bend strength of steels

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lsstaipei

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Jan 28, 2000
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What are the factors affecting bend strength of steels?
Hardness? Or more carbides=more bend strength ?
Is it okay to assume the bend strength of 1060 blade hardend to RC60 close to the bend strength of CPM M4 blade hardend to RC60?
Thank you for your education.
 
What do you mean by bend strength? You have to be specific when you talk about bend strength, and use terms very carefully. To compare based only on steel, which your example offers as the only variable, the blades have to be the same shape. How are you bending the blades? What would one do that would be considered better than the other? I know I'm asking some picky questions, but without these answers, your question can have as many answers as you want.
 
me2 said:
What do you mean by bend strength? You have to be specific when you talk about bend strength, and use terms very carefully. To compare based only on steel, which your example offers as the only variable, the blades have to be the same shape. How are you bending the blades? What would one do that would be considered better than the other? I know I'm asking some picky questions, but without these answers, your question can have as many answers as you want.
Click to expand...

your questions aren't picky. I don't understand the original question either.
 
lsstaipei, the thing that is most influental on bend strength is the thickness. Thicker blades, no matter how hard, are more difficult to bend. Carbide volume and all the other stuff related to heat treatment take a back seat to thickness, and geometry in general, in trying to bend a blade. A thin enough blade will bend 180 degrees ("U" shape, not multiple 90 degree bends) without cracking, and a thick enough blade just cannot be bent with hand pressure, regardless of hardnes, heat treatment, grain size, carbide volume, etc. Without more information, this is the best I can do for you.
 
I don't think it has to become so complicated. Hes question implies identical blades, which means same thickness, length and geometry.
The fact that thicker steel is harder to bend and longer steel bar at the same thickness will be easier to bend is something that every one of us has experienced, more than once :)
Therefore, I doubt he's looking for an answer of that type.

I am guessing his question can be rephrased as all else equal, what properties of the alloy influence bend strength.

We can pose a question even more precisely, given let's say 100mmx20mmx1mm steel bar, with ideally flat surfaces, form 1060, and M4, both at exactly 60HRC, fixed in a wise in the middle(50mm mark), which one will require more force to bend, for the sake of precision, let's say 45 deg.
Once that is answered, we can go into details what was it that made the difference, carbide amount/type or something else.
 
I think maybe he is referring to what is posted on the busse combat knives website about being able to bend there blades all the way to 35 deg and still have them return to straight and hold true...Although I could be wrong
 
Sorry for the confusion.And thank you all.:o

In deed,my question should be rephrased as all else equal, what properties of the alloy influence bend strength?which one will require more force to bend?
 
I think we need to differentiate between bend, and flex. If you bend steel, it is a permanent adjustment to its shape, this is otherwise known as plastic deformation. If you flex it, the steel moves back to it's original shape and you can't tell that anything was done to it afterward. IIRC this is elastic deformation.
 
lsstaipei said:
In deed,my question should be rephrased as all else equal, what properties of the alloy influence bend strength?which one will require more force to bend?
Click to expand...
Same geometry & same hardness will require the same force. The rockwell tester plastically deforms te steel with an indenter. The same machine, with the same indenter, measures on the same scale for all the alloys used.
 
http://en.wikipedia.org/wiki/High_speed_steel

"M2 is a high speed steel in tungsten-molybdenum series. The carbides in it are small and evenly distributed. It has high wear resistance. After heat treatment, its hardness is the same as T1, but its bending strength can reach 4700 MPa, and its toughness and thermoplasticity are higher than T1 by 50%.

At the same hardness,why are the bending strength different?Something wrong with wiki?
 
Minor differences in microstructure will make different blades at the same hardness have slightly different strengths. The carbides in M2 may be smaller, there may be less of them, they could be in a different location (grain boundary carbides vs. matrix carbides), the grain size may be different because of different austenizing temperatures, etc. For steels like M4, M2, T1 and any other high speed steel hardened to normal industrial hardnesses, there will be little measurable plastic deformation, so we are essentially talking about flex instead of bending.

The automotive industry does torsion tests of axles, and other parts I'm sure, I just haven't seen them. Different steels at the same hardness will have different strengths and different deformation, measured in axles using degrees of rotation, or maybe radians. For example, an axle of solid 4130 may take 100000 psi of torsional stress to twist it 180 degrees while a 4340 may take 120000 psi to twist it 220 degrees. These are still based on shape, it just may be the 4130 breaks sooner, so its load and deformation are less. These are just random example numbers. I don't remember the actual ones.

And yes, there is quite a bit wrong with Wiki, just maybe not in this article.
 
The answer is harder steel is harder to bend. It is also generally more brittle so bending it can, in fact, break it more easily than softer steel.
 
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