Heat Treat and Temper Problems

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pp47021

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Aug 9, 2014
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I am a relatively new knife maker however I have been using ATS 34 for over a year and made a number of fixed blade knifes so far. I have used the same recipe for my heat treat since the start. 1950 for 30 min pull out quench between 2 inch aluminum plates, then temper at 400 twice two hours each time, with a air cool down in between. This has consistently produced a 59-61 hardness for me. However I recently got a new batch of steel and used that same recipe but after the temper the blades were testing at 65 (yes I cleaned them off light sanding before testing). I did not test these three knives after they came out of heat treat, but I had two more in the oven, so after they quenched and cooled I tested them before temper and they tested at 65. I put them all in at 450 for two more hours and nothing, they all came back at 65 again....

So I put one knife in at 700 for 1.5 hours and it dropped 2 points to a 63. My questions...

1) is it ok to use a high temper on these fixed blade hunting knives? I have read that it takes some of the toughness out of the knives but how much? I am not making world class collectors, my customers are local people that use these knives daily in many cases.

2) Should I go up to 800 or 900? I really want to get these guys down to at least 61. How high is to high? What is the best way to get them down?

3) Next time I put a batch in to heat treat should I run them at 1900, instead of 1950? Or should I hold them at temp for less time so they don't come out at a 65?

4) I got my steel from a real reputable place (not sure If I should name them) but I have used them for sometime and many other knife makers do as well. But...Is there a possibility I don't have ATS34 here? Is there anyway to tell?

Any kind advise would be appreciated.
 
The as quenched hardness of CPM-154 is only Rc 63. With no sub-zero or cryo treatment, the hardness at a 400F temper is Rc60. 700F would yield Rc 55.
Something is wrong with your testing.

I would be just about positive that the tester is the problem.
First thing I would do is re-calibrate my hardness tester at Rc 60 to assure something isn't off in the test. Also inspect the indenter with a good magnifier loupe to make sure it does not have a tiny chip. It would be good to have the hardness test on your blades confirmed by a different source.

Next, I would confirm that the temper is truly being done at 400F and 700F. Use an independent thermocouple and reader or a tempil-stix to check. Thermocouples get old and don't read right sometimes. If the TC is old, it might be a good idea to swap it out for a new one.
 
154CM and ATS34 are identical when it comes to heat treating and are almost identical in composition. Like Stacy said, hardening comes out around 63-64 ish (I get 64RC). There is a secondary bump in Ht with this steel, but doesn't start to kick in until about 825 or so. 970 degrees will bring it to about 60-61, but has less corrosion resistance. With your first batch of steel you mentioned 59-61RC at 400 degrees which if hardened correctly is way too soft at that temp. I am still at around 62-63 at 400(cryo'd). So assuming your HT is good and your first batch was 59-61@400 (too low and too high a spread), second batch 65RC (too high), I am guessing your RC numbers from your tester is reading to high. Do you have a GOOD test block to verify the hardness?
 
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From what i understand cpm 154 and ats 34 are the basically the same except for the cpm being powdered metallurgy. I just did some cpm 154. Equalize at 1400 for 15, 1950 for 30, subzero, temper twice at 400. I got 61-61.5. I would have the hardness checked from another source until you make sure yours is good.
 
It was the tester, it was reading 7 points to high! I re-collaborated it with a friends testing blocks and checked it against his machine. Thanks for he help, I should have known its usually he simplest solution... should have started with the tester...
 
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