Wesley, I would say that is not bad. One thing you mentioned microchips after cardboard. I would try raising the tempering another 25 degrees to 400. The 1080 with a good heat treat regimen can reach 64 or higher rockwell. I think your heat treat sequence is pretty much on, so you might need to adjust your tempering, 375 might be too low. Edge retention is not only a product of hardness but toughness. 375 might leave it too hard, while 400 will bring the hardness down a bit but increase toughness a bit. You just have to experiment.

Brion

Thanks for the help Mr. Tomberlin! I can't say for sure that it was chips or not. It showed up as shiny spots along the edge when the sunlight hit it. But, I'll try raising the temp to 400F and see what happens.

I usually use 1084 but happened to have some 1080. Should 1084 hold a better edge than 1080 or about the same?

Sorry for so many questions. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//sad.gi f' class='bbc_emoticon' alt=':(' />

Wesley

Wesley, using the same heat treatment, they should be about the same. Depending on what other things are in the mix. If it is Aldo's 1084, I know it has a high manganese content which promotes deeper hardening. The 1080, I don't know. If it came from Kelly Cupples it is good steel. More experimentation, of course.

Brion

Thanks again Mr. Tomberlin. I use kelly Cupple's 1080 and Aldo's 1084 exclusively right now until I master the HT.

Wes

Wes,

It would be hard to tell the difference between 1080 AISI and 1084 AISI. As Brion indicated 1084 might have an increase in the depth of hardening but that should not affect the edge. A somewhat better quenchant that is a bit faster might improve depth of hardening if that is what you are after. For example, if I heat treat a 1.5 inch wide blade that is 1/4 inch at the spine and then break it, the first appearance of mostly pearlite in the core of the blade does not show until about halfway back from the edge. So, in most cases depth of hardening is not a factor in knife's edge holding. It may affect toughness but not the edge hardness.

What is missed in most heat treats with these simple alloy steels is grain size. I was just curious as to why you normalized the second time at 1600 F. I would normalize once at 1600 and the on the second normalization I would shoot for 1500. This would help refine the grain size in the pearlite being produced through the normalization process. 1600 would result in a larger grain size. Remember that martensite will form off of the grain size of the pearlite. The more refined and finer the grain size of the pearlite the smaller and more refined the martensite. Know that 1080 and 1084 are very close to the eutectic point where the balance of iron to carbon is about equal. Below 1080 (actually it might be closer to .78 carbon for the eutectic point) and the steel is hypoeutectic (not enough carbon to mate with all the iron in the steel)and above 1080 it becomes hypereutectic (excess carbon in the structure will exist in relation to the iron). This makes a steel like 1084 a really nice steel to work with. It will reach maximum hardness assuming no carbides (alloys like vanadium or chromium form carbides with the excess carbon V4C3 in hypereutectic steels and to some degree even in eutectic steels).

So for maximum edge holding you need a small grain size (10 or greater) in this type of steel. You can do it a couple of ways. Use a lower temperature on your last normalization and/or do a second quench. A second quench will help since you would then be going from a blade that at room temperature is mostly martensite. Martensite to martensite is very fast in terms of transformation time and can improve grain size. Actually, doing both is best: normalize to refine the grain size on your second normalization and then do a second quench.

One last thing, if you do a second quench you may end up with slightly less depth of hardening because you have somewhat less time to get below the nose of the curve that defines whether the steel turns to martensite or reverts back to pearlite. Where you may have had about 1 second or a bit less to go from 1500 to around 900 or below, now you have about 3/4 of a second or less. Canola oil is fine but better is a quality commercial quenchant that matches the steel you will be using.

As Brion indicated you should be tempering at 400 F. Remember that the edge with the hardest RC is not necessarily the one that has the best edge retention.

Dan

I just wanted to say how much I appreciate conversations like this being shared. I always learn from getting to eavesdrop. Thanks for all of the information.

Jeremy

Thank you Mr. Petersen, You have been very helpful!

I always wondered what the best normalizing sequence was. Do you suggest 1600F, 1500F, 1500F, or a different combination?

Also, can you achieve full martensite with canola oil? I also would like to know what type of quenching oil is best for 1080/1084? I will definitely experiment with the normalizing and 2nd quench since I am trying to get the full potential from this steel.

Wesley

Wesley,

I refine the grain in 1084, beginning with a soak at 1600F for 10 minutes. This soak relieves the stresses from forging, allows the carbon to diffuse evenly throughout the steel and begins to reduce the grain size.

Additional grain refinement is done by thermal cycling the steel. The steel is heated to 1475F then cooled to black heat in still air, followed by heating to 1450F and cooling to black, then 1425F and cooling to ambient air temperature.

Three thermal cycles are sufficient to reduce the grain size in 1084 and prepare it for hardening. More than three thermal cycles on 1084 can cause the same situation as Dan described with a double quench of martensite. The grain can be made too small in 1084, resulting in shallow hardening.

Thanks Mr. Culver.

Should the soak at 1600F be done just after forging and the thermal cycling right before heat treat?

One more thing. Do you guys anneal after forging or is this an unnecessary step?

I appreciate all the help.

Wesley

Wesley,

I'm not certain that there is a best time for doing these heat treating steps. You just need to work them into your process somewhere. Depending on the type of blade, available shop time, and often my mood, <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' /> I may do these heat treating steps at different times during the making of a blade.

Most of the time, I do the 1600 degree soak after forging. As there can be some scaling due to the high heat and length of time at temperature, this gets it over with before rough grinding. I usually do the three thermal cycles just before bringing the blade to temp for quenching. The lower temperature and shortened time at heat lessens the risk of scaling.

I have an argon injection system on my kiln, so I don't have to be concerned with scaling during these processes. This allows me to have some choice in when I do them. But, I most often try to avoid using the argon, unless there is a good reason for it.

I don't do a full anneal on my blades. The 1600 degree soak is sufficient for relieving stresses and softening the blade steel for rough grinding.

Thank you again Mr. Culver. This answers my questions.

I can't wait to HT my next blade! <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

Wesley