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Forge welding temps?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by A.McPherson, Apr 30, 2019.

  1. A.McPherson

    A.McPherson KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 27, 2012
    Hi there!

    So I was reading the article that @Larrin posted on forging temps and someone posted a question about forge welding temps.

    I’m wondering what you guys use. I know lots of people use very high temps, 22-2300 degrees, but this article recommends not going over 2100 while forging to reduce failures in the steel.

    Now I’ve only done 1 billet of Damascus and 1 of cable, so I really don’t have much knowledge in this area.

    I’ve been using the advice “heat until you flux looks like it’s boiling” to judge temps, but I just got my forge set up with PID control so I can be a bit more specific.

    What’s a good temp to start from? I’m using 15n20 and 1084.
  2. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    My recommendation wasn't just about failures but also microstructure optimization. It's certainly possible to make damascus with 2300°F, depending on the steels in question, soak time, and how it's worked.
  3. DevinT

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

    Jan 29, 2010
    Proper forge welding temps depend on several things.

    The lower the carbon and the lower the alloy content of a steel the higher you can forge weld at without problem. It still needs to be drawn out at lower temperatures.

    The bigger the hammer or press the lower the temperature you can forge weld at.

    For simple steels, the hotter you go the easier it is to move. For high alloy steels, sometimes hotter is not easier to move.

    Oxides are not stable at high temperatures, heat cleans the steel not the flux, unless it is in an oxygen rich atmosphere. Sufficient heat and soak time will allow better welding.

    Most smiths forge weld too hot. Too large a billet with too small a hammer = not good forge welding. Higher alloy does not = higher forge welding temps. A bad weld is a bad weld, no matter how many times you re-flux and try to re-weld. Get yourself a press or a good power hammer, soak for longer than you think and it will solve most of your welding problems.

  4. A.McPherson

    A.McPherson KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 27, 2012
    Thanks for the tips Hoss!

    Alas, I don’t have a press or a power hammer.
    Just a 3 lb hammer and my arm. If you were gonna be making small billets by hand, where would you start with temps?
    Ken H> and Justin Schmidt like this.
  5. Ken H>

    Ken H>

    Dec 31, 2011
    If the temperature gets a bit on the hot side while forging to mess up the microstructure etc - can this be salvaged by a good normalizing after drawing out the billet? especially in the case of San Mia with 416 SS cladding?

    Since lower carbon level is less of a problem at higher temps, would 1075 be a tad more forgiving than 1095 for the core with 416SS cladding San Mia?
  6. timgunn1962


    Apr 1, 2009
    There are guys (including those above) with the skills to forge weld at lower temperatures.

    I had no idea what temperature was needed for welding. When I was at a hammerin a few years ago, I had a type S thermocouple with me (what self-respecting geek doesn’t?) and measured the temperature of the forge that had been used for making Damascus all weekend. I measured 1280-1315 degC in the working zone.

    There was a good cross-section of folk using the forge (which was the one next to a 15 kg, 33 lb, Anyang power hammer) with experience ranging from beginner to expert. All were pattern welding, some with hand hammers, most with the Anyang. The forge had been set up on the first morning and had needed no adjustment thereafter.

    Based on this, I's suggest that 1300 degC, 2372 degF, or thereabouts, is a pretty good forge temperature for those starting out with welding: if your forge is running at that temperature and you are not getting good welds, the problem is almost certainly not the forge temperature and you should look to some other aspect of your process.

    As is the way of such things, the owner of the forge wondered how hot it could really get and properly gave it the beans. We measured 1470 degC, 2678 degF, and destroyed the forge lining in the process. This showed a couple of things. First was that the sort of folk who attend hammerins really should not be going anywhere without a responsible adult present. Second was that the forge was running at that temperature because the guy who set it up felt that it was the best temperature to run it at. He could have gone hotter or cooler, but didn't. The weekend of productive pattern welding was evidence that it was an effective temperature.
    Ken H> likes this.
  7. DevinT

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

    Jan 29, 2010
    Forge welding at 2350-2400f is too hot for any combination of steels. The chance that it will cause irreparable damage is very high. I watched a well known mastersmith over heat a piece of 5160 and then break it to show the grain size which was very coarse. He then tried to reduce the grain by thermal cycling several times at the correct temperature. No matter how many times he cycled it, the grain was still very large. In order to reduce the grain size in an over heated piece of steel, it requires a reduction in size by forging or rolling at correct temperatures.

    You can easily forge weld at higher temperatures, it’s just not good practice.

    I watched a mastersmith who competed on FIF forge some pattern welded damascus at too high a temperature and made a sword from it. He did what he thought was the proper thermal cycling at the end of forging. The piece was stunning. When the judges tested the sword, large chunks broke out of the edge and he lost to a less experienced maker.

    Some early smiths said/wrote that you needed to heat steel until it was almost melted in order to get good welds, not true. Every new smith I know thinks that if he has weld issues that it is caused by too low temperatures.

    I see lots of muddy looking damascus out there, most of it is caused by welding too hot.

    At lower temperatures, the problem is not usually temperature but soak time.

  8. A.McPherson

    A.McPherson KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 27, 2012
    Thanks Hoss, so if I was to set my PID to about 2100, would that be about right? A good place to start at least?
  9. DevinT

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

    Jan 29, 2010
    2200’ should be fine for the initial weld, draw at 2000 and finish lower.

