Welding Tips and Tricks

Hi Guys and Gals,
I've been working all weekend on a project that was supposed to be fairly easy!
The pinion bearing spun on a F450 truck. It looked like a little tig work and then set up on my mill and back in business but that didn't happen. I got the rear end on Saturday morning and had it welded by dinner time. I used 308L rod. The rear end is cast steel. Welding inside of a hole is not the easiest thing to do. I preheated the pinion portion of the casting to about 400F then started welding. Then I covered the casting with high temp blankets and let set till morning.
After I got it set up in the mill, I began boring. I've machined stainless before, but this stuff is tuff. The bore is about 3" OD. I began using HHS bit in a boring head. The bit lasted about 10 seconds with mill at slowest rpm. Carbide cemented bits seem to work best, but I need to resharpen about every 2 minutes. Am I missing something? Does 308L get tougher after cooling? Can it be annealed? I'm open to any and all suggestions. Thanks for your help.

Chuck
NW PA

Welcome, Chuck,

We have some welders with machinist experience, and some machinists with welding experience, so you will likely find your answer here with a little patience.

I suspect your issue has to do with carbon migration from the cast housing to the filler, combined with dilution of the filler at the weld interface. I also suspect this makes annealing possible, but I will defer to others on the truth of this and the process involved.

Steve S

Carbon migration is my bet too. The other thing that may be happening is that you are being too gentle on advancement rates. You need to get under the surface with some stainless or you will just surface harden it rather than remove material. I'm not sure how deep you are trying to cut but it needs to be at least .020 depth and a decent feed rate. It is freaky the first time you have to do it I know...

With what is now effectively high carbon stainless, you should also assume that it will both work harden and quench harden. You might try drawing it a bit. I wouldn't go above 1000F and at least 500F maybe 4 to 6 hours at temperature and then a nice slow return to room temp.

-Sandow

I do a few of these type repairs & if you use stainless filler it pretty much always ends up way too hard to machine without grief - I'm no metalurgist but assumed as Otto mentioned that carbon from the parent metal is the cause - the fact you slow cooled the part is probably the reason you can machine it at all & I doubt trying to anneal it will help plus stands the risk of the casting developing other issues - depending on the casting I would normally build up with nickel as this is not affected by the carbon or have used a high manganese rod used in rail repairs ( mostly because it was sponsored !! ) either works well & machines very nicely - if you are committed to carrying on then the best results I've had are with a replaceable tipped tool that was a very narrow angle - the less contact area / closer to knife tool the better - the other solutions I've used before are grind off all the stainless buildup plus a bit of the parent metal & re-weld with nickel then machine as normal or a bit redneck is setup & center the casting on a rotary table if not too big & you have one - then set up a diamond wheel on the mill if it's got good top end speed or improvise a die grinder with one clamped to the mill & use the table to move the "cut " & rotate the entire job against the wheel - last way is grind out the hard stuff then machine with a regular tool to make room for a transition bush made of low carbon / mild steel that you weld in & finish to size by boring in situ when cold.

Hope something there helps - may just be worth messaging Keith Fenner as this is much more his kinda thing - maybe he has a magic trick he'll share.

I think 308 is primarily for discimilar SS grades. I.e. 304-312. Or 304-316.

I've been building rear ends for about 35 years and I owned a rear end shop for 15 years. I've done a lot of rear end work and I haven't seen any rear end castings that I would call cast steel. Most, if not all of them are nodular iron. When you welded it you brought out the carbon and seriously hardened it. I only use N99 when welding on any cast rear end housing. You may have scrapped this housing.