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Bertie le Roux

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About Bertie le Roux

  • Birthday 10/08/1984

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  • Location
    Northern tip of South Africa
  • Interests
    Metallurgy, Bladesmithing, Outdoors
  1. Sauli You seem very enthusiastic and I love your eagerness to experiment! I would agree with most of the above, especially regarding what Dave said. Try not to get too excited about trying all the complicated stuff before you master the basics. You will find that getting really good at the seemingly trivial things is more rewarding and complicted than you might have thought initially, and will be an equally satisfying challenge to trying al sorts of other complicated things. It is easy to suppose using advanced materials will yield advanced results, but in my opinion it is more important that you are able to treat whichever material you are using correctly - and this is easier to do when starting with something less complicated that will probably be capable of yielding very good results anyway. To get used to pattern welding, two steels that are excellent on their own but give high contrast and are extremely compatible in welding would be a common sawblade steel called 15N20 combined with the plain as can be AISI 1075 or something very similar (W1, W2, 5160, 1095, 1085). Starting out with these will make your life a lot easier and chances are you will be very happy with the results achievable with these steels even though they are marvelously uncomplicated. You will have a lot of questions right now, and it is hard to answer all of them even when we know the answers... This is a great forum, and there is a great deal of information already on it... Beginning with the basics and reading everything you can find in previous posts will help a lot, and answer many questions before you even think of asking them Good luck and have fun!!!
  2. Yup - more than one way there certainly is... I guess what it comes down to is gaining the knowledge and experience and having the dedication to start doing it, getting results, and then being able to properly study and interpret these result in order to get an idea of whether you are doing a good job yet, and if not, how you could try to improve. In broad terms, making bainite or martensite or combinations of the two is not difficult. But both of these structures (not to mention combinations) have very variable properties depending on what exactly you have done, so doing it in a way that gives excellent or even usefull results may be another matter altogether. Figuring out the basic way in which something is done is an essential (and often the most exciting) step, but only the first of several. :0) I like this (paraphrased) quote: "Only in theory is there no difference between practice and theory" So, for making a blade with a differential structure of bainite and martensite, combined in a usefull way, you probably need to first have a good understanding of each of the separate aspects, including: properties and thermodynamics of bainite properties and thermodynamics of martensite properties and the production of blades with differential microstructures ...and then, last but by no means least - actually doing it! :0)
  3. Yup, quite a few options out there... Depends on how accurate you want to be and what your budget is. For spot checks or testing small amounts of material for which it is not worth while doing an expensive in depth analysis, I reckon using spark testing is quite common practice... As far as I know it is some kind of spectroscopy where a small portion of metal is vaporized using al electric arc (I may be totally wrong on how it works though hehe). Last time I checked it cost about $100 per test. It will probably only pick up the metal alloying elements and not carbon or nitrogen content... I know some gold inspectors carry portable testers or something like that to do spot checks for gold and silver purity or correct alloying at jewellery studios, so whatever they use could be relatively simple (I suspect spark testers). It is easy enough to determine carbon content through microscopy provided you can do the heat treatment of the sample properly to get a suitable microstructure. Easy for plain carbon, harder as alloying increases and pearlite gets harder to make. If you want to go minimum budget and just get a ballpark idea for own use you could just do a variety of thermal treatments and see what microstructures they give... Determine carbon content as above (use % area covered in pearlite and cementite multiplied by carbon content of pearlite and cementite for a very slowly cooled sample). With some knowledge of TTTs, CCTs and tempering curves you can match up the curves you get for your steel and compare it to known steels with similar C content. I have used this method a couple of times where they gave us mystery samples in practicals to heat treat. These are the tests that should require the minimum preparation and equipment I can think of. XRD and XRF are also not terribly expensive, but may need special sample prep and you would need training to operate the equipment and interpret the results yourself. With the specific types of XRF and XRD our geology dept. had, we only used these two methods on mineral samples (which were not allowed to contain metal due to issues with platinum crucibles used to melt samples into slags), so I have no idea of their applications in testing metal composition. The metallurgy dept. used "the other" methods
  4. Hmmm, not quite. Dendritic growth from a liquid is a very different way for crystals to from but does have one or two similarities to changes insolid phase causing crystals to grow through solid state reactions. Solidification structure has some relevance but is a whole new topic, and for this discussion it is perhaps best assumed that in the steels suitable for exploring the current discussion, it is sufficient to assume that the coarse and segregated as-cast dendritic structure of steels produced by liquid metal metallurgy (as opposed to powder etc) is carefully homogenized before and during hot rolling to make the steel suitable for use. There should be little enough "dendriticness" in these steels to ignore it in this discussion - at least for now. The short answer to your question about the grains necessarily having different orientations is yes. Each crystal will grow from its seed crystal in the orientation it was seeded in(this starts at the first few atoms arranged in a particular FCC, BCC, BCT or CPH lattice - i.e. less than a handful or atoms already having a crystal orientation). Grain boundaries arise where there is a buildup of dislocations as two misaligned crystals "clash" and the energy required to alleviate the dislocations or slightly re-align the molecules of one crystal to match that of the adjacent one is not available (i.e. grains won't "grow" or combine to form bigger ones when the metal is too cold). If two perfectly matched crystals grow into each other a perfect alignment would mean no grain boundary will form and they will just become one crystal. Grain boundaries are classified and differ in energy according to how misaligned the crystals on either side are. Because of the misalignment, built up energy and "space to move atoms around" due to high dislocation density at grain boundaries, the formation of new crystals during for instance a low driving force phase transformation ( austenite from pearlite) or precipitation (cementite in hyper eutectoid precipitation) occur at grain boundaries more easily. So more grain boundaries = more places for easier re-arranging or atoms for whatever wants to happen to start happening. The martensite reaction has a very very high driving force and thus does not really need a grain boundary to initiate twinning or needle growth (which happens at speeds in the vicinity of the speed of sound), but it is none the less influenced by grain boundaries. In equilibrium driven reactions and transformations, whatever is easiest will happen. So crystals always form where it is easiest for them to nucleate and grow. Growing through a grain boundary takes energy so when a martensite needle "can choose", it will take up an open space inside an austenite grain rather than go through a boundary. By the time all the open spaces are taken, much of the driving force has been spent on transformation, and it becomes even less likely for needles to go through grain boundaries. So even though the exact effect (especially on physical properties) is complex, the influence of austenite grain size on martensite properties is in part based on the above principles.
