Victorinox steel is 'soft' compared to what?

[Mikel_24]

Rockwell hardness has a non-linear correlation with yield strength and ultimate tensile strength. However, any curve is straight over a short enough scale, and with the range of hardness used in knives the behavior is effectively linear.

Thanks!

 

[Eversion]

Just a question. Is the RC scale linear? We know that higher RC means harder but... how much harder? What does in practical use mean a 2 point harder rating in the RC scale?

I know that RC is a measure of the depth of the indentation created by a device with a diamond tip (either conical or ball shaped) under certain amount of pressure but...I have no idea how the steel behaves under such circumstances.

Sometimes I feel that we start throwing RC ratings arround but might not really understand what it translates into.

Paging LARRIN!

Mikel

Disclaimer: I'm not Larrin. I do not have a PhD in this field and lots of real world experience, I only have a minor and some lab work in an academic setting. However, I would like to expand on his answer a little bit because I found it interesting.

Rockwell C is not necessarily measured linearly, but it can be seen as such. Here's a plot I threw together showing deformation caused by the indent process related to HRC value.

(thumbnail)
Here's where I ripped the data from, take it with a grain of salt because the exact methods aren't described here, and it can be argued that deformation surface area isn't an end all be all way of describing hardness measurement: http://bessex.com/forum/showthread.php?tid=287

You can see that as the hardness value increases, the material's resistance to deformation increases at a rate slightly greater than the value before. That is, hardness can be seen as increasingly "exponentially" here with HRC. (I don't like the word "exponential" here; it's really more parabolic. But not everyone cares about that minutia)

However, across the entire useful range of HRC values, this change in slope is less than 5%. Moreover, for hardness values that should be found in knives (non-steel or unhardened knife-shaped-objects aside), this effect is even less noticeable.

Hardness in this range is generally linearly proportional to tensile strength, as Larrin said, which is an important property from which other properties can be reasonably estimated.

So yeah. Not technically linear when you dive into the details, but practically speaking, it isn't wrong to assume the relationship is linear.

 

[Bigfattyt]

So many average people have SAKs,that are otherwise not knife nuts,and their sharpening skills are usually minimal, so i cant see hardening the steel they use to a point where the average person couldnt touch it up on a ceramic or other sharpening device.

I don't believe adding 3 or so RC to the steel used by SAK manufacturer would make the steel too hard to sharpen. Any sharpening stone you have would still work.

For me, steels that are in the 58-60 range just seem to take a sharp edge with less fussing on a wire edge/bur.

I have more than a few steels in lower hardness, and they seem to take more care to remove the but than the same steels in higher hardness.

 

[knarfeng]

So what do people mean when they say SAK blade steel is "soft" (56 RC rating I believe). Is this compared to modern super steels, or classic carbon steel like 1095? Please educate me as this is somewhat confusing.

"Soft" compared to most higher end current production blades, whether super steel or more pedestrian alloys.
For example: Victorinox and Buck both use essentially the same blade steel, 420HC.
♦ Victorinox hardens it to 55-56.
♦ Buck hardens it to 58-59.
The difference in performance is noticeable.

 

[Smaug]

In my electrical technician days, I carried and used SAKs for years. (first a Tinker, then a '61 Soldier, then a Super Tinker)

One day, I think about the time I joined here, I supplemented the Soldier with my Trusty Spyderco Walker. That was AUS8 at around 58 Rc, vs. 55 or so on a SAK blade, and by comparison, it felt like it NEVER got dull. Nowadays, AUS8 is considered on the soft side.

More recently, I had my Spyderco Native in Maxamet (Rc 68-70)in my desk drawer at work and broke down a few boxes a week for MONTHS and never needed to re-sharpen it.

However, that was a $175 knife, not a $25 knife.

It DOES have the effect of making SAK blade steel feel like a butter knife. Make a few cuts > sharpen > repeat. Although it is easy to sharpen, it has to be done frequently and that gets old, which leads to the steel snobbery we have here. :-D

I've suggested to Victorinox that they make the steel on one of the blades (for two-bladed models) a much harder steel. It's not an issue to most of their buyers though, so they stick with the cheaper stuff. Most buyers are used to cheap kitchen knives, and SAK steel is about on par with that; maybe even a bit better.