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 Name: Peter
Status: other
Grade: 12+
Location: MN
Country: USA
Date: Spring 2012

I took the back saw from my Millers Falls miter box to have the teeth sharpened and reset. The saw was made by Disston and is probably 60 or 70 years old. I was told they couldn't sharpen or set the teeth because the saw is old and the metal has become brittle. 1 or 2 teeth were broken in their attempt to sharpen it. The saw has always been stored in the house and only has some rust stains on it. My question is ,does steel become brittle with age

Hi Peter,

High carbon, heat treated steel, such as your saw was undoubtedly made from, does not become brittle with age. Hardened steel is simply iron with about 1% added carbon dissolved in the iron. Hardness is imparted by heating the steel to a red heat which causes the carbon to react with some of the iron to form an ultra-hard iron-carbon compound called Martinsite. Rapid cooling (by plunging the red hot steel into water or oil) results in the martinsite being distributed throughout the steel, imparting harness to the entire piece.

If the red hot steel were slowly cooled, this allows the Martinsite time to revert back to iron and carbon. This process is called annealing and results in a very soft steel.

But importantly, there is no known process that, over long periods, can cause additional Martinsite to form at normal temperatures, further increasing the hardness and brittleness of hardened steel. My suggestion is that your saw sharpener needs a little more practice!

Regards, Bob Wilson

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