What temperature to normalize O-1?

A

alexmin

Joined
Nov 16, 2005
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Guys,

what's the right temperature to Normalize O-1?
I found two contradicting numbers 1600F and 1450F.
Which one is right?
 
1450 F is correct .1600 F is way too high !! Typically the normalizing is 50-100 F above the critical temperature.
 
References to hardening are typically 1450-1500 F .The normalizing temperature should be the same .Certainly hardening at 1600 F would give you high retained austenite and large grain size . What would be the advantage of normalizing at 1600 F ???
 
mete said:
References to hardening are typically 1450-1500 F .The normalizing temperature should be the same .Certainly hardening at 1600 F would give you high retained austenite and large grain size . What would be the advantage of normalizing at 1600 F ???
Click to expand...

mete, this is right out of the ASTM heat treating manual:

O1 AISI
Carbon 0.85 to 1.00
Manganese 1.00 to 1.40
Silicon 0.50 Max
Nickel 0.30 Max
Chromium 0.40 to 0.60
Vanadium 0.30 Max
Tungsten 0.40 to 0.60

High dimensional stability during heat-treating. Relatively shallow hardening.

Forging max heat 1950 degrees F.
Do not forge below 1555 degrees F.

Normalizing - heat to 1600 F and cool in air. Hold from 15 minutes to 1 hour for large sections.

Annealing – heat to 1400 to 1455 F. Small parts at lower temperature and large parts at higher temperature. Holding time is approximately 1 to 4 hours depending on part size.

Hardening – heat slowly, preheat to 1200 F. Austenitize at 1455 to 1500 F for 10 to 30 minutes and quench in oil. Hardness will be 63 to 65 HRC.

Tempering – temper at 345 to 500 F for a hardness of 62 to 57 HRC. 345 to 400 F is most commonly used tempering range.
 
mete said:
References to hardening are typically 1450-1500 F .The normalizing temperature should be the same .Certainly hardening at 1600 F would give you high retained austenite and large grain size . What would be the advantage of normalizing at 1600 F ???
Click to expand...

I'm not sure. Kevin (Cashen) describes the benefits somewhere...

I do know that the data sheets for most of the tool steels I've seen say to normalize at 1600.

Also, for some reason my forgings tend to have a lot of alloy banding, and normalizing from 1600 makes things nice and homogeneous.
 
Guys,

I use stock removal method not forging. Does it make any difference for normalizing temperature?
 
Alexmin, for stock removal you don't need normalizing though you might do stress relief at 1200 F....Fox and Phillip , interesting , I'd like a technical explaination !I checked many sources on Google , some say 1600 F , some say 1450-1500 F .Some make no reference to normalizing .There are various methods of annealing too !! You just can't get two metallurgists to agree .
 
So far I never normalized my O-1 knives. The main reason I wanted to start normalizing is that I am about to HT my first integral knife made on milling machine out of 1/2" bar.
I suspect that milling might be more "stressful" that regular grinding on a belt.
 
mete said:
Alexmin, for stock removal you don't need normalizing though you might do stress relief at 1200 F....Fox and Phillip , interesting , I'd like a technical explaination !I checked many sources on Google , some say 1600 F , some say 1450-1500 F .Some make no reference to normalizing .There are various methods of annealing too !! You just can't get two metallurgists to agree .
Click to expand...

You see. . .you and Kevin have created monsters now that ya' got us readin' all that scientific stuff. . .:D

I do it pretty much the same way Phillip does and with excellent results. There is something about that first high heat that O1 seems to like.
 
mete said:
References to hardening are typically 1450-1500 F .The normalizing temperature should be the same .Certainly hardening at 1600 F would give you high retained austenite and large grain size . What would be the advantage of normalizing at 1600 F ???
Click to expand...

Mete

Digging into the dark corners of my memory, which has more grinding dust than useful information, I seem to remember that on some steels they:jerkit: use the decreasing temperature step normalizing because, the first cycle is used to dissolve the high temp carbides of vanadium, tungsten, etc. the following cycles are to reduce grain size. If I find where I read this, I'll pass it along.

Jim Arbuckle
 
DAMNENG said:
Mete

Digging into the dark corners of my memory, which has more grinding dust than useful information, I seem to remember that on some steels they:jerkit: use the decreasing temperature step normalizing because, the first cycle is used to dissolve the high temp carbides of vanadium, tungsten, etc. the following cycles are to reduce grain size. If I find where I read this, I'll pass it along.

Jim Arbuckle
Click to expand...

Thanks, Jim, that's what I was thinking. :thumbup:
 
All my info has 1600F,too. My understanding on it is the same as Jim's. 10-15 minutes should be more than enough for a knife blade. Reduced temperature cycles to refine the grain won't hurt, but should not really be necessary.


Here is some info from the ASM Heat Treater's Guide:
NORMALIZING
"The term normalizing does not characterize the nature of the process. More accurately, it is a homogenizing or grain refining treatment, with the aim being uniformity in composition throughout the part. In the thermal sense, normalization is an austenitizing heat cycle followed by cooling in still or slightly agitated air. Typically, work is heated to a temperature of approximately 55C (100F) above the upper critical line of the iron-carbide phase diagram, and the heating portion of the process must produce a homogeneous austenitic phase. The actual temperature used depends upon the composition of the steel,; but the usual temperature is around 870C (1600F)."

