This metal is hard!

Mark Barone

Well-Known Member
So sometimes I get stock from a reputable source and it cuts well on my band saw. Sometimes I have to heat to 1500 and let it cool again to soften it. Do some manufactures harden the metal? I’ve ruined some blades. Now I just cook them all.
 
Perhaps the steel is work hardening on your band saw as you cut it.
What blade are you using, and what steel?
 
There are some metals, 15N20 is a good example, that come at a certain degree of hardness as a standard due to the supply to industry.

Also, depending on the steel you are using, you need to watch assigning a temp like 1500F or whatever and just heating and cooling. Some temps, with some alloys, will make a mess that will laugh at your cutting tools and drill bits due to what it does to carbides. If you google up "15n20 data sheet" you should be able to find the manufacturers data sheet with normalizing, annealing, and hardening schedules to work with.
 
Perhaps the steel is work hardening on your band saw as you cut it.
What blade are you using, and what steel?

I use a Portaband with 14 or 18 blades. I know right away when I need to normalize ( if that’s the right term) the metal to soften it. The blade just rides on itm so the blade never gets hot.
 
There are some metals, 15N20 is a good example, that come at a certain degree of hardness as a standard due to the supply to industry.

Also, depending on the steel you are using, you need to watch assigning a temp like 1500F or whatever and just heating and cooling. Some temps, with some alloys, will make a mess that will laugh at your cutting tools and drill bits due to what it does to carbides. If you google up "15n20 data sheet" you should be able to find the manufacturers data sheet with normalizing, annealing, and hardening schedules to work with.
Interesting I’ll research that. I use 1095.
 
The correct word is annealing, to make soft. I annealed some 15N20 yesterday (and 1095 as the core of San Mai) so it would drill/saw easy. I put in oven at 1300F for an hour, turned oven off and allowed to cool overnight. Now it saws 'n drills just fine.
 
In my experience, what you're dealing with is spherodized annealed materiel. Let me guess.... you saw or drill a few thousandths....then hit "hard" material, and wreck the saw blade or drill bit? Spherodized annealing does other things, but it's a cheap/quick way for the steel mills to call their product(s) "annealed". I usually refer to is as "half way annealed." I've experienced it with just about any type/grade of knife steel I've ever used.
 
In my experience, what you're dealing with is spherodized annealed materiel. Let me guess.... you saw or drill a few thousandths....then hit "hard" material, and wreck the saw blade or drill bit? Spherodized annealing does other things, but it's a cheap/quick way for the steel mills to call their product(s) "annealed". I usually refer to is as "half way annealed." I've experienced it with just about any type/grade of knife steel I've ever used.
What does one do about this Spherodized Annealing? re-anneal?
 
The correct word is annealing, to make soft. I annealed some 15N20 yesterday (and 1095 as the core of San Mai) so it would drill/saw easy. I put in oven at 1300F for an hour, turned oven off and allowed to cool overnight. Now it saws 'n drills just fine.
Ok that’s basically what i do. i guess I don’t have to go up to 1500
 
In my experience, what you're dealing with is spherodized annealed materiel. Let me guess.... you saw or drill a few thousandths....then hit "hard" material, and wreck the saw blade or drill bit? Spherodized annealing does other things, but it's a cheap/quick way for the steel mills to call their product(s) "annealed". I usually refer to is as "half way annealed." I've experienced it with just about any type/grade of knife steel I've ever used.
Yes , I think, ok I got this , it’s moving, then schreeech my blade is ruined.
 
Ok that’s basically what i do. i guess I don’t have to go up to 1500

Ive never found an actual annealing step necessary with1095 or other simple steels.

If you have an oven, you could heat it to 1475 f. Hold for 5 minutes and air cool. You could do that twice and you'd probably be good with 1095.

If you slow cool (slower than just air cooling) a hyper eutectoid steel from near critical temps, you will get a nasty internal condition that will only exacerbate the problem.

