Procedure for a re-heat treat

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FunkCoaster

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Summary: a blade failed to harden. What do I need to do before another attempt at hardening?

I have a 1095 blade, about 6" long, 0.125" thick.

What I did:
Heat to 1475F, hold 10 minutes (kiln).
Preheat a gallon of vegetable oil using a red hot rebar quench. Temperature at quench is unknown.
Quench, slowly agitating up-down and slicing.
A file still grabbed, but I cleaned off most of the decarb and tried a temper cycle at 400F for 2 hours. Maybe the RA would convert to tons of fresh Martensite, he hoped.
The file was still attacking it, so it failed to harden.

After some research, I discovered:
1) As a beginner, I should have avoided 1095.
2) Parks fast quench oil is preferred, but water can work, with increased risk of cracking/warping.

What I plan:
Repeat the same steps, except using a 150F water quench.
Getting $150 of oil for one knife may be a bit steep for this stage of my tinkering.

Questions:
Is there anything that needs to be done before repeating the hardening attempt? Like normalizing or otherwise?
What would you do different than my plan?
Is a brine better than regular water? I'm under the impression that it would cool it faster, but that may be too fast.
 
If you are going to use brine, quench 3 seconds then finish the quench in oil. It's the second half of the transformation that puts the most stress on the blade, and switching to oil decreases that stress.

I prefer 1450/1460 for 1095 or other hypereuctoid water quench steels. Less retained austentite.


If you want to do this really well, 1650 for 10 min, air cool to magnetic, 1550 10 min, air cool to magnetic, 1450 10 min, air cool to magnetic, then quench in oil. Might as well clay for a hamon now after that effort. Now 1460f for 5 min, quench in brine for 3 seconds, then oil to complete. Temper at 450 for 1h x2. Should be in the low RC 60's. 425 is good for kitchen knives. 450 general purpose, 475-500 for more toughness (better to use a different steel instead.)
 
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A few comments from the peanut gallery here.....

You're right, 1095 can be problematic for beginners.

I would not try a brine quench. Yes, brine can be used on 1095 and other shallow hardening steels, BUT, with a 1 in 4 risk factor, more or less. There is no reason why canola oil will not harden 1/8" 1095, but the temp of the oil needs to be dialed in. 130°F seems to be the best temp for canola oil. It may have been TOO hot after your rebar quench.... it was only 1 gallon of oil after all. I don't really know how hot that oil was...which is a problem. Commercial oil like Parks 50 should be used between room temp and maybe 100F. But canola needs to be around 130°F. If you're dead set on brine quench, follow Warren's instructions in his post. I'm not positive about the best temp for a brine quench, I have not researched that, but 150°F seems way too hot. I'm thinking room temp brine is best, if you MUST use a brine quench. You may not get MAX hardness in canola with 1/8" 1095, you may be a point or two under max hardness, but should give pretty decent results. I used to use it on 1095 before the P50.

How much decarb did you take off to know that it did not harden? Let's assume that decarb is not the issue here....but it still could be. Shouldn't be too much decarb with a 10 minute soak at 1475°F, tho.

Here is the big thing about these spring steels, and Warren brought it up in the last part of his post. These spring steels often come heavily spheroidized, and as such they need to be normalized (and then thermal cycled) in order to harden properly. 52100 is notorious for this. For this very reason, spring steels get full normalizing and thermal cycling in my shop. 1084, 80CrV2, 1095, W2, 52100, 15n20.....all of these get normalized and thermal cycled. That way I know exactly the microstructure and how to proceed to hardening.

You CAN simply try to re-harden the blade at 1475°F, and this may prove to work, provided the quench oil is at the right temp. But the steel may need to be normalized first. My approach would be:
Normalize at 1600°F for 1095. 10 minutes, air cool.
Thermal cycle at 1525°F for 10 minutes, air cool.
Thermal cycle at 1475°F for 10 minutes, air cool.
Thermal cycle at 1425°F for 10 minutes, air cool.
Austenitize at 1475°F for 10 minutes, quench in 130°F canola oil.
Once able to hold bare handed, check your file test. After the normalizing and thermal cycling, if this was all done without decarb protection, there WILL be a decent layer of decarb to file thru before reaching hardened steel.
If the file begins to skate, you've made it harder than the file, that we know. I would start with a one hour temper at 375°F, and go up higher if needed.
 
@Willie71
quench 3 seconds then finish the quench in oil
Click to expand...
An instructor of mine - Derick Kemper - did something similar with a damascus blade, and referred to it as a "snap quench" if I recall correctly, but I may be misquoting.

