Welding Hardened 8620

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What would you suggest we use to weld to a 8620 planetary ring gear?We have an OEM piece that we are trying to strengthening due to the welds cracking. We have tried using the ER70 material that we have, but it doesn't work that well.Attach is the picture of the piece, you can see the one weld is ER70, with others being somewhat of a mystery. Although I had a material composition done on the weld and the properties are listed.  On the mystery weld you can see that it was not preheat due to the heat circles around the weld.The chemical composition of the mystery weld is as follows,%WTC = .172Mn = 1.334P =.020S = .012Si = .411Cr = .411Ni = .037Mo = .062Cu = .146V = .011Co = .008Al = .021B = .0013 Attached Images
Reply:I suspect your planetary gear may be carburized or had some other case hardening treatment; as this is common with gears.If this is true, welding this will prove very difficult as the surface of the gear is likely to be extremely high in carbon and/or nitrogen.8620 is weldable, however welding is normally done before the part surface is hardened.  Rather than ER70 TIG rod, I suggest you step up to a high strength filler metal.  8620 can have an ultimate tensile strength as high as 125KSI, when heat treated.  You need a filler metal with comparable mechanical properties.  ER70, with 70KSI tensile strength is severely undermatched for this material.I suggest you consult with the OEM and find out if this gear has had any carburizing, nitriding, carbo-nitriding, or other form of surface hardening.  You also need to know if the gear was quenched and tempered to a higher strength as well.  This will tell you what strength filler metal is best.If the gear is also case hardened, I don't have any good suggestions for welding.  You may get lucky with some high temp pre-heat(~500F) and slow cool down(100F per hour or slower) after welding.  But if the part is case hardened, as I suspect, you'll likely alter the case depth and surface hardness of the part during welding and post-weld heat treatment.  Even if your welds succeed, you may find that the durability of the gear has been compromised.IF you can't get any info from the OEM, here's another course of action.  Since you've demonstrated that you have acess to some analytical tools, and if it's worth the cost, I suggest you have someone perform a micro-hardness test on the surface of the gear.  Micro vickers or knoop hardness can measure the hardness of any surface heat treatment.  It can be done non-destructively, so the gear will be unaffected by the test.  A before and after welding test can reveal if the part is case hardened, and if the welding and PWHT have had any affect on the case properties.  A macro hardness test, like a rockwell test, on a non-critical location on the part may tell you about the core material's tensile strength.  Hardness does correllate to strength, and if info from the OEM is unavailable, the rockwell (C scale) hardness test will most likely punch through any surface hardening, and give you some clue as to the gear's core strength.  This will guide your selection of filler metal for welding.If I understand your original post, you're trying to strengthen this part for your own purposes.  If so, and if it's feasible, my best suggestion to you get a hold of one of these gears before it has been hardened; make your modifications, and then send it out for the appropriate surface hardening treatment.  This will garantee that the gear has the expected durability, and you should have no problems welding it.It's not a guarantee of success but depending on what the solution is worth, this should steer you in the right direction...Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Thanks for all the detailed info.I don't think the part is carburized before/after or heat treated after being welded.  In the picture at the very top you can see the raised boss section where the splines fit onto a shaft.  You can seel localized heating there, I'm assuming it would be flame hardened.So far my luck with the big welding suppliers has been disappointing.  ESAB, Lincoln have provide very little help.
Reply:Is this a one-time job, as from a machine in your shop which has once, or occasionally broken down, or is it a 'defective' part you often see in products you repair, as for example, automobile transmissions? Is information not available from the part manufacturer?I'm no engineer and am basing the following on skimpy details and no research, but see that your new weld appears cold and has not bonded well to the original material. The original welds did anneal the surrounding metal.I would look at those welds with a magnifying glass to determine where they broke; whether in the filler material or in the base metal. Maybe a continuous bead rather than multiple 'spot' welds would not concentrate stresses so preclude fracture.Maybe using a more ductile material like stainless steel or monel would help.  If a high C content in the base metal would cause poor bonding with that, a post-welding heat treat might help, or perhaps a higher nickel, lower chromium alloy.  Maybe a continuous weld with a high-strength, low-hydrogen material like E11018 or its wire counterpart might be better, after a pre-weld anneal. Can you test and compare different procedures like this?I'm surprised none of the better experts here haven't jumped all over this one yet (ADab excepted).
