Interesting reaction to quench galv steel.

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by soje, Jan 15, 2020.

  1. soje

    soje Basic Member Basic Member

    Dec 10, 2014
    TLDR: What is happening with this galvanized metal strap that I heated and quenched? After quenching, the metal showed a change that abruptly stops at this pronounced line. I think I scored the metal before tempering, but I'm not positive. Is there some kind of temperature threshold, where cooling happens at a different rate?

    I took a grinder and cut some width off of one end of a 1/8" x 1-3/8" x 12" piece of hot dipped galvanized metal strapping. I bent the narrower piece 90 degrees. I used butane torch to get the steel red hot and quenched it with water. It came out with this pronounced line that ran across both sides of the strap. You can see the metal is very different on either side of this line. The line itself is even shiny. I kind of remember scoring the metal prior to tempering it, but I'm not positive I did.

    Is this just my bad memory, where the rate of cooling changed abruptly at my score mark?

    Does the quenching process have some sort of temperature threshold, where the rate of cooling changes drastically?

    I'm sure it might be silly to some, but I was fascinated. I've never done metal work though.

  2. Randy3000


    Jun 3, 2017
    you shouldn't be heating up galvanized steel, it gives off poisonous fumes.
    allenkey, argel55, Bigfattyt and 2 others like this.
  3. TheEdge01


    Apr 3, 2015
    Never heat galvanized steel, even if you have proper ventilation. As mentioned, it puts off poisonous fumes.
  4. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    Zinc puts off fumes because it boils at such a low temperature (1665°F), and it melts at only 787°F. Don't try to heat it up and quench it.
    Bigfattyt and john april like this.
  5. soje

    soje Basic Member Basic Member

    Dec 10, 2014
    Oh yeah, I forgot to mention I later learned how dangerous it was. Luckily, I did it outside while there was a breeze. Thank you all for mentioning it.

    I'd still like to hear if anyone knows how/why it looks different on such a delineate line. I'm thinking I must have scored it.
  6. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Contrary to popular lore, the fumes from galvanized metal are NOT toxic. They will give you a headache and upset stomach, but will not kill or damage you.

    That is not to say that heating galvanized metal is a good idea. The metal will not harden, and the protective coating will burn off. Basically, you get useless damaged low carbon steel when you heat it up in the forge.
    Kevin McGovern, Ken H> and tkroenlein like this.
  7. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    Sounds pretty bad to me:
    Aidenag, Taqtaq and allenkey like this.
  8. tkroenlein


    Dec 10, 2016
    Y'all can take or leave what I'm about to say. I won't debate or otherwise further discuss heavy metal fume fever as it pertains to galvanized steel.

    I've worked in a manufacturing facility for 19 years where the annual tally of welded galvanized material is measured in millions of pounds. We use basic weld fume extraction to deal with the fumes. People aren't real religious about using those extractors, either. But the hazards are easily dealt with by unaware and uneducated folks easily enough, with the simple instruction, "suck up the smoke with this."

    Also in the same time, a very good friend of mine spent a night in the ER with a screaming high fever and the worst flu-like sick I've ever heard described, due to heavy metal fume fever. He made the choice to weld up a reasonably big job without taking the steps he needed to ventilate.

    Summary: Is there a risk? Yes. Is it easily mitigated? Also yes. Like everything else people work with, a little understanding goes a long way.
    SBuzek, Ken H>, Sam Dean and 2 others like this.
  9. 12345678910


    Jul 13, 2009
    The big discussion will be attracted to the metal fume fever -
    ( My experience yes it's real- it can lead to pneumonia especially if you're susceptible with Asthma or something else.)

    The reql problem with your post
    NOT all steel is knifeable.

    You have normal mild steel.
    Heat treatable steel is actually fairly rare

    Get some O1 from Fastenall
    something from Alpha Knife supply - they sell small amounts at low costs
    something from the

    Read the sticky's there's a tone of info for the newbie
    allenkey likes this.
  10. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    The line indicates where the zinc was vaporized due to heating the steel.

    Don Hanson III likes this.
  11. S obsessed

    S obsessed

    Dec 27, 2019
    In the same way a smith uses water on the anvil while forging to blast off the scale on the item is likely the reason for what you are seeing. I can see the sticker is still on the strap in one of the pics therefore you didn't have the whole thing real hot. The area that is different was hot enough to get above the melting point of the zinc and then when quenched the water blasted it off. The line is the same back and front so that is where the heat was low enough to prevent the zinc from being essentially washed away. What you have there is a strap with little to no galvanizing on the dark area and therefore it will rust. A building inspector may not let that fly especially in an outdoor situation. Those kinds of straps can be easily enough bent cold and retain their protective coating. Cutting them usually isn't an issue as it is just the edge that will rust and won't generally grow to affect the rest of the piece. Wouldn't hurt to throw a little paint or solvent based caulk/adhesive on the cut edges though.
    Ken H> likes this.
  12. Rick Marchand

    Rick Marchand Donkey on the Edge Moderator

    Jan 6, 2005
    The danger of poisoning is minimal with one piece of steel. Many of us remember ol' Paw-Paw from IFI. He burned off the galvanizing from several fittings and subsequently died. RIP, Paw. The fact is his fittings were very old and used high lead galvanizing... but the major factor is that he was already battling pneumonia at the time.
    tkroenlein likes this.
  13. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Yes, Paw-Paw had flu and pneumonia when he burned off a lot of galvanized and plated metals in a closed up shop. The smoke and fumes were so bad that he damaged his already ailing lungs and died of pneumonia. He did not die of metal toxicity or metal fume fever, as is often stated.

