저널

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 $I_f$, the scanning velocity $V_s$, and the initial flame holding time $t_h$, where the standard surface temperature $T_{s,;max}$, was maintained at $960^{circ}C$. The optimized conditions were $V_s=0.68mn/s;and;t_h=67sec$ for the $C_3H_8:O_2;=;5:20l/min,;V_s=0.80mm/s$ and $t_h=56sec$ for the $C_3H_8:O_2=6:24l/min,;V_s=1.01mm/s;and;t_h=48sec$ for the $C_3H_8:O_2=7:28l/min,;and;V_s=1.15mm/s$ and $t_h=39sec$ for the $C_3H_8:O_2$=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 $470{sim}490HV_{0.2}$in hardness and $-300{sim}-450MPa$ in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.

Flame hardening;12Cr steel;Steam turbine blade;Residual stress;Heart treatment;