1084 steel question

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JTheodore

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So I have started making knives/hatchets with 1084 steel from New Jersey Steel Baron and I have heard stories of heat treating where the knife becomes so brittle that it can break before tempering it. My dad who is a structural engineer and deals with steel did not believe me when I said that the steel becomes "brittle" but rather it comes under stress when it is quenched which I understand as well. But then he proceeded to heat it to "cherry red" and dropped it it cool water letting it coolto room temperature. After that, he put it in a vice and swung a a few hammer swings at it and it did not break at all but just bent like 45 degrees and stayed there.
So...is there something I am not understanding about 1084 heat treating as I thought it was supposed to be very hard and brittle after the quench? Thanks very much for any info! I am a newbie but love working with knives and steel and want
to do it right.
 
"cherry red" was not hot enough. 1084 needs 1470f and a soak for 2-3 minutes at temp, followed by a
quench in a fairly fast oil. hardened that way it will be quite hard and highly stressed. immediate tempering
would be needed to relieve stresses. 400f - 425f for an hour, then test hardness.
 
If you take a fully spheroidized stock of 1084 and quickly bring to cherry red and quench, chances are that you didn't put enough carbon into solution for hardening.
Do the same thing, but allow for a ten minutes soak at cherry red....maybe the temp won't be enough to reach full hardness, but you will enjoy a perfect brittle fracture in your vise if you try to bend it without tempering.
 
Thank you guys so much! I got a followup question:
What would happen if 1084 were heated to 1600 degrees and then quenched, or how would overheating by 100-200 degrees affect the metal?
 
You would greatly enlarge the grain. It will still harden, be brittle and with the enlarged grain be very weak.
Don't forget that TIME is an important factor as well in heat treating. If you just get the steel up to a target temp for only a few moments, basically nothing happens. Controlled soak times are important.
This is not easy stuff.
 
Ask your dad how they get a file so hard and why it breaks if dropped on concrete.
 
JTheodore said:
So I have started making knives/hatchets with 1084 steel from New Jersey Steel Baron and I have heard stories of heat treating where the knife becomes so brittle that it can break before tempering it. My dad who is a structural engineer and deals with steel did not believe me when I said that the steel becomes "brittle" but rather it comes under stress when it is quenched which I understand as well. But then he proceeded to heat it to "cherry red" and dropped it it cool water letting it coolto room temperature. After that, he put it in a vice and swung a a few hammer swings at it and it did not break at all but just bent like 45 degrees and stayed there.
So...is there something I am not understanding about 1084 heat treating as I thought it was supposed to be very hard and brittle after the quench? Thanks very much for any info! I am a newbie but love working with knives and steel and want
to do it right.
Click to expand...

My brother is an engineer too. He frequently gets the metallurgy wrong because he doesn't use that information regularily. He specializes in corrosion in oil pipelines.

Your dad is correct to a certain extent, but there's more going on in the steel than what you reported he said. Have him read this:

http://www.hybridburners.com/documents/verhoeven.pdf
 
JTheodore said:
What would happen if 1084 were heated to 1600 degrees and then quenched, or how would overheating by 100-200 degrees affect the metal?
Click to expand...

The grain grows larger, making a shear along the grain boundaries easier. As you increase the temperature before quench, and the time it is held there, the grains can grow to huge size. Really large grain can make the steel can look like coarse concrete. This makes the steel les strong and more likely to break. Fine grain is a product of controlled austenitization, and proper quench speed.

The structure formed above 1400F in steel is called Austenite. It is a very ductile form of steel where the carbon atoms are in a face centered cubic structure between the iron. If it is cooled at the right speed in HT, a new structure forms at 400F. This is called Martensite. Martensite is a very strong body centered cubic structure. The structure in its as-quenched state is also extremely brittle. It is called brittle martensite. This is tempered at around 400F to remove some of the brittleness and add more toughness.

A freshly quenched blade will shatter like glass if dropped on a concrete floor or struck with a hammer. Because the quench also creates great stresses along the grain boundaries, these stress can autonomously create a shear and the blade can crack just sitting around too long before tempering. This is why the temper should follow the quench as soon as practical.

Once tempered, there is less stress and less brittleness, but there is still a certain amount of both. If the stress is increased ( adding energy to the grain boundaries) by be ding or hitting the blade, it will snap in half. A fun fact is that the break proceed through the grains at the speed of sound. This is the sharp "SNAP" you hear in breaking a blade, and the "PING" you hear when water quenching a blade and it cracks.
 
"Once tempered, there is less stress and less brittleness, but there is still a certain amount of both."

I thought the tempering process was the end of it. Something more needs to be done? (I'm not a knifemaker, just fascinated. Pretty incredible, how iron ore turns into a knife steel.)
 
If the stress was fully relieved, you'd have annealed (soft) steel again. Think of a lattice like a net. Put some tension on it and it will support your weight. Put too much tension on it and it may snap with your weight. Put no tension on it and it's just limp.
 
To expand on what Stacy said, you can get the deadly ping from using a quench medium that is too "violent" My limited experience with those types of failures when everything else was done right causes me to give advice like "use AAA instead of #50 for thin sections ofCruForgeV." ;)
 
It wasn't harden. Don't go only by color when heat treating. I look at the color to make sure the blade is heated evenly and I use a magnet to check for critical temperature. Once the steel reaches about 1420 F it should be nonmagnetic. Heat it up just a little more to get in the 1450-1500 range and then quench in oil. If you do things correctly it will break if you repeat the vise and hammer test. Once hardened, you need to temper it to relieve stress and reduce hardness in order to have a proper cutting tool.

-Jeff
 
JTheodore said:
So I have started making knives/hatchets with 1084 steel from New Jersey Steel Baron and I have heard stories of heat treating where the knife becomes so brittle that it can break before tempering it. My dad who is a structural engineer and deals with steel did not believe me when I said that the steel becomes "brittle" but rather it comes under stress when it is quenched which I understand as well. But then he proceeded to heat it to "cherry red" and dropped it it cool water letting it coolto room temperature. After that, he put it in a vice and swung a a few hammer swings at it and it did not break at all but just bent like 45 degrees and stayed there.
So...is there something I am not understanding about 1084 heat treating as I thought it was supposed to be very hard and brittle after the quench? Thanks very much for any info! I am a newbie but love working with knives and steel and want
to do it right.
Click to expand...
JTheodore said:
So I have started making knives/hatchets with 1084 steel from New Jersey Steel Baron and I have heard stories of heat treating where the knife becomes so brittle that it can break before tempering it. My dad who is a structural engineer and deals with steel did not believe me when I said that the steel becomes "brittle" but rather it comes under stress when it is quenched which I understand as well. But then he proceeded to heat it to "cherry red" and dropped it it cool water letting it coolto room temperature. After that, he put it in a vice and swung a a few hammer swings at it and it did not break at all but just bent like 45 degrees and stayed there.
So...is there something I am not understanding about 1084 heat treating as I thought it was supposed to be very hard and brittle after the quench? Thanks very much for any info! I am a newbie but love working with knives and steel and want
to do it right.
Click to expand...
Some years ago I bought some scrap snow plow scraper blades at a junkyard that I just found out are 1084. Being,6+ feet of 4" wide by 5/8" I think 20$ was a pretty good price for that. Anyhow,has anyone tried making anything by stock removal or forging from this material? I'm gonna anneal a chunk and then cut some shapes out,going from there,thoughts?
 
This is a two year old thread. Please look at the date when you pull up a thread in searching.

I suggest you start a new thread about your scrap steel. I also suspect that your steel is not 1084.

Thread closed.
 
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