    No one should breath dust of fumes, regardless of what they are. Good ventilation and a respirator are absolute requirements if you are going to make knives.

    The internet is full of stuff about how poisonous galvanized metal is if you heat it up. These are mainly unsupported and range from inaccurate to false.

    For a very long time, all galvanizing is done with zinc. When you heat it hot enough, the white fumes coming off are zinc oxide. This is what is on lifeguards noses and in many skin care products and sun tan lotions, … and in your tooth paste. It is not harmful to humans. People confuse it with metallic zinc, which is toxic to some animals, but zinc poisoning is almost unheard of in humans. Zinc poisoning requires ingestion or inhaling actual zinc dust for a long time. Zinc oxide has strong covalent bonds and you can't absorb the zinc from it.

    It is hard to get the public to change ideas that they have been told for generations. Even medical professionals have these misconceptions. A survey of ER doctors found that 75% of them thought poinsettia leave are deadly toxic and children would die if they ate them. The leaves are not poisonous, and the worst you would get if you ate a salad bowl of them is a stomach ache.

    Same for metal fume fever. You will get a headache and upset stomach, but some fresh air, plenty of fluids, and a good nights sleep will have you ready for work the next day.
  14. timos-

    timos- KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Oct 22, 2012
    ok , but what about if cats eat poinsetta leaves, pretty sure i heard the cat will die. Unrelated but does anyone know if i can grind marble with my 2x72 and a ceramic belt?
  15. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Nope, part of the same wives tale. Cats will drool, throw up, and get diarrhea, but they won't die.

    I have been tempted to test people's certainty that Poinsettia is extremely toxic by making a bet. I have been in a room full of people who knew it was true because their mothers had told them so, and they had read it all their lives. I would offer to bet everyone in the room $20 each that I could prove it scientifically and beyond argument. After I got all the takers, I would grab a leaf off the poinsettia and eat it (probably accompanied by all screams and gasps). I would say that if I was still alive and well in three days they had to pay me. THe day may come when I have enough doubters n one room to do this.
    Last edited: Jan 17, 2020
  16. Randydb

    Randydb Basic Member Basic Member

    Sep 27, 2014
    There used to be a ton of threads on a woodworking site about the dangers of spalted wood dust. "Mold, fungus, spores etc in the wood cause awful health issues" (think moldy house issues) unless you used full respiration. Even had people who wouldn't play flutes made from spalted wood because of the danger. Of course these flutes were completely sealed with poly...but spalted wood dust was deadly.
    Eventually some people started doing a bit of research on the net and lo and behold this was just a wives tale. Similar to what Stacy said, "It's not really a good idea to be breathing any dust in general." But spalted wood dust is no more hazardous than any other wood dust.
    That was years ago, and there are still threads that the poisonous spalted wood gets brought up to this day.
    DevinT likes this.
  17. soje

    soje Basic Member Basic Member

    Dec 10, 2014

    Thank you. I was intrigued by how the distortion appears to have stopped immediately, creating a sharp line, rather than seeing a gradual fading off.

    I was making a one job use tool. The little piece I bent fits into the end of a camshaft, and allows me to turn the cam. It's not being used as a fastener or for any building purpose. I was only trying to get the end part, with the bent tab looking thing. It still ended up bending a little, when I used it, but I know squat about the actual practice of tempering.

    It's cool though. I learned something, and I'm one step closer to fixing my car.
  18. soje

    soje Basic Member Basic Member

    Dec 10, 2014
    I was building a little tool for one time use. I was impatient, and should have done some research on if the stuff could be tempered. The part was already pretty strong, so I was just trying to add a little extra, not knowing if it would even add strength. I know very little about steel/metal, but I've read and watched videos of guys explaining the importance of considering the metal's composition to develop a heat treat scheme. I've seen the data sheets on all the big name steel company sites too. I'm kind of fascinated with how precise the heat must be applied to some of these steels (or is it only alloys?).

    I appreciate everyone's information. I really want to study up, and set up a little forging shop. I've always been intrigued with the anatomy of metals and boggled by how people manipulate its properties with heat.
  19. S obsessed

    S obsessed

    Dec 27, 2019
    Hey Soje. As you found out, those straps aren't hardenable. Very few things you can buy are actually heat treatable besides buying new steel that is of known composition. Even steel suppliers don't generally have anything on hand except usually for some solid rounds for machining. If you want to in a pinch buy something to make a tool like that again and harden it to some degree then you could buy a flat pry bar like a wonderbar or even a shovel. These are usually simple medium to high carbon steel. Anneal or normalize to drill holes and research online how to heat treat. Thinner objects like concrete trowels or carpet/floor scraper blades are available to. Most of these items cost just as much as ordering some new known steel from places like new jersey steel baron though but they do work in a pinch if needed. Learning how to forge and setting up some stuff to be able to make your own tools is a real door opener and lots of fun.
  20. Aidenag


    Apr 16, 2009
    come on now, lets not downplay it to the point of not being accurate here Stacy... Studies have shown it also affects blood cell counts, can change your blood pressure and heart rate and a lot of other things beyond a headache and upset tummy... If you got any underlining health issues it could really ruin your day, or life...

    As you said, if you don't get too heavy a dose, yeah it will all go away after a few days or weeks and you'll be feeling back to normal. But there have been no long term studies done either to look into say if your chances of neurological diseases, heart or lung problems, etc go up either. It's really only been looked at from a immediate harm perspective. Personally, i err on side of caution as every day we find out something is horrible for ya that everyone said was fine or didn't cause long term health problems.
    allenkey likes this.

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