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I will give the standard metallurgist answer - it depends. Some straight mineral oils are very slow, especially if they are thick - say 100 SUS (standard cold commercial quench oil). If it has speed improvers and says fast oils - it will generally harden most steels. The best temperature is around 150F +/-. Be careful, most cold quench oils (meaning used below 200F) have a flash temperature around 350F. If you use canola, peanut oil, or something similar, you can go much higher. They also do not have a stable vapor phase so they are quick up top, where you get properties. They also have a high transition from nucleate boiling to convection phase - so they cool slowly at the Ms temperature - so low distortion - or lower - it depends. He may have a bit of decarb, so it appears to be soft. Remove a bit of the surface - then test. It is probably hard unless he is using something like 1008 - at which point nothing you do will make it hard.

You caught that one! Us metallurgists got to maintain some mystique! BTW - actually magnetic field can manipulate quenching and annealing - producing some interesting microstructures, and create very fine grain. There was an interesting study on strong magnetic fields done at Oak Ridge National Labs....: http://www.msm.cam.ac.uk/phase-trans/2004/magnet.html Really amazing stuff - by turning on/off the magnetic field, grain size was manipulated. Further, increadibly fine pearlite can be created, yielding very hard vet ductile materials..... But I digress - where was my astrolabe?

I really wouldn't recommend taking a K couple that high, unless it was very thick. At those temperatures it will start to drift badly, and not give accurate readings - but I am talking +/- 25 F or so....If you have a carbonacious atmosphere, the drift would be worse. A R or S couple is better for those temperatures - but much more expensive. But if you get acceptable results with the K couple at that temperature - use it. A lot of this is based on my experience with commercial heat treaters and my own experience. YMMV. Scott

OH OK - I see now! That is pretty! I suspect that the interface between the clay and the steel would cause the vapor phase to become unstable, and result in the initiation of nucleate boiling earlier. I think overall, you would get the vapor phase to be less stable, and the nucleate boiling region to initiate earlier. This will help with properties. I would watch for stuff that would capture bubbles. The rougher the surface, the more unstable the vapor phase becomes, because the rough surface initiates bubbling earlier (raises the Ledenfrost temperature - the transition between vapor phase and nucleate boiling). BUT, if the surface roughness becomes TOO large, the ridges will actually hold the bubbles longer, and make the vapor blanket more stable. OK - now the next question is - how big is too big. The answer is - I don't know. That answer your queestion? Scott

RKNichols is right - it is non-uniform heat transfer (center to surface or surface to surface) that causes warping from quenching. BUT, there are also a myraid number of other ways - non-uniform heating in the furnace; large gradients of residual stresses in the part before heat treatment; improper microstructure of the starting material; phase of the moon; design of the part; grinding stresses; decarb on the raw stock; banding in the material, etc. But it is always the heat treater or heat treatment that gets the blame. What sort of quenchant are you using? What is the temperature of the quenchant, and how much agitation do you have? All of these things, plus thos above greatly affect the distortion.

Don: That is a hard question - ad I will give the standard metallurgist response - "it depends". Often, in aerospace parts, especially large aluminum forgings, they use insulating blankets and that type of thing to locally slow down the quench. This is true on large transitions from thin to thick, where you want to even out the cooling on the part. I think the same sort of thig applies to the use of clays. By covering certain portions of the part with clay, you would locally slow down the quench. At the transition between clay/no-clay, unless it is blended (progressively thinner), there may be a risk of locally high residual stress, and with the worst case being cracking. I would suspect that the crack would run perpendicular to the clay, toward the material under the clay - but that is a guess. By using clays, I think that would be an effective way of slowing down the quench, particullarly if you made a good effort to gradually thin out the clay. That way there would be a progression of quench rates from fast (no clay) to slow (heavy clay). A lot depends on how the blade enters the quench. I would need a better description on how that is done with clay to better understand, and estimate any ill effects. Hope this makes sense. Scott

