High Speed Steel Composition

 

High speed steel is a high carbon tool steel. But it is used widely in the industry due to its great properties. And there are so many types of high speed steel due to different chemical composition. Let us understand the universal high speed steel composition.

Carbon (0.70%-1.65%) 

The plenitudinous carbide would increase the hardness, red hardness and wear resistance.

During the quenching and heating, parts of the carbonide will be dissolved in austenite to maintain the hardness of martensite. Alloy carbides would be dispersed during the tempering, it would cause the hardening secondary. And the carbides that are undissolved would prevent grain growing and make wear resistance get better.

If increase the carbon content, then the liquidus temperature would decrease, the molten steel fluidity and casting properties will be better. And the amount of primary austenite will decrease, the crystalloid will become more meticulous.

The influence of alloy elements on the hardness of carbide:
Ti>B>Nb>W>Mo>V>Cr>Fe>Mn

The effect of alloy elements on the hardness of carbide during the heat treatment or high temperatures condition:
Zr>Hf>Ta>Nb>Ti>W

Tungsten(W)

It can increase the red hardness of steel and wear resistance in high temperature.

Tungsten exists mainly in the form of M6C in high speed steel. It has a great impact on high speed steel wear resistance. Parts of M6C dissolves into austenite to improve the hardenability of high-speed steel during the high-temperature quenching.

Tungsten dissolves into the basal corpuscle would prevent precipitation during the tempering. Its atomic radius is big and has a high elasticity modulus. Interacts with dislocations to form solid solution strengthening.

The power of the tungsten atom and the carbon atom combine together is really big. That will increase the stability of martensite decomposes at high-temperature.

At the condition of high-temperature tempering, parts of the tungsten will be dispersed in the form of W2C. Which will make it get hardening secondly and improve the red hardness of HSS.

High Speed Steel chemical Composition

Molybdenum(Mo)

The same influence as W.

Molybdenum can decrease the solidification temperature of high speed steel. And the eutectic structure is very small and it is uniformly distributed. Which can make the toughness of high-speed steel get better.

The thermostability of molybdenum high speed steel is lower than tungsten high speed steel.

Molybdenum could prevent the carbides from separate out around the grain boundary during the tempering process. And the toughness of molybdenum hss is better than tungsten hss.

And the molybdenum can reduce the thermal conductivity of high speed steel.

Chromium(Cr)

Raise the hardenability, oxidative stability, decarburization and corrosion resistance of hss.

The chromium elements could make the M6C which exist in austenite be dissolved entirely. That would make the hardenability and red hardness of high speed steel become great.

As the chromium elements content be bigger, the critical cooling rate of pearlite transformation is decreased. And the hardenability of high speed steel is increased.

Vanadium(V)

Make the hardness and wear resistance in the condition of high temperature get better.

As the vanadium content increases, the amount of MC and M2C carbides is also increased. That would inhibit the formation of mc.

Cobalt(Co)

Increase the high-temperature hardness, secondary hardness and thermal conductivity of high speed steel.

Cobalt could make the meltingpoint of high speed steel be bigger. Then raise the quenching temperature. Make the W, MO, V and etc elements dissolve in the austenite. That will furtherance the separation of alloy carbide in the tempering. Then the hardness of secondary and red hardness will be better.

Cobalt can form intermetallics and cause the impact of dispersion. And prevents other carbides from combine together and become bigger.

High-speed steel was found in the 20th century. It causes a great impact on modern industry. And you can understand it like this: without hss, there will be no modern metal industry. Although alloy materials came out in the 1960s. But the high speed steel always in the top position because of its excellent chemical composition. It always is the best material for knife tools with complex shape and high toughness. Such as broaching tool, shaving cutter and etc.

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