Construction of liquidus surface of Fe – B – Mn – C – Cr five-component diagram

The authors used the technique of constructing the schemes of multicomponent diagrams ( n > 3) in traditional coordinates “temperature – concentration”, the basis of which are n – angles with a divergent coordinate grid at n > 4, to construct the liquidus surface of the Fe – B – Mn – C – Cr five-component system. Choice of the system was determined by the need to harden the surfaces of parts made from a large number of low-alloy steels by boriding. The critical points of the liquidus surface were melting points of the alloy chemical elements, melting points of borides and melting temperatures of eutectics of the phase diagrams, which are the sides of a pentahedral prism. Individual experimental melting temperatures of the steels and calculated melting temperatures of new eutectics during the interaction of eutectics of double phase diagrams were also taken into account. The latter were determined according to the eutectic reaction rule, which provides for the use of only melting temperatures of the initial eutectics in the calculation. At the same time, phase composition of the multicomponent boride eutectics of the system was determined. The resulting liquidus surface shows the temperature at which crystallization begins and the phase composition of the layer during boriding of casting mold coa­tings for surface hardening of castings. The calculated melting temperatures of eutectics form the solidus surfaces of the system. In accordance with the concentration values ​​of the elements, especially boron, five solidus surfaces are formed in the system at 1571, 1451, 1394, 1105 and 978 °C. These melting temperatures of eutectics are the boundaries between the diffusion and diffusion-crystallization mechanisms of formation of boronized layer in solid and solidifying states of treated surfaces, therefore, they determine the mechanism of formation of boronized layer, their phase composition, structural morphology and properties.