Carburizing of steel
Carburizing of steel is the heating of low carbon steel in carbon-rich media to high temperature (typically 900-950 C). Let the active carbon atoms penetrate into the surface of ah, to obtain high-carbon layer microstructure. After quenching and tempering at low temperature, the surface has high hardness, wear resistance and fatigue resistance, while the core still maintains sufficient strength and toughness. The chemical composition Carburized steel are as follows characteristics:
(1) the carbon content of carburized steel is in the range of 0.15-0.25%, for heavy duty cementite, It can be raised to 0.25-0.30, so that the core still has enough expectation and toughness after quenching and tempering at low temperature. However, the carbon content can not be too low, otherwise there is no guarantee of a certain strength.
(2) the function of the combined full element table in Carburizing steel is to improve the hardenability and refine the grain size to strengthen the solid solution, and to influence the thickness and microstructure of the carbonized layer in the infiltration layer. Manganese, chromium, nickel and molybdenum, tungsten, vanadium, bright and so on are commonly added in Carburizing steel. Carburized steel in common use can be divided into two categories: Carburizing steel and alloy Carburizing steel.
The main results are as follows:
(1) the surface hardness of carbon gauge Carburizing steel is 56 ~ 62 HRC after carburizing and heat treatment. However, the low hardenability is only suitable for small parts such as shaft sleeve, chain and so on, where the strength of the heart is not high and the force is small to withstand wear and tear.
(2) the permeability and core strength of low carburized steel such as 20Cr, 20Cr2MnVB and 20Mn2TiB are higher than that of carbon Carburizing steel, which can be used in the manufacture of more important Carburizing parts in machinery, such as gears and live pins in automobile and tractor.
(3) due to its high quenching property, high strength and toughness, middle alloyed carbon steel such as 20Cr2Ni4 18Cr2N4W 15Si3MoWV is mainly used to manufacture parts with large cross section and complex bearing capacity, such as gears and shafts of aeroengine. Carburizing temperature of Carburizing liquid Carburizing Gas in our country is 900950 ^ C, surface layer w (carbon is 0.8 1.2), layer depth is 0.5 2.0mm.