So today I wanted to make a drift for a hammer eye, but I don't have steel thick enough, and I really didn't want to upset the stuff I do have cuz it would take forever. I got some new coil spring last night, about 3/4" thick, so I decided to take 2 pieces about 14" long and form them to rectangles, and forge weld them together. One piece was 20" and the other was about 14" long, and when I was welding the end of the shorter piece on where the longer stock continued the bottom (longer) piece just fell off. I didn't burn it off, zero sparks, my first hammer blow made it just plain fall off. 

No problem, I can work with what I've got, so I continued, but then the end started just breaking apart. (See picture) I've never seen anything like this before, so thought I would ask and see if I was doing something wrong or maybe someone here has an idea. I know 100% that piece didn't burn off, (I've plenty of experience with that happening lol) it just plain fell off. It's only on 1 end, but this stuff is just falling apart on me. I got a picture of the weld ground down, it looks like it's fine to me.

I was using borax for flux and it looks like everything else took, it's just the steel at the one end coming apart

Was that piece quenched at all? I have had pieces of coil spring harden on me, and when I hit it the shock knocked a piece off.

I'm not sure, but the only thing that I can think would be that you did burn it. I know, I know, you insisted that you didn't, but if you were in direct sunlight (were you?) than there is a possibility that it burned without you being able to tell. For me I never (unless  I have to) forge weld mid-day, but try to save it for late evening when it starts getting darker so that I can see the true colors easier. Also, spring steel forge welds (and burns) at a lower temp than mild steel does, and so it could just be that you weren't use to it. If none of that is the case than my next guess would have to be just that the spring is full of fractures and cracks that you didn't notice until then. How cold were you working it? I would take a short section of the spring (like maybe 4 inches), straighten it out, and forge it in between a dull orange and a bright yellow. Take maybe about 4 heats and then observe if there are any cracks.

Just some (un-expert) thoughts.

                                                                                                                                                Littleblacksmith

It wasn't quenched at all, and it was a rather cloudy day today, so sunlight shouldn't have affected how hot I thought the steel was. When I'm forge welding I glance at the piece when I know it's close to temp, and turn the piece 180° every 5 seconds or so until I see just the surface start to bubble a little. Little to no sparks coming off during my welding. 

This is the first time I've forge welded anything but mild, but it's just odd that this one end just kinda wants to crumble under the hammer

stress fractures tend to grow when vibrated like from hammering...

also some alloys can "cottage cheese" when overheated.  Not sparking, not melted it just falls to pieces like cottage cheese.

I can see a stress fractures being the cause of the piece at the end just falling off, and I guess I must have overheated it welding like you suggest TP, I've never seen anything just crumble under the hammer like the last picture shows. I've never attempted a forge weld with any steel other than mild, so maybe this stuff doesn't like to be welded? I won't be trying another weld that long long with this either way, I'm going to grind the sides tomorrow to see if it's solid the whole way or just that one 6" spot I've already grinded 

The end grain picture looks just like the steel I have had red short.  The  cracks  in the end of the bar are just starting to  crumble.  First time you do it makes you say what just happened . JPH'S  first book has a section that tells which steels are red short. 

1 hour ago, Donniev said:

I've never attempted a forge weld with any steel other than mild, so maybe this stuff doesn't like to be welded?

Didn't we have an IFI thread about the difficulty of welding leaf spring to itself?

I was about to say that I thought I remembered discussing how hard it is to Forge weld 5160 to itself.

                                                                                                                  Littleblacksmith

 

3 minutes ago, littleblacksmith said:

I was about to say that I thought I remembered discussing how hard it is to Forge weld 5160 to itself.

                                                                                                                  Littleblacksmith

I can definitely agree with that!  I have had HC steel crumble on me before, too. never have figered out why. it seems like some pieces just don't like me to well.

I've had non farrier files do that.

Of course, we are all ignoring the elephant in the room, which is this:

WRONG STOCK FOR THE APPLICATION. 

The problem isn't the material itself.  A thick enough piece of spring steel would be fine, and lots of folks make their hammer eye drifts from torsion bar. No, the problem is the undersized stock and the complications that result from trying to weld it up into a useable size. 

Discussions of what may have gone wrong with steel and the world are fascinating from a technical point of view, but I think there is a really important lesson to be learned about the critical importance of picking the right steel for the job in the first place. 

JHCC has the right of it I think, but I've had exactly the same experience with 3/4" coil spring before.  That was in a coal forge and I wasn't trying to weld.  I have not had it happen in my propane forge.  My conclusion was/is that the steel got too hot in the coal forge.  Just like you said, it did not turn into a sparkler or show other symptoms we normally associate with burning.  It just broke off fairly cleanly with almost no force on it at all. After 2 or 3 attempts with pretty much the same results I decided to only use it in the propane forge and have not had a repeat incident with that spring since then.  In fact, the dagger I posted a few months ago was from that spring.