1075 Carbon Steel - grain size problem...

giedymin

giedymin

Knifemaker / Craftsman / Service Provider
Joined
Feb 8, 2012
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Hi guys. for a long time now i was trying to buy good quality 10xx steel in Poland (hard to get it:)) to try to make nice hamons. Finally i've managed to buy 1075 steel and even with quite high content of Mn i got some nice hardening lines on sample knives. The problem was the grain size. I do not know if the rules that i used for other steels (high alloy) are the same for 1075.... I've managed to reduce grain to pleasing size but i was using triple quenching process...
I would like to know if there is any other way to do that, maybe not involving quenching, as i would like to avoid unnecessary stresses. Or if using triple quenching how to optimize this process...
Please help. :) Maybe you know some good ways to reduce grain size in 1075 steel.
It would be very helpful:) I'm using electric furnace with automatically controlled temperature.
Regards
Giedymin
 
After forging:

bring to 870C, hold 5 minutes, air cool to ambient ( will remove forging stress and even grain size)

for further grain reduction:

bring to 815C, hold five minutes, air cool to "black heat" ( 425C),
bring to 787C, hold five minutes, air cool to "black heat,
bring to 773C, hold five minutes, air cool to ambient.

very standard treatment for simple steels,

John
 
Thank you very much. Appreciate it a lot. Seems like a normalization process. I will try:)
Somebody tried something else?
Regards
 
Pretty much do something similar with all my carbon steels. Works really well.
 
Giedymin,

Each time the steel changes phases, from pearlite to austenite, and vice versa, ( passes through critical, in either direction) a new set of grains are formed along the old grain boundaries. These grains are smaller than the former size, and, if not allowed to grow by heating above about 926C ( 1700F), each phase change will result in a reduction in overall grain size in the specimen. The "stepped down" series of normalization temperatures results in sequentially smaller grain size.

This process of grain reduction also occurs in the phase change from austenite to martensite, but, as you note, with greater residual strain.

Multiple quenches can achieve the same results as multiple normalizations, though the control of grain size by stepped normalization temperatures, and removal of residual strain make that process more attractive to me.

John
 
Thank you very much. I will try to test it today and hope for good results.
It seams easier, and safer than multiple quenching.
Thank you once more.
Regards
Giedymin
 
Hi. I've tried this process and the grain is a little bit smaller, not silky though. Can i repeat the process to obtain even smaller grain? Should i temper, or anneal after first one? Maybe instead of 3 cycles i should do 4 or more with? Or maybe i could use compressed air to speed up cooling? would that make any difference?
How do you think?
Once again thanks for help.
Giedymin
 
Giedymin,

Annealing is done after grain reduction, being careful not to austenize for annealing at a high, grain-growing temp, that is, heat only to the low normalization temp.

You can repeat the normalization process to achieve ever smaller grain.

Note, however, that as grain gets smaller, the steel becomes more "Shallow" hardening, and can be taken to the point that no quenching medium, even water, will "beat the nose" and harden the steel.

Note also, that faster rates of cooling have some effect on grain size, but may introduce other, unwanted phase states, such as bainite , etc. Air cooling in still air is the standard for normalization.

Finally, the emphasis on small grain size has been promoted by some as the primary quality goal. In fact, grain size in simple steels need be only small enough, and can easily be gotten too small.

It is my understanding that on the ASTM grain size scale, from -1( very coarse) to +14 (ultra fine), that a suitable value for simple steel knives would be in the range 6-7, or on the border of medium to fine.


John
 
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OK i understand. You are really helpful and i appreciate it a lot.
This are some test samples after only one quenching without normalization and before tempering.
g9ou.jpg

What do You think about this grain size?
Samples are 6mm (1/4 inch) thick, made by one powerful hammer stroke. Slightly smaller grain size for normalized samples.
Regards
 
This grain size looks too large.

Try sampling grain size after the (1+3=4) descending normalization cycles, and an 815C austenize/quench.

Grain size should be significantly smaller.

John
 
Shade 3 cutting glasses cost about $12 at the Welder's supply, and block everything that's an issue for gas forge work. I use them when forge welding and don't have any problems anymore, but using them during forge HT isn't very practical, since the colors change heavily.

When welding, you can either watch the flux, or watch the billet to go the same color as the liner, assuming your temp is right. I keep trying to get all my friends to use these.

Kayne and Sons sells some Didymium glasses that they claim are good for this purpose, but from the research I've done, they protect against sodium flare common in glass work, but not enough of the IR and such that we're dealing with forge welding. My experience has been, that they don't help my eyes, where as the cutting shades do. YMMV
 
John White said:
This grain size looks too large.

Try sampling grain size after the (1+3=4) descending normalization cycles, and an 815C austenize/quench.

Grain size should be significantly smaller.

