What is the thickness of the stock we are looking at? I'm not an expert in metallurgy, but it appears the grain is a little large. What measures did you take to insure tight grain structure?

I just heat treated some O1 over the weekend, I will try to find my test piece the I checked the grain structure with and see is I can get an image so we can see if they are any different. Perhaps we both can learn something from this.

Chris

|quoted:

What is the thickness of the stock we are looking at? I'm not an expert in metallurgy, but it appears the grain is a little large. What measures did you take to insure tight grain structure?

I just heat treated some O1 over the weekend, I will try to find my test piece the I checked the grain structure with and see is I can get an image so we can see if they are any different. Perhaps we both can learn something from this.

Chris

That's 0.125". I cool the steel often when grinding (again, this was a stock-removal blade). I grind my edges prior to HT to about a dimes width (at least 120 grit). Stamps are done before any HT. I normalize thrice at 1600F with a RAMP of 9999 (as fast as the kiln can) and allow the blades to cool in the kiln. I austenitize at 1480F with a RAMP of 9999; I haven't been using a pre-heat (I'm wondering if this attributes to grain growth?). I austenitize three blades at a time. The kiln is programmed for 35 minutes once it reaches 1480F, but I begin quenching at 30. Each blade is quenched in Chevron 70, preheated to 150F, until the smoke ceases. I temper in the same kiln, and it can take an hour or more for it to cool enough to temper (something else that I wonder about). Tempering times are 2 hours, RAMP is 9999, cycles are 475, 450 and 425 respectively. They are left in the kiln to cool. Final edge grinding is done slowly, cooling often. Flats are finished by hand.

I doubt those temps would cause grain growth, but it may not tighten it either. What I have done is Thermocycle with the first cycle @ 1475 second about 1200 third about 800 letting the work air cool between heats.

I found my test piece but the lighting is not showing it well enough for a picture.

Hopefully we will get someone else to come in here also.

Chris

|quoted:

I doubt those temps would cause grain growth, but it may not tighten it either. What I have done is Thermocycle with the first cycle @ 1475 second about 1200 third about 800 letting the work air cool between heats.

I found my test piece but the lighting is not showing it well enough for a picture.

Hopefully we will get someone else to come in here also.

Chris

Do you normalize after your thermocycle? I just got done reading a few posts; some guys do a thermocycle then normalize. I'm not terribly familiar with thermocycling.

How does your test piece look?

I'm hoping someone will chime in also.

I don't normalize after Thermocycle. After Thermocycle I soak @ 1475 and quench. My test piece is very tight. I will try to get a picture of it in good light.

Chris

Lots of questions there Chris and I'm no expert by any means, but here is what I think based on my experience, and I use O-1 almost exclusively for my single steel blades.

1. I think your oil is too hot for the quench, and that's why you missed the mark on the hardness. I usually heat my oil to between 120*-130*F. Too warm and the quench isn't fast enough to produce a higher HRC.

2. You didn't say what your tempering cycles were. I typically temper O-1 at 375* for an hour and then buck it up to 400* for another hour.

3. I do not stamp my mark in my blades, because I was taught not to. As far as I can tell, the jury is still out on whether or not stamping causes any stress risers. Ask three smiths and you will undoubtedly get four opinions, and a lively discussion as well. For sake of argument, use your experience to guide you. You noticed the cracks at the stamp on this blade. What was the stamp depth approximately? Try a shallower stamp and repeat the experiment. Try the same depth and repeat the experiment. Try stamping at different temps. Sooner or later, you will answer your own question as to whether or not the stamp caused the defect, and why.

4. I do not know what process you use to quench your blade. Are you grabbing the tang with tongs and trying to plunge it straight into the oil? If so, you probably aren't getting the blade in straight at all and causing warpage, which can in turn causes stresses. Do you stir while quenching, or just hold the blade still? All of these factors affect the blade.

5. Finally about the heat and cooling the kiln. I don't know what kiln you are using, but my Paragon won't even think about starting a heating cycle if the current temp is less than 100* below the program set point. I heat the blade up to 1480 or so for the quench, so I have to wait a few hours for the oven to cool down before I can even consider a tempering cycle.

|quoted:

Lots of questions there Chris and I'm no expert by any means, but here is what I think based on my experience, and I use O-1 almost exclusively for my single steel blades.

1. I think your oil is too hot for the quench, and that's why you missed the mark on the hardness. I usually heat my oil to between 120*-130*F. Too warm and the quench isn't fast enough to produce a higher HRC.

2. You didn't say what your tempering cycles were. I typically temper O-1 at 375* for an hour and then buck it up to 400* for another hour.

3. I do not stamp my mark in my blades, because I was taught not to. As far as I can tell, the jury is still out on whether or not stamping causes any stress risers. Ask three smiths and you will undoubtedly get four opinions, and a lively discussion as well. For sake of argument, use your experience to guide you. You noticed the cracks at the stamp on this blade. What was the stamp depth approximately? Try a shallower stamp and repeat the experiment. Try the same depth and repeat the experiment. Sooner or later, you will answer your own question as to whether or not the stamp caused the defect, and why.

