cementite

With increasing of tempering temperature from 250 to 650oC, the impact energy would increase which is related to the reduction in hardness, martensitic transformation to tempered martensite and consequently ferrite and cementite formation [6, 7, 10].

It is believed that this increase, which will happen when heating a carbon steel at 285[degrees]C, is due to the structure which becomes more homogenized accompanied with a slight increase in cementite that resulted in higher hardness.

In both cases, the ferrite grain edges featured inclusions of cementite Fe3[C.sub.III].

In area of the edge workpiece the structure is formed by ferritic matrix with cementite and ferrite grains rare (Table 3 - Fig.

The primitive microstructure at the bottom of HAZ consists of abundant pearlite and minute quantity of ferrite, whereas the composition of the microstructure at the top of HAZ is rich in ferrite with some needlelike or cryptocrystalline martensite and blocky cementite at eutectoid temperature.

"Quench Embrittlement: Intergranular Fracture Due to Cementite and Phosphorus in Quenched Carbon and Alloy".

During the heating of steel with spherodized cementite in ferrite matrix, the austenite phase nucleates at the ferrite-cementite boundary.

Among specific topics are the thermodynamics of phase transformations in steels, kinetics, proeutectoid ferrite and cementite transformations in steels, carbide-free bainite in steels, and nucleation and growth during the austenite-to-ferrite phase transformation in steels after plastic deformation.

Standard rail steel has a predominantly pearlitic structure with a nearly eutectoid content of carbon and fine plates of pearlitic cementite. Some authors claim that the temperature in the wheel-rail area of contact may extend the boundaries of transformation temperature for generation of austenite (Kout 2001, Mitura 1980) while the subsequent rapid cooling may be the cause for modification into martensite (Jergeus 1992) in a closely delimited area corresponding to the surface.

A so called ribbon-like method was proposed for measuring particles for discrimination lamellae from spheroids of cementite particles in pearlitic steels (Nutal et al, 2010).