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Telling the difference between Chromoly and MS

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  • Telling the difference between Chromoly and MS

    I have asked this question to a lot of people and posted it on a few forums. How do you tell the difference between Chromoly and Mild Steel with no markings? The answers I have received were as follows:

    1. Grind both pieces of metal and there will be a different spark pattern.

    (I ground a piece of Chromoly and Mild Steel and there was no difference in spark pattern.)

    2. Heat both pieces of metal red hot and quench them into water, the Chromoly will become brittle.

    (They both were same; one was no more brittle than the other.)

    3. There is an acid test you can use to determine the difference.

    (No one seems to know what kind of acid is used or the procedure to follow.)

    I have a Dragster frame and I don’t know what it is made of. If it’s Chromoly, then I just have to replace a couple of struts and add more to my roll cage to bring it to specs. If it is Mild steel, then I have to rebuild the whole thing. If anyone has a viable answer, Please let me know. Thanks in advance.

  • #2
    Unless I worked with chrome moly on a daily basis, I doubt I could tell the difference in a spark test either. The definitive method would involve either destructive testing of a specimen and noting it's yield/tensile strength or some non-destructive methods of xray,ultrasound,ebeam, electromagnetic, or acid. The acid test kits I did find cost a few hundred dollars, so that doesn't appear to be very cost effective either. If it were me, I'd call in a professional metallurgical service. I noticed you're in IL. Aston Metallurgical Services is in Wheeling ( or I'm sure the yellow pages could provide other listings as well. Good luck in your search.


    • #3
      Hi, I think I would call the division 3 office and ask how their certification guys make the distinction between the two. The last time I had my door car done they asked me what it was and after I answered they hit it with an automatic center punch. ( It's a CrMo tube frame car. The other option is to call the chassis mfgr as they should know. Good Racing, JEFF
      200DX 350P 625 Plasma & other stuff I forgot


      • #4
        I think the auto center punch sounds plausible. I think using a scrap piece of Chromoly as a reference, it should work.


        • #5
          I recommend talking to your divisional certification team before sinking a lot of modification time into an older chassis. Better yet, let them look it over. They may want to do sonic tests on the older tubes to check for inner corrosion anyway, and that would be worth its weitht in gold to avoid finding out after mods that an old chassis was not rebuildable.

          This might seem like a lot of trouble now, but getting a modified chassis certified later on will be a lot easier if you've talked to them up front.