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What type of steel is this?
4

What type of steel is this?

What type of steel is this?

(OP)
I've got a building built in 1993 that was built using (reportedly) recycled bridge steel (don't know when the bridge was built). We are doing a remodel and are having some trouble welding to the existing wide-flange beams (cracks have been visibly detected at all of the welds so far). I had them sample a couple of the flanges to have a chemical analysis done so we could try to determine exactly what type of steel we have and develop and weld procedure. It's a 3-story building and samples were taken from the bottom flanges of random beams at each level. After the analysis, the testing firm reported that there were actually two types of steel being used, 1018 and 1020 steel. Attached are the test results.

As you can see, there are a couple of other chemicals floating around in the steel sample as well. The testing firm, who is also acting as the CWI, tried a test weld by preheating the sample to 225 degrees F at approx 3" from the weld. During their bend test after welding, the sample cracked and broke in the preheated portion of the sample, not at the weld, and at not much of a bend angle either (see pic).

Are these results indicative of 1018 or 1020 steel? Has it been carburized and that's what is causing the welding difficulty and extra chemicals? My main issue is developing a weld procedure for the old steel. So far the testing firm has tried preheating and welding with a flux-core wire feed.

Any ideas?

RE: What type of steel is this?

The "other chemicals floating around" are not of concern. These are often termed "residual elements" and the levels observed are normal.

The Silicon content is interesting. It is normally in the 0.15-0.35% range, unless purposely kept low. It is usually kept low for weldability reasons, so this is not the issue, but it is interesting.

What is not reported in the levels of Vanadium (V), Titanium (Ti), Boron (B), or Columbium/Niobium (Cb/Nb--these are just different names for the same element). These are often used for added strength and their presence in the 0.03% level or higher could cause trouble (0.0005 for Boron). Just taking a wild guess, this is what you are dealing with.

rp

RE: What type of steel is this?

I agree with Redpicker about the residuals, it is the one's that aren't reported that are of concern. I don't see rock candy in the fractures, but would also take a good look at your aluminum content in case you are dealing with some aluminum nitride. Also considering the bridge material probably goes back a long time and melting/pouring methods weren't what they are today, you might consider residual gases as a cause for poor weldability.

RE: What type of steel is this?

(OP)
Thanks for your help, guys.

Redpicker, would Vanadium, Titanium etc normally be tested for in a chemical analysis or do you have to specifically test for each one?

Jwhit, I thought preheating the weld was in part to drive off any residual gases. Is this not the case? Also, I'm not familiar with aluminum nitride; why would it be present?

I should also tell you that the Rockwell B hardness tests for the two materials came back ranging from 70-83. Do you think we are still dealing with 1018 or 1020 steel? I've never heard of it being used for w-flange beams before.

RE: What type of steel is this?

You have a semi-killed, A-36 steel with large Fe/Mn sulfide type stringer inclusions, some of which are visible near the surface. Do take an Al analysis plus V and Nb.

RE: What type of steel is this?

The sulfur content could indicate you have inclusions resulting in laminations that are interfering with welding. I have seen this before in older steels.

RE: What type of steel is this?

When I was a steel mill metallurgist from '68 to '72, thinner thickness A-36 was commonly made semi-killed (.010 Si max.). We also downgraded materials into A-36 when ladle reactions (exothermic) occurred. A-36 was truly the "bottom of the barrel"; the only grade lower was "fence post". These materials would have multi-layers of sulfide stringer inclusions.

RE: What type of steel is this?

(OP)
I had assumed it was A36 during design and was pretty surprised when the test firm said it wasn't. Sounds like it still may be, but just on the crummy side, huh? Nice that we have slightly better than "fence post" steel holding this thing up. :)

As far as a plan of attack for getting a good weld on this, what would you recommend? Do we need the additional testing (Al, V and Nb) to figure this out?

I really appreciate your help, guys.

RE: What type of steel is this?

If you can remove a small sample for metallographic examination, this would confirm if you have stacked laminations. Welding will require more of a technique change to butter the surface with overlapping stringer beads to build a base for welding.

