Finally got some of my blades hardness tested today... and I’m not happy with the results

Jesse WW

Jesse WW

Joined
Jul 8, 2017
Messages
71
Hello all!

Recently I managed to find somebody willing to test my blades and I unfortunately was greeted by very disappointing results. One blade was 1075 and scored between 50 and 51, while the other was 1084 and scored between 45 and 48. Before testing I thought I’d at least get a 55 or something. :(

After ht I skid test every blade with great results and so I thought they were close to what I assumed to be close to a perfect ht. But apparently not.:eek:
Using the same ht methods with other blades, I have been able to hack through whole 2x4 twice and the blade can still shave no problem.

What could be causing such a low hardness? When testing the blades I was told the canola oil is most likely to be the culprit. Is it time to just bite the bullet and invest in a good quality quenchant? Would I actually see any significant improvements in hardness if I stop using canola oil and switch to say Hougton’s Quench K? Or am I just wasting money unless I use a dedicated HT oven with accurate temperature control?

I was also told that the angle of the bevel can alter the reading of the hardness, but to what degree? Is this true? What is usually the “proper” procedure when testing a blade?

Any advice/recommendations would be greatly appreciated!
 
Quick pic of the blades if anybody is interested:
89NHro.jpg
 
You don't want to measure hardness on the bevel; you can't measure hardness on the ricasso of a differently hardened blade!
You should read your HRC from a flat and parallel hardened section of your blade, as quenched and after removing a fair amount of surface affected by the forge athmosphere. That should be your reference. I suggest you to make little samples from your steel stock, for fine tuning your HT.
 
To get an accurate hardness reading you need a flat and parallel surface clear of any decarb, testing on the bevels will not give accurate readings.
Also differently hardened blades are almost impossible to get accurate readings. do acouple 1-1/2" square coupons and have them tested. leave one full hard and temper one and see if you're getting good results.
 
stezann said:
I suggest you to make little samples from your steel stock, for fine tuning your HT.
Click to expand...
This is as fundamental as it gets for "Backyard" heat treating. A File test is initially fine to determine if the steel got hard however it will not tell if it got hard enough. Hardness testing is done on a FLAT surface as mentioned earlier NOT on a bevel. The area to be tested should be CLEAN metal no oxide or decarb layer these can cause false readings. Your quench oil may be fine, but testing procedure could be a problem.
 
The problem has been answered well, I'll just chime in to confirm it's the testing procedure. Bevel doesn't affect the hardness, only the results of trying to rest on the bevel. Won't work - must be flat 'n parallel.

NICE looking blades, and with that very nice hamon you are testing up in the soft portion, not down on the very edge where it's hard.
 
I just spent alot of time with issues like this. What everyone is saying about the bevels is correct. You must test on a flat area parallel to the tester table. Also you may need to grind past the decarb. If you dont use antiscale this can be pretty deep. The test coupons are a good idea. Maybe grind spots to different depths after your quench and have the spots tested. If decarb is affecting the results your number will go up as you grind deeper.
 
Folks here are definitely right about testing procedures. But more than that, I can say that a simple carbon steel knife in the high 40s, low 50 isn't hacking through multiple 2x4s and staying razor sharp. And if you are actually skating a file post quench, you are getting pretty close to full hardness. You may be a couple points of HRC off from the ideal, but that isnt enough to put you in the 40s. Even if you had a HT that was a few points HRC off, it would still take a temper temperature somewhere in the 600 range to drop you below 50.

You may benefit from a better testing regimen for your HT, but I am guessing you aren't gonna see more than a 2-3 point HRC increase.
 
I was having issues with my 1084 from aldo's getting good numbers till I did some thermal cycling before my final heat and quench. I was heating to 1550 holding for about a min and quenching in canola at 125. Tempering at 400 and getting very low numbers in the high 40's to low 50's. Once i added a thermal cycle steps I was getting 61 after a 400 temper.
 
