Was bound to happen eventually.

[Malice9610]

First off, Steve, you were right, using " used and abused " steel does create moments of frustration when you spend a goodly number of hours working on something, only to have it not turn out. Once I have worked my way through the stock I have on hand, Its going to be all new Aldo steel for me moving forward. 

But, This gave me a chance to do some destructive testing on a fully heat treated knife, to both see how well my normalization went. and also to see how close to the bend test I am. This is the first time I have done any destructive testing. 

Here you can see the line that drew my attention, at first I thought this was just a gouge in the steel, So I hit it a few times with the belt sander but it wasnt going away. then I noticed where at the spine, there was an angle crack about 1/16th an inch down the blade, that went across the entire spine. I was cleaning the buildup off from tempering this blade when I noticed this, So I was probably about 4-6 hours into this particular piece when the cracks started to show. 

Tossed it into the vice, and put some muscle to it, but it wouldnt snap. So I braced my feet on the bench, and put ALL my weight on it ( 146 lbs give or take ) and it snapped right at the end of the crack in the spine. 



You can see a hint of the horizontal crack on the outer sides here, and the dark spots is obviously the much more serious crack in the spine.  Grain size is a bit larger then I expected, but not the worst I have ever seen on my work, I did triple normalize these, however I suspect they still cooled too quickly, as my normalization process involved heating them to non magnetic, then walking them about 10-15 feet to my garage and layed them down on the concrete, I suspect that was part of why a couple of the others also warped significantly, but this one, and a matching blade ( making a matched set for a friend of mine and his wife ) were the only ones to be hardened and tempered.  I checked the other blade over and there are no signs of any cracks at all on the surface points of the steel. I even ground it down a bit more just to make sure I wasnt missing something just another pass deeper in. 



Here is a shot after I broke the knife again about half way though the blade, The grain structure to me still seems a bit big for a triple normalization, but this section is / was thicker, and the grains appear smaller then nearer the tip. its no where near a factory heat treat, I would say it falls somewhere between the " 1 normalization / 2 normalization " range from the Picture of the file where they did multiple tests to show grain patterns. 

Breaking the knife at that point, required a breaker bar, its not overly thick, But I once I threw a cheater bar on it, it snapped with relative ease, which also leads me to think that I may also want to consider my Tempering temps as well, I started at 400 for an hour, cool to room temps, then 375 for an hour, cool to room temp, and then 350 for an hour, I think I should probably ramp that temp up with the same increments to a max temp of around 475-450 deg. 

The steel is 1976 Camaro Z-28 leaf spring, While not certain, I looked and from what I can tell it " SHOULD " be 5160, so that was the route I took with it, however considering my results I expect many will agree there is something off with my thinking. 

Sorry about the no so great photos. My " good " Digital camera is not the greatest by any means. but I did want to try and get some decent shots of the grain patterns to see what everyone else though on if I am close to my guesses on where I could improve my work. 

[Steve Sells]

the concrete floor is a big heat sink, almost all my blades have a 1/8 inch hole in tang  so I can hang them on a wire.  Remember this blade was not a failure,  for you did learn.

Edited July 7, 2015 by Steve Sells

[Malice9610]

So at the advice of a few other more experienced makers, I used a Pipe to normalize in my forge. and I cant complain one bit about the results, allows me to work during the day without overheating my knives, and allows for a more consistent heat along the entire blade. 

Here is what the first attempt using the pipe looks like after 3 temper cycles. 

next, I plan to try some 1084/15n20 in the pipe to see if it will help with forge welding. 
 

[ThomasPowers]

Do you throw some charcoal in it to make it a reducing atmosphere?  Easier if one of the pipe is sealed off

[Malice9610]

Yep

One end is closed up night and tight ( i wouldnt call it sealed, but its quite close ) and then I just take a few pieces of charcoal from the backyard fire pit and toss them in before adding the knife. 

my grain patterns on the knives I have destructive tested ( both intentional and unintentionally ) show a serious reduction in grain size since moving to the tube, for the next little while I expect to only do my normalization and hardening cycles in a tube like that. 

 

[SnailForge]

It's also a good idea to wear a full face shield if you're breaking a knife. I once had a shard zinging through the workshop when I broke a knife. Since then I always wear a face shield if I am breaking stuff.

[Frosty]

If you're breaking the knife as a test just wrap a piece of cloth over/around it as a scatter shield and wear PROPER PPE!

Frosty The Lucky.

[Malice9610]

I did have safety glasses on, and so far nothing has broken where shards came flying off. however your recommendation Frosty about the cloth is one I had not thought of, and will be employing it moving forward. 

 

[Ethan Paul Dobbins]

The grain does look a bit large, especially in the third picture. If you do your first normalization at a higher temp say just under 1600 degrees just to make sure you get everything into solution and  without really trying to reduce the grain size as much as trying to get it  all equal size with this heat, then drop the temperature of the next one to 1500 then drop to 1400 and do a couple at as low of a temperature as the magnet will not stick to  you might get finer grain structures that are more equal in size. Make sure you ramp up your heat slowly so you do not overheat the tip or edge. I like to do it in the shade to make sure The colors are not too hot.  I attached a picture of a color/temp chart showing the number of cycles I do at each heat. sometimes i will do extra, just depending on if I feel like doing more than usual, and intuition. I tried to take a picture of the grain size i get doing this, but an ipod camera seems to not want to focus very well. I will tell you it is comparable to a broken nicholson file, though somtimes slightly larger but  I am very happy with the results .