Optimization of Movable Flame Hardening Process for the Turbine Blade 12Cr Steel

摘要

In this study, the movable flame hardening process of 12Cr steel for a uniform hardness and desirable residual stress have been investigated. For this, the temperature cycles have been controlled accurately as a function of the three processing variables, the flame intensity If, the scanning velocity Vs and the initial flame holding time th, where the tandard surface temperature Ts,max was maintained at 960°C. The optimized conditions were Vs=0.68mm/s and th,=67sec for the C3H8:O2=5:20 l/min, Vs=0.80mm/s and th,=56sec for the C3H8:O2=6:24 l/min, Vs=1.01 mm/s and th,=48sec for the C3H8:O2=7:28 l/min, and Vs=1.15 mm/s and th=39sec for the C3H8:O2=8:32 l/min. The optimally flame-hardened surface exhibited uniform distributions of the hardness and residual compressive stress over the treated area with moderate levels of 470～490HVo.2 in hardness and -300～-450MPa in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.