Thread: RSO # 1

Originally Posted by JDM61

So does that mean that Mr. Blue's equally inexpensive suggestion of putting some charcoal in the muffle pipe to try to avoid an oxidizing atmosphere is also a useless suggestion? A jar of ATP641 anti-scale cost $15 from Brownells and will last a hobby maker perhaps as long as a year or more. Seems like a small investment to me. I was responding to the post where the gentlemen said that he was in the process of acquiring a heat treat oven with a digital controller so discussion regarding ways to reduce the occurrence of decarburization in the austenizing process seem mildly relevant regardless of what the final form of the blade will be, especially if he now has the capability to give the steel the manufacturer recommended soak for O1.

No, Mike's suggestion is not useless because it doesn't cost any time and can also be done while annealing which is a much longer timeframe at high temperatures, whereas painting anti scale paint, letting it dry, etc does take time. You are going to have to grind anyway because you NEED to grind the last of the hollow after heat treatment.

Originally Posted by JDM61

As for the minimum thickness of 1/16, was that a typo because that is .0625 inches or almost 1.6 millimeters, even thicker than the old adage of "leave it as thick as a dime" suggests. If you ask the professional heat treaters over here like Peters what the minimum thickness should be, they tell you to not grind any thinner than around .015 or .4 millimeter to avoid the possibility of "rippling" warpage at the edge. That comes directly from their website, not from me. .

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Yes, and by now you should know that unless these guys are razor makers, I really don't care. Something with the geometry of a razor behaves different than something with the geometry of a knife. You would know this if you started making razors and actually try the advice you are giving out unqualified. Razors are not knives, and knifemakers are not razor makers.

I dare you to grind an 8/8 razor in e.g 1095 with a spine that is at least 1/4" thick and an edge that is only 0.4 mm, and water quench that. Then you will understand why that is a terminally bad idea.

Knives also have a lot more mass behind the edge to provide the thermal mass that is necessary to make sure you can stay at the correct temperature while the piece is on route from the fire to the quench tank. Razors have very little thermal mass around the edge due to hollow grinding. If you make it .4 mm, the chances are high that the edge will coll below critical before you hit the quench, meaning you have a hardened razor with a soft edge. Especially with a shallow hardening steel, this is just asking for problems.

And that is why generic knife making advice is not directly applicable to razor making. If you want to learn about making razor, empty your cup and stop giving out advice that you've never tried for yourself.

Originally Posted by Mike Blue

Heat retention also works for me especially in the time to quench for steels like O-1 and thin cross sections like razors. Clays can offer just enough time to make a difference.

Mike, at the risk of adding confusion, could you elaborate a bit on this. I thought that part of what makes 0-1 an easy steel for beginners to work with was the relative slowness of the isothermal transition.

Originally Posted by bluesman7

Mike, at the risk of adding confusion, could you elaborate a bit on this. I thought that part of what makes 0-1 an easy steel for beginners to work with was the relative slowness of the isothermal transition.

I've attached the TTT diagram for O-1. For any steel, one of these diagrams should exist somewhere in the metallurgical world. The graphs of times and temperatures are based on thousands of samples taken. This example is the one I "go to" most frequently and I find that staying within the bounds of this graph gives me predictable steel performance, in my shop, using my tools.

Temperatures are the vertical left side, times are shown along the bottom. This graph includes relative percentages of pearlite, martensite and bainite. These are driven by the "plot", e.g. two intersections of time and temperature. Given this highly valid and reliable document, a heat treater can predict the behavior of this steel accurately, if they can control both time and temperature accurately.

If you search Google for these images, you will see several variations of this diagram that will not all match identically. I have seen some diagrams that the nose (the most left hand bulge/portion of the first curved line) that go off the chart to the left, for O-1. There is another that shows that the nose of the curve allows a ten second gap from the left side of the chart. It is at that point where Confusion enters into whether I, or another, believes that O-1 is a miserable project or a wonderful simple steel capable of far more than might have first been apparent.

John Verhoeven wrote a wonderful book on the behaviors of steels. Steel Metallurgy for the Non-Metallurgist - John D. Verhoeven - Google ¹Ï®Ñ
I cannot recommend this book enough. It's a well written beginning to understanding this stuff.

The transformation of austenite to martensite occurs at the speed of sound in most steels that I have used for cutlery. I'm not sure where the idea comes from that isothermal transformation is slow. Maybe because HT folks talk about brine being faster than water which is faster than oil. That has more to do with getting the temperature below the nose of the curve in time to achieve the desired result = hardness.

In this example, the key is getting the steel to cool from the specified austenitizing temperature (acc. to this diagram 1490F/810C) past the nose of the curve in less than two seconds. Compared to other steels that only allow one second, I suppose O-1 is slow, but there are more complicated steels that have a much greater window of time to get past the nose of the curve. And I admit that it depends on the TTT diagram being referred to. These have variability even within the context of O-1 as a single steel. Sometimes, belief depends on which version of the book (or author) you understand. It does not mean another chart/book/author is absolutely wrong.

