Nitriding 316 Stainless Steel? 3

[metalman8357]

Hello all,

Is nitriding austenitic stainless steels a common process? Normally we make a part made from 410 stainless that has a #3 drill point on it, and we quench and temper to give us a case hardness of around 50 HRc. In addition, it is meant to drill into 18 gauge sheet steel. Ideally we would like to use 316 stainless for the improved corrosion resistance over 410. Are there any complications with nitriding 316, and will this process effectively decrease the corrosion resistant properties of 316? It has been suggested that we look into Bodycote's 'Kolsterising', but I know that nitriding will be much cheaper and may offer the same desired outcome. Any thoughts on this would be great, thank you.

-M

 

[TVP]

Conventional nitriding decreases the corrosion resistance of austenitic stainless steels. Kolsterising is the way to go.

 

[metalman8357]

What about nitrocarburizing? I would imagine this is still cheaper than kolsterising? This study seems to have much success with the process (

http://metallurgy.iitm.ac.in/isrs/isrs04/cd/content/Papers/SE/PO-SE-2.pdf).

 

[EdStainless]

Do you really want to do this?
1. The core hardness will be that of annealed 316
2. The surface hardness will not be all that great, except for a very thin layer.
3. you need to use one of the ion implantation methods that is done at low enough temperatures to completely avoid the formation of carbides or nitrides, otherwise your corrosion resistance will not be any better.

What level of corrosion resistance/hardness do you need?
Have you considered H23? With high Cr and W and low C it has pretty good corrosion resistance.

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Plymouth Tube

 

[metalman8357]

The application is for small, self tapping fasteners. Currently, we make them from 410SS so that we can harden the drill point, but the corrosion resistance of this material has not been satisfactory. We are looking into using 316 but then finding a way to harden the drill point, and the idea of kolsterising came up but it is very expensive. This got me thinking about other ways to achieve the same outcome through traditional processes. Since these are self tapping fasteners, they must meet the 5 degree head ductility test and so through hardened tool steel is out of the question. Any other ideas?

 

[EdStainless]

Use tool steel and anneal the head/upper shank, leaving the tip full hard.

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Plymouth Tube

 

[metalman8357]

Wouldn't this require individual processing? Normally, we treat huge lots of these fasteners at a time.

 

[mcguire]

Why not use 301 that has been cold drawn to the desired hardness?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[metalman8357]

Because the drill point must be hardened to 50 HRc with a core around 30 HRc. Also, the material must be soft as to not impart too much wear on the thread rolling dies.

 

[EdStainless]

There are fasteners made all of the time that they either harden the tips,
or full harden and temper the heads.

It needs equipment that passes the parts oriented through the HT process.
Not hard, bowl feeders, alignment tabs, grippers and induction coils..

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Plymouth Tube

 

[metalman8357]

Can you recommend a US vendor that does this process? It might be worth investigating further. Assuming that we can have this process done, you suggested using H23 in an earlier post. Does this alloy have similar corrosion resistance to 316? I'm having a hard time finding information on this alloy.

 

[TVP]

FYI, contemporary practice is to use an austenitic stainless steel fastener to which a martensitic steel tip is welded. Elco's Bi-Flex-R is one such product:

http://www.elcoconstruction.com/Products/Metal-Fastening/Self-drilling-screws/Bi-Flex-R

 

[metalman8357]

Nice find TVP, that is actually our backup plan...