RE: What type of steel is this?

(OP)
The most critical welds I'm dealing with are 3/8" flare bevel welds to attach a 25' long HSS5x5 to the bottom of the bottom flange of the beams in several locations. The CWI has said that the stick welds of misc steel to these beams have looked acceptable, but these are all VI. They tried a line feed welder for the tubes and started running into trouble with cracks forming immediately. The CWI was skeptical of stick welding the tubes because they were worried of cracking of the welds due to starting and stopping while changing out sticks.

RE: What type of steel is this?

For best strength, you need to butter the flange with E7018 low hydrogen electrodes or other low hydrogen welding process with 2 layers prior to making the strength weld to the buttered layer.

RE: What type of steel is this?

You said in the first post that this was "re-cycled" bridge steel.

two things: I understand this means the bridge steel was taken down and rebuilt, NOT re-melted into new shapes, right?

If so, is there surface contamination and residuals on the weld areas (old salt, paint, oil/grease/tire rubber/atmospheric "gunk" maybe) that is fouling up your surface before and during welding? If you are grinding clean the weld areas, how "clean" are they, and how deep is the grinding "on average" and "in actual practice"? Just "shiny" may leave lost chemicals on the surface, smearing them into the metal pores.

RE: What type of steel is this?

(OP)
racookpe, yes. The bridge was disassembled and then the pieces used as-is. It's really an odd way to put a building together. Columns are not continuous, they stack on top of the girders. Most of the girders are 3 beams side by side and stitch welded together...weird. And yes, there is tons of welding that's already been done, nobody seems to know how though.

The steel all had lead paint on it that was removed by sand/water blasting. I'm not sure that they have done any grinding to try and clean the surface. I'll check and see.

RE: What type of steel is this?

This steel had been in service in a structure and may well have inherent residual stress that caused the cracking. The stresses may have been from installation as well as developed over time as the bridge was settling. I am assumming there were no preexisting cracks in the bend test sample (that would be a different discussion). I would take the steel to a heat treater to at least stress relieve if not anneal it before trying to use it in a repurposed application.

Of historical note: A36 was first published in 1960 and replaced ASTM A7, which was structural steel used for bridges and building. A7 may be your applicable spec depending on bridge age.

RE: What type of steel is this?

(OP)
Thanks, mrfailure, but I don't think it's A7. The chemical analysis doesn't match up. A7 looks like it has 10 times the amount of carbon and 200 times the chromium of my sample.

This building was built in 1993, so there won't be a possibility of any heat treating. No existing cracks in the steel have been found. Unfortunately, we have no idea when the steel was originally put into use.

RE: What type of steel is this?

Dirty secrets of the construction industry.
Let me know where that building is so I can put it on my list of structures never to enter.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

RE: What type of steel is this?

During the late '60s and early '70s Interstate 5 was being built in CA and a number of steel bridges came a tumbling down during or just after construction, usually at temperatures around 40F. We always breathed a major sigh of relief when we determined that the steel was not ours.

RE: What type of steel is this?

Quote (cookyp (OP))

Most of the girders are 3 beams side by side and stitch welded together...weird. And yes, there is tons of welding that's already been done, nobody seems to know how though.

The steel all had lead paint on it that was removed by sand/water blasting. I'm not sure that they have done any grinding to try and clean the surface. I'll check and see.

Hmmmn.

If a significant lead layer were still present after waterblasting - because I know shotblasting if done poorly will only drive paint articles deeper into the pores and scratches in old steel - would that lead screw up the welds towards the breakage you see? .. I've never gotten a satisfactory weld (GTAW especially) on old painted surfaces until they were ground "bright clean" (rough is OK, but they have to be clear metal. Whenever possible, even after paint removal, I specify a qualified SMAW (stick) weld because the greater heat burns through better.

Obviously, not all of the welds broke off. Is there any pattern to which ones broke and which ones were good... so far good, that is?

RE: What type of steel is this?