4. I do not know what process you use to quench your blade. Are you grabbing the tang with tongs and trying to plunge it straight into the oil? If so, you probably aren't getting the blade in straight at all and causing warpage, which can in turn causes stresses. Do you stir while quenching, or just hold the blade still? All of these factors affect the blade.

5. Finally about the heat and cooling the kiln. I don't know what kiln you are using, but my Paragon won't even think about starting a heating cycle if the current temp is more than 100* below the program set point. I heat the blade up to 1480 or so for the quench, so I have to wait a few hours for the oven to cool down before I can even consider a tempering cycle.

You may be right on the oil temp. I haven't played with that variable much.

Up in the discussion that the other Chris and I had, I posted my tempering cycles, but I probably should have put them in the original post. First cycle: 475F, 2 hours. Second cycle: 450F, 2 hours. Third cycle: 425F, 2 hours. After seeing your (and Chris') tempering numbers, I'm beginning to think that I've also simply been tempering too high.

I will be running more tests this week. Probably 3-5 test pieces. One or two controls with the rest having one variable change.

My quench: I austenitize no more than three blades at a time (usually three). The kiln ramps as fast as it can to 1480F and is programmed to hold temp for 35 minutes. After the blades have soaked for 30 minutes, I open the door, pull one blade by the butt of the tang, close the door as I position myself to quench, then--as smoothly as possible--I plunge the blade, tip-first, into the pre-heated oil. I "cut" spine to edge, back and fourth until the smoke stops. Now, as for my oil, the Chevron 70 is kept in a 1-gallon unused paint can. I keep it covered, but I likely need to replace it. I read yesterday that oil gets tired, and this gallon has been used for nearly 80 quenches (blades ranging from 3.5" to 4.5" typically).

I use an Evenheat KF18 with a Rampmaster computer (just means I can program the steps of my HT so I don't have to plug in every temp and time). It does take my kiln some serious time to come down in temperature. I pull out the ceramic stand and put cool (ambient temp, typically 60F or so at that usual time of night this time of year) fire bricks inside to "soak" up heat; I take them back out when they start to get hot. I suppose it begs the question; just how much time does one have with fresh-quenched (bare hand-hold-able) O1? Assuming it's sitting on a fire brick with warm air washing over it?

Thanks for the feedback, Joshua.

Let's talk about your quenching process for a minute. If I read it correctly, you have one gallon of quenching oil, you soak 3 blades at temp for 30 minutes and have the remaining 5 minutes to quench 3 blades. You quench the first blade and keep it in the oil until it's pretty well cooled. Where did all that heat go? It went into the oil. What temp is the oil at now that you are prepared to quench the second blade? We already know that you started with oil that was too warm, and now it's even warmer. By the time you are ready to quench the third blade, your oil is probably well over 200*F and the blade is not getting a full quench at all.

You have a couple of options here for adjusting your method.

1. Increase the amount of oil you use. My quench tub is an 8"x8"x1/4" square tub about 28 inches tall and it holds 5 gallons of quench oil. The amount of heat gain from a single blade quench is minimal because of the volume of oil.

2. Limit your quenching process to a single blade at a time and allow the oil to cool back down before you do another one.

3. Find a way to cool the oil off rapidly. Maybe getting a heavy copper bar to put in the oil after the first quench to draw some heat out of it. This might work, might not.

I also think you are leaving the blade in the oil for longer than is necessary, and you should probably hang the blade freely and let it air cool to room temp rather than using the fire brick method. The purpose of the quench is to rapidly cool the blade to harden the steel. Your fire brick is starting to warm the blade back up and is like a pre-tempering heat. Something you should strive for is consistent and controlled methods. You are applying heat to a quenched blade, but you don't know how much heat, and depending on whether the blade is balanced on the spine or laying flat, that heat is not being evenly distributed through the steel. Not an ideal technique.

Let the blade cool in free-hang, and let the oven cool off with the door open. Find something else to do while you wait, like start preparing the guard and handle materials. Patience is required. No good ever came from rushing this process.

Alright. Austenitizing one blade at a time sounds like a good idea, along with using a larger quench tank for better heat diffusion. I feel like I could have really been increasing my margin of error by Austenitizing three at a time, and severely limiting the oil's performance by using so little of it.

I'd heard and read stories of guys that had blades break within a few hours of quenching, and that's why I started doing the firebrick on the oven door-thing. I can see the folly in it now. heh I always rushed to get tempering started after quenching, and I was kinda terrified that the blades would cool *too much* and pop (not that I had any idea what *too much* was).

