Re: [CR]Stainless Steel Failures

(Example: Framebuilders:Bernard Carré)

From: "Ken Wehrenberg" <>
Subject: Re: [CR]Stainless Steel Failures
Date: Fri, 16 Sep 2005 11:32:32 -0500

Andrew, Joe, and Seth: Good points on formulation, grade, composition, etc. I might get myself into some trouble here, but the stainless Robergel used in the past for their spokes or that Wipperman is using at present for their chains is just kind of analogous to the alloy that Campy used for their NR cranks: not the ultimate metallurgical choice for the task at hand. We can still debate about how far they missed the bullseye, though.

Another thing-- stainless is a wonderfully overused term today as it covers things like the magnetic brushed material behind my laptop right now to which I have affixed many magnetic clips and magnets with messages, notes, etc. True stainless is never magnetic. Stainless steel exhaust systems vary tremendously as Chevy can say that magic word "stainless" to represent their material being the same as Volvo's or Lexus's, when they really are not. Also, stainless doesn't mean non rusting--I can rust high grade stainless to an amazingly ugly appearance in less than an hour with the right fairly common acid.

Carbon content, etc: (AISI American Iron and Steel Institute) numbers stainless from 300 to 502. Martensitic steels in the 400 series are really too brittle for spokes. Austenitic steels are in the 300 series and the differences are mainly due to the nickel content more than the carbon. Even here, fatigue from repeated stresses will bring about more work hardening. Also, if the smaller spoke required more processing or rolling to draw it out smaller, it could be noticeably more brittle. Sharp bends also will increase brittleness. In regard to spoke stress specifically, one of the principles of bending rod or wires is that the radius of the bend should never exceed 6 times the diameter of the material being bent. Ever measure your spokes with this in mind? Also, how the bend was put in makes a difference. When the wire or rod is bent at a steady rate, without jerkiness or abruptness of speed, the steel is given time for its internal structure to adjust to the bend.

I think I'll stop here.

Ken Wehrenberg, Hermann, MO... and yes Seth, I am a Diplomate--- of the American Board of Orthodontics