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intergranular failure of 420ss (martensitic)

intergranular failure of 420ss (martensitic)

intergranular failure of 420ss (martensitic)

(OP)
Anyou have any solid info or references they could point me towards for causes of inter granular failure in bending of 420 stainless (with 1%Mo addition)?

Nick
I love materials science!

RE: intergranular failure of 420ss (martensitic)

NickE;
I have two decent references - "Physical Metallurgy Handbook" by Sinha and "Handbook of Stainless Steels" by Peckner and Bernstein.

They both address ductility and notch sensitivity problems with the higher carbon martensitic grades of stainless (including 420) during forming. Can you provide more specific information, like;

What was the heat treatment condition or hardness of the 420 stainless steel when it was subjected to bending? Was the bending performed cold?

RE: intergranular failure of 420ss (martensitic)

This is covered fairly well in the ASM Stainless handbook also.
More details would be very helpful.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
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RE: intergranular failure of 420ss (martensitic)

(OP)
In service, HRc54, sandvik grade 7c27Mo2 (420ss+1%Mo) in flexure as a beam in single bend. (Q&T by sandvik, cut to shape, and finsihed to remove stress concentrators)

I was unable to get reliable chemistry data from the fracture surface. Some indications of S being present. (EDS)

Both trans and intergranular fracture noted on the fracture surface.

Thanks for the references, everything in my references deals with austenitics.

I'll see if I can get a copy of the ASM Handbook, but $ is tight at the end of the year.

Thanks
Nick

RE: intergranular failure of 420ss (martensitic)

Nick,

You might ask your management to pay for ASM Handbooks online.  For only a few hundred dollars per year (instead of thousands of dollars all at once), you have full access to all volumes.

I know you are in Metro Detroit.  If you can't get your own access, use the library of the nearest university (UM Ann Arbor, UM Flint, UM Dearborn, Wayne State, Oakland).

Regards,

Cory

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

RE: intergranular failure of 420ss (martensitic)

(OP)
Yeah a trip to Wayne state might be in order....

RE: intergranular failure of 420ss (martensitic)

I agree with a cruise through the ASM Handbooks - Volume 11 (Failure Analysis).  Possible mechanisms include Stress-corrosion cracking (Some slight information in "Stress Corrosion Cracking" ed. Russell Jones.  ISBN 0-87170-441-2), Hydrogen Embrittlement (at your hardness, there may be no reall difference between the two mechanisms).

RE: intergranular failure of 420ss (martensitic)

I was actually refering to the single volume Specialty Handbook on Stainless Steel.

Did these part fail during forming? or after?

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: intergranular failure of 420ss (martensitic)

(OP)
Not formed. The steel arrives in coil form at 50-55 HRc is stamped, then finished.

(I'm trying to avoid too many details about our process, there is nothing new, and no process changes have been implemented.)

I looked at an older (blue books) volume of the Failure Analysis handbook. No information given on this specific steel type, nor any info on intergranular failure in martensitic stainless.

RE: intergranular failure of 420ss (martensitic)

You need to focus on grain size and various grain boundary precipitates.
These alloys are very strain rate sensitive.  If you have speeded up an operation even slightly, or if the material may have been a little cold, or a stamped edge was a little rough, any of these could push you over into problems.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

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