Effect of phosphorus on hardenability and isothermal transformation behavior in high-purity 0.35% carbon steels

It was confirmed by Jominy end-quench testing, dilatometric measurement, and metallography that phosphorus increased the hardenability. The Jominy distance parabolically increased with phosphorus content, and the phosphorus effect tended to saturate at high phosphorus content around 0.04%. Metallography showed that the hardenability was limited by the pearlite (degenerate pearlite) transformation at around 820 K. The growth rate of pearlite nodules at 823 K decreased by addition of phosphorus, but the nucleation rate did not. It is concluded that the enhancement of hardenability by phosphorus addition was caused by the retardation of pearlite growth because of the solute drag effect.