Plane blade tempering

[Mr T]

Hi

At a recent sharpening and fettling course we came across this tempering pattern on a new Stanley plane blade. Note the darker stripes above the felt tip marks.

When the blade was sharpened and used the points where the stripes meet the edge were obviously softer. I have not come across this before, has anyone else.

Chris

 

[Argus]

.

New on on me..... why would they want to do that?

Probably a defect in manufacture.

.

 

[xy mosian]

At first sight, to me, that is remeniscent of older plane baldes, where steel was forge welded to a softer backing. Initially I thought that unlikely, but them I remembered that hacksaw blades were sometimes bi-metal. I could see a similar process being used to save material costs. Starting with a bi-metal strip the width of which was equal to the length of the blade.
With second thoughts I wonder if it is evidence of some form of 'zone hardening' much as is used on hard point saws.
xy

 

[Cheshirechappie]

The soft stripes look to be fairly evenly spaced. My guess (and it is just a guess) is that the blade was in contact with some part of the tempering furnace that it shouldn't have been in contact with, and ended up with stripes about 50C to 100C hotter than the rest of the blade, and consequently over-tempered.

Very unusual; almost certainly a manufacturing fault.

 

[xy mosian]

There you are you see I just read Cheshire's post and of course the veil has been lifted from my eyes, Please ignore my previous post.
xy