Approximation of concentrational relationship of double-component system equilibrium properties proposed by the authors before is used for mathematical description of double-component metal system phase diagram, in particular for melting point (solidus level) description in this work. Using experimental data permanent coefficients of the applied equation for 20 systems were calculated with the help of the least-squares method. A number of necessary permanent coefficients were compared with metal position in periodic system and other factors.

Key words: phase diagram, hard solution, temperature of melting and crystallization, power number, absolute deviation, permanent coefficients.