Which material treatment?

[loki3000]

what kind of material treatment would you recommend for a extrudor screw

http://www.extruder-screw.com/wp-content/uploads/2010/08/extruder-screws.jpg

if it has to serve bakelite (basically plastics reinforced with glass fibre - very abrasive)? the material is standard 42CrMo4 (AISI 4142, quenched and tempered to 30HRC hardness). it is then nitrided (don't know exact hardness, but standard procedure), but the thin layer supposedly wears off quite fast.
we would prefer not to use X38CrMoV51 (AISI H11, UTOP Mo1), as it is prohibitely expensive for the application.

any ideas, suggestions?

 

[edrush]

I would consider an EN (electroless nickel). It is hard and "lubricious". You will have to determine the best phosphorus content. I think the biggest risk would be the coating tearing off starting at a flaw in the coating. But in my opinion it would be worth a try. I don't know how the cost compares with nitriding, but I suspect nitriding is much more common and readily available at a local level (and hence less expensive).

Your picture does not provide any scale perspective. How long is one of these screws?

Note: this is a suggestion without any real experience in abrasive wear to back it up. People who build loaders and mining equipment should have knowledge regarding cost effective abrasion resistant steels.

 

[Frederick]

Have it treated with a true cryogenic treatment. This would involve a slow cool down to -300F, a hold of at least 12 hours at -300f and a slow warm up. Then temper. This will increase wear resistance considerably.