THE Z-PHASE IN 9Cr FERRITIC/MARTENSITIC HEAT RESISTANT STEEL

Abstract

The precipitation behavior of Z-phase was investigated during long-term aging at 650 degrees C in an ultra low Carbon 9Cr ferritic/martensitic heat resistant steel. The steel was prepared by vacuum induction melting followed by hot forging and rolling into a plate. The plate was normalized at 1100 degrees C for 1h, cooled in air and tempered at 700 degrees C for 1h. Bimodal nano-sized MX precipitates distribute densely and homogeneously in the matrix within martensitic lath after normalizing-and-tempering heat treatment. After aging at 650 degrees C for 1200h, the Z-phase was found to nucleate on the larger nanosized MX. The Z-phase and MX have the following orientation relationship: (112)(Z-phase)//(001)(MX) and (1 (1) over bar0)(Z-phase)//(200)(MX).