Alex Posted September 20, 2009 Share Posted September 20, 2009 I've been hobby forging for a while with a very rudimentary set up. Recently I've started to take heat treating seriously and am having problems. I made two knives both out of pry bar steel. I wanted to put them through their paces, test them out to make sure they were good, and of course, they both broke. The first was quenched in warm brine, the second in motor oil. They were both tempered in an oven and then differentially tempered by heating the spine and tang with a torch while dipping the edge in water. When the first blade broke I assumed it was just a poor tempering job, so when I tempered the 2nd blade I baked it at 350 for 2 hours. After seeing no colour change I raised the temperature about 25-50 degrees every hour or so until I was maxing out at 475 something like 6 or 7 hours later. At that point the blade was a healthy yellow brown. Heating with the torch left the spine and tang anywhere from a pale to dark blue. I've attached 3 pics so you can see. In the cross section pic you can see the core of the blade. Does tempering only do surface colour change? I'm wondering if maybe for whatever reason my temper isn't going deep enough. Besides using a commercially produced steel (and not an unknown pry bar steel) is there anything that you can recommend? I don't want to keep making pieces that are prone to breakage, if anything I want them overly tough. Thanks, Alex Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted September 20, 2009 Share Posted September 20, 2009 Glad you posted the picture of the break. The grain is HUGE! A break like that should be satiny gray. You are using finishing heats and maybe quenching heat that is way too high. With grain like that I don't think you can get a proper heat treat. Keep your later heats down lower and normalize at just a blood red heat. Stay with the oil quench for something this thin. Use a magnet and quench where it just gets non-magnetic. Don't play with fancy heat treats till you get basic heat treating down. It ain't a turkey, the heat goes all the way through. Quote Link to comment Share on other sites More sharing options...
son_of_bluegrass Posted September 20, 2009 Share Posted September 20, 2009 I agree. That grain is too big. Before you quench you should normalize or anneal. During this step you can refine the grain. Watch your heat carefully when heat treating so you don't grow the grain during the heat treat. The specifics for the heat treat depend on the alloy you are using. I commonly hear of prybars being 1060 to 1080. But I don't know if this is true or not. ron Quote Link to comment Share on other sites More sharing options...
Alex Posted September 21, 2009 Author Share Posted September 21, 2009 Thanks a lot guys, I appreciate it. I'm sure you'll hear back from me if it doesn't work! Alex Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted September 21, 2009 Share Posted September 21, 2009 Looking at the break, I think it might even be "burned". This would be from severe overheating and cannot be fixed by any means. Only use orange heats, don't get into yellow with high carbon. You're not working out in the sunshine by any chance, are you? Quote Link to comment Share on other sites More sharing options...
forgemaster Posted September 21, 2009 Share Posted September 21, 2009 (edited) Now don't great minds think alike, I actually tried to post this same question this morning but the post got lost some how, so I've come back this arvo only to see that Grant has beaten me to it. I reckon looking at the grain size that this piece has been either burnt or oversoaked at high temps. Seeing as the material is only known as pry bar and we don't know the exact chemical comp it would be critical to keep in a safe forging range, too hot and you'll burn, it too cold and you'll crack it. As Grant hinted at working in direct sunlight can cause you to underestimate the heat you are taking your work to. It is also wise to remember that an increase in carbon content brings about a coresponding decrease in the melting point of steel. I recall many years ago as an 2nd year apprentice driving a 20CWT hammer for a newly qualified tradesman ( ie an apprentice just finished his time) we were to forge some what we called P8 which was a work hardening manganese steel (1.2% carbon 12% manganese was used for strong room and safe wall reinforcement)) we just chucked it into the furnace when it was nice and hot (1250 deg C) pulled it out over to the hammer and wacko. Well it just about disintergrated into 1000000s of little grains of steel sand all over the die with the first hit. So OK, into the chipper with that one, into the office and look at the book, ah ha, preheat slowly and uniformly to about 600 deg, raise quickly to forging temp of about 950 to 1050 degrees. forge straight away don't soak, cease forging and reheat at 900 deg, anneal immediately after forging. Lesson learnt. Different steels require different procedures and will forge at different temps. To have a known outcome it really helps to have a known steel grade. Have fun Phil Edited September 21, 2009 by forgemaster missed some letters from some words Quote Link to comment Share on other sites More sharing options...
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