Case hardening

[Garry ColesParticipant @garrycoles69390]

Hi,

I like to use stainless steels when possible to stop corrosion, but not sure if those parts that need to be case hardened, such as pins and pivots will be okay in stainless. Or should I just use steel.

Thanks Garry

[bernard towersParticipant @bernardtowers37738]

surely a lot of it depends on the use the parts get and are they model or full size?

[Garry ColesParticipant @garrycoles69390]

I forgot to mention that these parts will be used on a 5in gauge loco and I follow what the drawings advise.

[Chris KaminskiParticipant @chriskaminski64716]

It would be interesting to see who is recommending (and for what part) stainless steel?

You can nitride stainless…

[FulmenParticipant @fulmen]

I think it’s possible to carburize stainless, but it will probably reduce the corrosion resistance. Not something I would do without some serious testing though.

[SillyOldDufferModerator @sillyoldduffer]

Though Chris mentions Nitriding I don’t think stainless steels steels can be case hardened with Carbon in the way mild-steel is.  Might be wrong because there are hundreds of different Stainless Steels, and maybe a few do.

The problem is chemistry and physics.   Stainless Steel is a largish family of alloys consisting of a solution of Chromium with,  maybe, some Nickel & Molybdenum dissolved in Iron.    This alters the physical structure of the atomic lattice, radically affecting the alloy’s mechanical properties, and also the Chemistry.  Chromium protects the Iron from Oxygen.  “Rustless”.

Many Stainless Steels are difficult to machine because they work-harden like crazy, making rubbing the metal a way of hardening it. But you have to choose the right alloy!   If the work-hardening variety takes the edge off HSS,  stainless can quickly become as hard, or harder, than HSS.  But can be machined successfully provided the HSS is kept cutting – no dilly dallying! Carbide driven aggressively is safer, but work-hardening stainless can still put up a fight.

Stainless is problematic unless you know which alloy it is.  The stuff used to make kitchen sinks is quite different from the stainless used to make knives.   For that reason I avoid it!  Not all stainless work-hardens, some varieties machine well-enough, others are meh!

Carbon Steels are more predictable in the workshop.  How about Silver Steel for the pins and pivots.  Machines well, and then fairly easy to harden and temper in a controlled way?

Which loco and designer is this?   The loco series in ME&W at the moment calls for cast stainless steel cross-slides, but I don’t think the author explains why.   I’m ignorant and he isn’t, and I like to be educated.  Any clue in your words and music?

🙂

Dave

 

 

[Neil AParticipant @neila]

This web site makes an interesting read on hardening stainless steels.

https://www.worldstainless.org/files/issf/non-image-files/pdf/euro_inox/surface_hardening_en.pdf

Neil

[bernard towersParticipant @bernardtowers37738]

If case hardening mild steel Id recommend the box hardening process. I use it for small instrument parts (shafts and wheels sub 5mm) it does away with any clean up and scaling.

[Mark RandParticipant @markrand96270]

Use a 400 series (martensitic) rather than a 300 series (austenitic) stainless steel . It’ll have much of the corrosion resistance, but can be through hardened. It’s what kitchen knives etc. are made from. 440C will harden to 60HRC

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