Thank you again, Joshua. Thank you ABS, for that matter; the only knifemaker that I've ever met in person (that wasn't handling Pakistani blades and selling them at a Craftsman's Fair) wasn't half so concerned with heat treatment and broke 1/10 blades in the quench. I'm blessed to have the opportunity to learn here, from folks who take pride in what they do.

I got a good image of the grain on my test piece of O1 from the weekend.

Hope this shows.

Chris

|quoted:

I got a good image of the grain on my test piece of O1 from the weekend.

Ahh, I see. It does appear much finer!

On a side note, the new hose for my forge came in today along with the assembly instructions for the forge that I requested from NC Tool. After looking over the instructions, I had to order a ball valve, 57L connector and M3-18 tank connector (couldn't find any of it in-stock around here). I'm going to rebuild the gas line and replace the igniter.

Hello Chris,

First, as has been discussed, the grain size could be finer. This can be dealt with in two ways, pre-hardening heat treatments and the austenitizing temperature for hardening. Your austenitizing temps are good for O-1 (1475F-1480F). Your normalizing temp of 1600F is good but your oven cool procedure is not, normalizing cooling should be done in still room temperature air. Slow cooling the steel via insulation or oven is annealing rather than normalizing and will result in heavy segregation of carbide constituents and even some grain growth. Normalize once at 1600F, and air cool. This will homogenize the internal structure particularly regarding carbide. Next, follow this up with thermal cycles to refine the grain size- heat more around 1475F or 1500F and air cool.

You did good in full quenching O-1, many for years thought that O-1 couldn’t be edge quenched because it will air harden but that is not the full story. O-1 will not truly harden the same in air as it will in oil, what it will do instead is make a ugly mix of structures that will include upper bainite by cooling too slowly. Upper bainite is the worst of both worlds it lacks both strength and toughness and will increase the chance of failure. I always customize my lawnmower blades with L6 inserts, L6 will reach 62HRC from air cooling, so I once decided to be lazy and just heat them and air cool before tempering and putting them on the mower. In the first pass around the yard huge chunks blew out of the edges. With a proper heat treatment my improved blades will hit just about anything and rarely need resharpening. There is so much more to this whole game than just temps and Rc numbers.

All that being said with the amount of alloying in O-1, rarely is the quenchant a factor in troubleshooting this steel, but your ideal oil temp is indeed around 130F. O-1 won’t care as much but your oil will last longer. To austenitize for the quench, I prefer to bring the oven to temp, let it equalize, and then introduce the blade. Allow for about a 10 minute soak and then quench with good agitation.

Can a stamp cause a stress riser? Yep, but so can grinder scratches, sharp plunge cuts, abrupt changes in cross section, carbide clusters, interruptions in the metals anisotropic flow lines, the tides, looking at it cross-eyed, etc… etc…. A little common sense comes into play on how much to worry about the stamp/stress riser thing. If you have a stamp that is a sharp line that goes almost from the spine to the bottom you are probably asking for trouble, just as notching your steel with a hot cut before quench it would be a break point. But an unobtrusive letter in the center of the ricasso being a threat to the blades structural integrity has been a bit over-exaggerated by some, in my opinion. The drastic change in cross-section right next to it (where ricasso becomes tang) makes it a rather moot point. So don’t sweat it.

O-1 is a fine cutting steel that works best for abrasion resistant edge holders like small hunters, skinners and kitchen knives, it has a peak Charpy toughness to hardness ratio at around 62-63HRC, if one needs more toughness they should go to another steel as this will save money and produce better results than handicapping this steel in its potential by forcing it to be tougher. I would say temper no higher than 400F. unless you find the HRC has not dropped below 64.

Oh, one final note- your concerns about the fractures can be answered by color, if the fractures initiated during or before any of the heat treatments they will be a different color for the rest of the fractured surface. If they are a silver as all the other parts of the break but look different in texture then you merely have different modes of fracture due to differences in microstructure, differences like... ooh let's see perhaps carbide segregation from cooling too slow from normalizing. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />

Thank you Kevin. I do not work with O1 so I could not provide help. You did.

Brion

Sometimes Kevin confuses me ......actually, most of the time <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//unsure.gi f' class='bbc_emoticon' alt=':unsure:' />

Kevin,

Here is my typical working sequence for O-1:

1. After forging is complete, I put it back in the forge and bring up to an orange heat, remove from the forge, and let it cool on the rack.

2. Anneal in the Paragon: heat to 1480 and soak for 20 mins, bring the oven down to 1000 (+/- about 100*/hr) soak for 10 mins, heat up to 1250 and soak for 20 mins, bring the oven back down to 800 and soak for 10 mins and shut the oven off. (this is all programmed)

3. Rough grind, and harden in the paragon by heating to 1480, quench in oil, clamp in copper jawed vice until it can be handle bare-handed, and let it hang until it gets to room temp.

4. Temper at 375* for an hour, then at 400* for an hour, remove and cool in free hang to room temp.

Do you see anything that needs adjustment or improvement in that process?