Magnetic Evaluation of Water-Quenched Modified 9Cr1Mo Steel Subjected to High Temperature Aging

The present work adresses the evaluation of modified 9Cr-1Mo steels magneic hystersis loop and magnetic Barkhsuen emission techniques for the samples subjected to high temperature ageing for different durations. The initially quenched and then tempered material revealed different magnetic behaiour with ageing. The relxation of stresses and reduction of high value of dislocations due to quenching in the initial perriod of ageing was observed with lowering of coercivity and an increase in MBE signal. Further ageing above 150 hours led to fine distribution of carbides in the matrix which led to the subsequent magnetic hardening. The formaiton of the fine carbides was also observed from Scanning electron micrographs. At higher ageing periods beyond 500 hours, the carbides migrated towards the grain boundary leading to loweing in the density of the fine carbides in the matrix and a consequent magnetic softening due to easy domain wall propagation.