Thank you to everyone for the help. Both blades were tempered. I will need to get some different samples made up right away both tempered, untempered, along with various grind depths. The fact that the test procedure has not been done correctly is somewhat reassuring (just to confirm the bevel was not parallel and was on an angle when tested), however it wont be known definitively how bad my ht'ing really is until i have had the samples tested correctly.:eek:

Just for those who may be curious about my ht method... this is pretty much how i go about it:
I grind the bevel down to 2mm and finish at 240 grit (i cut my blades from stock as i unfortunately don't have the space for a decent forging area).
Apply satanite and bake in the oven for an hour or so at ~140c.
Warm up the canola to ~40c to be ready for the quench.
When cooking the blade, i essentially just stick it into the forge and move it backwards and forwards to keep the heat uniform. While doing so i test with a magnet every 30 seconds and when the magnet ceases to work (typically after 3-4 minutes or so) i typically give it another 30 seconds to get the blade just that little bit above critical.
When ready i quench the blade moving it slowly forwards and backwards until its just barely a handle-able temp.
As for tempering, typically i do two 1 hour cycles at 200c or 220c depending on blade length. If its warped i may do a third cycle.

Edit: I never thermo cycled in the past as i thought it was unnecessary. However from what is mentioned in this case it sounds like something i should definitely start reading into and start implementing it into my ht'ing routine!
 
Last edited:
The Rc numbers will read a little low testing on a bevel, but your numbers are still too low.
Thermal cycling will probably help a Lot.
 
Yes thermal cycle. In this case, I am assuming you are getting very close to full hardness with the procedure you described and 1075/1084. I really suspect that some combo of bevel angle and differential hardening is at play. Test those edges via brass rod and maybe a cutting/edge retention test. If they pass (and I suspect they will), treat them as normal.
 
Thermal cycling is generally around critical temp, and it's purpose is aus grain refinement. Normalizing, on the other hand, will help break up spheroidial cementite, and help that carbon come into solution better (give you higher post quench HRC numbers). 1084 is normalized at 1600f. Soak at 1600f for 10 minutes and let it air cool. Then you can proceed to thermal cycling to set up your aus grain. Cycle 3 times around critical temp (1500f). You can do 1500f, then 1450f, then 1425f. Air cool (or quench on the last cycle). Don't forget about decarb, too, like Tom mentioned above, which needs to be ground thru before testing on a flat surface. The satanite will help mitigate some of that decarb.

Normalizing is usually not needed when just doing stock removal, unlike forging where you really should be normalizing. The issue is that some of the steel we are seeing is heavily annealed at the mill, so that the carbon is held captive in jail (bail denied) as spheroidial cementite. You need to break that carbon out of jail by setting the jail on fire first, a 1600°F fire.
 
samuraistuart said:
Thermal cycling is generally around critical temp, and it's purpose is aus grain refinement. Normalizing, on the other hand, will help break up spheroidial cementite, and help that carbon come into solution better (give you higher post quench HRC numbers). 1084 is normalized at 1600f. Soak at 1600f for 10 minutes and let it air cool. Then you can proceed to thermal cycling to set up your aus grain. Cycle 3 times around critical temp (1500f). You can do 1500f, then 1450f, then 1425f. Air cool (or quench on the last cycle). Don't forget about decarb, too, like Tom mentioned above, which needs to be ground thru before testing on a flat surface. The satanite will help mitigate some of that decarb.

Normalizing is usually not needed when just doing stock removal, unlike forging where you really should be normalizing. The issue is that some of the steel we are seeing is heavily annealed at the mill, so that the carbon is held captive in jail (bail denied) as spheroidial cementite. You need to break that carbon out of jail by setting the jail on fire first, a 1600°F fire.
Click to expand...

I do not see the point of hitting 1600 then starting the cycling at 1500?

The way I do it with NJSB steels is the same way I have told countless others to deal with it. Heat to 1650 and let it even out, then air cool. Then drop to 1550° And heat like befor and air cool. The do your last cycle at 1450°. The take it up to the austonite temp and quench. I have had nothing but great results from this and so have the people asking me for advise.
 
You must log in or register to reply here.
Back
Top