Welding AISI 4145 1

[teb1]

I have a herringbone type gear rim that has multiple crack locations on only one side. The cracks are initiating at the pitchline of the gear tooth and severing the gear's rim. The gear was originally a fabrication. The rim is 4145 forging while the interior support plates are A-36. The root of the tooth to the inside diameter of the rim is approximately 5".

I am assuming that the gear was fabricated, heat treated to thru harden the rim to a Brinnel of 346 and then hobbed. The carbon equivalenent of the material is .958.

I am not going to try to match the original tensile strength of the rim or replace the broken teeth. My objective is to repair the actual cracks in the rim to give my client approixmately 4-5 weeks run time should his current gear set fail.

My current plan is to use a "temper bead" method of welding utilizing LH7018 H4 electrodes. The weld locations will be preheated to approximately 400F and maintained there while the welding is being performed. I have gone so far as to rent Metalax equipment to minimize distortion and stress relieve the part since I don't want to try raise the temperature of the part beyond 800F for fear of loosing the temper in the remaining teeth or causing some type of temper embrittlement.

I would appreciate any comments or suggestions regarding this proposed procedure. We are still in the process of air arc gouging and then grinding the surfaces of the bevels for welding. I am a couple of days away from starting to weld.

Thanks,

Tommy

 

[metengr]

teb1;
First –off, I would perform a complete wet fluorescent MT (nondestructive test) of the gear to evaluate the extent of cracks. Have you performed a wet fluorescent magnetic particle test (wet MT) of the gear teeth? You might be surprised that that are more cracks.


Why are you air arc gouging? The heat from this process will surely adversely affect the bulk properties of the gear material. You had me when you mentioned the temper bead process but lost me with air arc gouging.

 

[teb1]

Metengr

The rim has been dye checked. There are four (4) main crack locations. There is serious spauling on the pitch line of the individual teeth on one side of the herring bone. There is no doubt serious sub cracking under the spauling. My problem is not why this gear failed, or any sub critical length cracks, those are problems for another day. My problem is achieving a weld in this rim so that it won't rip apart if the gear set in service fails before the new gear set arrives. Hopefully, this welded rim will never see service.

Having said that.

The reason we are air arc gouging is because that is the most expediant way to achieve a full penetration weld bevel in 4.75" thick material. We are gouging from the back side of the rim and from the tooth side of the rim. Once the bevels are gouged we are going hand grind with carbide burrs to remove approximately 1/8" more material from the surface of the bevels.

This piece weighs approximately 100,000lbs. It is a very large heat sink. The heat input is very localized and disipates very quickly due to the cold air which is no doubt quenching the material in the immediate path of the arc gouge.

Please continue with your thoughts!

Thanks,

Tommy

 

[metengr]

Tommy;
If you have or can get access to portable hardness testing equipment, I would run some hardness checks to assure the rim material adjacent to and away from the excavations has not been affected from arc gouging. You might need to grind more like 3/16" along the entire side walls of each excavation to remove additional heat affected material
(arc gouging with no preheat on this hardenable steel with 0.45% C will provide conditions for maximum cooling and hardening, and 1/8” might not be enough to remove heat affected material). If you had arc gouged with a local preheat, 1/8” would do it.


Have you ever welded with the temper bead technique? Deposition of the butter layer and second weld layer are critical. All weld layers must remain on top of the butter layer - no contact with base metal. The interpass temperature MUST be monitored and kept below 800 deg F. This is critical to avoid over-tempering the rim material away from the weld regions.

Use electric resistance for preheat, NOT torches, and soak the entire rim at 400 deg F for 30 minutes at temperature, prior to welding.

Use 3/32" diameter E7018 H4 rod or you can even use E8018 B2 H4 weld rod for the butter layer with tight stringer beads using about a 50% bead overlap. Deposit the second weld layer entirely on top of the butter layer with 1/8" diameter rod for increased heat input. Use tight stringer with about a 50% bead overlap. Follow the same for the 3rd layer. When the 3rd layer is completed, you can even switch to a 5/32" diameter weld rod using a conventional welding technique.

Keep the rim wrapped and stagger the temper weld locations (opposite each other) to reduce distortion. When the excavation is filled add 1/8” weld reinforcement, which will be subsequently removed to expose tempered metal. After blend grinding is completed, NDT.

 

[teb1]

Thanks, Metengr,

I can tell you from chipping this material after the arc gouging that it is hard!!! A little more gringing is going to be necessary in order to just smooth out the contours in the weld bevel geometry.

We are going to be using electric thermal blankets for the preheat and to maintain the interpass temperatures.

Yes, I have used the "temper bead" method before. The bevels for this particular geometry are approximately 2 3/8" deep from each side with a 1/4" radius (from a 1/2" diameter carbide burr.) I am planning on having two welders working opposite each other at one location. All of this welding will be on a diagonal and out of position. Lots of fun!!!

How much more crack sensitive will the 8018 be as opposed to the 7018 or will it be less? My metallurgy lab warned me that the stronger the electrode the more likely the possiblity of cracking.

Have you had any experience with the Metalax equipment from Bonal?

Thanks again.

