CPM-D2 Bar Stock
D2 steel has been around for a very long time and is a proven knife steel. It is NOT a stainless steel but it is near stainless with a little over 11% Chromium. It takes 14% Chromium content to be classified as stainless steel. This is a high carbon steel that resists rust better than most. It's tough and holds an edge. If you don't like stainless steel, give this a try.
Note: CPM bar stock normally comes with a very hard black exterior from the foundry. This bar stock has been sand blasted by Crucible to remove most of the hard "bark" but there will still be deep surface marks and surface inclusions to grind away. The bar stock comes oversize to take this into account. The following dimensions are typical.
Nominal thickness Typical thickness
Tip: If you are going to cryo treat your blade with Dry Ice use kerosene instead of Acetone for the bath. It is still flammable but not as explosive as Acetone is.
The proprietary Crucible Particle Metallurgy (CPM®) process has been used for the commercial production of high speed steels and other high alloy tool steels since 1970. The process lends itself not only to the production of superior quality tool steels, but to the production of higher alloyed grades which cannot be produced by conventional steelmaking. For most applications the CPM process offers many benefits over conventionally ingot-cast tool steels.
Conventional Steelmaking vs.Particle Metallurgy Processing
Conventional steelmaking begins by melting the steel in a large electric arc furnace. It is usually followed by a secondary refining process such as Argon Oxygen Decarburization (AOD). After refining, the molten metal is poured from the furnace into a ladle, and then teemed into ingot molds.
Although the steel is very homogeneous in the molten state, as it slowly solidifies in the molds, the alloying elements segregate resulting in a non-uniform as-cast microstructure. In high speed steels and high carbon tool steels, carbides precipitate from the melt and grow to form a coarse intergranular network. Subsequent mill processing is required to break up and refine the microstructure, but the segregation effects are never fully eliminated. The higher the alloy content and the higher the carbon content, the more detrimental are the effects of the segregation on the resultant mechanical properties of the finished steel product.
The CPM process also begins with a homogeneous molten bath similar to conventional melting. Instead of being teemed into ingot molds, the molten metal is poured through a small nozzle where high pressure gas bursts the liquid stream into a spray of tiny spherical droplets. These rapidly solidify and collect as powder particles in the bottom of the atomization tower. The powder is relatively spherical in shape and uniform in composition as each particle is essentially a micro-ingot which has solidified so rapidly that segregation has been suppressed. The carbides which precipitate during solidification are extremely fine due to the rapid cooling and the small size of the powder particles. The fine carbide size of CPM steel endures throughout mill processing and remains fine in the finished bar.
The powder is screened and loaded into steel containers which are then evacuated and sealed. The sealed containers are hot isostatically pressed (HIP) at temperatures approximately the same as those used for forging. The extremely high pressure used in HIP consolidates the powder by bonding the individual particles into a fully dense compact. The resultant microstructure is homogeneous and fine grained and, in the high carbon grades, exhibits a uniform distribution of tiny carbides. Although CPM steels can be used in the as-HIP condition, the compacts normally undergo the same standard mill processing used for conventionally melted ingots, resulting in improved toughness.
CPM Eliminates Segregation
Conventionally produced high alloy steels are prone to alloy segregation during solidification. Regardless of the amount of subsequent mill processing, non-uniform clusters of carbides persist as remnants of the as-cast microstructure. This alloy segregation can detrimentally affect tool fabrication and performance.
CPM steels are HIP consolidated from tiny powder particles, each having uniform composition and a uniform distribution of fine carbides. Because there is no alloy segregation in the powder particles themselves, there is no alloy segregation in the resultant compact. The uniform distribution of fine carbides also prevents grain growth, so that the resultant microstructure is fine grained. Advantages of CPM
For the End User:
From one of the internet forums:
I e-mailed Crucible about the CPM-D2 and got a response, Asked if it was OK to put it up here and got a, "Yes, please copy/paste entire". I'm going to link them to the thread.
We have not published a data sheet for CPM D2. We have not made very much of it, only a couple of heats for knife blade stock. We have not promoted it as a regular grade in our tool steel product line, thus the lack of published info.
It is exactly the same as regular D2 except made via our CPM process instead of our conventional steelmaking process.- in other words, it starts as a powder, not a cast ingot. Other than that it's the same animal.
Because of the CPM process, CPM D2 has a more uniform microstructure, better polishability, and a little better fracture resistance along the edge than regular D2. Heat treatment is the same, although we are told you might get very slightly higher hardness, maybe 1/2 to 1 point more at best, using the same heat treat procedure you might use now for regular D2.
This product has been of interest to knifemakers because of its polishability, toughness, and novelty. In our industrial tooling market, customers can get the same toughness in other alloys, and the polishability and novelty does not mean so much to them, so they would generally not pay the price of a CPM grade for a grade they could get conventionally manufactured for a lower price. It's one of the differences between the craft aspect of the knife market, versus the utility of the industrial tool market.
Chief Product Metallurgist
CPM, Tool, and High Speed Steel
Crucible Specialty Metals