@samuraistuart

To say I removed most of the decarb, in the grind/edge region I filed it off, then did an aggressive 80 grit hand scraping until it was shiny steel. I didn't remove much from the handle or spine, but I did my file testing on the grind/edge.
I'm assuming that a normalization and thermal cycle could only make things better, so:

I'll try to do the normalization, thermal cycling, and then the quench in water followed by oil. I'll be doing that tomorrow, so I'll report back with what will no doubt be a resounding success... maybe...
 
Have it tested. Just because a file grabs it doesn't mean it's not hard. A have my recipe down for 1080/1084 and get 59Rc and a sharp file will still grab the edges after hardening.
 
txmm10 said:
Have it tested. Just because a file grabs it doesn't mean it's not hard. A have my recipe down for 1080/1084 and get 59Rc and a sharp file will still grab the edges after hardening.
Click to expand...
You don't do the file test after temper. You do it after the quench when the blade is around 65HRC or better. There are some files out there harder than 67, but most files are not above the maximum hardness you're gonna pull from these carbon steels, and as such they won't begin to dig in. You can even give it some pressure, the file will glide over the hard steel, and will feel like you're trying to file a piece of glass or something.

To be sure, tho, a file test doesn't tell everything. But it can tell you if your harder than the file. If the file "grabs it" then there is either a decarb layer to get thru, or the steel did not harden properly.
 
Most folks don't realize how much decarb there can be on a piece of steel held at HT temp for 10 minutes. If the blade was forged, there is even more. A quick trip to the grinder after temper may show no sparks for a second or so, then showers of fine sparks as the belt gets down to the hard steel. There can be several thousandths of an inch of decarb.

The first pass I make post-HT is to grind the edge back a few thousandths. This removes the decarb as well as gives me a shiny and flat edge line to use as a reference when I clean up the bevels.



The HT regime you gave should have hardened your blade. I assume the blade was placed in the hot oven after it reached 1475F, and the time was started after it rebounded.
The only place I see a worry was the oil temp.
Your canola oil should be about 120-130F. Use a cheap HF laser thermometer to check it. If just guessing, err on the lower side, as it greatly looses quenchability as the temp rises. What it should feel like is warm oil, not hot oil. Also, a gallon is just barely enough for a 6" blade. two gallons would be better.
When you quench, go straight in fast. Then slowly lift and slice at the oil for the next ten seconds. At that point, the blade can be removed and checked for warp. It can be hand straightened with gloved hands until it stiffens as it cools to around 400F (Ms). Below 400F it must be left to rest and cool slowly to room temp, then tempered.

As Willie pointed out, a 1095 knife fully hardened needs a temper in the 425-450F range.
His double quench is sound metallurgy. The first one second of the quench in warm brine (130F) will drop the steel past the pearlite nose, then the warm canola oil will allow the cooling rate to slow down and reach the martensitic start point (Ms). From there to room temperature the cooling should be slow and undisturbed. After about 60 seconds, remove and air cool to ambient. Tempering immediately after reaching room temp is important to avoid cracking/breaking as well as stabilizing RA.
 
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txmm10 said:
That's why I said "after hardening"
Click to expand...
I misunderstood your point. I thought you were trying to say that your file would grab at 59 HRC.....yes it indeed would! But it should not....after...hardening. Unless the decarb layer is not taken into account.
 
My overdue followup.

I executed my plan as described. Luckily, I read the thread before completing my plan, and noted Mr. Apelt's statement about how much decarb there can be.
I pulled it out of the second quench (oil), and did a quick warp fix. Then rough sandpaper removed scale until it was shiny.
A file test showed... that it was grabbing similar to annealed steel.
But wait! I took it to the grinder and removed an estimated 0.002" from the bevel.
Another file test and it skated around like I hoped it would.
Followed by temper, and it seems to be okay.

This suggests to me that the heat treat worked. A proper hardness test would be preferable to confirm this, but the budget disagrees.
It also suggests that the first heat treat may have worked. Alas.

Pics: https://www.instagram.com/p/_Xrp_buoiC/ - before and after cleanup.

Many thanks to the detailed and helpful feedback.
 
The results were as I expected. You can continue to use your HT process and feel confident. Just remember to remove the decarb.

To get a better feel for how successful it was, make two 2X1X.125" coupons from the same steel. HT them both, and temper one. Grind them both back at least .005" on all sides. Take to a machine shop and ask if they will test them for you so you will know the results of your HT regime. Mark them with the results in white metal marker. Use them as comparison pieces in the future when file testing blades.
 
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