@Kevin R. Cashen could give a much better/more detailed explanation
 
Not trying to badmouth any company, especially because this is second-hand info, but there was a recent discussion on another forum by a guy who does HT as part of his business where he documents a lot of difficulties with HTing 1095 from NJSB. So if the steel in question is part of this batch, you might have to contact the supplier for information on what to do.
(Moderators, feel free to delete if this is against the rules...)
 
...@Kevin R. Cashen could give a much better/more detailed explanation

Did I hear my name?

There are three heating operations that are involved in this discussion- normalizing, and two types of annealing. I will take them in order of how soft they will make your metal. The first is normalizing, since it will do the least in softening the metal because that is not the primary goal of normalizing. Normalizing is a homogenizing operation to bring uniformity to the internal condition of the steel and, most importantly, the carbide condition. But this is regardless of the final hardness of the material, and one will find that normalizing will often result in chatter and dulled drills, mills or saw blades. Some alloy steel will even be significantly harder Rockwell after normalizing. Normalizing also involves the highest heat of these operations.

Next comes the two types of annealing. The first is lamellar annealing. This is a process of simply heating the steel high enough to put carbide into solution and then cooling very slowly to allow it to seperate out into segregated groupings within the iron matrix. We call is “lamellar” because the form the carbide will take will be sheets of alternating carbide and iron, called lamellae. This results in a phase within the steel known as pearlite, because the alternating bands in the lamellae scatter the light of a metallographic to make it look like mother of pearl. This is the most common phase that you will get whenever you are heating or cooling steel, as it is the natural form that the carbide will want to take when coming out of solution. Since this phase results in sheets, or lamellae, it will also chatter drills and give resistance to cutting when the cutter encounters these carbide sheets between the soft iron. With steels above .83% carbon there will be even greater degrees of carbide segregation and in more undesirable forms. One should never lamellar anneal any steel that has carbide volumes above the eutectoid, or above .83% as will not only trash your tools it will be very detrimental to the steel itself.

The last, and most thorough, method of annealing is spheroidizing, or spheroidal annealing. It gets its name from the resulting form the carbide takes, which is balled up into little spheroids scattered uniformly throughout the iron matrix. Spheroidizing is so thorough and affective because it does not put the carbide into solution with its heating temperature. To do this properly you will always stay below the temperature at which the carbide will go into solution, avoiding the sheeting effects of pearlite. Think of it like this- drop a bunch of wax shavings or solder on a metal plate and begin to heat it. As the wax/solder begins to melt the first thing it will do is ball up, only after you really heat the plate will the wax/solder then spread out in a sheeting action over the surface.

I have described the difference in cutting material in the two conditions like this- imagine that you have to shovel a pile of metal pieces, one pile is in the form of various sized plates, the other is in the form of a pile of ball bearings- which will be the easiest to plunge the shovel into? This is exactly why spheroidizing works so well, and why it is indeed the most thorough and complete form of annealing if you wish to soften the metal, and that is the reason that steel mills supply the industry with spheroidal annealed material. If you have steel that is hard to cut as received it will often be cold rolled. Cold rolled material may come annealed or it may be as is, in which case it will be a bit springy as it will obviously be work hardened. This is often the case with 15n20. Unless it is precision ground, the really clean looking stuff will be cold rolled and not annealed. The matt silver or clean light gray looking stuff will be CRA (cold rolled annealed). The dark gray stuff with rounded edges is hot rolled, and will generally be a bit softer in carbon steel.

Here are micrographs to clearly show the difference between lamellar and spheroidal annealing:

pearlite24WM.jpgdamspherWM1.jpg

The lamellar has the layered condition of pearlite as well as proeutectoid carbide networking in the grain boundaries, indicating that it is 1095, and this condition is bad for your tools and bad for the steel itself.

The spheroidized material, on the other hand is very uniform, and will easily be the softer of the two. If I have to mill a piece of steel, I will definitely spheroidize it. If I make Damascus for others, I will always do a complete industrial spheroidal anneal on it so that the customer can easily cut it.
 
