Influence of P on Solubility of C and on Snoek Peak in Low Carbon Steels

The influence of P on the solubility of C in ferrite equilibrium with cementite was investigated in low carbon steels containing P ranging from 0 to 0.21 mass% over a temperature from 573 to 973 K. Internal friction method was employed together with chemical analysis of C by means of the infrared absorption method after combustion.It has been clarified that P increases the solubility of C in ferrite in equilibrium with cementite, whereas P reduces the Snoek peak height despite the fact that the amount of C in solid solution is constant. The proportionality constant K in the equation, Sol. C (mass ppm)=K×Qmax−1(10−4), was experimentally determined as a function of P content and it was clarified that K increases with increasing P content.Taking into account the fact that the reduction of Sneok peak height increases with Co, Mn, and P addition in this order, the elastic strain around the substitutional atom due to the diffrence in atomic radius is postulated to be the main reason why Snoek peak height decreases with the addition of alloying elements. Here, the solute C in the lattice-strained region is supposed to be unable to contribute to the Snoek peak.