(OP)
So far, other than the 3 test samples I sent, only the wire feed welds have cracked. The stick welds (mostly puddle welds of deck and welding angles to the existing girders) have been fine based on a visual inspection. I was at the site yesterday and we decided to try out welding the tubes via stick welds and then testing them. I'll recommend that they grind the welding surface to a clear metal condition as well. Thanks for your ideas, everyone. I'll keep you posted.

RE: What type of steel is this?

"Only the wire feed welds have cracked." Solid wire (short circuiting transfer?) or flux cored wire (self shielded or gas shielded)? AWS classification?

RE: What type of steel is this?

(OP)
Flux core. I'm not sure about the AWS classification.

RE: What type of steel is this?

hmm, i'm not sure i'd use flux core to weld these. stick buttering is a good suggestion. I'd use 7018 the whole way if possible.

i feel that you could probably monkey with the weld geometry to prevent the weld from pulling across the rolling direction to prevent the suspect laminations from giving away.

surface preparation before welding (light grinding, wire wheeling) to remove oxides, dirt and other crap, and prep the joint for welding is key. if surface preparation is the issue, also check holding oven temperatures for low hydrogen stick electrodes (7018). if they're out of the oven four hours they're no good.

RE: What type of steel is this?

Self shielded E70T-4 or E70T-11 and their like should not be used for these welds.

RE: What type of steel is this?

(OP)
I'll pass this along. They are going to try a test weld tomorrow and MP test it. I'll let you know how it goes. Thanks!

RE: What type of steel is this?

(OP)
Weldstan/DeleteriousPhases,

Are you saying flux cored welding shouldn't be used for this type of welding, or you wouldn't use it knowing what we know now after all of the testing we did? The GC is going to ask for more time/money because he said he bid the job for wire feed welding. I don't want to screw him over, I would just like some input on whether wire feed should have ever been considered, and what's the actual time difference we are looking at.

For any of you still following, the MP test on the root weld and the final weld both passed and the SI is going to do a VI after 48 hours as well. The ended up grinding the surface of the steel and using E7018 electrodes. Thanks for all of your help on this one.

RE: What type of steel is this?

I have not stated that FCAW should not be used; only the self shielded wires as stated. These wires and similar have not been able to consistently pass bend tests at ambient temperatures up to nearly 100F. They have very poor toughness. They are not low hydrogen filler metals.

RE: What type of steel is this?

(OP)
Gotcha. What about the speed of the welding? The GC now wants 5x more $$ for the welding portion of this work. This seems high to me, but I'm not a welder.

RE: What type of steel is this?

What process is he now using? SMAW? In the field, they will be lucky to get deposition rates greater than 1 to 1.5 lbs per hour with SMAW and E7018 electrodes versus up to 5 lbs per hour with FCAW with E71T-1 electrodes.

RE: What type of steel is this?

1.5 pounds per hour in the field for SMAW (Stick)? Should be 1 rod per minute once they actually get started in place, even in the field. Allow 3/4 working rate though.

Figure a 7:00 am "payday start. If on a bridge scaffolding or deck, "maybe" 8:30 when the first rod is struck.

RE: What type of steel is this?

With proper supervision, I would agree that greater productivity can be obtained with low hydrogen SMAW; however, left on their own, don't count on much more than was stated. Going to lunch - 1/2 hour to lunch area and 1/2 hour back. Getting more electrode from Rod Room - 1/2 hour going and coming. Smoke breaks. BSing intervals, interpass cleaning time, etc., etc.

RE: What type of steel is this?

(OP)
Ha ha! All true.

They started with FCAW and the welds were visibly cracked. So, they took a couple of coupons, welded them up using the same process (but they preheated this time) and the welds failed the bend test. So, now I've had them grind the existing weld surface clean and weld the tubes up with low hydrogen SMAW. This way passed the MP tests and the VI. Now the GC is asking for more money because he said he bid FCAW and SMAW is going to take a lot longer. Our specs say weld per AWS D1.1 AND use E70 low hydrogen electrodes so I think we are covered on that.

Does anyone know if the procedure for FCAW overhead is prequalified? I didn't think it was.

RE: What type of steel is this?

FCAW procedures can be "prequalified" if Constant Voltage power supplies are used.

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