dodo knives Posted August 24, 2016 Share Posted August 24, 2016 Hey guys so I heat treated a batch of knives and grinded a couple and test with brass rod. I know that is not a accurate way to judge hardness but its good enough to know that this batch came out MUCH softer than usual. I don't know why I did everything as I usually do I guess there is something I over looked but I can not figure it out...I have never had this problem so the only way I see to fix it is to re harden so I guess my question is what do I have to do..oh the steel is 440C I see on the spec sheet annealing instructions do I have to anneal everything before I re harden?? I have heard with some steels you have to normalize but there is nothing about normalizing on the spec sheet I was also told that 440c may not be able to normalize since it is a air hardening steel. any help would be appreciated thanks guys Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted August 24, 2016 Share Posted August 24, 2016 So what did you do that didn't work? Quote Link to comment Share on other sites More sharing options...
dodo knives Posted August 24, 2016 Author Share Posted August 24, 2016 I have absolutely no idea did the same as always preheat 1400 for 10 min then up to 1875 for 30 mins quench in parks 50 oil then into liquid nitrogen over night then I always temper low at first at 370 for 1 hour mainly just to relive stress then I always grind one and do a brass rod test in the past the first brass rod test has always been to hard then I re temper and redo brass rod test raising the temp by 15 degrees at a time when it gets to where I want it then I temper the rest of the blades at that temp. the final temper has always been either 400 or 415 I do it this way because sometimes I have noticed the size and thickness has a small effect on how hard it gets and what is the best temper temp. I try and keep all the blades in each batch around the same size big knives one batch small another either way that original temper at 370 has always been too hard I almost didn't even do the brass rod test this time at 370 because like I said it has always been to hard but I am glad I did because when I did it the blade was soft that deflection off the rod didn't spring back when it should have been hard at that point I have always had the edge chip alil when the temper is that low I did grind another blade to check and that one was soft too...obviously something was done differently but I cant figure it out so I guess I have to re harden all these but I don't know if I need to anneal and or normalize Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted August 24, 2016 Share Posted August 24, 2016 Has other pieces made from this exact same bar hardened correctly in the past? I know of at least 1 maker where the steel monger messed up and sent the wrong alloy with all the paperwork for the right one. Quote Link to comment Share on other sites More sharing options...
dodo knives Posted August 25, 2016 Author Share Posted August 25, 2016 hmm I would have to look and try to remember in this batch I had 1 and 1/2 bars that I have had for a while and yes I have done knives from them (it was actually 3 half bars) but there were also 2 new bars from a newer order that got cut up so I don't know wich came from what... Quote Link to comment Share on other sites More sharing options...
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