the microstructure of steel at different carbon contents and temperatures. At a temperature of 1400°F, in a carbon content between about 0.55-0.7% the steel is inside “austenite” region where no carbides/cementite occurs. If quenched from that temperature the ultimate microstructure is tough martensite without carbides. If the carbon content articles are increased above 0.7% then carbides can be found at the high temperature, resulting in a final microstructure of martensite with carbides. The carbides contribute to wear resistance. The more carbon is added above 0.7% the greater the quantity of carbide occurs: The amount of carbon “in solution” to bring about hardness continues to be the same with a fixed temperature despite the increasing bulk carbon content, for the reason that carbon is adding to carbide formation. However, if your temperature is increased then this carbon in solution rises along the queue. If we look with a 1% carbon steel at 1400°F (point 1) there is the same 0.7% carbon in solution as a steel with some other steel with carbon higher than 0.7%. Dotted lines show the carbon in solution vs the majority composition with the steel. At 1450°F there's 0.8% carbon (point 2), and 1% carbon in solution at about 1570°F (point 3). The length from the dotted line shortens with increasing temperature indicating the level of carbide is decreasing, until point 3 where you can forget carbide is found possesses reached the “austenite” field: The addition of a single.5% Cr shifts the positioning in the iron-carbon phase diagram, to higher temperatures reducing carbon contents: The shift in the phase diagram ensures that for that same bulk carbon content, there is certainly less carbon in solution as well as a greater volume fraction of carbide. This is why the recommended hardening/austenitizing temperatures of 52100 is more than 1095, usually 1550°F instead of 1475°F. The lowering of carbon in solution vs 1095 helps improve toughness, as carbon above about 0.6% in solution leads to plate martensite which reduces toughness. Experimentally, 52100 has about 0.63% carbon in solution with a hardening treatment from 1550°F [11] which supplies maximum hardness without forming plate martensite. Lower hardening temperatures further lessen the carbon in solution for better toughness. You can read more on this page about the hardness of steel. The rise in carbide fraction also improves the wear resistance of 52100, where heat treated 52100 has around 6-10% carbide volume [12], and 1095 has approximately half that. Ease in Forging, Quenching, and Heat Treating With its low chromium content compared to air hardening steels like A2 or D2, 52100 is really a good option for forging. It will not have carbides present at forging temperatures like those air hardening steels meaning it moves quicker underneath the hammer. Its medium-low hardenability also helps it be the ideal choice. The low hardenability of 1095 means water or extremely fast oil is necessary for quenching, while 52100 is a bit more forgiving with slower quenches. Slower quenches slow up the chance of warping and quench cracking. A more hardenable steel like O1, or air hardening steels, are incredibly forgiving using this standpoint, but that creates them difficult to anneal with no controlled temperature furnace. Those steels can also be difficult or impossible to normalize as they will harden when cooled in air, instead of forming the desired pearlite. High hardenability steels are also more prone to crack when forging at lower temperatures, or simply when cooling to room temperature after forging. Therefore, the amount of hardenability in 52100 is really a good compromise for flexibility in quenching while still being possible to normalize and anneal with simple cycling. The increased temperature and time required for austenitizing relative to simple carbon steel, however, makes austenitizing more challenging when heat treating in the forge or using a torch in lieu of a PID-controlled furnace. Heat Treatment of 52100 We now have a very separate article about how to best heat treat 52100. As discussed above, helping the hardening/austenitizing temperature of 52100 contributes to an increase in carbon in solution along with a decline in carbide fraction. That is seen experimentally too, though numbers are somewhat diverse from those predicted through the phase diagrams, as those predictions are on an infinite hold time at temperature, instead of the 10-30 minutes employed in heat treating. As the carbon in solution increases, the level of retained austenite after quenching also increases. You can learn about why in this post about cryogenic processing of steel. The peak in hardness arises from an austenitizing temperature of approximately 1650°F; above that excessive retained austenite forms which reduces hardness. Here is retained austenite and carbide volume vs austenitizing temperature [8]: With lower tempering temperatures far better austenitizing temperatures, hardness is increased. Using 1650°F and 300°F brings about approximately 66 Rc [8], though that condition likely also brings about relatively low toughness. A typical heat management of 1550°F austenitizing and 400°F tempering results in about 61.5 Rc. Many knifemakers use 1475°F and 400°F, which may result in about 59.5 Rc. I’m not quite sure why they will use 1475°F, perhaps it emanates from copying recommended heat treatments from 1095. Knifemakers, like all kinds of other people, like round numbers, so an austenitizing temperature that leads on the round number of 60 Rc