Carburizing Stainless Steel

[Lcubed]

Hi All,
Can SS be carburized? I have a shaft with a spline on it which is carburized to Rc 58 or so. Is it possible that this shaft is made of stainless?

Thanks and regards.

 

[israelkk]

If you carburize a stainless steel it will no longer will be stainless at the outer surface. Stainless steel are usually nitrided. This too will reduce the corrosion resistance ability of the stainless steel but not as much as adding carbon.

 

[lewtam]

LCubed, I'd like to know what bought up the possibility that it may be stainless. Bit of a leap to go from surface hardness to material identification without other info. How did you determine that the spline is carburised?

LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.

 

[CoryPad]

thread330-43513

thread338-70369

thread330-88958

thread330-49696

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Lcubed]

lewtam-
The drawing calls out the carburization, but not the material spec. We are thinking about trying a little reverse engineering, and I thought that if SS cannot be carburized, our shaft must not be stainless. Incidentally, the shaft is slightly magnetic. This is not really critical, because there is no reason to make the part from stainless, but we are curious. Being structural, and not a metallurgist, I just wanted to inquire and learn what I could.

CoryPad and Israelkk-
Thank you for the leads.

I appreciate your help and advice.

Regards,

Lcubed

 

[diamondjim]

Not likely to be stainless steel.
possibly 1050, 4140, 4150, 8660
or
4023, 5120, 4118, 8620, and 4620
or
4320, 4817, and 9310

 

[NickE]

diamondjim- Lcubed mentions slightly magnetic. That confuses me, do you mean A) slightly attracts metal objects? or B) is only slightly attracted to a magnet?

if A, then it could be regular steel as diamondjim states, if B, I am at a loss as to how high of a hardness you've got along with lack of ferro-magnetism.

 

[Lcubed]

NickE,
The answer is 'B'
Regards,
Lcubed

 

[NickE]

This is for carburize and IsraelKK-

If this shaft was made of a non-magnetic SS (IE 304) and the surface was carburized to get hardness as great or greater than common martensitic (420 or 440) stainlesses. Then would the case behave like the martensitic grades? and would the shaft then have the magnetic properties that Lcubed described?

I just dont see how steel will have a HRc of 58 while remaining non-magnetic.

 

[SMF1964]

First option is to run an alloy analysis on the actual shaft - this can be done non-destructively with any number of portable analyzers.

Very High Hardness -> does anyone know if Maraging steels are non-magnetic?

 

[metengr]

SMF1964;
I believe the maraging steels are magnetic. The relatively low carbon Fe-Ni martensite forms after solution annealing. This allows forming operations and upon subsequent aging, precipitates form in the martensite resulting in excellent toughness and strength. Magnetic properties do change with aging.

 

[Carburize]

NickE - Sorry for the delay - just got back from a visit to Europe -Carbon is an austenite stabilizer, so increasing the surface carbon content on a material like 304 would just make it more likely to behave as a fully austenitic material with lower ferro-magnetism.

 

[azgearpro]

probably 8620, of 9310

 

[EdStainless]

There are some systems to put C and N into stainless at low enough temp that you get almost no carbide formation, just intersitial strengthening. You would never get anywhere near this hardness with that though.

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

 

[unclesyd]

Take a look at this process.

http://www.industrialheating.com/CDA/Archives/29ae4460f1cb7010VgnVCM100000f932a8c0____

 

[TEV]

A couple of other possibilities. I assume the shaft is made of cold drawn barstock. If it is austenitic stainless steel, the cold deformation could induce enough transformation to martensite to give the slight magnetic response noted. Also, some of the austenitic stainlesses on the market now are so lean in nickel (due to the price of Ni) that they contain some magnetic ferrite phase.

With respect to carburization, the "traditional" carburizing processes that have been applied to stainless steel significantly reduce the corrosion resistance due to chromium precipitation with the carbon. But there have been a few new processes developed that are performed at temperatures low enough that the chromium does not diffuse to form the carbides. Kolsterizing is an example. These processes are generally applicable only to austenitic stainlesses. The carbon occupies interstitial sites in the austenite FCC lattice structure. The result is corrosion resistance at least equivalent to the unhardened alloy, superior SCC and fatigue resistance (due to the high residual compressive stress state in the hardened case), and hardness in the range about 70 Rc.

I am familiar with the Kolsterizing process, as we have used it for over 15 years with great success. Details of the process are confidential, however.

 

[rms1956]

Maraging steels are magnetic. The only way I know of to get that high of a hardness out of an austenitic stainless is to cold work it. BTW this may also make it slightly magnetic.

 

[rayband1]

And the cold work may well have come from peening the surface, which has other benefits as well. But that's not 'on the spec'.