It can be confusing. I admit I often quote a few of my own teachers when I say the answer "depends." That does not improve potential confusion. I am going to pause at this point. This is as simple as I can make it, but I am happy to keep working on the problem until anyone who doesn't understand, does.

Mike, in looking at the graph, it appears the start of the curve is at around 1300F for O1 austenized at 1490F. The Curie point for iron is 1043K or around 1417F. I have been told that can move up or down a tiny bit depending on alloying, but does the chart reflect something else that I have heard which is that while the conversion to austenite as the heat rises is at the Curie point and above, hence checking to see when the steel becomes non-magnetic, but, for hardening purposes, the undesirable conversion back into stuff like pearlite (assuming no partial martenstic or bainitic formation from air cooling like in stuff like Crucible Champaloy) starts at that lower point as the temperature falls?

Thanks Mike.

I'm on my second reading of Verhoeven's book.

JDM,

It's my understanding that the relationship of the curie temperature and the austenitizing temperature is casual and that the two effects have nothing to do with each other. They just happen to occur at relatively close to the same temperatures. Austenite is always non magnetic but steel or iron above the curie temperature is not necessarily austenite.

Originally Posted by JDM61

Mike, in looking at the graph, it appears the start of the curve is at around 1300F for O1 austenized at 1490F. The Curie point for iron is 1043K or around 1417F. I have been told that can move up or down a tiny bit depending on alloying, but does the chart reflect something else that I have heard which is that while the conversion to austenite as the heat rises is at the Curie point and above, hence checking to see when the steel becomes non-magnetic, but, for hardening purposes, the undesirable conversion back into stuff like pearlite (assuming no partial martenstic or bainitic formation from air cooling like in stuff like Crucible Champaloy) starts at that lower point as the temperature falls?

The chart is a simple time at temperature relationship. This chart is for O1, not iron, nor other alloys. If you want to discuss iron or other alloys we need to be looking at other TTT diagrams.

For O1: Pick a point on the graph and at that temperature held for that length of time you can expect the particular structure identified at the relative percentages estimated.

For hardening: O1 must be cooled to below 1000 degrees in two seconds according to this chart. By example: heat a piece of steel to 1490F cool it quickly to below 1000F in less than two seconds and from there to below 200F in fifteen seconds and you can safely predict 95% martensite at somewhere above 58 Rc. According to your concern, we are well below 1300F and far removed from the beginning of the curve. My HT operations begin at the left hand of the graph, not in the middle.

Another example, this time annealing. If you want to anneal O1 to 100% pearlite, hold it at 1000F for 8 minutes. It's even more certain if you hold it overnight for 8 hours as tradition seems to indicate, but essentially according to this curve you're done in 8 minutes.

I was asking about the curve because I appears to start at around 1300F and I have read elsewhere that says that the Curie point for say 1075 is down around 1340F. I know that is different that the temperature that gets everything into proper solution. On a simple eutectic steel like that< would austenize it at 1475-1500. i ask the question in part because I have heard that the whole thing about needing to get for the fire to the quench in a nanosecond is probably exaggerated. the "speed" issue is having a quenching that can get you from the "top" or starting point of the curve past the nose in 1, 2 or however many seconds. You see supposedly see some TTT diagrams that say you CAN"T get really shallow hardening steels like 1095, W1, W2 Hitachi White, etc past the most no matter what you do, but from what I have been told, those are based on through hardening samples that are considerably thicker than anything that we would be quenching.

Originally Posted by Mike Blue

The chart is a simple time at temperature relationship. This chart is for O1, not iron, nor other alloys. If you want to discuss iron or other alloys we need to be looking at other TTT diagrams.

For O1: Pick a point on the graph and at that temperature held for that length of time you can expect the particular structure identified at the relative percentages estimated.

For hardening: O1 must be cooled to below 1000 degrees in two seconds according to this chart. By example: heat a piece of steel to 1490F cool it quickly to below 1000F in less than two seconds and from there to below 200F in fifteen seconds and you can safely predict 95% martensite at somewhere above 58 Rc. According to your concern, we are well below 1300F and far removed from the beginning of the curve. My HT operations begin at the left hand of the graph, not in the middle.

Another example, this time annealing. If you want to anneal O1 to 100% pearlite, hold it at 1000F for 8 minutes. It's even more certain if you hold it overnight for 8 hours as tradition seems to indicate, but essentially according to this curve you're done in 8 minutes.

