Firstly, I was not sure where to put this, so I apologize if it's in the wrong section. 

Now, a brief story... I have never been very good at forge welding, most definitely due to lack of experience, but I made an ax the other day by welding a few sections of leaf spring together after wrapping it around a pipe for the eye. I thought I was starting to get it down.... 

But i digress, a friend of mine asked me to make him a Hardie cut off tool, and I only have some mild steel thick enough to fit into a Hardie hole, just needs to be made square. So I figured I would forge weld a section of tool steel onto the top for the actual cutting section. I cleaned both pieces and tack welded them. I got three heats in on the piece, brushing and fluxing in between each, and before the first. It felt good under the hammer. All seemed well. So I began shaping the tool, and they split apart. Not immediately, but about two or three heats into shaping it. So, I rushed back to the grinder and cleaned both pieces up again, and re-tack welded them. Three more heats, just as described above, and they split on me yet again. I am fairly confident each heat was at the correct temperature. Both pieces were relatively close in size, so they heated pretty evenly as well. Unfortunately, the tool steel is not large enough to use by itself though. Only on the third heat of the first attempt did I burn the steel slightly, very few sparks flying though. I made very sure to turn my blower slowly to reduce excess oxygen that could get to the steel, but just fast enough to get to welding temp. I am scratching my head wondering exactly what I did wrong. I have read about people welding mild steel and tool steel before, but are the dissimilar steels that hard to stick together? Did that one burn affect it in a way I am unaware of? Is there some detail I am overlooking? I do not know what I did wrong, and my confidence is a bit shaken, so any help would be appreciated. Apologies for the long post, and thanks in advance for your time.

Will W

Make sure both peices are brought up to heat evenly and slowly, make it is adequately fluxed, and make sure to work it over until you can't see the line between the metals.
 If that doesn't fix your problem you might be using a tool steel with a lot of chromium which hates welding.

Some alloys are tough to weld; some are easy what alloy did you use?

What kind of weld was it? Lap, butt, cleft, etc?  As some alloys move a lot differently that others welding two of them together can put a lot of stress on the weld as you change the cross section substantially.

Were you forging it very hot or very cold or very medium?

The thicker the material, the harder you must hit it to get the weld. Dinky blows on thick stock doesn't get it.

Iron Poet, I did all that, and still no success. The part that really bugs me is the line between the two was gone. Seemed solid. I am not positive on the amount of chromium, though I have made several knives from the same steel, and they don't seem to be corrosion resistant like would be expected with chromium. Would low levels make a difference? I used to weld high chromium stainless steel (tig welding) quite a bit, and I know that is a pain. 

Frank Turley, I thought I was hitting it quite hard. Not ridiculously hard, as I did not want to bend the pieces, but as it felt more and more solid, I increased the power behind each hit. 

ThomasPowers, unfortunately I don't know the exact alloy. It was crowbar steel, if that helps. It was just a butt weld though. I thought, only after the fact, that I should have tried to scarf it somehow. Exactly what would be best though, I'm not sure. But after the welds, i was forging it pretty medium, I suppose. A nice orange-ish glow. 

The question I'd be asking myself, ... is WHY forge weld ?

Why attempt to employ a process developed for use with wrought iron, to join modern steel of unknown alloy ?

Sure, ... I "get" that you'd like to perform this process, in this fashion.

But perhaps, it's just a bad idea.

----------------------------------------------------

I'm not singling out this particular post.

This question of employing the wrong process, in order to simulate an outcome, ... troubles my Pragmatic nature.

 

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I understand what you mean. The same thought ran through my head, only after the attempt. That is just what seemed like the best method at the time. Based on the amount of trouble it has given me, I think upsetting the tool steel to fit the Hardie may be a better solution. This will likely be my next attempt. Even when you fail, there is always something to learn i suppose. Thank you to everybody for the input. It is greatly appreciated. 

Failing is when you learn the most. Just make sure you're paying attention and you'll see where you failed and hopefully be able to figure out a solution.

 

Unfortunately, I have learned that lesson the hard way numerous times, as many definitely have, and I am bound to do it a whole lot more. If anything, you figure out how something does not work. Haha. 

If you think chrome is the problem then finish cleaning the joint faces with wet sand paper and oil, the oil will prevent contact with the air and the chrome won't oxidize. Forge welding flux will stick to the oil even. 

What kind of SS were you tig welding? I loved tig welding SS, it made the prettiest beads I've ever run. The stuff flows like a canoe's wake, smooth, even and pretty.

Welding Ti is a whole nother story depending a LOT on the alloy.

Frosty The Lucky.

Frosty, I would have figured the oil would inhibit the flux. Good to know that it helps. I may try that in the future. 

I agree completely. The nice gold, blues, and purples you can get is just remarkable. When I was learning how to tig weld stainless though, I can't tell you how many of  my welds just came out black haha. 

Most of what I did was 4140 though. Basic stuff. I've done some 440A (I think that's what is was) on kitchen equipment, and some 316 (again, I am pretty sure) in pipe welding. Numerous welds on unknown alloys as well. I've welded some chrom-moly as well, on race car frames, and in my experience, that stuff will never cooperate haha. 

Will W.  I'm far from an expert but reading through your posts here I saw you mentioned that you didn't scarf. 

Quite a few of my references and instructors agree that getting the surfaces to meet such that flux, etc. gets ejected is critical to avoiding inclusions. 

 

They were just butted on top of each other. I hadn't even considered the possibility that a large inclusion formed in the center. Now that you mention it, it seems likely. The outer edges probably welded up, and then broke when i applied the pressure of shaping it. Thanks for writing that. Perhaps i need to think these plans through a little more haha. I ended up just taking some tool steel and upsetting it to fit the hardie, so in the end, problem solved.