And a good reason O-1 is a popular learning steel:
CHARACTERISTICS
" High dimensional stability during heat treating. Relatively shallow hardening. High resistance to decarburization. Very high safety in hardening."

Stacy
 
As mete has pointed out industry normally goes around 100F higher than hardening for normalizing. Here is how I would do it and why:

Start at the high temperature (1600F or better) to homogenize the steel and smooth out all the havoc you have inflicted in forging. There will be segregation of the carbon, alloying and totally uneven grain size throughout. If the grain grows a little on this first normalizing - so what? At this point it is more important to have the grain equal in size than small. Allow it to air cool at least to 500F-600F before reheating.

Reheat to a proper austenitizing temperature typical to hardening on the next heat. Here, as with any heat in normalizing, the most critical factor is that you heat EVENLY, bring the entire blade evenly up to the same temperature or you will defeat the very purpose of "normalizing". This heat will refine the grain size and disperse the carbides a little better. The less time you hang around the Ac1 temp the less segregation will be put back into the blade, so a quick (but even) heat is the best. One could even quench on this heat to get finer grain quicker on the next heat, but if you quench remember that you will need to go all the way to room temp to see benefits. Allow it to air cool below the upper bainite transformation temp. or quench to Mf or you will simply be reheating the same old untransformed austenite and accomplish nothing.

The third reheat can be to the same temp or cooler and allowed to air cool. for extra grain refinement and stress relieve.

On a typical heat-cool and reheat cycle you will have at least three entirely new sets of crystalline structures form, along with any proeutectoid constituents that precipitate (carbide etc...). The more carbide and grain boundaries (as you get with finer grain) the more readily diffusional processes that form new structures will begin.

At the grain refining part of the process, having uneven grain size can be disastrous to making finer grain since large grains grow at the expense of smaller ones, so leaving a few large grains will create monsters surrounded by all the food they need to bloat themselves, this is also a pitfall of cold working (anything under PROPER forging temperature) for just a few minutes at the end of the forging, incomplete deformation results in germination, a condition where uneven grain size causes localized exaggerated grain growth. See Page 224 of "Principles of Heat Treatment” by Grossman and Bain, or Page 84 of "Metallurgy" by Johnson and Weeks, if my explanation of this phenomenon is insufficient for you.
 
One of the manufacturers mentions 1600 F normalizing "suitable for large forgings" but doesn't mention if it would be a different temperature for small forgings ! Having had experience with large sections of tool steel the situation is very different . The larger section you have the larger are the carbides and higher normalizing temperatures would be appropriate. Smaller sections are different and I don't think 1600 F is necessary .If you use it make sure you follow with lower temps as Kevin and I have suggested...Good sources for tool steel info ; www.crucibleservice.com , www.latrobesteel.com , www.cartech.com ,www.bucorp.com
 
Kevin R. Cashen said:
Reheat to a proper austenitizing temperature typical to hardening on the next heat. Here, as with any heat in normalizing, the most critical factor is that you heat EVENLY, bring the entire blade evenly up to the same temperature or you will defeat the very purpose of "normalizing". This heat will refine the grain size and disperse the carbides a little better. The less time you hang around the Ac1 temp the less segregation will be put back into the blade, so a quick (but even) heat is the best.
The third reheat can be to the same temp or cooler and allowed to air cool. for extra grain refinement and stress relieve.
Click to expand...

Kevin,

thanks for the info. I have some more questions for you. What "Ac1" means?
When you say "The less time you hang around the Ac1 temp the less segregation" do you mean that it'll be be the best to preheat an oven to a 1500F and then put a cooled to 500F-600F blade inside?

Thanks,
Alex
 
On the rising heat there are three “critical” temperatures of concern to us here. There is the point at which the shift from alpha iron to gamma iron first begins, this is known as Ac1. The next is where iron will lose ferro-magnetism this is designated Ac2. The last is where all the proeutectoid (left over after .8% carbon has been dissolved) constituents is into solution, for steel with less than .8% carbon this is known as Ac3, for steels with more than .8% carbon this is known as Acm.

Ac1 is of concern because when it is reached and gamma iron begins to form the ability of carbon to move increases significantly but there is not quite enough heat to break the bonds on the heavier carbides. So if you hang around at this temperature for extended periods, you can get the heavy segregation that we are talking about. This is why so many guys who forge at low temperatures will end up with banding and other nasties that need to be dealt with by higher temperature normalizing. Don’t believe me, give it a try, take some O1 and repeatedly cycle it just under nonmagnetic and then etch it and see how you have made mono-steel damascus out of it. Now to make it go away simply heat to a temperature nearer to Acm where you can get full solution and “poof” all those funny lines and patterns will suddenly disappear! Imagine that! It is not magic just simple metallurgical process’s at work.

Heat treating is moving carbon around in iron to get the desired results, heat is the tool we do it with. Certain temperatures will put the carbon in certain places, once we learn which is which, we can pretty much make it do anything we want.
 
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