Reply:It is a part from an automotive transmission, the piece is quite common to fracture.  Unfortunately no information is available from the piece manufacturer, as they are unknown.Under microscope the welds them selvesbroke not the base material.  We are currently investiagting a continous bead around the unit.
Reply:Who makes the transmission or the vehicle it's from? Is this from an older or 'obsolete' vehicle?
Reply:Its a Chrysler transmisson from a Ram pickup.Last edited by diesel59; 03-23-2009 at 01:31 PM.
Reply:As I mentioned before, micro-hardness testing will tell you if the part has been surface hardened.  The heat tint you're referring to could be from flame hardening.  It could also be from induction hardening, although I'm not sure this is the case.  If this is from a mass produced vehicle transmission, then I'll bet you a cup of coffee that the part is either heat treated and/or case hardened.  Transmission gears take an awful pounding, especially in manual transmissions.  They simply have to be hardened in order to meet the typical car manufacturer's powertrain warranty.I'll second the questions that oldiron asked... Originally Posted by diesel59Thanks for all the detailed info.I don't think the part is carburized before/after or heat treated after being welded.  In the picture at the very top you can see the raised boss section where the splines fit onto a shaft.  You can seel localized heating there, I'm assuming it would be flame hardened.So far my luck with the big welding suppliers has been disappointing.  ESAB, Lincoln have provide very little help.
Reply:Whoops, I was posting at the same time as you replied.  Apologies for repeating questions you already answered.Again,  I'm not surprised the welds broke, if they were made with ER70 filler metal.  Along with case hardening, I'll bet you another cup of coffee that the alloy used in the gear has a much higher tensile strength....Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Yes I agree the part has been heat treated.  But it definitly looks like it has been treated before the welding operation.I think we may try the 680S rod made by Eutectic.  I will let you know how it works out.
Reply:Pretty much what A_Dab said.  "AISI 8620 is a common, carburizing alloy steel used for a variety of medium-strength applications including gears, camshafts, fasteners, and chains/chain pins. Flexibility in hardening treatments allow optimization of case/core properties."  Right from MatWeb, hence the full quotation marks.Case hardness after carburizing will often run right around Rc60, which is pretty hard and UNWELDABLE in the carburized and hardened state, and the core hardness on quenched and tempered  carburized 'thin' sections (about 1/2 inch thick or so) can run around Rc 20-30 or there-abouts.To weld the hardened steel, you'll pretty much have to preheat it.  And if you preheat/reheat it, you WILL mess with the metallurgical properties on the gear teeth.  To my quick eye, it looks like the part was made in two pieces for manufacturing ease.  But that also means that the two parts are rather easily changing from one supposed part back into two parts.  Warranty work?  From the little bit I can glimpse of the gear teeth faces, the part looks new and/or barely used (no signs of face polishing or wear on the teeth that I can see in the picture, although the picture isn't -really- of the gear teeth).   Have Chrysler fix it.  Get a hungry product liability law shark to take on the case and/or file a complaint with the Feds (NHTSA or such) about design/material/manufacturing defect in the transmission gear being a safety defect.  Etc, etc.Trying to beef it up for yourself or some buds?  Or looking to make your own aftermarket 'Better and Stronger' version?  No real practical way to do so after the fact.It would probably take annealing the part, then preheating and welding and post-heating, possibly with something like a chill block gear to keep the existing gear teeth cool, then re-heat treating the rewelded assembly.  Oh, and then runnning QC on the gear teeth and spline teeth to check for dimensional issues.You really can't just go and take a new OEM ring gear and try to slap some more welds on it to try and make it 'stronger'.  The best laid schemes ... Gang oft agley ...
Reply:not real sure this will help but I have worked in the steelmill for 20years and the chemistry you have listed is not like any 8620 heat I ever made, and we supplied alot of steel to the auto industry.The Mn is way too high and the ni and moly are to low.When I worked in the machine shop we always preheated and post heated any alloy steel for shafts and such.
Reply:I think the chemistry he listed is for one of the weld beads on the part, not the actual 8620 material.The chemistry shown is generally consistent with a lot of different welding filler metals. Originally Posted by brickernot real sure this will help but I have worked in the steelmill for 20years and the chemistry you have listed is not like any 8620 heat I ever made, and we supplied alot of steel to the auto industry.The Mn is way too high and the ni and moly are to low.When I worked in the machine shop we always preheated and post heated any alloy steel for shafts and such.
Reply:For hard mystery steel I always turn to "Supper Missile" GTAW filler.