  5. I just want to check what exactly you mean... Was the smith unable to harden the steel properly, or was the abrasion resistance found to be inferior at a similar hardness to larger grain sizes? I ask because I can verify that small grainsize lowers hardenability, so on a marginally hardenable steel you may become unable to harden it at small grainsizes. Can't really comment on grain size vs. abrasion resistance/edge holding at the same hardness if that was the case.
  6. Bruce - a very good reply! Just to be a bit technical with terminology or to add to your explanation... Strong carbides like VC precipitate due to a high driving force so they are generally smaller than carbides of weaker carbide formers. But more importantly - even if you were able to get a weaker carbide like Cr-carbide to be just as small in size to begin with - the important thing about a stronger carbide is that it will STAY small in stead of for instance speroidizing like FeC as temperature increases. The more spread out it stays the better. Even before anything starts to dissolve FeC and Cr-carbides can become so coarsely condenced (as opposed to small and spread out) that they are no longer any real obstacle for grains that are trying to grow around them. You can make the grain of any steel fine, but V and other strong carbides will make it easier and keep it that way better. Vanadium will only have an infuence on the soak time requied to dissolve carbon necessary for hardening if most of the carbon in the steel is bound to it. So if you have a small amount of V in an otherwise plain steel (as in W2), the V is never really meant to be dissolved in the final austenitizing cycle (so it can keep grains fine) and so little of the total C in the steel is bound to it that it will not lower potential hardenability too much if it is not dissolved. The plain FeC in W2 will dissolve fast and do its job. On the expanded topic of Nb - it does the same thing as V, just more tenaciously. I worked in an mill making ultra low alloy pipieline steels with grainsize as their main way of strengthening, and the temps to dissolve NbC before rolling were quite extreme! Works more efectively than V but harder to get it to do what you want it to. Ti is also an option. All of these have an effect from as little as 0.01%
  7. Phase diagrams can be quite usefull in figuring out a mix that might work without or with less of an ingredient or two when you can't find them btw. Unfortunately phase diagrams aren't easy to find I would add advice on making your own recipes, but because this stuff really can be very dangerous I would rather stick to suggesting you use existing recipes.
  8. These calculators can be very usefull but it is hard to take into consideration all the factors that influence the shape of a TTT or CCT curve (there are MANY). Usually they are only really usefull if used in the "context" they are designed to be used in... i.e. they are based on a combination of empirical data and theoretical physics in a certain application or composition range and can tell you what the result of a certain degree of variation would probably be. Some of the variables they don't give you an option to input may very well be making a difference because in your application it is varied but in the intended application it is a constant or at least a different typical value. Usually the TTT's are a bit more accurate than the CCTs due to a very variable cooling rate being taken into consideration on CCTs but not TTTs. Even if nothing looks the way it "should", it is very interesting playing with these to get a bit of a gut feel for what does what
  9. John N - I agree wholeheartedly! It has always amazed me to see how much hard earned knowledge people are kind enough to share on forums like these. You can find more than enough on any topic I can think of to have the necessary background theory and be well on your way to gaining practical personal experience, which I believe is critical to true understanding and healthy learning. There are very good procedures to follow out there that enable you to create excellent work, but it would be fair to say you should expect to have to go a step further in the direction of working at mastering your trade to be the best or at the cutting edge. We should all be very thankful for the opportunities to learn given to us in discussions like these, contributed to by the wonderful people hosting and posting on this and other forums. Thank you all very much. Edited: tendency to ramble is a serious illness.
