303 stainless work hardening

[nickjk]

I have a design that utilizes a cylinder made from 303 stainless. The I.D. of the cylinder has splines broached in it. The original designed was made from 440C stainless, but the change was made based on the increased machinability and better galling characteristics of 303.
I am now wondering if I made a mistake.

While visiting with a tool & die shop for a different reason I was told that using a diamond hone on 303 stainless will allow the hone material to enbed itself into the 303 and you will not be able to remove it. This is the current process to bring the I.D. to its final diameter. If there is abbrasive diamond material embeded into the cylinder it could explain some of the problems I am having with the PVD coated shaft that rides in the cylinder. Is this true?

I was looking into removing the honing process by finish circular broaching the cylinder after the cylinder is pressed into its bore. I was told by the broach designer this would be a problem because the light cut required would work harden the 303 and kill tool life. My research is finding this to be true. Would 440C prove to be better?

I am also wondering if the cylinder is workhardening during the honing process. Could this be true?


Any help or suggestions would greatly be appreciated

Thank You

Nick

 

[arunmrao]

I am also wondering if the cylinder is workhardening during the honing process. Could this be true?

Yes this is prone to work hardening. You may consider 316 alloy instead for your application. 440C will also be suitable provided corrosion resistance is not a prime facor. Hope this helps.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[EdStainless]

Yes the 303 will work harden. You may also have trouble coating it because of the inclusions added to the steel to improve machinability.
With a softer material you should use a harder abrasive (the bonding) and you should not get any abrasive embedded in the surface.
The 303 will be soft. The work hardening is only superficial. If you want more work hardening and a better surface you might consider roller burnishing to get size and finish.
I trust that when you made these from 440C you rough machined and then heat treated (Q&T) and then finish machined. These would be much harder and have a better surface finish.
If you want better corrosion resistance than 440C, and better machinability I suggest that you look into LDX2101. This is a duplex stainless, it is much stronger than 303 but not near 440C. It has good corrosion resistance and good machining properties.

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Plymouth Tube

 

[unclesyd]

We never used 303 SS where a fine finish was required for contact without liquid nitriding the part first. I don't recall having any problems with any machining operations. All our fine finish work was given the QPQ process prior to honing.

It looks like you have an application for materials like Nitronic 60 or Stellite 6B. Both of these materials have low wear rates and excellant galling resistance. Nitronic 60 has the better galling resistance.

http://www.hpalloy.com/alloys/brochures/NITRONIC60.pdf

http://www.stellite.com/ProductsSer...tellite6BandStellite6K/tabid/342/Default.aspx

 

[nickjk]

Thanks for the replies.

The reason I am looking at changing material from 303 to 440C is based on finishing broach life. I was told that the nickel content in 303 is to high and will work harden and kill broach tool life. I am not sure but the research I have done on LDX2101 and Nitronic 60 shows a high nickel content that I believe will also work harden. I was not looking at heat treating the 440C, I was considering it because of its low work hardening characteristics.
At this time I do not believe I will go this way because of decreased machinability.

I do find the QPQ process very interesting and need to research it more.

Thanks again.

Nick

 

[TVP]

Nick,

Don't focus on just the Ni content. LDX2101 is a duplex alloy, meaning it has a microstructure of both ferrite and austenite. Type 303 is a typical austenitic stainless steel (nominally 18Cr-8Ni) which means that it is quite susceptible to galling. Nitronic 60 is an austenitic alloy but it's composition is quite different, and therefore has much different galling behavior when compared to conventional 18-8 austenitic alloys.

 

[unclesyd]

We have no problem machining Nitronic 60 even in large L/D holes and broaching. The same goes for 303 SS.

If you stay with the 303 SS approach you might want to look at this material from Carpenter. Here is a machining table and at the very bottom they have information on broaching.

http://cartech.ides.com/ImageDispla...Workability.gif&IMGTITLE=Machinability+Tables

Liquid nitriding.

Liquid nitriding, actually carbo-nitriding, is a an excellant approach to mitigate some especially bad wear and galling problems. As I've stated many times that I've used the nitrided 17/4 vs Nitronic 60 as pump parts for nearly 30 years with outstanding results. I just got a call about two 1200 hp split case horizontal pumps used on a waste injection well where N60 and N17/4 components replaced all the potential wear and galling components, mainly ceramic and 400 SS. In one pump the parts were pristine and the other the parts had evidently kissed several times, there were no scars and the parts will be reused at the dame clearance. The parts were in installed in the 80's and last serviced in 1995. There was no problems with the pumps and were taken offline due to low demand and the opportunity was taken to checkout them out.
I also I have put a lot of SS pipe in service using this process to prevent wear and erosion in conveying systems for materials like dry kaolin and wet boric acid crystals.

Here are some very good papers on the process

http://www.nitromet.com/

If you can could you give the physical dimensions of the part?

 

[EdStainless]

I suggested LDX2101 because Outokumpu also makes Prodec stainless grades that have improved machinability, and 2101 machines better than they do.

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Plymouth Tube