The compared results in heat treatment testing under different temperature after two hours show that the deformed microstructure of the shot-blasted layer may be degraded as the heating temperature being higher than 750 ℃

and the degradation speed of microstructure at broken grain layer is faster than that at multi-slide layer

the microstructure degradation of deformed layer will further result in the reduction of Cr diffusion capability from base metal to the surface.The shot-blasted quality can remarkably affect the resistant capability to high-temperature softening of the deformed layer..The short-blased Super 304 tube is 100 ℃ higher than that on domestic shot-blasted S30432 steel tube due to higher hardness and better uniformity of said hardness of the former.In order to fully utilize the hardening ability of surface treatment on shot-blasted tubes

the shot-blasted quality should be ensured

and the heating temperature during post bending and post welding has to be less than 730 ℃.