Originally Posted by JDM61

I was asking about the curve because I appears to start at around 1300F and I have read elsewhere that says that the Curie point for say 1075 is down around 1340F. I know that is different that the temperature that gets everything into proper solution. On a simple eutectic steel like that< would austenize it at 1475-1500. i ask the question in part because I have heard that the whole thing about needing to get for the fire to the quench in a nanosecond is probably exaggerated. the "speed" issue is having a quenching that can get you from the "top" or starting point of the curve past the nose in 1, 2 or however many seconds. You see supposedly see some TTT diagrams that say you CAN"T get really shallow hardening steels like 1095, W1, W2 Hitachi White, etc past the most no matter what you do, but from what I have been told, those are based on through hardening samples that are considerably thicker than anything that we would be quenching.

In simpler terms, I think your asking if 'the clock doesn't start until the steel hits 1300 F.'?

10pups are you still here? Sorry for hijacking your thread. Perhaps we should start another for this topic.

Originally Posted by JDM61

I was asking about the curve because I appears to start at around 1300F ....

When I look at the start of the curve, the first thing that comes to mind is that it's not possible to travel backward in time. The time to quench begins on the left most line of the chart, not the right side of the curve. Time moves left to right on this chart.

...and I have read elsewhere that says that the Curie point for say 1075 is down around 1340F. I know that is different that the temperature that gets everything into proper solution. On a simple eutectic steel like that< would austenize it at 1475-1500. i ask the question in part because I have heard that the whole thing about needing to get for the fire to the quench in a nanosecond is probably exaggerated. the "speed" issue is having a quenching that can get you from the "top" or starting point of the curve past the nose in 1, 2 or however many seconds. You see supposedly see some TTT diagrams that say you CAN"T get really shallow hardening steels like 1095, W1, W2 Hitachi White, etc past the most no matter what you do, but from what I have been told, those are based on through hardening samples that are considerably thicker than anything that we would be quenching.

Are you measuring the Curie temperature? Or are you testing the hot billet to determine it's magnetism? If the billet is non magnetic you're undoubtedly past the Curie point. If so, then focusing on a one-point temperature isn't necessary when you have the state of the metal where you want it before you attempt to harden it.

If you want me to respond to what you've been told, I'd prefer to have a conversation with the fellows that told you. I can respond to what you have personally experienced quenching steels much easier. Have you had trouble quenching to acceptable hardness any of the steels you mention? I can say that in my experience, a TTT diagram can seem to indicate that I can't move fast enough to quench a steel taken from the heat and into a quench medium fast enough (and I grow slower every day.) But, if I don't dawdle from the fire to the quench, the steel seems to harden just fine. I'm trying to simplify the process so beginners can get started and be successful.

Paragraphs don't help me watch what you are doing to know if what you do in your shop is working. Only you can know that given the limits of this media.

And yes, the metallurgists who developed these curves were not heat treating either knife-shaped or razor-shaped cross sections. As a general guide, the TTTT diagrams are helpful. Where the shape of the materials we work in creates a potential for not-knowing or uncertainty...it is up to the smith/maker with their hand on their work to determine how comfortable they are working in an area not defined very well. You have to heat treat a lot of blades and ttake good notes for yourself. Then you'll have learned something the metallurgists can't tell you.

My experience in getting from my Paragon oven to the patented turkey fryer quench tank full of Parks #50 or MacMaster-Carr medium-fast oil is that same as yours. The only hardening "issues' that I have had are incidents of the old "accidental hamon" with thicker W2 blades, but that is not an issue of hand or quenchant speed.

Originally Posted by Mike Blue

When I look at the start of the curve, the first thing that comes to mind is that it's not possible to travel backward in time. The time to quench begins on the left most line of the chart, not the right side of the curve. Time moves left to right on this chart.



Are you measuring the Curie temperature? Or are you testing the hot billet to determine it's magnetism? If the billet is non magnetic you're undoubtedly past the Curie point. If so, then focusing on a one-point temperature isn't necessary when you have the state of the metal where you want it before you attempt to harden it.

If you want me to respond to what you've been told, I'd prefer to have a conversation with the fellows that told you. I can respond to what you have personally experienced quenching steels much easier. Have you had trouble quenching to acceptable hardness any of the steels you mention? I can say that in my experience, a TTT diagram can seem to indicate that I can't move fast enough to quench a steel taken from the heat and into a quench medium fast enough (and I grow slower every day.) But, if I don't dawdle from the fire to the quench, the steel seems to harden just fine. I'm trying to simplify the process so beginners can get started and be successful.

Paragraphs don't help me watch what you are doing to know if what you do in your shop is working. Only you can know that given the limits of this media.

And yes, the metallurgists who developed these curves were not heat treating either knife-shaped or razor-shaped cross sections. As a general guide, the TTTT diagrams are helpful. Where the shape of the materials we work in creates a potential for not-knowing or uncertainty...it is up to the smith/maker with their hand on their work to determine how comfortable they are working in an area not defined very well. You have to heat treat a lot of blades and ttake good notes for yourself. Then you'll have learned something the metallurgists can't tell you.