Toughness At Low HRC

[Bushcraft-O-Maniac]

Hello everyone,

is there a difference in toughness between a lower end steel (420HC for example) and a higher qualtiy steel (let's say S35VN) if you have two identical knives which are hardened at 55 HRC or below?

1. Do they need the same amount of force to get them to the point where flexing ends and plastic deformation begins?
2. Which knife would suffer more internal steel damage from plastic deformation?
3. Are we talking about a huge or a small difference?

Thanks for reading and have a nice day.

 

[shane45-1911]

Yes, there is a difference. Different alloys have different binding/flex properties, and the carbides are also distributed differently and are of different sizes. HRC is only part of the equation.

 

[PMQ]

Yes, there is a difference in toughness in 420HC and S35VN. For some, it's noticeable, like 3V and S110V, for some, it's not noticeable, like S35VN and S45VN.

Even with the same steel, at the same hardness, same knife, there can be a noticable difference: a 420HC poorly heat treated will be less tough than a 420HC heat treated by Bos ( a popular heat treater)

1. This is a very complex topic that requires some background in engineering to fully comprehend, but to oversimplified: you need different amount of force to flex different types of steel.

2. What do mean by "internal damage"? Like micro cracking inside? Steel with large carbide will tend to be easier to micro crack.

3. If you use a knife to cut things, then no, you will not notice any diffence. If you use a knife to baton, stab through barrel, digging,... then yes, there is a big difference.

 

[coolbreezy37]

At the end of the day, it all boils down to the heat treat of said steels.

 

[Twindog]

I see hardness as a pretty good proxy for strength (resistance to deformation, such as rolling and bending), not toughness (resistance to chipping or breaking).

 

[justjed]

Unless you're talking about a kitchen knife, I don't know why you would want a quality stainless alloy at lower than 55RC. Too many compromises...

 

[LimpCroissant]

Exactly like J justjed said, the thing is you don't want a knife under 55 hrc, unless it were a tool like a sharpened shovel or hatchet or something, so it's kind of a moot point. That's why we compare knife steels at optimal or rather the hardnesses that companies and makers are actually providing the knives at. If you take the same knife in 420hc and S35vn at say 58-59 HRC, the 420hc would be a lot tougher, yet the S35vn would have more wear resistance. You could of course make the knives yourself if you wanted them at 55 hrc, but it'd be leaving a ton of performance on the table.

 

[JoeBusic]

For monomaterials it's easy. Softer is tougher. For polymaterials (or compound) it depends on the interaction between the base and filler, which in steel are the matrix and carbides. Carbides are crack propagation points. So if the steel is too soft it will spread easier and crack at that point which will become a starting point for a collapse. That's why softer is not tougher in steels. More carbides makes soft steel equally untough as is hard steel.
Finding a balance for a designated use is key.