Effect of Carbon and Titanium Variations in Fe-Based Heat-Resistant Superalloy A286 on TiC and η Phase Formation

Fe-based heat-resistant A286 superalloy is an age-hardened austenitic stainless steel. Age-hardening is greatly affected by TiC particles and eta-Ni3Ti phases. Herein, the evolution of TiC and eta (hcp-Ni3Ti) precipitations is investigated in six different A286 alloys with simultaneous variations of C and Ti contents, such as 0.00C-2.38Ti, 0.02C-2.46Ti, 0.04C-2.54Ti, 0.05C-2.58Ti, 0.06C-2.62Ti, and 0.08C-2.69Ti wt%. During microstructure evolution from solutioning state (900 degrees C for 2 h) to aging state (720 degrees C for 16 h), nodular/needle-like TiC (fcc) and platelet lamellar structures of eta (eta (hcp-Ni3Ti)) phases are observed in the austenitic matrix of superalloys. Statistical analysis of TiC and eta phases after microstructural examination indicates that mean size goes up to 3.3 and 6.8 mu m(2) in 0.08C-2.69Ti wt% alloy, respectively. Yield strength and ultimate tensile strength are increased from 350 to 510 MPa and 530 to 650 MPa as a result of the strengthening mechanism of TiC from 0.00C-2.38Ti to 0.08C-2.69Ti wt% alloys, respectively. However, precipitation of these phases leads to brittleness of the alloys and elongation decreases from 20% to 12% with the increment of these phases. The strengthening mechanism is explained by stress-strain curves and fracture topography.