The CPM process, which stands for
Crucible Particle Metallurgy refers to the actual and patented method that the steel is prepared (via a PM, or
Powder Metallurgy, process). So in Crucible's case, CPM is applied to American steels that Crucible offers. However, not all PM processes are necessarily American (ex: Bohler U., DAMASTEEL, Carpenter/Latrobe, etc. also use a PM processes, which like Crucible are patented PM processes and all are slightly different, and IIRC Bohler is German or something like that.)
Here's some information on the CPM Process and PM steels in-general:
http://www.crucibleservice.com/eselector/general/generalpart3.html
The way I have come to understand it is that, in simplified terms, applying a powder metallurgy process to an existing conventional steel yields improved homogeneity while reducing segregation, more or less taking an existing steel and making it more consistent without modifying the actual alloy contents. This greater consistency can result in better performance over the exact same steel made with conventional methods; sometimes this is very pronounced and other times it is not.
The advantages of a PM process are often very applicable in the world of knives because the performance areas we value most are generally the ones most enhanced by a PM process, and many popular knife steels (ex: tool steels) are the kinds of steels that tend to benefit greatly from a PM process. The real-world benefit the CPM process (and other PM processes) yields us can be improved wear resistance with greater toughness and less chipping. Simultaneously, the CPM process can make sharpening easier. A PM steel at a higher hardness can be more practical for the end-user than their conventional counterparts at the same high-hardness. One example is 154CM vs. CPM-154 in that 154CM @62HRC would not be very practical, but CPM-154 @62HRC is
tough as hell, plenty practical, and holds a screaming sharp edge for a very long time (and far longer than 154CM).
It's also worth noting that not all steels benefit equally from a PM process. For example, M4 via a PM process benefits much, much, much more than M2 does and M4 benefits so much that it is only available as CPM-M4 IIRC. CPM-154 makes huge improvements over 154CM, where as CPM-D2 does not make such notable improvements over D2. Whereas the higher price of CPM-154 is without doubt justifiable due to a huge boost in performance, it is less justifiable with CPM-D2.
Someone else will have to correct me if my non-technical explanation does not make sense, but that's how I've come to understand it. I found all of this really confusing at first. I think part of it is because you have "CPM" and "PM" which are pretty close!!! Also, the availability of PM steels can make things more confusing...Crucible offers some steels in conventional-only, other steels in both conventional and CPM, and other steels in CPM-only. The use of the word "generation" in regards to PM steels is also kind of confusing, and the CPM process is sometimes referred to as "first generation powder metallurgy" or something like that. This is somewhat misleading because the "second" and "third" generation PM processes are technically just different rather than generational improvements.
