FatFrumos Posted January 17, 2019 Share Posted January 17, 2019 Hello. I have a small propane forge, and so far I've been working only with 1084, doing all of my HT using magnet and waiting for about a minute after non-magnetic before quenching. I've gotten pretty good results, but I want to become more scientific about it. So I bought a piece of black iron pipe and a thermal probe to be able to control the temperature better. Most of the sources I looked at say that I have to bring the steel to about 1500 and soak it for some time (this is where they start differing, suggesting times between 2 and 10 minutes). My understanding is that if the temperature remains around 1500, the actual time of soak is not that important because the carbon just stays in the solution. My question is - what exactly constitutes soaking time? Is it a time from the moment I put steel into the forge or time from the moment it reached austentizing temperature? If it's the latter, how long does it usually take for a room-temperature piece of steel of standard knife proportions (1 inch tall, 1/8 thick, 3-4 inches long) to go up to 1500 when surrounded by 1500 temperature in the pipe? Thank you! Luka Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted January 17, 2019 Share Posted January 17, 2019 Soak time is the time spent at (or very near) a specific temperature. Time spent heating up or cooling down would be considered "ramp time" (ramping up or down). You will see a lot of variation in suggested soak times. Manufacturers normally specify times based on thickness, normally starting at 1 inch thick and then additional time for each additional inch. Since knife blades are nowhere near that thick the piece is thoroughly heated through the center in a much shorter time. If you are able to maintain a very stable temperature then you probably want to err on the side of a little more soak time. As I understand it the soak time at specified temperatures for a given alloy allows the elements present in the steel to go into solution and distribute evenly throughout the steel. Some of the complex steels specify soak times at more than one temperature to get the most out of the steel. Someone with more knowledge or a greater understanding than I have can explain it better perhaps. I can't tell you exactly how long it would take to bring the knife blank up to 1500 degrees in your example. There are still a number of variables that could come into play, but the general answer is not very long. It is the nature of physics that the closer an object gets to the surrounding temperature, the slower the rise in temperature of the cooler object. In other words the first 100 degrees will happen very quickly. The last 100 degrees will take significantly longer. Quote Link to comment Share on other sites More sharing options...
FatFrumos Posted January 17, 2019 Author Share Posted January 17, 2019 Thanks for a detailed answer. But still, when you say "not very long" - what's a ballpark for it? A minute? 3 minutes? Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted January 17, 2019 Share Posted January 17, 2019 It's hard for me to give you a good answer on that. I've never been able to get my propane forges to maintain a stable temperature that low, and I've only recently acquired the equipment to accurately monitor the temperature in my forge when I want to go through the trouble of hooking it up. If I were to put a knife blank the size you describe in my forge at a stable temperature in preparation for a quench I would guess about 3 minutes, maybe less. If you can maintain a stable temperature where you want it and you plan to do a soak it's not that critical. For instance if you plan to do about a 10 minute soak and you give the knife blank 13 minutes from the time you put it into your preheated and temperature stable forge you can be fairly confident that your steel is ready for quenching when the 13 minutes has elapsed. A minute or two difference in the soak time is probably not going to give you a perceptibly different outcome. As long as you don't let the blank get much hotter than you intend, and you maintain a reducing atmosphere in the forge there shouldn't be much of an effect on the steel. Too high of a temperature will promote grain growth in the steel, and exposure to oxygen during the soak can cause decarburization of the steel. Quote Link to comment Share on other sites More sharing options...
FatFrumos Posted January 17, 2019 Author Share Posted January 17, 2019 Thank you! Quote Link to comment Share on other sites More sharing options...
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