If you can get a small piece of Ni-Cr wire (also called Nichrome) commonly used in heating elements - you may be able to get some at Radio Shack - use thin gauge wire. Put a pice where you can watch it. If it starts to melt, then the temperature is 2100F-2300F. It also goes by the trade name of Unimetal. You can use this to calibrate your eyes, or a pyrometer. There are also cones that you can buy at a ceramic shop that people use to get the temperature of their ceramic kilns just right. You can get a wide range of temperatures, and they are very accurate too. Use one below and above the temperature you want - when the low temperature one starts to sag, you are above that temperature, and below the higher temperature cone. Here is a link for kiln cones: http://www.miniworlddolls.com/evenheat/ConeInfo.htm Hope that helps. Scott

One good way of judging temperatures accurately, is using Tempil Sticks. They are like crayons that melt at a specific temperature. You should be able to find them at a welding supply house. They use them for setting proper preheat and post heat temperatures. Use two crayons - one fro the lower boundary temperature, and the temperature that you don't want to exceed. When you see the lower temperature melt, and not the high temperature one melt - you know that you are at the right temperature. You can also use them for making sure you are at the right tempering temperature. You can also use ceramic cones that you buy at a ceramic store - people use them to set the temperature of their kilns. They are very accurate in temperature. Again use two, and do it the same way as the Tempil Sticks. When the lower temperature one starts to sag and the tip bends over, you are at the desired temperature. Ceramic cones is the best and most accurate way. Here is a link to kiln cones: http://www.miniworlddolls.com/evenheat/ConeInfo.htm Judging color by color is an art which only comes from experience - and the proper color changes with each alloy. BTW, what quenchant are you using? Good luck. Scott

The grinding direction DOES matter. You will get different quenching effects with different grind patterns. The longitudinal grinding lines will have a faster quench if put in the quenchant in the direction of the lines. Horizontal lines perpendicular to the direction of quench will be slower, as the lines tend to hold on to the bubbles during the vapor phase. Initiation of nucleate boiling will also be delayed. It will also slow the rate at which the nucleation wave front progresses. This can contribute to higher residual stresses and more distortion - with cracking just the extreme case of residual stresses. Scott

It almost looks like a lap or a seam. Perhaps a large inclusion. I am not sure of the discoloration. What did you quench it in? Did you see if you over tempered it during grinding? This can be checked using dilute nitric acid in methanol or entanol - you can also use nitric acid and water. A max of about 5% nitric acid. Use a cotton swab, and lightly rub the solution on the blade. 10-30 seconds is all that is required - then rinse the blade throughly in water, and dry. If you have burned it or locally over tempered it, it will turn a darker shade. If you really felt your wheaties, then you could have locally turned it to martensite, and it won't etch, but there will be a darker band of over tempered martensite. Banding is also a possibility, and this will also show in etching. You will have nice longitudinal grains in the direction of forging. Very interesting - pretty blade too. Scott

While not a bladesmith yet, I hope to be - at least create my own forge, or own my own forge shop. I am humbled by all the beautiful craftsmanship I see on this board. There is something magical about watching a billet of material being shaped by the force of the human hand. I have worked with open and closed die shops, helping them to understand their heat treating process - this could be anything from titanium blades in VT, superalloy sections of jet engines in France, of large gun barrels in PA, or golf club heads in IL - I enjoy just watching. There is something very powerful and fullfilling about seeing and participating in manipulating metal to the desired shape and use. Born 1956, and knew from a very early age that I was going to be an engineer. It wasn't until high school that I knew I wanted to be a metallurgist. I attended Carnegie Mellon for a couple of years before I flunked out. Took a year off to verify and confirm what I wanted to do. I finished my BS in Metallurgical Engineering at Ohio State University. Started to work as a manufacturing engineer responsible for the aluminum and steel heat treat shop at a small aircraft company in St. Louis, where they assembled the F/A-18, F-15 and AV-8B. My shop did everything, from heat treating the F/A-18 landing gear, to wing skins for the MD-11. I did this for 13 years. At the same time I got my MS Metallurgical Engineering degree from the University at Missouri-Rolla. I designed a small endothermic generator to invstigate carburizing kinetics. Management decided that heat treating was non-value added, and I started doing failure analysis and crash investigations. I did this for 6 years, and really enjoyed it. In this time I started work on my PhD in Metallurgical Engineering, working on the development of microstructure of thick plate aluminum during hot rolling. Within a week of graduation, my services were no longer needed. Immediately afterwards, I started working for an international company that produced metal working products - with the primary focus on quenchants. I knew thay made good products, as I would only allow these quenchants in my shop. So the family moved to Valley Forge PA, where I am the traveling "guru" on heat treating and quenching. I have been everywhere from Beijing to Zagreb visiting all sorts of heat treating shops, forge shops - anywhere that needed some help in heat treating, and control of distortion. Once I remember helping a small Catholic school in Sri Lanka make repair parts - they would forge them, carburize and quench. Using simple things like a bicyle, we were able to design and fabricate an agitated quench tank, and help them improve the quality of their carburizing, using simple tools, and materials that they could make or scrounge. I still hear from some of the students today. In the past 5 years, I have 1,000,000 seat miles traveling the world at customers, conferences and the like. In reality I am the technical guy who helps the salesperson make the sale from the technical side. I love heat treating. I am on the Board of Directors of the ASM Heat Treating Society. I enjoy helping people with heat treating questions, and other metallurgical type questions. Just being on the board the short time that I have, I have learned a great deal about the practical side of blade smiting, and in awe with the beauty of the blades. If you have a metallurgical question, quenching question, or heat treating question, please feel free to ask. I will try to answer. I will also ask a lot of dumb questions, like "why?" and "how you do that?". Thank you. Scott

