Is there a quantitative measurement for toughness?

Yes there are measurements for toughness. Notched bar impact tests ,such as the Charpy V notch test,measure the energy absorbed, in ft-lbs ,to fracture the sample. The toughness of steels is dependent on chemical composition and heat treatment. Typically the more carbon and the higher hardness decrease toughness. Alloying elements such as vanadium and nickel increase toughness.
 
There are two I'm aware of and I'm too stupid to explain them:

1. C-notch charpy scale. I think it measures the needed force a lateral impact needs to shatter the metal while it's supported (clamped? glued? static-electricitied?)

2. Izod scale. I think it measures the same forces, but with an unsupported piece of metal. Sounds more like they put the piece of metal in a golf shirt with a little gator logo and measure how many bullies are needed to pummel the steel into oblivion.
 
Marcelo Cantu :

why is it that certain steels are more or less brittle at the same rockwell hardness?
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Because they are able to absorb energy very fast. If the energy can not be absorbed then the steel will fracture. Take a piece of rubber and drop it on the ground, what happens, nothing, the rubber bends and absorbs the shock. Now take the same piece of rubber and freeze it solid with liquid nitrogen, it loses all its ability to flex and will shatter if dropped easily because now it can absorb the energy. The specific tests for toughness in steels is just to hit them with a big hammer hard enough so they break and measure how much energy was absorbed during the impact.

-Cliff
 
Originally posted by Cliff Stamp
The specific tests for toughness in steels is just to hit them with a big hammer hard enough so they break and measure how much energy was absorbed during the impact.
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Some people have the coolest jobs.
 
In general you may say: The more homogeneous a steel grade is, the tougher it is. Pure carbon more than alloys and the better carbide distribution increases thoughness over badly distributed carbides. That´s why PM steels are a bit tougher, as long as they are not overloaded with alloys.

As long as i get it, there are no elements, that increase toughness over pure, 0,5% carbon steel.
 
Here are a pic of Charpy and Izod testing mechanism. This should give you an good idea of the mechanics of these tests.

img00007.jpg
 
:eek: Wow thanks for the explanations fellas, I'll just pretend that I get it. So basically a steel can be hardened to a desired hardhess (eg. Rc 59-60), but it is the initial make-up or alloy of the steel that determines toughness? That being the case, can one get the same performance of a supersteel from a HC steel through heat treating? Or will some steels retain their toughness better throughout the Rockwell scale?
 
The toughness of a steel demends very strongly on the hardness and you can see even halving of hte toughness by changing a few hardness points. As well there are large differences in various steels and these differences are so large that the changes that quality heat treatments make are secondary to the inherent properties of the steel. For example L6 is *much* tougher than ATS-34, so much so that the very best heat treatment of ATS-34 is still going to leave it much more brittle than just a competent heat treatment of L6.

-Cliff
 
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