短語詞組短語backstep flow 后臺階流動backstep sequence 分段后向法;分段退焊backstep welding 分段退焊;逐步退焊法;反向焊;分段逆焊annular backstep 環(huán)形后臺階backstep method backstep 方法backstep sequence detail 分段退后次序backstep welding sequence 分段退焊次序backstep -welding 后退焊接backstep sequence welding 分段退焊 返回 backstep