2026 Hatem Direct Tempering AISI431

Post-build tempering response was investigated for AISI Type 431 martensitic stainless steel produced via laser-based Directed Energy Deposition (DED-LB) at temperatures ranging from 350 to 650 °C. The study aimed to quantify phase evolution and stored strain, utilizing electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) with Rietveld refinement, and correlate these factors with hardness and build-oriented tensile properties. A wrought AISI 431 hardened-and-tempered bar served as a benchmark reference in the assessment. The as-deposited DED-LB microstructure exhibited highly strained lath martensite, with included d-ferrite pockets and retained austenite. It was noted that a low-temperature austenite reversion window peaked at approximately 6.7% following tempering at 350 °C, leading to a significant ductility increase, noted as elongation rising from 1.2% to 10.2%, while retaining tensile strength above 1180 MPa. Tempering at 450 °C achieved secondary hardening, resulting in a peak hardness of 606 HV5, though elongation decreased. At temperatures above 550 °C, a transition occurred towards a predominantly tempered martensitic microstructure, which was primarily driven by matrix recovery. The findings suggest an effective thermal processing strategy for optimizing strength-ductility trade-offs in additively manufactured martensitic stainless steels.