A relatively new stainless bearing alloy

[GrantP]

Just to give folks a heads-up as there appears to have been no mention of this alloy on the forum; it's called Cronidur 30.

Fe-15Cr-1Mo-0.3N-0.33C

It's German designation is X30CrMoN 15-1. It's a martensitic stainless made by electroslag remelting under high pressure nitrogen (hence all that nice N). It can be hardened "in depth" (?) to 58 HRC while having much greater corrosion resistance than 440C.

Some links to more info:
http://www.ehis.navy.mil/jcnews3.htm
http://www.manufacturingcenter.com/tooling/archives/0300/0300tu.asp

And a link to a distributor in Germany:
http://www.firth-steel.com/english/firth/sonderwerkstoffe_index.html

From the above link, it appears to already be in use for surgical scissors and knives in Europe. The ONR article mentions that licensing was being arranged for some domestic production, but I haven't found any mention of a maker other than VSG Energie- und Schmiedetechnik GmbH.

I haven't been able to reach VSG's home page, but contact info and a link is here:
http://www.georgsmarienhuette-holding.de/organigramm/pu14.html

First-time poster! Does some dumb noisemaker go off or something?

Cheers!
Grant

 

[steve porter]

Grant,
Sounds interesting I'd like to know more,so
I've taken a copy of the links and will try
later.
Regards
Steve
P.S I am only new to the forum myself but welcome aboard

 

[AchimW]

Thanks, but that is not a steel for knifemaking. As you mentioned, it can be hardened "in depth". The proper general term is case hardening. Its only the surface of the steel which gets hard. Which maybe would be fine for some knife uses, too, if the heat treating process involved in doing so wouldn't be sooo complicated. You have to follow cycles of pre-heating, case hardening (directly, single or double),carburization, cooling after case hardening in the right medium (water, oil, hot bath, salt bath, case hardening box), core hardening, intermediate annealing and final surface hardening (with quench in water, oil od hot bath).
Impossible to do if you don't have an industrial size heat treating plant.

Achim

 

[GrantP]

Achim,

I figure you'd be in a position to possibly know more than I do about this alloy. However, quoting from the ONR article...

"Through Hardening: Solution, quench and temper are carried out similarly to the processing of conventional bearing steels. After solution and quench treatment hardness is approximately 56 Rc. Subsequent tempering precipitates semi-coherent hard carbo-nitrides throughout the microstructure that strains the martensitic matrix leading to hardnesses of between 58 and 60 Rc."

"Dual Property (DP) Processing: DP processing is an induction hardening treatment applied to the bearing surfaces. It is carried out in three steps: (1) conventional hardening and high temperature tempering to a medium hardness, tough core condition followed by (2) localized gradient induction heat treating to case harden the steel, and (3) finally cold treating the hardened case to lower the retained austenite level and tempering the case to 58 Rc."

"After **conventional** [my emphasis - Grant] heat treatments to the same hardness and fracture toughness, Cronidur 30 appears to demonstrate superior strength, ductility and toughness over the commonly used corrosion resistant stainless steel AISI 440C. The room temperature tensile yield and ultimate tensile strength of Cronidur 30 (heat treated to 58 Rc throughout) were found by the developers to be 270 ksi and 315 ksi, respectively; elongation to failure was reported at 4%. This compares favorably with AISI 440C (heat treated to 58 Rc throughout), for which yield strength is 185 ksi, ultimate tensile strength is 254 and elongation is 0.8%. Perhaps more significantly, the published impact energy of Cronidur 30 is 120 J/cm2 compared with 19 J/cm2 for AISI 440C. Cronidur’s reported mechanical behavior at elevated and cryogenic temperatures is similarly impressive."

The complicated dual property treatment I believe you are referring to requires that the core of the bearing be quenched to martensite and then tempered beyond optimum hardness right along with the surface.

Carburization is never mentioned. This alloy likely never gets carburized as it would defeat its purpose: substitute N for C to allow similar hardenability with less matrix Cr depletion. They'd have done away with *all* of the C if there wasn't this limit to the amount of N that can be added by PESR.

Powder metallurgy alloys can get around this restriction by being nitrided while they are still in powder form before consolidation (N is queer in that liquid Fe has lower solubility for it than Fe in the solid state). I'm working my way into Graviljuk and Berns' book...(High Nitrogen Steels, Springer Verlag, 1999) hopefully I've not made some basic misunderstanding.

Grant

 

[Bronco]

Welcome aboard, Grant. Thanks for such an interesting post your first time out of the box.

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Semper Fi

-Bill