1084 triple tempering

[Ed Caffrey]

If its still chipping at 450F, then I would say go to 475F and test again.....another thought just came to me.....how much flex are you educing? All you want to see is the very edge flex and return to true.....If your trying to get too much flex during the test, the edge is going to chip until you get so much temper into it, that it just bends.

Another questions is: What size of brass rod are you using? The smaller the diameter of the rod, the more likely the knife will chips because of the small radius.....1/4" is the smallest I would recommend using.


Just some random thoughts to see if we can help figure out whats going on. In my experience, with a fine edge geometry, 1084 should be flexing and stay bent at 450F.....unless there is something else going on that we haven't considered yet.

[tomh]

ok, i am using a 1/4" brass rod, and this knife is thick so I am reefing down on it to get the edge to flex. this is the knife we talked about that I wanted to grind thicker, so I convexed it from about .025
It definitely is not bending. this time the chips were very small, just the very edge. before they were pretty big, and got smaller with each temper cycle.
i want this style of knife to be very tough.
guess I can just finish it out and beat the crap out of it, or just do a 90 degree bend test and see what happens.

for a bigger thicker knife, should allowances be made and use a higher temperature?

thanks!

[Ed Caffrey]

Absolutely! Different types of of grinds/geometries on the same steel are going to required slightly difference heat treating methods. For example, my average blade of 1084 is tempered at 415-425F. If I make a heavier geometry on a blade, sorta like your talking about, I would likely tempering it a bit lower. The reason is that if the edge is thicker, it will generally tolerate a higher hardness level without chipping.

You have to take "the overall package" into consideration with every knife.... turning out a good blade involves many more aspects than just the steel type and the heat treat, all the aspects have to fall in line too.

I didn't think to ask more that what I did, but now I understand....if you left that edge that thick, I suspect that the pressure it takes to flex that edge would be of an amount that likely no blade would stand up to without chipping. I think your on the right track with finishing it up and testing to see how it works.....thats about the only real way your going to find out if its what you want.

[tomh]

thanks Ed!
I did not know that a thick blade is a no go on the brass rod. that makes me feel better.

what would be a good test to do on a blade like this, instead of an edge flex. I chopped a 2x4 with it,but that hurts with no handle! maybe I should rig up a pair with bolts so I can remove them afterwards.

take care!

[Ed Caffrey]

Your going to want to design some tests that are repeatable....that way you can mimic it with other blades. The first thing you have to do is establish a baseline.....what are you wanting the blade to do? What is the intended use of the blade.....and that sort of thing. Then YOUR the one who has to choose the most important characteristics in a given blade/knife type, and create tests that will give you concrete answers to the performance criteria that you've chosen.

Hope that makes sense!

[Carcar?_BR]

Brass rod test

Hi friends, I?m a little confuse about this kind of test, maybe I?m loosing something at my translation to portuguese or maybe I?m justing not getting the point, so I can?t visualize that.

Can anyone help me here? How the test is done?

[Carcar?_BR]

Someone knows if there is some video showing the test at the internet?

[jdm61]

If you are using some of Aldo's 1084, remember that the larger stock had a carbon content (the first batch may have been as high as .89) that is up at the high side of the range for 1084. It will chip out at 400 from my experience.

[RandyScott]

Originally Posted by Carcar?_BR

Brass rod test

Hi friends, I?m a little confuse about this kind of test, maybe I?m loosing something at my translation to portuguese or maybe I?m justing not getting the point, so I can?t visualize that.

Can anyone help me here? How the test is done?

There is a good narrative description in post #26 in this link: http://www.synobyte.com/forums/showthread.php?p=889922

If you have Wayne Goddard's '$50 Knife Shop' book, see page 88.

I have not been able to locate a video of the process.

[Gary Mulkey]

I would think that a temper at 450 would be sufficient to eliminate chipping but here is a thought. I certainly am no metalurgist but wouldn't it be possible that if the quench wasn't fast enough that some cementite formed. As I understand it this could make it more brittle & succeptable to chipping. Hopefully some of the metalurgists will help me with this.

Gary

[GHEzell]

Something I don't think has been mentioned yet, is that ovens are not very precise... have you checked the oven to see if it is under-heating? My little toaster oven is about 25 degrees cooler than the thermostat says it is. If you don't have one, get a good oven thermometer and check it, it could be the cause of your problems.

[DRN]

I'm a new bee at this.
What does tempering do for the knife.
What reason is it necessary to temper the blade.

Thanks (drn)

[GHEzell]

The short answer:
When the blade is quenched, it is converted to a very hard, brittle form. It will break and chip. This is why we temper, to soften the structure so the blade will have the right mix of hardness and toughness. A file and a spring can be made form the same type of steel, the only difference being the tempering, a knife needs to be somewhere between these two extremes.

[Ed Caffrey]

Often times, people in general, who are not familiar with heat treating, refer to the entire process as "tempering". I've heard this numerous times through the years, and have always tried to use the opportunity to educate those individuals....if they're receptive.

In general terms, the two most important steps to the "heat treating" process, is "Hardening", and "Tempering".

In plain english, Hardening can be defined as:

Making a piece of steel as hard as it can possibly be. Along with hardness, always comes Brittleness....the steel is hard, but in many cases its "glass" hard, meaning that it will easily break or even shatter.

This is were the next step, "Tempering" comes in. In essence, tempering is nothing more than a controlled softening. Accomplished by exposing the steel to heat, for specific period of time, which causes the interior matrix of the material to change, "softening" the material to a more usable state. (relieving some of the brittleness).

The whole key to tempering is to discover the correct temperature to utilize, in order to achieve the optimum "working hardness" for the particular steel, and grind geometry.

[LRB]

tomh, how was the steel prepped before HT? Did you normalize it well? Did you give some soak time? What did you quench it in? What approx temp did you bring the steel to for the quench? From what you say, it sounds like an uneven quench, uneven heat, or uneven carbon distribution. Are you resonably sure this is 1084?