Temperature and dew point dependent segregation of phosphorus and sulfur in Fe–Mn–P–S model alloy

The dependence of surface segregation of P and S, on temperature and dew point of the annealing atmosphere was studied for an Fe–1Mn–0.02P–0.008S (all in wt.%) model alloy. The specimens were annealed for 1 min within a temperature window of 400 to 800 °C, in N2–5%H2 gas atmospheres with a wide range of dew points − 80 to 0 °C. Surface analyses were carried out by using XPS and FE-SEM. At the dew points − 80 and − 40 °C segregation of P was observed at 400 and 600 °C but S segregation occurred only at 800 °C. Phosphorus accumulation increases significantly with increase of dew point and, moreover, at the higher dew point, P replaces S at 800 °C.

Research highlights
► Effect of temperature and dew point on phosphorus and sulfur segregation is examined.
► Dew point (DP) is the most critical factor in controlling P and S accumulation.
► At low DPs − 80 and − 40 °C, sulfur segregated only at 800 °C and precipitated as MnS.
► At higher DP 0 °C, sulfur is replaced by phosphorus by manganese phosphate formation.
► By increasing the DP, segregation profile of P shifting towards higher temperatures.