Abstract: The causes of cracks in super duplex stainless steel 5 A pump casing castings are analyzed. It is found out that the structure of the casting undergoes eutectoid transformation of the ferrite phase in the slow cooling process in the mold. σ phase and secondary austenite phase precipitate from the ferrite phase, and the σ phase is the main reason for the cracking of pump casing castings. The change of contraction stress and thermal stress aggravate the cracking tendency of pump shell castings. The cracking of pump casing castings can be effectively avoided by adopting hot sand falling + hot charging furnace process or slow cooling + slow heating process.