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Posts posted by kb0fhp

  1. What about carbides? Fe3C is certainly "molecular", with covalent bonding. There are all the other carbides too which also have covalent bonding, and then there are inclusions, such as MnS, which exhibits both covalent and ionic bonding. We should also include the oxides, such as Al2O3, FeO, Fe3O4, Fe2O3, etc....


    Just thought I would stir things up..... :D

  2. Anyone know about or can find info on DH-2 tool steel? It seems to be a listing used only by Caterpillar for hardened teeth and edge plates for earth movers. I have a pile of the plates (3/4 to 1" thick) and can get more as I live in between 4 quarries. They scrap piles every 6 months or so.


    I'm really interested in heat treating specifics as I can cut down the plates easy enough to make blades with the big plasma


    Kerry Stagmer



    This is a pdf of a description of the material, and typical chemistries. It also provides a description of typical hardness. The austenitizing temperature can be calculated from the chemistry.


    Hope this helps




  3. Depends on the oil used. For a commercial quench oil, it is typically anyway from 100-200F. But depends on the flash point of the oil. Remember to have enough oil - about 1 gallon for every pound of part - minimum 1 gallon. What kind of oil? Peanut/canola is a good choice.


    Commercial quenchants also work well.




    How much carbon there is in 1045?



    You can tell from the name - for AISI steels, they are in 4 digits - like 1045, or 4160. The first two digits indicate the alloying elements - the last 2 digits indicate carbon content. So, for a 1045 steel, there is 0.45 carbon, and for a 4160 steel, there is 0.60% carbon.



    For a description of the quench, I suggest you review the attached PDF file. It is essentiall a very fast quench, with a series of surfactancts and salt.


  5. Inconell thermowells can be obtained from most normal instrument houses....stainless steel ones will work - just make sure you have upscale thermocouple protection on your temperature controller. Just regularly inspect the thermowell, and you should be ok....


    Often in the set up menu of temperature cotrollers, they have a setting for upscale thermocouple break protection. It is often an option in the menu - always enable it. However, not all controllers have it - only buy those that do....sometimes you have to specify it when buying new

  6. I always recommend to my customers to use a nickel based alloy, such as Inconel 600 for their salt baths. If the cost is too dear, then use a high quality stainless steel, that has substantial lap joints when welding.


    The thermocouple wells should always be inconel or stainless - grounded with MgO inside. THermocouples should be checked EACH TIME YOU USE THEM - ESPECIALLY IN INTERMITTANT OPERATION.


    Always wear safety glasses, bloves and appropriate personal safety equipment. A faceshield is always recommended too - to protect everyone's pretty faces....



  7. Thanks Scott


    Would the heat in the epoxy coating oven have an effect? I was planning on having the frame coated matt black and the swingarm re-enforced and polished.




    Often companies age their aluminum parts at the same time that they are curing the paint - the automotive people do this a lot. Since the part has already been aged - I would expect it to soften it. I would not recommend it since it is a safety related item....



  8. I saw that there were a few guys on this forum that were very knowledgable re Aluminium a while back. Since then there has been this nagging question in the back of my head:


    A few months ago I wanted to have the Aluminium frame of my Motorcycle polished. The guys that I asked to do it refused, because, they said, it would "soften" the frame. They went on to say that polished frames can bend and/or crack. I know that these frames are probably made from a totally different alloy of aluminium than the climbing equipment, but does the same rule apply?


    I was about to have the thing epoxy coated, but running it through an oven worried me even more.


    I ride this baby really hard and wouldn't like the frame parts to part company at 180 mph! That's just gonna turn my day sour!






    That doesn't make a lot of sense.....unless they were REALLY putting a lot of grinding into it - and heated it up. Then it could soften it.


    Polishing will improve fatigue resistance....THere must be some sort of reason why tyhey won't polish it....THe reason they gave might not be right - but the results may be....





  9. Aluminum heat tereating is a bit strange. When solution heat treated and quenched, it is soft. As you age the part at elevated temperature (say 250F), it becomes harder, goes through a peak (T6) then becomes softer.


    More than likely the temper would become softer, and not more brittle since you are not heating it up to 1000f or so.


    In the off chance that you did heat it up to 1000F or so, and quenched it in water - then held it at room temperature, it would only get harder and stronger because of natural aging....


