Nondestructive evaluation of steels using acoustic and magnetic barkhausen signals—II. Effect of intergranular impurity segregation

Abstract

The present paper has studied the influence of intergranular impurity segregation on acoustic and magnetic Barkhausen signals induced during magnetization in an undoped nickel-chromium steel and doped steels with antimony, tin or phosphorus. While the intergranular impurity segregation did not affect the magnetic hysteresis loop at all, it caused the characteristics of the acoustic and magnetic Barkhausen signals to change in a different manner. The impurity-doped steels produced a higher magnitude of the acoustic signal than the undoped one. However, the acoustic signal intensity of the impurity-doped steels remained the same independent of the quantity and type of segregants. With increasing quantity of segregants, the magnitude of the magnetic signal initially decreased and then increased above 0.078 atomic fraction. The magnetic signal also did not depend on the type of segregants. The effect of segregated impurities on the grain boundary energy and the magnetostatic energy at grain boundaries which change the nucleation and growth processes of domains is discussed.