gearhartironwerks Posted January 13, 2013 Share Posted January 13, 2013 Saturday is my "play day" in the shop where I work/play for myself. I had 5 knives to heat treat and decided to try a new quench (to me)...canola oil heated to 120 deg. The blades were heated for 5 mins to 1500 deg in a salt bath, then immediately quenched in the oil. After an hour tempering at 350 deg, the Rockwell was in the upper 40's/low 50's. Most of the blades were 1095/L6, and one was O1/L6. Three of the five were chef blades, and the others are hunters. As my good friend Stuart Sinclair, a Scotsman, would have said: Wot ahh shi..y day. Steve, Rich,others, any ideas? Thanks for any suggestions. John Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted January 13, 2013 Share Posted January 13, 2013 are you sure you read the gauges correctly ? I would use rockwell files to get the idea of where its hardness is. A diamond tip tool will not give consistant readings in pattern welded steels, (take various test at various locations to see what I mean) Why I ask about gauges.. I dont use that type of oil but I know many others do and I dont understand why it would not harden if you got it in the quench fast enough. 1500F is 50 degrees lower than I use, but you added a short soak time, so that should not be a problem either, using the 350F salt bath should give at least middle 50s RhC and if you moved fast enough to get the blade into the salts before reaching the martinsite transformation temps, may even have a nice percentage of bainite in there also. so did you read the temp guages corectly ?? One other possibility which is rare I admit but posssable... That being in forge welding at close temps and the multiple thermal cycling you may have reduced grain size too much, to the point of reducing hardenability. try again ? Quote Link to comment Share on other sites More sharing options...
gearhartironwerks Posted January 13, 2013 Author Share Posted January 13, 2013 Steve, Thanks for the ideas. I woke up at 3am today for the usual reason old guys do, then couldn't get back to sleep. As such, I think I may know part of my problem. I think the thermal cycling sucked out a lot of heat from the salt bath and I didn't give it enough time to reheat. My tube is only 4x18", and I cycled 2 blades at a time x 2 and on the third heat, went to the quench. I'll try your suggestion of 1550 deg today and will hopefully not work after my 3am calling. :) John Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted January 13, 2013 Share Posted January 13, 2013 I got my rockwell tester from a machinest/knifemaker,he cautioned me not to use it on welded billets as the difference in the two metals may cause the diamond tip to slip the lieast bit sideways and break. With that in mind I have a file i use and everytime I pull a piece from the oil I see if the file skates, if not I try again, if still not it is scrap. All that said I think yoiu know what happened. Quote Link to comment Share on other sites More sharing options...
JNewman Posted January 13, 2013 Share Posted January 13, 2013 Make sure you grind off your decarb before checking. I picked up some chisels/scrapers I do for a steel mill from the heat treater this week. They were still in the sandblasting cabinet when I got there. The guy checked the hardness because they had drawn them at a slightly lower temp and were concerned they might be too hard. They came in at 38RC, target was 40-43RC. The boss took the chisel and ground it a little with a dynafile and it came in at 42RC. I had another forged part I was checking the week before which came in in the low 30s but when I checked the cutting edge which had been ground with a set of hardness files it came in in the low 40s Quote Link to comment Share on other sites More sharing options...
gearhartironwerks Posted January 14, 2013 Author Share Posted January 14, 2013 Thanks guys for the help. I had a better day today and kept tight controls on every step including maintaining the quench at 120 deg. The results were much better and after testing in several spots on a clean blade, the hrc after tempering 1 hr @350 was btw 56-59 on the chef blades. The O1/L6 hunter blade came in at 60, so my thinking is another temper to lower it a bit. I also ordered another thermocouple as a backup as I have a hand held battery powered remote to double check the temps. A friend gave me some low temp salts and I have yet to build the setup. Any suggestions on heating/maintaining the temp? John...who is enjoying a scotch and hopes to get a good night of non bladesmithing sleep. After all, tomorrow is a work day. :) Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted January 14, 2013 Share Posted January 14, 2013 impressive numbers, if accurate, and those steels CAN be left that hard with out problems in shorter blades. Quote Link to comment Share on other sites More sharing options...