  10. I have also been toying with this idea... Induction heating seems pretty efficient compared to kilns or fired furnaces but I have yet to read up properly on the topic. Please keep us posted on anything you find out! Years ago when asked about salts a lecturer of mine suggested melting a small section of salts and then inserting an electrode to heat the salts by using the resistance the molten salt itself has to an electrical current flowing through it. Would only work with ionized salt (i.e. molten or dissolved) so you can't do this from a cold start. PLEASE make sure how and if this would work if you want to try it...It was years ago and my theory is rusty. If your container is conductive you will also need to consider how this could affect the "route" the current will take through the salt. I'm getting back into the whole metallurgy thing at the momens and will definitely be building a salt pot again as soon as I can afford some shop upgrades. I will definitely be trying both of the above methods
  11. Depending on how little distortion can be allowed, and how much something going wrong might cost, you might have to be really carefull... To harden a thick section of 1045, you will need an extermely drastic quench (brine), and will probably stil only be able to harden about 5mm deep. Only hardening the surface will not be that bad, and will increase fatigue resistance if done correctly, but needing a fast quench to do it will be bad, because cooling of thick sections easily causes large temperature gradients, and - depending on geometry - could very easily cause warping (especially with a fast quench) This is why dies are often made out of steels that can be hardened using a mild quench (slow oil or air). The D in D2, etc, is for 'Die steel', and I think all D-series steels are air hardenable in reasonable sections... Heating to austenitizing temp has a rule of thumb of around 20min/inch thickness, and 1045 really will not need a very long soak after temp has been reached, due to simple alloying. You should look up the proper austenitizing temp (but am guessing around 820oC) Even temperature will be important. A kiln with some sort of inert atmosphere (or enclosing the whole piece in a box that can safely contain an inert environment and putting this inside a furnace) will probably be best, as scling could cause changes in the surface dimentions, and could be difficult to remove (depending on how intricate the die is). A stress relieving step or three might also be advisable
  12. Hey Maleck Nope, sorry - only understand a few words of French at best. Have been able to trace back to when my ancestors moved to S.A. from France, but that was over 200 years ago Realy cool research, though! I am very interested in the statement about precipitations not influencing GB mobility. That's only for the type of cases you are looking at though, not in general, right? In the stuff containing C (which I think could make it very different), precipitation of VERY tiny (Nb,M)(C,N) on the GB is trigered by a critical amount of strain at a given temp, and almost totally arrests GB motion and recrystallization below 1273K. Less than the critical amount just increases the amount of energy available to move boundaries, and increases grain growth... There are a few different 'schools' in HSLA/GS control steels. Some focus primarily on the effects of precipitates (because less alloying is needed for great effects), and others more on GB retardation by solutes (as per your research). I think the solute stuff is used less, and is not understood as well. I feel that this should perhaps not be the case, because the precipitation-based processes cause a drastic increase in the strength of the metal during rolling, which limits the possibility of employing such processes to newer, stronger rolling mills... Therefore - very interested in your results... Good luck!
  13. Mr Fogg I remember reading an article on your website about a katana forging class you hosted years ago. In the section regarding the experimentation with a choice of HT for the blades, you mentioned trying out a process where the blades were 'converted to bainite'. I was just curious as to how (and how successfully) formation of bainite was achieved. As I recall, the blades were a medium C 10XX steel. I guess my question comes down to the quench rates possible with heated quenchants like salts or hot oil (for forming bainite), and whether they are (in practice) sufficient to allow a shallow hardening steel to form bainite (after missing pearlite). From what I have been able to find out, quenching salts have quench rates similar to those of quenching oils... Also, does it sound plausible that salts could have a less detrimental vapour jacket effect, due to having a higher bp than oil in most cases?
  14. Sorry - do not exactly have any useful info to offer, but am very interested in this topic... Do I understand correctly that your work is on the retarding of recrystallization by solute atoms - as opposed to GB precipitates? I encountered the application of this phenomenon while working in a linepipe steel mill, producing some Mn-Ti-Nb HSLA steel. Aparently a Mo-Nb combo was the most effective, if I recall correctly... Might find some info in articles about HSLA steels, but many don't go that deep into the basic theoretical stuff... The temperatures you mention seem very low! What is the C/N content of your alloy? I'm guessing really low, because in rolling 0.14%C+N steel, temps had to be kept above 1123K or so to keep all the Nb from precipitating too soon... Does your work include the effects of deformation rates of RX/diffusion/ (?precipitation?)?
  15. It could be higher than criticlal, but will not necessarily be higher than needed for solutionizing (or even high enough), due to the time dependancy of dissolution. Critical is just where the carbide becomes unstable, and therefore able to dissolve (for hyper eutectoid you can start dissolving 0.8% at the eutectoid temp (Ar), and dissolve all carbide at Ac or critical, which is the same as eutectoid temp for a 0.8%C steel). It does not say anything about how long it will take to do so, and exactly at critical, it will take forever (literaly). A rule of thumb is to go about 100oC above critical to ensure a high enough rate for simple alloys, but stuff like Cr can make carbides that take very long to dissolve near critical, and may need 950oC or so to get them all, if you want to... Therefore, the advice in the previous posts is very good - you should know the exact temp you want to be at (after doing the necessary homework), and then merely use the curie point as an easily spottable temperature reference which should be within a few hundred degrees from where you want to be.
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