What did I do wrong?

[Will Brouwers]

I hope this is in the right place, if it is not, Mods please have mercy. I am not trying to cause chaos with my posts.

I forged this hot cut hardy out of leaf spring, and while using it today, the cutting edge started chipping and then suddenly the shank and the rest of it cracked. Attached are pictures of the grain. I don't know if that was the problem, or if there could have been microfractures, or if the way that I got it to fit in the hardy hole (heating it up and hitting it hard) is what led to it's demise.

It was also interesting, the top kept deforming, even though I had quenched it in water, and then it cracked. It seemed like it was too soft, and then too hard. I am only a beginner, especially when it comes to heat treating.

[Frosty]

Next time do NOT quench it in water! That wasn't your problem though. I can't enlarge the pic of the shank break well enough to get a good look at the "grain" (crystal growth, the boundries are shiny so it looks like grains of something. Hense the  term) What I can see it looks okay, smooth and gray.

However the break itself is troubling, it has one final initiation point at the top left of the large fracture section. The rest of the shank is a bunch of fractures that didn't connect leaving the platform of the final break for last. 

Tells me two things, there were cold shuts in the shoulder between shank and blade. Two it wobbled in the hardy hole on the narrow axis. 

Make another hardy but don't draw it down like that, fold the shank section in half and forge weld the joint. AND without drawing it down except where it fits in the folded shank section. The shank folds together and over the blade section all of it gets welded together.

Normalize and sharpen it with an acute slightly convex bevel it'll be stronger, stay sharp longer and drive through cuts more easily.

It was a good first attempt Will. Better luck next time.

Frosty The Lucky.

 

[George N. M.]

Will, 

First, leaf springs can be problematic as source material.  Newer cars have springs made of weird alloys which do not heat treat well in a home shop.  I have found that as a general rule, the older the spring the better it is at blacksmithing.  If you can find a leaf spring off an old wagon/buckboard seat it will be wonderful metal.

Second, did you do any tempering on your cut off or just harden it?  If you did not temper, "Well, there's your problem."  I would have only quenched the cutting edge and tempered it to a straw or bronze color and left the lower part of the body and the tongue that goes in the hardy hole unhardened.

Third, it appears to me that what you did ended up with the cut off being too brittle and breaking at the edge and the base.  I might even try to use it completely unheat treated and only get into that if it was dulling too fast or bending in use.

Try, try again.  Good luck on the next try.

GNM

PS I agree with Frosty, particularly about doubling the tang back to better fill the hardy hole except that I'm not sure if it is necessary to forge welding the tang.  I might even double the tang back in a U shat to completely fill the hardy hole.

[Frosty]

I was thinking holding the blade in the folded shank section would eliminate the problems of forging old leaf spring but the blade and shank need welding. Forge or arc, a friction  fit wouldn't last.

Frosty The Lucky.

[swedefiddle]

Good Morning Will,

Find a piece if square stock that you can make fit your Hardy, make it so it will sit higher than your Anvil Face. Weld the stem to the backside of your Leaf Spring stock. This will give the Leaf Spring, full support against the Anvil Face. Pre-Heat your pieces before welding and Post Heat after welding, let cool in still air. A Hot Cut is for cutting 'Hot Material' not cold material like you tried earlier.

Neil

[BillyBones]

If you plan on forge welding the shank i would highly suggest a piece of filler between the 2 pieces. I have found leaf spring to be quite finnicky about welding to itself, but not as difficult to weld to other steels. I get wide peices of band strapping at work that i use. But i would think that any piece of sheet or thin flat bar would work, with in reason, i get some strap material that is high carbon and that i would not use just becuase it is so thin and easy to burn. 

[Latticino]

Agree with other posts: 

1. Leaf spring should be quenched in oil, not water.  Grain looks fine for the tool in question.
2. Temper after hardening.  Ideally up to straw color at the business end (after surface cleaning so you can see the oxide colors).  Shank should be well past that, to a dark blue. at least.  If you heat the entire piece during hardening you can "auto-temper" the bit by only quenching that section, letting the shank cool in air, and watching the "colors run" up to the edge.
3. Shank should fit securely in the hardy hole, but not bind.  It is a bit of a juggling act there.
4. If I recall correctly JLP has a wonderful video on forging a hot cut.  Some of the techniques there might be a little past your skill level right now, but still well worth a watch.
5. Also, how were you using it:  As the name suggests, the stock being cut needs to be hot (at least glowing).  Once it cools down to black, reheat before using the tool.  Also avoid hitting the top of the tool with your hammer face.  Once it gets thin enough, grab with two tongs (or the like) and bend it till it separates.

[Steve Sells]

leave the shank to blade part rounded, a sharp inner corner like that is a stress riser

[Rojo Pedro]

I would not harden it at all. If done right you can make your cut without hammer / tool contact. If you mess up, it is easy to dress the tool and less hammer damage. My .02$ 

[Will Brouwers]

Thank you to all the replies! This was very, very helpful!

I forgot to add that I tried to quench it the first time in motor oil (I know, not a recipe for success) but the edge kept deforming when I tried to mark things cold, so then I moved up to a water quench, and it still deformed. 

I am aware that leaf spring is not an ideal material, which is part of the reason why I decided to make this experiment and then learn from it, with the help of everyone here!

I should have added that I do have a hot cut from Ken's Custom Iron that is not hardened, and when I would try to score material cold, it would deform. My intent with this tool was to use it as a cold cut hardy, while also getting rid of some of the leaf spring I have. I should have thought more about it and shaped it like a cold cut hardy, instead of so thin like a hot cut.

I will definitely put all these comments and thoughts into use the next time I try something like this, and will most likely make the degree of the cutting edge more steep.

[Latticino]

Cold cuts and hot cuts are two different animals.  Honestly I have a cold cut hardy and never use it.  They need a very steep edge angle and hardening and tempering are much more critical than for hot cuts IMHO.  Even if you only use them for marking mild steel, the cold cut will deform over time.  That is why I use a cheap, flea market cold chisel for any markings of that sort; which is easy to regrind.

18 hours ago, Will Brouwers said:

hot cut hardy

 

[Will Brouwers]

Aha! Thank you!

[Irondragon Forge ClayWorks]

When using my hot cut hardy, I use a 3 pound brass hammer so as not to slip and hit the cutting edge with my cross peen hammer. If you have an arc welder you can weld the shank back on, regrind the cutting edge after heat treating it and save your first hardy.

I can't control the wind, all I can do is adjust my sails. ~ Semper Paratus

[George N. M.]

Just a comment on the use of a hardy for marking:  I have found it difficult to use a hardy for marking accurately on the bottom of a piece of steel, either hot or cold.  I have found it much easier to mark on the top either using a hand held chisel or and handled cutter.  If the piece is heavy enough to need to be cut hot I will mark it cold with a chisel and then finish the cut hot with the hardy tool.  Once you have a groove cut in cold you can feel it "click" onto the hardy tool when hot and you will know that your cut is in the correct position.

"By hammer and hand all arts do stand."