OK....the material is a relatively low carbon content, and is edge hardened by carburizing, or induction or just quenching the end. Once austenitized (a nice cherry red) and quenched, the whole part should get hard. Since it is a relatively simple grade of steel in the mower blade, it will not get as hard as spring tooth steel - which is typically a 5160 or similar grade. The carbon content is higher - so it gets harder. The additional elements only make the steel harden deeper - it is the carbon content that governs ultimate hardness. Normalizing is the process of heating the material up to the critical range, then slow cooling it - typically in air. Glad you wear your safety glasses......

Thank you Tracy - I appreciate it. While I don't know much about smithing, or blade making, I will try and help with any metallurgy, heat treating or quenching questions. Scott

That is absolutely fantastic - I really like the pattern and the handle. Very clean lines.....

Adriaan and Tracy are both right. Soy oil has a good high flash temperature. It has a unstable vapor phase so it is quick at the top when you want properties, and slow at the bottom where you can get distortion. Agitation is important. Because you are making knives, go up and down. You may also want to make a simple pump and piping that forces the quenchant up from the bottom. You want to make the heat extraction on both sides, so up and down is best. Baby oil is a mineral oil - I think. But it is thin, and may have too low a flash point, or it will have a low vapor phase. I really don't know - it certainly is cheap enough to try. I just hate to see you ruin a blade quenching in something like that. One thing you could try, is to get some waste quench oil from a commercial heat treater. If you talk nice - they may give you some. Using soy, canola or peanut oil also works very well for the reasons cited above. Hope that helps. Scott

Message me. I do, but want to avoid any personal commercial interests as my company makes them - all sorts. Scott

Also agitate it more. Agitation will help. But I suspect that the quenchant that you are using is too slow. Try a canola oil, or a mineral oil quenchant that you can get from Brownells - that one is a good one. As a good rule of thumb, use a gallon of oil per pound of parts. This will limit the temperature rise of the oil and prevent it from igniting. You will see some flash as it enters, but it should extinguish quickly. You should see no more that a 50-100F rise in temperature if that rule of thumb is followed. You may have to use more quenchant if the part is large - high surface area. Hope that helps Scott

You could also score it where you want it to break - the notch will act as a stress concentration and result in cracking at that location. Brine will get it slightly harder than plain water - the reason is that the salt acts as a nucleation site for boiling, and it will help defeat the long vapor phase of straight water. Strong agitation also helps. The harder the water, the less benefit of brine. WEAR SAFETY GLASSES AT ALL TIMES. Eyes are difficult to replace, and your face looks funny when they are gone. As I recall, most lawn mower blades are often just hardened on the edge. The reason is that the softer material backing the blade will prevent the crack from impact from propagating, and prevent shattered blades. I will do some digging and see what the material is - but I do not think it is very fancy. Maybe low carbon steel that has been carburized at the edge. Scott

