General questions re. refining hearth steel

[Carl Chandler]

Hey Everyone,

 

My name is Carl and I’m new to this forum. 
I’ve been in the knife making hobby for a while now but only recently got really interested in bloomery iron, wrought iron, hearth steel, etc.

Anyways, I saw Emiliano’s video on making hearth steel from random bits or iron/low carbon steel with his 7 brick hearth and gave it a try. I tried to emulate the setup as closely as possible - I wired together the bricks, broke one off about 1/3 of the way down to make room for the tuyere and had a ball valve to control airflow and made a bowl shaped bed of ash in the bottom. I basically just tried to copy his video.

I broke up charcoal into about inch sized bits and used some wrought iron from a wagon wheel as feed stock.

the results actually came out better than expected for a first try.

The first image is of the puck after I consolidated it a bit. To me, it sparked like medium carbon steel and after I folded it several times and quenched in water, it got hard enough so that my good fine tooth file was skating across most of the surface. 
However when I etched the piece, I noticed a bunch of tiny short cracks on the surface and edges perpendicular to the folds. After a couple hrs of research it seems like the material is hot shorting for some reason. 
The other pictures show some of the cracks.

 

The question I’m looking to have answered is: are these cracks normal in your experience when consolidating porous and inconsistent bloom-like material or do y’all suspect there is some impurity in my starting stock that is causing hot shorting?

 

Thanks in advance for any advice. I think I put this question in the correct section of the forum but if I need to move it, let me know. 

[Alan Longmire]

Welcome aboard!

 

Hearth steel can really mess with your head.  Just looking at the colors in the etch, I suspect you've got some high phosphorus wrought.  That stuff is fun because it's both hot AND cold short, especially if there's any sulfur in there as well.  Try forging a rod about 3/8" square from that wagon tire.  Do it hot, like at near-welding heat.  Don't quench it, just let it air cool.  When it's completely cold, saw it halfway through and bend it double.  If it snaps immediately, it's got issues.  Then heat it to orange and try to hot cut it.  If you get about halfway through and the end pops off well before it's cut, it's high phosphorus for sure.  If it crumbles when forged at white heat, it's got sulfur.

 

Finally, as we discovered a few weeks ago, if you do everything right and fine surface cracks appear while you're polishing it, it could be copper.  

 

When you make your own steel, you become your own metallurgist.  

[Carl Chandler]

Hi Alan,

 

Thanks for the feedback. I’ve lurked here quite a bit looking at all the awesome stuff people make and am glad to make my first post.

As to your suggestions, I’ve forged quite a bit of the wrought from my batch of tires at a white or near white heat and I’ve never had it crumble. As for the other behaviors, I’ll give your suggestions a shot this week and see what happens.
Does any amount of phosphorus prevent all carbon uptake or is it a gradient? The reason I ask is because I’ve made shear steel from the same wrought a few months ago and it worked like a charm - the edge of the knife I made from it was at least as hard as my file. 

[Alan Longmire]

I'm afraid that's about the limit of my knowledge.     every bit of wrought is different, even from inch to inch. I've got about 20 wagon tires, and they're all different. 

 

on the phosphorus,  there is a point, but I don't know what it is.