THE CAUSES OF LOCAL HARDNESS INCREASING IN POWEH,PLANT ROTORS AND ITS MODIFICATI N BY TEMPERING

Local hardness increasing on the surfa ce of the power plant rotor may result in severe damage s. One major solu tion for rapid repairing of the rotors is the adap tive tempering heat treatment. For this purpose, after identification of the damaged rotor, initial investigations and tests (such as visual inspection, chemical analys is, nondestructive hardness measurements and rep lica or on-site metallographic tests) were performed on the rotor journ al. The result s showed that, the occ urrence of local phase trans formation (i .e, tempered baini te to austenite and finally martensite) is the main factor. Finally. based on the aforementioned results. temper ing heat treatment method was selected as a modifying so lution for thc following purposes: I. Decreasing hardness in embrittlcd places (i.e. 400690 HV) and, 2. invariable or admissible decrease of hardness in undamaged areas (250-300 HV). Experiments showed that by choos ing the 680°C/4hr as an optimum condition for tempering heat treatment. the two mentioned objec tives can be met.