Department of foundry of ferrous and nonferrous metals

National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute"

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The influence of the chemical composition and thermal processing

Steel that contains one or more special items containing more than 1%, called - doped.

To enter special alloy steel alloying elements that significantly alter their mechanical, physical and chemical properties. These elements include chromium, nickel, molybdenum, tungsten, vanadium, cobalt, titanium and others. Manganese in an amount of more than 1% and 0.5% over silicon is also alloying.

Properties alloy steels determined by the number entered alloying elements and the nature of their mutual action with the main components - iron and carbon. On this basis alloying elements can be divided into two groups: elements which do not form carbides (Ni, Co, Si, Al, Si); karbidoutvoryuvalni elements (Cr, Μn, Mo, W, V, Ti, Zn, Nb).

Entering alloying elements contributes to better quality of heat treatment, as they provide great stability austenite.
The influence of alloying elements on the structure and properties of steel

Chromium - cheap alloying element. It is widely used for doping (30%). It increases the hardness and strength of steel, while the slight decrease ductility and toughness. It partially dissolves in ferrite and simultaneously offers a strong carbide. Chromium improves the corrosion resistance - at content above 13% Cr steel is neirzhavnoyu. In addition, chromium enhances heat resistance, and changes the magnetic properties of steel. Due to the high wear resistance of chrome steel bearings manufactured it.

Nickel - a valuable alloying elements (in structural steels 1 ... 5%) - has a steel strength, high ductility and toughness. It is used in large quantities if you want to get a non-magnetic steel and steel antykoroziynosti. Dissolved in ferrite, nickel strengthens it.

Vanadium - element karbidoutvoryuvalnyy - increases hardness stalii gives it chervonostiykosti, promotes the formation of fine-grained structure pidvyschuyepruzhnist.

Molybdenum - karbidoutvoryuvalnyy element - increases the hardness and strength of steel at high temperatures. It promotes the formation dribnozernystosti. Molybdenum is introduced into the structural and heat-resistant steel.

Cobalt - increases heat resistance, magnetic properties, increases resistance to shock.

Titan - increases strength, promotes grinding grains, improves machinability and corrosion resistance.

 

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