美国用17-4PH钢制造的固体推进剂火箭发动机壳体,要求它在点燃其内的推进剂时保持完整无损。在无损检验的技禾条件中规定:成品壳体应无表面缺陷,在棒坯中用超声检出的缺陷信号不得大于0.25×0.025厘米标准切口产生的信号。过去一直用磁粉法检验成品壳体,以滿足无表面缺陷的技术条件。长期以来发现有表面缺陷的很少,故认为这种方法是可用的。然而在1980年前不久,用磁粉法检验的一批360个壳体竟有175个不合格。这样高的不 The U.S. solid propellant rocket engine casing made of 17-4PH steel requires that it remain intact when it ignites its propellant. Non-destructive testing in the technical conditions and conditions: the finished shell should have no surface defects in the billet with ultrasonic detection of defects in the signal shall not be greater than 0.25 × 0.025 cm standard incision signal. In the past, the finished case was inspected by the magnetic powder method to meet the technical condition without surface defects. For a long time there are few surface defects found, so that this method is available. However, shortly before 1980, a batch of 360 shells examined by the magnetic particle method failed as many as 175. No such high