Ask a metallurgist

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22 Responses

  1. At what point does the cooperation between cementite and ferrite, during the growth of pearlite, break down?

  2. hkdb> Please refer to recent publication at phase transformations website http://www.msm.cam.ac.uk/phase-trans/2015/pearlite.html while I compose an appropriate response for the bainite blog.

  3. Hi Matthew, I bought a wedding ring made of tungsten carbide. Is there some test I can perform, that I can use to determine the material used as a binder (cobalt, nickel, or something else)?

  4. Did you try using a magnet, I think it would be sensible to exclude the possibility that you have a steel with a tunsgten carbide coating. A good non destructive technique might be to measure the density. That would involve measuring the weight and the volume, it is also possible to do it by weighing in air and suspended in a liquid (e.g. water). In a full lab there is equipment to measure the composition, for example X-ray spectrometer or scanning electron microscope fitted with similar device. Those devices involve exciting the atoms with a beam and then measuring what characteristic X-rays are emitted.

  5. Thanks for the response! I did try using a magnet, and the ring didn’t respond.

    I haven’t tried measuring density, because I assumed that the relatively low proportion of the binder material, plus the fact that I don’t know the exact proportion, would make it difficult to tell which binder was used from the density. But I will give it a shot, at least to confirm the ring is actually tungsten carbide. I think it is, though, since it feels pretty heavy in the hand.

    My chief concern is that the cobalt binder leaves the ring more susceptible to corrosion, and I’ve read stories about them turning fingers green over time. It’s my understanding that the nickel binder is superior for jewelry applications.

    I assume X-ray spectrometry is prohibitively expensive for my needs🙂 (but maybe not?). I wound up ordering a cobalt spot test kit designed to detect cobalt as an allergen by producing a visible chemical reaction when a test solution is applied with a swab (it changes color). I have no idea whether this will work, but it was the only “home” option I could find after quite a bit of digging.

  6. Hi Mathew,
    Lot of works in literature (Tomita and Okabayashi) pointed out that after a certain heat treatment, steel with mixture of lower bainite and martensite for a certain volume fraction of lower bainite shows greater strength than Martensite. Will that happen in every steel or this has something to do with steel chemical composition.

  7. Hi Rohith, I was hoping to have time to give a better answer… Tomita and Okabayashi reported results for 4340 steel, Fe-0.25Si-0.-01P-0.009-0.75Mn-1.79Ni-0.82Cr-0.2Mo wt%. Improvement in strength is due to partitioning of carbon into the residual austenite and a composite effect of having bainite and martensite together (according to Young and Bhadeshia MST 1994). Strength improvement is not completely general but easy to achieve, it depends on strength contribution from the bainite (transformation temperature) and the martensite which forms will always be stronger than martensite in the bulk (and then you have additional term). Examples were strength could be lowered by a mixture are (1) if the bainite forms at much higher temperature than the martensite, or (2) if martensite formation is suppressed resulting in large fraction of austenite. Therefore, an optimum strength can be achieved with mixture of bainite and martensite in many cases, including carbide free steels.

    • Thanks a lot for the nice explanation Mathew. I have another simple doubt, unfortunately I don’t get proper answer for this through my search.

      How to calculate the molar volume of Austenite phase. ?.

  8. Hi Mathew,
    I have a very simple question: why adding Mn,Cr,Mo,Ni (except Co) hardenability improves?
    Thank you in advance.

  9. Hardenability (ability to transform to martensite at lower temperature) depends on transformation kinetics of the various phases during cooling from the austenite phase field. Effect of alloying elements which improve hardenability is by delaying the pearlite or other transformations that occur at higher temperature range. Usually by lowering thermodynamic driving force.

    • Thank you very much for the answer, but I can’t figure out why pearlite transformation (for instance) is delayed….looking to a CCT it seems that all these elements stabilize austenite even if they contract the gamma field in phase diagrams.

      • Seems like you understand to me. Effect on nucleation and diffusion during growth may also be important. Austenite grain size is also important for hardenability.

  10. I know CR-Mo-W-V steel is available as castings; would you know if this is also available as an alloy in bar form (e.g.,”readymade” ) ?

  11. Hi there. I am designing a unique telescopic baton and wanted to know what metal would best balance cracking and bending resistance against weight over fairly prolonged use. Ideally a lighter metal as this isn’t designed to be a club lol.

    • Steel would be best obviously. Aluminium alloys might be an option. What you are talking about is optimisation of a tube. Stiffness and cracking resistance depend on diameter of the tube, also wall thickness and material properties. One way to decide is to write an equation to describe which material you should choose, a merit index. If you look at bike design you can see it’s possible to make good tubes with lots of materials. Most economic choice also depends on volume you will make and resources available to you.

  12. Hi. Our product http://www.givengohockey.com uses high strength low alloy sheet steel 10ga A1011 Gr 50 teeth to prevent it from moving on the ice when a puck hits it. The teeth are strong but not strong enough because they can still be bent if the unit is accidentally bumped into the boards. Is there an even stronger HSLA 10ga steel we can use or can what we are using be heat treated to make then even stronger? the material must be able to be welded onto a carbon steel frame as well. The teeth are sharp and 1/8 in thin so they are able to pierce the ice and keep the unit in place. There is a picture on our website under the gallery tab. Any help would be greatly appreciated! Thanks!

    • A saw there are two classes of A1011 Gr 50, with carbon content 0.15 and 0.25, those seem very different beasts to me. There is also similar classes of Gr 55.

      Advantage of HSLA steels is the toughness and weldability… not really strength. That makes them very forgiving. Since you fabricate by welding maybe it’s best to look at other ways of avoiding the teeth being damaged, like larger teeth, a retracting cover, or moving position of handles, etc.

      Give-N-Go Hocky Passing Aid

      It’s possible to get much stronger steels, but you need to see what the limits are to the welding equipment and procedures you have available. Attaching a separate part which is just teeth might be an idea (slot in or bolt on), then that can be replaced if damaged, and rest of construction can be made from usual low/medium carbon steel.

  13. What platings can be used to plate gold to provide hardness (besides nickel due to allergen reasons)? Are there any plating options that are clear in color?

    Thank you!

    • Maybe very thin oxide could be clear?

      Glass ceramic or pottery glazings I expect are harder if you can apply them without crazing. Maybe a glue like epoxy.

      Is this for jewelry? I wonder if surface hardness can be increased by deformation, peening or shot peening. You can use a lower carat gold which is alloyed producing a harder surface or you could alloy with platinum which preserves the carat but which is more costly.

      Titanium nitride films are used on steels to produce a wear resistant surface and have a gold colour.

  14. This may come off as unserious, but I am genuinely curious to know what properties such an alloy would even have.

    • Haha, heavy, not particularly toxic, possibly can be made very strong at high temperatures also utilising intermetallic phase which are known to exist in Au-Ti system. Only a matter of time till someone tries to make this as a high entropy alloy or checks to see if it is a high temperature super conductor.

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