Effect of Heat Treatment on the Precipitation Behavior and Hardness of the Second Phase of 0Cr21Mn17Mo3N0.8 High Nitrogen Alloys

The effects of different heat treatment processes on the morphology, quantity and size of the precipitated nitrides phase of 0Cr21Mn17Mo3N0.8 high nitrogen alloy were studied. The microstructure of the alloy was observed and characterized by metallographic microscope, transmission electron microscope, etc. And the hardness of high nitrogen alloy under different treatment processes were tested. The results showed that sample alloy was cooling in the furnace after heat preservation of 1140°C for 8h. Lamellar nitride is precipitated from the alloy, its composition is Cr2N, its size is about 50-100nm, and the precipitation process mainly occurs 1-2mm below the surface layer. This can make the alloys to form surface-reinforced composites. Meanwhile, the hardness of the alloy has increased significantly from 29.3HRC to 61.3HRC, because of the precipitation of the second phase. The high nitrogen alloys after slow cooling treatment were treated with spheroidization at the temperature lower than that of the complete austenitizing, and the layered deposition began fusing at 950°C. Under the temperature of 1120°C heat preservation for 8h, then water quenching, slice layer deposition completely dissolved into granule, and the particle size is about 20nm to 50nm, the alloy of hardness after spheroidizing has decreased to 48.3HRC.