Hardening problem

[OSUWE2010]

We have a very large built up girders that had some large holes drilled into the flanges which are 3" plates, A572, Gr. 50 steel. The problem we are running into is that these holes that were drilled into the flanges were too big and revised to a smaller size. So now after fit up of the girder, including pre heating of the flange and web for welding, we are filling up the holes and when we try to re-drill the hole our drill bit is unable to do so. Any ideas why this is occuring and what can we do to prevent this or even fix it? Our guess would be hardening has occured through the preheating process along with welding of the web to flange with sub arc, and now after filling the hole even more heating up and cooling down has occured. If anyone has any ideas let me know. Thanks everyone!

 

[Metalguy]

Sounds like you have some untempered martensite there, which could be as hard as Rc40 or so. The relatively high amount of Mn is the culprit.

A sharp cobalt-steel drill bit should be able to drill it. How high was the preheat?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[metengr]

I would also suspect the filler metal strength. Agree with the comment above.

 

[bhollands]

If I am understanding you correctly; the holes were drilled too large. The holes were welded up and now you are trying to drill through the weld for a smaller hole. You also did some other welding of a web to the flange.

What filler metal did you use and what temperature did you preheat to?

Bob

 

[OSUWE2010]

The entire story now comes down to this...the hole patterns for this were drilled and now are being changed. So we are needing to plug all of the holes, 3" wide through 3" plate. Once these holes are plugged and fixed, a new pattern will be set down on these plates and some holes might be in the same place, some might be moved by 1/4", 1/2", and so on. But the holes will be drilled in the field and we don't want them to run into a problem drilling through this thick of a plate through the filler metal. Hopefully that makes sense. What they are talking about doing is possibly finding a sfter filler metal that still falls in the E70 electrode class. They want to be able to use the drills and drill bits they have in the field, but with the normal wire, E71T-1, the bits don't seem to be able to drill through the weld metal very well at all.

 

[Metalguy]

Again, what was the preheat temp?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[metengr]

OSUWE2010;
Just an observation and take this advice for what it is worth – nothing. I have a fundamental problem with your approach because you are letting tooling dictate a solution to your problem. First - you are welding on HSLA structural steel which requires a qualified welding procedure. Preheat requirements should have been spelled out. Presuming you have a qualified welding procedure, modifying the filler metal to accommodate a "softer" filler metal is not going to happen.
Suck it up and use the appropriate drill bits or tooling for drilling correctly placed holes. I have been down this path before and this is the correct approach. Attempting to modify welding on critical structural members to allow use of existing drill bits makes no sense. Local PWHT may adversely affect the base metal properties of the HSLA steel.

 

[OSUWE2010]

The preheat temp was 225*F, for 3" plate

 

[OSUWE2010]

Metengr:
I couldn't agree more with what you said, but the man with the money makes the rules and my boss wanted to go in a different direction. I don't agree with it but I figured i'd try to get the informtation I could about other routes to take. But thank you for your advice.

 

[mk1979]

My friend your problem is common and happened likely in this type of steel A372,according the high Mn content 1.3-1.6,means a hard cementite formed.but you can make annealing in order to relief the structure after welding,then make a machining that you,d like(drilling),then make normalizing to obtain an uniform structure,with fine grains.hope to be useful