78sharpshooter Posted October 30, 2015 Share Posted October 30, 2015 (edited) Old leaf spring so I am assuming it's 5160. I forged out a 5/8" x 0.2" flat bar on the power hammer. I plasma cut 1" long sections and tested a rang of different temps from 1550 to 1465 followed by room temp peanut oil quench in about 5/8 gallon jug. I tested each piece in 6 different spots on the rockwell hardness tester and found my best result of a 62 RC average with 1475. So I then forged a knife from this same leaf, ground it to rough shape, went with the 1475 and quenched into 4 gallons of rom temp peanut oil. I only got to 45 RC and tried different Temps and also agitated the oil with a drill and paint mixer. Still only 45 RC. So I then water quenched and the bevel stress fractured so I could not get reliable measurements but the spine got to 60. So I am thinking my oil quench was too slow but based on the results with the test pieces I thought it would work. Does heating the oil to 150 or so have such a huge impact on the cooling rate that the larger mass of the knife versus the test pieces caused insufficient cooling? Edited October 30, 2015 by 78sharpshooter Clarification of room temp Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted October 30, 2015 Share Posted October 30, 2015 Did you measure/monitor the oil temp during the first range of experiments? In other words, do you know what the oil temp was on the sample that yielded 62 RC (or any of the other ones)?My first thought was decarb problems but you ground it so that's probably not the issue. You might try an oil preheat with a big block of scrap steel if you don't have another way to heat the fluid.I made a big Kukri from a leaf spring, then did two full normalizations before HT. I pre-heated 5 gallons of Quenchtex B with a 2" bar heated in the forge. I did not measure oil temp but it was uncomfortable to touch so probably around 130 or so. That blade quenched at 56 then I drew the spine back to soft and left the edge hard. I have no idea what type of steel but the springs came off an 80's Chevy truck. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted October 30, 2015 Share Posted October 30, 2015 the pre heating of the quenchant reduces viscosity, a thick oil will allow gas pockets to form, reducing the quench speed, where as heated oil flows more easily and little to no gases are formed, making for a faster and more even quench than the cold quenchant could produce. water and brine is the same effect but less easy to see. Quote Link to comment Share on other sites More sharing options...
Indianer Posted November 10, 2015 Share Posted November 10, 2015 So...has this been solved..? If 78Sharpshooter´s knife was heavier than the test pieces it would have heated the oil up more than these could do. This said, it should be a fast and more even quench with the knives (after Steve sells, if i got him right). Still, he says the knives RC was lower... Would somebody explain this to me, since his case seems important to me? Greetings Quote Link to comment Share on other sites More sharing options...
JME1149 Posted November 11, 2015 Share Posted November 11, 2015 The one thing that keeps jumping out at me when I re-read the original post is that you plasma cut the samples from the forged bar then did varying different test quenches. When you made your blade, did it get the same plasma cut to start with? I have to think that the melting temperature the metal went through on the test pieces prior to the 1500° quench had to have some impact on the end results. Quote Link to comment Share on other sites More sharing options...
78sharpshooter Posted November 12, 2015 Author Share Posted November 12, 2015 The test pieces were much smaller than the test blade. I have since heated the oil to 160 F and it solved the problem. The plasma cutter has a small heat zone and I could almost touch the test piece after the cut so I dont think that had an effect. I have a new problem with the heat treat oven that I am working on now. I was using nichrome wire on a 120V circuit and it seemed to be working well (oven vertical and the element was mostly free hanging) until the element broke. So I decided to try a kanthal A1 on a 240V and have the oven horizontal and ran about 20 amps through it. Within 1 minute it broke into 4 pieces. I had the element laying on kaolin/zircon coated ceramic wool and it appeared to break where it contacted the kaolin/zircon. I went back to the nichrome and horizontal and the element broke at the contact surface. Either the heat at the contact surface was too high for the element or the kaolin/zircon is causing the element failure. I am going to try putting the new element onto soft firebrick and see if that changes anything or if anyone has suggestions I would be grateful. Quote Link to comment Share on other sites More sharing options...
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