EN40 nitrided repair

We have some cam levers lost wax cast in EN40 then machined and subsequently selectively (at least according to the drawing) nitrided. The tappet pad it turns out is in the wrong position so we could do with building this up with weld and the re-profiling and re-hardening.

Does anyone have any words of wisdom on how to go about this?

Thanks

Ian

Perhaps look up "hard facing repair" on the net.

The Nitrided area will be, or should be, remarkably wear resistant, but the end result surface will depend on the material used to build up the surface.

Someone with professional metallurgical knowledge will be better placed, than I, to comment on the effect of adding hard facing material to the Nitrided area, and any possible problems resulting. (Cracking, brittleness, machinability etc )

Howard

Hi Ian when we had worn through the hard layer on cams we repaired them with stellite tig welded and if any of the original profile was intact you could grind down the proud weld to match. You will have to use a good welder with previous experience. The man we used retired a few years ago.

David

Depth of nitriding will depend on how long it was done for so may only be 0.008"/0.0012" deep.

Speak to your heat treater who did the process it is possible to reverse it back to where you started at the risk of a little distortion. I have had this done with "P20" (Din 2311/2312)

Get some of the same material you made them from. Create sticks of that same material, and then get it welded up with that material. Grind through the nitrided layer first for the area to be welded up. Then recut to correct profile and re nitride again. Welding with parent material is the best solution. Remove the nitrided area first, as the nitrided material is no longer the same as the original material, and it will crack trying to weld through the nitrided area.

Neil

Thanks for all those thoughts, I think finding the specialist welder and agreeing the plan with him sounds like an essential first step.

Ian

Ian, a bit of a way from Cheshire but ABR Specialist welding in West Bromwich, West Midlands could help you,

I have to agree with Howard Lewis that simply resurfacing a nitrided area can be very difficult. The problem is usually the transition area where you grind through the nitride surface, unless done very carefully and gently you can create micro-cracking in the nitriding which will propagate when under load.

I think that you may need to completely remove the nitrided area before considering resurfacing, doing a crack detect at each stage. Even then I would not be sure of the long term success of the repair.

It may be safer to start again, you will have to decide on the cost of remaking against the value of the finished item.

Sorry not to be optimistic.

Neil

As David suggests, grind back and get an expert to build it up with stellite TIG rods, it will be better than the original.

Neil

I had forgotten about ABR welding they were the welders we used after local welder retired and are very good. Explain the job and they can weld it.

David

Lots of good stuff in these replies.

I think the best solution may be to scrap the faulty levers and go back around the casting loop. If we make new waxes with the old tooling, we can correct the waxes by hand before casting in EN40, then machine and nitride as usual.

Ian

Thanks for letting us all know what action you have decided on. I'm sure you feel much happier in your own mind with this rather than attempting what could be a difficult repair.

One of my colleagues at work always said that you need to be very careful when attempting repairs that you are not just enhancing the value of scrap.

I also remember listening to him one day explaining to someone from Quality Control, who was trying very hard to get him to accept a repair that was "better than new", that he must have scrapped tens of thousands of pounds worth of components that "might have worked", but why should he take the risk? You have to consider the consequences of the repair failing.

Good luck with your project, we all what to see how it turns out.

Neil