Identify and weld a type of steel?

Date 10-18-2001 20:43

I would guess you are dealing with cast steel. We repair all types of equipment for ourselves and others, from clam shell buckets to things people have never seen before and likely never will again. Unless the specific type of steel is known, we usually use E7018 low- hydrogen and E71T-1 flux-cored electrodes. We preheat to about 225 degrees F as a minimum and bring up the temp gradually. This has worked well for us.
Hope this helps,
CHGuilford

By don

Date 10-19-2001 01:26

Great reply. Just one question. Do you post heat after the weld and attempt to cool at a slower rate or allow to cool at a normal rate? Just so I know for future reference.

By RonG

Date 10-19-2001 11:58

I do not belive he intended to write a WPS for the man just give him a little insight.

Not knowing the material or its mass, what kind of equipment and the conditions makes it tough to guess the best things to do.

Haveing worked with heavy earth moveing equipment more many years, I would have guessed the same and recomended 7018 also. From the discription I would bet a PWHT would not make a big difference.

By don

Date 10-19-2001 19:03

Sorry guys, my intention was not to ask for code specs but just to find out if you experienced problems with normal cooling rate of the Heat Affected Zone on cast steels. I have only welded on them twice, both with 7018. The first time a crack developed, about two months later, about a quarter inch off the weld running parellel with the weld face. I only preheated that time. It was on a dozer blade. The second time I preheated to 250 deg. welded and cooled it as slowly as I could. No problems 2 years later.

By Nate Date 10-19-2001 02:13

Thanks for the advice. Have you ever used 11018 electrodes? I have never heard of them until yesterday. One guy suggested those. I'm also interested in the answers to Don's questions. Nate

By RonG

Date 10-19-2001 12:04

What is the function of the broken piece? How big is?

If the piece has enough mass it will tend to cool rapidly. Will the repair be done in place or can the part be removed.

The reason I ask is there is the possiblity of doing as much harm as good with a lot of heat, not just to the part you are repairing.

By CHGuilford (****)

Date 10-19-2001 15:04

We haven't worked on anything that needed Post Weld Heat Treatment but I'm sure there could be some applications where that may be required. It just isn't usually required in what we've run into. However, I do need to say that wherever possible we contact the manufacturer for their repair procedures and follow them carefully. Most manufacturers will provide the info if you ask.

My advice for 7018 is assuming a steel casting because that is what you usually will be dealing with in arms or main structural elements on heavy equipment. Those are normally similar to structural steel (A36, A572-50, etc.).

You might run into some steels where 8018 is a better strength match but usually undermatching w/7018 will work fine when you aren't sure what you have.

11018 electrodes are used for some some types of hardened steel but I wouldn't use them on main elements unless the manufacturer said so. You could be overmatching the filler metal / base metal if you do and that could lead to further breakage. Cutting edges and wear plates are where you might need 11018 and usually those are bolted not welded to the the machine. The last time we used 11018 electrodes was special application on a lattice boom for our own equipment per a repair procedure. The manufacturer came to our shop to inspect and certify the boom. (I should mention that we do not repair cranes or booms on any but our own equipment for liability reasons.)

On most repairs we go with a 225 deg F preheat because there has been grease, and oil all over the equipment and it's difficult to be sure all of it has been removed. But we don't overdo it either. As mentioned in another post, too much heat or in the wrong places can cause problems. And if you do have hardened parts near the heating you could ruin them.

These are just some general guidelines that we have used in our situation. I really can't give specific answers without knowing more about the conditions. I will say that if life and limb are at stake in using your equipment, by all means contact the manufacturer if you can and/or a qualified repair facility near you. And remember that something made your part break. Probably fatigue and/or overloading, but if it happened once it's going to happen again eventually. (That's the business side of my comments. The personal side is- If I owned the rig, I'd just go with 7018)

Hope all works out for you
CHGuilford

By CHGuilford (****)

Date 10-19-2001 15:11

Forgot to answer the other question. If the repairs are in a critical area like around a knuckle or a pivot we wrap fire blankets around them to slow the cooling. Otherwise we just allow them to air cool.
CHGuilford

By Nate Date 10-20-2001 00:30

Rather than reply to each person, I'll try to give the info I know for everyone. The piece is on the back of an older 4500 Ford backhoe. It was made in Copenhagen, Denmark according to the id. plate. So the local dealer doesn't have a clue. It's the big bracket that connects the main boom to the hydraulic swing motor. It's 2 pieces of 3/4" plate with a boxed in gusset inside. It has 1 1/2" holes on top, forward and rear and 2" holes on bottom, forward and rear. One side pinned to the hydraulic motor and the other side pinned to the boom and lift cylinder. It's a bit of a wedge shape looking from the side and about 16" wide and 21" tall. The motor holes were just machined in the plate, no bushings. The cylinder hole has bushings and the boom hole has a piece of round tubing welded in between with a bushing inside.

I hope maybe you can picture it. Having said all that. About a year ago I had some new pins and bushings made for the egg shaped holes at the motor side. I cut the plate and welded the bushings in place with 7018. It worked ok until last week, but the hoe isn't used that much. I hit a big rock while digging a hole and broke the bottom bushings out. This is where the plate broke below the bushings. About 1" broke off both sides on the bottom front. While assessing the damage, I noticed most of the weld cracked around the bushings. It did the same on one of the top bushings, the other looks fine. At the time I welded the bushings, I thought it was just steel plate bacause of the torch marks and I was able to cut it. Now I get about as many opinions as people I ask around this area.

I was gonna cut off the front portion of the plates and weld a new piece on, but today I cleaned everything up and v-ed it all out and put everything in place to be welded. I have only about 2/3rds weld area around the bottom bushings where most of the force is. I have the pieces that broke off, but they are only about 1" thick.

Man this is getting long, so I'll stop for now. I really appreciate all the help. I have the 7018 rods on hand, so unless you think otherwise, I go with them. Let me know if I've confused more.

By - Date 10-19-2001 21:46

If it was cast iron, it would not cut easily with a torch. I therefore would draw the conclusion that it was a steel of some sort. Often steels can also break in a "grainy texture", especially if the fracture was a brittle fracture of a material that had a coarse grain structure. If your material is a cast steel, it could easily have a coarse grain if there was no heat treatment following the casting operation.

A brittle fracture would typically occur if the component experienced an impact load or if it was used while very cold.

If at all possible, try to have some hardness tests done on the component. They are easy to perform, and anybody with the right equipment would not charge you too much for this test. The results would quickly tell you if the material was an ordinary low carbon steel or something a bit more exotic.

Regards
Niekie

By Sean

Date 10-20-2001 02:59

It really is not prudent to weld any materials unless you know what they are. There is a reason there are thousands of grades of ferrous metals. By welding a material with the wrong electrode you will generally create more problems for yourself. In the long run it will be worth your time to identify the material. Since you can't get any mat'l info from the OEM, take some drillings from plate (make sure the area you take the drillings from is clean) and have them analyzed. Then do some hardness testing. From the chem analysis and hardness testing you will have an idea of the material's weldability and get a better idea of what electrode to use. Considering the replacement costs of equipment, the cost to do this type of testing is quite minimal.

The other possibility (assuming that its a financially viable alternative), is getting metallurgist or welding engineer involved to do the mat'l id and develop a repair procedure. Good luck with the repair.

Regards,
Sean