Equilibrium Grain Boundary Segregation Of Phosphorus And Molybdenum In A 2.25Cr1Mo Steel

Many serious accidents are caused by intergranular brittle fracture in engineering practice. It is a challenge in the world to predict and control the intergranular brittle fracture. Grain boundary segregation and grain boundary brittleness play an important role in material brittle fracture and are paid more and more attention by the materials researchers.The development process of grain boundary segregation theory is briefly introduced in this paper. Cr-Mo steel and its several main failure models are concisely described and also some main surface analysis techniques. Solute segregation to grain boundaries may result in changes of grain boundaries state and influence the mechanical behavior of engineering materials. The segregation of solute atoms at grain boundaries may be classified into equilibrium segregation and non-equilibrium segregation. The phosphorus grain boundary segregation, which is affected by the temperature, strain, eradiate and other elements, is an important factor causing the grain boundary brittleness. The effect of molybdenum on phosphorus segregation is discussed in this paper.The specimens are made from 2.25Cr1Mo steels in this paper. They are normalized at 920℃for 50min and cooled to room temperature, austenized at 980℃for 30min in argon atmosphere and cooled to room temperature, tempered at 650℃for 2h and cooled to room temperature, and aged at different conditions. The grain boundary concentrations of phosphorus and molybdenum are examined by Auger electron spectroscopy (AES). Based on the grain boundary segregation theories along with the experimental data, the thermodynamic parameters for grain boundary segregation of phosphorus and molybdenum and their interaction are examined.The reaults show that the segregation of molybdenum has reached equilibrium while the segregation of phosphorus has not after aging for 800h at 480℃. Both phosphorus and molybdenum have reached equilibrium segregation after aging for 500h at 520℃and aging for 100h at 560℃. The standard molar free energies of segregation of phosphorus and molybdenum are about 38kJ·mol^-1 and 17kJ·mol^-1, respectively, and their segregation molar...