Ben's magnetic straight edge
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  1. #1
    Join Date
    Nov 2007
    Leinster, Ireland
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    Default Ben's magnetic straight edge

    A thought occoured while looking through Ben's straight edge thread - as a thought is something of a rare occurance, here goes.

    Ferrite, the main phase you'd hope for in a fully annealed and stress relieved cast iron, should not remain magnetic (please correct me if I'm wrong on that).

    For the straight edge to be magnetic, implies that there is some martensite in there, either that or some seriously distorted ferrite or austenite

    any of those imply that the anneal or stress relief process has not been sufficeint, and also, that the casting will be harder than intended.

    result; both greater instability and harder work scraping.

  2. #2
    Join Date
    Jun 2001
    downhill from Twain\'s study outside Elmira, NY
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    Interesting observation on the magnetic marker for potential stress.

    However, I prefer a slightly harder tool (SE, angle, prism, etc) for better wear. IOW, Class 40 at least. I don't know enough to understand if ductile would be better. I always had my straight edges cast with class 40 as it was sort of a sweet spot of "metallurgical" properties vs cost vs willingness of the foundries to pour and spec it. OTOH, I never verified what the result was after heat treat (thermal stress relief) which can change it to a lower #.



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