2 cycles at 165 is actually not very important with 15n20 since you're not likely to have had any retained austenite transforming in your first temper. Below 150 is actually not considered tempering, so I wouldnt count those.allright. just tested with a file after 2h of 165C and the file is just barely starting to dig in, but not like a mora where it very clearly dug in.
What I was trying to say is that it likely wont make a difference. As long as it doesn't get hotter, the hardness won't change.ok. should i do another 2h at 165?
any guesstimate as what hardness this would result in?
What I was trying to say is that it likely wont make a difference. As long as it doesn't get hotter, the hardness won't change.
Guesstimate is really difficult as it's not possible to know what as quenched hardness you had. But if we guess you where above 65 as quenched you should be in the 63-65 range I would say.
ok last temper done.
tested it with 2 different bahco files and they just barely dig in.
wanting to quantify this, i tested my files on my yoshikane skd (d2) edge and also a kurosaki r2 (have to regrind these tomorrow) and its skating about as well on my blade as the edges of those other 2. so i'm satisfied with the results. i would have imagined that the files would not scratch the r2 and d2 at all but they did. the files must be over 60 hrc, maybe even 62 or so, i guess.
Discoloration from tempering colours is a good indication of overheating. To be fair, if you temper really low you'll never see much of a colour change slightly above the tempering heat. It's more like if you find purple spots on your knife, you've really done goofed.
Also, sometimes discolouration just turns out to be rust.
There's a neat trick I worked out thanks to studying phase changes - For me, judging heat by touch alone goes out the window above 80°C, but if you spray the knife with water to cool it down instead of submerging it all the way, you can more accurately work out how hot the steel is getting in the 80-150°C range by observing how the water interacts with the surface. It can do anything from steam softly to boil vigorously. Observing this, you can more spend more time on the grinder while knowing how fast it's heating up.
Too late now but I know many others will temper 15N20 no higher than 300F or 150C. They are getting 66-67 HRc with optimized HT (lower end of austenitizing temp and short soak around 10 minutes?). Even backyard HT of 15N20 I've been very impressed with how nicely it performs.
Single temper of a simple carbon steel like 15N20 is sufficient as there probably won't be retained austenite to transform on the first temper that needs to be tempered with a second temper. Edited to add: Additional tempers are useful when you need to remove a warp; I clamp the blade overbent in the opposite direction of the warp and temper one or two hours, check, then repeat possibly with more increased overbending if it doesn't seem to be coming out. I don't bend before the first temper to avoid breaking the untempered blade.
Tempering is a time and temperature process but it takes extended time at temperature to negatively affect the hardness. Basically on the order of 24-48 hours and more from what I found in the scientific and engineering literature.
I think you're missing the part where I say this doesn't work if you submerge the blade. I'm betting you did this instead of spraying water on it.I didn't really see water boiling off the blade at all.
btw anyone ground out a blade on stones??
At my job we only have this industrial belt grinder and its doing about 7,3 million m/s belt speed or so. the alternative is a flapdisc on an anglegrinder.
no i use compressor oil. it has a high flash point. and i saw no flame when i quenched the 15n20 one.
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