gearhartironwerks Posted January 14, 2013 Author Share Posted January 14, 2013 Steve, Since I tested in multiple spots, my guess is that it's fairly accurate overall. I probably am not as astute a bladesmith as some members, but I have to start somewhere and the rockwell tester seems to me to be a start. It certainly showed flaws in my heat treating on Sat. What I really learned is that temperature is everything...even a few deg make a difference. I only wish I had more time to make blades... I appreciate your support. Thanks, John Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted January 14, 2013 Share Posted January 14, 2013 you will make time when you can, we all know how life can get in the way. lets see the end result when you find time to finish it :) Quote Link to comment Share on other sites More sharing options...
Richard Furrer Posted January 14, 2013 Share Posted January 14, 2013 A friend gave me some low temp salts and I have yet to build the setup. Any suggestions on heating/maintaining the temp? John...who is enjoying a scotch and hopes to get a good night of non bladesmithing sleep. After all, tomorrow is a work day. :) Mine is a mild steel tube for low temp..have a vertical and horizontal. You can use stainless, but I did not. The horizontal: Made a capped on both ends 4" square tube with a slot on the top and hinged lid. That sits in an insulated (inswool) box and has underneath inside the insulation a 3/4" pipe with 1/8" holes every inch. I plugged the far end of the 3/4 pipe (flatten and weld) and placed a furnace venturi burner on the inlet with a gas line and fine turn valve. I also have a ball valve on the same line so I can leave the fine tuned valve set and just run 5PSI it the thing from the tank. It looks like a 36 port bunsen burner...or ribbon burner. It is 40" long and takes about 60 minutes to come up to temp...longer if not fired and water gets in as the water boils off first. It will temper swords and knives well. There is no flame sensor so you do have to make sure a breeze does not snuff the flame and allow for gas to fill the floor. I have a stainless long neck thermometer set into the bath....surplus on Ebay or such. You can use an inconel thermocouple as well. I find this simpler for long items than a vertical unit. I have thick wire set as hooks to place the blades...they hang above the floor of the pot in the middle of the bath. The whole unit is on a $20 moving dolly and I roll it under the layout table when not in use. Ric Quote Link to comment Share on other sites More sharing options...
gearhartironwerks Posted January 16, 2013 Author Share Posted January 16, 2013 Thanks Ric, I'm still working on the low temp salt part. How long are you soaking blades, say 1095/L6, O1/L6 etc and at what temp? Is there a loss of hardness by letting the blade cool to room temp after the low temp soak? I am still confused about using anything other than oil. It won't break my heart to get away from that combined salt/oil mess, even though it works. John Quote Link to comment Share on other sites More sharing options...
Richard Furrer Posted January 17, 2013 Share Posted January 17, 2013 For most modern steels you can quench right into the low temp salt....the structure and hardness depends upon the "S" or "TTT" curve of that particular steel and the temp of the salt pot. Keep in mind that martensite can keep forming well below room temp and is retained in solid solution on high alloy steels in large percentages with higher temp quenches and non-cryo tempering. So: I suggest you go from high temp to low temp and keep the salt pot at about 450F for the above steels. Pull it out to straighten after 25-30 seconds or so and then back in for an hour. Quench to room temp and back into the pot. The second temper can be higher temp or longer if required. No loss of hardness by letting it slow cool after tempering vs dipping it in a water or oil bath....well a point CAN be made for any time at temp having an influence, but the theoretical reality is not enough to worry about....just don't burn yourself on the 400F+ item. You can also quench from high temp into oil and then use the low temp pot as a tempering cycle only. The chemistry and physics of heat treating can get very involved. If you are into that sort of thing then dive in..if not then best not to do anything but dip you toe...the pool of information out there has a way of puling you in. Ric Quote Link to comment Share on other sites More sharing options...
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