School Project: How is blade steel made?

[JS_KnifeNerd]

Hey, it's JS_KnifeNerd :spyder:
I am currently at school and I am doing an 8-week unit on Blade Steel. My very first project is about how steel is made. I thought that I could ask you guys some questions, and my teacher said yes. Sadly I have not found any websites other than Spyderco that describe specifically how BLADE steel is made. I have found lots of information about how building steel and other steel products are made.

I would really REALLY appreciate if someone described in detail how BLADE steel is made, from the mining of iron ore to what method they use to add elements to the iron. I already know what a blast furnace is and what EAF, BOS, and open-hearth processes are. Another question I have is I know that when you are hand forging knives you use a billet of steel. What I am wondering is what form of steel do they use in factories? Do they use billets as well, or do they use blumes, ingots, or slabs?


THANK YOU SO MUCH!!!!!!!! :) :) :)

[curlyhairedboy]

I'm sure Larrin might be able to help with a lot of the details since he's much closer to that part of the industry, but you've got a decent idea of steel processing already. His website is knifesteelnerds.com

It's difficult to answer your first question as it's very broad - there's a lot of different steels out there.

A very basic definition of steel is mostly iron mixed with some carbon. The iron and carbon can form different crystal structures inside the steel, and the type and amount of these structures determine the properties of the steel. The nice thing about most steels is that you don't have to re-melt the steel if you want to change the properties. Due to iron's lattice structure, just heating it above a certain temperature allows you to (very simply) "clear the slate" and start over.

Maybe a good first approach would be to explain that steels are generally made to suit the needs of an application. It's fairly rare for a steel to be designed specifically for hand-held manual cutting, such as in pocket knives or fixed blades.

Instead, the demands of industry can be a big driver of steel development.

Take m390, for instance. Bohler's product page (https://www.bohler-edelstahl.com/en/M390.php) explains that it's mainly designed for plastic molding. It just so happens that the properties that make it a good mold steel also make it pretty good for pocket knives cutting abrasive media like cardboard.

As for your second question, factories tend to use all sorts of steel depending on the final product they're making. Sometimes a casting is good enough, but other times a part needs to be forged to shape to ensure mechanical properties.

This is by no means a complete set of answers, but it's all I have time for right now :)

[TkoK83Spy]

https://en.wikipedia.org/wiki/Crucible_Industries

[missouried]

https://en.wikipedia.org/wiki/Crucible_Industries

That is a very interesting read. Spyderco is clearly using some of the very best knife steels available. Helped me to understand why I like S35vn, M390, S90v and s110v.

[Cambertree]

Hi JS,

This quote comes from a 2006 post on this forum by Zac discussing CPM3V steel. I'm not sure where he sourced it from, but it's a pretty good description of the ingot vs particle metallurgy processes.

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.

My understanding is that most steel grades which are used for blades are actually made from recycled scrap steel which is remelted, rather than raw iron ore. This is why there are often trace amounts of various elements in steel. The steel is tested during the melt, and adjustments are made by adding elements as needed.

As mentioned above, many of the steels used in modern knives are not specifically designed to be knife blade steels.

A few examples of steels which were actually designed for edged tools are the Japanese White Paper (Shirogami) and Blue Paper (Aogami) series steels, VG10 from Takefu Special Steel also in Japan, and 12C27 from Sandvik in Sweden. N690Co is basically a European version of VG10, perhaps slightly improved. CPM S30V made by Crucible Steel was also developed for blades. (The 'Paper' in the name for Shirogami and Aogami series steels comes from the coloured paper labels which were originally stuck onto the billets to identify them, although the billets I have seen in forges in Japan just had coloured paint on the ends to identify them.)

The steel used in industrial knife manufacture is rolled into sheets of different thicknesses and the blade blanks are cut out of that sheet, usually either by waterjets at very high pressure with abrasive particles in the water, or lasers.

The blade blanks are then ground into nearly their final shape, then heat treated and finish ground and sharpened.

Billets (in the machine shop sense, not the rolling mill sense) are generally used for smaller scale knifemaking. When I made a knife of my own design, I drew a few life size designs on paper until I was happy with one, then cut it out and traced the shape onto a billet of D2 steel. It was then roughly cut out with an angle grinder then cleaned up and shaped with abrasive belts, before heat treating, being cleaned up again, then hafted (having the handle fitted and shaped), finish ground, sanded, and sharpened.

I hope that helps. Good luck with your project! If you need any further explanation for any of these terms or processes, ask away! There's a lot of very knowledgable people here, who I'm sure will be glad to assist your learning.

[koenigsegg]

Have you read any material from knifesteelnerds.com? I would check it out, the writer is here in the forums too he's a nice guy

[Bill1170]

Factory knives are most often cut from sheets of steel, but bolstered blades are forged from thicker stock. Simpler steels with lower carbon content are typically blanked by stamping. Stamping is fast and inexpensive when done at scale. However, higher end steels don’t stamp well, at which point lasers and water jets come into play.

[JS_KnifeNerd]

Wow, guys thank you so much!!!
THANK YOU THANK YOU THANK YOU you have been so nice.
I will make sure to show you the finished product :)

[Larrin]

Yes, the steel is produced with Electric Arc Furnaces using recycled steel and various ores to get the appropriate composition. The steel is then either poured into ingots or produced using powder metallurgy. The steel is hot rolled, annealed, and delivered to the customer. The customer heat treats the steel by austenitizing, quenching, and tempering. Any of those steps I just mentioned could be described in very great detail, of course.