Systems design of high performance stainless steels I. Conceptual and computational design

Application of a systems approach to the computational materials design led to the development of a high performance stainless steel. The systems approach highlighted the integration of processing/structure/property/ performance relations with mechanistic models to achieve desired quantitative property objectives. The mechanistic models applied to the martensitic transformation behavior included the Olson–Cohen model for heterogeneous nucleation and the Ghosh–Olson solid-solution strengthening model for interfacial mobility. Strengthening theory employed modeling of the coherent M2C precipitation in a BCC matrix, which is initially in a paraequilibrium with cementite condition. The calibration of the M2C coherency used available small-angle neutron scattering (SANS) data to determine a composition-dependent strain energy and a composition-independent interfacial energy. Multicomponent pH-potential diagrams provided an effective tool for evaluating oxide stability. Constrained equilibrium calculations correlated oxide stability to Cr enrichment in the metastable spinel film, allowing more efficient use of alloy Cr content. The composition constraints acquired from multicomponent solidification simulations improved castability. Then integration of the models, using multicomponent thermodynamic and diffusion software programs, enabled the design of a carburizable, secondary-hardening martensitic stainless steel for advanced bearing applications.