Advantages of D2 over S30V

http://www.equipped.org/pop_up_cpms30v.htm

This is where I got this. There was a pic at the bottom of that page that did not paste here. It had the corrosion resistance comparison. Interesting.


CPM S30V

The following information has been adapted from the Crucible Materials Corporation Web site and Data Sheets for CPM S30V. It provides some technical comparisons to other common high-end knife steels and can explain, to a degree, why CPM S30V excels.

CPM S30V is a martensitic stainless steel designed to offer the best combination of toughness, wear resistance and corrosion resistance. Its chemistry has been specially balanced to promote the formation of vanadium carbides which are harder and more effective than chromium carbides in providing wear resistance. CPM S30V offers substantial improvement in toughness over other high hardness steels such as 440C and D2, and its corrosion resistance is equal to or better than 440C in various environments.

The process of producing CPM (Crucible Particle Metallurgy) steels involves gas atomization of pre-alloyed molten steel to form powder. This powder is then screened and then isostatically compressed into 100% dense compacts. The CPM process produces steels withe no alloy segregation and extremely uniform carbide distribution characterized by superior dimensional stability, grindability, and toughness compared to steels produced by conventional processes.

CPM S30V AISI 440C

CPM S30V is made by the proprietary CPM process, which results in a homogeneous, finegrained microstructure with uniformly dispersed carbides, as can be seen in the magnified photo above. The composition of S30V is balanced to promote the formation of vanadium-rich (MC type) carbides which provide better wear resistance than chromium-rich (M7C3 type) carbides.
Conventional AISI 440C is a martensitic stainless steel containing chromium (M7C3 type) carbides for wear resistance. This typical 440C sheet microstructure reveals carbide banding which reduces toughness and, depending on the severity and location, can cause chipping at a very fine edge.



Carbide Type and Volume
Vanadium-Rich Chromium-Rich Total
CPM S30V 4% 10.5% 14.5%
440C 0% 12.0% 12.0%
154 CM 0% 17.5% 17.5%


Crucible CPM S30V Alloy Composition
Carbon 1.45%
Chromium 14.00%
Vanadium 4.00%
Molybdenum 2.00%


Toughness (Transverse Charpy C-notch Testing) Grade Impact Energy
CPM S30V 10.0 ft. lbs.
440C 2.5 ft. lbs.
154CM 2.5 ft. lbs.


Although the longitudinal toughness for all three of these grades is about 25-28 ft. lbs., the transverse toughness of CPM S30V is four times greater than that of 440C or 154CM. These higher transverse toughness results indicate that CPM S30V is much more resistant to chipping and breaking in applications which may encounter side loading. In knifemaking, its higher transverse toughness makes CPM S30V especially good for bigger blades.

Edge Retention (CATRA Testing Relative to 440C) Grade %
CPM S30V 145
440C 100
154CM 120


The CATRA (Cutlery & Allied Trades Research Association) test machine performs a standard cutting operation and measures the number of silica impregnated cards which are cut (TCC = total cards cut). It is considered a measure of relative wear resistance.

Corrosion Resistance Average Pitting Potential measurements (below) from Polarization Curves run in 5% NaCl (Sodium Chloride) Solution at Room Temperature: (Higher voltage pitting potential indicates better corrosion resistance.)



Note: Properties shown are typical values. Normal variations in chemistry, size and heat treat conditions may cause deviations from these values.






© 2003 Crucible Materials Company
© 2004 Douglas S. Ritter and Equipped To Survive Foundation, Inc. - All rights reserved.
http://www.equipped.org/pop_up_cpms30v.htm
 
Damn, I wish we could have more threads like this. The makers section is a bit specialised, but if we could get consistent info like this on a variety of knife related materials, be it blades, handles or sheaths it would be very cool.
 
To add some detail to what Cliff says about M2 chipping. M2 is only less prone to chipping if the hardening temperature is kept low. Low meaning under 2000F. If a higher hardening temperature is used, M2 will have too much alloy dissolved and the chipping resistance will drop as much as 50%. This is why M2 has always shown wide variation in properties due to the lack of heat treatment to optimize the toughness.
 
Relative to what is transverse vs. longitudinal toughness measured? Or to say it differently: How is transverse different from longitudinal toughness?
 
HoB said:
How is transverse different from longitudinal toughness?
Click to expand...
Transverse toughness applies to fractures along the grain of the steel, longitudinal is through it. It is much easier to crack steel along the grain just like it is fora round of wood which is why transverse toughness is much lower in steels, a fraction of longitudinal.

In regards to knives, transverse toughness, the one CPM promotes is actually near irrelevant because the primary mode of fracture failure is always longitudinal because the grains of steels never runs in knives in such a way as to allow loading of the transverse toughness in the first place.

This is one of the first rules of machining parts, always set the grain so that the primary impact loads will never stress the transverse toughness. Note even in the CPM steels the transverse toughenss is still just a fraction of the longitudinal.

Note all the CPM steels have better transverse/longitudinal toughness ratios, even the other steels like S90V and S60V, both which are known to be very brittle in practical use.

-Cliff
 
Transverse does come into play. It will never be fully transverse but if a knife is laid flat and hit on the edge and it cracks down the length of the knife this is technically transverse. The term is long transverse. If the blade split through the thickness it is short transverse. Twisting motions that promote those nasty half moon chucks out of a knife edge are a combination of longitudinal and transverse failure. Unless the force acting on the blade is 100% ninety degrees to the rolling direction, some transverse loading applies and is the weakest link. Tip breaking and breaking in a vise would be nearly 100% longitudinal.
 
Satrang said:
..if a knife is laid flat and hit on the edge and it cracks down the length of the knife this is technically transverse.
Click to expand...
Yeah, have done it, you can see them in the X42 review :

http://www.physics.mun.ca/~sstamp/images/recondo_bits.jpg

But that is really difficult to see in actual use, most impacts are on the spine or edge.

The primary more of failure of broken knives through impact is longitudinal, that this is how the Raven broke when Simonich impacted it for example.

Twisting motions that promote those nasty half moon chucks out of a knife edge are a combination of longitudinal and transverse failure.
Click to expand...
The initiation is longitudinal as I have seen them not fully broken out. If you can gain transverse, great, but if you keep the longitudinal the same it isn't like you can scale greater functional toughness simply on the transverse alone which is what Crucible is doing in the above. For that to be true it would have to be the primary and dominant crack method, it isn't.

-Cliff
 
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