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Sorry, I got to work for the day and realized that I didn’t give much info on how to do these treatments. For lamellar annealing, simply heat the steel well above non-magnetic and cool slowly via insulation, such as vermiculite or the inside of a cooling gas forge, or kiln. However, I no longer teach nor recommend this type of annealing at all. It is less than effective in softening the material and is detrimental, due to things like grain boundary carbide networks. In simple carbon steels I would say that a quick normalization would be equally effective, as it would form finer pearlite with less grain boundary carbide.

To spheroidize it is important not to exceed 1335°F where full solution will occur and you will get pearlite when it is cooled. Instead heat to 1300°F several times, or hold there for at least 10 to 40 minutes and then cool. Spheroidizing will work better if it follows a homogenizing treatment such a normalizing, as coarse pearlite spheroidizes within the pattern of the lamellae making what looks like segregated strings of black pearls.

Full industrial type spheroidization takes advantage of another phenomenon in iron carbon interaction know as the “divorced eutectoid transformation”, you don’t need to know that, but just think of it as growing carbides around seed points as it comes out of solution. For a full industrial spheroidization, heat the steel to 1375°F and hold for 1 hour and then cool no faster than 50°F per hour to around 800°F. This does require a ramping programable oven, but I know of no way to get the steel softer than what this operation will do. In fact, you may want to add a little time your hardening heat to get this super soft steel fully hardened again. The resulting stable spheroids will take more time or temp to dissolve and put back into solution.
 
Sorry, I got to work for the day and realized that I didn’t give much info on how to do these treatments. For lamellar annealing, simply heat the steel well above non-magnetic and cool slowly via insulation, such as vermiculite or the inside of a cooling gas forge, or kiln. However, I no longer teach nor recommend this type of annealing at all. It is less than effective in softening the material and is detrimental, due to things like grain boundary carbide networks. In simple carbon steels I would say that a quick normalization would be equally effective, as it would form finer pearlite with less grain boundary carbide.

To spheroidize it is important not to exceed 1335°F where full solution will occur and you will get pearlite when it is cooled. Instead heat to 1300°F several times, or hold there for at least 10 to 40 minutes and then cool. Spheroidizing will work better if it follows a homogenizing treatment such a normalizing, as coarse pearlite spheroidizes within the pattern of the lamellae making what looks like segregated strings of black pearls.

Full industrial type spheroidization takes advantage of another phenomenon in iron carbon interaction know as the “divorced eutectoid transformation”, you don’t need to know that, but just think of it as growing carbides around seed points as it comes out of solution. For a full industrial spheroidization, heat the steel to 1375°F and hold for 1 hour and then cool no faster than 50°F per hour to around 800°F. This does require a ramping programable oven, but I know of no way to get the steel softer than what this operation will do. In fact, you may want to add a little time your hardening heat to get this super soft steel fully hardened again. The resulting stable spheroids will take more time or temp to dissolve and put back into solution.

Thank you Kevin. I was going to ask about procedural info.

One question just to clarify.....if one was going to spheroidize...heat to 1300 f. and hold then cool, is the cooling just air cooling? You still wouldn't need to (or even want to?) slow cool this, correct? And I'm referring to simple hypereutectoid steels here like 1095, w1, w2.
 
Thank you Kevin. I was going to ask about procedural info.

One question just to clarify.....if one was going to spheroidize...heat to 1300 f. and hold then cool, is the cooling just air cooling? You still wouldn't need to (or even want to?) slow cool this, correct? And I'm referring to simple hypereutectoid steels here like 1095, w1, w2.

That is the beauty of it, it doesn't really matter. In this process, all the work is done at temperature, rate of cooling doesn't matter as much, and slower cooling only really adds up to more time at temperatures where spheroidizing may occur. With the other industrial, or isothermal method, cooling rate is much more critical because if it is not slow enough for the transformation to occur the carbon that is in solution will go lamellar. If you are just heating to 1300°F in a forge, cycling, rather than a hold, will not only probably be necessary, but it could be beneficial as the repeated cycles could result in more seed carbides for the spheroids to grow around.

If I don't have to do any serious machining and can do it with the quick 1300°F cycles I prefer to do so since the spheroids will be finer and more numerous. The larger the spheroids, the few there are, it is very soft but not as even of a microstructure.
 
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