following a nice round number temper of 400°F may perhaps be appealing. Using lower austenitizing temperatures can result in improved toughness, that you can find out about in this article on austentiizing. Typically, it is better to relieve both austenitizing temperature as well as the tempering temperature, in lieu of to keep up the same austenitizing temperature and improving the tempering temperature. One reason is because the carbon in option is reduced in the event the austenitizing temperature is lower, as described above. Another issue is the “tempered martensite embrittlement” (TME) range when tempering too much, you can see a drop in toughness inside the figure below when you use a tempering temperature of 230°C (450°F) You can read more to do with TME in this post on silicon additions, core part that minimizes embrittlement. You can see the improved toughness of 52100 with lower austenitizing temperature with this figure [11]: Increasing the austenitizing temperature also increases hardness, but even if the toughness is plotted vs hardness, the development with lower austenitizing temperature still holds. I removed the as-quenched and 230°C tempered conditions because those conditions had poor toughness: Triple Quenching Ed Fowler also popularized “triple quenching” of 52100, a process where the steel is austenitized and quenched several times for grain refinement and improved toughness. 52100 isn’t particularly any more suitable for triple quenching than other low-alloy steels but 52100 can often be associated with it in order that it is worth mentioning. I wrote about how exactly multiple quenching works as well as potential benefits in this article. We also performed triple quenching on CruForgeV and tested its toughness but didn't find a marked improvement, which you'll want to read about in this article. Austempering and Bainite 52100 is comparatively perfect for austempering to form bainite, instead of forming martensite with a quench and temper heat treatment. Austempering involves quenching to a intermediate temperature, such as 500°F and holding there for minutes or hours, which leads for the formation of bainite which can be a phase that's much like tempered martensite but somewhat different properties. There is some evidence to point out that bainite has greater toughness than tempered martensite. You can read more to do with bainite and a few experiments that are actually performed on 52100 in this article on austempering. When steels have high hardenability, austempering takes to much time being feasible. To reach high hardness levels, relatively high carbon content articles are necessary with austempering. So 52100 carries a good combination of high carbon and medium hardenability for ease in austempering. Toughness of 52100 Despite all from the studies on 52100, it is somewhat hard to find good comparisons when it comes to toughness compared to other steels. Many from the studies focus on 52100 itself, because it is the place to start being one of the most widely used bearing steel. Tool Steels [13] rates 52100 like a “4” from 10, which can be comparable to A2, and more than O1, M2, and D2, reducing than L6 and shock resisting steels, according for the book. We will be testing a sample of 52100 soon to match with your current toughness dataset. And if someone knows anything good published comparative toughness numbers please send these to me. Using the Tool Steels ratings we are able to position 52100 within other steels with reported toughness values from Crucible [14][15][16][17]: Edge Retention of 52100 Edge retention of 52100 is not particularly high, just like other carbon and low alloy steels. The relatively low volume of carbide, in addition to the low hardness of cementite, means there are more steels with higher wear resistance and slicing edge retention. In CATRA tests by Verhoeven [18], 52100 was found to get superior edge retention to 1086 and Wootz damascus, though less good as AEB-L, a stainless-steel. 1086 is really a lower carbon steel for lower carbide volume, and AEB-L has harder chromium carbides, hence the result is sensible. You can read more regarding how good the slicing edge retention of 52100 is in relation to other steels inside articles on CATRA edge retention: Part 1 and Part 2. In rope cutting tests by Wayne Goddard [19], 52100 was discovered to possess similar slicing edge retention along with other 60 Rc steels; there was clearly less effect of steel in his testing and hardness was the main factor, though Vascowear (CruWear) was somewhat better: Summary 52100 originated inside early 1900’s, and first used in 1905. It was created for use within bearings. It has been employed in many knives, partly because of its good properties in forging and in part because bearings are a fairly easy way to obtain scrap steel. The chromium addition improves hardenability, and decreases the carbide size to have an improvement in toughness. The chromium addition also ensures that 52100 requires higher austenitizing temperatures, and carries a greater level of carbide compared to a simple carbon steel for improved wear resistance. The mix of reduced carbide size but increased carbide volume fraction gives 52100 a good mixture of toughness and wear resistance compared to other carbon and alloy steels. Lower austenitizing temperatures bring about improved toughness. The medium hardenability of 52100 means it really is suitable for forging, and also a fantastic candidate for austempering to create bainite.
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