petersenj20 Posted February 23, 2009 Share Posted February 23, 2009 I forged this some time ago from a nicholson file and finally decided my need of the tool meant I should put some handles on it. I tried to get all the teeth marks out. This was done following the BP0387 blueprint except that I water quenched. I didn't heat the tanges when I heated to orange. I then kept in the oven at 450 for an hour and a half and left it to cool. I didn't know if I should quench for that step. I was gently tapping the handles on and it broke. What did I do wrong? There is a distinct color difference in the cross sections so don't know if it had a crack or what. Here are the pics. I need to make another one so help is appreciated. Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted February 23, 2009 Share Posted February 23, 2009 The water quench was probably too harsh - try oil the next time or even an air quench may be enough as compressed air on a blade will cool it quickly enough in some cases to make a great edge. In addition, did you draw or anneal prior to quench? If not, that probably set up some excessive stresses, plus any notch left by grinding or not completely removing the teeth can create a stress riser and start a crack. I have a draw knife that I made out of a spring and drew it closer to 500-600 degrees after an oil quench because they are more like a hatchet than a chisel with regard to hardness. You want something tough and easy to sharpen rather than a blade that will keep an edge forever. Quote Link to comment Share on other sites More sharing options...
dablacksmith Posted February 23, 2009 Share Posted February 23, 2009 ya that was the water quench ... i will not use water quench anymore for anything with any carbon in it..ive broken or cracked too many blades over the years. switch to oil quench ! i use vegtable oil its relatively cheap and dosent smell bad like motor oil... also ide temper that to a blue ... file steel is real hard and a draw knife needs to be more tough than hard... have fun! Quote Link to comment Share on other sites More sharing options...
son_of_bluegrass Posted February 23, 2009 Share Posted February 23, 2009 I have to disagree on the hardness. I have Granddad's old draw knife and a file just barely touches the edge. From the discoloration in the first 2 photos I'm guessing there was a crack in the edge, possibly from the water quench, maybe from before that. For files, oil is fast enough to get a good edge. ron Quote Link to comment Share on other sites More sharing options...
Woody Posted February 23, 2009 Share Posted February 23, 2009 In the photo's that show the two edges of the break together, I notice a dark part that starts at the cutting edge and goes a ways into the blade, then the break is clean bright metal for the rest of the way. I think that perhaps the blade was cracked on the edge at the time it was heat treated and it broke the rest of the way when it was subjected to the mild shock of tapping on the handles. The original crack could have been from several sources, hammering it when it was too cold, not getting all the file teeth ground off, bad karma etc. Quote Link to comment Share on other sites More sharing options...
nitewatchman Posted February 23, 2009 Share Posted February 23, 2009 The photographs of the break would indicate it started from a crack that occured during the quench or at least before the tempering operation. The dark color appears to be blue which would indicate that the surface was present during the tempering operation. If the surface was black or had the appearance of hot oxides or even scale this would indicate that the defect existed before the quenching operation. The whiteish color may indicate untempered Martensite which is a little less ductile that glass. A quick way to detect untempered Martensite is to etch with 2% Nitol or 2% Nitric Acid in Alcohol. Tempered Martensite or Pearlite etchs gray where untempered Martensite etchs white or silver. With experience the degree of temper can be judged by the shade of gray. A word of caution regarding Nitol. While the final solution is realitively harmless, concentrated Nitric Acid is not. Always add acid to alcohol never the other way round and always do this outside. If the mixture generates brown or orange fumes it is oxidizing the alcohol and producing dangerous gases. Leave it along and wait until it stops fuming. To dispose of the acid pour over crushed limestone and allow to react. gary Quote Link to comment Share on other sites More sharing options...
Woody Posted February 23, 2009 Share Posted February 23, 2009 Mixing alcohol, a flammable liquid, with nitric acid, a powerful oxidizer, is not recommended. They could ignite. Nitric acid in concentrations over 40% when shipped is not placarded corrosive, it is placarded an oxidizer. Although it is extremely corrosive, the oxidizing potential is considered to be the greater hazard. Remember you need 3 things for a fire, something to burn, in this case alcohol. Oxygen, in this case, Nitric Acid, HNO3. A source of ignition, the heat that can be produced by the reaction of the acid and the alcohol. The IDLH concentration, that is the concentration of vapors that is Immediately Dangerous to Life and Health, is 25 ppm, the odor threshold is 27 ppm, that means by the time you can smell it you are over the IDLH limit. The permissible exposure limit, PEL is 2 ppm that means by the time you can smell it you are 10 times over that limit. The LC50, or lethal concentration that killed 50% of the test animals, in this case rats, is 67 ppm. Quote Link to comment Share on other sites More sharing options...
petersenj20 Posted February 23, 2009 Author Share Posted February 23, 2009 Thanks for the help folks. I will quench in oil next time. I won't be playing with any chemicals other than that though. Do I quench after the oven draw or just let air cool? Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted February 23, 2009 Share Posted February 23, 2009 after the tempering cycle its not needed, but if you are in a hurry to handle, go ahead, as it won't hurt either. Quote Link to comment Share on other sites More sharing options...
nitewatchman Posted February 24, 2009 Share Posted February 24, 2009 Woody, You are correct in concerns with Nitric Acid, however Nital is the most common lab etchant used in metallurgy. It is commonly found in concentrations of 2% to 5%. It's ability to discern different phases of steel structure are very handy. Nital may also be purchased pre-prepared. Attached are photos of Untempered Martensite in a background of Pearlite or Tempered Martensite. The UTM is the white or silver material, it was either caused in a weld Heat Affected Zone, by trasformation during grinding or as retained Austenite. These are from rail which coincidentially is C1080-C1085. One huge problem we have is rails breaking during bending. In almost every case other than inadequate bending radii, the cause of the break is Untempered Martensite formed during grinding. A layer of UTM as thin as .002" is enough to initiate a crack. nitewatchman MSDS for Nital - http://www.reagents.com/pdf/MSDS/N-1030.pdf Quote Link to comment Share on other sites More sharing options...
petersenj20 Posted February 25, 2009 Author Share Posted February 25, 2009 For what its worth, I have decided to make the big piece of this knife into a scorp for carving spoons. Find the silver lining. I hope there are no more cracks. Quote Link to comment Share on other sites More sharing options...
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