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Everything posted by kb0fhp

  1. Typically the gears are forged then machined. They are then austenitized and caburized for a case of 0.18 to 0.25 inches deep. The cycle takes up to 7 days. The parts are then quenched and tempered. Distortion is an issue - that is why they take care with the type of agitation and racking. Usually they are ground slightly after tempering - but it is kept to a minimum because it is so expensive. The case is martensitic with a pearlitic core.
  2. Take a look at Houghton on Quenching - a good little tome that is pretty non-commercial. It will give you the basics. The file size is too big (just over the 2Mb limit). But I can email it to you - email me at smackenzie@houghtonintl.com. Maybe I can get Don to put it in the archives. Scott
  3. You could also try hardening in a polymer quenchant - a couple of percent would be appropriate. It would provide a quench a bit slower than water but faster than oil so you would get the hamon desired. Also as other indicate, the edge is a bit thin - I would thicken it up a bit. Use of a brine quench is also good - but very fast.
  4. As you can tell, I have been absent a lot lately - I have been doing a lot of traveling all over the world working with heat treaters and forge shops. I just thought I would post a few pictures..... All these parts are forged so should be of interest.
  5. Assuming a low alloy steel (just iron and carbon), you will not see any increase in hardness at all with an identical quench. The hardness obtainable is governed by the carbon content. Above about 0.65%, you reach a point of diminishing returns - very little additional hardness is obtained. See attached graph. Carbon can be absorbed by the steel - but only at elevated temperatures in the austenitizing range and from a carbonaceous atmosphere - like a controlled atmosphere or packed in carbon. It does not occur during quenching.
  6. See attached. Of all the curves on this sheet - I like the Bio-Quench 700 the best: It has virtually no vapor phase; a very fast maximum cooling rate; and a very high nucleate boiling to convection transition temperature. Scott_Blade.pdf
  7. Sorry - unfortunately, that is one of the problems. However, if you need more, you could contact a local heat treater - they may have some old oil that you may want to try. Glad you found a source. BTW, vegetable oil is good too.
  8. That is the only thing that really makes sense. I am not sure what the tube was made of - if it was refractory (like many are) the melting temperature is much higher that of steel. Because of the color of the salt after the "incident" I would suspect it was consumed. I do know that nitrate salts do produce a strong exothermic reaction if heated to typical austenitizing temperatures.
  9. I can do that when I get my laptop back. I am actually going to a conference in Jacksonville FL in two weeks, where they are discussing this very topic. I am interested in seeing the papers. George Totten (a close friend of mine) is giving a historical review paper on vegetable oils for heat treating.
  10. That isn't a real good idea either - unless you spend a long time drying out the furnace. The best way and also the most tedious, is to chip it all out. Because of the exothermic reaction I really do think that the blade was consumed. Think of it as a type of thermite reaction. You are really very lucky.
  11. Absolutely nitrates can do that - they have an exothermic reaction that is really impressive. High temperature salts for austenitizing are all chlorides. Martemp salts are nitrates. If it was pink, then it is likely that it was nitrates.
  12. DO NOT ADD ACETONE OR KEROSENE TO ANY OIL! They will flash early in your face. I was involved with a fire that happened at a major aerospace company because some idiot didnt want to dispose of some solvent. I dont like getting calls from the local Fire Marshall at home at 4 AM because of something stupid. I dont want to see anybody hurt. Now regarding canola, it is a fast oil with nice properties. I would compare it to a medium to fast oil. It has virtually no vapor phase and a very high break from nucleate boiling to convection. Agitation will make it faster. There are some additives that make it faster, but unfortunately they are proprietary. We sell the only commercial canola quench oil. I would recommend going to a lower viscosity canola if you want faster or use a fast quench oil). I can show cooling curves in a few days if anyone is interested. Scott
  13. A couple of issues - first regarding the salt: Your furnaces look nice - well put together it appears. It sounds like you had a great deal of moisture present. Or you had a T/C fail - you should have an excess temperature T/C wired separately to shut off the heating elements in the even of a thermocouple failure. It sounds like you had a considerable amount of nitrate salt present. This can cause a violent exothermic reaction - maybe enough to cause the blade to be consumed. The discoloration of the salt leads me to believe that this is the case. I would really be interested in finding out the other brand of salt used, and its name. Second, in the first picture, you have a solvent can directly adjacent to the salt bath. There is also a lot of paper and other debris present which is a BIG fire hazard. There are also a lot of aerosal cans and other flammable solvents and similar near to the furnace - not a good idea. I am glad you are not hurt - or that you didn't lose any major property. It could have been ugly. Scott
  14. You can see exactly where the origin of cracking started - at a flaw in the edge midway up the blade. The chevron markings point directly back to the initiation site. It looks to be a steel that has not been carburized but a quench and temper steel. I would suspect that it may be a variety of steels including high carbon 1080 or 5160. I doubt it would be 4340 as it is very expensive. I would lean more toward a 1080 type. A spark test would give you a good clue.
  15. It is a very slow quenchant. The cold temperature won't do a thing. When you immerse the hot blade, you get a very stable insulating vapor blanket and lots of nitrogen as fog. Now, if it were strogly agitated, you would get a much stronger quench - but you would still have a stable insluating blanket. You would need to agitate it at least 1m/s to do any good - and may require more agitation.
  16. this should show a few possibilities vol3_issue3.pdf
  17. There are a variety of fast quench oils available in Austrailia - look at Houghton K. YOu could probably contact a heat treater to buy some from them or you can try some local sources.
  18. If you need the salts, you can make them easily. See the recipe at the beginning or google MIL-S-10699. As an alternative, you could also try contacting Houghton customer service.
  19. From a simple metallurgist point of view, I suspect that it has to do with the relative growth of the various phases present. Martensite would grow or expand the most, followed by bainite, and then pearlite. It also depends on when transformation starts. I had an interesting problem like this when a manufacturer decided to go from an 8620 carburized gear to a 4320 carburized gear. It was though that the distortion would be less because of the greater hardenability but because of the timing of the transformation the 8620 had much superior distortion (and was the cheaper solution too).
  20. Depends on the alloy. Many of the precipitation hardening steels like PH13-8Mo or 17-4 have delta ferrite at room temperature. It is a problem after welding as the delta ferrite hurts toughness. apps_support-tech-notes_vol3iss7-tn37.pdf
  21. Personally for many industrial applications and for control of distortion and residual stress, I happen to prefer a spherodation anneal. Nice fine grain, uniform response to heat treatment and low distortion. I think several people here have tried it and liked it. One of the really nice things is that it removes the forging residual stresses.
  22. Multiple causes of distortion and warping - all related to non-uniform quenching. Causes of Distortion-steel.pdf Distortion Fishbone.pdf
  23. The slow oil is essentially a 100 SUS mineral oil with no additives. The second oil is a medium speed oil that gets its speed using an additive (the reason it is darker). There are a variety of quench oils available that would work well for your application. I am a bit biased in my choice but I work for one of the largest suppliers of quench oil in the world. For information regarding the effect of oils on hardness and similar things - I would suggest reading Houghton on Quenching (I can email you a copy if you want - just send me an email or note smackenzie@houghtonintl.com). There is another reference book which is really excellent called the Handbook of Quench and Quenching Technology by G. Totten. I am working with George now to rewrite that book and update it with the changes that have occurred in the past 20+ years. Scott Overview Quench Oils.pdf
  24. Shell Voluta appears to be a straight 100 SUS oil with no additives or magic pixie dust for anti-oxidation resistance or speed improvers (at least that is the way I read the data sheet). I need to look regarding McMaster Carr.
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