Tommy

 

[metengr]

Tommy;
I was looking at it from a closer match to the rim material yield and tensile strengths in service. Your weld excavations are not minor, in my opinion, these are considered major structural weld repairs. If this weld repaired gear goes into service you are going to have significant torsional and shear stresses acting on the rim, so that is the reason for my filler metal suggestion. Certainly, a lower strength or undermatched filler metal can be used if you feel more comfortable.

We have performed many temper bead weld repairs on our 1-2.25% Cr- ½-1%Mo boiler components using E8018 B2 weld rod with no problems. Since you are using low hydrogen electrodes, I don't believe the use of 80XX versus 70XX is going to increase susceptibility to delayed cracking or cracking in the base metal due to ductility concerns
despite the fact that E8018 B2 weld metal exhibits slightly lower ductility (19% min) in comparison to E7018 weld metal (24% min).

Reheat cracking should not a real concern either because you are remaining below 1000 deg F (no PWHT) using the temper bead method and there is no Vanadium in the base metal. Typically, for low alloy steels, reheat cracking is driven by Cr and Mo alloy additions and to a greater extent by V.

Good Luck. Let us know how it turns out.

 

[metengr]

Tommy;
[Forgot to answer your question below;
quote]Have you had any experience with the Metalax equipment from Bonal? [/quote]

I did a quick review of the literature. I am not a subscriber nor a believer to relieving of weld residual stresses using this method. Thermal methods work best.

 

[unclesyd]

Have you considered using an electrode like Allstate 275 from ESAB. This electrode is the workhorse in our fab shop for repair work especially on alloy steels. This eliminates some potential cracking problems with the weld metal.

http://www.esabna.com/EUWeb/AS_handbook/596as9_4.htm

In the hands of one well versed in the art, ArcAir gouging has never been problem with alloy steel.

I have to second metengr's suggestion of a Wet MT inspection. My experience with current crop of PT materials leave a lot to desired.

 

[metengr]

unclesyd;
I concur that Arc gouging using proper technique and local preheat (if required) is fine. The problem I see in the field is that there are fewer and fewer experienced boilermakers from our local hall that have demonstrated proper technique. I have seen careless applications of arc gouging that I have to go back and perform additional weld repair.

 

[teb1]

Unclesyd,

Can you give me a quick synopsis of why Allstate 275 would be superior to 7018 or 8018?

I am running an FEA of the gear rim assembly right now. If the normal operating stresses in the rim are alarmingly high I will have to look at the possibility of using a higher strength electrode.

Thanks to both of you for your comments and help.

Tommy

 

[unclesyd]

I'm going to get in trouble with a lot of people for saying this, but here goes. We used Allstate 275 as a universal welding electrode for any unknown alloys or dissimilar metals. We had process components made from 1035, 4140-4150, AH5, D2, H11 that sometimes required expedient weld repair to prevent unscheduled outages and 275 was the electrode of choice. We also used it for routine repair of the above components.

Allstate 275 is essentially 312 SS, with an excellent flux, and it is like several other maintenance electrodes on the market. 275 was one of the first on the market so it was picked up and kept after trying several other late comers.

There is no problem with 7018 for welding the low alloys we have always preferred 275 when there was any question of the welding conditions or parameters. Though 275 is Austenitic it's work hardening properties are at times a benefit.

Allstate 275 or slight variations of it was the electrode of choice by the people who repair large backup dies for many years.

 

[unclesyd]

Flood Welding
I don't think this will be applicable as your part is so large, but would be something you may consider in the future for large weld repairs.

http://www.mpdwelding.com/floodwelding.htm

http://www.cor-met.com/Equipment.htm

 

[macmil]

About 26 years ago i was involved in a large gear repair by welding~~ actually the experts came in and pushed me aside and after about 3 weeks the welds were sound but the shrinkage from the welds completely distorted the pitch of the affected teeth. If it's not too late, I would use splice plates ~ mechanical~ to maintain your pitch.
just so you know the end of the story, a gear to be used on another mill ( 3700 hp ) was pressed into use, a replacement was ordered, and the welded one was sent out for recutting as a spare.

 

[teb1]

To all that responded to the above thread, thanks for the advice.

I happy to report that we (I and two of my techicians) finished the welding of the gear rim last week. There turned out to be four locations that required extensive repairs.

As pointed out there was a significant difference in the hardness of the surface of the air arc gouged weld bevels and the parent material. Grinding with stones to remove the "glaze" and then with carbide burrs removed the hard surface material. This required removing approximately 1/8" of material from the bevel surfaces. The bevels were approximately 2 1/2" deep from each side.

The first weld pass was the most difficult because of the crack edge left for the first pass. The magnetic north south pole effect of the crack played havoc with the arc until the two edges were completely joined.

It took approximately 350 pounds of electodes to fill up the bevels. The preheat was maintained at 380 degreesF for the duration of the project. The proper application of the "temper bead" method of welding a groove like this required extreme patience.

The final dail indicator run out readings showed that machined areas adjacent to the weld repairs had "sucked" in approximately 0.007", the total runnout for this gear after we finished was +.007 to -.007".

Our inhouse FEA of this gear assmebly indicated that the rim stresses were well within the limits for electrodes that we chose to use.

Again,

Thanks and a Merry Christmas to you all!

Tommy Breaux, Mech. Eng.
President
Engineered Casting Repair Services, Inc./ METALOCK CORP

http://www.Casting-Repairs.com