John
Click to expand...
Yes I thought so. I will try to do as you suggested. 4 normalization cycles and quench. Hope for better results. Thank you.

bladsmth said:
The above advice is all good. The reasoning is this:
Your forge is running at around 1680°F ( BTW, how was that determined?). That is the parameter you can't change.
You put a piece of O-1 or 1095 in and want to hold it at 1475°F for ten minutes - How will that happen? - It won't.
You can move the blade in and out ( called "pumping" the blade) to get an even heating from tip to tang, but if the forge is 200° too hot, the blade will quickly become too hot if it stays in there too long. This will cause severe grain growth and other problems with the blade upon quench.
What most people with only a forge do is run it at as low as temperature as it will stay stable, and pump the blade slowly from back to front of the forge, getting an even color on the blade. As it gets to a bright red, pull it out and check with a magnet placed on the side of the forge to see when it gets non-magnetic. For practical terms, call this 1400°F ( it is a few degrees higher than that actually). You want to heat it about two shares of red brighter to around 1475-1500°F. Once it gets there, keeping it in the roughly 1700° chamber will be counterproductive. Pull it out and quench it. The steel would do better with a longer soak ate 1475°F, but since that can't happen in your scenario, you just quit when you have to. The damage by a 10 minute soak at higher temperature will be far more than the slight loss in hardness and toughness by a too short soak time.
Click to expand...

Bladsmth I do not think this is the case. For those tests i used electric oven with controlled temp. and my thermocouple was recently calibrated. But obviously i do something wrong as i got very poor results of decreasing grain size of that steel using above normalization method and others as well.

This is the first time it happens to me as HT other steels like NZ3 (S1 with more carbon), O2 etc. I had no problems ant the fractures were smooth like silk. Super fine i would say for NZ3.

Regards
Giedymin
 
My apologies, I accidentally posted this answer on the wrong thread. It was intended for another thread with a question about grain size. He was using an uncontrolled forge for HT.
 
Hi. Still no good results with normalization. The grain is slightly smaller but still to big. Is it possible that the fracture view show something else than the grain size, that is somehow caused by for example way of breaking or something of that kind?
Or maybe the steel should be somehow HT before normalization process - maybe annealed somehow...
On one sample (normalization followed by double quench) i had big difficulty to break it, and i had to hit several times. Part of fracture there had really nice grain and other part just next to it (broken somehow in different direction) had much bigger grain... no transition, the boundary was the edge between cracks made in the different direction. What could be the reason of that?
Another strange thing is that it was definitely harder to break normalized and double quenched sample than normalized and quenched only once .
Regards
Still testing though :)
Giedymin
Giedymin
 
Interesting thread. I'm busy with the same thing right now. You can see what I did right here: http://www.britishblades.com/forums...-quenching-in-heat-treatment-oven-normalizing

You asked about other methods, well here is one. I'm using an air quench inside my oven. The reason for that is I can control my temperatures all the time during the process, I'll keep the knife hot enough so it won't form bainite (>550 degrees C). Also, I enter the pearlite nose early so I get fine plated pearlite instead of coarse pearlite.

About your problem, what has created the coarse grain in the first place? What have you been doing to the knife prior to your heat treatments? I've never used 1075 from Poland, but I have investigated 1.2842 (O2) that I buy here in The Netherlands, my fist analysis tell me it has a really nice fine grain straight from the steel plant, ~ASTM grain size 10 but i'm not 100% confident about that jet.

Anyway, about your testing, I wouldn't do breaking tests on quenched (martensite) test samples. Untempered martensite will always break easily. I'd rather do tests on pearlite only, in other words in a normalized or soft annealed condition.


Good luck!
 
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Thanks for answer Van Zanten.
The samples on the picture above are made just form flat bar (no forging, grinding etc.)

I've seen your thread on BB and i was wondering if the fast temp. change due to forced air flow wont affect furnace materials.... don't you afraid that it can be damaged this way?

Also could you share some more info about normalization process that you used? Austenizing temperatures and soaking times for both high and low temperatures?

Your sample after normalizing looks like it have quite big grain as well, did you managed to reduce it size even more?

All the best
 
So far my oven materials don't show any weird reactions so I think it will be fine. The size of the broken sample is 10mmx2,5mm, so small stock and a magnified photo. I had to beat like crazy to break the normalized piece, and it bent more than 45 degrees before breaking. I did 4 normalizing cycles, so I could do more for finer grain, but the initial grain was extremely coarse. It was like sugar.

You can get your own times and temperatures from the 1075 CCT diagram. For O2 I do the following: preheat oven to 810 degrees C, soak 2 minutes (2,5mm stock, thicker might need a little longer), cool down to 550 in 2:30 minutes, faster is better but, the important factor is to not get below 500, forming bainite. At 550 I soak until pearlite transformation has completed, you can read it from the diagram, in my case I soak at 550 for 7 minutes. It's a bit longer than necessary but I like to be on the safe side. After transformation completion I ramp up again, as fast as my oven will allow to 810 and repeat the process.

I'm doing this on my damascus right now, I've made samples and have been grinding, polishing and etching them and i'm trying to determine ASTM grain.
 
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