I believe that CHTE (Center for Heat Treating Excellence) at WPI has some information on their page. If not there, then you can try some of the recent ASM Conference proceedings on Heat Treating. If not there, I may have some that we have done - specifically Canola Oil. If fact we have a product that we sell that is manufactured from Canola Oil that does a wonderful job - except it is expensive. One of the troubles with using salad oil that you buy from the grocery store, is that it has a quantity of water in it that changes the cooling curve. This can cause soft spots, or potentially cracking - depending on the water content. I may also have it on my "Information for Heat Treaters" page, under the topic "Advances in Quenching". I will see what I can find... maybe I will figure out how to attach stuff. BTW - I go by Scott.....

Neither propylene or ethylene glycol will work suitably as a quenchant. Neither one of those chemicals has the inverse solubility (like a PAG) necessary to achieve a limited vapor blanket and good distortion control. The cooling curves are TERRIBLE, and are likely to crack a part. The PAG (polyalkylene glycol) quenchants marketed by two companies (my employer and my competitor) are suitable for quenching steels and aluminum. There are a number of large forge shops using our quenchants. Some of the forgings are the size of an SUV....some are quenching very thin blades for cutlery and surgical type instruments.... You can try it - but I wouldn't recommended it. In the Houghton on Quenching reference, it has a good NON-COMMERCIAL description of the various polymer quenchants available (they are not limited to PAGs), and the mechanism of how they work. Hope that answered your questions. Scott

Check out the old Alcoa books "Heat Treating Alcoa Aluminum", or AMS 2770 - that gives specific information regarding hardness, conductivity, and the proper heat treating temperatures and sequence. There is also the old MIL-spec MIL-H-6088. That also gives the heat treating times, temperatures. Some of the aging temperatures are quite long - 24 hours or more. Temperature tolerances on aluminum solution heat treating are tight - especially for 2XXX and 7XXX alloys (typically +/- 10F) because you are very close to the melting temperature..... Forming is often done in the as-quenched condition. The material is soft and pliable. Then it is aged to the final condition.

The forging process (and the cooling process) does induce residual stresses - particularly in a highly hardenable alloy like 4340 or 4140. This is because there is some residual local concentrations of hardenable alloying elements like Cr that do not necessarily get broken up during the billet operation, or subsequenct forging operations. 4340 is especially bad about this. As the part is slow cooled, some local areas may harden, while other may not - depends on the local concentration of C and Cr. This can contribute to residual stresses that relieve themselves on heating. For example, we had large 800 lb landing gear forgings for the F/A-18 that were forged from 300M stock. These were received in the normalized (1600F, then air cool) condition. These were closed die forgings. After machining, we had a lot of surface roughness variations due to local hardness variations. We were also seeing large variation in distortion during hardeing operations - often resulting in quench cracking or gross distortion. Straightenening these large forgings was out of the qquestion, as the straightening operation could induce additional residual stresses that could cause premature failure in the field. This was cured by performing a spherodazation anneal on the forgings as they were received from the forge shop. This resulted in a much better machined surface, and much better response to heat treatment. In addition, much of the distortion was reduced. A little additional furnace time resulted in large cost savings in machining, distortion and residual stress control, and improved hardening response. While this is an extreme case, it does show the benefits of sphereodization annealing. Scott

I am trying to set it up so I can attach it, and people can download it - but I am having trouble attaching things........ Scott

I have tried to upload the file - with no luck. If you want to store it in some place where others can get to it - please feel free. I don't know if there is a file storage area - if so, I can put it there. Scott

Check out http://extranet.houghtonintl.com/HeatTreat/Index/ for a bunch or articles I have written, and the text "Houghton on Quenching" - it is an excellent beginning text on quenching. While the articles are written primarily for the commercial heat treater, the concepts and topics are very valid for all types of quenching. I would especially recommend "The Houghton on Quenching" text, as it is a solid reference, that has been published since the 1900's. I used it as a reference in college, and still refer to it today. Email me if you have any questions, or want a copy (pdf format) of any of the articles. You can also download them directly from the site. Thanks Scott