steel overheating.

peter r

peter r

Joined
Jun 8, 2009
Messages
1,690
i got some flat ground o-1 and am going to cut out a blank. do i need to worry about the steel heating up when i grind? or will heat treating process fix any problems ?
 
Do not worry about the steel heating during grinding prior to heat treat. The heat treat will take care of this. When you have to be careful is any final grinding done after heat treat.

Enjoy and post some pictures when you get it done.

Glen
 
Just keep a dip bucket next to your grinder and keep the heat reasonable. It is actually a bad practice to turn your steel blue on the grinder any time, whether it is before or after the heat treat. Many folks believe that heat cannot have any effect before the HT but that is a false assumption. While you are not losing any hardness, since it is yet to be hardened, you are introducing variables that can lead to distortion if not corrected before the final heat treat. Distortion just from uneven grinding from one side to other other is a quite observable phenomenon in the final heat treatment.

The dip bucket will do several things for you- it will be kinder to the steel, it will be safer since a blade that is too hot to hold onto with your bare hands is a hazard to have around power equipment, and it will be kinder to your belts as long as you don't overdo it with the "wetness". The cooler you keep your work and your belts the longer your belts will last.

There are tools specifically for heat treating and the grinder it not one of them;).
 
Kevin: What is the source of your information? Years ago we did photomicrographs of steel we had purposefully turned blue from using old belts, we could find no significant difference, not Rex in his lab or in performance of blades after and during heat treat.
 
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Ed, it would be much more atypical if your or Rex’s findings were to parallel my own, so I find no distress in the differences. But it must first be pointed out that residual strain energy is not observable in micrographs unless the deformation is significant enough to produce slip or twinning bands, which would be the result of severe cold working. But don’t sweat it as I find a lot of people have wrong ideas about what can be revealed with microscopy and what can’t. What was it you were expecting to see in the micrographs?

Just one of my sources of information is the very old and well understood concepts in steel working which produced thermal treatments such as stress relieving to insure strain from heavy machining does not result in distortion of parts in heat treating, but I am sure you or Rex are well aware of such operations. Some of my other sources are much the same as most of yours, my own personal experiences and observations.

As I am sure you found and have noted over the years good sharp belts do not produce as much heat as they tend to cut more cleanly, and in the process produce less residual strain than dull abrasive overheating and smearing metal around. Moreover heavy, hot, grinding on one side of a symmetrical part with unequal application on the inverse can indeed result in distortion, not only at the time of machining but also later. This is easily observable in parts which are ground carefully and evenly either through automation with coolant application or even in blades that are hand done with scribed lines carefully laid out for symmetry as I am sure many of our stock removal bothers could attest to.

While it is known that the application of heat below recrystallization temperatures can result in recovery, paradoxically it is this effect that can contribute to the problem if not done evenly. Uniformity is the name of the game in any thermal treatment, but is the very essence of operations such as normalizing and stress relieving. I have yet to see a grinder uniformly overheat an entire blade to the exact same temperature, so even if hot enough, this in itself would produce an inhomogenous, partial recovery of what would have been more equalized natural grinding stresses.

I am not sure if your findings would also be different than mine that overheated belts have a shorter life (for which I would refer you to the recommendations of any abrasive manufacturer) or that having a comfortable, cool, grip on a blade while working power equipment may be a more prudent course. I can only say that I would find it disappointing if you felt differently in these areas as well.

The case for a cool and cleanly ground blade comes from many other directions even if the steel itself survives the thermal effects.
 
For a knifemaker, I would think that letting the metal get hot at any stage of grinding is just establishing a bad habit, even if it didn't have any effect on the metal prior to heat treatment. Maybe I am just too habit-oriented but repetitive processes like grinding seem to demand consistent working habits for me, if I allow the blade to get hot during the hundreds of passes on the grinder before HT there is a very good chance that the habit will bite me in the ass sooner or later when grinding a HT'd blade.
 
"What was it thats you were tyring to see in the photomicrographs?"
Rex was trying to identify the source of a problem for one of his clients in the manufacture of a part.

At first the problem was identified on the basis of the old wives tale of over heating while grinding destroying 'the integrity of the steel'. They blamed the machine shop.

It turned out to be a design fault, rather than the technique.

I agree that it is best to keep things even and uniform, from a wear standpoint on abrasives as well as its influence on the environment folks are working in.

To claim that just because a piece of steel is heated to a blue color from grinding, (before hardening and tempering), that it is ruined could not be validated by any experiments we did through photomicrographs, distortion in heat treat, or performance. At least with 52100 and 5160 which we were working with.

Uniformity in forging, grinding and heat treat are good habits to develop.

Turning a tip or edge of a blade blue before heat treat is not a critical event, there are much more significant events to consider in my experience.
 
Ah so we are in agreement, good. We shouldn’t need much lab work to dismiss something as patently absurd as an exaggeration that heating while grinding could “destroy” anything in the steel. Heck, as long as there isn’t burning, one can restore steel from much more massive overheating than anything a grinder could do. Words as melodramatic as “destroying” or “ruining, the integrity of the steel” are rather indicative of the inherent weakness of the argument so I am glad Rex was able to dismiss such an overstated and nonspecific claim. When a party engages in such ambiguous straw man arguments, not only should folks like Rex provide contrary evidence but they should urge them to be more specific with their specious claims.

To say something as exaggerated as a piece of steel would be “ruined” by overheating on a grinder would be yet another example of such an overstatement that certainly I personally would stay clear of in this situation. Neither could I imagine anybody would resort to such a straw man in inferring that I would use such hyperbole. So I am glad we see eye to eye there as well.

