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Torch Hardening and Annealing Help

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  • Torch Hardening and Annealing Help

    Until recently I had access to a proper heat treating and drawing oven. Alas, that is no long available to me. I understand hardening with a torch, e.g. heating and checking with a magnet, etc. The rub is drawing. I see references to heating to a straw color, then allowing the part to cool naturally. The reference to the straw color is sort of open to interpretation. So, the question is, does anyone have a color reference chart they could post or refer me to another source for this?
    John B

  • #2
    "Drawing Temperature Color Chart", Google, third item down

    Edit: that was for wood working tools, if that makes a difference to you. Its not nearly as complete as the listing is say "Machinery's Handbook" , which, at least in my version, also shows temps of Lead Bath Alloys and "Tempering Temperatures for Various Tools" (in the general "Heat Treatment of Steel section, in mine is P 1454 or so)
    Pale straw is 450*, Straw is 460*, Deep straw is 470* to use your example
    Last edited by RussZHC; 08-13-2011, 09:24 AM.


    • #3
      You could get some temp sticks. They look like over sized crayons and are made to melt at specific temps. An IF thermometer may also be useful.


      • #4
        Thanks for the feedback Gentlemen. Actually, my current project is making a cutting tool for scrimshaw. I suppose, as with many things, I'll play around with it and go from there. It probably doesn't help that I'm working with mystery metal from my scrap, but I'm 90% certain that it was tool steel. Before I annealed it to begin shaping the cutter it was harder than woodpecker lips. My best file just skidded across it. Temp sticks are probably the best approach in the long run, but with the economy, etc., I was trying to save money.
        John B


        • #5
          I used Tempilac brush on lacquer many years ago. Trouble was,when the stuff melted,showing the correct temperature,it would etch an ugly scar into the metal. I hope the crayons don't do that like the liquid,paint on stuff did.

          Depending upon your metal type,different steels can look different colors at the same temperature. In reality,there is only a 25 degree "gate" to get optimal results from a given steel. Unless you are making a super expensive set of dies or punches,though,you should be o.k..


          • #6
            Here is a chart giving colors for "carbon steel", but as George mentions, different steels produce different colors.


            For smaller parts, a toaster oven and a good thermometer can give reasonable results. For your purposes, temperatures in the 400-600*F ranges can be achieved with this combo.
            Jim H.


            • #7
              I use a toaster oven with an inserted high temp. thermometer from Brownell's Gunsmithing Supplies. It has a long thermocouple rod on the back side.

              You cannot trust the thermometer on ANY kitchen type oven. They can be 75 degrees off.


              • #8
                Heat treating with SS envelope

                I am having great success with my new Paragon SC2 kiln. At issue is finally stainless steel 309 envelopes have solved carbon and mill scale issues.
                The question I have is does anyone know how many times the SS packets can be used?
                I tried what I thought were SS cans but I think they were just nickel plated.
                I am heating at 1750F for 20 minutes for A2.


                • #9
                  20 minutes? How thick is the piece?


                  • #10
                    Here is another chart with larger colour patches. Makes it easier to compare. Comparison should be done inside under normal lighting. Outside it's too bright and the colour is altered by skylight.

                    Last edited by Evan; 12-02-2011, 10:26 PM.
                    Free software for calculating bolt circles and similar: Click Here


                    • #11
                      I'll go out on a limb here and most of the those published colour charts for tempering are hogwash - toss 'em. My own experiments, and a brief little blurb in the ASM volume on heat treating say the metal does not go through infinite colour changes but that its a step change. Here's a polished 10" long bar i heated from one end, there are only a few colours and they're distinct.

                      As industry doesn't rely on colour for temp, this is done in a timed temperature controlled ovens, its not something you'll find much current authoritative info/research on, but try it yourself if you doubt.

                      Also, tempering is NOT just temperature dependent...its time as well. Left long enough at a straw colour temp, it'll eventually let down to the same rockwell as another high colour temp used for a shorter time

                      For the OP, its less confusing that an endless spectrum suggests

                      here are the ASM colours presented as a step change

                      Approximate Colour F° C°
                      Faint straw 400 205
                      Straw 440 225
                      Deep straw 475 245
                      Bronze 520 270
                      Peacock 540 280
                      Full blue 590 310
                      Light blue 640 340
                      Grey 700 370

                      my experiments



                      • #12
                        +1 for McGyver. Early 1903 Springfield rifles are known for actions exploding for this very reason. They were heat treated by "eye" and they were not consistent. People see colors differently and lighting as Evan said can change every thing. In an era when an IF thermometer can be had for peanuts it makes no sense to gamble.


                        • #13
                          For small stuff, including gun springs, I use a Nitre Blue bath, chemicals from Brownells. Molten at around 275 F., useable up to about 800 F. Low temp stuff would take a heavy steel or stainless steel saucepan on a hotplate with a good lead pot thermometer to help control temperature. The stuff is actually a heat treat salt compound.

                          David Kaiser
                          “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
                          ― Robert A. Heinlein


                          • #14
                            Is the steel likely a carbon steel, or is it a highly alloyed steel?

                            I'm pretty sure the heat to magnetic, then quench plan is OK with 1080, but doesn't work as well with O1, and is way off with D2 and other chromium alloys.
                            Esoteric Garage


                            • #15
                              Tempering by colours is very approximate since the colour change is highly influenced by the alloy ingredients. Even though carbon steels are not considered alloy steels they still have small percentages of other metals intentionally added to obtain certain properties. Foremost is manganese which may be as high as 1.6% without the steel being considered alloy steel.

                              These ingredients will change the alloy colours for a given temperature. I don't agree on the step change idea as my experience is that it can be very continuous. Again, that may depend on the alloying ingredients but this example is pretty smooth on the colour change.

                              Which colours show up will vary with the heating rate and what contamination might be present on the surface too.
                              Free software for calculating bolt circles and similar: Click Here