Carbide V.S. High Speed Steel

CARBIDE VS. HIGH SPEED STEEL

In the machine trades industry there is constantly new technology coming out. The introduction of the newest CNC machines, CAD/Cam software, and tooling has made the manufacturing industry grow by leaps and bounds in the last ten years. But out all of those items the one growing the most has is the tooling. Tooling is everything when cutting metal. The types of tooling can vary from high speed steel, tool steel, carbide, cubic boron nitride, and diamond. This day in age, carbide is the leading material used to cut metal. Carbide tooling has several advantages over conventional high speed steel.

Discovery

Actually high speed steel and carbide were discovered about the same time. They were discovering in the early 1900's. (Machinery's Handbook) Carbide was kind of left on the shelf as you would say because people were unable to cut the material and make tools with it. With this in mind high speed steel was used extensively. Tools being made of high speed steel included, drills, end mills, boring bars, taps, dies, and other miscellaneous tools. During this time high speed steel was as good as sliced bread. High speed steel allowed for material to be removed faster and more efficiently at a low price. Before high speed steel, machinists would use plain carbon steel for cutters. Cutting materials with carbon steel took a lot of time. Usually the material being cut was about the same strength as the carbon steel cutter. This caused the cutter to wear out quickly. High speed steel was a great innovation at the time, but as carbide was slowly being developed, it showed many advantages over high speed steel. There were not as many variations of carbide tools as high speed steel.

Process of Making

As time when on engineers started to understand the powers of carbide. The process of making high speed steel and carbide vary immensely. High speed steel involves a process of liquid metal being poured into a casting of a tool. The casting is then split and solid tool is made. But that is just the beginning step. It is then taken to precision grinders and the major diameter of the tool is made along with the sharp edges for cutting. (Tooling U) All of this work is done by grinding. After the tool is sharpened and has a definite size, it is then taken to another station for a coating. High speed steel usually comes with a titanium nitride coating. This coating allows the tool to have more strength and lubricity. Sometimes the tool is not coated at all. The tool doesn't last as long as a coated, but it is a little cheaper. After this is done the tool is inspected and ready to sell.

Carbide on the other hand is made by a process of sintering. (Modern Machine Shop) Powdered carbide is mixed with a metallic binder, cobalt, and is injected in to a mold. These molds are made oversize to compensate for the sintering process. When injected the mold heats up causing the cobalt and carbide to glue together. It is then taken to a sintering oven. In this oven the piece part made from the mold is heated up to around two thousand degrees. This amount of heat causes the tool to shrink. The shrinking of the tool allows the particles of the tool to compact even more giving carbide its strength. Depending on the tolerances of the tool it can be taken to a grinding operation or it can go straight to the coating operation. During grinding carbide tools receive edge prep and certain features that give extra strength to the tool. These features will determine what type of material will be cut with the tool. The geometry of a tool that cuts aluminum is totally different from a tool that cuts steel. It is then taken to get coated. Carbide can receive many different types and layers of coatings. Some of the most familiar coatings are: titanium nitride, titanium aluminum nitride, titanium carbide, aluminum oxide, and titanium carbon nitride. (Tooling U) Sometimes many of these coatings are put on in different layers to give the tool strength, wear resistance, lubricity, and heat prevention. Also, there are two types of ways to put the coatings on. One way is chemical vapor disposition. During this process, the tools are put in an oven that heats up to around four-hundred degrees. Then a vapor containing the coating is put into the oven and sticks to the tool. Another type of way to put coatings on is physical vapor disposition. This type of operation is more or less done by spraying the tools a liquid. The tool then dries and coating sticks to the tool. There are many different types of grades and coatings of carbide depending on the use of the tool.

Strength

When comparing carbide and high speed steel on strength, carbide is by far a harder material. On the Rockwell scale, high speed steel usually tests around twenty-five to thirty. Carbide on the other hand is about twice as hard testing around sixty. (Machinery's Handbook) Although carbide is a lot harder, it toughness is not the greatest. This means that carbide is a lot more brittle. That is the way all cutting materials work. PCD diamond is the hardest cutting material that is made right now, but it also has the least amount of toughness. The slightest shock or mess up can cause catastrophic damage to the tool. High speed steel can be dropped or take a lot of shock and it will not cause the tool to be destroyed. It is a very tough material. If the same things happen to carbide the tool will be junk. An extra amount of safety comes with handling carbide. That doesn't mean forget about high speed steel, proper handling of the cutting tools will allows the tools longevity to increase. The longevity of a tool also is a factor upon the material being cut. There are many different materials with different hardness and certain properties. Softer non-ferrous materials like plastics, aluminum, copper, magnesium, and wood, high speed steel tools would be used. But when it comes to the harder materials like stainless steel, graphite, and hard carbon steels, carbide tools will be needed.

Longevity

Another big issue between the two materials is the longevity. Companies that produce carbide tools say that all of there carbide tools will last fifteen minutes of actual cutting. (Tooling U) That doesn't seem like a lot of time, but actually it is. High speed steel usually lasts about ten minutes of actual cutting. Some people would think well that right there shows that carbide is an obvious winner, but that is not all the way true. High speed steel may not last as long, but tools like drills made of high speed steel can be sharpened