I am still puzzled about the use of micrographs though. Was the steel annealed, pearlitic, spheroidized, or hardened at the time of grinding? Darkened or slightly spheroidized martensite may say something about the heat but the other phases would be quite stable in this range. But then I need to remember that this was for a manufacturing client of Rex, or was this for your knife blades? Either way you both must have been using the same 5160 and 52100 in similar fashion.

Ed Fowler said:
...I agree that it is best to keep things even and uniform, from a wear standpoint on abrasives as well as its influence on the environment folks are working in...

...Uniformity in forging, grinding and heat treat are good habits to develop...
Click to expand...

Once again good, fundimentally we do agree after all!:)

Ed Fowler said:
Turning a tip or edge of a blade blue before heat treat is not a critical event, there are much more significant events to consider in my experience.
Click to expand...

Indeed, there is always something more significant when taking things individually, yet every little thing can count in pursuit of success.
 
Without getting into a huge debate, I also believe we agree, maybe! (smile)

The blades I worked with in the experiment were forged, then three post forging quenches, then two quick trips from above critical to below critical then a full normalizing heat, above critical to room temp. at 70 f. Then a low temp anneal, 988 f.
for two hours, one hour to 988 f from room temp and cooled slowly in the Paragon, then to the home freezer, three times in three days.

I do not remember what condition the steel was in that Rex was working with, it was his experiment that led to our experiment.

Rex and I vowed to keep the description of our work simple in order that the average reader could understand it without going to a metals textbook. This may be the source of some of our disagreement, we may not be speaking or hearing the same language while our thoughts may be similar.

My first experience with warp in machining was when I tried to convert a 36 inch round barrel to a six sided swamped barrel using hand files. Needless to say I learned a lot!
Do those lessons learned apply to knives? Probably, but not the the extent they did to that rifle barrel.
 
ok in a nut shell
over heated pre HT not great but not the death of a blade (we should all be working to the make the most of our blades)

we all have a set of cycles that we work with to get what we are looking for in our "pet" steels for the "pet " applications in pre HT and as part of the HT


so no 2 cooks make the same meal even with all the same tools and supplys dont we all have different tastes :)

im liking this thread
 
Ed Fowler said:
...Rex and I vowed to keep the description of our work simple in order that the average reader could understand it without going to a metals textbook. This may be the source of some of our disagreement, we may not be speaking or hearing the same language while our thoughts may be similar...
Click to expand...

No problem, please don't hold back on my account Ed. I have spent more than my share of time with the textbooks and testing in order not to be the average reader, so by all means if it could avoid future miscommunications please feel free to cut loose and expound on anything that you may have learned in the lab over the years. From the volume of time you have mentioned spending in such research you must have picked up quite a bit, but I am confident I could keep up, and there should be so much for us to discuss if we found a more efficient level of communication.:thumbup:
 
Don't you think repeatedly dipping a hot blade in water is going to stress it even more? That's thermal shock isn't it?

I'd be kind of careful with that. Air cooling is kinder and friendlier to the steel. :)

Why is everyone always in such a frigg'n hurry?

That's what I like about files,... the steel never gets very hot. Files are friendlier to the steel.
 
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Ed Fowler said:
Without getting into a huge debate, I also believe we agree, maybe! (smile)

The blades I worked with in the experiment were forged, then three post forging quenches, then two quick trips from above critical to below critical then a full normalizing heat, above critical to room temp. at 70 f. Then a low temp anneal, 988 f.
for two hours, one hour to 988 f from room temp and cooled slowly in the Paragon, then to the home freezer, three times in three days.

I do not remember what condition the steel was in that Rex was working with, it was his experiment that led to our experiment.

Rex and I vowed to keep the description of our work simple in order that the average reader could understand it without going to a metals textbook. This may be the source of some of our disagreement, we may not be speaking or hearing the same language while our thoughts may be similar.

My first experience with warp in machining was when I tried to convert a 36 inch round barrel to a six sided swamped barrel using hand files. Needless to say I learned a lot!
Do those lessons learned apply to knives? Probably, but not the the extent they did to that rifle barrel.
Click to expand...

Ed, sorry for getting off topic, but I'm trying to learn something here.
Are the temps that you're listing the same for both 52100 and 5160?
Thanks,
Mitch
 
If you feel you must use a belt grinder, just put some gloves on (which you should be doing anyway) and if it gets too hot to hold, set it aside and let it air cool. If you are still worried about it, stress relieve it (post stock reduction) just prior to the quench.
 
Tai Goo said:
If you feel you must use a belt grinder, just put some gloves on (which you should be doing anyway) and if it gets too hot to hold, set it aside and let it air cool. If you are still worried about it, stress relieve it (post stock reduction) just prior to the quench.
Click to expand...

Why not just keep it cool to begin with? you don't have to wait until it gets hot to dip it. I grind bare-handed, try to keep a finger tip on the thin edge area, and I rarely feel more than moderate warmth when grinding.
Of course, I dip every pass. If the steel is getting too warm on each pass, I just speed up on the next pass until I reach a comfortable balance.
 
Mitch: The temps we use in the realm of what this discussion is all about are the same for Rex's 52100 and jd 5160. Alsays keep in mind that all 52100 and all 5160 are not the same.

Just for the record, I do not grind a blade to the point where it turns blue very often, but do not worry about it when it happens.

I do not use gloves except when welding or on my left hand while forging.
First - they are expensive and don't heal like my skin will.
Second - I like to know how hot the steel is by feel.
Third - I don't want anyting tied to me around belts or buffers that can get caught up in my work.
 
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