Effect of isothermal holding temperature on NGS kinetics of phosphorus and temper embrittlement

When failure occurs in material, it is often occurs by fracture along some grain boundaries and often by the micro-segregation of embrittling impurity to the grain boundaries, In the present work, the non-equilibrium grain-boundary segregation (NGS) kinetics of phosphorus and the temper embrittlement at the same solution treatment and different isothermal holding temperature in steel 2.25Cr1Mo are studied. The NGS kinetics curves of phosphorus at the same solution temperature (1050 degrees C)and different isothermal holding temperature (540 degrees C and 600 degrees C) are given. Experimental results provide a direct evidence of NGS kinetic model and show that the grain boundary segregation concentrations of phosphorus for specimen isothermal holding at 540 degrees C are higher than those at 600 degrees C. The peak values of AES patterns of solute atoms for specimen isothermal holding at 540 degrees C are also higher than those at 600 degrees C. It is therefore concluded that the lower the isothermal holding temperature, the higher the segregation concentration of phosphorus at the grain-boundaries, and also the higher the degree of embrittlement.