Can welding "un-anneal" steel?

[lastcowboy32]

I was working on an old piece of farm equipment last night.  The piece that I was working on was a plate welded on to patch some thinning metal.  The particular piece of machinery is about forty years old.  I've had it for two; so I have no idea when this plate was added.

I was using a large conical countersink to add a taper to two bolt holes in the same plate.  Explanation:  This particular application uses conical bolts and nuts, similar to lug nuts.

Anyway, I was countersinking both holes in the same plate.  In one hole, the countersink brought out thin pieces of shavings, similar to short drill filings that you would expect in steel.  When I removed the countersink, the taper was smooth and shiny.   In the other hole, the countersink chattered, no matter what I did.   Instead of shavings, it brought up little chips, similar to what I would expect when drilling cast iron.  The final taper was not very smooth, it had little tiny ridges all around it that required filing to smooth.

I'm assuming that this patch plate started as steel.  Could the person that welded it on have done something to one end of it that would essentially revert that section back to cast iron-like properties?

Is there a way for me to reverse this with my oxy-acetylene or oxy-propane torch?

Thanks?

Or perhaps it was done before it was even welded?  Maybe they used a torch to cut the piece for the patch and did the damage then?

[jlpservicesinc]

A picture of the repair area always helps with making and educated reply.. 

Of the cuff it's very hard to tell from a description. I can tell you if the repair was done later it was more than likely a different material than originally used..  

[lastcowboy32]

I understand about the picture.  I can't get that right now.  What I perhaps didn't explain completely is that both holes that I was countersinking were in the same piece of metal.  The whole piece of metal had been welded on as a patch to thicken a plate where two conical fasteners are seated.

The patch plate is a rectangle about 1-1/2" wide and 4" long.  It's about 1/8" thick.  The base metal underneath the patch platet that it's welded to is also about 1/8" thick.

There are two 1/2" diameter holes in this patch plate.  One near each end of it.   

In the same piece of metal (this patch plate), one hole drills/countersinks like cast iron.  The drill or countersink removes chips. The resulting countersink taper required filing and sanding so smooth.    The other hole drills/countersinks like steel.  The drill or countersink removes shavings.  The resulting countersink taper was smooth and shiny.

Both holes are in the same piece of metal.  The only thing that I can think of is that something during the process of cutting or welding that piece of metal accidentally heat treated one end of it.

[Latticino]

Cutting and welding certainly get steel up to a temperature where it can either get locally hardened or locally annealed, depending on the type of steel and the speed at which it is cooled off.  You might also want to consider that your countersink may have started out sharp, and in the process of use on the first hole got blunted.

[lastcowboy32]

I thought about that.  I actually did four holes.  Two on the other side of the assembly and two on this side.  I did the two on the other side first.  They were both smooth.

The "chippy" hole was the third one.  The countersink started acting weird.  It was chattering, throwing chips, etc.  

I pulled it out and tried the fourth hole.  No problem, nice and smooth.  I finished the fourth hole and went back to the third one.  (What I'm calling the "third" and "fourth" hole here in this reply are the ones that I've been talking about.  They are both in the same piece of patched on metal.)

I went back to the third hole, and the countersink chattered and chugged, throwing chips all of the way to the end of the process.

Just for another sanity check, I put it back into the fourth hole.  It was still smooth and throwing filings.

I'm thinking that the countersink is still OK.

[ThomasPowers]

Yes steel can "autoquench" after welding which can result in cracking in the HAZ and why preheats and post heats may be required.  Working with *old* farm equipment---say the 1930's---I have often run into cases where repairs were done with whatever was in the scrap pile and so two identical bars may have one out of high carbon steel and the other out of zilch carbon real wrought iron.

Yes drawing temper on an area that has hardened can be done with a torch. You will not anneal it but hopefully draw temper till it will be soft enough to drill.

[Kozzy]

Heat Affected Zone, HAZ from welding is actually a common issue.  Most people discover the problem when the locally hardened area cracks near the weld, usually in what was good metal.  It gets worse on some "farm" repairs where the person doing the work might have poured a little water on after welding so they could get on with the work more quickly.  

As TP mentioned, you can draw the temper if it's a problem---and I would do that any way at stress points that have already cracked and are being repaired.  However, I'd bet that most people just battle the issue a bit and consider the drill bit a bit sacrificial to the hard spot.  6 one way, half a dozen the other.

We actually had to go back to gas welding some critical stuff we make rather than TIG welding--the gas heats a bigger area so the metal doesn't self-quench right at the HAZ as much.  

[arkie]

cowboy, how about the rotating speed or alignment of your countersink bit?  I have found that there is a "sweet spot" when I make countersinks...too fast and it chatters and chips and too slow, it takes longer to ream out.  The chatter is more common with hand-held drills where the speed may vary or angle of attack changes than a drill press.  This is on stock steel (mild, stainless, high carbon, etc.) that has not been heated in any way since I've had it.

[lastcowboy32]

Kozzy, 

I do quite a bit of gas welding, and it IS really tempting to drop a piece in a bucket or something just to get on with with whatever work I'm doing.   I've had pieces be too hot to touch for what seems like eternity...especially when it's a piece of farm equipment, and you have stuff to do.  But I don't; because I don't want to make my welds as fragile as glass :-)

Arkie,

You're correct about the hand drill.  I was using a high quality Milwaukee drill with variable speed.  I tried varying the speed, pressure and angle of attack (a little..since my goal was to be perpendicular) on that one hole with no success.  In all of the other three holes that I made, I never had any problems.  The metal just shaved smoothly as I would expect.

[John McPherson]

The problem with dealing with unknown steels is all of the unknown variables introduced. It takes about 12% chromium to make steel stainless, but it makes it presence known above about 1%.

If there is enough chromium content or other alloying elements in the metal to make it air hardening in thin sections (less than 1 inch or 25mm) then yes, just welding nearby without a preheat, and letting it cool will cause hardening. Large sections of cold metal nearby acting as a heat sink, application of water or just a breeze on a cold day will make it worse, as will thinner sections, like your 1/8" plate.

The good news is that spot heating to bright red with a propane plumbers torch, and then slowing the cooling rate, can give you enough softening to drill or file, and make it less likely to break in the future.