In this modern era of knife manufacture, there seems to be a constant demand for new and different blade steels. Mainly, such steels tend to be of the stainless variety. It is remarkable, then, when steel that isn’t all that new and definitely not stainless, garners the interest of some knife makers. The steel I am referring to is CPM M4, or simply M4.
M4 is one of several tool steels made by Crucible and has been in their inventory for a number of years. One thing that has changed about this steel is the use of powder metallurgy in its manufacture. The CPM process (“compacted powder metallurgy”) is a proprietary process whereby molten steel is passed through a series of high pressure air jets. This results in the steel rapidly solidifying into tiny particles. Packed into a cylinder and subjected to heat and pressure, the individual particles adhere one to another to form a solid billet of steel. The major difference between a CPM billet and conventional poured ingot processed steel billet is the consistency of the CPM steel grain microstructure and the thorough distribution of the various alloying elements. In comparison to standard poured M4, the CPM process imparts superior wear resistance, improved toughness and a higher attainable hardness to this new steel variant.