由组织结构引起的声能衰减、散射、声束扭曲会使得奥氏体不锈钢焊缝的超声检测较为困难。分析了焊缝中超声波衰减及散射的各向异性特征及其影响因素，并提出了基于超声TOFD技术的二次波检测方法。通过调整探头间距改变焊缝目标区域的检测声束折射角，深入分析声束入射方向及晶粒生长方向对检测信号信噪比的影响。结果表明：检测波在奥氏体不锈钢焊缝中的传播呈现明显的各向异性特征；当检测声束与柱状晶生长方向成较小夹角时，可获得较高的检测信号信噪比。因此，当探头置于焊缝余高侧时，为获得较小的检测声束与柱状晶生长方向间的夹角，采用基于超声TOFD技术的二次波检测方法可提取焊缝中缺陷的衍射波特征信号。

Ultrasonic attenuation, scattering and beam distortion caused by the organization structure lead to great difficulties in ultrasonic testing of austenitic stainless steel weld. The anisotropy characteristics of ultrasonic attenuation and scattering are analyzed, and the secondary wave inspection based on ultrasonic TOFD (time of flight diffraction) method is proposed. Influences of beam incidence direction and grain direction on signal to noise ratio (SNR) of testing signal are revealed through changing the diffraction angle of testing wave in target area with the method of adjusting the probe′s distance. The research indicates that the ultrasonic propagated in the stainless steel weld reflects obvious anisotropy characters, and that higher signal to noise ratio can be acquired when the angle between the columnar grain and ultrasonic beam is small. Thus, the secondary wave method based on ultrasonic TOFD becomes very necessary when the probes cannot put on the side of the weld root, and the diffraction wave of defects in stainless steel sheet can be abstracted by the method.