  10. Ken H>

    Ken H>

    Dec 31, 2011
    Thank ya'll for mentioning temps and sharing info. Would 2200°F be enough for welding 416SS clad San Mia with 1075 or 1095 core?
  11. A.McPherson

    A.McPherson KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 27, 2012
    Thanks again!
  12. DevinT

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

    Jan 29, 2010
    I’ve made a million good welds and two million bad welds, now you guys go out there and do the same.

  13. Maelstrom78


    Sep 21, 2013
    There it is boys. That just about sums it up for life as well.
    Don Hanson III and DevinT like this.
  14. Stacy E. Apelt - Bladesmith

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

    Aug 20, 2004
    I'll add a little physics to the metallurgy here. The explanation below isn't meant to be an exact scientific discussion, but is intended to explain the transfer of energy involved in forging and welding.

    A weld is when the two metal surfaces combine into a unified structure. It is basically like having the two melt together along the junction of their surfaces at an grain size level.
    This requires enough heat to allow the grains to move and interlock with each other. Further refinement by forging down ( or rolling) increases the unified bond and makes the joint stronger.

    Heat is energy, and heating an object is merely the absorption of energy. Bend a coat hanger and it gets hot because you are adding energy in the bend. Compress air rapidly and it gets hot because you added energy to the molecules/atoms. Hammer a bar of steel and you add energy to the grains as you force them together.

    In forge welding by hand, it is all a factor of how efficiently you swing a hammer the weight of the hammer, the distance it falls, etc. - For practical purposed a 3 to 4 pound hand hammer is the limit you can effectively swing, and an 8 to 10 pound sledge is all a striker can easily swing.
    A power hammer delivers multiple blows with a bigger hammer. They range from 25 pounds to hundreds of pounds in hammer weight. The normal range for knifemakers is 33 to 100 pounds.
    A press delivers many tons of pressure, witch is roughly equivalent to a very large hammer. Forging presses usually deliver a fairly quick force of around 40,000 pounds (20 tons). This is a lot of energy, but you only get a few presses at welding heat before the mass drops below the fusion point.
    A rolling mill squeezes the metal from both sides and delivers a very intense addition of energy at the rollers. This is the most efficient way of reducing thickness or welding laminated ... but not practical for small shop knifemaking.

    If a hammer was big enough, theoretically you could weld at room temp. In practicality, the steel has to be at least 1600°F to weld with a giant hammer or rolling mill.

    The range where the atoms can move enough to fuse but not mush the billet apart is roughly 1600°F to 2300°F. For most hand forgers, the upper limit of 2200-2300F is the advised range, For those with a press or power hammer, 2100-2200°F is better. I would suspect that the big places with giant 500 pound hammers and 100 ton presses go down as low as 1800°F.

    The sweet spot for welding is a temperature where the steel is still solid enough to survive the pressure of welding, but not so high that the grains slide apart or fully melt. The exact temperature is almost always judged by eye and learned by experience on your set of equipment. The bigger the hammer or press, the lower the temperature of the billet can be. As the hammer or press delivers energy to the billet, the temperature rises. You can see this when forging. As the steel drops to a duller red, strike the bar hard with a hammer. You will notice the color jumps up a good bit at the spot impacted … and quickly drops back to the lower heat color as the energy gets dissipated into the surrounding steel.

    All forge welded billets should get grain refinement procedures to lower the grain size. You need to both refine the grain as well as release any internal stress from the welding and reducing procedures. Everyone has their own methods, but they should include reduced cycling temperatures ending in a quench, This is best done as soon as the billet is reduced to the thickness desired and/or the blade rough shaped by forging. These procedures need to be done prior to the hardening quench to assure a blade with internal integrity.

    Metallurgically, the forging range of most knife steels is between 1600F and 2100F. If steel is in this range the damage to the grain is minimal and correctable. For forging you have enough energy in the steel for the task of moving the grains around to re-shape the billet as needed. For welding you need more energy. Picking a place where the steel's structures are still unaffected but the added energy fuses the weld is what you are shooting for. Start at what you think is the bottom of the range. If you can master that range and get solid welds, your blades will benefit. If the welds aren't solid enough with your methods and equipment, then raise the temperature. The only practical gauge is your eye.
    Once the layers are bonded, lower the heat by around 100 degrees to work and solidify the billet. Proper stress and grain reduction should follow the welding and reduction .
    Last edited: May 5, 2019
  15. Ken H>

    Ken H>

    Dec 31, 2011
    Some of the best info yet! Shows why we sometimes get differing info on forge welding temps. The correct answer is as Stacy says depending on "arm" power or mechanical powered hammer.
    Volkert Forge likes this.
  16. A.McPherson

    A.McPherson KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 27, 2012
    Thanks for the details Stacy!
  17. Salem Straub

    Salem Straub KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Oct 20, 2008
    In response to an earlier question, I make 410SS/CruforgeV san mai with no problems, at 2150f to weld. In fact that's currently my default temperature for welding in my PID ribbon forge, for combos of 15n20 with either CruForgeV or 1080.
    As Devin says, it produces a very sharp contrast, not muddy looking from excess heat.
    Ken H>, Larrin and DevinT like this.

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