Hardenable and Corrosion Resistant 4

[Tagger]

What would be a good material that is hardenable by heat treatment (up to 40 to +50C), corrosion resistant, and can handle subzero temps. down to -50°F (-46°C). I was looking at 440C SS but am concerned with the low temps. and becoming brittle. Is 440C rather ductile at -50°F?
How about a nickle based alloy?
Thank you

 

[kenvlach]

I recommend against using 440C:

"Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures."
---

http://www.azom.com/details.asp?ArticleID=1024

Also, the corrosion resistance of 440C is so poor in the hardened condition that it really isn't a stainless steel:
440C contains 0.95-1.20 wt% C and 16-18 wt% Cr. Hardened, most of the Cr is in the form of the carbide Cr₂₃C₆. One gram atom C can tie-up 3.8333 gram atoms Cr, so 1 wt% C can tie-up 16.6 wt% Cr, leaving a non-stainless metal matrix.

 

[israelkk]

You can use Carpenter's Custom 455 or Custom 465

 

[unclesyd]

Depending on your application I would look at 17-7 Ph SS and 13-8 Ph SS.
We have use both of these materials at LN2 temperatures with no problems.

If possible comeback with you specific application to obtain a little more information.

 

[Tagger]

I would be using the material for wire for a spring that needs to be corrosion resistant and handle temps. at times down to -50°F up to 200°F.

 

[israelkk]

If it is for a wire spring then the material to go is probably 17-7PH at condition C heat treated to CH900 after coiling.

Is it for an aerospace/military use?

http://www.webspawner.com/users/israelkk/

 

[TVP]

I agree with israelkk-- 17-7 PH (also called Type 631 or X7CrNiAl17-7) is probably the best material for the application. This is a readily obtained spring wire in NA, Europe, or Asia.

 

[Tagger]

As for Bar stock can 17-7PH SS be hardened to 55-60 Rc? Where can I find the strenghts based on the hardness? Components I haved designed around the spring need to be corrosion resistant, and as hard as possible. Precision Balls of 440C are being used in the design and I want the other components that will be in contact with the balls to be almost as hard, but not hard enough to damage the balls.

 

[Tagger]

I did a little research and decided that 17-7 cannot get as hard as I would like. I am looking at Nickel based alloys.

 

[israelkk]

You can use 440C and heat treat it to lower RC, or use 420 and heat treat to ~50 RC. The 440C balls are not more than 58RC.

 

[TVP]

Tagger,

Nickel alloys will not be any better than 17-7 PH stainless steel in terms of surface hardness. No matter what the material is, a spring needs to be properly designed for the operating environment, stresses, etc., and therefore most spring materials have a surface hardness of 55 HRC or less, because above this they do not possess sufficient fracture toughness to be resistant to stress concentrations, surface defects, etc.

Spring steels that have high carbon contents (> 0.50%) and have been quenched and tempered to a martensitic microstructure will possess the best surface characteristics in terms of wear resistance. ASTM A 401 and ASTM A 877 define the requirements for Cr-Si steel spring wire (essentially SAE 9254), with the Valve Quality material having fewer allowable surface defects, decarburization, and non-metallic inclusions. If the spring requires a wire diameter greater than 18 mm, then you may need to consider a bar that can coiled and then heat treated, instead of purchasing wire that is already quenched and tempered.

 

[EdStainless]

17-7PH in the CH condition isn't hard enough??? What strength level are you looking for? Strength will depend on your wire size, but you are looking at strengths over 230ksi.
If you want higher then MP35N or Elgilloy may be your only options.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rorschach]

Inconel X750, MP35N, and Elgiloy can all be heat treated and cold drawn to the hardness range you specified and all three are at least as corrosion resistant as 17-7PH which would have been my first choice as well for cost reasons. All of the above are available in cold drawn wire form for spring manufacture, most spring manufacturers around here stock them. comparing wire forms in spring temper to wrought bar are not quite an apples and apples comparison. the wire will be much stronger and somewhat harder.