Zirconium press plates have been developed for the production of melamine coated particle board, using shot-peening to achieve the desired plate (and therefore coated particle board) surface texture. Service temperatures of the press plates approach 200��C. This study examined the microstructural effects of extended exposure of shot-peened zirconium to temperatures of 200��C and 300��C. Softening of the surface may reduce wear resistance and possibly the surface morphology of the plate, affecting the usability of the plates. It was discovered that the shot-peened surface of the plates experienced a loss in hardness from approximately 230 VHN (DPH) to about 220 VHN after 560 hrs at 200��C. The same drop in hardness was experienced after only 5.5 hrs at 300��C. This decrease in hardness was determined from hardness profiles before and after heat treating the zirconium to various times from 0.5 hours to 4458 hrs and 2790 hrs at 200��C and 300��C respectively. The decrease in hardness is believed to be a result of static recovery, the annihilation of point and/or line defects and/or alignment of dislocations into relatively low misorientation substantially relatively close to the shot-peened surface (about 35 ��m), and decreased more modestly over the next 100 ��m until virtually no drop was experienced further than approximately 150 ��m from the surface. The shot-peening hardens the surface region which extends about 150 ��m from the surface. Thus, the level of recovery appears to depend on the stored energy associated with cold work, or ambient temperature deformation. This increases from about 2-3% cold work (equivalent percent cold reduction from rolling) in the bulk of the specimens to near 99% at the surface resulting from shot-peening. The dislocation structure of the shot-peened zirconium was examined in the as-peened as well as the annealed conditions using transmission electron microscopy. / Graduation date: 1997

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