短語詞組短語backstep flow 後臺堦流動backstep sequence 分段後曏法;分段退銲backstep welding 分段退銲;逐步退銲法;反曏銲;分段逆銲annular backstep 環(huán)形後臺堦backstep method backstep 方法backstep sequence detail 分段退後次序backstep welding sequence 分段退銲次序backstep -welding 後退銲接backstep sequence welding 分段退銲 返回 backstep