Cast stainless steels have been in use for a number of years with controlled amounts of ferrite in an austenitic matrix. Industrial uses have shown these cast alloys to be more corrosion resistant in many environments than the wrought fully austenitic stainless steels. The cast alloys have permitted greater flexibility than conventionally wrought alloys in terms of matching composition and structure to service requirements. This has been particularly so with respect to seamless tube and pipe. A paper by Prescott and Heller describes the use of centrifugally cast straight lengths of modified HF alloy pipe1 (21-29 Cr, 6-11 Ni, 0.25-.35 C, ferrite 5-15%, Grade A-297). Flanges and reducers were also centrifugally cast, turned, and bored; and elbows were statically cast. With mechanical properties of about 621 MPa (90 ksi.) ultimate tensile and 276 MPa (40 ksi.) yield strength, the alloy showed no tendency to corrode nor stress corrosion crack after three years of service. M. G. Fontana, et al2 presented data illustrating a marked increase in resistance to stress corrosion cracking and improved mechanical properties with increasing amounts of ferrite in austenitic alloys. Fontana's alloys were cast grades such as CF-8 M. The use of duplex stainless alloys was also cited with respect to applications in chemical, food, and petrochemical fields.3