    Confusing isn't it?



  10. There are two types of embrittling phenomina in quenched and tempered steels. The first is called tempered martensite embrittlement (TME)- and is associated with temperatures from 500-700F - it has also been called 350C or 500F embrittlement. FOr us old guys - I have heard the term "blue brittlenes"....


    There is also Temper embrittlement (TE) - which is related to tempering in the range of 707F to 1070F.


    TME develops fairly quickly, and is size or section thickness independent. It may or may not be associated with impurity atom segregation to grain boundaries, but it is associated with the formation of cementite during tempering. For intergranular fracture, the segregation of P to the grain boundaries, and the interaction of P and cementite is necessary for the intergranular form of TME.


    Temper Embrittlement is associated with the compositional requirement that specific impurities must be present. These are typically Sb, P, Sn and As. Only about 100 ppm is necessary to be present. Hi Si and Mn also can cause TE. Plain carbon steels are not considered susceptable as long as the Mn level is kept to below 0.5%. Cr-Ni steels are the most prone, except when Mo is used as a gettering element. Mo additions support the formation of (Mo,Fe)3P or Mo-P atom clusters which prevent segregation of P to the grain boundaries.


    I hope that that didn't confuse matters - but clarified them.



  11. Temper embrittlement is supposedly casued by the partioning of Phosphorus and Antimony to the grain boundaries. Makes it a lot more brittle at the temperature ranges of around 650-700F (or so - I can't quite recall). There is also another type of embrittlement - called blue brittleness - which is formed at much lower temperatures. I am not sure of the mechanism though....

  12. An initial quick reply/comment regarding Shuiha Ma Thesis. The probe they used has one major flaw, but is the same flaw that made it nice to use - it was thin, and had small thermal mass. This made it weasy to calculate heat transfer coefficients, but did not develop enough of a thermal mass to develop a persistant vapor barrier.


    We have been a memeber of CHTE since the beginning, and there has been some useful and interesting work out of it.

  13. Any one of those methods - high velocities through quenchant - it doesn't matter if it is the part of the quenchant - it is the relative motion that is important, will tend to wipe the vapor phase. If you move it so quick, with sufficinetly high volume, that you prevent both film formation and boiling - then you have "intensive quenching", developed by Dr. Kobasko of the Ukraine. Really a neat method. There is lot of information on the web.



  14. If the quenchant is too hot, you run the risk of a slow cool, clipping the pearlite/bainite knee of the curve.


    If the oil is a little below the martensite start temperature, a little martensite will form on the outside of the part first, but the rest of it will also transform at about the same time....allow to equilibrate in temperature, then pull out, and allow to air cool.

  15. So I'm thinking....what if I quenched in slightly (for safety reasons) boiling canola oil, and let the blade sit in it until it reached the temp of the oil, then let it air cool? This wouldn't quite be considered a marquench would it, but it would give you slow cooling through martensite formation to keep stress in the steel down. Thoughts?



    NOPE - use a lower temperature - I would feel safe doing that. Use a MUCH lower temperature - say 200F. You will still get the results you want, but still be safe. You can go as high as about 100F below the flashpoint - no higher to be safe

  16. The waviness - kind of like a sine wave on the knife edge is casued by the material contracting, and having too much restraint from the backing material. I think that the whole band cooled quickly, instead of the edge first, then the back edge - this causes the waviness...have seen this in commercial heat treat shops - especially with aluminum....

  17. So basically, you go below MS, but you are not going all the way down to MF so that there is less stress in the hardened piece, correct?


    Thanks Scott.



    Absolutely correct! The purpose is to reduce distortion from differential temperatures - center to surface, or surface to surface. If there is no distortion (with cracking a limiting case of distortion), then there is no reason to do martempering, or to do interrupted quenching.



  18. Now, why is it that when martempering, the oil is above MS, but when interrupted quenching, you pull the part out after it has dropped below MS temperature?



    Actually in martempering, you quench till you reach the MS temperature or a little below, then hold at that temperature to let the center catch up (cool down) to the surface temperature. When you do an interupted quench, you have to let the surface get a lot colder to make sure the center gets to the MS temperature...unless you don't care what the center microstructure is, or it is too thick to transform to martensite....


    Did that answer your question?



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