where T0 is the initial temperature (470 oC); Td is the temperature at location d when the quenched surface temperature reaches 100 oC, and t is the corresponding time. Fig. 7 shows the average cooling
rate (v) at different distances from the quenched surface of the sam-
ples (point P2 and P3, as shown in Fig. 1) with different flux densi- ties and spraying pressures. These curves show some similar variations: when the flux density keeps unchanged, the cooling rate increases with the increasing spraying pressure; when the spraying pressure keeps unchanged, the cooling rate increases with the increasing flux density.
For the quenched samples, the residual stress near the quenched surface is compressive stress, and the interior residual stress is tensile stress. The typical through-thickness variation of the residual stress is shown in Fig. 8. It can be seen that, the tensile stress and the compressive stress are neutralized at the ‘neutral- stress area’ (residual stress = 0). As the increasing of the distance from the neutral-stress area, both of the tensile stress and the com- pressive stress increase. As shown in Fig. 9, the flux density keeps