K490 heat treat troubleshoot

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K490 heat treat troubleshoot

Postby Andre Grobler » Fri Sep 15, 2017 2:18 am

https://www.google.co.za/url?sa=t&sourc ... uvVnlCpgig

Ok just googling bohler uddeholm k490 might be easier...

Anyhow i made 4 test samples of this apparent hybrid between d2 and cpm3v... because i kinda like D2 better than n690 and maybe even elmax and if i can get smaller carbides i will take it and the substantial amount of tungsten might be useful and there is some corrosion resistence... so everyday carry steel or even a slicer in the kitchen after some tests?

1030degc soak 20min oil quench cryo temper 150 degc cryo temper 180 got Rc 63

1050degc soak 20min oil quench cryo temper 150 degc cryo temper 180 got Rc 62

1070degc soak 20min oil quench cryo temper 150 degc cryo temper 180 got Rc 62 this sample fell over and cracked in apparently the quench - no heavy oxidation or decarb in cracks... for the moment i am assuming the direct raduation from the floor elements through 2cm ceramic plate caused overheating in the steel because it presented a broad surface to this radiating area whereas the others presented a surface similar to the thermocouple...

1090degc soak 20min oil quench cryo temper 150 degc cryo temper 180 got Rc 61 got apparently surface cracks which ground out...

So my thinking is this the range for this steel working hardness is rc62-rc64... this steel is actually made for 2nd hardening curve and 3 tempers... which just says decompose ra is the thing for this steel...so getting 63 at 180degc temper with a low aus temp should be good result. If it ends up cutting well...

I was surprised that there was no normal distribution curve as i usually see when going so wide with hardening temps... i might have to try 1020 though...

Question is then this... is my thinking regarding the 1070 sample sound? I am surprised that if it overheated or maybe heated unevenly it still got rc62... i would expect lower values...

One other thing the rc meter at first showed what seemed to be incorrect values... it under read by 5 or more points... it was then tested on the sample block and measured 5pts low and the second reading was bang on target... after this the readings appeared normal and in line with expectation..

So i am assuming the given readings are correct... but this is obviously something to consider if the results for do not make sense...

So in conclusion... getting good results take a bit more dedication than this test... and getting good on sample results to translate to blades are even more troublesome...

And low austenizing temps and low tempers and cryo would appear to behave for this steel as landes predicted for 3v
Most of our's not to reason why, but to control heat or die... ;-)
Andre Grobler
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Re: K490 heat treat troubleshoot

Postby Stefano Z. » Wed Sep 20, 2017 8:51 am

Without being absolutely certain about your kiln temperature readings, i would try also the 1020 °C to see what happens.
Did you soak your samples long enough after rebound? Do you shield them from athmosphere? Antiscale compounds just stop scale, but only lessen decarburation to a certain extent; and i'm talking about short soaking low temp HT simple carbon steels.
From experience i know how decarburation can be unexpectedly deep, so i would resume one of your samples and grind it with coolant before taking a second reading.
The steel specs. look very intriguing, i'll follow your progression, thanks for sharing!! :)
Stefano Z.
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Re: K490 heat treat troubleshoot

Postby Andre Grobler » Fri Sep 22, 2017 2:27 pm

Hi Stefano

My kiln seems fine... only concerns are a gradient form centre to front and rear with only about 30cm at the "right" temp... samples are typically fine in the sweet spot but long heavy blades can show a point difference centre to tip and heel... i improved insulation and it seems better... no real tests though... and big heavy blades drop the temp by 200degc... i minimised this by preheating blades to 230 and iven now drops by 50 degrees for 240mm x70mm x4mm blades... i also partially grind the blades for less thermal inertia...
Results the rc 63 sample grinds easier than elmax at 61... and it forms a really fune edge on waterstones with really no trouble it doesnt even seem to form a burr... the rc62 sample forms a normal burr leading me to think it does have some ra left over... i covered all in condursal 1100 which is supposed to minimise decarb... but i did cool grind all the samples to make sure... l left o.3mm 1mm behind edge flat and hollow grind and put edge at 15 dps which chopped very hard wood with no damage at all and very little blunting... i chopped a nail and it chipped out quite badly on both the 63 and 62 rc sample. In hindsight i chould have put the nail on something hard maybe and not on a piece of wood... the edge got pinched and broke about 4mm into edge... so i dont think tough at hardness is perhaps that great... but some people say it is more the geometry than heat treat that passes that test... i dont know... what i really think it will do well is slice and get very sharp courtesy of hardness and possibly chop lightly it may get a bit better than O1 for that but i am not sure maybe a bit more corrosion and wear resistant... the carbides seem small and fairly few in this steel...
Most of our's not to reason why, but to control heat or die... ;-)
Andre Grobler
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Re: K490 heat treat troubleshoot

Postby Andre Grobler » Tue Nov 28, 2017 2:45 pm

Well a sample austinitized at 1020 gave a slightly lower hardness 62.75 after 180degc temper and 1030 degC gave in this instance Rc63 again... but here's the kicker these samples are easily scratched by RC62 and Rc63 samples on the same surface that tests Rc63????... aebl O1 and even the same steel... so i annealed my perfectly heat treated 2 chef's knives because they got scratched so easily... using a file on these things seemed to be deadsoft... so it seems decarb even with decarb protection compound is a substantial issue with this steel, I cannot imagine why exactly D2 and N690 heat treated exact same technique different temp.s both skate a file like nobody's business... I don't know why this is, if anybody has an idea that would be useful... my edge testing still seems good, is a right royal pain to sharpen with waterstones... even moreso than elmax... at rc62. could it be that the high wear resistence only comes to the fore with high tempers? or that the very small carbides allow the file to cut steel better on a macro scale?
Most of our's not to reason why, but to control heat or die... ;-)
Andre Grobler
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