Austenitic-Ferritic Stainless Steels with High Cr-Low Ni Content

We studied low carbon Fe-Cr-Ni alloys in order to develop the steel which has two phases, austenite and ferrite, and the resistance to stress corrosion cracking in the chloride environment.The martensitic hardening occurs when the (Cr+Ni) content is less than 24% and the (Cr-Ni) content is more than 18%. And the characteristic intergranular corrosion of the ferritic steel can be arrested when the austenite phase is precipitated more than 10%.The quantities of the two phases, austenite and ferrite, are equal when the (Cr-1.5Ni) content is about 14∼15%, and in this case it has the maximum resistance to stress corrosion cracking. We consider that the advance of ferrite precipitation is to arrest the propagation of cracks and to strengthen its matrix.It is concluded that the optimum composition of these steels is about 22%Cr and 5%Ni.